Effect of porosity on carbonation and hydration resistance of CaO materials

CaO pellets with different porosity were carbonated at 700 °C in CO2 atmosphere. The carbonation rate was controlled by the diffusion of CO2, regardless of the difference in porosities. For the low-porosity pellet, carbonation reaction only occurred on the surface, with a dense CaCO3 film thus formed, which combined well with the substrate material; while for the pellet of high-porosity, the carbonation reaction occurred simultaneously both on surface and inside pores, and each CaO grain was surrounded by CaCO3 film that contained microfissures. Hydration test results showed that carbonation treatment could effectively improve the hydration resistance of CaO materials regardless of porosity, but the carbonated high-porosity pellet was prone to breakage due to poor combination between the carbonated CaO grains. Therefore, for the purpose to improve the hydration resistance by carbonation treatment, it is recommended that the CaO materials should be either with less appreciable apparent porosity or with a limited carbonation ratio for the high-porosity CaO material.