In an article published by the MIT Concrete Sustainability Hub, Andrew Logan, Communications Assistant, describes how MIT researchers investigated the carbon uptake [or absorption] of pavements throughout the United States.

The article describes the work of Dr. Hessam AzariJafari, a post-doctoral associate working within the MIT Concrete Sustainability Hub (CSHub). He is the first author* of a paper that was published last month in Resources, Conservation and Recycling.

The article begins with a characterization of the carbonation process.  “Just along concrete’s gray surface, a chemical reaction is occurring. Known as carbonation, this reaction forms calcium carbonate, a benign chalk-like material, but it can also affect climate change,” Logan writes. “That’s because calcium carbonate forms when CO2 from the air reacts with water in concrete pores, and then with calcium compounds in concrete — meaning that concrete is a potential carbon sink. Estimating the extent of its carbon uptake at scale, however, has proven difficult.”

The article describes how Dr. AzariJafari used thousands of simulations to predict how uncertainties would likely play out the span of a 30-year analysis period. He then used those predictions to calculate the potential carbon uptake in each state based on the road conditions, maintenance actions, budgets, and road lengths from his model.

Throughout the United States, the total amount of CO2  that could be sequestered in concrete pavements is significant, the research suggests.

“In total, we found that 5.8 MT [million tons] CO2 could be sequestered, with 2.8 MT CO2 coming from the use phase and 3 MT CO2 coming from end-of-life,” Dr. AzariJafari said. He found that states with large networks with many concrete pavements, such as Texas and California, saw a greater uptake during the use phase, while states that paved with composite designs (an asphalt overlay over a concrete layer) saw greater carbon uptake during end-of-life.­­

“The study finds that the carbonation process could offset 5% the CO2 emissions generated from cement used in US pavements.” Logan writes. “Much of those offsets, the researchers find, could occur years after pavements have been demolished, especially in states that use composite pavement designs.”

Click here to read more about the study.

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* Co-authors of the paper were Fengdi Guo, an MIT civil and environmental engineering graduate student; Dr. Jeremy Gregory, CS Hub Executive Director; and Dr. Randolph Kirchain, Co-Director of the CS Hub.