Performance and durability of geopolymer-stabilized laterite soil against wetting-drying cycles

Durability is a key factor affecting the long-term performance of stabilized pavement materials when exposed to environmental conditions. This study examined the durability and cyclic mechanical behavior of geopolymer-stabilized laterite soil (LS) under repeated wetting–drying (WD) cycles and compared its performance with that of cement-treated LS. Three geopolymer mixtures were prepared using 20%, 30%, and 40% fly ash (FA) combined with 10% ground granulated blast furnace slag (GGBS), activated with NaOH–Na 2 SiO 3 solutions. A mixture stabilized with 12% cement was also included as a reference. The results showed that the geopolymer-stabilized mixtures exhibited significantly superior durability compared with the cement-treated mixture. From 0 to 12 WD cycles, the unconfined compressive strength (UCS) values of the FA30 and FA40 mixtures increased from 1.79 and 1.85 MPa to 7.95 and 7.48 MPa, corresponding to increases of approximately 4.4 and 4.0 times, respectively. Similarly, the splitting tensile strength (STS) values of the FA30 and FA40 mixtures increased to 0.73 and 0.62 MPa after cyclic exposure. In contrast, the cement-treated mixture reached its maximum UCS value of 2.54 MPa after 10 WD cycles and subsequently decreased to 1.73 MPa after 12 WD cycles, indicating the onset of durability degradation under prolonged moisture cycling. In addition, the geopolymer mixtures exhibited substantially lower weight loss (1.3–3.2%) than the cement-treated mixture (approximately 6%) after 12 WD cycles. Cyclic triaxial tests further demonstrated that the geopolymer-stabilized mixtures maintained higher resilient modulus values under repeated loading conditions. Scanning electron microscopy (SEM) observations together with X-ray diffraction (XRD) results indicated that 30% and 40% FA content promoted the development of a denser geopolymer gel matrix, which helped limit the formation of microcracks during repeated wetting and drying. These results demonstrate the strong potential of geopolymer stabilization for improving the durability of laterite soil under WD conditions. The findings also suggest that 12 WD cycles may still be insufficient for a full assessment of long-term durability because geopolymerization and matrix densification were continuing to develop during the later stages of testing.