The carbonation mechanism of calcium hydroxide and calcium silicate hydrates with CaO/SiO2 mole ratio 1.23 and 0.40, was studied by real-time measurements of the absorption of carbon dioxide gas (concentration 10%) and the weight change under 30, 60 and 80% relative humidity.
The rates of carbonation were remarkably changed with relative humidity. the carbonation of calcium silicate hydrates is proceeded ed gradually with carbonation time, but the carbonation of calcium hydroxide is developed rapidly at early stage, except carbonated under 30% relative hu-midity, and the carbonation of calcium hydroxide does not occurred at late stage.
Generally, the carbonation reaction is slower at 30% R. H. as compared to the carbonation at 60 and 80% R. H. It is necessary that the surfaces of hydrates are saturated with water in order to occur the carbonation reaction. But, the carbonation of calcium silicate hydrate with CaO/SiO2 ratio 0.40 is rapidly proceeded. Because it's carbonation products, which is calcium carbonate and silica gel, were absorbed with a large amounts of water and the surface was easily saturated with water.
The polymorphism of calcium cabonates is formed by the differents of relative humidity and CaO/ SiO2 ratio of calcium silicate hydrates.
