Reusing recycled powder as eco-friendly binder for sustainable GGBS-based geopolymer considering the effects of recycled powder type and replacement rate

Utilizing recycled powder (RP) as binder for geopolymer reduces the construction waste and contributes to the development of sustainable geopolymer materials, but the effects of RP type and replacing rate on the characterization of sustainable geopolymer with RP received less consideration in previous investigations. Therefore, this investigation showed the upcycling of various RPs as an eco-friendly binder for sustainable GGBS-based geopolymer, and the micro-characteristics, mechanical strength and transport performance of geopolymer containing RP up to 100% were measured. The results indicated that RP from various construction waste mainly consisted of hydrated products, un-hydrated cement particle, quartz and calcite. Incorporating high-volume RP enlarged the pore structure of GGBS-based geopolymer, and substituting RP for 100% GGBS resulted in relatively loose micro-structure of sustainable geopolymer. Incorporating RP decreased the autogenous shrinkage of GGBSbased geopolymer, but the mix of high-volume RP increased the drying shrinkage of GGBS-based geopolymer. The mechanical strength and resistance to water ingress of GGBS-based geopolymer decreased as the RP replacing rate was increased, and substituting RP for 100% GGBS led to a significant reduction of mechanical strength and water absorption resistance. However, the mechanical strength of geopolymer with 100% RP from hardened cement paste waste was much better relative to geopolymer with 100% RP from mortar waste or concrete waste, because hydrated cement particle in RP has relatively high polymerization activity. Optimizing RP type and replacing rate can prepare sustainable geopolymer with good performance, and the upcycling of 100% RP for fully recycled geopolymer is feasible and sustainable.