The Yorkshire Post - Carbon Storage in Concrete

Carbon Sequestration in Concrete to Mitigate Environmental Impact

Article Summary

Concrete, the most extensively used manmade material worldwide, carries a significant environmental burden, contributing to 8% of anthropogenic GHG emissions. With a staggering 30 Gt produced annually, the material consumption is over 3.5 tonnes of concrete per person annually. The majority of the emissions (88.5%) emanate from cement production, the essential ingredient in concrete.

Carbon sequestration in concrete presents a promising avenue to offset these emissions. This process, often referred to as carbonation or mineralisation, essentially reverses the initial cement production steps, where carbon dioxide is detached from calcium carbonate (limestone). Controlled carbonation of cementitious material, although first proposed in the 1970s, is recently garnering increased attention due to its substantial potential to mitigate against the colossal emissions from concrete production.

However, carbonation is not without its challenges. Uncontrolled, it can lead to the corrosion of steel in reinforced concrete and the formation of harmful compounds, jeopardising the structural integrity of buildings. Yet, advancements in controlled carbonation methodologies have demonstrated the potential to not only sequester carbon dioxide but also enhance the properties of concrete.

One such method involves utilising accelerated carbonation chambers to carbonate pre-cast materials, offering control over essential parameters such as CO₂ concentration, humidity, and temperature. This impacts the rate and depth of carbonation, with the formation of calcium carbonate in the exterior pores blocking further carbonation.

Emerging techniques explore embedding CO₂-rich materials within the concrete mixture. A notable investigation by MIT researchers examined incorporating sodium bicarbonate, which dissolves and releases CO₂ during curing. This innovative method not only sequesters carbon but also addresses the detrimental impacts of late-stage carbonation, such as shrinkage and crack formation.