Slag-Based Cements That Resist Damage Induced by Carbon Dioxide

The use of sodium carbonate as an activator to prepare alkali-activated cements from blast furnace slag and calcined hydrotalcite offers many attractive performance and environmental benefits. However, the understanding of the long-term performance of these cements is limited. In this study, the resistance of sodium carbonate-activated slag cements to carbonation attack was determined under natural (0.04%) and elevated (1.0%) CO2 concentrations. Two calcium carbonate polymorphs, calcite and vaterite, were formed as carbonation products at a longer time of CO2 exposure. A cross-linked alkali aluminosilicate gel and a Ca-deficient calcium (alumino)silicate hydrate gel were identified to form by decalcification of the main binding phases initially present in these cements. However, despite these carbonation-induced mineralogical changes, the mechanical strength after carbonation was comparable to that of noncarbonated specimens, which is contrary to previous observations of strength loss due to carbonation of slag-rich cements. The high carbonation resistance of sodium carbonate-activated slag cement indicates these materials have the potential to resist attack by atmospheric CO2 in service with sustained mechanical performance.