Micro-properties and mechanical behavior of high-ductility engineered geopolymer composites (EGC) with recycled concrete and paste powder as green precursor

Abstract

Construction waste contains a high proportion of concrete waste and cement paste waste. The reuse of ground recycled powder, namely recycled concrete powder (RCP) and recycled paste powder (RPP), for high-ductility engineered geopolymer composites (EGC) benefits the effective recycling of construction waste and reduces the needs for mineral precursors. RCP and RPP mainly consisted of C–S–H, SiO 2 and CaCO 3 , and RPP had better repolymerization activity than RCP in EGC. Incorporating an appropriate dosage of recycled powder as a substitute for both fly ash and ground granulated blast furnace slag (FA-GGBS) had no obvious impact on the micro-characteristics. However, replacing 100 % of FA-GGBS with recycled powder degenerates the polymerization reaction and micro-structure. The substitution of recycled powder for FA-GGBS reduces the shrinkage/permeability resistance and strength of EGC. Under a uniaxial load, the crack width was decreased and the crack number was increased with the inclusion of moderate recycled powder in EGC. When replacing 25–50 % of FA-GGBS with recycled powder, including RCP contributed to the ultimate stress enhancement, while incorporating RPP helped the ultimate strain improvement of blended EGC. Particularly, the 100 % recycled powder-based EGC still has a high-ductility. When FA-GGBS was replaced with 0 % RPP/RCP, 50 % RPP, 100 % RPP and 100 % RCP, the tensile strain capacity of EGC was approximately 7.4 %, 9.9 %, 6.5 % and 4.4 %. Moreover, RPP-based EGC had superior micro-characteristics and mechanical behavior to RCP-based EGC. EGC containing recycled powder as FA replacement had better micro-characteristics and mechanical behavior than EGC containing recycled powder as GGBS replacement. Optimizing recycled powder type and substitution ratio can achieve sustainable EGC owning good micro-characteristics and mechanical behavior.