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To control the cement-stabilised crushed gravel (CSCG) shrinkage crack and improve the road performance, analysing the composition of CSCG structure on performance influence law and cut-off of coarse and fine aggregate, the strong interlocking skeleton gradation (SISG) of CSCG based on vertical vibration test method (VVTM) was proposed and its performance was verified. The mechanical strength prediction equation of CSCG was established. The results demonstrate that 4.75 mm was the demarcation point of coarse and fine aggregates. When the coarse aggregate forms a stable framework and cement stone is completely filled in the framework, it can form SISG and reduce the shrinkage deformation. In particular, SISG includes coarse aggregates having sizes of 19–31.5, 9.5–19, and 4.75–9.5 mm in a mass ratio of 50:30:20, a fine aggregate grading I value of 0.65, and a coarse-to-fine-aggregate ratio of 65:35. The maximum dry density, CBR value, unconfined compressive strength, and splitting strength of SISG increased by ∼1.3%, 9%–17%, 4%–12%, and 4%–8%, respectively, compared with the gradation median values obtained based on the Chinese standard. Furthermore, the error between the simulated CBR values and the measured values was <7%. The proposed mechanical strength prediction equations exhibit high reliability. [ABSTRACT FROM AUTHOR]

Red beds (RBs) are widely distributed in all continents of the world. With the rapid development of road and railway construction, the construction of roads and railways in RB areas is increasing. However, when RB is the filler, it will expose three aspects of serious deficiencies in compaction, mechanical bearing capacity, and water stability, which will cause fatal harm to the subgrade. Therefore, RB has to be abandoned and cannot be used as a subgrade filler. In this paper, different microwave irradiation temperatures (DMITs) from room temperature of 25°C to 700°C were used to reveal the enhancing mechanism of RB in three aspects based on the analysis results of microscopic composition and structure. The microscopic composition and structure show that RB can be divided into a low-temperature section (25°C–400°C) and a high-temperature section (500°C–700°C) under the microwave condition. The low-temperature section has some improvement in the engineering performance of RB, but the influence is limited. The engineering performance of RB is improved completely in the high-temperature section. Specifically, the coarse size of RB increases with the rise in microwave temperature, which is beneficial for improving fine size. The compaction property of RB is not largely affected by the water content and can still meet the most stringent subgrade filler requirements, even under saturated conditions or 0. The California bearing ratio (CBR) value can maintain more than 20% under the ultimate working condition, far higher than the code requirements. The increase of internal friction angle and cohesion can enhance the stability of the cut slope, which is conducive to construction in remote mountainous areas. The water resistance of RB is positively correlated with the microwave irradiation temperature, especially at 700°C; RB experiences secondary hardening after encountering water, the mechanical strength increases, and the softening coefficient reaches 107.44%. The research shows that after microwave high-temperature stabilization, the engineering characteristics of the RB are thoroughly strengthened, and it becomes a high-quality subgrade filler to eliminate the three diseases of RB subgrade completely. Compared with the traditional method of adding stabilizers, microwave in situ RB stabilization reduces the site construction's complexity, saves a lot of stabilizer use and transportation costs, and can effectively reduce carbon emissions. This study provides a positive perspective on the in situ application of the RB soft rock subgrade. It could be a starting point for understanding the microwave-based stabilization of soft rock soils subgrade filler in situ. [ABSTRACT FROM AUTHOR]

• The construction ambient temperature has a significant impact on Silt-based foamed concrete. • The optimum construction temperature of Silt-based foamed concrete is 15–35℃. • The study on the construction ambient temperature of Silt-based foamed concrete provides data for effective construction. Foamed concrete involves pouring layers at different ambient temperatures. However, the mechanical indexes in the specification are obtained under standard curing conditions. This paper addresses the respective influences of different ambient temperatures on the mechanical strength of silt-based foamed concrete. Next, comprehensive experiments exploring the mechanism of effect of temperature on silt-based foamed concrete, including compressive strength, flexural-tensile strength, splitting strength and elastic modulus, California bearing ratio (CBR), scanning electron microscope (SEM), and X-ray diffraction (XRD), were conducted. The test results show that the compressive strength of silt-based foamed concrete distributed in the shape of a saddle with increasing ambient temperature. The optimal strength was obtained at approximately 20 ℃. Below 0 ℃, the hydration ceased to influence the structure significantly. The structure of the concrete could be repaired to some extent under the standard curing conditions. When the ambient temperature rose to 20 ℃, the mechanical strength of the concrete rose almost lineally. From 15 to 35 ℃, the change in mechanical strength was not apparent. When the temperature exceeded 35 ℃, the mechanical strength dropped significantly with the rise of temperature influenced by the evaporation. Although the mechanical strength could be improved to some extent with the progression of age after the temperature returned to 20 ℃, the strength was lower than the standard strength, especially in frozen state and high temperature state. [ABSTRACT FROM AUTHOR]