The effect of slag chemistry on CO₂ binding capacity of C₃S-slag (-gypsum) system

Abstract

In this paper, the authors investigated the correlation between slag chemistry and CO₂ binding capacity of the blended system. To simplify the composition of mixture, model paste containing C₃S, slag covering the common composition range and gypsum was employed. After accelerated carbonation test, three CO₂-binding phases were identified in the system as: carbonated Ca-Al AFm phases, carbonated hydrotalcite-like phase, and calcium carbonate, irrespective of slag chemistry and the addition of gypsum. On the other hand, carbonated Ca-Al AFm phases played a minor role in absorbing CO₂, sharing less than 5% of CO₂ among all carbonate phases. Hydrotalcite-like phase was able to bind up to ∼10% CO₂, depending on the Mg/Al atomic ratio of raw slag. CaCO₃, originated from the carbonation of portlandite and C−S−H gel phase, took up more than 85% CO₂ after carbonation. Moreover, the carbonation degree of C−S−H gel phase was found to be negatively related with the Al₂O₃ content and Ca/Si ratio of raw slag.