Cementitious properties of sustainable alkali-activated materials with ground GGBS-based geopolymer waste powder as recycled precursor

Abstract

Employing ground geopolymer waste powder as a recycled precursor for new alkali-activated materials and geopolymer not only mitigates the amount of geopolymer waste, but also provides a novel alkali-activated binder. This work investigated the repolymerization and cementitious properties of ground granulated blast-furnace slag (GGBS)-based geopolymer blended with geopolymer waste powders as the substitution of GGBS. The geopolymer paste powder (GPP) and geopolymer mortar powder (GMP), both ground from GGBS-based geopolymer waste, contain abundant C-(N)-A-S-H, showing good repolymerization effect and alkali-activated activity. The GPP had better repolymerization effect and alkali-activated activity than GMP. Although replacing GGBS with GPP/GMP negatively impacted the micro-characteristics, 100% GPP/GMP-based geopolymer paste still possessed a relatively dense microstructure. Besides, 100% GPP-based geopolymer paste has finer micro-structure than the 100% GMP-based geopolymer paste. Mixing GPP/GMP as GGBS replacement decreased the autogenous shrinkage, while raised the drying shrinkage of GGBS-based geopolymer mortar. Reusing GPP/GMP as substitutes for GGBS resulted in a reduction of both strength and impermeability of GGBS-based geopolymer mortar, and an obvious decrease in strength and impermeability appeared when GPP/GMP replacement rate was above 90%. Reducing the particle size of GPP/GMP could improve the properties of GPP/GMP blended geopolymer mortar, and GPP-based geopolymer mortar had better properties than GMP-based geopolymer mortar. In particular, the geopolymer mortar made with 100% GPP/GMP still possessed relatively high compressive strength (49.3–64.7 MPa). Utilizing GPP/GMP as recycled precursor for sustainable alkali-activated materials and geopolymer is feasible, and the maximum substitution ratio of GPP/GMP can be up to 100%.