Guidance for Developing Performance Standards and Specifications for Concrete
Suggestions for stakeholder roles and test options to trial PSS on a next project
Executive Summary
Performance standards and specifications (PSS) — which focus on desired properties rather than recipes — have long been highlighted as enabling sustainability, reducing costs, and improving both the durability and performance of cement and concrete in the construction industry. However, adoption has been slowed by bottlenecks, such as the need to develop a suite of specifications that can substantially help guarantee concrete performance and the need to develop better durability and long-term performance tests. In the United States, the movement away from ordinary Portland cement (OPC) to blended cements like Portland Limestone Cement (PLC) and Limestone Calcined Clay cement (LC3), combined with increasing considerations of project Global Warming Potential (GWP), mean that now is the time to overcome these bottlenecks and develop PSS. Ultimately, a standard PSS that specifies key tests, parameters, and roles can help unlock scalable, replicable, and efficient construction in a diversified low-carbon concrete future.
The change process has long been a barrier for the adoption of PSS. This insight brief explores tactical recommendations for project stakeholders to develop PSS on their next project, including:
- Owners and developers: allow for testing, report performance, fund test trials
- Government and industry associations: fund test trials, compile results to create a standardized PSS, create knowledge-sharing spaces
- Architects: provide performance requirements for concrete
- Structural engineers: guide test selection for trials and incorporate existing performance-based specifications
- General contractors: develop holistic testing plans from project inception
- Concrete suppliers and contractors: incorporate additional testing into processes ranging from mixture design to finishing
- Testing teams (i.e., third-party labs): be equipped and proficient to conduct newly specified performance tests, adhere to test procedures
- Project lead: oversee progress, report results publicly
- Research community: continue developing performance tests for long-term performance and durability, convene stakeholders
Exhibit ES1 A Roadmap for PSS
Case studies of these roles in action, as well as specific tests to trial, include:
- A National Concrete Pavement Technology Center project that highlights how gathering field performance data to relate test results to well-performing mixtures supports the development of PSS.
- A data center project that shows how trialing new tests and concretes with good data-gathering practices clarifies roles and data inputs for PSS.
- A Minnesota road project that demonstrates how performance-oriented test matrices can be developed for new concretes.
- Architecture, engineering, and construction (AEC) groups that show how stakeholders are capable of project-level innovation and test trialing.
These projects try performance tests and share their data and learnings, bringing industry closer to the long-term vision for a standard PSS.
For those wondering where to start trialing PSS on a project, several recent efforts provide starting points, such as new performance-oriented ASTM tests and redlined Department of Transportation (DOT) specifications. Overall, developing a suite of PSS requires testing for workability, strength, and durability. Even selecting a few performance tests from these categories to create project data points helps develop PSS, especially if extra testing is already occurring on low-carbon concrete projects. Each data point upskills workforces and increases stakeholder comfort with a new mode of work. Moreover, test coordination can inform eventual roles delineated by PSS. Together, projects can combine datapoints and vetted tests, leading to a robust, standard PSS that avoids trial and error and helps guarantee performance on future projects.
In the meantime, performance-oriented GWPs and common-sense specification changes enable industry to benefit from PSS today. Though PSS requires overcoming risk-aversion and adopting new education practices, constant discussion and field evidence (such as the rise of C1157 cements) indicate that the time has come for PSS, and that PSS is needed to align the industry with climate goals in the next decade. Finally, PSS development and long-term visions should include equity principles especially around workforce training.
Introduction to Performance Standards and Specifications (PSS)
Globally and in the United States, performance standards and specifications (PSS) have long been discussed as a way of enabling the acceptance of low-carbon concrete mixes in construction, which could lower sector emissions by 25% or more.[1] By specifying performance properties rather than the recipe for concrete, performance standards more readily allow for the use of low-carbon concretes. Outside of low-carbon benefits, PSS also enables more freedom in mixture design, reduced costs for concrete suppliers, and a greater focus on the long-term performance and durability of concrete, the source of many structural failures.
Background and Context
Market changes since initial PSS conversation
Within the past five years, the US concrete industry has undergone marked change with the introduction of PLC and other low-carbon binders like blended cements. The rapid introduction of PLC to the market has required concrete specifiers ranging from DOTs to structural engineering firms to alter specifications (specifically, change C150 to C595) to accommodate blended cements. Additional blended cements are now coming to the market, such as fly-ash, ground granulated steel blast furnace slag (GGBS), and calcined clay cements.[2]
On the other end of the value chain, owners, AEC stakeholders, and policymakers have begun focusing on reducing building material GWP, also referred to as the “embodied carbon” of the project. For example, the General Service Administration of the federal government is actively constructing 154 low embodied-carbon projects. Reducing embodied carbon on projects puts a spotlight on the carbon content of concrete, a key building material.[5]
To meet embodied carbon goals set by owners, project teams have incorporated lower-carbon blended cements into concrete for more projects. Notable projects using blended cements include university buildings in Boston and sports centers in Seattle.[3] Even 100% OPC-free low-carbon cements have been used in concrete at places like Boston’s Seaport and JPMorgan Chase’s New York building, with owner support (though supply of OPC-free cements is still tight).[4] Overall, in the past five years, both the types of low-carbon concrete coming to market and the number of low-carbon concrete projects have dramatically increased.
Importantly, the cement, concrete, and AEC industries are realizing that typical practice, including materials specification, is geared toward OPC-based concrete and does not necessarily apply to new concretes coming to market, resulting in delays and complications. History reveals why: OPC was the cement widely available when prescriptive construction specifications were written and concrete practices were established. Now, real-world project experiences indicate traditional quality test checks may not lead to the same workability or performance in new blends. At a larger scale, project teams are realizing that traditional specifications and operations need to be adjusted to the behavior of new materials. With real-world experiences adding up, it is clear that current specifications need to be updated for new concretes.
Opportunity to unlock PSS
Though industry generally agrees that PSS can reduce materials costs, the chances of long-term structural failures, and emissions (the US Portland Cement Association (PCA) notes that improving performance testing is key to reaching carbon neutrality[6]), bottlenecks still exist to successful PSS adoption in the United States. Setting aside the bottleneck of adopting well-known specification switches (see sidebar: common-sense specification switches that can be done today), a key bottleneck is not knowing what suite of tests can assure concrete performance when composition is not specified. A second key bottleneck is the lack of tests in general that reliably and consistently predict concrete durability, long-term performance, and workability. Though industry started encouraging PSS more than a decade ago, because of these bottlenecks, adoption is not widespread.[7]
With the increasing demand for lower carbon concretes however, a convergence of market and opportunity is occurring. The market is experiencing challenges related to current standards and specifications, and a known opportunity exists to improve concrete sustainability, lower costs, and ensure better building performance; all positive characteristics a project owner looks for. The time is now to invest in the development of PSS through test trialing on projects. PSS developed now would ease the adoption process for new concretes coming to market, providing the AEC industry with means to vet new materials. Understanding how to characterize performance of a variety of concretes is critical to project success, and getting smart on testing and specifications now will minimize construction cost overruns, unexpected schedule delays, and structural issues on future projects.
Moreover, developing PSS now will provide much-needed uniformity in project development involving the use of low-carbon concretes, compared to current one-off, time-consuming project collaborations that are the norm. Robust and trusted PSS would enable project teams to incorporate new concrete using predefined roles, a well-known process, and uniform testing practices. These PSS could define a true “standard” used across jurisdictions and owners, providing consistency across the AEC industry. Ultimately, developing PSS now will bring the global cement and concrete industry closer to safely mitigating emissions to 1.5 degree-levels, by adopting low-carbon concretes in the critical next decade.
A vision for the development of PSS: roles and responsibilities
Development of robust, well-trusted, and standard PSS could proceed by building toward a suite of tests that can holistically predict the performance of concrete. Additionally, it would be important to trial new tests that better measure the durability, long-term performance, and workability of concrete. Overall, the entire cement and concrete value chain has a role to play in developing PSS.
Key Roles for Deployment and Case Studies
How can the development of a list of performance tests, including new workability and durability tests, proceed? The answer is, real-world projects can move the needle on PSS development if used as opportunities to trial tests. Real-world projects already require additional collaboration and testing when a new, low-carbon concrete is used, as outlined in the PCA’s low-carbon protocol.[8] Adopting some performance-oriented tests would support PSS development in tandem.
Real-world projects do not necessarily have to be purpose-engineered to trial PSS. PSS trials could be tacked onto a project for a low-risk component, or for an especially novel low-carbon concrete component. Moreover, hybrid projects that use both OPC concretes and new types of concretes would be perfect for PSS development, because conducting tests on both OPC concrete and new concretes allows for direct performance comparisons. Test results would help confirm whether current test methods and test limits are suitable for assessing new types of concrete. If new tests are trialed, industry will have an opportunity to find the right replacement tests where needed.
Understandably, not all trial tests required for a PSS will be performed on one project due to the singular environment and realistic cost constraints. However, a comprehensive PSS can be pieced together by compiling trial data across multiple projects. Sharing trial test results publicly is critical to developing a comprehensive PSS, as only through multiple sets of data can most appropriate tests and test limits be verified. Public sharing could be facilitated or intermediated by government or industry associations, and further unlocked via creative funding mechanisms. Overall, with the right funding support, real-world projects can start trialing PSS tests today, learning through doing to move towards a long-term PSS vision.
Key roles for deployment
A suggested delineation of PSS development responsibilities for a project with test trials is shown below. Trialing new tests on projects will require the entire project team’s involvement. Stakeholders should work together during the project design phase to determine which components to conduct tests on, what tests to trial, and who is responsible for specific testing needs. Clearly delineating responsibilities for additional testing at the start of the project helps testing to proceed with less hassle.
Exhibit 1. Stakeholder roles for test trialing[9]
Testing ahead of time facilitates the use of more low-carbon materials (and lower project GWP). For example, six months of testing data can adequately determine performance even if the concrete is not allowed under current specifications and standards.
Common testing team entities
Accredited third-party testing labs can typically act as the testing team; otherwise, lab technicians from other stakeholders can fill in. The Coons Tillis Senate bill (S.3439), currently in the Committee on Energy and Natural Resources, proposed a Manufacturing USA institute to conduct testing for concrete.[10] Some projects have partnered with academic labs in addition to third-party testing labs, such as the case studies featured below. In case the primary partnership is remote, a secondary partnership should be established with a local testing lab or concrete supplier.
Responsibility-sharing in a PSS world
PSS may redistribute the responsibilities of the concrete supplier, concrete contractor, general contractor, and structural engineers. Currently, concrete suppliers are responsible for concrete mixtures meeting prescriptive and performance specifications through point of delivery, contractors are responsible for the placing and finishing process of concrete as well as project schedule, and structural engineers are responsible for writing the correct specifications. Under PSS, concrete suppliers may see increased responsibility to meet performance specifications pre-and during project construction (along with greater freedom in mixture design). PSS could clarify contractors’ responsibility for concrete performance by requiring testing of concrete at various points post-delivery such as during placing and finishing. Though a yet unapplied concept, testing at multiple points clarifies concrete performance at each stage and identifies the stakeholder responsible for good or bad performance. Finally, structural engineers (or their functional equivalents) would still be responsible for the ultimate version of PSS used on the project, but if a failure occurs, the specifications may not have the sole point of responsibility. Overall, as seen throughout this piece, responsibilities will be redistributed in a PSS world, not have the sole point of responsibility with more data available.
Going one step further, the PSS should incorporate language around responsibility into writing. Canada’s CSA A23.1: Concrete materials and methods of concrete construction/Test methods and standard practices for concrete is a performance specification that explicitly details responsibilities, resulting in its successful adoption. In the standard, owners and specifiers are responsible for concrete performance if prescriptive requirements are added to the specification, creating an incentive to keep things performance oriented. The concrete supplier is responsible for concrete as delivered, the contractor for concrete in place, and the testing company for accurate and precise test results. Incorporating responsibility division into standard PSS further clarifies redistributed responsibilities and can be a useful addition when developing PSS.
Though PSS clarifies responsibilities, risk aversion still slows down change. Risk aversion stems from engineering life safety concerns, unknown performance characteristics, and aversion to costs from unexpected, PSS-related schedule delays. To tackle risk aversion, comfort around PSS should be built up gradually, such as through trials of PSS-specified concrete mixtures on low stakes project elements. PSS-specified concrete mixtures could undergo additional, independent engineering certification to further assuage risk concerns. Design submittals and contracts could be reworked to manage risk in a PSS world, which would require building relationships today. Appropriate risk-sharing, contracting, and legal frameworks can develop today alongside PSS trials. It is important to remember that a major risk the industry faces is not knowing how to specify new materials after they are introduced to the market, which was seen during the swift transition to PLC. It is time to overcome risk aversion to develop future-proof PSS.
Case studies
The projects described below had project structures and testing practices that can facilitate PSS development. Project stakeholders can adopt these responsibility divisions and testing practices for their first PSS trialing projects. As seen from these case studies, trialing PSS on projects is possible today, and experiences can provide data points on testing, parameter-setting, and role-assignment for future PSS.
1. The National Concrete Pavement Technology Center helps develop performance-oriented concrete pavement mixture standard practice
The National Concrete Pavement Technology Center (CP Tech Center) trialed a suite of new performance tests on several 2022 DOT pavement projects, contributing to the development of AASHTO’s R101 performance-oriented pavement standard practices now adopted by several state DOTs.[11] This CP Tech project highlights key success factors needed to make PSS a reality, including gathering field performance data to relate test results to well-performing mixtures, as well as PSS-appropriate stakeholder roles and responsibilities.
In the trials, CP Tech conducted additional performance-oriented tests on concretes for several DOT pavement projects. These additional performance-oriented tests included the Super Air Meter test, hardened air, resistivity, formation factors, and V-Kelly ball tests, in addition to box and resistivity field tests. Importantly, CP Tech then monitored field performance around salt damage, transport, and freeze-thaw. Using this field data, CP Tech assessed how well the new performance-oriented tests measured concrete properties, eventually relating test results to well-performing mixture designs.[12] Data from the study enabled performance-based tests and acceptance ranges for concrete workability, aggregate stability (D-cracking and alkali-silica reactivity), transport, freeze thaw, and shrinkage to be adopted into AASHTO R101, the standard practice for developing performance engineered concrete mixtures. Using AASHTO R101, DOTs have been able to replace some prescriptive specifications with performance ones.
Unique roles and responsibilities on the project allowed for successful PSS development. Unique roles and responsibilities included willing project owners (state DOTs) integrating testing into active project development, and government and industry associations pooling resources to fund testing. New roles and responsibilities also included concrete suppliers training employees to conduct new tests and providing lab space via quality control labs, concrete contractors incorporating up to multiple testing periods a day into construction plans, and academic and industry experts deciding which tests to trial and subsequently training owner’s team engineers on test methods. The success of this project relied on stakeholders contributing space, time, training, and/or funding. Overall, the CP Tech project provides insight into roles and responsibilities that can facilitate the development and practice PSS. Though the study was focused on concrete pavement, the results lay the groundwork for PSS development in other applications.
2. Tech company “hyper scalers” fund concrete tests for data centers in the Midwest
A group of technology companies that are “hyper scaling” data center construction recently funded a concrete trialing project at Midwest testing lab WJE, which involved replacing a warehouse floor (slab-on-ground) with low-carbon concrete from Ozinga.[13] The goal of the project was to understand if Ozinga’s low-carbon concrete could be used as data center floors. This project highlights how good data-gathering processes on trial projects assists in PSS test and role development.
In this project, WJE tested 70+ cylinders of four mixes of the new low-carbon concrete. Testing was done before, during, and after the pour. Additional test trials included real-time strength-gain sensors, temperature monitors for match-curing, and 56-day strength gain. Importantly, test data and insights from stakeholders were recorded with an intent to publish to the public. The collected test data not only verified mixtures but also provided valuable PSS information on, for example, strength and field performance. Future projects can build off WJE’s data on 56-day strength gain requirements for slab-on-ground, for example, to further develop PSS. Overall, professional data gathering made this project impactful for PSS development.
This project also clarified stakeholder roles and responsibilities in PSS development and practice. Importantly, the concrete contractor provided feedback on placing and finishing, finding that setting time and chemical compatibility were important characteristics for a PSS to specify, thus informing PSS development. If recorded well, project learnings can inform what properties to specify for in PSS. The project also showed that buyers can pool resources to test concretes not covered in prescriptive specifications so they can be included in PSS. Moreover, the testing facility contributed expertise and knowledge of best-in-class testing practices, as well as a willingness to conduct post-placement tests and analyze test results. The project leads supported PSS by releasing test data, a potential first for the private sector on this project. Through trial projects, roles and responsibilities that facilitate PSS development and practice can be clarified.
Case studies of the performance standard for cement being deployed in the field
When the topic of PSS is raised, the apparent lack of use of existing performance standard ASTM C1157 is sometimes used to question the utility of PSS. C1157 is a performance-based standard for cements that has been around since the 1990s.[14] Yet against historic trends, recently there has been a rise of C1157 cement use in projects as seen in Exhibit 2 below. The rise in C1157 cement use shows that sustainability-minded end-users are driving industry to change business as usual, and that new cement blends are maturing and becoming ready for scale-up.
Exhibit 2. Performance-based standard C1157 cements used in the field.
3. MnROAD: A group of DOTs conduct extensive testing on interstate test segments
The National Road Research Alliance (a group of 15 DOTs) tested and placed 16 low-carbon concrete mixtures at the MnROAD facility on I-94 in Minnesota, which subjects the pavements to live traffic, de-icing, and heavy loads from snowplows.[15] Project specifiers can learn from the test matrix development process for this project, which clarified key PSS performance tests and role distributions. A similar and smaller-scale process can be pursued on other projects.
