Abstract
Sulfate saline soil in the seasonally frozen zone generate soil freeze-thaw cycles, as well as saline expansion and thawing, which causes road engineering issues, thus they should be strengthened. This work investigates the effect of alkali content on the activation of fly ash (FA) stabilized sulfate saline soil by conducting unconfined compressive strength (UCS), splitting strength, and freeze-thaw cycles (FTs) tests. The results demonstrate that as NaOH concentration increases, the UCS and splitting strength tend to increase first, then decrease. N3 (stabilized soil with 0.5 M stimulated FA) had the best performance, with UCS and splitting strength of 7.18 MPa and 1.89 MPa, respectively. The residual values of the UCS and N3 splitting strength after 5 FTs were 46.35% and 39.92%, respectively. The NaOH activated FA hydration products consisted primarily of C-S-H, C-A-H gel and ettringite, with the gels linking the saline soil particles and filled the cracks between them. As a result, the mechanical characteristics and frost resistance of saline soil were much enhanced. The results of the study can provide a reference for the solidification treatment of sulfate saline soil foundations in seasonally frozen regions.