Jian Sun

In an effort to overcome the problems of modified asphalt mixture using the typical wet process, the dry process was used to modify 70# base asphalt with the SBS/crumb rubber composite modified masterbatch. Box–Behnken response surface methodology was used to create a regression model with the interactions of five factors, which gave the optimum preparation parameters. The results show that there are many factors that have substantial influence on the laboratory performance of asphalt mixture, and the created quadratic regression model has good fitting accuracy and predictive capability. The optimum preparation parameters were an asphalt–aggregate ratio of 4.5%, modifier dosage of 2%, dry mixing time of 65 s, wet mixing time of 107 s, and mixing temperature of 189 °C. Compared to the 70# base asphalt mixture and the wet-process asphalt mixtures, the dynamic stability of the dry-process asphalt mixtures is significantly improved by 503% and 36.6%, respectively. The TSR increased by 11.4% and 4.8%, respectively, as did the residual stability by 9.6% and 2%, respectively. Compared to the 70# base asphalt mixture, the maximum flexural strain increased by 46%, though it was slightly lower under the dry process than under the traditional wet process. The results confirm the practicality of the proposed optimization strategy for the dry process.

To enhance the comprehensive performance of crumb rubber (CR)/SBS-composite-modified bitumen, an orthogonal experimental design was first adopted to analyze the effects of process parameters—including the addition sequence, shearing duration, shearing temperature and shearing speed—on the conventional properties of bitumen. Furthermore, based on the Box–Behnken response surface methodology, quadratic regression predictive models for the dosages of SBS, waste crumb rubber and aromatic oil were constructed, and the entropy-weighted TOPSIS method was introduced to comprehensively evaluate and multi-objectively optimize the proportioning schemes. The results indicate that a reasonable preparation process can significantly promote the uniform dispersion of modifiers, distinct non-linear interactions exist among the dosages of each modifier, and the optimal proportion balancing both high- and low-temperature performance was obtained through optimization. The constructed models exhibit good predictive accuracy, and the optimized CR/SBS-composite-modified bitumen showed excellent conventional properties and storage stability, which can provide a theoretical reference for the recycling of waste tires and the engineering application of composite-modified bitumen.

To support the achievement of the carbon peaking and carbon neutrality goals and promote the resource utilization of industrial solid waste, a ternary solid waste composite cementitious material was prepared by blending ground granulated blast-furnace slag (GGBFS), fly ash (FA), and carbide slag (CS) with cement. The optimal mix ratio was determined through single-factor experiments and response surface methodology. The synergistic hydration mechanism was elucidated using microstructural characterization techniques, including XRD, FTIR, TG-DTG, and SEM. The composite material was then applied to a semirigid base course, and its mechanical properties and durability were systematically evaluated. The results indicate that the optimal levels of FA, GGBFS, and CS investigated in the single-factor experiments are 20–40%, 30–50%, and 2–6%, respectively. The optimal mix ratio of the ternary solid waste composite is 21.0% FA, 36.3% GGBFS, and 5.7% CS. The underlying microstructural mechanism is that carbide slag creates a highly alkaline environment, which activates the pozzolanic activity of GGBFS and fly ash, leading to the formation of hydration products dominated by C-(A)-S-H gel. With increasing curing age, the gel structure evolves from a loose and disordered state to a dense and ordered state, ultimately forming a compact microstructure based on a highly polymerized C-(A)-S-H gel matrix. The 7-day unconfined compressive strength of the stabilized gravel using the solid waste-based composite cementitious material reached 5.93 MPa, and the 28-day drying shrinkage coefficient was reduced by 18.3% compared with that of cement-stabilized gravel. After 18 freeze–thaw cycles, the compressive strength increased by 2.4%, with the pore structure characterized by a “macropores decreasing, micropores increasing” refinement pattern. After 18 wetting–drying cycles, the cumulative strength loss was 11.26%, outperforming cement-stabilized gravel. Combined with SEM observations, these performance improvements are attributed to the densely intertwined hydration products, particularly C-S-H gel, which effectively fill the voids between aggregate particles and significantly enhance the volume stability, freeze–thaw resistance, and wetting–drying durability of the stabilized gravel. The application of this cementitious material in a semirigid base course demonstrates excellent mechanical and durability properties, providing a theoretical basis and technical support for the widespread application of industrial solid waste in road engineering.

This study combined experimental analysis with deep learning to investigate the effects of curing age, steel slag content, and gradation composition on the mechanical properties of cement-stabilized steel slag (CSSS). The strength evolution patterns and underlying microscopic mechanisms were systematically elucidated. Experimental results showed that CSSS strength grows nonlinearly with curing age, with optimal mechanical performance achieved at a 60% steel slag content. The microstructural evolution characterized by SEM-EDS and XRD revealed that steel slag incorporation promotes the formation of AFt and densifies the gel network. In later curing stages, natural carbonation of Ca(OH)₂ and secondary hydration of reactive steel slag components produce CaCO₃ and additional C-S-H gel, which fill pores and significantly enhance long-term strength. A CNN-GRU-Attention model was developed to predict the unconfined compressive strength (UCS) and splitting tensile strength (STS) of CSSS. In a single data split, the model achieved R² values of 0.9875 for UCS and 0.9911 for STS, with RMSEs of 0.2577 MPa and 0.0234 MPa, and MAEs of 0.2059 MPa and 0.0184 MPa, outperforming all benchmark models. Under rigorous 5 × 5 repeated cross-validation, it maintained the highest average R² (UCS: 0.9417, STS: 0.9329) and the lowest error metrics, confirming its robustness and generalization capability. SHAP and Pearson correlation analyses identified cement content as the primary strength determinant, while steel slag content exhibited a threshold effect, highlighting the importance of prudent gradation control in practical engineering. This study provides both a theoretical foundation and a methodological framework for analyzing variable interactions and predicting the strength development of CSSS.