The project testing team developed a comprehensive test matrix and acceptance criteria for the 270’x29’x7.5” pavement test segments by specifying tests across the categories of workability, strength, and durability. They also developed a construction quality assurance plan for field verification (to correlate test results), which included aggregate stockpile checks, materials verification, and ready-mix plant and field observation. Overall, 520 cylinders and 40 beams were used to test around 15 blends, proving the comprehensiveness of the test matrix. New performance tests trialed include the super air meter test, unit weight test (as a way of verifying lab and field material equivalence), box tests and the V-Kelly test, and Microwave and Phoenix water content tests. Additional quality assurance tests conducted beyond a typical project included unrestrained volume change, ASR accelerated mortar beams, time to critical saturation, the Phoenix aggregate test, ASR long-term concrete prisms, expansion of mortar bars in sulfate solution, semi-adiabatic calorimetry, freeze-thaw durability, air voids in hardened concrete, and petrographic analysis of hardened concrete.
To correlate true concrete properties with initial tests, the team is now testing hardened concrete samples with carbon sequestration quantification, electrical resistivity tests, pH tests, pore solution expression tests, and chemical composition analysis. Concrete was also rated on handling, mixing, transportation, workability, placement, consolidation, finishing, and curing, which provides standardized data that can be used to correlate initial testing with final product workability. The development and use of a comprehensive test matrix and quality assurance tests shows how PSS can be trialed on concrete elements for live use.
MnROAD provides contractors and owners insight into the tactical development of a matrix of tests that is more performance-based and applicable to new concretes. Funding from a pooled transportation fund of public and private entities allowed for the testing to occur on this project. The testing team was able to create a comprehensive list of tests to perform on materials, fix their ranges of acceptance, and develop quality assurance plans for new materials and methods, tapping into deep, cross-organization expertise. Startups worked with independent laboratories to demonstrate how trial batch mixtures met these newly required performance properties. Concrete suppliers budgeted time for new and extended quality assurance tests at the plant and on site. Overall, MnROAD gives a glimpse of the test matrix development process for PSS trials as well as stakeholder roles in trialing and ultimately practicing PSS. Replicating the project on smaller scales could lead to significant progress in PSS development across concrete use-cases.
4. Skanska and MKA show how innovation and extended testing are possible on private projects
Skanska, a global construction and development firm with strong climate commitments, is trialing new concretes in projects, such as a test pour of 200 yd3of glass pozzolan concrete (70% cementitious replacement) for a concrete equipment pad on an industrial project in Phoenix, Arizona. The team observed pumping, placing, set time, and finishing characteristics, correlating workability to initial test results on the material. Owners and contractors interested in sustainability could set aside a portion of their project for trialing PSS on newer concretes, working with onsite teams to gather data about performance before, during, and after placement.
Structural engineering firm MKA has previously worked on 10,000, 12,000, and 14,000 psi, high-performance projects that require a significant amount of testing, which they envision to be similar to the level of testing required to practice PSS. They learned to spend more time testing on the front end, prior to project build. MKA’s experience shows that private project teams can conduct extensive testing on projects, meaning PSS trials and practice on private projects is possible.
Education of project stakeholders
Education is critical to successfully adopting PSS. Education includes classroom education and experience-related education. To be successful, education should shed entrenched training techniques from a prescriptive-only, OPC-based era. Classroom education in architecture/design programs could unlock a PSS mindset on projects for the next generation of designers. In the field, technicians and crews can gain field experience by trialing new tests on test slabs or low-risk applications of new concrete. Together, classroom and experience-related education can create an open attitude towards PSS that is critical for a sustainable, lower cost, and long-term performance and durability-focused construction industry.
Starting points for PSS test development
Testing needs
Completely specifying concrete based on performance requires tests measuring strength, durability, and workability. The best tests are practical, quick, and reproducible across labs and in the field (with appropriate ranges for normal variability). Current test procedures for concrete done in the lab and in the field during quality control are a good start but need to be followed more completely, especially in the field, and need to expand beyond slump, total air content, and strength. Moreover, tests need to be specific to end use, for example specific to certain strength and exposure classes. Achieving the right balance of specificity and generalizability will be key to creating a suite of performance tests with which to specify concrete.
Strength
Appropriate strength tests include tests determining set-time and 28- or 56-day strength. Strength specifications typically are performance-based already and require the least change in language. Real-time strength monitoring or match-cure tests may be a more accurate way of testing for strength as sensor technologies come down in cost. Several startups and innovative sensor companies measure strength, including a startup that uses piezoelectric sensors coupled with electromechanical impedance to measure real-time strength non-destructively.[16] New strength tests could be trialed in projects to better understand their ability to predict performance.
Durability
The standards and specifications world has been focusing increasingly on durability, but many durability properties remain uncorrelated to tests included in specifications. Opportunities abound to verify and specify new ASTM and academic tests coming to market. Durability tests include tests for permeability, resistance to winter weather such as freeze-thaw and chemical effects of de-icing chemicals, shrinkage, metal corrosion, aggregate stability, creep, scaling, volume stability, carbonation, and sorptivity. Examples of tests to trial are given in Exhibit 3.
Exhibit 3: Durability tests to trial, by property
Workability
Finally, room for development exists regarding tests for workability, especially past the point of delivery of concrete, which can clarify responsibilities and reduce errors on pours of current and future concretes. An application that may need unique tests here is interior slabs, which concrete contractors have noted differ substantially from other applications. In general, field tests should fit mostly into existing schedules. Tests predicting workability or checking workability in the field include tests for elastic properties, flowability, uniformity, segregation, consolidation, air-void, smoothness, and thermal cracking. ASTM tests like ASTM C1749-17a and C1874-20 methods for measuring rheological properties aim to measure workability.[17] Unit weight measurements can help guarantee material similarity in the lab and in the field, ensuring consistent fresh characteristics. Further research to develop comprehensive workability tests is underway through the Performance Centered Concrete Construction pooled fund.[18] These test examples and other emerging tests can be trialed on projects to confirm their correlations with workability, bringing project teams one step closer to a comprehensive suite of PSS.
Software opportunities
Opportunities for performance measuring also exist in software. New optimization software could inform RMC materials storage, mixture proportioning, admixture addition, mixing time, and time in mixer drum choices, producing a well-performing concrete in the field. In an ideal world, a software program could correlate material composition to field performance, reducing or eliminating batch cylinder testing. Universities like Oregon State University have been working on such software, which can translate properties like SCM content into performance parameters like porosity.[19] In the future, requirements for software results could potentially be built into PSS.
A note on variability
Variability in performance data and test data exists; yet there are ways to characterize and manage variability for PSS and general testing. Importantly, performance of concretes may depend on conditions during placement and curing, such as weather and temperature. To manage the variability in performance and account for conditions, these conditions should be recorded and performance results viewed with knowledge of placement and curing conditions. This will allow a robust PSS to be developed that can correlate to performance even given variability in construction conditions. Some variability in test results may also exist due to testing conditions and technician-based variability. Variability can be accounted for by using both average values and allowing for individual values within a certain expected deviation or range.
Performance-oriented GWP limits
The principles of PSS can be applied to emerging specifications for materials used in a construction project, namely GWP limits. Performance-oriented GWP limits do not prescribe GWP thresholds by concrete member. Rather, GWP limits could be set on a project basis over total square feet, a move industry has indicated leads to lower GWP on projects, or even set as criteria for bid selection. Overall, performance-oriented GWP limits could stretch ambition on projects and send a market signal to contractors that bids are won based on their ability to execute low-carbon construction.
Common-sense specification switches that can be done today
While industry pursues PSS development, several prescriptive specifications can be altered today, including SCM limits, water-cementitious (w/cm) ratios, minimum cementitious material content, restrictions on fly ash, and restrictions on aggregate grading, as listed in Exhibit 4. Underlying these alterations is a move to specify concrete by exposure and durability classes, detailed in the most recent ACI 318 Building Code Requirements for Structural Concrete update. Shifting to specifying concrete by exposure and durability classes reduces unnecessary restrictions on concrete recipes, for example. Class specifications can lead to lower carbon projects: a campus re-development project in the Pacific Northwest switched to specifying by exposure classes instead of assigning blanket w/cm ratios, which resulted in 30% below-average GWP for concrete with no cost premium.[20]
Exhibit 4. Prescriptive specifications commonly identified as having near-term opportunities for change, with recommendations on specification shifts.
More complete recommendations can be found in RMI’s State DOT Concrete Specifications report, Central Concrete’s specifications resource, NRMCA’s Specifications-in-Practice, ClearPath’s Performance Specifications report, and NRMCA’s Exposure Classes and Requirements for Durability resources.[21]
Test options to select from
The industry would not be starting from zero in PSS development. ASTM International, a global standards development organization, continues to develop new performance-oriented standards and standard test methods that can be adopted in specifications. The latest PSS-oriented developments from ASTM include reactivity tests for SCMs (C1897-20), a test method for compressive strength of alkali-activated cementitious mortars (C1928), a performance-based specification for SCMs (WK70466) currently on ballot, and standards covering the performance of non-hydraulic carbonating cements (C1905 and C1910).[22] ASTM’s library of standards and working group items are informed by real-world data and can serve as catalogs for PSS trialing.
Additionally, published performance specifications like Canada’s CSA A23.1 and the U.K.’s BSI Flex standards provide PSS frameworks to follow.[23] Canada’s CSA A23.1 has been implemented since 2009 and resulted in almost all specifications in Canada becoming performance based. CSA A23.1 includes a table of exposure classifications that lists minimum requirements for performance properties. The U.K. recently released BSI Flex 350 v2, a performance-based standard specification for alternative binder system (ABS) concretes. ABS concretes include alkali-activated materials, natural or manufactured pozzolanic materials, and carbonating materials. The specification lists specific ASTM and British Standard tests and acceptable ranges to meet. If an ABS concrete meets BSI Flex, it is more likely to be accepted by project specifiers on a project. Both CSA A23.1 and BSI Flex provide US testing communities with a goalpost for developing a similar suite of tests for concrete.
Reports from ACI, NRMCA, Georgia DOT, and AASHTO also provide comprehensive rough drafts of performance specifications for various applications.[24] Though the DOT and AASHTO documents are pavement-focused, the PSS process and general test types can be extended to other applications. Structural engineers and testing teams can use these guides as a starting point for editing concrete specifications to be more performance-based with minimal guesswork.
Finally, for the task of developing new tests to more completely measure the durability and workability of concrete, previous research from academic and industry organizations provides ideas for which tests to try in the field. Examples include assessing air voids with a super air meter, the Box and V-Kelly tests for workability, and the Weiss electrical resistivity test for determining chloride resistivity.[25] Test methods for sorptivity, conductivity, and resistivity are also in development.[26] These tests can be trialed in the field as they are developed, enabling the movement toward a robust future PSS for industry.
Conclusion
PSS can help transition the concrete industry to net-zero, lower costs, and ensure long-term performance and durability of projects. To enable PSS, performance-predicting tests need to be determined and developed. We have a unique opportunity now to trial these tests on low-carbon concrete projects happening today. Case studies of test development with DOTs, private owner consortiums, and supply-chain stakeholders show that PSS trialing on tests is possible and occurring now.
The rest of the concrete industry has a role to play, applying PSS trialing to local geographies and diverse concrete applications. If testing is done now, industry will be ready with a robust, proven PSS by the time new concretes hit the market at large scale. Startup innovators would then have a target to hit for their low-carbon concretes, accelerating innovation.
Each stakeholder can act today to develop PSS. Owners can fund testing either individually or through consortiums, reaping the benefits of additional monitoring and measurement on their projects. Government and industry associations can fund trials and facilitate public publication of results, building towards a robust PSS. Structural engineers and contractors can explore trialing performance-predicting tests on upcoming projects, and in the meantime, make those common-sense specification switches. Contractors can incorporate test trials into project plans from inception. Materials suppliers can prepare for extra testing at the batch plant. Testing labs can provide consulting, conduct robust testing, and analyze test results to correlate finished material properties to performance tests. Finally, research communities can continue developing cutting-edge tests to trial for durability and workability. Working together on a project, stakeholders can clarify roles, create datapoints on tests, and meaningfully further the development of PSS, ultimately preparing for the diversified concrete future.
Exhibit 5. Roles in developing PSS.
Ultimately, PSS enables lower-carbon, lower-cost, and more durable projects that reduce lifetime maintenance costs. A standardized PSS would enable the safe and uniform use of low-carbon concrete at scale, across firms rather than on individual projects, resulting in the reduction of carbon pollution while avoiding delays and failures. We are at the convergence point of opportunity and market need to develop better performance tests; now is the time to start trialing PSS.
Endnotes
[1] Making Net-Zero Concrete and Cement Possible, Mission Possible Partnership, 2023, https://www.missionpossiblepartnership.org/cc-report-get-the-report/.
[2] “Blended Cement,” Heidelberg Materials, accessed November 6, 2024, https://www.heidelbergmaterials.us/products/cement/blended; and “Industrial Demonstrations Program Selected and Awarded Projects: Cement and Concrete,” US Department of Energy, accessed November 6, 2024, https://www.energy.gov/oced/industrial-demonstrations-program-selected-and-awarded-projects-cement-and-concrete.
[3] “Case Study: Net-Zero Building at Boston University,” Marine Construction Magazine, 2024, http://digitaledition.marineconstructionmagazine.com/article/Case+Study%3A+Net-zero+building+at+Boston+University/4599501/794979/article.html; Lisa Barnard, “Seattle Storm Facility Design with Low Embodied Carbon Concrete,” Gb&d Magazine, March 29, 2024, https://gbdmagazine.com/seattle-storm-facility-design/.
[4] Sam Drysdale. “New Seaport Tower Showcases Low-Carbon Cement from Somerville Firm,” CommonWealth Beacon, October 2, 2024, http://commonwealthbeacon.org/environment/new-seaport-tower-showcases-low-carbon-cement-from-somerville-firm/; “C-Crete Technologies’ Cement-Free Concrete Poured in Manhattan,” Global Cement, October 14, 2024, https://www.globalcement.com/news/item/17974-c-crete-technologies-cement-free-concrete-poured-in-manhattan.
[5] “Low-embodied carbon program details,” US General Servies Administration, last accessed November 22, 2024, https://www.gsa.gov/real-estate/gsa-properties/inflation-reduction-act/lec-program-details.
[6] Roadmap to Carbon Neutrality, Portland Cement Association, October 2021, https://www.cement.org/a-sustainable-future/roadmap-to-carbon-neutrality/.
[7] Karthik H. Obla, Colin L. Lobo, “Prescriptive Specifications: A Reality Check,” Concrete International, August 2015. https://www.nrmca.org/wp-content/uploads/2020/09/prescriptive_specifications.pdf; Report on Performance-Based Requirements for Concrete, American Concrete Institute, 2010,https://www.concrete.org/Portals/0/Files/PDF/Previews/ITG-8R-10web.pdf; Kenneth C. Hover, John Bickley, and Doug R. Hooton, Guide to Specifying Concrete Performance: Phase II Report of Preparation of a Performance-Based Specification for Cast-in-Place Concrete, NRMCA P2P Initiative, March 2008, https://www.nrmca.org/wp-content/uploads/2020/09/GuideSpecFinal.pdf.
[8] Lower Carbon Concrete: Voluntary Guidelines for Developing a Protocol, Portland Cement Association, October 2024, https://www.cement.org/wp-content/uploads/2024/11/PCA_Voluntary_Guidelines_10-31-24_v1_FINAL.pdf
[9] Testing ahead of time facilitates the use of more low-carbon materials (and lower project GWP). For example, six months of testing data can adequately determine performance even if the concrete is not allowed under current specifications and standards.
[10] Concrete and Asphalt Innovation Act of 2023, S.3439, US Congress, December 7, 2023, https://www.congress.gov/bill/118th-congress/senate-bill/3439/all-info.
[11] R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, AASHTO, 2022, https://store.transportation.org/Item/PublicationDetail?ID=4993; “Performance-Engineered Mixtures (PEM),” National Concrete Pavement Technology Center, accessed November 3, 2024. https://cptechcenter.org/performance-engineered-mixtures-pem/.
[12] Commentary on AASHTO R 101, Developing Performance Engineered Concrete Pavement Mixtures, National Concrete Pavement Technology Center, June 2024, https://cdn-wordpress.webspec.cloud/intrans.iastate.edu/uploads/2024/06/commentary_on_AASHTO_R_101_manual_web.pdf.
[13] “Leading Data Center Companies Partner with Open Compute Project Foundation and WJE to Trial Green Concrete!,” Open Compute Project, August 20, 2024, https://www.opencompute.org/blog/leading-data-center-companies-partner-with-open-compute-project-foundation-and-wje-to-trial-green-concrete.
[14] Standard Performance Specification for Hydraulic Cement, ASTM, last updated December 31, 2010, https://www.astm.org/c1157-08a.html.
[15] Nick Weitzel, Development of Mix Designs and Matrix of Materials for MnROAD Low Carbon Concrete Test Site, Minnesota Department of Transportation, March 2024, https://mdl.mndot.gov/items/NRRA202401.
[16] “Products,” Wavelogix, accessed November 4, 2024. https://wavelogix.tech/products/.
[17] Standard Guide for Measurement of the Rheological Properties of Hydraulic Cementious Paste Using a Rotational Rheometer, ASTM, last updated May 24, 2017, https://www.astm.org/c1749-17a.html.; Standard Test Method for Measuring Rheological Properties of Cementitious Materials Using Coaxial Rotational Rheometer, ASTM, last updated July 28, 2020, https://www.astm.org/c1874-20.html.
[18] “Performance Centered concrete Construction,” Transportation Pooled Fund, last updated September 10, 2024, https://pooledfund.org/Details/Study/749.
[19] Keshav Bharadwaj et al., “Predicting Pore Volume, Compressive Strength, Pore Connectivity, and Formation Factor in Cementitious Pastes Containing Fly Ash,” Cement and Concrete Composites 122 (September 1, 2021): 104113. doi:10.1016/j.cemconcomp.2021.104113.
[20] Don Davies, “Performance Concrete Specifications for Lower Carbon Footprints,” Structure Magazine, September 2019, https://www.structuremag.org/article/performance-concrete-specifications-for-lower-carbon-footprints/.
