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.

The protection of the ecological environment and the scarcity of renewable resources are increasingly concerning global issues. To address these challenges, efforts have been made to use desert sand and fly ash in the preparation of building materials. This study attempts to replace river sand with desert sand and cement with fly ash to create an environmentally friendly and economical building material-desert sand dry-mixed mortar (DSDM). Through preliminary mix ratio experiments, five grades of DSDM were developed, and their durability in the saline soil regions of northwest China was studied. The study conducted macro-performance tests on the five strength grades of DSDM after sulfate dry-wet cycles (DWCs), analyzing changes in appearance, mass loss rate, compressive strength loss rate, and flexural strength loss rate. Using SEM, XRD, and NMR testing methods, the degradation mechanisms of the DSDM samples were analyzed. Results indicate that sulfate ions react with hydration products to form ettringite and gypsum, leading to sulfate crystallization. In the initial stages of DWCs, these erosion products fill the pores, increasing density and positively impacting the mortar's performance. However, as the number of cycles increases, excessive accumulation of erosion products leads to further expansion of pores and cracks within the DSDM, increasing the proportion of harmful and more harmful pores, degrading performance, and ultimately causing erosion damage to the mortar. Among the samples, DM5 exhibited the poorest erosion resistance, fracturing after 30 cycles with a mass loss of 43.57%. DM10 experienced failure after 60 cycles, with its compressive strength retention dropping to 78.86%. In contrast, DM15, DM20, and DM25 showed the best erosion resistance, with compressive strength retention above 75% after 120 cycles. Finally, the Wiener random probability distribution was used to predict the remaining life of DSDM samples under different degradation indicators, with flexural strength being the most sensitive indicator. Based on the flexural strength loss rate, the maximum sulfate DWCs for DM5, DM10, DM15, DM20, and DM25 were 132, 118, 78, 52, and 35 cycles, respectively. This study provides a theoretical basis for the promotion and use of DSDM in desert fringe areas.