Mechanism and Microstructure of Co2 Internal-Curing Cementitious Composites

Abstract

The cement carbonation technologies are drawing more and more interests but the most CO2 curing technology are limited in on-site applications. Herein, a CO2 internal curing route was present and be proved feasibly. Zeolite NaX was selected as CO2 carrier with good adsorption capacity (16.2 g CO2/ 100 g drying zeolite) and stability (0.16% weight loss) at room temperature to internally carbonate cement. CO2 saturated zeolite released the adsorbent once it contacted with water in the mixing process and CO2 dissolved in paste solution to give carbonation products. It was found that not like the main products-calcite polymorphs in CO2 curing condition, monocarbonate and calcite were the main carbonation products in CO2 internal curing cement composites. Besides acceleration the hydration of C3S, zeolite NaX was found to react with cement systems and facilitate the formation of aluminocarbonates. The resultant composites exhibited quicker and higher strength development and modulus, reduced porosity and smaller pore intrusion radius, and little of volume expansion. Additionally, the formation of monocarbonate was related to the volume expansion of composites system from thermodynamic calculation and autogenous shrinkage experiments. Lastly, carbon sequestration capacity of 4.86 g CO2 /100 g drying solid composites and 71% of CO2 solidification in minerals was determined in the composites.

Keywords: CO2 sequester, Internal curing, zeolite NaX, monocarbonate, cement carbonation