Microstructure and Phase Assemblage of Low-Clinker Cements during Early Stages of Carbonation

This study investigates the effects of carbonation following short curing periods (72 hours) on CEMI and composite cement systems (30% PFA, 30% & 60% GGBS). Modifications in carbonation behaviour were observed compared to ‘idealised’/28 day lab cured samples. Following 72 hours curing, consumption of Ca(OH)2, via carbonation, was subsequently followed by decalcification of C-S-H, with notable changes in the C-S-H phase only occurring once Portlandite was completely depleted. Both calcium and aluminium were removed from the C-(A)-S-H phase as a result of exposure to ambient [CO2], and at early stages of carbonation CaCO3 microcrystals were observed in Op regions only. The carbonate species formed, and the rate and extent of carbonation, was reliant on the replacement material and level, as well as the degree of hydration.