Phase evolution and strength development during carbonation of low-lime calcium silicate cement (CSC)

Abstract

Abstract CO2 cured calcium silicate cement (CSC) can substantially improve the sustainability of concrete-like materials when used as an alternative to ordinary portland cement (OPC). CSC is produced from the same raw materials as the OPC but at kiln temperatures around 250 °C lower than those required for the production of the OPC. This paper presents a summary of the results from a comprehensive study on the evolution of microscopic phases, reaction kinetics, and strength development in CSC paste and mortar samples during carbonation. The primary carbonation products of CSC are calcium carbonate and Ca-modified silica gel. All three polymorphs of crystalline calcium carbonate (i.e. calcite, aragonite, and vaterite) were found to be present in carbonated CSC paste, calcite being the most abundant polymorph. Influences of water to cement ratio (w/c, by weight), temperature, relative humidity, and CO2 concentration on the carbonation rate constants of CSC have been studied here. The carbonation rate constants of CSC were found to be the highest for w/c of 0.4 in a 99.9% CO2 environment. The carbonation activation energies of these systems varied from about 44 kJ/mol to about 57 kJ/mol, depending on the carbonation curing conditions (i.e., w/c ratio, CO2 concentration, etc.). The CSC mortar samples achieved compressive strength as high as 40 MPa after only 3 days of carbonation.