Building the Future Without Destroying It

 Dallas O’Connor


As you read this, you’re likely surrounded by one of the largest contributors to global emissions. That’s because it happens to be the most produced material worldwide and due to rapidly growing infrastructure needs, its impact will not be eliminated anytime soon. Of course, I am talking about concrete. Unlike other large emission producers such as transportation and electricity, concrete is rarely included in conversations about combating climate change. However, its impact should not go unnoticed. According to Scientific American, the production of concrete and all its processes accounts for roughly 9 percent of all global CO2 emissions.1 But how do we change that? The truth is, it's difficult to balance accommodating the world’s infrastructure needs while ensuring we protect the future generations that will benefit from it. The question then becomes how do we build the future without destroying it?

As someone soon to be working as a structural engineer, I have a fundamental understanding of concrete and its impact, but that is not the case for the general public. I would guess that most people don’t know how concrete is made or even what it is made of. Concrete is made by mixing cement, water, fine aggregate (like sand), and coarse aggregate (like gravel), which harden together through chemical reactions. However, the component of concrete that causes the tremendous amount of CO2 emissions is the production of cement. Unfortunately, cement is one of the most energy intensive products in the world because it is made by heating limestone and clay in kilns up to 2,700 degrees Fahrenheit almost exclusively using fossil fuels. To make matters even worse, carbon dioxide is also a byproduct of the chemical reactions involved. 

It doesn’t help that global production of concrete has quadrupled and CO2 emissions have tripled since 1990. In fact, according to a study published by iScience, in 2020, 26 Gigatons of concrete was produced which is 26 billion metric tons or 57.3 trillion pounds.2 Also, for every kilogram of concrete produced, 1 kilogram of carbon dioxide is released which means for now, the use of concrete is a double-edged sword. And despite the mitigation efforts which have contributed to emission savings, the increase in production has greatly outweighed the impact of these efforts. The impacts of cement production and overall production growth on CO2 emissions can be seen in Figure 1.


Figure 1: CO2 Emissions of the Global Concrete Cycle


Although, using concrete is not entirely bad for the environment. A chemical process called carbonation is actively carried out by concrete which is the reaction that occurs between carbon dioxide in the air and calcium hydroxide in concrete. In simpler terms, concrete actually absorbs carbon dioxide from the environment, albeit at a much slower rate compared to the amount it releases in production. However, due to the sheer number of concrete structures, a study published by Nature reported that a total of 4.5 Gigatons of carbon dioxide was captured by concrete materials during a 15-year period.3 This helps provide some optimism in the field and directs research towards ways to increase carbonation as a means to create net-zero concrete structures. One area of research involves the use of carbonation curing which is when concentrated CO2 is exposed to freshly mixed concrete, instead of using traditional water-based curing, which effectively traps carbon dioxide in the concrete.

Introducing methods to reduce emissions is extremely challenging for the world’s most produced material which is why finding a balance between the present and the future is so difficult. Some of the technologies that have been proposed like Carbon Capture and Storage which aims to collect CO2 at the source are extremely expensive, energy-intensive, and not yet widely available. It is equally as challenging to enact drastic change when the demand for the product has never been higher. Adopting low-carbon alternatives is a slow process that depends on regulatory approval, market acceptance, and significant/expensive changes in production practices. 

At the center of most climate change issues is the battle between good conscience and profit. While many of the top grossing cement companies like Holcim Group and China National Building Materials are dedicated to reducing carbon emissions and have proven to do so over the last three decades, expecting every concrete manufacturer to do the same is naively optimistic.4 In many cases, concrete producing companies are not able to adopt greener practices whether it be due to the investments necessary or their location makes it nearly impossible.

In order to make considerable change and bring concrete production close to net-zero emissions, it will require a massive investment to cement alternatives, Carbon Capture technology, improved energy efficiency, and research and development. Balancing the need to improve global infrastructure while shifting to greener concrete is challenging, but ultimately, concrete is only valuable if there is a future to build.


References


  1. Fischetti, M., Bockelman, N., & Srubar, W. (2023). Solving Cement’s Massive Carbon Problem. Scientific American. https://doi.org/10.1038/scientificamerican0223-52


  1. Watari, T., Cao, Z., Serrenho, A. C., & Cullen, J. (2023). Growing role of concrete in sand and climate crises. iScience, 26(5), 106782. https://doi.org/10.1016/j.isci.2023.106782


  1. Kazemian, M., & Shafei, B. (2023). Carbon sequestration and storage in concrete: A state-of-the-art review of compositions, methods, and developments. Journal of CO2 Utilization, 70, 102443. https://doi.org/10.1016/j.jcou.2023.102443


  1. Ramsden, K. (2020, November 3). Cement and Concrete: the Environmental Impact. PSCI. https://psci.princeton.edu/tips/2020/11/3/cement-and-concrete-the-environmental-impact

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