[21] Satyam Maharaj and Anish Tilak, “The Road to Decarbonization: Unlocking State DOT Concrete Specifications,” RMI, April 5, 2024, https://rmi.org/the-road-to-decarbonization-unlocking-state-dot-concrete-specifications/; “Specification Guide: Capturing the Value of Low Carbon Mixes,” Central Concrete Supply Company, n.d., https://files.vulcanmaterials.com/central-concrete/Specification-Guide-Capturing-Value-LowCarbon.pdf; “Specification in Practice (SIP),” NRMCA, accessed November 3, 2024, http://www.nrmca.org/association-resources/research-and-engineering/specification-in-practice-sip/; Paving the Way to Innovation: Moving from Prescriptive to Performance Specifications to Unlock Low-Carbon Cement, Concrete, and Asphalt Innovations, ClearPath, February 2024, https://clearpath.org/wp-content/uploads/sites/44/2024/02/202402_PBS-Research-Report_Final.pdf; Obla, Selecting Exposure Classes and Requirements for Durability, 2023.
[22] Standard Test Methods for Measuring the Reactivity of Supplementary Cementitious Materials by Isothermal Calorimetry and Bound Water Measurements, ASTM, last updated August 6, 2020, https://www.astm.org/c1897-20.html; Standard Test Method for Compressive Strength of Alkali Activated Cementitious Material Mortars (Using 2-in. [50 Mm] Cube Specimens), ASTM, last updated May 25, 2023, https://www.astm.org/c1928_c1928m-23.html; Standard Specification for Concrete Aggregates, ASTM, last updated December 31, 2010, https://www.astm.org/c0033-03.html; Standard Specification for Cements That Require Carbonation Curing, ASTM, last updated July 6, 2023, https://www.astm.org/c1905_c1905m-23.html; Standard Test Methods for Cements That Require Carbonation Curing, ASTM, last updated September 4, 2023, https://www.astm.org/c1910_c1910m-23.html.
[23] CSA A23.1:24/CSA A23.2:24, CSA Group, last updated 2024, https://www.csagroup.org/store/product/2701210/?srsltid=AfmBOorxQm5UQNrgwFiQZQSCWDj3UJo0U-Od8ha82guIJdWqVgI0qrHs; Code of practice., BSI, last updated September 30, 2024, https://knowledge.bsigroup.com/products/alternative-binder-systems-for-lower-carbon-concrete-code-of-practice-11?version=standard.
[24] Report on Performance-Based Requirements, 2010; Hooton, Guide to Specifying Concrete Performance, 2008; Recommendations for Future Specifications, 2024; R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, 2022; BSI Flex 350 v2.0:2024-09 Alternative binder systems for lower carbon concrete.
[25] “Practical Workability Tests for Paving Concrete: Observations from the FHWA Mobile Concrete Technology Center,” FHWA, n.d., https://www.fhwa.dot.gov/pavement/concrete/trailer/resources/hif20061.pdf; W. Jason Weiss et al., Implementing Rapid Durability Measure for Concrete Using Resistivity and Formation Factor, Joint Transportation Research Program, 2020, https://doi.org/10.5703/1288284317120.
[26] Specification in Practice 2 – Limits on water-cementitious materials ratio (w/cm), NRMCA Research Engineering and Standards Committee, 2015, https://www.nrmca.org/wp-content/uploads/2020/04/SIP2.pdf.
Acknowledgements
Thank you to the following people from outside organizations for providing helpful feedback on a draft report (listed in alphabetical order): Chris Bird, Don Davies, Nathan Forrest, Rafae Ghani, Jessica Haberstock, Doug Hooton, Lionel Lemay, Ruth Ni, and Leif Wathne
Disclaimer: Reviewers were not asked to agree with all statements in this report. All remaining errors are the author’s responsibility alone.
Thank you to Ben Skinner and Anish Tilak from RMI for providing feedback and guidance, Mukta Dharmapurikar, previous RMI intern, for research support, and James Sun and Swathi Shantharaju for research support.
Finally, thank you and heartfelt appreciation to the ClimateWorks Foundation for its support and partnership in funding this work.
Performance standards and specifications (PSS) — which focus on desired properties rather than recipes — have long been highlighted as enabling sustainability, reducing costs, and improving both the durability and performance of cement and concrete in the construction industry. However, adoption has been slowed by bottlenecks, such as the need to develop a suite of specifications that can substantially help guarantee concrete performance and the need to develop better durability and long-term performance tests. In the United States, the movement away from ordinary Portland cement (OPC) to blended cements like Portland Limestone Cement (PLC) and Limestone Calcined Clay cement (LC3), combined with increasing considerations of project Global Warming Potential (GWP), mean that now is the time to overcome these bottlenecks and develop PSS. Ultimately, a standard PSS that specifies key tests, parameters, and roles can help unlock scalable, replicable, and efficient construction in a diversified low-carbon concrete future.
The change process has long been a barrier for the adoption of PSS. This insight brief explores tactical recommendations for project stakeholders to develop PSS on their next project, including:
- Owners and developers: allow for testing, report performance, fund test trials
- Government and industry associations: fund test trials, compile results to create a standardized PSS, create knowledge-sharing spaces
- Architects: provide performance requirements for concrete
- Structural engineers: guide test selection for trials and incorporate existing performance-based specifications
- General contractors: develop holistic testing plans from project inception
- Concrete suppliers and contractors: incorporate additional testing into processes ranging from mixture design to finishing
- Testing teams (i.e., third-party labs): be equipped and proficient to conduct newly specified performance tests, adhere to test procedures
- Project lead: oversee progress, report results publicly
- Research community: continue developing performance tests for long-term performance and durability, convene stakeholders
Exhibit ES1 A Roadmap for PSS
Case studies of these roles in action, as well as specific tests to trial, include:
- A National Concrete Pavement Technology Center project that highlights how gathering field performance data to relate test results to well-performing mixtures supports the development of PSS.
- A data center project that shows how trialing new tests and concretes with good data-gathering practices clarifies roles and data inputs for PSS.
- A Minnesota road project that demonstrates how performance-oriented test matrices can be developed for new concretes.
- Architecture, engineering, and construction (AEC) groups that show how stakeholders are capable of project-level innovation and test trialing.
These projects try performance tests and share their data and learnings, bringing industry closer to the long-term vision for a standard PSS.
For those wondering where to start trialing PSS on a project, several recent efforts provide starting points, such as new performance-oriented ASTM tests and redlined Department of Transportation (DOT) specifications. Overall, developing a suite of PSS requires testing for workability, strength, and durability. Even selecting a few performance tests from these categories to create project data points helps develop PSS, especially if extra testing is already occurring on low-carbon concrete projects. Each data point upskills workforces and increases stakeholder comfort with a new mode of work. Moreover, test coordination can inform eventual roles delineated by PSS. Together, projects can combine datapoints and vetted tests, leading to a robust, standard PSS that avoids trial and error and helps guarantee performance on future projects.
In the meantime, performance-oriented GWPs and common-sense specification changes enable industry to benefit from PSS today. Though PSS requires overcoming risk-aversion and adopting new education practices, constant discussion and field evidence (such as the rise of C1157 cements) indicate that the time has come for PSS, and that PSS is needed to align the industry with climate goals in the next decade. Finally, PSS development and long-term visions should include equity principles especially around workforce training.
Globally and in the United States, performance standards and specifications (PSS) have long been discussed as a way of enabling the acceptance of low-carbon concrete mixes in construction, which could lower sector emissions by 25% or more.[1] By specifying performance properties rather than the recipe for concrete, performance standards more readily allow for the use of low-carbon concretes. Outside of low-carbon benefits, PSS also enables more freedom in mixture design, reduced costs for concrete suppliers, and a greater focus on the long-term performance and durability of concrete, the source of many structural failures.
Background and Context
Market changes since initial PSS conversation
Within the past five years, the US concrete industry has undergone marked change with the introduction of PLC and other low-carbon binders like blended cements. The rapid introduction of PLC to the market has required concrete specifiers ranging from DOTs to structural engineering firms to alter specifications (specifically, change C150 to C595) to accommodate blended cements. Additional blended cements are now coming to the market, such as fly-ash, ground granulated steel blast furnace slag (GGBS), and calcined clay cements.[2]
On the other end of the value chain, owners, AEC stakeholders, and policymakers have begun focusing on reducing building material GWP, also referred to as the “embodied carbon” of the project. For example, the General Service Administration of the federal government is actively constructing 154 low embodied-carbon projects. Reducing embodied carbon on projects puts a spotlight on the carbon content of concrete, a key building material.[5]
To meet embodied carbon goals set by owners, project teams have incorporated lower-carbon blended cements into concrete for more projects. Notable projects using blended cements include university buildings in Boston and sports centers in Seattle.[3] Even 100% OPC-free low-carbon cements have been used in concrete at places like Boston’s Seaport and JPMorgan Chase’s New York building, with owner support (though supply of OPC-free cements is still tight).[4] Overall, in the past five years, both the types of low-carbon concrete coming to market and the number of low-carbon concrete projects have dramatically increased.
Importantly, the cement, concrete, and AEC industries are realizing that typical practice, including materials specification, is geared toward OPC-based concrete and does not necessarily apply to new concretes coming to market, resulting in delays and complications. History reveals why: OPC was the cement widely available when prescriptive construction specifications were written and concrete practices were established. Now, real-world project experiences indicate traditional quality test checks may not lead to the same workability or performance in new blends. At a larger scale, project teams are realizing that traditional specifications and operations need to be adjusted to the behavior of new materials. With real-world experiences adding up, it is clear that current specifications need to be updated for new concretes.
Opportunity to unlock PSS
Though industry generally agrees that PSS can reduce materials costs, the chances of long-term structural failures, and emissions (the US Portland Cement Association (PCA) notes that improving performance testing is key to reaching carbon neutrality[6]), bottlenecks still exist to successful PSS adoption in the United States. Setting aside the bottleneck of adopting well-known specification switches (see sidebar: common-sense specification switches that can be done today), a key bottleneck is not knowing what suite of tests can assure concrete performance when composition is not specified. A second key bottleneck is the lack of tests in general that reliably and consistently predict concrete durability, long-term performance, and workability. Though industry started encouraging PSS more than a decade ago, because of these bottlenecks, adoption is not widespread.[7]
With the increasing demand for lower carbon concretes however, a convergence of market and opportunity is occurring. The market is experiencing challenges related to current standards and specifications, and a known opportunity exists to improve concrete sustainability, lower costs, and ensure better building performance; all positive characteristics a project owner looks for. The time is now to invest in the development of PSS through test trialing on projects. PSS developed now would ease the adoption process for new concretes coming to market, providing the AEC industry with means to vet new materials. Understanding how to characterize performance of a variety of concretes is critical to project success, and getting smart on testing and specifications now will minimize construction cost overruns, unexpected schedule delays, and structural issues on future projects.
Moreover, developing PSS now will provide much-needed uniformity in project development involving the use of low-carbon concretes, compared to current one-off, time-consuming project collaborations that are the norm. Robust and trusted PSS would enable project teams to incorporate new concrete using predefined roles, a well-known process, and uniform testing practices. These PSS could define a true “standard” used across jurisdictions and owners, providing consistency across the AEC industry. Ultimately, developing PSS now will bring the global cement and concrete industry closer to safely mitigating emissions to 1.5 degree-levels, by adopting low-carbon concretes in the critical next decade.
A vision for the development of PSS: roles and responsibilities
Development of robust, well-trusted, and standard PSS could proceed by building toward a suite of tests that can holistically predict the performance of concrete. Additionally, it would be important to trial new tests that better measure the durability, long-term performance, and workability of concrete. Overall, the entire cement and concrete value chain has a role to play in developing PSS.
Key Roles for Deployment and Case Studies
How can the development of a list of performance tests, including new workability and durability tests, proceed? The answer is, real-world projects can move the needle on PSS development if used as opportunities to trial tests. Real-world projects already require additional collaboration and testing when a new, low-carbon concrete is used, as outlined in the PCA’s low-carbon protocol.[8] Adopting some performance-oriented tests would support PSS development in tandem.
Real-world projects do not necessarily have to be purpose-engineered to trial PSS. PSS trials could be tacked onto a project for a low-risk component, or for an especially novel low-carbon concrete component. Moreover, hybrid projects that use both OPC concretes and new types of concretes would be perfect for PSS development, because conducting tests on both OPC concrete and new concretes allows for direct performance comparisons. Test results would help confirm whether current test methods and test limits are suitable for assessing new types of concrete. If new tests are trialed, industry will have an opportunity to find the right replacement tests where needed.
Understandably, not all trial tests required for a PSS will be performed on one project due to the singular environment and realistic cost constraints. However, a comprehensive PSS can be pieced together by compiling trial data across multiple projects. Sharing trial test results publicly is critical to developing a comprehensive PSS, as only through multiple sets of data can most appropriate tests and test limits be verified. Public sharing could be facilitated or intermediated by government or industry associations, and further unlocked via creative funding mechanisms. Overall, with the right funding support, real-world projects can start trialing PSS tests today, learning through doing to move towards a long-term PSS vision.
Key roles for deployment
A suggested delineation of PSS development responsibilities for a project with test trials is shown below. Trialing new tests on projects will require the entire project team’s involvement. Stakeholders should work together during the project design phase to determine which components to conduct tests on, what tests to trial, and who is responsible for specific testing needs. Clearly delineating responsibilities for additional testing at the start of the project helps testing to proceed with less hassle.
Exhibit 1. Stakeholder roles for test trialing[9]
Testing ahead of time facilitates the use of more low-carbon materials (and lower project GWP). For example, six months of testing data can adequately determine performance even if the concrete is not allowed under current specifications and standards.
Common testing team entities
Accredited third-party testing labs can typically act as the testing team; otherwise, lab technicians from other stakeholders can fill in. The Coons Tillis Senate bill (S.3439), currently in the Committee on Energy and Natural Resources, proposed a Manufacturing USA institute to conduct testing for concrete.[10] Some projects have partnered with academic labs in addition to third-party testing labs, such as the case studies featured below. In case the primary partnership is remote, a secondary partnership should be established with a local testing lab or concrete supplier.
Responsibility-sharing in a PSS world
PSS may redistribute the responsibilities of the concrete supplier, concrete contractor, general contractor, and structural engineers. Currently, concrete suppliers are responsible for concrete mixtures meeting prescriptive and performance specifications through point of delivery, contractors are responsible for the placing and finishing process of concrete as well as project schedule, and structural engineers are responsible for writing the correct specifications. Under PSS, concrete suppliers may see increased responsibility to meet performance specifications pre-and during project construction (along with greater freedom in mixture design). PSS could clarify contractors’ responsibility for concrete performance by requiring testing of concrete at various points post-delivery such as during placing and finishing. Though a yet unapplied concept, testing at multiple points clarifies concrete performance at each stage and identifies the stakeholder responsible for good or bad performance. Finally, structural engineers (or their functional equivalents) would still be responsible for the ultimate version of PSS used on the project, but if a failure occurs, the specifications may not have the sole point of responsibility. Overall, as seen throughout this piece, responsibilities will be redistributed in a PSS world, not have the sole point of responsibility with more data available.
Going one step further, the PSS should incorporate language around responsibility into writing. Canada’s CSA A23.1: Concrete materials and methods of concrete construction/Test methods and standard practices for concrete is a performance specification that explicitly details responsibilities, resulting in its successful adoption. In the standard, owners and specifiers are responsible for concrete performance if prescriptive requirements are added to the specification, creating an incentive to keep things performance oriented. The concrete supplier is responsible for concrete as delivered, the contractor for concrete in place, and the testing company for accurate and precise test results. Incorporating responsibility division into standard PSS further clarifies redistributed responsibilities and can be a useful addition when developing PSS.
Though PSS clarifies responsibilities, risk aversion still slows down change. Risk aversion stems from engineering life safety concerns, unknown performance characteristics, and aversion to costs from unexpected, PSS-related schedule delays. To tackle risk aversion, comfort around PSS should be built up gradually, such as through trials of PSS-specified concrete mixtures on low stakes project elements. PSS-specified concrete mixtures could undergo additional, independent engineering certification to further assuage risk concerns. Design submittals and contracts could be reworked to manage risk in a PSS world, which would require building relationships today. Appropriate risk-sharing, contracting, and legal frameworks can develop today alongside PSS trials. It is important to remember that a major risk the industry faces is not knowing how to specify new materials after they are introduced to the market, which was seen during the swift transition to PLC. It is time to overcome risk aversion to develop future-proof PSS.
Case studies
The projects described below had project structures and testing practices that can facilitate PSS development. Project stakeholders can adopt these responsibility divisions and testing practices for their first PSS trialing projects. As seen from these case studies, trialing PSS on projects is possible today, and experiences can provide data points on testing, parameter-setting, and role-assignment for future PSS.
1. The National Concrete Pavement Technology Center helps develop performance-oriented concrete pavement mixture standard practice
The National Concrete Pavement Technology Center (CP Tech Center) trialed a suite of new performance tests on several 2022 DOT pavement projects, contributing to the development of AASHTO’s R101 performance-oriented pavement standard practices now adopted by several state DOTs.[11] This CP Tech project highlights key success factors needed to make PSS a reality, including gathering field performance data to relate test results to well-performing mixtures, as well as PSS-appropriate stakeholder roles and responsibilities.
In the trials, CP Tech conducted additional performance-oriented tests on concretes for several DOT pavement projects. These additional performance-oriented tests included the Super Air Meter test, hardened air, resistivity, formation factors, and V-Kelly ball tests, in addition to box and resistivity field tests. Importantly, CP Tech then monitored field performance around salt damage, transport, and freeze-thaw. Using this field data, CP Tech assessed how well the new performance-oriented tests measured concrete properties, eventually relating test results to well-performing mixture designs.[12] Data from the study enabled performance-based tests and acceptance ranges for concrete workability, aggregate stability (D-cracking and alkali-silica reactivity), transport, freeze thaw, and shrinkage to be adopted into AASHTO R101, the standard practice for developing performance engineered concrete mixtures. Using AASHTO R101, DOTs have been able to replace some prescriptive specifications with performance ones.
