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Recycling concrete at a building demolition site.

Recycling concrete at a building demolition site.

The Secret Life of Materials

You are surrounded. Whether you’re reading this on your phone or computer, if you’re sitting in an office chair, on a park bench, or waiting for your coffee order, you’re likely surrounded by concrete, wood, and countless other familiar materials. We experience these materials every day, but we usually don’t know where they came from, how they were made, and where they’ll go when they’re replaced. What we experience is a short moment in a material’s life cycle, which encompasses a much longer time span. It’s a life cycle that includes the construction, transportation, manufacturing, and raw material extraction that occurs before we use the material for its intended purpose. It also includes the recycling or demolition and disposal that occurs when the material is replaced.

Hidden from our day-to-day experience is the carbon emitted during the extraction, manufacturing, transport, and construction of the materials that surround us. If we take a closer look, we can uncover the sheer magnitude of carbon embedded in these materials and begin to see the significant opportunities that lie in its reduction.

Embodied carbon (yellow) and operational carbon (blue) across the life-cycle stages of a building. © Carbon Leadership Forum

Embodied carbon is the sum of all greenhouse gas (GHG) emissions produced during each stage of a material’s life cycle. Although embodied carbon emissions from the building sector produce 11 percent of annual global GHG emissions, the impacts of embodied carbon in building materials and products often go unaddressed. Most of the attention paid to carbon emissions in the building sector has historically focused on reducing operational energy use—the energy needed for a building’s heating, cooling, lighting, and so on.

To reach our climate goals, it is necessary to reduce the carbon embodied in materials. As building operations become more efficient, the impacts related to producing building materials have emerged as a critical issue to address. We can reduce the embodied carbon in materials through clever design, better material manufacturing, and preferential policy approaches that create market demand for low-embodied-carbon materials.

 

Beyond Cradle-to-Grave

The majority of materials that make up our built environment are manufactured, used, and disposed of within a flawed “cradle-to-grave” life cycle. This means that a material begins its life when it is extracted from a virgin source, before being manufactured, installed, and used only once, after which it is disposed of in a landfill. A “cradle-to-cradle” life cycle is a circular, closed-loop system in which a material is reused or turned into a new product when it reaches the end of its useful life. These materials typically carry less embodied carbon than their cradle-to-grave counterparts by circumventing raw material extraction and disposal, requiring less energy during the manufacturing and installation process, and often reducing the need for transportation over long distances.

Many plant-based materials, such as mass timber and cellulose, sequester more carbon than is expended in their manufacture, reducing their impact on climate change. But what other value do they bring to the consumer, manufacturer, and local communities?

  • For consumers, purchasing low-embodied-carbon materials and products can make projects more resilient to future resource and material scarcity, as well as hedge against volatile energy costs. Recycled materials can be more durable and longer lasting and thus are more appropriate for the expected lifetime of a building, resulting in reduced maintenance and replacement costs. More efficient localized transportation and construction processes for low-embodied-carbon materials can also lower first costs.
  • For manufacturers, the recovery of used materials for recycling creates a new resource stream that is often more affordable than virgin materials due to lowered transportation costs and lower energy costs of manufacturing into new products. The new product may be valued higher than comparable materials with higher levels of embodied carbon due to increasing demand for low-embodied-carbon products from consumers and policymakers.
  • For communities, a robust reuse, recycling, and deconstruction industry creates jobs and strengthens local economies. Reducing emissions from manufacturing building materials improves public health and environmental justice for communities of color, who are most directly impacted by industrial emissions in their neighborhoods. Communities near construction sites where these materials are being used will also enjoy cleaner air due to the reduction in emissions from a streamlined construction process.
Not Just about Reducing Emissions

Cradle-to-cradle material life cycles reduce GHG emissions and provide an array of benefits that support local economies. Take, for example, the decommissioned Stapleton International Airport, which was Denver’s primary airport until 1995. The airport’s hangars, terminals, and other buildings were demolished to make way for a new commercial and residential neighborhood. In the process, the city commissioned a Colorado-based recycling company to clear away and recycle 6 million tons of high-quality concrete and asphalt that paved the roads and runways of Stapleton. The city paid nothing to the recycling company for its work, but once the company had extracted the materials from the site, it was free to sell the recycled concrete and asphalt.

The recycler offered these materials in a number of formats, including large slabs called “StapleStone,” to local concrete companies. The recycled materials were also used in construction projects across Denver, including the Denver International Airport, Rocky Mountain Arsenal, and the new residential and commercial development at the Stapleton site itself. The material sold for $1 to $2 more per ton than virgin materials but remained economical due to the reduction in costs of hauling to local sites.

StapleStone didn’t catch on at first because recycled concrete was traditionally viewed as inferior to concrete with freshly mined aggregates. Just as people prefer new cars and clothes over used ones, the building industry tends to undervalue the resource potential of used materials, keeping cradle-to-grave products in favor. Things that could be reused are thrown away without thought or consequence to the cost of maintaining landfills, the pollution that comes from disposal, and the energy—and cost—required to extract and manufacture virgin products. It took a cultural shift for purchasers in Denver to realize the value of StapleStone, and that same culture shift is beginning to gain traction across the United States. Now StapleStone is part of a larger sustainability narrative that Denver residents and businesses value.

The hidden impacts of materials are beginning to be uncovered. The emerging awareness of material life-cycle impacts is helping the building sector choose wisely and move toward achieving our 1.5°C climate goal. The increasing interest in low-embodied-carbon materials from corporate purchasers; city, state, and federal policymakers; and architects and engineers has put pressure on suppliers to provide products that meet low-embodied standards and that can be reused or recycled at the end of their useful life. Those innocuous materials around us just might hold one of the keys to a stable climate future.