Cement-stabilized soil is a commonly used pavement base/bottom base material. Adding a suitable curing agent to cement-stabilized soil can effectively reduce the dosage of cement, meet the strength requirements, and also greatly improve its water stability. In this paper, three kinds of cement dosage (6%, 8%, and 10%) of cement-stabilized soil were selected to add a 0.04% organic liquid curing agent, and then compared with high-dose cement (10% and 12%)-stabilized soil. The influence of wetting–drying cycles on the mechanical properties of the five stabilized soils was discussed. The mineral composition of cement-stabilized soils before and after the addition of a curing agent was analyzed by X-ray diffraction (XRD), and the microscopic morphology of 10% cement-stabilized soils with a curing agent was studied by scanning electron microscopy (SEM). The macroscopic test shows that the unconfined compressive strength of solidified cement-stabilized soil can be divided into three stages with the increase in the times of the wetting–drying cycles, which are the rapid decay stage, stable enhancement stage, and stable decay stage. The wetting–drying stability coefficient first increases, and then decreases with the increase in the times of the wetting–drying cycles. The microscopic test shows that the addition of a curing agent can enhance the content of hydration products in the cement-stabilized soil specimen; at the curing age of 28 d, with the increase in the times of the wet–dry cycles, the structure of the solidified cement-stabilized soil gradually broke down. The surface porosity P and pore diameter d showed an overall upward trend but decreased at the fifth wetting–drying cycle. The pore orientation weakened. The results show that the resistance of cement-stabilized soil with a curing agent is obviously better than that of cement-stabilized soil under wet–dry conditions.

To explore the damage evolution law of cement-stabilized weathered sand under the action of freeze–thaw cycles, relevant experimental research was carried out on stabilized weathered sand with a cement content of 3%, including unconfined compressive strength (UCS), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP) testing. Using the surface appearance, mass, and UCS of the specimen, combined with the changes of microscopic characteristics, the freeze–thaw damage law and microscopic degradation mechanism of cement-stabilized weathered sand were analyzed. The test results showed that with the increase of the number of freeze–thaw cycles, the surface appearance of the specimen continued to deteriorate, the unconfined compressive strength gradually decreased, and the mass of the specimen first increased and then decreased. After nine freeze–thaw cycles, the specimen was seriously damaged, and the strength loss was as high as 55%. From a microscopic point of view, the freeze–thaw cycles caused the pore water inside the specimen to continuously change between ice crystals and liquid. Frost heave and shrinkage weakened the cement bond between the weathered sand particles and made the pores in the specimen develop and expand continuously. With the decrease of the number of micropores and the increase of the number of medium and large pores, the particle skeleton changed from a dense structure to a porous structure, which eventually led to the deterioration of the macroscopic properties of the cement-stabilized weathered sand.

In order to produce high-viscosity and high-toughness asphalt for ultra-thin overlays, the conventional asphalt cement was modified with high-content SBS and micro carbon fiber (MCF). The performances of the modified asphalt were studied by tests of penetration, softening point, ductility, kinematic viscosity, multiple stress creep recovery (MSCR), and by dynamic shear rheometer (DSR) and bending beam rheometer (BBR). Mixture properties were studied by tests of rutting, low-temperature bending, freeze–thaw splitting, four-point bending fatigue and dynamic modulus. The results reflect that the addition of MCF could enormously improve the high- and low-temperature properties, increase the viscosity of asphalt, and improve the toughness of asphalt. When SBS content was 6%, with the increase of MCF content, G*/sin δ and R values first increased and then decreased, and the J_nr value first decreased and then increased. When MCF content was 0.8%, the overall performance was best. Adding MCF into an asphalt mixture or increasing the content of SBS improved the rutting resistance, low-temperature crack resistance, water stability, and fatigue performance of the asphalt mixture. At the same temperature and frequency, there was little difference in phase angle between the 6%SBS + 0.8%MCF and 5%SBS + 0.0%MCF modified asphalt mixtures, and the dynamic modulus was slightly higher over the whole range. It can be concluded that the addition of SBS and MCF can enormously enhance the viscosity and toughness of asphalt. The viscosity of the 6%SBS + 0.8%MCF modified asphalt met the performance requirements of high-viscosity asphalt. When used for ultra-thin overlays, it had great road service performance and met the application requirements.

