Carbonation behavior of concrete produced using CO2 as an admixture

In the existing practice, CO2, is mainly added to concrete through accelerated carbonation, which has many limitations, such as a low diffusion rate and the requirement of a large airtight chamber, which applies to pre-cast elements only. To overcome these limitations, this paper presents a novel beneficial use of CO2 in concrete production through the mineralization of CO2. CO2 is sequestered into a slurry of calcium-rich cementitious material in the first step of this process and then blended with the remaining materials to make concrete in the second step. The two-step mineralization process in the present work simplifies the CO2 mineralization into concrete and reaches 99% efficiency of applied CO2. The CO2 reacts with calcium-rich cementitious materials to form nano-scale calcium carbonate beneficially impacted concrete hydration. Microstructural analysis suggests that the carbonates seed the hydration and contribute to developing a stronger microstructure. For these reasons, the carbonation resistance of hardened concrete and the compressive strength is improved. The finding of the experimental investigation of the present research shows that an optimum amount of CO2 mineralization into concrete improves compressive strength by 18.2%, 18.8%, and 17.9% less carbonation at 180 days of testing. Furthermore, the major greenhouse gas, CO2, can be utilized, contributing towards sustainable and environmentally friendly production of concrete and construction practices.