Hydration mechanism and mechanical properties of a developed low-carbon and lightweight strain-hardening cementitious composites

Strain-hardening cementitious composites (SHCC) have been widely studied due to their high toughness and durability. The high cement content increases a huge burden on the cost and CO2 emissions of SHCC. To reduce the environmental impacts of SHCC, this study first develops low-carbon and lightweight SHCC by using high-volume recycled concrete powder (RCP) as supplementary cementitious materials and cenosphere waste as lightweight aggregate. The influence of RCP content (0%, 15%, 30%, and 45% by mass) on the hydration mechanism, mechanical properties, and sustainability of low-carbon and lightweight SHCC was investigated. The results showed that the incorporation of RCP in the SHCC matrix resulted in a decrease in hydration heat with increasing RCP content. The filling and pozzolanic effects of RCP were significantly lower than those of cement. The increased porosity and the presence of the interface transition zone due to RCP incorporation led to reduced compactness of the SHCC, which consequently led to decreased compressive strength and fracture toughness of the cement matrix. While the fracture toughness of the cement matrix was reduced, the SHCC still exhibited remarkable bending toughness and tensile ductility. The developed low-carbon and lightweight SHCC containing 45% RCP showed a density of 1482.5 kg/m3, a tensile strength of 3.94 MPa, and a tensile strain capacity of 6.80%, which successfully pushed the performance of low-carbon and lightweight SHCC. The replacement of cement with high-volume RCP in the low-carbon and lightweight SHCC resulted in a significant reduction in embodied carbon compared to conventional SHCC. Therefore, SHCC combines the advantages of lightweight, low-carbon, and highly ductile, making it a promising material for widespread utilization in concrete structures.