Carbon sequestration in earth-based alkali-activated mortar: phase changes and performance after natural exposure
Pitabash Sahoo, Nikita Rao, Sheetal Kumar Jain, Souradeep Gupta
Abstract
This research investigates the effect of carbon sequestration via accelerated carbon curing (ACC) in alkali-activated earth-based alkali-activated mortar (25S-AAM) on the long-term engineering performance, chemical bonding and microstructure. The addition of clay accelerates hydration kinetics and promotes the formation of more cross-linked calcium–(sodium) alumino silicate hydrates (N-A-S-H and C-(N)-A-S-H). This contributes to early strength and a 25% reduction in total shrinkage after 60 days. Although ACC promotes higher carbon sequestration and increases 1-d compressive strength by 13%, it leads to severe decalcification of 25S-AAM after 365 days of natural exposure, resulting in coarsening of the pore structure in the mesoporous size range of 10–100 nm. Due to a relatively low Ca/Si ratio, 25S-AAM is more adversely affected by natural carbonation during the 365-d exposure period than the control (without clay). In summary, ACC is not recommended for earth-based AAM products especially if they are applied for outdoor constructions.