Utilizing waste geopolymer powder as partial cement replacement for sustainable cement mortar: Micro-macro properties and modification

Abstract

The increasing application of alkali-activated geopolymer materials generates more geopolymer waste, but the reuse of geopolymer waste has been given less consideration until now. The ground waste geopolymer powder (WGP) has the potential to be used as supplementary cementitious material. Therefore, this study examined the characteristics of cement-based materials with WGP as a substitute for particle cement. The mortar samples (70.7 × 70.7 × 70.7 mm) were prepared for strength and transport properties measurement. The findings indicated that WGP ground from various geopolymer wastes mainly contained C–(N)–A–S–H, mullite, SiO2 or CaCO3. Substituting WGP for partial cement negatively impacted the paste micro-structure and increased the percentages of harmful and more harmful pores. The addition of WGP reduced the mechanical strength and increased the transport properties, and the maximum capillary absorption coefficient of 30% WGP mixed mortar was 154.0% higher than that of reference mortar without WGP. When WGP replacing level was the same, the water absorption of mortar incorporating WGP ground from FA-based geopolymer waste was obviously lower than that of mortar with WGP ground from GGBS-based geopolymer waste, because WGP ground from FA-based geopolymer waste contained some un-treated FA particles which benefited filler effect and pozzolanic activity. The addition of active admixtures could enhance the performance of WGP blended mortar. Specifically, the mortar containing 20% WGP and 10% silica fume/metakaolin had similar strength and lower transport properties compared with reference mortar, and the properties of WGP blended mortar were improved with the mix of Nano-SiO2.