Reaction Products in Carbonation-Cured Lightweight Concrete

The effect of early-age carbonation curing on the microstructure and properties of lightweight concrete with expanded slag aggregates was examined. Carbonation was performed on concretes either immediately after casting or after 18-h air curing. Their corresponding carbon uptake was 8 and 23%, respectively, based on cement content. A process involving initial air curing, carbonation curing, water compensation, and subsequent hydration was developed to maximize the degree of carbonation and hydration. Reaction products of carbonation-cured concretes at early and late age were characterized by using thermogravimetrical (TG) analysis, X-ray diffraction analysis, and scanning electron microscopy. Although the presence of calcium carbonates was evident, the microstructure was nevertheless typical of amorphous. It was believed that early carbonation of concrete consumed calcium hydroxide, calcium silicate hydrates, and anhydrous calcium silicates while producing calcium carbonates of different polymorphs and amorphous calcium silicate hydrocarbonates.