Using Biomaterials to Shrink the Building Industry’s Carbon Footprint

A Q&A with Dr. Wil Srubar of the University of Colorado Boulder

As the building industry seeks to lower its carbon emissions, scientists and entrepreneurs are exploring novel solutions to reduce the so-called embodied carbon of building materials. Embodied carbon refers to the cumulative emissions across a product’s life cycle, from extraction to manufacturing and beyond.

The solutions range from low tech (using less material) to high tech (using specially engineered biomaterials that mimic or improve on traditional material properties). To learn more about the latest in novel biomaterials for construction, RMI’s Victor Olgyay and Matt Jungclaus spoke with Dr. Wil Srubar III, an associate professor at the University of Colorado Boulder. Srubar’s work ranges from “living concrete” and portland cement made from microalgae to a marketplace for embodied carbon offsets. An edited transcript follows.


RMI: How did you get into working with biomaterials for construction?

Srubar: I’m a structural engineer by training. I was working at a structural engineering firm in the mid-2000s, around the time the green building movement began to build momentum. I kept asking my supervisor at the time, what are structural engineers doing to advance sustainability?

She shrugged and really had no answers for me, other than, well, we put fly ash in concrete, and then it’s up to the energy engineers to make buildings energy efficient. Her answer never sat well with me. I thought there was more that we could do.

I had fallen in love with concrete and materials chemistry while I was getting my master’s degree at UT Austin. So when I went on to get my Ph.D. at Stanford, I wanted to study emerging materials, like biomaterials, and understand how they could be used in construction. During my Ph.D., we were looking at bioplastics grown using bacteria. These particular bacteria used methane as their carbon source to make and store bioplastic—a lot like how we store excess calories as fat. We could harvest the bioplastic and engineer that into fully biobased, durable building materials, like wood-bioplastic composites.

When I got my Ph.D. around 2013—which was not that long ago—I was still very much an outlier advocating for the use of lower-carbon and even carbon-storing biomaterials in construction.

Dr. Wil Srubar III of the University of Colorado Boulder. Credit: CU School of Engineering


Now you have a whole lab dedicated to living materials. How did you get there?

I had a background in structural engineering, but also biomaterials science, and I have always been really environmentally minded—probably because I grew up on a farm. So my research program at the University of Colorado Boulder is really focused on integrating biology with traditional construction materials science to create low-carbon and carbon-storing biobased building materials.

Around the time that I started at CU, I met Kate Simonen at the Carbon Leadership Forum. She had already assembled what she affectionately calls a group of nerds who were really interested in quantifying the sustainability of construction materials—more explicitly, quantifying and reducing embodied carbon emissions. Everyone involved with the CLF quickly realized that it’s a significant problem, and we have to do something about it.

My lab believes that growing building materials using biology is part of the solution.


What aspect of your research is particularly exciting to you?

A tiny little organism called the coccolithophore! They’re tiny little microalgae that form calcium carbonate shells. And they grow really rapidly. They grow in seawater. What’s really exciting is that growing calcium carbonate is a form of carbon capture and storage.

My lab is particularly interested in taking the coccolith’s shells and using that as an input for making portland cement, rather than mining or quarrying limestone and burning off the CO2 that has been stored for millennia. We kind of had this epiphany a few years ago—why not grow the limestone in real time and make a carbon-neutral portland cement?

My NSF Career Award is based on the idea of using this grown, carbon-storing limestone for cementitious materials. We spun out a company that has licensed this intellectual property to make portland cement from these calcareous microalgae. And we’re going all in on this because when we look at the true hot spot problems in construction, it’s cement, first and foremost.


That company is Minus Materials?

Yes. I have two other startups as well. Prometheus Materials recently spun out of a five-year collaboration I have had with three very talented professors, Dr. Mija Hubler, Dr. Sherri Cook, and Dr. Jeff Cameron. Prometheus Materials licensed our living concrete technology that was featured in the New York Times. We’ve brought a CEO on board, and we have some additional funding from DARPA to accelerate commercialization. We have customers already lined up, so we’re laser-focused on scaling that technology.

