Natural and accelerated CO2 binding kinetics in cement paste at different relative humidities

Natural carbonation and accelerated carbonation are compared in terms of CO2 combination. Thermogravimetrical analysis, neutron diffraction and weight measurements were used to quantify the amounts of CO2 in samples exposed to different CO2 and relative humidity (RH) conditions. An exponential equation is proposed to describe temporal evolution: combination rates and maximum values are obtained both for natural and accelerated processes. The influence of RH in these parameters is analyzed. At 100% CO2 an increase of RH from 53 to 75% diminishes the combination rate considerably, but increases slightly the maximum CO2 binding. At 0.5% CO2 both the rate and the maximum are higher for intermediate RH, with a linear relation between both variables. Equivalences between the different processes have been calculated: the amount of CO2 combined in 1 h at 100% CO2 and 65% RH carbonation is equivalent to approximately 36 days of natural exposure outside and 54 days inside.