Unique roles and responsibilities on the project allowed for successful PSS development. Unique roles and responsibilities included willing project owners (state DOTs) integrating testing into active project development, and government and industry associations pooling resources to fund testing. New roles and responsibilities also included concrete suppliers training employees to conduct new tests and providing lab space via quality control labs, concrete contractors incorporating up to multiple testing periods a day into construction plans, and academic and industry experts deciding which tests to trial and subsequently training owner’s team engineers on test methods. The success of this project relied on stakeholders contributing space, time, training, and/or funding. Overall, the CP Tech project provides insight into roles and responsibilities that can facilitate the development and practice PSS. Though the study was focused on concrete pavement, the results lay the groundwork for PSS development in other applications.
2. Tech company “hyper scalers” fund concrete tests for data centers in the Midwest
A group of technology companies that are “hyper scaling” data center construction recently funded a concrete trialing project at Midwest testing lab WJE, which involved replacing a warehouse floor (slab-on-ground) with low-carbon concrete from Ozinga.[13] The goal of the project was to understand if Ozinga’s low-carbon concrete could be used as data center floors. This project highlights how good data-gathering processes on trial projects assists in PSS test and role development.
In this project, WJE tested 70+ cylinders of four mixes of the new low-carbon concrete. Testing was done before, during, and after the pour. Additional test trials included real-time strength-gain sensors, temperature monitors for match-curing, and 56-day strength gain. Importantly, test data and insights from stakeholders were recorded with an intent to publish to the public. The collected test data not only verified mixtures but also provided valuable PSS information on, for example, strength and field performance. Future projects can build off WJE’s data on 56-day strength gain requirements for slab-on-ground, for example, to further develop PSS. Overall, professional data gathering made this project impactful for PSS development.
This project also clarified stakeholder roles and responsibilities in PSS development and practice. Importantly, the concrete contractor provided feedback on placing and finishing, finding that setting time and chemical compatibility were important characteristics for a PSS to specify, thus informing PSS development. If recorded well, project learnings can inform what properties to specify for in PSS. The project also showed that buyers can pool resources to test concretes not covered in prescriptive specifications so they can be included in PSS. Moreover, the testing facility contributed expertise and knowledge of best-in-class testing practices, as well as a willingness to conduct post-placement tests and analyze test results. The project leads supported PSS by releasing test data, a potential first for the private sector on this project. Through trial projects, roles and responsibilities that facilitate PSS development and practice can be clarified.
Case studies of the performance standard for cement being deployed in the field
When the topic of PSS is raised, the apparent lack of use of existing performance standard ASTM C1157 is sometimes used to question the utility of PSS. C1157 is a performance-based standard for cements that has been around since the 1990s.[14] Yet against historic trends, recently there has been a rise of C1157 cement use in projects as seen in Exhibit 2 below. The rise in C1157 cement use shows that sustainability-minded end-users are driving industry to change business as usual, and that new cement blends are maturing and becoming ready for scale-up.
Exhibit 2. Performance-based standard C1157 cements used in the field.
3. MnROAD: A group of DOTs conduct extensive testing on interstate test segments
The National Road Research Alliance (a group of 15 DOTs) tested and placed 16 low-carbon concrete mixtures at the MnROAD facility on I-94 in Minnesota, which subjects the pavements to live traffic, de-icing, and heavy loads from snowplows.[15] Project specifiers can learn from the test matrix development process for this project, which clarified key PSS performance tests and role distributions. A similar and smaller-scale process can be pursued on other projects.
The project testing team developed a comprehensive test matrix and acceptance criteria for the 270’x29’x7.5” pavement test segments by specifying tests across the categories of workability, strength, and durability. They also developed a construction quality assurance plan for field verification (to correlate test results), which included aggregate stockpile checks, materials verification, and ready-mix plant and field observation. Overall, 520 cylinders and 40 beams were used to test around 15 blends, proving the comprehensiveness of the test matrix. New performance tests trialed include the super air meter test, unit weight test (as a way of verifying lab and field material equivalence), box tests and the V-Kelly test, and Microwave and Phoenix water content tests. Additional quality assurance tests conducted beyond a typical project included unrestrained volume change, ASR accelerated mortar beams, time to critical saturation, the Phoenix aggregate test, ASR long-term concrete prisms, expansion of mortar bars in sulfate solution, semi-adiabatic calorimetry, freeze-thaw durability, air voids in hardened concrete, and petrographic analysis of hardened concrete.
To correlate true concrete properties with initial tests, the team is now testing hardened concrete samples with carbon sequestration quantification, electrical resistivity tests, pH tests, pore solution expression tests, and chemical composition analysis. Concrete was also rated on handling, mixing, transportation, workability, placement, consolidation, finishing, and curing, which provides standardized data that can be used to correlate initial testing with final product workability. The development and use of a comprehensive test matrix and quality assurance tests shows how PSS can be trialed on concrete elements for live use.
MnROAD provides contractors and owners insight into the tactical development of a matrix of tests that is more performance-based and applicable to new concretes. Funding from a pooled transportation fund of public and private entities allowed for the testing to occur on this project. The testing team was able to create a comprehensive list of tests to perform on materials, fix their ranges of acceptance, and develop quality assurance plans for new materials and methods, tapping into deep, cross-organization expertise. Startups worked with independent laboratories to demonstrate how trial batch mixtures met these newly required performance properties. Concrete suppliers budgeted time for new and extended quality assurance tests at the plant and on site. Overall, MnROAD gives a glimpse of the test matrix development process for PSS trials as well as stakeholder roles in trialing and ultimately practicing PSS. Replicating the project on smaller scales could lead to significant progress in PSS development across concrete use-cases.
4. Skanska and MKA show how innovation and extended testing are possible on private projects
Skanska, a global construction and development firm with strong climate commitments, is trialing new concretes in projects, such as a test pour of 200 yd3of glass pozzolan concrete (70% cementitious replacement) for a concrete equipment pad on an industrial project in Phoenix, Arizona. The team observed pumping, placing, set time, and finishing characteristics, correlating workability to initial test results on the material. Owners and contractors interested in sustainability could set aside a portion of their project for trialing PSS on newer concretes, working with onsite teams to gather data about performance before, during, and after placement.
Structural engineering firm MKA has previously worked on 10,000, 12,000, and 14,000 psi, high-performance projects that require a significant amount of testing, which they envision to be similar to the level of testing required to practice PSS. They learned to spend more time testing on the front end, prior to project build. MKA’s experience shows that private project teams can conduct extensive testing on projects, meaning PSS trials and practice on private projects is possible.
Education of project stakeholders
Education is critical to successfully adopting PSS. Education includes classroom education and experience-related education. To be successful, education should shed entrenched training techniques from a prescriptive-only, OPC-based era. Classroom education in architecture/design programs could unlock a PSS mindset on projects for the next generation of designers. In the field, technicians and crews can gain field experience by trialing new tests on test slabs or low-risk applications of new concrete. Together, classroom and experience-related education can create an open attitude towards PSS that is critical for a sustainable, lower cost, and long-term performance and durability-focused construction industry.
Starting points for PSS test development
Testing needs
Completely specifying concrete based on performance requires tests measuring strength, durability, and workability. The best tests are practical, quick, and reproducible across labs and in the field (with appropriate ranges for normal variability). Current test procedures for concrete done in the lab and in the field during quality control are a good start but need to be followed more completely, especially in the field, and need to expand beyond slump, total air content, and strength. Moreover, tests need to be specific to end use, for example specific to certain strength and exposure classes. Achieving the right balance of specificity and generalizability will be key to creating a suite of performance tests with which to specify concrete.
Strength
Appropriate strength tests include tests determining set-time and 28- or 56-day strength. Strength specifications typically are performance-based already and require the least change in language. Real-time strength monitoring or match-cure tests may be a more accurate way of testing for strength as sensor technologies come down in cost. Several startups and innovative sensor companies measure strength, including a startup that uses piezoelectric sensors coupled with electromechanical impedance to measure real-time strength non-destructively.[16] New strength tests could be trialed in projects to better understand their ability to predict performance.
Durability
The standards and specifications world has been focusing increasingly on durability, but many durability properties remain uncorrelated to tests included in specifications. Opportunities abound to verify and specify new ASTM and academic tests coming to market. Durability tests include tests for permeability, resistance to winter weather such as freeze-thaw and chemical effects of de-icing chemicals, shrinkage, metal corrosion, aggregate stability, creep, scaling, volume stability, carbonation, and sorptivity. Examples of tests to trial are given in Exhibit 3.
Exhibit 3: Durability tests to trial, by property
Workability
Finally, room for development exists regarding tests for workability, especially past the point of delivery of concrete, which can clarify responsibilities and reduce errors on pours of current and future concretes. An application that may need unique tests here is interior slabs, which concrete contractors have noted differ substantially from other applications. In general, field tests should fit mostly into existing schedules. Tests predicting workability or checking workability in the field include tests for elastic properties, flowability, uniformity, segregation, consolidation, air-void, smoothness, and thermal cracking. ASTM tests like ASTM C1749-17a and C1874-20 methods for measuring rheological properties aim to measure workability.[17] Unit weight measurements can help guarantee material similarity in the lab and in the field, ensuring consistent fresh characteristics. Further research to develop comprehensive workability tests is underway through the Performance Centered Concrete Construction pooled fund.[18] These test examples and other emerging tests can be trialed on projects to confirm their correlations with workability, bringing project teams one step closer to a comprehensive suite of PSS.
Software opportunities
Opportunities for performance measuring also exist in software. New optimization software could inform RMC materials storage, mixture proportioning, admixture addition, mixing time, and time in mixer drum choices, producing a well-performing concrete in the field. In an ideal world, a software program could correlate material composition to field performance, reducing or eliminating batch cylinder testing. Universities like Oregon State University have been working on such software, which can translate properties like SCM content into performance parameters like porosity.[19] In the future, requirements for software results could potentially be built into PSS.
A note on variability
Variability in performance data and test data exists; yet there are ways to characterize and manage variability for PSS and general testing. Importantly, performance of concretes may depend on conditions during placement and curing, such as weather and temperature. To manage the variability in performance and account for conditions, these conditions should be recorded and performance results viewed with knowledge of placement and curing conditions. This will allow a robust PSS to be developed that can correlate to performance even given variability in construction conditions. Some variability in test results may also exist due to testing conditions and technician-based variability. Variability can be accounted for by using both average values and allowing for individual values within a certain expected deviation or range.
Performance-oriented GWP limits
The principles of PSS can be applied to emerging specifications for materials used in a construction project, namely GWP limits. Performance-oriented GWP limits do not prescribe GWP thresholds by concrete member. Rather, GWP limits could be set on a project basis over total square feet, a move industry has indicated leads to lower GWP on projects, or even set as criteria for bid selection. Overall, performance-oriented GWP limits could stretch ambition on projects and send a market signal to contractors that bids are won based on their ability to execute low-carbon construction.
Common-sense specification switches that can be done today
While industry pursues PSS development, several prescriptive specifications can be altered today, including SCM limits, water-cementitious (w/cm) ratios, minimum cementitious material content, restrictions on fly ash, and restrictions on aggregate grading, as listed in Exhibit 4. Underlying these alterations is a move to specify concrete by exposure and durability classes, detailed in the most recent ACI 318 Building Code Requirements for Structural Concrete update. Shifting to specifying concrete by exposure and durability classes reduces unnecessary restrictions on concrete recipes, for example. Class specifications can lead to lower carbon projects: a campus re-development project in the Pacific Northwest switched to specifying by exposure classes instead of assigning blanket w/cm ratios, which resulted in 30% below-average GWP for concrete with no cost premium.[20]
Exhibit 4. Prescriptive specifications commonly identified as having near-term opportunities for change, with recommendations on specification shifts.
More complete recommendations can be found in RMI’s State DOT Concrete Specifications report, Central Concrete’s specifications resource, NRMCA’s Specifications-in-Practice, ClearPath’s Performance Specifications report, and NRMCA’s Exposure Classes and Requirements for Durability resources.[21]
Test options to select from
The industry would not be starting from zero in PSS development. ASTM International, a global standards development organization, continues to develop new performance-oriented standards and standard test methods that can be adopted in specifications. The latest PSS-oriented developments from ASTM include reactivity tests for SCMs (C1897-20), a test method for compressive strength of alkali-activated cementitious mortars (C1928), a performance-based specification for SCMs (WK70466) currently on ballot, and standards covering the performance of non-hydraulic carbonating cements (C1905 and C1910).[22] ASTM’s library of standards and working group items are informed by real-world data and can serve as catalogs for PSS trialing.
Additionally, published performance specifications like Canada’s CSA A23.1 and the U.K.’s BSI Flex standards provide PSS frameworks to follow.[23] Canada’s CSA A23.1 has been implemented since 2009 and resulted in almost all specifications in Canada becoming performance based. CSA A23.1 includes a table of exposure classifications that lists minimum requirements for performance properties. The U.K. recently released BSI Flex 350 v2, a performance-based standard specification for alternative binder system (ABS) concretes. ABS concretes include alkali-activated materials, natural or manufactured pozzolanic materials, and carbonating materials. The specification lists specific ASTM and British Standard tests and acceptable ranges to meet. If an ABS concrete meets BSI Flex, it is more likely to be accepted by project specifiers on a project. Both CSA A23.1 and BSI Flex provide US testing communities with a goalpost for developing a similar suite of tests for concrete.
Reports from ACI, NRMCA, Georgia DOT, and AASHTO also provide comprehensive rough drafts of performance specifications for various applications.[24] Though the DOT and AASHTO documents are pavement-focused, the PSS process and general test types can be extended to other applications. Structural engineers and testing teams can use these guides as a starting point for editing concrete specifications to be more performance-based with minimal guesswork.
Finally, for the task of developing new tests to more completely measure the durability and workability of concrete, previous research from academic and industry organizations provides ideas for which tests to try in the field. Examples include assessing air voids with a super air meter, the Box and V-Kelly tests for workability, and the Weiss electrical resistivity test for determining chloride resistivity.[25] Test methods for sorptivity, conductivity, and resistivity are also in development.[26] These tests can be trialed in the field as they are developed, enabling the movement toward a robust future PSS for industry.
Conclusion
PSS can help transition the concrete industry to net-zero, lower costs, and ensure long-term performance and durability of projects. To enable PSS, performance-predicting tests need to be determined and developed. We have a unique opportunity now to trial these tests on low-carbon concrete projects happening today. Case studies of test development with DOTs, private owner consortiums, and supply-chain stakeholders show that PSS trialing on tests is possible and occurring now.
The rest of the concrete industry has a role to play, applying PSS trialing to local geographies and diverse concrete applications. If testing is done now, industry will be ready with a robust, proven PSS by the time new concretes hit the market at large scale. Startup innovators would then have a target to hit for their low-carbon concretes, accelerating innovation.
Each stakeholder can act today to develop PSS. Owners can fund testing either individually or through consortiums, reaping the benefits of additional monitoring and measurement on their projects. Government and industry associations can fund trials and facilitate public publication of results, building towards a robust PSS. Structural engineers and contractors can explore trialing performance-predicting tests on upcoming projects, and in the meantime, make those common-sense specification switches. Contractors can incorporate test trials into project plans from inception. Materials suppliers can prepare for extra testing at the batch plant. Testing labs can provide consulting, conduct robust testing, and analyze test results to correlate finished material properties to performance tests. Finally, research communities can continue developing cutting-edge tests to trial for durability and workability. Working together on a project, stakeholders can clarify roles, create datapoints on tests, and meaningfully further the development of PSS, ultimately preparing for the diversified concrete future.
Exhibit 5. Roles in developing PSS.
Ultimately, PSS enables lower-carbon, lower-cost, and more durable projects that reduce lifetime maintenance costs. A standardized PSS would enable the safe and uniform use of low-carbon concrete at scale, across firms rather than on individual projects, resulting in the reduction of carbon pollution while avoiding delays and failures. We are at the convergence point of opportunity and market need to develop better performance tests; now is the time to start trialing PSS.
Endnotes
[1] Making Net-Zero Concrete and Cement Possible, Mission Possible Partnership, 2023, https://www.missionpossiblepartnership.org/cc-report-get-the-report/.
[2] “Blended Cement,” Heidelberg Materials, accessed November 6, 2024, https://www.heidelbergmaterials.us/products/cement/blended; and “Industrial Demonstrations Program Selected and Awarded Projects: Cement and Concrete,” US Department of Energy, accessed November 6, 2024, https://www.energy.gov/oced/industrial-demonstrations-program-selected-and-awarded-projects-cement-and-concrete.
[3] “Case Study: Net-Zero Building at Boston University,” Marine Construction Magazine, 2024, http://digitaledition.marineconstructionmagazine.com/article/Case+Study%3A+Net-zero+building+at+Boston+University/4599501/794979/article.html; Lisa Barnard, “Seattle Storm Facility Design with Low Embodied Carbon Concrete,” Gb&d Magazine, March 29, 2024, https://gbdmagazine.com/seattle-storm-facility-design/.
[4] Sam Drysdale. “New Seaport Tower Showcases Low-Carbon Cement from Somerville Firm,” CommonWealth Beacon, October 2, 2024, http://commonwealthbeacon.org/environment/new-seaport-tower-showcases-low-carbon-cement-from-somerville-firm/; “C-Crete Technologies’ Cement-Free Concrete Poured in Manhattan,” Global Cement, October 14, 2024, https://www.globalcement.com/news/item/17974-c-crete-technologies-cement-free-concrete-poured-in-manhattan.
[5] “Low-embodied carbon program details,” US General Servies Administration, last accessed November 22, 2024, https://www.gsa.gov/real-estate/gsa-properties/inflation-reduction-act/lec-program-details.
[6] Roadmap to Carbon Neutrality, Portland Cement Association, October 2021, https://www.cement.org/a-sustainable-future/roadmap-to-carbon-neutrality/.
