Impact of CO2 curing on the microhardness and strength of 0.35 w/c cement paste: Comparative study of internal/surface layers

Abstract

The aim of this paper is to investigate the effect of carbonation on the microhardness and mechanical-related properties of carbonated and uncarbonated layers of cement pastes. The microhardness and mechanical property changes were examined 1 day after demolding and then 3, 7, 14, and 28 days with further CO2 and water curing. CO2 treatment yielded substantial impacts on the microstructure and densification of the surface layer of the paste by consuming calcium hydroxide and forming calcium carbonates. The maximum carbonation depth of 5 mm was recorded at 28 days, and the microhardness of the surface layer was significantly enhanced compared to the internal layer as well as uncarbonated paste samples. However, despite improved surface hardness, the overall compressive strength of carbonated sample was lower than that of water-cured samples, probably due to the non-preconditioning (to remove excess water for carbonation) of the carbonated samples and better hydration in the internal layer of the samples cured in water. In addition, the thin denser surface layer of the carbonated samples could decrease the cement hydration process. However, the denser and lower surface water absorption relation to CO2 treatment could facilitate long-term durability performance of concrete structures.

Keywords

• CO2 curing
• Microhardness
• Microstructure
• Compressive strength
• Internal/surface layers