With the increase of expressway construction in seasonal frozen soil region, the freeze-thaw problem of subgrade soil has attracted more and more attention. In addition, the comprehensive utilization of industrial solid waste has become an important measure to build a resource-saving and environment-friendly society. In order to improve the frost resistance of subgrade soil and realize the resource utilization of industrial solid waste, carbide slag (CS) and coal gangue powder (CG) were applied to the subgrade soil. The unconfined compressive strength (UCS) test, freeze-thaw cycle test, dry shrinkage test, temperature shrinkage test and scanning electron microscope (SEM) test were carried out on CS-CG stabilized soil with a ratio of CS:CG = 70:30 and dosages of 5%, 10% and 15%. The freeze-thaw cycle degradation model of CS-CG stabilized soil was constructed to show the freeze-thaw deterioration mechanism after the mechanical properties, pore structure, and durability characteristics of the stabilized soil were examined. The results showed that the CS-CG stabilized soil had good frost resistance. After 6 freeze-thaw cycles, the UCS at 7d and 28 d was 2.86 MPa and 3.79 MPa, respectively, which were 22.6% and 35.5% lower than in samples that underwent no freeze-thaw action. The CS-CG stabilized soil had good crack resistance, slightly better dry shrinkage strain than lime stabilized soil, and excellent temperature shrinkage performance. With the increase of CS-CG dosage, the hydration products increased continuously. After freeze-thaw cycles, however, large pores and cracks gradually appeared in the stabilized soil, which led to an increase of porosity and pore diameter, and a decrease of pore abundance. Due to the influence of hydration degree, the porosity change at 7 d was less than that at 28 d. There was a $f(n)/f_0=\beta \exp \left(-\lambda \Delta \mathrm{h}\right)$ relationship between UCS residual ratio and porosity variation of the CS-CG stabilized soil, and it had a good correlation. The CS-CG stabilized soil had good frost resistance and shrinkage characteristics, and could replace traditional cementitious materials such as Portland cement (PC) and lime for subgrade soil improvement in regions with seasonal frozen soil. Future research needs to focus on the performance regulation of CS-CG stabilized soil, which can make it more widely used.

The accumulated plastic deformation induced by a cyclic traffic load will lead to destruction of the subgrade. Coarse-grained soil is a widely used subgrade filler. The GDS dynamic triaxial test was carried out on typical coarse-grained soil fillers to investigate the influence of different confining pressures, consolidation ratios and numbers of cyclic actions on the hysteresis curve under step cyclic loading. The results show that surrounding pressure can significantly reduce the energy lost from a soil sample under cyclic loading. Under the same stress level, increasing the consolidation ratio can effectively reduce the area enclosed by the hysteresis curve. When the stress is increased above a certain value, the strain of the response clearly changes with an increase in the number of cyclic loading. The research findings can theoretically guide the design of coarse-grained soil roadbeds in practical engineering.

The application of alkali-activated slag (AAS) cementing material to the curing of soft soil foundations has a good engineering application prospect and is economical and environmentally friendly. In this study, three different activators (Na₂O·nSiO₂, NaOH, Ca(OH)₂) were used to alkali-activate slag powder to solidify and improve soft soil in inland port areas. In order to explore the mechanical properties and strength formation mechanism of AAS-solidified soil under different activators, mechanical properties, and microscopic tests were carried out. Firstly, with unconfined compressive strength as the evaluation index, an orthogonal test of three factors, such as the type of activator, the amount of activator, and the amount of slag powder, was designed. Then, the unconfined compressive strength, resilience modulus, shear strength, and compression modulus of AAS-solidified soil were tested with the three activators under optimal dosage. Finally, phase composition, SEM-EDS, TG-DTG, and FT-IR analyses were carried out with the three AAS-solidified soils. The results show the following: (1) The factors affecting the unconfined compressive strength of AAS-solidified soil are ordered as follows: the type of activator > the amount of activator > the amount of slag powder. In addition, the optimal factors were as follows: activator type: Na₂O·nSiO₂; amount of activator: 3%; and amount of slag powder: 20%. (2) In considering the macroscopic mechanical properties, the effect of the activator is Na₂O·nSiO₂ > NaOH > Ca(OH)₂, and the Na₂O·nSiO₂ AAS-solidified soil has good early strength. (3) The hydration products of AAS are mainly C-A-S-H gel, N-A-S-H gel, and C-S-H gel, which increase the strength and cohesion of solidified soil. The results show that AAS-solidified soil with 0.7-modulus Na₂O·nSiO₂ as the activator has good engineering characteristics and can be used for curing soft soil foundations.