Ultra-high performance concrete (UHPC) exposed to the harsh western saline soil environments in western China experience accelerated damage due to the combined effects of dry-wet cycles, corrosive salt ions, extreme temperatures, and freeze-thaw cycles. This study developed a laboratory erosion protocol to simulate these conditions and evaluate the sulfate resistance of UHPC, investigating the degradation mechanisms associated with variations in water-binder ratio, silica fume content, and fiber type. Wiener theory was employed to predict the lifespan of various UHPC mixtures exposed to these conditions. The results indicate that UHPC demonstrates negligible degradation in performance under erosion simulation conditions when the water-to-binder ratio for the UHPC is 0.20, the silica fume content (relative to the total cementitious material content) is 26 %, and steel fibers are used. After 240 days of erosion, the compressive strength, bending strength and equivalent bending toughness of UHPC reinforced with polyvinyl alcohol (PVA) fiber decreased by 7.79%, 35.48% and 42.01 % respectively, with a decrease in the relative dynamic modulus of elasticity to 97.29%. These declines were more pronounced than in specimens with steel fibers. Phase composition and micro-structural analyses identified that the primary products of sulfate attack in UHPC as ettringite and gypsum, alongside the physical crystallization of anhydrous sodium sulfate, which induced expansion and crystallization stress, forming harmful pores and microcracks. A reliability function curve, based on compressive strength, effectively modeled the degradation process of UHPC under these conditions, predicting a potential durability lifespan exceeding 70 years in western saline soil environments.

Cement soil stabilization is widely used in civil engineering to improve the performance of soils subjected to freeze-thaw (F- T), wet-dry (W-D), and sulfate attack (SA). Due to the negative impacts associated with manufacturing cement, the development of eco-friendly and sustainable additives is highly desirable. Coal-derived char is a cost-effective byproduct of the coal pyrolysis process. In this study, the influence of coal char on mineralogical, microstructural, physical, and mechanical properties of cement stabilized soils (with cement contents of 0%-20% and char contents of 0%-30%) subjected to F-T cycles, W-D cycles, and SA is investigated. Compared to cement stabilized soils, char-cement stabilized soils exhibit up to 60.8% fewer volume changes during F-T cycles and 31.6% fewer during W-D cycles. The compressive strength of char-cement stabilized soils with cement contents of 5%, 10%, and 20% are on average 7.9%, 17.6%, and 11.0%, respectively, higher than that of cement stabilized soil subjected to F-T cycles, W-D cycles, or SA. The inclusion of char promotes cement hydration and results in the formation of more amorphous hydration products that fill voids or cover soil minerals. The findings indicate the promising potential of coal char in enhancing soil performance under a range of challenging environmental conditions.