Effect of carbonation with different CO2 phases on early-age properties of coal char-cement mixture

Abstract

Coal-derived char has exhibited great potential in terms of improving the engineering performance of various cement-based construction and building materials. Due to the characteristic porous structure of char materials, one of the important environmental benefits is the capability of effectively utilizing CO2, which has been confirmed by previous studies on b1iochar. However, for coal char with a similar structure and pyrolysis process, there is no relevant research on quantifying the effect of carbonation on the properties of cement-based mixtures. An experimental study on the effect of carbonation with gas, liquid, and supercritical (SC) CO2 on the early-age (i.e., 7 d) mineralogical, microstructural, and strength properties of coal char-cement mixtures was conducted. The X-ray diffraction results confirm the formation of calcium carbonate polymorphs, including calcite, aragonite, and vaterite, in char-cement mixtures carbonated by three CO2 phases. Carbonated samples show up to 102.6 % higher estimated calcium carbonate content, 17.3 % higher degree of hydration, and 13.3 % higher compressive strength, compared to sealed samples. Among all sealed and carbonated samples, the SC CO2-treated sample has the highest calcium carbonate content of 68.5 % and the highest roughness average of 28.2 μm, while the gas CO2-treated sample exhibits the highest compressive strength of 28.1 MPa at 7 d, as excessive carbonation in SC CO2 reduces compressive strength in char-cement mixtures. The experimental results of this study would be beneficial for promoting the novel coal char-cement based materials in terms of utilizing CO2 for various sustainable engineering applications.