High-strength mortar (HSM) gradually has wide applications due to its exceptional strength, micro-expansion properties, and excellent fluidity. Behavior deterioration of structures in saline soil areas is primarily attributed to freeze-thaw cycles and sulfate attack. In this study, the coupling effect of freeze-thaw cycles and sulfate attack on the appearance, mass loss, and relative dynamic elastic modulus of HSM was investigated during erosion. Then, compressive experiments were conducted to assess the mechanical properties of HSM subjected to both freeze-thaw cycles and sulfate attack. The influences of coupling freeze-thaw cycles and sulfate attack on the compressive properties of HSM were quantified through regression analysis of experimental results. Empirical models for compressive stress-strain curves and damage constitutive behavior of HSM were developed, taking the coupled adverse effect into account. The results indicate that the coupled effect of freeze-thaw cycles and sulfate attack causes performance deterioration of HSM. The empirical models reproduce the compressive behaviors of HSM subjected to freeze-thaw cycles and sulfate attack.

Building structures located in saline soil areas are more vulnerable to damage due to the combined effects of loading and sulfate erosion. Polypropylene fibers lithium slag concrete (PFLSC) exhibits good corrosion resistance, which can mitigate damage to building structures in saline soil areas. However, the eccentric compression behavior of PFLSC columns under sulfate erosion and external loading remains unclear. Therefore, in this study, an eccentric compression test was conducted on 10 PFLSC columns after exposure to combined sulfate erosion and external loading, with corrosion time and stress ratio as the research variables. The failure modes, load-displacement curves, failure loads, and strains of rebars were investigated. The results indicate that polypropylene fibers and lithium slag can effectively inhibit the corrosive effects of sulfates and significantly enhance the ductility and ultimate axial capacity of the specimens. Additionally, taking into account the prior load levels and the damage caused by sulfates to the concrete, a damage factor has been introduced to determine the strength of the concrete after undergoing loads and sulfate exposure. Ultimately, a model has been proposed to calculate the ultimate axial capacity of PFLSC columns under the coupled effects of loads and sulfuric acid. The calculated results showed excellent agreement with the corresponding experimental results. It provides reliable guidance for the durability design of PFLSC columns.

Concrete pavements in saline soil environments of cold regions are not only subjected to vehicle loads but also severely impacted by freeze-thaw cycles (FTC) and composite salts, resulting in durability issues that shorten their designed service life. This paper induced fatigue damage in concrete based on the fatigue cycles derived from the residual strain method. It investigated the variations in the physical and mechanical properties of fatigue-damaged concrete during 100 cycles of FTC and chloride-sulfate attack, revealing the deterioration mechanisms through NMR, XRD, and SEM analysis. Utilizing the GBR algorithm, the prediction model for damage layer thickness were developed. The results showed that, due to physical crystallization, salt freeze-thaw damage, expansion of ionic attack products, and fatigue loading damage, Friedel's salt and ettringite were initially the primary products formed. Subsequently, gypsum emerged, and ultimately Friedel's salt underwent decomposition. After 10 attack cycles, the porosity and the proportion of macropores and capillary pores continued to increase, resulting in a rapid decrease in mass, dynamic elastic modulus, and flexural strength, accompanied by an increase in damage layer thickness. As fatigue damage degree increased, the pore structure degraded, thereby amplifying these changes in macroscopic properties. Incorporating basalt fibers into concrete could enhance its resistance to degradation, with the optimal dosages being 0.15 % and 0.10 %. The GBR-based model of damage layer thickness demonstrated a high degree consistency with experimental data, resulting in a correlation index of R2 = 0.989. This study lays the foundation for assessing the durability of pavement concrete in salt-freezing environments.

Severe scaling and spalling are commonly observed on tunnel lining surfaces in sulfate-rich environments. Due to humidity gradients, sulfate solution in rock fissures migrates through capillary action to the concrete exposed face, leading to physical crystallization precipitation at free-face zone and chemical sulfate attack at soil-facing zone, resulting in concrete expansion and crack. Existing models focus on full immersion or wet-dry cycles, which have obvious errors in predicting concrete damage under similar partial immersion. Considering the time- varying characteristics of saturation, porosity, calcium leaching and crack, a transport-reaction-expansion model for lining concrete under dual sulfate attacks and water evaporation was established. The spatiotemporal distribution of phase composition and the influence of modeling parameters on concrete expansion were revealed. The expansion strain caused by dual sulfate attacks and changes in the water evaporation zone was discussed. These findings provide a theoretical foundation for the durability design of lining concrete in sulfate- rich environment.

