To investigate the durability of cementitious materials under complex environmental conditions in Xinjiang, this study conducted durability tests on mortar specimens with different fly ash contents under dry/wet sulfate attack conditions, with standard curing and steam curing at 70 °C. The appearance loss and flexural and compressive strength variations in the specimens were analyzed, and an evolution model of the mortar strength under a dry/wet sulfate attack was established. Moreover, XRD and SEM techniques were used to characterize the erosion products and microstructure, and to explore the erosion resistance mechanism of fly ash cementitious materials. The results showed that, after 160 cycles of erosion, the flexural strength of the specimens decreased with the increase in the fly ash content. In the context of steam-cured mortar specimens, throughout the entire erosion period, specimens with a fly ash content of 45% exhibited the highest relative compressive strength. The established strength evolution model had a minimum determination coefficient of 0.879, indicating a good agreement between the model and experimental results. Microscopic research showed that fly ash would undergo a pozzolanic reaction under the action of sulfate and calcium hydroxide, which was beneficial to the improvement of the erosion resistance. As the fly ash content increased, the erosion products of the specimens gradually became dominated by gypsum.

This study aims to explore the mechanical behavior of Desert Sand Concrete (DSC) under freeze–thaw (F-T) cycles. By adjusting the number of F-T cycles, the research analyzed the impact of various desert sand replacement ratios on the frost resistance of concrete. The study focused on the dynamic changes in mass loss of concrete specimens, relative dynamic elastic modulus, cubic compressive strength, splitting tensile strength, and axial compressive strength. Scanning electron microscopy was employed to analyze the micro-morphology of specimens after F-T cycles. This analysis aimed to predict the service life of DSC and provide practical recommendations for the maximum compressive strength loss rate within the designed service life. The results indicated that although the frost resistance of DSC was similar to that of ordinary concrete before 50 F-T cycles, it subsequently exhibited a nonlinear degradation trend correlated with increasing desert and replacement ratios, with both frost resistance and compactness reaching optimal levels at a 40% replacement rate. Additionally, the F-T damage model proposed in this study demonstrated high applicability and fitting accuracy. This model provided effective theoretical support for understanding and predicting the mechanical behavior of DSC.

Chloride erodes steel bars through concrete pores, seriously affecting the durability of reinforced concrete structures. Improving the binding ability to chloride is an important measure. We explored the effects of W/C, curing age, and premixed Cl⁻ concentration on the compressive strength and Cl⁻ binding capacity in cement pastes. The results indicate that a premixed 5% concentration of Cl⁻ can improve the compressive strength, whereas an excessive Cl⁻ negatively impacts the mechanical properties. The total Cl⁻ content in cement pastes is a crucial factor that influences the binding ability of Cl⁻. When the total Cl⁻ content is within 2% (i.e., the premixed Cl⁻ concentration is 5%), the cement paste has a strong binding ability of Cl⁻. W/C and curing age indirectly affect the binding ability by affecting the total Cl⁻ content. Furthermore, with the increase in content of Cl⁻, the adsorption content of Cl⁻ by C-S-H increased, while the proportion of Cl⁻ bound by Fs to the total bound Cl⁻ initially declines and then tends to stabilize. It is worth noting that a premixed concentration of 5% is a “safety limit” for cement paste, but for reinforced concrete, the presence of free Cl⁻ above normative thresholds should not be underestimated.

The utilization of aeolian sand (AS) as a substitute for river sand (RS) in ultra-high-performance concrete (UHPC) offers a sustainable solution to address natural sand resource shortages while enhancing AS utilization. This study systematically evaluates the influence of AS content (0–100% RS replacement by mass) on the workability, mechanical properties, and microstructure of UHPC under different curing regimes. All mixtures incorporate 0.65% by volume of straight steel fibers to ensure adequate fiber reinforcement. The results reveal that the spherical morphology, smooth surface nature, and fine particle size of AS enhance the matrix fluidity and reduce the early autogenous shrinkage of UHPC. By employing steam curing at 90 °C for 2 d followed by standard curing for 7 d (M3), UHPC samples with a 60% and 80% AS substitution achieve a compressive strength of 132.4 MPa and 130.8 MPa, respectively; a flexural strength exceeding 18 MPa; a porosity below 10%; and a gel pore content exceeding 60%. The steel fiber reinforcement contributes significantly to the flexural performance, with the fiber–matrix interface quality maintained even at high AS replacement levels. These findings highlight the feasibility of AS as an alternative fine aggregate in UHPC.

This study systematically investigates the effects of varying Cl⁻/${\mathrm{S}\mathrm{O}}_4^{2-}$ concentration ratios in saline solutions on the drying shrinkage, mechanical properties, and microstructure evolution of a cementitious system under simulated saline–alkali conditions. The underlying influence mechanism is elucidated via TG-DTG, XRD, and SEM analyses. Experimental results indicate that increasing the Cl⁻/${\mathrm{S}\mathrm{O}}_4^{2-}$ concentration ratio of the mixing water from 0.2 to 2.5 leads to a significant rise in early-age drying shrinkage, with an increase of approximately 19%, while it simultaneously enhances the early-age compressive strength of the cementitious matrix, achieving increases of approximately 13% at 1 d, 14% at 3 d, 14% at 7 d, and stabilizing at about 7% by 28 d. Microscopic characterizations reveal that as the Cl⁻/${\mathrm{S}\mathrm{O}}_4^{2-}$ concentration ratio increases, the ettringite content decreases, the contents of Friedel’s salt and calcium hydroxide increase, and the cementitious microstructure accordingly becomes denser. This work aims to provide theoretical and experimental references for the durability design and performance optimization of cement-based materials in saline–alkali regions.