As the population grows, adding buildings to accommodate more people moving to cities is a necessary step. Buildings are responsible for approximately 39% of the annual global greenhouse emissions. Building operations alone results in 28% of the annual global CO2 emissions. So, building materials that are designed to meet new regulations and environmental standards will be key in creating a sustainable future.
The sustainable future of concrete
Three building materials are responsible for more than half of these emissions: steel, aluminum, and concrete. Concrete is used in every building designed, whether it’s the main building material or the frame, foundations, walls, floor, etc. This means the concrete industry shares much of the environmental impact. Given this responsibility, the concrete industry is stepping up and taking steps toward a sustainable future. Making the right choices for the future means being informed and aware of the impact the materials we are using are having on the environment.
The concrete industry is achieving this education through transparency and innovative concrete solutions.
Let’s look at a few of the tools the concrete industry and the AEC industries (architecture, engineering and construction) are taking to reduce carbon emissions in infrastructure, buildings, and materials.
Operational Carbon vs. Embodied Carbon
The two biggest contributors to emissions are operational carbon and embodied carbon.
Operational Carbon: The carbon emissions emitted during the day-to-day operations of a building.
Since 2005, the U.S. building sector has reduced operational carbon emissions even though they’ve added over 30 billion square feet of buildings.
Embodied Carbon: Embodied Carbon is the CO2 emitted during operations. Operations include the extraction, manufacture, and transport of building materials and products, and the construction of buildings and infrastructure.
Reducing these types of carbon emissions will involve transparency. Frances Yang, Americas Region Sustainable Materials Leader for Arup notes, “Disclosure is an interesting mechanism. You can’t improve what you’re not measuring.”
Embodied carbon is linked to the makeup of the products that build it, so by releasing the makeup of a product, we can understand and hopefully reduce its carbon output.
Mechanisms for Transparency
Transparency, as defined by Underwriters Laboratories (UL), “requires that companies share insight about what their products contain, how they are made, and what impact products may have on the community, environment, and end users.”
There are a few different mechanisms used to achieve transparency in building operations and materials.
Life Cycle Assessments (LCAs) and the Environment
Life Cycle Assessments are the investigation and evaluation of the environmental impacts of a product, process or service in each stage of its life. Each stage is considered independently and the inputs and outputs at each stage are tracked. The four life cycle stages include:
- Raw materials acquisition.
- Recycle/Waste Management.
Some possible outputs include:
- Atmospheric emissions.
- Waterborne wastes.
- Solid wastes.
An LCA is one of the best ways to determine the impact of a product’s life cycle on the environment and the information derived can be used to make decisions that could result in a lower environmental impact.
Environmental Product Declaration (EPD)
An EPD is like a nutrition label for a building product. Rather than calories and fat content, the EPD gives information about environmental impacts such as global warming potential, smog formation, and water use.
EPDs are provided by a certified third party and published by the manufacturer to provide upfront information about the impact the products will have on the environment.
This is a relatively new tool and until recently, not many project specifications or standards have required EPDs. Today, standards and initiatives such as LEED v4, Architecture 2030 Challenge for Products, ASHRAE 189.1 and the International Green Construction Code (IgCC) require both EPDs and LCAs in order to be transparent and improve environmental performance.
The concrete industry has more product specific EPDs than any other industry by far—over 22,000!
Concrete and the Environment
Through LCAs, the concrete industry has created an impressive directory of EPDs which has made them the product leader when it comes to disclosing environment impacts of the various lifecycles of their products.
The concrete industry also discloses regional environmental benchmarks. Through their work with the Athena Sustainable Materials Institute (ASMI), they calculated the environmental impacts of eight different regions in the U.S. Not only are they increasing their EPDs for concrete, but also for raw materials such as cement, aggregate, and supplementary cementitious materials (SCM).
Concrete might be one of the three biggest contributors to emissions, but the industry is working with environmental organizations in order to meet AEC industry demands and help communities become sustainable. When transparency is achieved, the focus can move to creating better products that achieve environmental benchmarks.
The Concrete Industry’s Role in Carbon Reduction
The National Ready Mixed Concrete Association recently announced that its members have lowered their carbon footprint by 13% in five years according to its latest industry wide LCA and benchmark report.
The reductions can be attributed mainly to a more efficient use of portland cement, the primary binder used to make concrete.
The association has been promoting performance-based specifications for nearly two decades, which has helped eliminate prescriptive limits on concrete formulation such as minimum cement content and low water-to-cement ratio. These unnecessary limits drive up content, the main contributor to carbon emissions.
Reduction techniques include:
- Using blended cements like a portland-limestone mix which has up to 15% limestone additions, lowering the embodied carbon of cement by up to 10%.
- Using fly ash and slag cement, both waste byproducts of other industries, which can reduce carbon footprint by more than 70%.
- Utilizing carbon capture technology which can make concrete with a net negative carbon footprint.
Using Carbon Capture to Improve Concrete
While not widely used yet, one company uses CO2 captured from industrial emissions. These emissions are then purified, liquefied and delivered to partner concrete plants in pressurized tanks. The emissions are injected into the concrete while the concrete is being mixed, which then converts the CO2 into a solid-state mineral within the concrete. The minerals enhance the strength of the concrete.
Emissions are reduced in two ways:
- Through direct sequestration of CO2 injected into the concrete mixture.
- By reducing cement demand, since this concrete requires less cement to produce concrete at a specified strength.
Another company has found a way to utilize carbon capture technology and reduce their concrete’s carbon footprint by 70%.
Their concrete uses all the same materials used to produce portland cement but changes the ration. They use less limestone than portland cement which allows it to be fired at lower temperatures requiring less energy and producing 30% less greenhouse gases and other pollutants.
Beyond being environmentally friendly, this concrete:
- Offers reduced efflorescence, meaning that salt staining will appear less severely and less frequently.
- Has a compressive strength of about 10,000 psi.
- Is compatible with non-conventional aggregates and recycled glass. This allows further reduction of material cost and environmental benefits.
Reducing and sequestering technologies are already commercially viable since they can be produced by existing equipment. Carbon capture is a promising solution to reducing the environmental footprint of concrete.
The AEC industry is better positioned to introduce sustainability into their construction thanks to the use of EPDs, programs like LEED, and the goals and recommendations of experts. The concrete industry is poised and ready to deliver products that contribute to sustainable building and reduce carbon emissions.