Reactions involved in carbonation hardening of Portland cement: effect of curing temperature

CO2 curing of fresh concrete is one of the solutions allowing direct carbon sequestration within the construction industry. Additionally, it enhances the early mechanical performance when comparing to traditional hydration curing. Temperature of carbonation curing has pronounced impact on both reactions involved in hardening of Portland cement: carbonation and hydration. Both reactions are accelerated with rising temperature, while the formed products and resulting microstructure are altered. Higher curing temperature promotes the precipitation of silica gel and C-S-H phase with reduced Ca/Si ratio. Furthermore, alumina and sulfate distributions among the reaction products are different. Temperature of carbonation curing has a distinct impact on the cement paste hydration after carbonation curing. The high curing temperature results in a densification of the matrix which limits further reaction progress, compared to the samples cured at lower temperatures. During the post hydration, calcium deficient system changes into C-S-H phase with higher Ca/Si and eventually portlandite.