[7] Karthik H. Obla, Colin L. Lobo, “Prescriptive Specifications: A Reality Check,” Concrete International, August 2015. https://www.nrmca.org/wp-content/uploads/2020/09/prescriptive_specifications.pdf; Report on Performance-Based Requirements for Concrete, American Concrete Institute, 2010,https://www.concrete.org/Portals/0/Files/PDF/Previews/ITG-8R-10web.pdf; Kenneth C. Hover, John Bickley, and Doug R. Hooton, Guide to Specifying Concrete Performance: Phase II Report of Preparation of a Performance-Based Specification for Cast-in-Place Concrete, NRMCA P2P Initiative, March 2008, https://www.nrmca.org/wp-content/uploads/2020/09/GuideSpecFinal.pdf.
[8] Lower Carbon Concrete: Voluntary Guidelines for Developing a Protocol, Portland Cement Association, October 2024, https://www.cement.org/wp-content/uploads/2024/11/PCA_Voluntary_Guidelines_10-31-24_v1_FINAL.pdf
[9] Testing ahead of time facilitates the use of more low-carbon materials (and lower project GWP). For example, six months of testing data can adequately determine performance even if the concrete is not allowed under current specifications and standards.
[10] Concrete and Asphalt Innovation Act of 2023, S.3439, US Congress, December 7, 2023, https://www.congress.gov/bill/118th-congress/senate-bill/3439/all-info.
[11] R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, AASHTO, 2022, https://store.transportation.org/Item/PublicationDetail?ID=4993; “Performance-Engineered Mixtures (PEM),” National Concrete Pavement Technology Center, accessed November 3, 2024. https://cptechcenter.org/performance-engineered-mixtures-pem/.
[12] Commentary on AASHTO R 101, Developing Performance Engineered Concrete Pavement Mixtures, National Concrete Pavement Technology Center, June 2024, https://cdn-wordpress.webspec.cloud/intrans.iastate.edu/uploads/2024/06/commentary_on_AASHTO_R_101_manual_web.pdf.
[13] “Leading Data Center Companies Partner with Open Compute Project Foundation and WJE to Trial Green Concrete!,” Open Compute Project, August 20, 2024, https://www.opencompute.org/blog/leading-data-center-companies-partner-with-open-compute-project-foundation-and-wje-to-trial-green-concrete.
[14] Standard Performance Specification for Hydraulic Cement, ASTM, last updated December 31, 2010, https://www.astm.org/c1157-08a.html.
[15] Nick Weitzel, Development of Mix Designs and Matrix of Materials for MnROAD Low Carbon Concrete Test Site, Minnesota Department of Transportation, March 2024, https://mdl.mndot.gov/items/NRRA202401.
[16] “Products,” Wavelogix, accessed November 4, 2024. https://wavelogix.tech/products/.
[17] Standard Guide for Measurement of the Rheological Properties of Hydraulic Cementious Paste Using a Rotational Rheometer, ASTM, last updated May 24, 2017, https://www.astm.org/c1749-17a.html.; Standard Test Method for Measuring Rheological Properties of Cementitious Materials Using Coaxial Rotational Rheometer, ASTM, last updated July 28, 2020, https://www.astm.org/c1874-20.html.
[18] “Performance Centered concrete Construction,” Transportation Pooled Fund, last updated September 10, 2024, https://pooledfund.org/Details/Study/749.
[19] Keshav Bharadwaj et al., “Predicting Pore Volume, Compressive Strength, Pore Connectivity, and Formation Factor in Cementitious Pastes Containing Fly Ash,” Cement and Concrete Composites 122 (September 1, 2021): 104113. doi:10.1016/j.cemconcomp.2021.104113.
[20] Don Davies, “Performance Concrete Specifications for Lower Carbon Footprints,” Structure Magazine, September 2019, https://www.structuremag.org/article/performance-concrete-specifications-for-lower-carbon-footprints/.
[21] Satyam Maharaj and Anish Tilak, “The Road to Decarbonization: Unlocking State DOT Concrete Specifications,” RMI, April 5, 2024, https://rmi.org/the-road-to-decarbonization-unlocking-state-dot-concrete-specifications/; “Specification Guide: Capturing the Value of Low Carbon Mixes,” Central Concrete Supply Company, n.d., https://files.vulcanmaterials.com/central-concrete/Specification-Guide-Capturing-Value-LowCarbon.pdf; “Specification in Practice (SIP),” NRMCA, accessed November 3, 2024, http://www.nrmca.org/association-resources/research-and-engineering/specification-in-practice-sip/; Paving the Way to Innovation: Moving from Prescriptive to Performance Specifications to Unlock Low-Carbon Cement, Concrete, and Asphalt Innovations, ClearPath, February 2024, https://clearpath.org/wp-content/uploads/sites/44/2024/02/202402_PBS-Research-Report_Final.pdf; Obla, Selecting Exposure Classes and Requirements for Durability, 2023.
[22] Standard Test Methods for Measuring the Reactivity of Supplementary Cementitious Materials by Isothermal Calorimetry and Bound Water Measurements, ASTM, last updated August 6, 2020, https://www.astm.org/c1897-20.html; Standard Test Method for Compressive Strength of Alkali Activated Cementitious Material Mortars (Using 2-in. [50 Mm] Cube Specimens), ASTM, last updated May 25, 2023, https://www.astm.org/c1928_c1928m-23.html; Standard Specification for Concrete Aggregates, ASTM, last updated December 31, 2010, https://www.astm.org/c0033-03.html; Standard Specification for Cements That Require Carbonation Curing, ASTM, last updated July 6, 2023, https://www.astm.org/c1905_c1905m-23.html; Standard Test Methods for Cements That Require Carbonation Curing, ASTM, last updated September 4, 2023, https://www.astm.org/c1910_c1910m-23.html.
[23] CSA A23.1:24/CSA A23.2:24, CSA Group, last updated 2024, https://www.csagroup.org/store/product/2701210/?srsltid=AfmBOorxQm5UQNrgwFiQZQSCWDj3UJo0U-Od8ha82guIJdWqVgI0qrHs; Code of practice., BSI, last updated September 30, 2024, https://knowledge.bsigroup.com/products/alternative-binder-systems-for-lower-carbon-concrete-code-of-practice-11?version=standard.
[24] Report on Performance-Based Requirements, 2010; Hooton, Guide to Specifying Concrete Performance, 2008; Recommendations for Future Specifications, 2024; R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, 2022; BSI Flex 350 v2.0:2024-09 Alternative binder systems for lower carbon concrete.
[25] “Practical Workability Tests for Paving Concrete: Observations from the FHWA Mobile Concrete Technology Center,” FHWA, n.d., https://www.fhwa.dot.gov/pavement/concrete/trailer/resources/hif20061.pdf; W. Jason Weiss et al., Implementing Rapid Durability Measure for Concrete Using Resistivity and Formation Factor, Joint Transportation Research Program, 2020, https://doi.org/10.5703/1288284317120.
[26] Specification in Practice 2 – Limits on water-cementitious materials ratio (w/cm), NRMCA Research Engineering and Standards Committee, 2015, https://www.nrmca.org/wp-content/uploads/2020/04/SIP2.pdf.
Acknowledgements
Thank you to the following people from outside organizations for providing helpful feedback on a draft report (listed in alphabetical order): Chris Bird, Don Davies, Nathan Forrest, Rafae Ghani, Jessica Haberstock, Doug Hooton, Lionel Lemay, Ruth Ni, and Leif Wathne
Disclaimer: Reviewers were not asked to agree with all statements in this report. All remaining errors are the author’s responsibility alone.
Thank you to Ben Skinner and Anish Tilak from RMI for providing feedback and guidance, Mukta Dharmapurikar, previous RMI intern, for research support, and James Sun and Swathi Shantharaju for research support.
Finally, thank you and heartfelt appreciation to the ClimateWorks Foundation for its support and partnership in funding this work.
Market changes since initial PSS conversation
Within the past five years, the US concrete industry has undergone marked change with the introduction of PLC and other low-carbon binders like blended cements. The rapid introduction of PLC to the market has required concrete specifiers ranging from DOTs to structural engineering firms to alter specifications (specifically, change C150 to C595) to accommodate blended cements. Additional blended cements are now coming to the market, such as fly-ash, ground granulated steel blast furnace slag (GGBS), and calcined clay cements.[2]
On the other end of the value chain, owners, AEC stakeholders, and policymakers have begun focusing on reducing building material GWP, also referred to as the “embodied carbon” of the project. For example, the General Service Administration of the federal government is actively constructing 154 low embodied-carbon projects. Reducing embodied carbon on projects puts a spotlight on the carbon content of concrete, a key building material.[5]
To meet embodied carbon goals set by owners, project teams have incorporated lower-carbon blended cements into concrete for more projects. Notable projects using blended cements include university buildings in Boston and sports centers in Seattle.[3] Even 100% OPC-free low-carbon cements have been used in concrete at places like Boston’s Seaport and JPMorgan Chase’s New York building, with owner support (though supply of OPC-free cements is still tight).[4] Overall, in the past five years, both the types of low-carbon concrete coming to market and the number of low-carbon concrete projects have dramatically increased.
Importantly, the cement, concrete, and AEC industries are realizing that typical practice, including materials specification, is geared toward OPC-based concrete and does not necessarily apply to new concretes coming to market, resulting in delays and complications. History reveals why: OPC was the cement widely available when prescriptive construction specifications were written and concrete practices were established. Now, real-world project experiences indicate traditional quality test checks may not lead to the same workability or performance in new blends. At a larger scale, project teams are realizing that traditional specifications and operations need to be adjusted to the behavior of new materials. With real-world experiences adding up, it is clear that current specifications need to be updated for new concretes.
Opportunity to unlock PSS
Though industry generally agrees that PSS can reduce materials costs, the chances of long-term structural failures, and emissions (the US Portland Cement Association (PCA) notes that improving performance testing is key to reaching carbon neutrality[6]), bottlenecks still exist to successful PSS adoption in the United States. Setting aside the bottleneck of adopting well-known specification switches (see sidebar: common-sense specification switches that can be done today), a key bottleneck is not knowing what suite of tests can assure concrete performance when composition is not specified. A second key bottleneck is the lack of tests in general that reliably and consistently predict concrete durability, long-term performance, and workability. Though industry started encouraging PSS more than a decade ago, because of these bottlenecks, adoption is not widespread.[7]
With the increasing demand for lower carbon concretes however, a convergence of market and opportunity is occurring. The market is experiencing challenges related to current standards and specifications, and a known opportunity exists to improve concrete sustainability, lower costs, and ensure better building performance; all positive characteristics a project owner looks for. The time is now to invest in the development of PSS through test trialing on projects. PSS developed now would ease the adoption process for new concretes coming to market, providing the AEC industry with means to vet new materials. Understanding how to characterize performance of a variety of concretes is critical to project success, and getting smart on testing and specifications now will minimize construction cost overruns, unexpected schedule delays, and structural issues on future projects.
Moreover, developing PSS now will provide much-needed uniformity in project development involving the use of low-carbon concretes, compared to current one-off, time-consuming project collaborations that are the norm. Robust and trusted PSS would enable project teams to incorporate new concrete using predefined roles, a well-known process, and uniform testing practices. These PSS could define a true “standard” used across jurisdictions and owners, providing consistency across the AEC industry. Ultimately, developing PSS now will bring the global cement and concrete industry closer to safely mitigating emissions to 1.5 degree-levels, by adopting low-carbon concretes in the critical next decade.
A vision for the development of PSS: roles and responsibilities
Development of robust, well-trusted, and standard PSS could proceed by building toward a suite of tests that can holistically predict the performance of concrete. Additionally, it would be important to trial new tests that better measure the durability, long-term performance, and workability of concrete. Overall, the entire cement and concrete value chain has a role to play in developing PSS.
How can the development of a list of performance tests, including new workability and durability tests, proceed? The answer is, real-world projects can move the needle on PSS development if used as opportunities to trial tests. Real-world projects already require additional collaboration and testing when a new, low-carbon concrete is used, as outlined in the PCA’s low-carbon protocol.[8] Adopting some performance-oriented tests would support PSS development in tandem.
Real-world projects do not necessarily have to be purpose-engineered to trial PSS. PSS trials could be tacked onto a project for a low-risk component, or for an especially novel low-carbon concrete component. Moreover, hybrid projects that use both OPC concretes and new types of concretes would be perfect for PSS development, because conducting tests on both OPC concrete and new concretes allows for direct performance comparisons. Test results would help confirm whether current test methods and test limits are suitable for assessing new types of concrete. If new tests are trialed, industry will have an opportunity to find the right replacement tests where needed.
Understandably, not all trial tests required for a PSS will be performed on one project due to the singular environment and realistic cost constraints. However, a comprehensive PSS can be pieced together by compiling trial data across multiple projects. Sharing trial test results publicly is critical to developing a comprehensive PSS, as only through multiple sets of data can most appropriate tests and test limits be verified. Public sharing could be facilitated or intermediated by government or industry associations, and further unlocked via creative funding mechanisms. Overall, with the right funding support, real-world projects can start trialing PSS tests today, learning through doing to move towards a long-term PSS vision.
Key roles for deployment
A suggested delineation of PSS development responsibilities for a project with test trials is shown below. Trialing new tests on projects will require the entire project team’s involvement. Stakeholders should work together during the project design phase to determine which components to conduct tests on, what tests to trial, and who is responsible for specific testing needs. Clearly delineating responsibilities for additional testing at the start of the project helps testing to proceed with less hassle.
Exhibit 1. Stakeholder roles for test trialing[9]
Testing ahead of time facilitates the use of more low-carbon materials (and lower project GWP). For example, six months of testing data can adequately determine performance even if the concrete is not allowed under current specifications and standards.
Common testing team entities
Accredited third-party testing labs can typically act as the testing team; otherwise, lab technicians from other stakeholders can fill in. The Coons Tillis Senate bill (S.3439), currently in the Committee on Energy and Natural Resources, proposed a Manufacturing USA institute to conduct testing for concrete.[10] Some projects have partnered with academic labs in addition to third-party testing labs, such as the case studies featured below. In case the primary partnership is remote, a secondary partnership should be established with a local testing lab or concrete supplier.
Responsibility-sharing in a PSS world
PSS may redistribute the responsibilities of the concrete supplier, concrete contractor, general contractor, and structural engineers. Currently, concrete suppliers are responsible for concrete mixtures meeting prescriptive and performance specifications through point of delivery, contractors are responsible for the placing and finishing process of concrete as well as project schedule, and structural engineers are responsible for writing the correct specifications. Under PSS, concrete suppliers may see increased responsibility to meet performance specifications pre-and during project construction (along with greater freedom in mixture design). PSS could clarify contractors’ responsibility for concrete performance by requiring testing of concrete at various points post-delivery such as during placing and finishing. Though a yet unapplied concept, testing at multiple points clarifies concrete performance at each stage and identifies the stakeholder responsible for good or bad performance. Finally, structural engineers (or their functional equivalents) would still be responsible for the ultimate version of PSS used on the project, but if a failure occurs, the specifications may not have the sole point of responsibility. Overall, as seen throughout this piece, responsibilities will be redistributed in a PSS world, not have the sole point of responsibility with more data available.
Going one step further, the PSS should incorporate language around responsibility into writing. Canada’s CSA A23.1: Concrete materials and methods of concrete construction/Test methods and standard practices for concrete is a performance specification that explicitly details responsibilities, resulting in its successful adoption. In the standard, owners and specifiers are responsible for concrete performance if prescriptive requirements are added to the specification, creating an incentive to keep things performance oriented. The concrete supplier is responsible for concrete as delivered, the contractor for concrete in place, and the testing company for accurate and precise test results. Incorporating responsibility division into standard PSS further clarifies redistributed responsibilities and can be a useful addition when developing PSS.
Though PSS clarifies responsibilities, risk aversion still slows down change. Risk aversion stems from engineering life safety concerns, unknown performance characteristics, and aversion to costs from unexpected, PSS-related schedule delays. To tackle risk aversion, comfort around PSS should be built up gradually, such as through trials of PSS-specified concrete mixtures on low stakes project elements. PSS-specified concrete mixtures could undergo additional, independent engineering certification to further assuage risk concerns. Design submittals and contracts could be reworked to manage risk in a PSS world, which would require building relationships today. Appropriate risk-sharing, contracting, and legal frameworks can develop today alongside PSS trials. It is important to remember that a major risk the industry faces is not knowing how to specify new materials after they are introduced to the market, which was seen during the swift transition to PLC. It is time to overcome risk aversion to develop future-proof PSS.
Case studies
The projects described below had project structures and testing practices that can facilitate PSS development. Project stakeholders can adopt these responsibility divisions and testing practices for their first PSS trialing projects. As seen from these case studies, trialing PSS on projects is possible today, and experiences can provide data points on testing, parameter-setting, and role-assignment for future PSS.
1. The National Concrete Pavement Technology Center helps develop performance-oriented concrete pavement mixture standard practice
The National Concrete Pavement Technology Center (CP Tech Center) trialed a suite of new performance tests on several 2022 DOT pavement projects, contributing to the development of AASHTO’s R101 performance-oriented pavement standard practices now adopted by several state DOTs.[11] This CP Tech project highlights key success factors needed to make PSS a reality, including gathering field performance data to relate test results to well-performing mixtures, as well as PSS-appropriate stakeholder roles and responsibilities.
In the trials, CP Tech conducted additional performance-oriented tests on concretes for several DOT pavement projects. These additional performance-oriented tests included the Super Air Meter test, hardened air, resistivity, formation factors, and V-Kelly ball tests, in addition to box and resistivity field tests. Importantly, CP Tech then monitored field performance around salt damage, transport, and freeze-thaw. Using this field data, CP Tech assessed how well the new performance-oriented tests measured concrete properties, eventually relating test results to well-performing mixture designs.[12] Data from the study enabled performance-based tests and acceptance ranges for concrete workability, aggregate stability (D-cracking and alkali-silica reactivity), transport, freeze thaw, and shrinkage to be adopted into AASHTO R101, the standard practice for developing performance engineered concrete mixtures. Using AASHTO R101, DOTs have been able to replace some prescriptive specifications with performance ones.