The composite rapid soil stabilizer (CRSS) is a newly developed material for rapid curing of sludge with fast setting, fast hardening, and high strength properties. CRSS was used to solidify the sludge, and the durability test of the solidified sludge under the action of sulfate erosion was carried out to analyze the influence of erosion time and Na2SO4 and MgSO4 concentration on the physical and mechanical properties of the solidified sludge. The research results showed that as the erosion time increased, the mass of soaked samples increased gradually. Additionally, the strength of samples soaked in clear water continued to rise, while the strength of samples soaked in sulfate increased first and then decreased. After 112 days of erosion, the higher the concentration of SO42-, the greater the mass of the soaked sample and the lower the strength. At the same concentration, the mass of the soaked sample with MgSO4 was the largest, but the strength was the lowest. Under the action of sulfate attack, the soaked samples produced a large number of expansive products, and the cumulative pore volume first decreased and then increased. The microstructure of the MgSO4-soaked samples suffered the most damage due to the double corrosion of Mg2+ and SO42-. Based on the macroscopic and microscopic test results, the microscopic evolution mechanism of the durability of solidified sludge under Na2SO4 and MgSO4 erosion environments was revealed. The solidified sludge with CRSS has good sulfate resistance durability, which lays a theoretical foundation for the engineering application of CRSS.

Concrete surfaces in the evaporation zone above sulfate-rich soils are subject to severe damage from scaling. Such a physical sulfate attack (PSA) on concrete is a consequence of a cyclic regime between hot-dry and cold-wet environments, during which sodium sulfate crystals expand within the porous media (binder matrix or aggregate) and exert high pressure on the pore walls. Currently, no accepted standard exists for evaluating the resistance of concrete to the PSA phenomenon. In this study, an accelerated physical sulfate attack test protocol was used to determine the effect of blended cement and water-to-binder ratio on concrete resistance to PSA. The testing included a preconditioning protocol for presaturating concrete specimens in a 10% sodium sulfate solution for 15 days, with heat-drying specimens at 50 degrees C before and after immersion. Specimens were then partially immersed in a 10% sodium sulfate solution and subjected to a cyclic regime composed of hot-dry [40 degrees C, 30% RH] and cold-wet [8 degrees C, 85% RH] conditions for 19 h each, separated by a 4-h transition at room temperature. Silica fume (GUb-SF), limestone (GUL), and slag (GUb-S) blended cements were used and compared with general use (GU) cement. A fifth binder (GUL-GP) contained 20% glass powder as a partial replacement of the limestone-portland cement was also used. Three different water-to-binder ratios were used for each binder: 0.35, 0.45, and 0.55. As expected, mixes with lower water-to-binder ratios showed the best performance against PSA, i.e., the lowest mass loss after 15 cycles of exposure (30 days). GUb-SF cement improved the resistance of mixtures with a high water-to-binder ratio compared to GU mixtures. Contrary to silica fume and slag, limestone reduced the resistance of concrete to PSA and showed the highest rate of visual damage for all water-to-binder ratios.

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.

This study focuses on the development of eco and user-friendly mechanochemically-activated geopolymeric stabilizers, surpassing the limitations inherent in traditional geopolymerization methods. A comparative analysis was undertaken with conventionally activated geopolymer stabilizers to establish benchmarks for effectiveness in soil stabilization applications. Additionally, the research delves into the impact of granulated blast-furnace slag (GGBS) content on the mechanical and durability properties of stabilized soil samples. In addition, the investigation focuses on the influence of the activation method on soil effectiveness and strength post-exposure to sulfate attack. The durability performance is rigorously assessed through the immersion of specimens in a 1 % magnesium sulfate (MgSO4) solution for 60 and 120 days. The comprehensive evaluation includes visual appearance, mass changes, Ultrasonic Pulse Velocity (UPV), Unconfined Compressive Strength (UCS), and Fourier-Transform Infrared (FTIR) spectra of geopolymer-stabilized soil specimens. The results showed that before the exposure to the MgSO4 solution, the UCS of mechanochemically activated geopolymer (MAG) samples was higher (12-45 %) than that of conventionally activated geopolymer (CAG)-stabilized soil. Furthermore, the strength of the geopolymer-stabilized soil improved by 114 %, 247 %, and 361 %, at 50, 75, and 100 % GGBS content, respectively. On the other hand, after exposure to the MgSO4 solution, the results showed that the mechanochemically activated geopolymer-stabilized soil has better resistance to sulfate erosion than the conventionally activated geopolymer-stabilized soil. The residual UCS for MAG and CAG samples were 93 % and 89 % when exposed to 1 % magnesium sulfate solution for 60 days, whereas they declined to 70 % and 58 %, respectively, after 120 days of immersion.