Strain-Hardening Cementitious Composites Enhanced by the Synergistic Effects of Carbonized Recycled Concrete Powder and Carbonation Curing

Due to the reduced strength caused by dilution, the amount of recycled concrete powder (RCP) used to replace ordinary portland cement in concrete is limited. The synergistic effects of carbonation curing and carbonized recycled concrete powder (CRCP) on the strength, bending toughness, tensile behavior, and permeability of low-carbon and lightweight strain-hardening cementitious composites (LL-SHCCs) were investigated in this paper. The results showed that some calcium hydroxide and hydration products in RCP could carbonize, and the resulting calcium carbonate crystals provide more nucleation sites for the subsequent hydration reaction. The compressive strength and flexural strength of LL-SHCC were increased by 19.32% and 13.43%, respectively, under the action of carbon curing. Carbonation curing promotes cement clinker minerals, calcium hydroxide, and hydrated calcium silicate in the matrix to carbonize with carbon dioxide to form calcium carbonate crystals, refining the internal pore structure of the matrix and improving the mechanical strength and permeability resistance of LL-SHCC. However, carbonation curing reduces the bending toughness and tensile ductility of LL-SHCC due to the increase of the fracture energy of the matrix. Furthermore, it was found that CRCP and carbon dioxide curing play a synergistic role in promoting the carbon capture performance of LL-SHCC, thereby improving the sustainability of LL-SHCC.