Carbonation kinetics of a bed of recycled concrete aggregates: A laboratory study on model materials

Taking advantage of atmospheric carbonation of recycled concrete aggregates (RCA) seems particularly attractive to partially reabsorb the chemical part of CO2 emitted during limestone calcination. The purpose of this article is to investigate the carbonation mechanism of a heap of RCA. As a first approximation, the rate of CO2 absorption is studied on model materials made of sieved grains of cement paste made of CEM I. Carbonation penetration is measured by gamma-ray attenuation and by thermogravimetric analysis. A model is proposed and verified thanks to experiments. It is based on a dual-scale approach, associating CO2 diffusion through a granular bed and carbonation of the cementitious matrix. Information is provided concerning the influence of the characteristics of the cementitious phase attached to the original aggregates on the CO2 absorption rate. Moreover a study of the carbonatable amount of hydration products is performed according to the composition of the material and the CO2 concentration.