In seasonally frozen soil regions, the influence of temperature change on reinforced-soil engineering cannot be ignored. In particular, the mechanical properties of the reinforced-soil interface have an important impact on the overall stability and long-term service performance of reinforced soil engineering. To explore the interface characteristics and reinforcement mechanism between geogrids and coarse-grained soil under negative temperatures, this paper takes the typical coarse-grained soil in Xinjiang as the material and carries out a direct shear test of the reinforcement–soil interface under different normal stresses, water contents and temperatures. The curve characteristics of the shear displacement-shear stress, the change trend of the peak shear stress and the formation mechanism between the geogrid and coarse-grained soil interface under freezing and nonfreezing conditions are thoroughly analyzed. The formation mechanism of the dilatancy characteristics of the reinforced-soil interface is explained by combining the Mohr-Coulomb strength criterion and apparent friction coefficient. It is concluded that the trend of the shear displacement-shear stress curve between the geogrid and coarse-grained soil interface under the nonfreezing state and freezing state is basically the same. In a state of low normal stress, the curve has no obvious peak, which is closer to the ideal elastic-plastic double linear model. In a state of high normal stress, the curves have more obvious peaks, and the curve type is closer to the elastic-strain softening type. In the nonfreezing state, the shear strength of the reinforcement–soil interface has a great correlation with the water content, which is different in the freezing state. The main sources of the difference are the cementation of pore ice in the soil skeleton in the frozen state, the improvement of the strength of the soil particles themselves, and the further interlocking effect of the geogrid on the soil. In comparison with the reinforced coarse-grained soil under the nonfrozen state, the shear strength under the frozen state is significantly improved. In comparison with coarse-grained soil reinforced by geogrids in the nonfreezing state (0 °C), the shear strength of the frozen state (−5 °C) is significantly improved. Under normal stresses of 40 kPa, 60 kPa, and 80 kPa, when the water content is 2%, the corresponding peak shear stress increases by 19.39%, 21.71% and 11.34%, respectively. When the water content is 4.5%, the corresponding peak shear stress decreases by 29.98%, 16.17%, and 13.83%. When the water content is 7%, the corresponding peak shear stress decreases by 50.85%, 18.64%, and 21.96%. The apparent friction coefficient between the geogrid coarse-grained soil interface in the nonfrozen state and frozen state decreases with increasing normal stress. With the decrease in temperature, the dilatancy phenomenon of the reinforced soil composite is more obvious. The research results can provide a reference for the construction of reinforced engineering in seasonal frozen soil areas.

Aeolian sand is abundant in arid deserts, but its high replacement in cement-stabilized bases can reduce strength and raise cracking risk. Strain localization and crack evolution are also poorly quantified. This study aimed to optimize the early age performance of cement-fly ash stabilized aeolian sand gravel (CFSAG) and clarify its failure mechanism. A Box–Behnken response surface methodology varied the cement content, cement-to-fly ash ratio, coarse aggregate gradation, and aeolian sand content. The 7-d unconfined compressive strength (UCS) and splitting tensile strength (STS) were tested. Digital image correlation (DIC) recorded full-field strains and crack metrics in compression and splitting. SEM–EDS was used to interpret microstructural changes. The aeolian sand content dominated UCS, whereas the cement content and cement-to-fly ash ratio mainly controlled STS. Factor interactions were non-negligible and supported the joint optimization of the two strength indices. DIC identified a crack propagation threshold near 0.9 P_max in splitting. Excess aeolian sand (>50%) caused earlier localization, more cracks, and wider openings. In the appropriate amount of aeolian sand mixtures, hydration products filled voids and improved paste continuity. SEM–EDS indicated that excessive fines increased porosity and weakened the interfacial transition zone. Overall, the combined RSM–DIC–SEM approach links mix design with deformation and microstructure evidence. It provides practical guidance to balance strength and cracking resistance at early ages for cement-stabilized bases in desert highway engineering.

Public geopolymer concrete (GPC) databases can support retrospective screening of records with lower reported CO₂ emissions under strength constraints, but reliable ranking also requires correct response matching and stable threshold-based eligibility. Using 274 records, this study reconstructed the strength–CO₂ correspondence from 19 mix proportion and preparation fields, yielding 273 mix design identifiers (MixIDs). Eight regression algorithms were evaluated under MixID-grouped validation, and CatBoost with derived descriptors was retained as the primary model. It achieved R² = 0.969 and RMSE = 2.096 MPa on the fixed test set; across 30 repeated holdouts, mean RMSE was 2.390 ± 0.234 MPa. Because observed strength was available for every record, the model served as an internal consistency filter rather than a predictor of untested formulations. At 40, 50, and 60 MPa, 176, 65, and four records met the observed strength and mean prediction criteria, while 174, 62, and three records also satisfied the empirical fifth-percentile (Q05) criterion. Q05 was treated as a descriptive measure of partition sensitivity, and the 60 MPa result was regarded as exploratory. A CO₂ assignment negative control showed weak agreement between row-wise and key-matched values (Pearson r = 0.065) and low Pareto-set overlap (Jaccard = 0.045–0.105). Thus, prediction accuracy alone does not ensure valid lower-CO₂ ranking. The workflow provides an auditable basis for screening observed records within the database domain.

To address the challenges of road construction aggregate scarcity and cost control in desert regions, this study utilized solid wastes (steel slag powder, fly ash) to prepare geopolymer for stabilizing aeolian sand and gravel mixtures as road base materials. The feasibility of applying fibre-reinforced geopolymer stabilized aeolian sand gravel (FGSG) mixture was demonstrated through systematic investigation of its mechanical properties, frost resistance and micro-mechanisms. The results showed that the alkali content had the most significant effect on the compressive strength of geopolymer paste. The optimal mix ratio was a slag-to-fly ash ratio of 3:7, an alkali content of 8%, and a water glass modulus of 1.4. Furthermore, the incorporation of basalt fibre at a dosage of 0.15 v% and a length of 12 mm significantly enhanced the mechanical strength of the mixture and improved the frost resistance. The compressive strength of FGSG gradually decreased with the increase in freeze-thaw cycles; however, it remained over 80% of its original compressive strength after 12 cycles. Microstructural analysis revealed that polymerization reaction occurred around the basalt fibres, effectively filling gaps and connecting cracks. This reaction enhanced the connectivity within the mixture, thereby increasing overall strength and reducing both mass and strength losses. Notably, freeze-thaw cycles induced fatigue damage within FGSG, leading to structural deterioration and ultimately resulting in strength reduction.