Characterization and mechanism study of sulfate saline soil solidification in seasonal frozen regions using ternary solid waste-cement synergy

Infrastructures built on sulfate saline soil foundations in seasonal frozen regions are highly susceptible to salt-frost heave damage and salt corrosion. To address this issue, a method has been proposed utilizing a ternary blend of industrial solid waste materials - fly ash (FA), silica fume (SF), and brick powder (BP) - in conjunction with Portland cement (PC) for the solidification of sulfate saline soil. The feasibility of this solidification technique has been validated through a series of tests, including unconfined compressive strength tests, freeze-thaw cycle tests, salt leaching tests, and microstructural analysis. The results showed that: The unconfined compressive strength of the solidified saline soil at 56 days increased by up to 61.27 times compared to untreated saline soil. During the freeze-thaw cycles, the volume of salt-frost heave in the solidified saline soil was only 10.75% of that in untreated soil, with a reduction in salt-frost heave force by up to 90.94%. Furthermore, during the salt leaching process, the rate of salt migration in the solidified saline soil could be slowed by up to 4.15 times, while the total amount of salt leached was only 31.34% of that in untreated saline soil. Additionally, through the combined use of X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS), it was discovered that the interactive synergistic effect of the solidifying agents in a SO42- rich environment facilitated the dissolution of Si-O and Al-O micro-lattices on the surface of the solidifying agent particles. This led to the extensive formation of C-(A)-S-H gels and AFt products, resulting in the transformation of the soil structure from dispersed to flocculated. The comprehensive test results indicate that the mechanical properties, frost resistance, and salt corrosion resistance of the solidified saline soil have significantly improved, with an optimal solidifying agent mixture ratio of 3% PC, 5% FA, 5% SF, and 6% BP. These findings can provide a reference for the solidification treatment of sulfate saline soil foundations in seasonal frozen regions.