Experimental study on performance and durability of Guangzhou soft soil solidified by a new slag-fly ash based cementitious material

The development of sustainable alternatives to Portland cement for soft soil stabilization is of great significance for reducing carbon emissions and enhancing infrastructure longevity. This study investigates a one-part slag-fly ash geopolymer binder containing solid sodium silicate for stabilizing Guangzhou soft clay. The optimal mix proportion was a slag-to-fly ash ratio of 90:10, a solid activator dosage of 14% relative to the precursor mass, and a water-to-binder ratio of 0.6, achieving a 28-day compressive strength of 2.01 MPa, 14.9% higher than the pure slag system. After 25 wetting-drying cycles, the geopolymer showed a strength loss of 6.5%, compared with 31.2% for cement. After 100 freeze-thaw cycles, the losses were 34.8% and 36.5%, respectively. After 100 days of sulfate immersion, the losses were 32.3% and 44.2%. Under the coupled sulfate immersion-drying-freeze-thaw protocol, the geopolymer remained intact after 100 cycles with a 47.3% strength loss, whereas the cement-treated soil disintegrated. SEM showed qualitative differences in apparent matrix continuity, visible voids, and particle morphology among the mixtures; morphology alone did not establish phase identity or a definitive damage mechanism. The results indicate that this one-part binder can improve the measured strength and durability of Guangzhou soft clay under the tested conditions.