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

Differences in carbonation behaviour of paste samples exposed to ambient CO2 concentrations were investigated. Modifications in behaviour were observed between samples cured for short periods of time (72 hours) and those subjected to ‘idealised’ lab cured conditions (28days), as well as between CEMI and blended cement systems. Carbonation of AFm phases occurs very early, with decomposition of AFt only occurring after much longer exposure times, if at all. Although decalcification of C-S-H is evident when CH is present, it is once CH is no longer available that significant changes in the C-S-H structure are observed. The formation of carbonation products such as gypsum and silica gel were clear in blended systems after only 60 days exposure to ambient CO2 concentrations and 72 hours curing.