Effect of an alkali activators on the compressive strength and reaction mechanism of coal gangue-slag-fly ash geopolymer grouting materials

To enable effective raw coal gangue use, the effects of various alkali activators on coal gangue-slag-fly ash geopolymer grouting material (CSFGM) were investigated. Results showed that for sodium silicate modulus at 1.4, sodium silicate content at 12% and Na2O content at 6%, CSFGM showed the highest compressive. The compressive strength of CSFGM was related to the porosity and the proportion of 0.01–1 μm pores, and the main reaction product was C-(N)-A-S-H gel. The sodium silicate modulus had no significant effect on the reaction products. An increased sodium silicate content caused ordering of the C-(A)-S-H gel, but the consumption of Na2O reduced muscovite depolymerization. The higher Na2O content increased the C-(N)-A-S-H gel, leading to a further refined microstructure with reduced porosity. At 4% sodium silicate incorporating, the increase of Na2O content mainly promotes the depolymerization and polycondensation reaction of precursors. At 12% of sodium silicate incorporating, the increase of Na2O content promotes the better participation of sodium silicate in the polycondensation reaction of precursors.