Effect of pre-carbonation hydration on long-term hydration of carbonation-cured cement-based materials

Duo Zhang , Xinhua Cai , Beata Eliza Jaworska

Abstract

In the context of CO2 storage in construction materials, early-age carbonation curing of cement-based materials has been extensively studied in recent decades. Here, the effect of cement chemical and mineralogical alterations caused by initial hydration before early-age carbonation (i.e., pre-carbonation hydration) on subsequent hydration and strength development after early-age carbonation (i.e., post-carbonation hydration) is studied as a new parameter for controlling the curing process. Cement pastes were examined immediately after early-age carbonation using thermogravimetric analysis (TGA) and at 28 d by means of TGA, X-ray diffraction and vapor sorption, and were further associated with mortar strength development. The efficiency of early-age carbonation was found to noticeably decrease by delaying CO2 exposure. The post-carbonation hydration, however, was enhanced under the same condition and formed higher 28-d strength and bound water content compared to the non-carbonated reference. The use of limestone cement emphasized this observation and tended to advance its occurrence at shorter pre-carbonation hydrations. It is inferred that carbonation introduced after the late deceleration period of cement hydration can potentially enable a nucleation seeding effect to promote long-term hydration. The findings of this study confirm the importance of controlling pre-carbonation hydration age as a critical parameter for synergistically optimizing CO2 sequestration and technical properties of CO2-embodied materials.