Abstract: The fundamental mechanism by which alkali-excited geopolymer gelling material can effectively cure the sulfated soil lies in the improvement of the microstructure of the solidified soil. By comparing the unconfined compressive strength and microstructure of saline soil specimens solidified by water glass, lime-fly ash and water glass-lime fly ash, we examined the microstructure of saline soil solidified by water-glass alkali-activated fly ash geopolymer. Test results evinced that lime and fly ash together improved the particle gradation of saline soil, cut the pore size range, reduced the pore volume, and thus enhanced the compressive strength; water glass cemented the soil particles into agglomerates, reduced porosity and pore volume, and its compressive strength was markedly affected by concentration. The pore characteristics of saline soil solidified by water glass-lime fly ash were not optimal; but the compressive strength was the highest because hydration gel material formed by alkali-excited geopolymer filled the intergranular pores and improved the particle cementation condition. The solidification effect of alkali-excited geopolymer is affected by the degree of alkali-induced reaction. The higher the degree of reaction, the better the curing effect.

Key words: solidified saline soil, microstructure, geopolymer, water glass, lime and fly ash, mercury injection