Performance Assessment of Carbon Dioxide Sequestration in Cement Composites with a Granulation Technique

The cement industry emits a significant amount of carbon dioxide (CO₂). Therefore, the cement industry should recycle the emitted CO₂. However, sequestration by carbonation in cement composites absorbs a very small amount of CO₂. Therefore, a direct way of achieving this is to improve the absorption performance of CO₂ in cement composites. In this study, to improve absorption, unlike in existing studies, a granulation technique was applied, and the material used was calcium hydroxide (CH). In addition, granulated CH was coated to prevent a reaction during the curing of cement paste. The coated CH granule (CCHG) was applied to 5% of the cement weight as an additive material, and the specimens were cured for 91 days to wait for the coating of CCHG to fully phase-change. The experiment of CO₂ absorption showed an unexpected result, where the use of blast furnace slag (BFS) and fly ash (FA) had a negative effect on CO₂ sequestration. This was because BFS and FA had a filler effect in the cement matrix, and the filler effect caused the blocking of the path of CO₂. In addition, BFS and FA are well-known pozzolanic materials; the pozzolan reaction caused a reduction in the amount of CH because the pozzolan reaction consumed the CH to produce a calcium silicate hydrate. Therefore, the pozzolan reaction also had a negative effect on the CO₂ sequestration performance combined with the filler effect. The CO₂ sequestration efficiency was decreased between ordinary cement paste and BFS-applied specimens by 45.45%. In addition, compared to cases of ordinary cement paste and FA-applied specimens, the CO₂ sequestration performance was decreased by 63.64%. Comprehensively, CO₂ sequestration performance depends on the porosity and amount of CH.