Simultaneous Formation and Decomposition of Calcium Silicate Hydrate Under Carbonation in Water

Abstract

Carbonation curing captures CO2 while rapidly gaining strength, as calcium silicate hydrate (C-S-H) precipitates and carbonates simultaneously. The simultaneous formation and decomposition of C-S-H under carbonation was investigated systematically in C-S-H suspensions at an initial pH of 13.5. Four distinct periods were observed:  initial carbonation, rapid decomposition, slow ongoing and stable period. During the initial time, large quantities of C-S-H formed at maintained high pH, Subsequently, calcium in the liquid and C-S-H interlayer was consumed. With Ca/Si decreased to below 0.78, the rapid decomposition period proceeded with the decomposition of the main layer, while the silicate chains dissolved. Silica gel is formed in the slow ongoing period with pH <11.0, which dominates with calcium carbonate in the stable period at a stable pH of 10. Understanding the simultaneous formation and carbonation process of C-S-H contributes to understanding the microstructural evolution of cements during carbonation curing.

Keywords: Calcium silicate hydrate, Carbonation, Formation, Decomposition