Unique roles and responsibilities on the project allowed for successful PSS development. Unique roles and responsibilities included willing project owners (state DOTs) integrating testing into active project development, and government and industry associations pooling resources to fund testing. New roles and responsibilities also included concrete suppliers training employees to conduct new tests and providing lab space via quality control labs, concrete contractors incorporating up to multiple testing periods a day into construction plans, and academic and industry experts deciding which tests to trial and subsequently training owner’s team engineers on test methods. The success of this project relied on stakeholders contributing space, time, training, and/or funding. Overall, the CP Tech project provides insight into roles and responsibilities that can facilitate the development and practice PSS. Though the study was focused on concrete pavement, the results lay the groundwork for PSS development in other applications.
2. Tech company “hyper scalers” fund concrete tests for data centers in the Midwest
A group of technology companies that are “hyper scaling” data center construction recently funded a concrete trialing project at Midwest testing lab WJE, which involved replacing a warehouse floor (slab-on-ground) with low-carbon concrete from Ozinga.[13] The goal of the project was to understand if Ozinga’s low-carbon concrete could be used as data center floors. This project highlights how good data-gathering processes on trial projects assists in PSS test and role development.
In this project, WJE tested 70+ cylinders of four mixes of the new low-carbon concrete. Testing was done before, during, and after the pour. Additional test trials included real-time strength-gain sensors, temperature monitors for match-curing, and 56-day strength gain. Importantly, test data and insights from stakeholders were recorded with an intent to publish to the public. The collected test data not only verified mixtures but also provided valuable PSS information on, for example, strength and field performance. Future projects can build off WJE’s data on 56-day strength gain requirements for slab-on-ground, for example, to further develop PSS. Overall, professional data gathering made this project impactful for PSS development.
This project also clarified stakeholder roles and responsibilities in PSS development and practice. Importantly, the concrete contractor provided feedback on placing and finishing, finding that setting time and chemical compatibility were important characteristics for a PSS to specify, thus informing PSS development. If recorded well, project learnings can inform what properties to specify for in PSS. The project also showed that buyers can pool resources to test concretes not covered in prescriptive specifications so they can be included in PSS. Moreover, the testing facility contributed expertise and knowledge of best-in-class testing practices, as well as a willingness to conduct post-placement tests and analyze test results. The project leads supported PSS by releasing test data, a potential first for the private sector on this project. Through trial projects, roles and responsibilities that facilitate PSS development and practice can be clarified.
Case studies of the performance standard for cement being deployed in the field
When the topic of PSS is raised, the apparent lack of use of existing performance standard ASTM C1157 is sometimes used to question the utility of PSS. C1157 is a performance-based standard for cements that has been around since the 1990s.[14] Yet against historic trends, recently there has been a rise of C1157 cement use in projects as seen in Exhibit 2 below. The rise in C1157 cement use shows that sustainability-minded end-users are driving industry to change business as usual, and that new cement blends are maturing and becoming ready for scale-up.
Exhibit 2. Performance-based standard C1157 cements used in the field.
3. MnROAD: A group of DOTs conduct extensive testing on interstate test segments
The National Road Research Alliance (a group of 15 DOTs) tested and placed 16 low-carbon concrete mixtures at the MnROAD facility on I-94 in Minnesota, which subjects the pavements to live traffic, de-icing, and heavy loads from snowplows.[15] Project specifiers can learn from the test matrix development process for this project, which clarified key PSS performance tests and role distributions. A similar and smaller-scale process can be pursued on other projects.
The project testing team developed a comprehensive test matrix and acceptance criteria for the 270’x29’x7.5” pavement test segments by specifying tests across the categories of workability, strength, and durability. They also developed a construction quality assurance plan for field verification (to correlate test results), which included aggregate stockpile checks, materials verification, and ready-mix plant and field observation. Overall, 520 cylinders and 40 beams were used to test around 15 blends, proving the comprehensiveness of the test matrix. New performance tests trialed include the super air meter test, unit weight test (as a way of verifying lab and field material equivalence), box tests and the V-Kelly test, and Microwave and Phoenix water content tests. Additional quality assurance tests conducted beyond a typical project included unrestrained volume change, ASR accelerated mortar beams, time to critical saturation, the Phoenix aggregate test, ASR long-term concrete prisms, expansion of mortar bars in sulfate solution, semi-adiabatic calorimetry, freeze-thaw durability, air voids in hardened concrete, and petrographic analysis of hardened concrete.
To correlate true concrete properties with initial tests, the team is now testing hardened concrete samples with carbon sequestration quantification, electrical resistivity tests, pH tests, pore solution expression tests, and chemical composition analysis. Concrete was also rated on handling, mixing, transportation, workability, placement, consolidation, finishing, and curing, which provides standardized data that can be used to correlate initial testing with final product workability. The development and use of a comprehensive test matrix and quality assurance tests shows how PSS can be trialed on concrete elements for live use.
MnROAD provides contractors and owners insight into the tactical development of a matrix of tests that is more performance-based and applicable to new concretes. Funding from a pooled transportation fund of public and private entities allowed for the testing to occur on this project. The testing team was able to create a comprehensive list of tests to perform on materials, fix their ranges of acceptance, and develop quality assurance plans for new materials and methods, tapping into deep, cross-organization expertise. Startups worked with independent laboratories to demonstrate how trial batch mixtures met these newly required performance properties. Concrete suppliers budgeted time for new and extended quality assurance tests at the plant and on site. Overall, MnROAD gives a glimpse of the test matrix development process for PSS trials as well as stakeholder roles in trialing and ultimately practicing PSS. Replicating the project on smaller scales could lead to significant progress in PSS development across concrete use-cases.
4. Skanska and MKA show how innovation and extended testing are possible on private projects
Skanska, a global construction and development firm with strong climate commitments, is trialing new concretes in projects, such as a test pour of 200 yd3of glass pozzolan concrete (70% cementitious replacement) for a concrete equipment pad on an industrial project in Phoenix, Arizona. The team observed pumping, placing, set time, and finishing characteristics, correlating workability to initial test results on the material. Owners and contractors interested in sustainability could set aside a portion of their project for trialing PSS on newer concretes, working with onsite teams to gather data about performance before, during, and after placement.
Structural engineering firm MKA has previously worked on 10,000, 12,000, and 14,000 psi, high-performance projects that require a significant amount of testing, which they envision to be similar to the level of testing required to practice PSS. They learned to spend more time testing on the front end, prior to project build. MKA’s experience shows that private project teams can conduct extensive testing on projects, meaning PSS trials and practice on private projects is possible.
Education of project stakeholders
Education is critical to successfully adopting PSS. Education includes classroom education and experience-related education. To be successful, education should shed entrenched training techniques from a prescriptive-only, OPC-based era. Classroom education in architecture/design programs could unlock a PSS mindset on projects for the next generation of designers. In the field, technicians and crews can gain field experience by trialing new tests on test slabs or low-risk applications of new concrete. Together, classroom and experience-related education can create an open attitude towards PSS that is critical for a sustainable, lower cost, and long-term performance and durability-focused construction industry.
Starting points for PSS test development
Testing needs
Completely specifying concrete based on performance requires tests measuring strength, durability, and workability. The best tests are practical, quick, and reproducible across labs and in the field (with appropriate ranges for normal variability). Current test procedures for concrete done in the lab and in the field during quality control are a good start but need to be followed more completely, especially in the field, and need to expand beyond slump, total air content, and strength. Moreover, tests need to be specific to end use, for example specific to certain strength and exposure classes. Achieving the right balance of specificity and generalizability will be key to creating a suite of performance tests with which to specify concrete.
Strength
Appropriate strength tests include tests determining set-time and 28- or 56-day strength. Strength specifications typically are performance-based already and require the least change in language. Real-time strength monitoring or match-cure tests may be a more accurate way of testing for strength as sensor technologies come down in cost. Several startups and innovative sensor companies measure strength, including a startup that uses piezoelectric sensors coupled with electromechanical impedance to measure real-time strength non-destructively.[16] New strength tests could be trialed in projects to better understand their ability to predict performance.
Durability
The standards and specifications world has been focusing increasingly on durability, but many durability properties remain uncorrelated to tests included in specifications. Opportunities abound to verify and specify new ASTM and academic tests coming to market. Durability tests include tests for permeability, resistance to winter weather such as freeze-thaw and chemical effects of de-icing chemicals, shrinkage, metal corrosion, aggregate stability, creep, scaling, volume stability, carbonation, and sorptivity. Examples of tests to trial are given in Exhibit 3.
Exhibit 3: Durability tests to trial, by property
Workability
Finally, room for development exists regarding tests for workability, especially past the point of delivery of concrete, which can clarify responsibilities and reduce errors on pours of current and future concretes. An application that may need unique tests here is interior slabs, which concrete contractors have noted differ substantially from other applications. In general, field tests should fit mostly into existing schedules. Tests predicting workability or checking workability in the field include tests for elastic properties, flowability, uniformity, segregation, consolidation, air-void, smoothness, and thermal cracking. ASTM tests like ASTM C1749-17a and C1874-20 methods for measuring rheological properties aim to measure workability.[17] Unit weight measurements can help guarantee material similarity in the lab and in the field, ensuring consistent fresh characteristics. Further research to develop comprehensive workability tests is underway through the Performance Centered Concrete Construction pooled fund.[18] These test examples and other emerging tests can be trialed on projects to confirm their correlations with workability, bringing project teams one step closer to a comprehensive suite of PSS.
Software opportunities
Opportunities for performance measuring also exist in software. New optimization software could inform RMC materials storage, mixture proportioning, admixture addition, mixing time, and time in mixer drum choices, producing a well-performing concrete in the field. In an ideal world, a software program could correlate material composition to field performance, reducing or eliminating batch cylinder testing. Universities like Oregon State University have been working on such software, which can translate properties like SCM content into performance parameters like porosity.[19] In the future, requirements for software results could potentially be built into PSS.
A note on variability
Variability in performance data and test data exists; yet there are ways to characterize and manage variability for PSS and general testing. Importantly, performance of concretes may depend on conditions during placement and curing, such as weather and temperature. To manage the variability in performance and account for conditions, these conditions should be recorded and performance results viewed with knowledge of placement and curing conditions. This will allow a robust PSS to be developed that can correlate to performance even given variability in construction conditions. Some variability in test results may also exist due to testing conditions and technician-based variability. Variability can be accounted for by using both average values and allowing for individual values within a certain expected deviation or range.
Performance-oriented GWP limits
The principles of PSS can be applied to emerging specifications for materials used in a construction project, namely GWP limits. Performance-oriented GWP limits do not prescribe GWP thresholds by concrete member. Rather, GWP limits could be set on a project basis over total square feet, a move industry has indicated leads to lower GWP on projects, or even set as criteria for bid selection. Overall, performance-oriented GWP limits could stretch ambition on projects and send a market signal to contractors that bids are won based on their ability to execute low-carbon construction.
Common-sense specification switches that can be done today
While industry pursues PSS development, several prescriptive specifications can be altered today, including SCM limits, water-cementitious (w/cm) ratios, minimum cementitious material content, restrictions on fly ash, and restrictions on aggregate grading, as listed in Exhibit 4. Underlying these alterations is a move to specify concrete by exposure and durability classes, detailed in the most recent ACI 318 Building Code Requirements for Structural Concrete update. Shifting to specifying concrete by exposure and durability classes reduces unnecessary restrictions on concrete recipes, for example. Class specifications can lead to lower carbon projects: a campus re-development project in the Pacific Northwest switched to specifying by exposure classes instead of assigning blanket w/cm ratios, which resulted in 30% below-average GWP for concrete with no cost premium.[20]
Exhibit 4. Prescriptive specifications commonly identified as having near-term opportunities for change, with recommendations on specification shifts.
More complete recommendations can be found in RMI’s State DOT Concrete Specifications report, Central Concrete’s specifications resource, NRMCA’s Specifications-in-Practice, ClearPath’s Performance Specifications report, and NRMCA’s Exposure Classes and Requirements for Durability resources.[21]
Test options to select from
The industry would not be starting from zero in PSS development. ASTM International, a global standards development organization, continues to develop new performance-oriented standards and standard test methods that can be adopted in specifications. The latest PSS-oriented developments from ASTM include reactivity tests for SCMs (C1897-20), a test method for compressive strength of alkali-activated cementitious mortars (C1928), a performance-based specification for SCMs (WK70466) currently on ballot, and standards covering the performance of non-hydraulic carbonating cements (C1905 and C1910).[22] ASTM’s library of standards and working group items are informed by real-world data and can serve as catalogs for PSS trialing.
Additionally, published performance specifications like Canada’s CSA A23.1 and the U.K.’s BSI Flex standards provide PSS frameworks to follow.[23] Canada’s CSA A23.1 has been implemented since 2009 and resulted in almost all specifications in Canada becoming performance based. CSA A23.1 includes a table of exposure classifications that lists minimum requirements for performance properties. The U.K. recently released BSI Flex 350 v2, a performance-based standard specification for alternative binder system (ABS) concretes. ABS concretes include alkali-activated materials, natural or manufactured pozzolanic materials, and carbonating materials. The specification lists specific ASTM and British Standard tests and acceptable ranges to meet. If an ABS concrete meets BSI Flex, it is more likely to be accepted by project specifiers on a project. Both CSA A23.1 and BSI Flex provide US testing communities with a goalpost for developing a similar suite of tests for concrete.
Reports from ACI, NRMCA, Georgia DOT, and AASHTO also provide comprehensive rough drafts of performance specifications for various applications.[24] Though the DOT and AASHTO documents are pavement-focused, the PSS process and general test types can be extended to other applications. Structural engineers and testing teams can use these guides as a starting point for editing concrete specifications to be more performance-based with minimal guesswork.
Finally, for the task of developing new tests to more completely measure the durability and workability of concrete, previous research from academic and industry organizations provides ideas for which tests to try in the field. Examples include assessing air voids with a super air meter, the Box and V-Kelly tests for workability, and the Weiss electrical resistivity test for determining chloride resistivity.[25] Test methods for sorptivity, conductivity, and resistivity are also in development.[26] These tests can be trialed in the field as they are developed, enabling the movement toward a robust future PSS for industry.
Conclusion
PSS can help transition the concrete industry to net-zero, lower costs, and ensure long-term performance and durability of projects. To enable PSS, performance-predicting tests need to be determined and developed. We have a unique opportunity now to trial these tests on low-carbon concrete projects happening today. Case studies of test development with DOTs, private owner consortiums, and supply-chain stakeholders show that PSS trialing on tests is possible and occurring now.
The rest of the concrete industry has a role to play, applying PSS trialing to local geographies and diverse concrete applications. If testing is done now, industry will be ready with a robust, proven PSS by the time new concretes hit the market at large scale. Startup innovators would then have a target to hit for their low-carbon concretes, accelerating innovation.
Each stakeholder can act today to develop PSS. Owners can fund testing either individually or through consortiums, reaping the benefits of additional monitoring and measurement on their projects. Government and industry associations can fund trials and facilitate public publication of results, building towards a robust PSS. Structural engineers and contractors can explore trialing performance-predicting tests on upcoming projects, and in the meantime, make those common-sense specification switches. Contractors can incorporate test trials into project plans from inception. Materials suppliers can prepare for extra testing at the batch plant. Testing labs can provide consulting, conduct robust testing, and analyze test results to correlate finished material properties to performance tests. Finally, research communities can continue developing cutting-edge tests to trial for durability and workability. Working together on a project, stakeholders can clarify roles, create datapoints on tests, and meaningfully further the development of PSS, ultimately preparing for the diversified concrete future.
Exhibit 5. Roles in developing PSS.
Ultimately, PSS enables lower-carbon, lower-cost, and more durable projects that reduce lifetime maintenance costs. A standardized PSS would enable the safe and uniform use of low-carbon concrete at scale, across firms rather than on individual projects, resulting in the reduction of carbon pollution while avoiding delays and failures. We are at the convergence point of opportunity and market need to develop better performance tests; now is the time to start trialing PSS.
Endnotes
[1] Making Net-Zero Concrete and Cement Possible, Mission Possible Partnership, 2023, https://www.missionpossiblepartnership.org/cc-report-get-the-report/.
[2] “Blended Cement,” Heidelberg Materials, accessed November 6, 2024, https://www.heidelbergmaterials.us/products/cement/blended; and “Industrial Demonstrations Program Selected and Awarded Projects: Cement and Concrete,” US Department of Energy, accessed November 6, 2024, https://www.energy.gov/oced/industrial-demonstrations-program-selected-and-awarded-projects-cement-and-concrete.
[3] “Case Study: Net-Zero Building at Boston University,” Marine Construction Magazine, 2024, http://digitaledition.marineconstructionmagazine.com/article/Case+Study%3A+Net-zero+building+at+Boston+University/4599501/794979/article.html; Lisa Barnard, “Seattle Storm Facility Design with Low Embodied Carbon Concrete,” Gb&d Magazine, March 29, 2024, https://gbdmagazine.com/seattle-storm-facility-design/.
[4] Sam Drysdale. “New Seaport Tower Showcases Low-Carbon Cement from Somerville Firm,” CommonWealth Beacon, October 2, 2024, http://commonwealthbeacon.org/environment/new-seaport-tower-showcases-low-carbon-cement-from-somerville-firm/; “C-Crete Technologies’ Cement-Free Concrete Poured in Manhattan,” Global Cement, October 14, 2024, https://www.globalcement.com/news/item/17974-c-crete-technologies-cement-free-concrete-poured-in-manhattan.
[5] “Low-embodied carbon program details,” US General Servies Administration, last accessed November 22, 2024, https://www.gsa.gov/real-estate/gsa-properties/inflation-reduction-act/lec-program-details.
[6] Roadmap to Carbon Neutrality, Portland Cement Association, October 2021, https://www.cement.org/a-sustainable-future/roadmap-to-carbon-neutrality/.