And then the third company is Aureus Earth, which has created the first market-based incentive program that financially incentivizes building owners to use and specify low-carbon and carbon-storing building material alternatives. We know project owners and design teams have a choice: do you choose the materials with high carbon intensity? Or do you choose the lower-carbon alternative, which can sometimes come at a green premium?

The best example we can give is this: consider you are a developer and are interested in building a mid-rise commercial building. Should you build out of concrete, steel, or mass timber? The price of lumber is quite volatile, and it’s at an all-time high right now, so there’s certainly a green premium to build with mass timber.

Aureus Earth’s model is to interject very early in the design process to incentivize project owners to select low-carbon or carbon-storing alternatives. We do this by monetizing the delta in the carbon emissions that project teams avoid and by monetizing the actual carbon asset—the physical biogenic carbon stored in the building. We convert the carbon emissions avoidance and the biogenic carbon storage into carbon offset equivalents, which are sellable on the voluntary carbon market. It’s really a win-win-win for builders, buyers of carbon offsets, and the planet.


What other products are you paying attention to?

Mass timber, namely cross-laminated timber (CLT), is by far the poster child for the biotechnology revolution in construction. It doesn’t matter which manufacturer is making CLT; products are now standardized. I really think that the success of CLT and its ability to break through political, code, and technical barriers over the past 10 years provides a roadmap for other biobased building material technologies.

I think everybody in the construction industry is really excited about Blue Planet’s potential. Blue Planet creates artificial aggregates for concrete by reacting CO2 with a calcium source, which they get from waste concrete. If you look at the volume of concrete, more than 80 percent of it is aggregates. So if you can create or synthesize all of that aggregate from waste CO2, you’re effectively making a carbon-negative concrete. I know Blue Planet is building a pilot plant in the Bay Area, and we’re all watching to see if it’s successful.

It’s not on everybody’s radar, but regional manufacturers of hemp-based products are popping up, because we’re now able to cultivate hemp in the United States. It is a wickedly fast-growing plant. And it is a super-strong fiber.

You have hemp fiber insulation that’s really competing well with cellulose insulation. You have hemp boards that are being pressed into structural boards, much like an OSB or plywood. And you have hempcrete, which is usually used as an insulation material. There’s a lot of regional variation in the products, because the economics of these agricultural products just do not work out if you’re looking at nationwide distribution.


Are the main barriers for these low-carbon materials just awareness and limited demand? Or are there other factors?

I think there are two primary barriers, and one can be cost—not only the cost of materials, but the cost of labor. We see this with straw bale construction. And we see this with hempcrete applications, where contractors and construction crews just aren’t as familiar. There’s a learning curve that has to occur. And we see the price premium for products like CLT and mass timber. That’s what Aureus Earth is hoping to address head-on.

The second barrier is risk. We’re in a very risk-averse industry. A lot of times developers and building owners do not want to be the first to incorporate a new product, or a new way of building, because the data aren’t there yet to show that in 30 years, it’s still going to hold up. We see that risk even for contractors, because they don’t want to be held liable for any failures that occur due to faulty installation.


What advice would you give to a building owner who wants to start lowering the embodied carbon of their buildings?

I would say, first and foremost, engage your architect and your engineer and ask how you can minimize the embodied carbon in your building. The second thing I would recommend is to pick up some resources to educate yourself. Really start to understand the landscape of different material alternatives and the true impact that those material decisions can have on the total carbon footprint of your building.

I stand by the Carbon Leadership Forum’s resource library. And I always recommend the EC3 tool to folks who are just curious about the variability of embodied carbon within the same material category—like how different insulation products can really vary in terms of their embodied carbon.

What’s fortunate for building owners and developers is that architects and engineers now have a common language by which we understand, educate, and communicate about embodied carbon. Ten years ago, that was not the case.


One last question. Are you optimistic about the adoption of low-embodied carbon materials?

I am a perpetual optimist, probably to a fault. My glass is always half full. For me, it comes down to inspiring others to believe what’s possible. We have incredible ideas, we have big dreams, and we have a great vision.

The industry in the United States has begun to coalesce behind the mission of reducing and eventually eliminating embodied carbon in buildings by 2050. That mission comes with optimism, and a commitment to find out how to do it. Because I’m an engineer, I always think there’s a viable solution. So to answer your question, yes. I am an optimist. And I think optimism is contagious.