Posted on June 10, 2021
Two decades into the 21st century, almost everyone in the construction industry looks for ways to be more sustainable. Demonstration projects focus attention on what is possible. One example is a new low-carbon "House of Tomorrow" in France. This project shows how to reduce carbon emissions throughout the structure’s lifecycle.
House of Tomorrow and Low-carbon Innovation
In October 2020, construction began on the home in Saint-Caprais-de-Bordeaux in southwestern France. The residence incorporates are variety of low-carbon innovations, including those coming from LafargeHolcim’s global research and development center.
These are not exotic materials. Project managers committed to using cement and concrete products readily available in France. Affordability also remained a key consideration. The results are impressive. The carbon footprint of the construction materials is 40 percent lower than those used in a traditional home.
For the foundation, designers specified ECOPact AA concrete. This is a new formulation launched in 2020. It is a low-carbon concrete that incorporates binders delivering exceptional performance. ECOPact AA reduces carbon emissions up to 80 percent compared to traditional mixes.
For the compression slab, the contractor used ECOPact A concrete. This mix yields emissions 50 to 70 percent lower than standard concrete. Various ECOPact formulations are available in 13 countries, including the United States.
Mineral wall insulation
Wall insulation features an aqueous slurry called Airium. It is healthy, environmentally friendly and affordable. Well-distributed air bubbles enhance thermal comfort on both hot and cold days. The recyclable mineral-based insulator is fire-resistant, insect-resistant and rodent-resistant. The cement-based slurry is fluid enough to readily fill any corner or shape. The easy-to-use product improves efficiency at job sites.
Green Concrete: The 5Cs
A key to the success of this demonstration home is the use of low-carbon concrete. The “Five Cs” of carbon reduction in the industry are: clinker, cement, concrete, construction and carbonation. Long-term success requires systematic improvement in every one of these five areas.
Clinker comes from heating a homogeneous mixture of raw materials in a rotary kiln. Limestone and other raw materials aggregate together at about 1,450 degrees C to create clinker. It is then ground to a fine powder and used as a binder in various cement mixes. Clinker production is by far the most energy-intensive part of cement production. There are two key ways to reduce the environmental impact of clinker. First, find alternatives to the fossil fuels ordinarily used to fire the kilns. Second, use less of it by adding SCMs.
Researchers look for ways to reformulate cement mixes to reduce carbon emissions. Limestone calcined clay cement (LC3) is a good example. In LC3, calcined clay and finely ground limestone replace some of the clinker. Less clinker means reduced carbon emissions.
There are many ways to reduce reliance on natural or virgin aggregates. Refined processes make the use of recycled concrete aggregates (RCAs) more viable. Local sourcing reduces transportation-related carbon emissions.
There are ways to reduce carbon emissions at the jobsite as well. For example, careful scheduling limits the time mixers must wait to unload.
Chemical reactions continue in exposed concrete. Calcium ions interact with carbon dioxide in the air to form carbonates. Over time, exposed concrete pulls significant CO2 from the air. Leaving concrete unsealed promotes carbonation. It is also possible to increase carbonation when recycling concrete. Crushing multiplies the surfaces exposed to air and moisture. It is ideal to expose the crushed concrete to air and moisture before using it in recycled aggregate concrete (RAC). This increases carbonation, vital to removing excess carbon dioxide from the air.
Challenges in the Quest for Low-carbon Construction
Low-carbon construction faces hurdles all too common when new techniques arrive. Costs, supply chains and popular acceptance can all slow or derail projects. By contrast, government and other incentives can speed the adoption of low-carbon solutions.
Should also weigh the positive impact on one’s brand. Industry leaders will emerge that lead the transition to low-carbon construction. Branding as a leader in sustainability may prove valuable in the decades to come.
Low-carbon construction, and specifically, low-carbon concrete, comes at a cost. However, available tax credits and incentives will often make low-carbon options more attractive. Stakeholders should factor in the intangible benefits of embracing sustainability. It is beneficial to embrace more sustainable construction methods for competitive reasons. In the future, decisionmakers will prioritize low-carbon options more than ever.
Always stay abreast of the changing landscape of tax credits and other incentives. Federal tax credits make carbon capture more economically viable. State incentives may appear as well.
Stakeholders should be aware of changes in the materials availability. The changing availability of supplementary cementitious materials (SCMs) is a specific case. For example, the availability of fly ash will diminish as coal-fired plants close. Supplies of fly ash recovered from landfills will also grow scarce over time.
Education and acceptance
Given concrete’s impact on global emissions, even incremental change means a lot. Awareness of low-carbon innovation speeds action. Together, leaders contribute to important reductions in the industry’s overall carbon footprint. Finally, it is vital to overcome myths about the true cost of carbon reduction. Circumstances change quickly in the construction industry. For example, soaring lumber prices impacts decisions over whether to use ICF or wood-frame construction.
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