Sulfate erosion resistance of slag-fly ash based geopolymer stabilized soft soil under semi-immersion condition

In this paper, the sulfate resistance of slag-fly ash based geopolymer stabilized soft soil under semi-immersion condition was investigated. The slag/fly ash ratios were set as 10:0, 9:1, 8:2 and 7:3, respectively, while cement stabilized soft soil was used as the control group. The samples of geopolymer stabilized soil and cement stabilized soil were semi-immersed in 2.5% sodium sulfate (Na2SO4) solution for 3, 7, 28, 60 and 90 days. The appearance, unconfined compressive strength (UCS) and mass changes of the samples were tested to evaluate their sulfate erosion resistance. The effects of sulfate erode on the microstructure of the samples were analyzed by scanning electron microscopy (SEM) and X-ray diffractometer (XRD). The results show that the geopolymer stabilized soil has better resistance to sulfate erosion than the cement stabilized soil. After the semi-immersing in Na2SO4 solution, the cement stabilized soil showed serious physical deterioration, while the geopolymer stabilized soil was relatively intact. With the increase of immersion age, the UCS of geopolymer stabilized soil gradually decreased, while the UCS of cement stabilized soil increased gradually and then decreased sharply until the bearing capacity was completely lost.