Everyone is familiar with some form of concrete. It’s everywhere. Homes, schools, stores, roads, bridges, wastewater management…it’s hard to miss. The abundance of concrete in our society reflects its necessity. It is the most used building material in the world. But what does that mean for the environment? In this article we will discuss the impact of concrete, particularly concrete masonry units (CMUs), on the environment.
Carbon sequestration is a term used to define the ability of a material to capture and store carbon compounds from the environment. Carbon emissions being a significant contributor to global warming (EPA, 2024). The Concrete Masonry and Hardscape Association (CMHA) has reported that within two years of manufacture, CMUs can collect twenty percent of the total carbon emitted from producing the material. The absorbed CO2 becomes chemically locked into the concrete (CMHA, 2024).
Furthermore, a CMU wall system is very much aligned with wood or steel wall systems in terms of total embodied carbon, and as we can see in the chart below, it has been shown to have less than half the total embodied carbon of a tilt up wall.
Total embodied carbon often reflects the overall amount of carbon emissions from sourcing of raw materials, manufacturing the product, transporting the product, and finally the implementation of using the product.
Choosing to replace cement with alternative and recycled cementitious products to make CMU will have a significant impact on the environment too. Products like slag and fly ash are used instead of cement to lower the carbon footprint of the concrete. Cement production contributes about five to eight percent of man-made CO2, so any drop in usage will have a positive impact (Cheng, Reiner, Yang, & al, 2023).
The resiliency, durability, service life, and building energy efficiency of CMUs also contribute to lowering its carbon footprint. These factors are not actively engaged in removing carbon emissions, like carbon sequestration, but passively they are still very influential. A reinforced CMU wall has been proven to withstand up to hundred and fifty miles-per-hour winds, which is about the higher end of a category four hurricane. Similarly, most of us are likely familiar with the home from Mexico Beach shown here. This concrete reinforced home is one of the very few structures to have survived and withstand hurricane Michael in 2018.
The resiliency of CMU structures speaks to its long-life cycle. It will not rust, burn, or rot like other building materials. It increases the durability of structures and as such reduces material use over time. Like the house on Mexico Beach, no rebuild saves a lot of material, resources, and waste.
In terms of energy usage, building materials will contribute to the required heating and cooling loads. This is interpreted as operational carbon usage. Materials in this category are often measured in their ability to keep the desired internal conditions. The thermal mass of concrete will allow it to absorb and store heat during the day. Essentially, removing heat from the indoor environment. This will help keep climatized structures cool and limit the usage of cooling systems. The concrete will hold on to this heat until the surrounding area cools down and at that time it will release the stored heat and warm the area around it. This means concrete can simulate a type of heating system when ambient temperatures drop. Both the cooling and heating conditions will limit the need for excess energy and reduce the buildings’ operational carbon emissions.
Throughout the life cycle of a concrete masonry unit it is sequestering carbon, reducing waste, and saving energy. It is a ‘living’ sustainable product that will give back to the environment throughout its usable life. The CMHA - Carbon Sequestration Webinar offers more information on carbon sequestration, and Portland Cement Association offers more information on cement and concrete sustainability.
Cheng, D., Reiner, D. M., Yang, F., & al, e. (2023). Projecting future carbon emissions from cement production in developing countries. nature communications, 8213.
CMHA. (2024). CMHA Courses - Carbon Sequestration of CMU. Retrieved from CMHA: https://www.pathlms.com/cmha/courses/66372?_hsenc=p2ANqtz-9xvY3aXlrt7osXRKtkuh_8DSruIPIthscI1-SBbsefjb0a7V9dD-HpmnoehoS952EOIdCd&utm_medium=email&utm_source=hs_email
EPA. (2024, July 8). Sources of Greenhouse Gas Emissions. Retrieved from EPA: https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions#:~:text=Carbon%20dioxide%20(CO2)%20makes,natural%20gas%2C%20to%20produce%20electricity.
Levenson, E. (2018, October 16). This home on Mexico Beach survived Hurrican Micahel. That's no coincidence. Retrieved from CNN: https://www.cnn.com/2018/10/15/us/mexico-beach-house-hurricane-trnd/index.html
Oldcastle Architectural. (2018, June 29). Capitalizing on thermal mass to improve efficiency in construction. Retrieved from Echelon Masonry: https://www.echelonmasonry.com/2018/06/29/capitalizing-on-thermal-mass-to-improve-efficiency-in-construction/
