Carbonation of CaO clinkers and improvement of their hydration resistance

Two kinds of CaO clinkers, with 70% (low) density and 95% (high) density, were prepared and treated at 500-800degreesC in a carbon dioxide atmosphere. The low-density clinker was carbonated both on the exterior surface and inside the pores, with each CaO grain being encompassed by a layer of CaCO3 film; whereas the high-density one was only carbonated on the exterior surface with a lower rate. The carbonation processes for both samples were controlled by the diffusion of CO2 through the formed CaCO3 film. The carbonation rate increased with temperature rising, and reached the maximum at 700degreesC. The microstructure of the formed CaCO3 film was significantly affected by carbonation temperature, and a dense texture of CaCO3 with grains about 2 mum in thickness was obtained at 700degreesC. Slaking test showed that the carbonated sample with low-density was easily broken due to the weak bond among the carbonated grains in spite that the hydration resistance was improved. For the high-density sample, the hydration resistance was improved significantly after this treatment. An induction period of 7 d was achieved and the sample was not broken after 21 d slaking at 70degreesC in 90% humidity.