CO₂ Curing Efficiency for Cement Paste and Mortars Produced by a Low Water-to-Cement Ratio

Curing by CO₂ is a way to utilize CO₂ to reduce greenhouse gas emissions. Placing early-age cement paste in a CO₂ chamber or pressure vessel accelerates its strength development. Cement carbonation is attributed to the quickened strength development, and CO₂ uptake can be quantitatively evaluated by measuring CO₂ gas pressure loss in the pressure vessel. A decrease in CO₂ gas pressure is observed with all cement pastes and mortar samples regardless of the mix proportion and the casting method; one method involves compacting a low water-to-cement ratio mix, and the other method comprises a normal mix consolidated in a mold. The efficiency of the CO₂ curing is superior when a 20% concentration of CO₂ gas is supplied at a relative humidity of 75%. CO₂ uptake in specimens with the same CO₂ curing condition is different for each specimen size. As the specimen scale is larger, the depth of carbonation is smaller. Incorporating colloidal silica enhances the carbonation as well as the hydration of cement, which results in contributing to the increase in the 28-day strength.