Effect of Synthesized Sol-Type Nano-SiO2 on the Mechanical Properties and Drying Shrinkage of Fly Ash–Slag-Based Geopolymer

Abstract

In this study, nano-SiO2 was synthesized using the sol-gel method to modify the properties of fly ash-slag geopolymers (FASGs). FASGs with six contents of sol-type nano-SiO2 (0, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%) and two alkali dosages (5% and 7% of Na2O) were prepared. The influences of sol-type nano-SiO2 and alkali content on the compressive strength, flexural strength, drying shrinkage, and microstructure of FASG were studied. The results demonstrated that the early-age compressive and flexure strength of FASG can be enhanced by sol-type nano-SiO2 due to the improved microstructure and the reaction products. The improvement effect of sol-type nano-SiO2 on mechanical properties was more significant for FASGs with lower alkali dosages. The optimized content of sol-type nano-SiO2 in FASG was 0.2% for the mechanical properties. The addition of the sol-type nano-SiO2 can mitigate the drying shrinkage of the FASG when the content is lower than 0.4%. The sol-type nano-SiO2 can promote the formation of reaction products in FASG and result in a denser microstructure of FASG.