To study the effect of steel fibers on the mechanical properties of desert sand concrete (DSC), three lengths (12 mm, 16 mm, and 20 mm) of steel fibers and five volumetric admixtures (0.4%, 0.8%, 1.2%, and 1.6%) of steel fibers were selected to make 13 groups of concrete specimens (78 cubic specimens and 39 prismatic specimens). Compressive test, splitting test and flexural test were carried out on the specimens of DSC after curing for 28 days. According to the test results, the influence law of each parameter on the mechanical properties of DSC was analyzed, and the working principle of steel fibers to improve the mechanical properties of DSC was described by combining macroscopic and microscopic methods. The results showed that the addition of steel fibers can effectively improve the damage pattern of DSC, and all the mechanical properties of DSC are improved; 12 mm steel fibers were relatively effective in enhancing the compressive strength of DSC and 20 mm steel fibers were relatively effective in enhancing the splitting and flexural strength of DSC; Both macroscopic and microscopic results showed that the addition of appropriate amount of steel fibers can effectively fill the internal pores of DSC. The results can provide theoretical basis and technical support for the engineering application of steel fiber reinforced DSC.

In cold regions, saline soils can cause dissolution, settlement, and salt expansion of the roadbed under the influence of freeze–thaw cycles, so they need to be stabilized during road construction. In this study, lime, fly ash (FA), and polyacrylamide (PAM) were used to stabilize sulfate saline soils, and the stabilized saline soils were subjected to the unconfined compressive strength test (UCS), splitting test, and freeze–thaw cycle tests (FTs). The stabilization mechanism of the three materials on saline soils was also studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and X-ray photoelectron spectroscopy (XPS). The test results showed that the addition of lime, FA, and PAM to saline soils can improve the mechanical properties and frost resistance of saline soils. After 28 d of curing, the UCS of FA-, PAM-, and lime-stabilized saline soils increased by at least 55%, 23%, and 1068%, respectively, and the splitting strength increased by at least 161%, 75%, and 2720%, respectively. After five freeze–thaw cycles, the residual strength ratios (BDRs) of the UCS of L2 (lime 8%), F2 (FA 11%), and P2 (PAM 1%) stabilized soils and saline soils were 71.78%, 56.42%, 39.05%, and 17.95%, respectively, and the decreasing trend tended to be stable. The saline soils stabilized by lime and FA were chemically stabilized, and their mechanical properties and frost resistance were better than the physical stabilization of PAM.

In recent years, with the development of the construction industry and the wide application of concrete materials, the demand for natural resources such as sand and gravel in China has continued to grow. The Xinjiang region is rich in natural desert sand resources due to its large desert area, which are inexpensive and easy to obtain, providing new possibilities for the production of concrete materials. The use of natural desert sand as concrete aggregate not only reduces the cost of construction but also contributes to the protection of the environment and the rational development and utilization of natural resources. However, poor particle gradation in natural desert sand leads to poor concrete properties. In this study, the Dinger–Funk equation was used to optimize the aggregate gradation of natural desert sand from Toksun, Xinjiang, and concrete specimens were prepared for mechanical properties and sulfate erosion resistance tests. The test results show that the four groups of aggregates optimized by the Dinger–Funk equation are better than the single gradation and natural gradation in terms of apparent density, bulk density, void ratio, mechanical properties, and durability of concrete. Where the distribution modulus n = 0.3 was the best, the compressive strength, splitting strength, and flexural strength were increased by 13.14%, 15.71%, and 11.08%, respectively, as compared to the natural gradation. After 90 sulfate erosion and dry–wet cycles, the mass change rate and relative dynamic elastic modulus of concrete specimens first increased and then decreased, and at the distribution modulus n = 0.3, the aggregate particles of 0.3–0.6 mm, 0.6–1.18 mm, and 1.18–2.36 mm accounted for 26.98%, 32.33%, and 40.69%, respectively, and the smallest of the mass change rates of durability was the best.

To study the influence of cement-sand ratio, fly ash content, steel slag content, and fiber content on the performance of iron tailings premixed dry mixed mortar based on Box-Behnken, the regression model of compressive strength and fiexural strength and the above four factors was established, and the optimized mix ratio parameters were obtained. The results showed that the significance of the effect on compressive strength is ranked as follows: cement-sand ratio is greater than fly ash content than steel slag powder content than fiber content, and the significance of the effect on flexural strength is ranked as follows: cement-sand ratio is greater than fiber content than steel slag powder content than fly ash content.

Summary. Practicability of granular mixes of iron tailings treated with cement and complex additives (basalt fiber and cationic latex) application for construction of road pavements has been studied by the results of experimental research of compressive strength, splitting strength, maximum structural strength and temperature crack-resistance index. Simultaneous application of basalt fiber and cationic latex to the composition of granular mix of iron tailings treated with cement has been found to increase compressive strength and splitting strength. It was proved that the material modified with basalt fiber and cationic latex had lower structural defect index compared to the material treated with cement only. Addition of basalt fiber to granular mix from iron tailings treated with cement or both basalt fiber and cationic latex results in higher crack-resistance as indicated by increase of the maximum structural strength and the temperature crack-resistance index. Keywords: granular mix, cationic aqueous latex, basalt fiber, iron tailings, compressive strength, splitting strength, structural defect index, maximum structural strength, temperature crack-resistance index.