We present here the results of experimental research on the speed of absorption of CO2 by Portland cement pastes and pure and additive mortars. The samples, introduced in a chamber, are exposed to a high concentration of CO2, simultaneously monitoring the temperature, relative humidity, pressure and concentration of CO2 present inside. The results show greater rapidity of carbonation both in cement pastes and in mortars when they are added with plasticizers, air incorporators or workability additives.