[7] Karthik H. Obla, Colin L. Lobo, “Prescriptive Specifications: A Reality Check,” Concrete International, August 2015. https://www.nrmca.org/wp-content/uploads/2020/09/prescriptive_specifications.pdf; Report on Performance-Based Requirements for Concrete, American Concrete Institute, 2010,https://www.concrete.org/Portals/0/Files/PDF/Previews/ITG-8R-10web.pdf; Kenneth C. Hover, John Bickley, and Doug R. Hooton, Guide to Specifying Concrete Performance: Phase II Report of Preparation of a Performance-Based Specification for Cast-in-Place Concrete, NRMCA P2P Initiative, March 2008, https://www.nrmca.org/wp-content/uploads/2020/09/GuideSpecFinal.pdf.
[8] Lower Carbon Concrete: Voluntary Guidelines for Developing a Protocol, Portland Cement Association, October 2024, https://www.cement.org/wp-content/uploads/2024/11/PCA_Voluntary_Guidelines_10-31-24_v1_FINAL.pdf
[9] Testing ahead of time facilitates the use of more low-carbon materials (and lower project GWP). For example, six months of testing data can adequately determine performance even if the concrete is not allowed under current specifications and standards.
[10] Concrete and Asphalt Innovation Act of 2023, S.3439, US Congress, December 7, 2023, https://www.congress.gov/bill/118th-congress/senate-bill/3439/all-info.
[11] R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, AASHTO, 2022, https://store.transportation.org/Item/PublicationDetail?ID=4993; “Performance-Engineered Mixtures (PEM),” National Concrete Pavement Technology Center, accessed November 3, 2024. https://cptechcenter.org/performance-engineered-mixtures-pem/.
[12] Commentary on AASHTO R 101, Developing Performance Engineered Concrete Pavement Mixtures, National Concrete Pavement Technology Center, June 2024, https://cdn-wordpress.webspec.cloud/intrans.iastate.edu/uploads/2024/06/commentary_on_AASHTO_R_101_manual_web.pdf.
[13] “Leading Data Center Companies Partner with Open Compute Project Foundation and WJE to Trial Green Concrete!,” Open Compute Project, August 20, 2024, https://www.opencompute.org/blog/leading-data-center-companies-partner-with-open-compute-project-foundation-and-wje-to-trial-green-concrete.
[14] Standard Performance Specification for Hydraulic Cement, ASTM, last updated December 31, 2010, https://www.astm.org/c1157-08a.html.
[15] Nick Weitzel, Development of Mix Designs and Matrix of Materials for MnROAD Low Carbon Concrete Test Site, Minnesota Department of Transportation, March 2024, https://mdl.mndot.gov/items/NRRA202401.
[16] “Products,” Wavelogix, accessed November 4, 2024. https://wavelogix.tech/products/.
[17] Standard Guide for Measurement of the Rheological Properties of Hydraulic Cementious Paste Using a Rotational Rheometer, ASTM, last updated May 24, 2017, https://www.astm.org/c1749-17a.html.; Standard Test Method for Measuring Rheological Properties of Cementitious Materials Using Coaxial Rotational Rheometer, ASTM, last updated July 28, 2020, https://www.astm.org/c1874-20.html.
[18] “Performance Centered concrete Construction,” Transportation Pooled Fund, last updated September 10, 2024, https://pooledfund.org/Details/Study/749.
[19] Keshav Bharadwaj et al., “Predicting Pore Volume, Compressive Strength, Pore Connectivity, and Formation Factor in Cementitious Pastes Containing Fly Ash,” Cement and Concrete Composites 122 (September 1, 2021): 104113. doi:10.1016/j.cemconcomp.2021.104113.
[20] Don Davies, “Performance Concrete Specifications for Lower Carbon Footprints,” Structure Magazine, September 2019, https://www.structuremag.org/article/performance-concrete-specifications-for-lower-carbon-footprints/.
[21] Satyam Maharaj and Anish Tilak, “The Road to Decarbonization: Unlocking State DOT Concrete Specifications,” RMI, April 5, 2024, https://rmi.org/the-road-to-decarbonization-unlocking-state-dot-concrete-specifications/; “Specification Guide: Capturing the Value of Low Carbon Mixes,” Central Concrete Supply Company, n.d., https://files.vulcanmaterials.com/central-concrete/Specification-Guide-Capturing-Value-LowCarbon.pdf; “Specification in Practice (SIP),” NRMCA, accessed November 3, 2024, http://www.nrmca.org/association-resources/research-and-engineering/specification-in-practice-sip/; Paving the Way to Innovation: Moving from Prescriptive to Performance Specifications to Unlock Low-Carbon Cement, Concrete, and Asphalt Innovations, ClearPath, February 2024, https://clearpath.org/wp-content/uploads/sites/44/2024/02/202402_PBS-Research-Report_Final.pdf; Obla, Selecting Exposure Classes and Requirements for Durability, 2023.
[22] Standard Test Methods for Measuring the Reactivity of Supplementary Cementitious Materials by Isothermal Calorimetry and Bound Water Measurements, ASTM, last updated August 6, 2020, https://www.astm.org/c1897-20.html; Standard Test Method for Compressive Strength of Alkali Activated Cementitious Material Mortars (Using 2-in. [50 Mm] Cube Specimens), ASTM, last updated May 25, 2023, https://www.astm.org/c1928_c1928m-23.html; Standard Specification for Concrete Aggregates, ASTM, last updated December 31, 2010, https://www.astm.org/c0033-03.html; Standard Specification for Cements That Require Carbonation Curing, ASTM, last updated July 6, 2023, https://www.astm.org/c1905_c1905m-23.html; Standard Test Methods for Cements That Require Carbonation Curing, ASTM, last updated September 4, 2023, https://www.astm.org/c1910_c1910m-23.html.
[23] CSA A23.1:24/CSA A23.2:24, CSA Group, last updated 2024, https://www.csagroup.org/store/product/2701210/?srsltid=AfmBOorxQm5UQNrgwFiQZQSCWDj3UJo0U-Od8ha82guIJdWqVgI0qrHs; Code of practice., BSI, last updated September 30, 2024, https://knowledge.bsigroup.com/products/alternative-binder-systems-for-lower-carbon-concrete-code-of-practice-11?version=standard.
[24] Report on Performance-Based Requirements, 2010; Hooton, Guide to Specifying Concrete Performance, 2008; Recommendations for Future Specifications, 2024; R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, 2022; BSI Flex 350 v2.0:2024-09 Alternative binder systems for lower carbon concrete.
[25] “Practical Workability Tests for Paving Concrete: Observations from the FHWA Mobile Concrete Technology Center,” FHWA, n.d., https://www.fhwa.dot.gov/pavement/concrete/trailer/resources/hif20061.pdf; W. Jason Weiss et al., Implementing Rapid Durability Measure for Concrete Using Resistivity and Formation Factor, Joint Transportation Research Program, 2020, https://doi.org/10.5703/1288284317120.
[26] Specification in Practice 2 – Limits on water-cementitious materials ratio (w/cm), NRMCA Research Engineering and Standards Committee, 2015, https://www.nrmca.org/wp-content/uploads/2020/04/SIP2.pdf.
Acknowledgements
Thank you to the following people from outside organizations for providing helpful feedback on a draft report (listed in alphabetical order): Chris Bird, Don Davies, Nathan Forrest, Rafae Ghani, Jessica Haberstock, Doug Hooton, Lionel Lemay, Ruth Ni, and Leif Wathne
Disclaimer: Reviewers were not asked to agree with all statements in this report. All remaining errors are the author’s responsibility alone.
Thank you to Ben Skinner and Anish Tilak from RMI for providing feedback and guidance, Mukta Dharmapurikar, previous RMI intern, for research support, and James Sun and Swathi Shantharaju for research support.
Finally, thank you and heartfelt appreciation to the ClimateWorks Foundation for its support and partnership in funding this work.
Testing needs
Completely specifying concrete based on performance requires tests measuring strength, durability, and workability. The best tests are practical, quick, and reproducible across labs and in the field (with appropriate ranges for normal variability). Current test procedures for concrete done in the lab and in the field during quality control are a good start but need to be followed more completely, especially in the field, and need to expand beyond slump, total air content, and strength. Moreover, tests need to be specific to end use, for example specific to certain strength and exposure classes. Achieving the right balance of specificity and generalizability will be key to creating a suite of performance tests with which to specify concrete.
Strength
Appropriate strength tests include tests determining set-time and 28- or 56-day strength. Strength specifications typically are performance-based already and require the least change in language. Real-time strength monitoring or match-cure tests may be a more accurate way of testing for strength as sensor technologies come down in cost. Several startups and innovative sensor companies measure strength, including a startup that uses piezoelectric sensors coupled with electromechanical impedance to measure real-time strength non-destructively.[16] New strength tests could be trialed in projects to better understand their ability to predict performance.
Durability
The standards and specifications world has been focusing increasingly on durability, but many durability properties remain uncorrelated to tests included in specifications. Opportunities abound to verify and specify new ASTM and academic tests coming to market. Durability tests include tests for permeability, resistance to winter weather such as freeze-thaw and chemical effects of de-icing chemicals, shrinkage, metal corrosion, aggregate stability, creep, scaling, volume stability, carbonation, and sorptivity. Examples of tests to trial are given in Exhibit 3.
Exhibit 3: Durability tests to trial, by property
Workability
Finally, room for development exists regarding tests for workability, especially past the point of delivery of concrete, which can clarify responsibilities and reduce errors on pours of current and future concretes. An application that may need unique tests here is interior slabs, which concrete contractors have noted differ substantially from other applications. In general, field tests should fit mostly into existing schedules. Tests predicting workability or checking workability in the field include tests for elastic properties, flowability, uniformity, segregation, consolidation, air-void, smoothness, and thermal cracking. ASTM tests like ASTM C1749-17a and C1874-20 methods for measuring rheological properties aim to measure workability.[17] Unit weight measurements can help guarantee material similarity in the lab and in the field, ensuring consistent fresh characteristics. Further research to develop comprehensive workability tests is underway through the Performance Centered Concrete Construction pooled fund.[18] These test examples and other emerging tests can be trialed on projects to confirm their correlations with workability, bringing project teams one step closer to a comprehensive suite of PSS.
Software opportunities
Opportunities for performance measuring also exist in software. New optimization software could inform RMC materials storage, mixture proportioning, admixture addition, mixing time, and time in mixer drum choices, producing a well-performing concrete in the field. In an ideal world, a software program could correlate material composition to field performance, reducing or eliminating batch cylinder testing. Universities like Oregon State University have been working on such software, which can translate properties like SCM content into performance parameters like porosity.[19] In the future, requirements for software results could potentially be built into PSS.
A note on variability
Variability in performance data and test data exists; yet there are ways to characterize and manage variability for PSS and general testing. Importantly, performance of concretes may depend on conditions during placement and curing, such as weather and temperature. To manage the variability in performance and account for conditions, these conditions should be recorded and performance results viewed with knowledge of placement and curing conditions. This will allow a robust PSS to be developed that can correlate to performance even given variability in construction conditions. Some variability in test results may also exist due to testing conditions and technician-based variability. Variability can be accounted for by using both average values and allowing for individual values within a certain expected deviation or range.
Performance-oriented GWP limits
The principles of PSS can be applied to emerging specifications for materials used in a construction project, namely GWP limits. Performance-oriented GWP limits do not prescribe GWP thresholds by concrete member. Rather, GWP limits could be set on a project basis over total square feet, a move industry has indicated leads to lower GWP on projects, or even set as criteria for bid selection. Overall, performance-oriented GWP limits could stretch ambition on projects and send a market signal to contractors that bids are won based on their ability to execute low-carbon construction.
Common-sense specification switches that can be done today
While industry pursues PSS development, several prescriptive specifications can be altered today, including SCM limits, water-cementitious (w/cm) ratios, minimum cementitious material content, restrictions on fly ash, and restrictions on aggregate grading, as listed in Exhibit 4. Underlying these alterations is a move to specify concrete by exposure and durability classes, detailed in the most recent ACI 318 Building Code Requirements for Structural Concrete update. Shifting to specifying concrete by exposure and durability classes reduces unnecessary restrictions on concrete recipes, for example. Class specifications can lead to lower carbon projects: a campus re-development project in the Pacific Northwest switched to specifying by exposure classes instead of assigning blanket w/cm ratios, which resulted in 30% below-average GWP for concrete with no cost premium.[20]
Exhibit 4. Prescriptive specifications commonly identified as having near-term opportunities for change, with recommendations on specification shifts.
More complete recommendations can be found in RMI’s State DOT Concrete Specifications report, Central Concrete’s specifications resource, NRMCA’s Specifications-in-Practice, ClearPath’s Performance Specifications report, and NRMCA’s Exposure Classes and Requirements for Durability resources.[21]
Test options to select from
The industry would not be starting from zero in PSS development. ASTM International, a global standards development organization, continues to develop new performance-oriented standards and standard test methods that can be adopted in specifications. The latest PSS-oriented developments from ASTM include reactivity tests for SCMs (C1897-20), a test method for compressive strength of alkali-activated cementitious mortars (C1928), a performance-based specification for SCMs (WK70466) currently on ballot, and standards covering the performance of non-hydraulic carbonating cements (C1905 and C1910).[22] ASTM’s library of standards and working group items are informed by real-world data and can serve as catalogs for PSS trialing.
Additionally, published performance specifications like Canada’s CSA A23.1 and the U.K.’s BSI Flex standards provide PSS frameworks to follow.[23] Canada’s CSA A23.1 has been implemented since 2009 and resulted in almost all specifications in Canada becoming performance based. CSA A23.1 includes a table of exposure classifications that lists minimum requirements for performance properties. The U.K. recently released BSI Flex 350 v2, a performance-based standard specification for alternative binder system (ABS) concretes. ABS concretes include alkali-activated materials, natural or manufactured pozzolanic materials, and carbonating materials. The specification lists specific ASTM and British Standard tests and acceptable ranges to meet. If an ABS concrete meets BSI Flex, it is more likely to be accepted by project specifiers on a project. Both CSA A23.1 and BSI Flex provide US testing communities with a goalpost for developing a similar suite of tests for concrete.
Reports from ACI, NRMCA, Georgia DOT, and AASHTO also provide comprehensive rough drafts of performance specifications for various applications.[24] Though the DOT and AASHTO documents are pavement-focused, the PSS process and general test types can be extended to other applications. Structural engineers and testing teams can use these guides as a starting point for editing concrete specifications to be more performance-based with minimal guesswork.
Finally, for the task of developing new tests to more completely measure the durability and workability of concrete, previous research from academic and industry organizations provides ideas for which tests to try in the field. Examples include assessing air voids with a super air meter, the Box and V-Kelly tests for workability, and the Weiss electrical resistivity test for determining chloride resistivity.[25] Test methods for sorptivity, conductivity, and resistivity are also in development.[26] These tests can be trialed in the field as they are developed, enabling the movement toward a robust future PSS for industry.
PSS can help transition the concrete industry to net-zero, lower costs, and ensure long-term performance and durability of projects. To enable PSS, performance-predicting tests need to be determined and developed. We have a unique opportunity now to trial these tests on low-carbon concrete projects happening today. Case studies of test development with DOTs, private owner consortiums, and supply-chain stakeholders show that PSS trialing on tests is possible and occurring now.
The rest of the concrete industry has a role to play, applying PSS trialing to local geographies and diverse concrete applications. If testing is done now, industry will be ready with a robust, proven PSS by the time new concretes hit the market at large scale. Startup innovators would then have a target to hit for their low-carbon concretes, accelerating innovation.
Each stakeholder can act today to develop PSS. Owners can fund testing either individually or through consortiums, reaping the benefits of additional monitoring and measurement on their projects. Government and industry associations can fund trials and facilitate public publication of results, building towards a robust PSS. Structural engineers and contractors can explore trialing performance-predicting tests on upcoming projects, and in the meantime, make those common-sense specification switches. Contractors can incorporate test trials into project plans from inception. Materials suppliers can prepare for extra testing at the batch plant. Testing labs can provide consulting, conduct robust testing, and analyze test results to correlate finished material properties to performance tests. Finally, research communities can continue developing cutting-edge tests to trial for durability and workability. Working together on a project, stakeholders can clarify roles, create datapoints on tests, and meaningfully further the development of PSS, ultimately preparing for the diversified concrete future.
Exhibit 5. Roles in developing PSS.
Ultimately, PSS enables lower-carbon, lower-cost, and more durable projects that reduce lifetime maintenance costs. A standardized PSS would enable the safe and uniform use of low-carbon concrete at scale, across firms rather than on individual projects, resulting in the reduction of carbon pollution while avoiding delays and failures. We are at the convergence point of opportunity and market need to develop better performance tests; now is the time to start trialing PSS.
Endnotes
[1] Making Net-Zero Concrete and Cement Possible, Mission Possible Partnership, 2023, https://www.missionpossiblepartnership.org/cc-report-get-the-report/.
[2] “Blended Cement,” Heidelberg Materials, accessed November 6, 2024, https://www.heidelbergmaterials.us/products/cement/blended; and “Industrial Demonstrations Program Selected and Awarded Projects: Cement and Concrete,” US Department of Energy, accessed November 6, 2024, https://www.energy.gov/oced/industrial-demonstrations-program-selected-and-awarded-projects-cement-and-concrete.
[3] “Case Study: Net-Zero Building at Boston University,” Marine Construction Magazine, 2024, http://digitaledition.marineconstructionmagazine.com/article/Case+Study%3A+Net-zero+building+at+Boston+University/4599501/794979/article.html; Lisa Barnard, “Seattle Storm Facility Design with Low Embodied Carbon Concrete,” Gb&d Magazine, March 29, 2024, https://gbdmagazine.com/seattle-storm-facility-design/.
[4] Sam Drysdale. “New Seaport Tower Showcases Low-Carbon Cement from Somerville Firm,” CommonWealth Beacon, October 2, 2024, http://commonwealthbeacon.org/environment/new-seaport-tower-showcases-low-carbon-cement-from-somerville-firm/; “C-Crete Technologies’ Cement-Free Concrete Poured in Manhattan,” Global Cement, October 14, 2024, https://www.globalcement.com/news/item/17974-c-crete-technologies-cement-free-concrete-poured-in-manhattan.
