Internal carbonation reinforcement of cementitious materials: Mechanism and performance

Abstract

Cement carbonation technologies are garnering increasing interest, but most CO2 curing methods have limited on-site applications. In this study, a CO2 internal curing route was presented and proven to be feasible. Zeolite NaX was selected as a CO2 carrier due to its good adsorption capacity (16.2 g CO2/100 g drying zeolite) and stability (0.16% weight loss) at room temperature for internal carbonation of cement. CO2-saturated zeolite released the adsorbent once it was exchanged by water molecules during the mixing process, and the dissolved CO2 in the paste solution produced carbonation products. It was discovered that, unlike the main products (calcite polymorphs) in CO2 curing conditions, monocarbonate and calcite were the primary carbonation products in CO2 internal curing cement composites. In addition to accelerating the hydration of C3S, zeolite NaX was found to react with cement systems and facilitate the formation of aluminocarbonates. The resulting composites exhibited quicker and higher strength development, increased modulus, reduced porosity, smaller pore intrusion radius, and minimal volume expansion. Moreover, the formation of monocarbonate was found to be correlated with the volume expansion of the composite system, as determined through thermodynamic calculations and autogenous shrinkage experiments. Finally, the composites exhibited a carbon sequestration capacity of 4.86 g CO2/100 g dry solid composites, with 71% of the CO2 being solidified in minerals.