Reaction mechanism of Ca(OH)2-based carbon storage suitable for the production of building materials

Abstract

The development of CaCO3 oxyfuel combustion and calcium looping techniques offers opportunities for Ca(OH)2 production with near-zero CO2 emissions. This study investigated the viability of Ca(OH)2-based CO2 storage for use in the production of building materials. To resolve the deficient strength gain of Ca(OH)2 carbonation, siliceous materials, using fly ash as a model compound, were introduced into the raw mixture, and hydrothermal curing was applied to promote the pozzolanic reaction. Two microstructural features, i.e., inner and outer CaCO3 formations, were identified during Ca(OH)2 carbonation via backscattered electron imaging. Inner CaCO3 formation is characterized by Ca(OH)2–CaCO3 conversion within the edge of Ca(OH)2 particles. Outer CaCO3 formation is characterized by the dissolution of Ca(OH)2 and the precipitation of CaCO3 in capillary pores, which generates hollow microstructures. The hollow space can be further filled by Al-tobermorite during hydrothermal curing. The prepared materials are capable of storing up to 16 % CO2 by the mass of the raw mixture. Furthermore, the pore structure influenced by inner and outer CaCO3 formation demonstrates the feasibility of adjusting the material's mechanical and CO2 storing properties by controlling the carbonation and hydrothermal curing schemes.