[5] “Low-embodied carbon program details,” US General Servies Administration, last accessed November 22, 2024, https://www.gsa.gov/real-estate/gsa-properties/inflation-reduction-act/lec-program-details.
[6] Roadmap to Carbon Neutrality, Portland Cement Association, October 2021, https://www.cement.org/a-sustainable-future/roadmap-to-carbon-neutrality/.
[7] Karthik H. Obla, Colin L. Lobo, “Prescriptive Specifications: A Reality Check,” Concrete International, August 2015. https://www.nrmca.org/wp-content/uploads/2020/09/prescriptive_specifications.pdf; Report on Performance-Based Requirements for Concrete, American Concrete Institute, 2010,https://www.concrete.org/Portals/0/Files/PDF/Previews/ITG-8R-10web.pdf; Kenneth C. Hover, John Bickley, and Doug R. Hooton, Guide to Specifying Concrete Performance: Phase II Report of Preparation of a Performance-Based Specification for Cast-in-Place Concrete, NRMCA P2P Initiative, March 2008, https://www.nrmca.org/wp-content/uploads/2020/09/GuideSpecFinal.pdf.
[8] Lower Carbon Concrete: Voluntary Guidelines for Developing a Protocol, Portland Cement Association, October 2024, https://www.cement.org/wp-content/uploads/2024/11/PCA_Voluntary_Guidelines_10-31-24_v1_FINAL.pdf
[9] Testing ahead of time facilitates the use of more low-carbon materials (and lower project GWP). For example, six months of testing data can adequately determine performance even if the concrete is not allowed under current specifications and standards.
[10] Concrete and Asphalt Innovation Act of 2023, S.3439, US Congress, December 7, 2023, https://www.congress.gov/bill/118th-congress/senate-bill/3439/all-info.
[11] R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, AASHTO, 2022, https://store.transportation.org/Item/PublicationDetail?ID=4993; “Performance-Engineered Mixtures (PEM),” National Concrete Pavement Technology Center, accessed November 3, 2024. https://cptechcenter.org/performance-engineered-mixtures-pem/.
[12] Commentary on AASHTO R 101, Developing Performance Engineered Concrete Pavement Mixtures, National Concrete Pavement Technology Center, June 2024, https://cdn-wordpress.webspec.cloud/intrans.iastate.edu/uploads/2024/06/commentary_on_AASHTO_R_101_manual_web.pdf.
[13] “Leading Data Center Companies Partner with Open Compute Project Foundation and WJE to Trial Green Concrete!,” Open Compute Project, August 20, 2024, https://www.opencompute.org/blog/leading-data-center-companies-partner-with-open-compute-project-foundation-and-wje-to-trial-green-concrete.
[14] Standard Performance Specification for Hydraulic Cement, ASTM, last updated December 31, 2010, https://www.astm.org/c1157-08a.html.
[15] Nick Weitzel, Development of Mix Designs and Matrix of Materials for MnROAD Low Carbon Concrete Test Site, Minnesota Department of Transportation, March 2024, https://mdl.mndot.gov/items/NRRA202401.
[16] “Products,” Wavelogix, accessed November 4, 2024. https://wavelogix.tech/products/.
[17] Standard Guide for Measurement of the Rheological Properties of Hydraulic Cementious Paste Using a Rotational Rheometer, ASTM, last updated May 24, 2017, https://www.astm.org/c1749-17a.html.; Standard Test Method for Measuring Rheological Properties of Cementitious Materials Using Coaxial Rotational Rheometer, ASTM, last updated July 28, 2020, https://www.astm.org/c1874-20.html.
[18] “Performance Centered concrete Construction,” Transportation Pooled Fund, last updated September 10, 2024, https://pooledfund.org/Details/Study/749.
[19] Keshav Bharadwaj et al., “Predicting Pore Volume, Compressive Strength, Pore Connectivity, and Formation Factor in Cementitious Pastes Containing Fly Ash,” Cement and Concrete Composites 122 (September 1, 2021): 104113. doi:10.1016/j.cemconcomp.2021.104113.
[20] Don Davies, “Performance Concrete Specifications for Lower Carbon Footprints,” Structure Magazine, September 2019, https://www.structuremag.org/article/performance-concrete-specifications-for-lower-carbon-footprints/.
[21] Satyam Maharaj and Anish Tilak, “The Road to Decarbonization: Unlocking State DOT Concrete Specifications,” RMI, April 5, 2024, https://rmi.org/the-road-to-decarbonization-unlocking-state-dot-concrete-specifications/; “Specification Guide: Capturing the Value of Low Carbon Mixes,” Central Concrete Supply Company, n.d., https://files.vulcanmaterials.com/central-concrete/Specification-Guide-Capturing-Value-LowCarbon.pdf; “Specification in Practice (SIP),” NRMCA, accessed November 3, 2024, http://www.nrmca.org/association-resources/research-and-engineering/specification-in-practice-sip/; Paving the Way to Innovation: Moving from Prescriptive to Performance Specifications to Unlock Low-Carbon Cement, Concrete, and Asphalt Innovations, ClearPath, February 2024, https://clearpath.org/wp-content/uploads/sites/44/2024/02/202402_PBS-Research-Report_Final.pdf; Obla, Selecting Exposure Classes and Requirements for Durability, 2023.
[22] Standard Test Methods for Measuring the Reactivity of Supplementary Cementitious Materials by Isothermal Calorimetry and Bound Water Measurements, ASTM, last updated August 6, 2020, https://www.astm.org/c1897-20.html; Standard Test Method for Compressive Strength of Alkali Activated Cementitious Material Mortars (Using 2-in. [50 Mm] Cube Specimens), ASTM, last updated May 25, 2023, https://www.astm.org/c1928_c1928m-23.html; Standard Specification for Concrete Aggregates, ASTM, last updated December 31, 2010, https://www.astm.org/c0033-03.html; Standard Specification for Cements That Require Carbonation Curing, ASTM, last updated July 6, 2023, https://www.astm.org/c1905_c1905m-23.html; Standard Test Methods for Cements That Require Carbonation Curing, ASTM, last updated September 4, 2023, https://www.astm.org/c1910_c1910m-23.html.
[23] CSA A23.1:24/CSA A23.2:24, CSA Group, last updated 2024, https://www.csagroup.org/store/product/2701210/?srsltid=AfmBOorxQm5UQNrgwFiQZQSCWDj3UJo0U-Od8ha82guIJdWqVgI0qrHs; Code of practice., BSI, last updated September 30, 2024, https://knowledge.bsigroup.com/products/alternative-binder-systems-for-lower-carbon-concrete-code-of-practice-11?version=standard.
[24] Report on Performance-Based Requirements, 2010; Hooton, Guide to Specifying Concrete Performance, 2008; Recommendations for Future Specifications, 2024; R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, 2022; BSI Flex 350 v2.0:2024-09 Alternative binder systems for lower carbon concrete.
[25] “Practical Workability Tests for Paving Concrete: Observations from the FHWA Mobile Concrete Technology Center,” FHWA, n.d., https://www.fhwa.dot.gov/pavement/concrete/trailer/resources/hif20061.pdf; W. Jason Weiss et al., Implementing Rapid Durability Measure for Concrete Using Resistivity and Formation Factor, Joint Transportation Research Program, 2020, https://doi.org/10.5703/1288284317120.
[26] Specification in Practice 2 – Limits on water-cementitious materials ratio (w/cm), NRMCA Research Engineering and Standards Committee, 2015, https://www.nrmca.org/wp-content/uploads/2020/04/SIP2.pdf.
Acknowledgements
Thank you to the following people from outside organizations for providing helpful feedback on a draft report (listed in alphabetical order): Chris Bird, Don Davies, Nathan Forrest, Rafae Ghani, Jessica Haberstock, Doug Hooton, Lionel Lemay, Ruth Ni, and Leif Wathne
Disclaimer: Reviewers were not asked to agree with all statements in this report. All remaining errors are the author’s responsibility alone.
Thank you to Ben Skinner and Anish Tilak from RMI for providing feedback and guidance, Mukta Dharmapurikar, previous RMI intern, for research support, and James Sun and Swathi Shantharaju for research support.
Finally, thank you and heartfelt appreciation to the ClimateWorks Foundation for its support and partnership in funding this work.
[1] Making Net-Zero Concrete and Cement Possible, Mission Possible Partnership, 2023, https://www.missionpossiblepartnership.org/cc-report-get-the-report/.
[2] “Blended Cement,” Heidelberg Materials, accessed November 6, 2024, https://www.heidelbergmaterials.us/products/cement/blended; and “Industrial Demonstrations Program Selected and Awarded Projects: Cement and Concrete,” US Department of Energy, accessed November 6, 2024, https://www.energy.gov/oced/industrial-demonstrations-program-selected-and-awarded-projects-cement-and-concrete.
[3] “Case Study: Net-Zero Building at Boston University,” Marine Construction Magazine, 2024, http://digitaledition.marineconstructionmagazine.com/article/Case+Study%3A+Net-zero+building+at+Boston+University/4599501/794979/article.html; Lisa Barnard, “Seattle Storm Facility Design with Low Embodied Carbon Concrete,” Gb&d Magazine, March 29, 2024, https://gbdmagazine.com/seattle-storm-facility-design/.
[4] Sam Drysdale. “New Seaport Tower Showcases Low-Carbon Cement from Somerville Firm,” CommonWealth Beacon, October 2, 2024, http://commonwealthbeacon.org/environment/new-seaport-tower-showcases-low-carbon-cement-from-somerville-firm/; “C-Crete Technologies’ Cement-Free Concrete Poured in Manhattan,” Global Cement, October 14, 2024, https://www.globalcement.com/news/item/17974-c-crete-technologies-cement-free-concrete-poured-in-manhattan.
[5] “Low-embodied carbon program details,” US General Servies Administration, last accessed November 22, 2024, https://www.gsa.gov/real-estate/gsa-properties/inflation-reduction-act/lec-program-details.
[6] Roadmap to Carbon Neutrality, Portland Cement Association, October 2021, https://www.cement.org/a-sustainable-future/roadmap-to-carbon-neutrality/.
[7] Karthik H. Obla, Colin L. Lobo, “Prescriptive Specifications: A Reality Check,” Concrete International, August 2015. https://www.nrmca.org/wp-content/uploads/2020/09/prescriptive_specifications.pdf; Report on Performance-Based Requirements for Concrete, American Concrete Institute, 2010,https://www.concrete.org/Portals/0/Files/PDF/Previews/ITG-8R-10web.pdf; Kenneth C. Hover, John Bickley, and Doug R. Hooton, Guide to Specifying Concrete Performance: Phase II Report of Preparation of a Performance-Based Specification for Cast-in-Place Concrete, NRMCA P2P Initiative, March 2008, https://www.nrmca.org/wp-content/uploads/2020/09/GuideSpecFinal.pdf.
[8] Lower Carbon Concrete: Voluntary Guidelines for Developing a Protocol, Portland Cement Association, October 2024, https://www.cement.org/wp-content/uploads/2024/11/PCA_Voluntary_Guidelines_10-31-24_v1_FINAL.pdf
[9] Testing ahead of time facilitates the use of more low-carbon materials (and lower project GWP). For example, six months of testing data can adequately determine performance even if the concrete is not allowed under current specifications and standards.
[10] Concrete and Asphalt Innovation Act of 2023, S.3439, US Congress, December 7, 2023, https://www.congress.gov/bill/118th-congress/senate-bill/3439/all-info.
[11] R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, AASHTO, 2022, https://store.transportation.org/Item/PublicationDetail?ID=4993; “Performance-Engineered Mixtures (PEM),” National Concrete Pavement Technology Center, accessed November 3, 2024. https://cptechcenter.org/performance-engineered-mixtures-pem/.
[12] Commentary on AASHTO R 101, Developing Performance Engineered Concrete Pavement Mixtures, National Concrete Pavement Technology Center, June 2024, https://cdn-wordpress.webspec.cloud/intrans.iastate.edu/uploads/2024/06/commentary_on_AASHTO_R_101_manual_web.pdf.
[13] “Leading Data Center Companies Partner with Open Compute Project Foundation and WJE to Trial Green Concrete!,” Open Compute Project, August 20, 2024, https://www.opencompute.org/blog/leading-data-center-companies-partner-with-open-compute-project-foundation-and-wje-to-trial-green-concrete.
[14] Standard Performance Specification for Hydraulic Cement, ASTM, last updated December 31, 2010, https://www.astm.org/c1157-08a.html.
[15] Nick Weitzel, Development of Mix Designs and Matrix of Materials for MnROAD Low Carbon Concrete Test Site, Minnesota Department of Transportation, March 2024, https://mdl.mndot.gov/items/NRRA202401.
[16] “Products,” Wavelogix, accessed November 4, 2024. https://wavelogix.tech/products/.
[17] Standard Guide for Measurement of the Rheological Properties of Hydraulic Cementious Paste Using a Rotational Rheometer, ASTM, last updated May 24, 2017, https://www.astm.org/c1749-17a.html.; Standard Test Method for Measuring Rheological Properties of Cementitious Materials Using Coaxial Rotational Rheometer, ASTM, last updated July 28, 2020, https://www.astm.org/c1874-20.html.
[18] “Performance Centered concrete Construction,” Transportation Pooled Fund, last updated September 10, 2024, https://pooledfund.org/Details/Study/749.
[19] Keshav Bharadwaj et al., “Predicting Pore Volume, Compressive Strength, Pore Connectivity, and Formation Factor in Cementitious Pastes Containing Fly Ash,” Cement and Concrete Composites 122 (September 1, 2021): 104113. doi:10.1016/j.cemconcomp.2021.104113.
[20] Don Davies, “Performance Concrete Specifications for Lower Carbon Footprints,” Structure Magazine, September 2019, https://www.structuremag.org/article/performance-concrete-specifications-for-lower-carbon-footprints/.
[21] Satyam Maharaj and Anish Tilak, “The Road to Decarbonization: Unlocking State DOT Concrete Specifications,” RMI, April 5, 2024, https://rmi.org/the-road-to-decarbonization-unlocking-state-dot-concrete-specifications/; “Specification Guide: Capturing the Value of Low Carbon Mixes,” Central Concrete Supply Company, n.d., https://files.vulcanmaterials.com/central-concrete/Specification-Guide-Capturing-Value-LowCarbon.pdf; “Specification in Practice (SIP),” NRMCA, accessed November 3, 2024, http://www.nrmca.org/association-resources/research-and-engineering/specification-in-practice-sip/; Paving the Way to Innovation: Moving from Prescriptive to Performance Specifications to Unlock Low-Carbon Cement, Concrete, and Asphalt Innovations, ClearPath, February 2024, https://clearpath.org/wp-content/uploads/sites/44/2024/02/202402_PBS-Research-Report_Final.pdf; Obla, Selecting Exposure Classes and Requirements for Durability, 2023.
[22] Standard Test Methods for Measuring the Reactivity of Supplementary Cementitious Materials by Isothermal Calorimetry and Bound Water Measurements, ASTM, last updated August 6, 2020, https://www.astm.org/c1897-20.html; Standard Test Method for Compressive Strength of Alkali Activated Cementitious Material Mortars (Using 2-in. [50 Mm] Cube Specimens), ASTM, last updated May 25, 2023, https://www.astm.org/c1928_c1928m-23.html; Standard Specification for Concrete Aggregates, ASTM, last updated December 31, 2010, https://www.astm.org/c0033-03.html; Standard Specification for Cements That Require Carbonation Curing, ASTM, last updated July 6, 2023, https://www.astm.org/c1905_c1905m-23.html; Standard Test Methods for Cements That Require Carbonation Curing, ASTM, last updated September 4, 2023, https://www.astm.org/c1910_c1910m-23.html.
[23] CSA A23.1:24/CSA A23.2:24, CSA Group, last updated 2024, https://www.csagroup.org/store/product/2701210/?srsltid=AfmBOorxQm5UQNrgwFiQZQSCWDj3UJo0U-Od8ha82guIJdWqVgI0qrHs; Code of practice., BSI, last updated September 30, 2024, https://knowledge.bsigroup.com/products/alternative-binder-systems-for-lower-carbon-concrete-code-of-practice-11?version=standard.
[24] Report on Performance-Based Requirements, 2010; Hooton, Guide to Specifying Concrete Performance, 2008; Recommendations for Future Specifications, 2024; R101 Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, 2022; BSI Flex 350 v2.0:2024-09 Alternative binder systems for lower carbon concrete.
[25] “Practical Workability Tests for Paving Concrete: Observations from the FHWA Mobile Concrete Technology Center,” FHWA, n.d., https://www.fhwa.dot.gov/pavement/concrete/trailer/resources/hif20061.pdf; W. Jason Weiss et al., Implementing Rapid Durability Measure for Concrete Using Resistivity and Formation Factor, Joint Transportation Research Program, 2020, https://doi.org/10.5703/1288284317120.
[26] Specification in Practice 2 – Limits on water-cementitious materials ratio (w/cm), NRMCA Research Engineering and Standards Committee, 2015, https://www.nrmca.org/wp-content/uploads/2020/04/SIP2.pdf.
Thank you to the following people from outside organizations for providing helpful feedback on a draft report (listed in alphabetical order): Chris Bird, Don Davies, Nathan Forrest, Rafae Ghani, Jessica Haberstock, Doug Hooton, Lionel Lemay, Ruth Ni, and Leif Wathne
Disclaimer: Reviewers were not asked to agree with all statements in this report. All remaining errors are the author’s responsibility alone.
Thank you to Ben Skinner and Anish Tilak from RMI for providing feedback and guidance, Mukta Dharmapurikar, previous RMI intern, for research support, and James Sun and Swathi Shantharaju for research support.
Finally, thank you and heartfelt appreciation to the ClimateWorks Foundation for its support and partnership in funding this work.