Warm mix flame retardant asphalt mixture can reduce the energy dissipation and harmful gas emissions during asphalt pavement construction, as well as mitigate the adverse effects of road fires. For this, this paper studies the design and performance of a mixture modified with a combination of warm mix agent and flame retardant, and the pavement performance and flame retardancy of the modified mixture are evaluated. Additionally, a flame retardancy prediction model based on the radial basis function (RBF) neural network model is established. On this basis, the principal components analysis (PCA) model is used to analyze the most significant evaluation indicators affecting flame retardancy, and finally, a three-dimensional finite element model is developed to analyze the effects of loading on the pavement structure. The results show that compared to virgin asphalt mixture, the modified mixture shows a reduction in mixing and compaction temperatures by approximately 12 °C. The high-temperature performance of the mixture is improved, while the low-temperature performance and moisture stability slightly decrease, but its flame retardancy is significantly enhanced. The RBF neural network model revealed that the established flame retardancy prediction model has a high accuracy, allowing for precise evaluation of the flame retardancy. Finally, the PCA model identified that the combustion time has a significant effect on the flame retardancy of the asphalt mixture, and the finite element model revealed that the displacements of the warm mix fire retardant asphalt mixture were lower than virgin asphalt mixture in all directions under the loading.

Under the action of freeze–thaw cycles, the internal temperature and water distribution of slope soils in cold regions change significantly, which directly affects the stability of slopes. In order to study the differences in hydrothermal reactions at different depths and their impacts on the stability of slopes. This study establishes both a freeze–thaw model and a hydrothermal coupling model, combining field measurements with numerical simulations to examine the dynamic changes in hydrothermal characteristics within the slope. The results indicate that the variation in slope temperature with depth can be divided into three stages: initial freezing, stable freezing, and thawing. In the freezing stage, the negative temperature gradient drives water to migrate towards the freezing front, forming segregated ice and inducing frost heave. In the thawing stage, the latent heat released by the phase change in segregated ice promotes water to move towards the slope toe, increasing the water content there and indirectly exacerbating the risk of slope instability. The heat and moisture transfer in frozen soil slopes shows non-linear and dynamic characteristics. The unique process of one-way freezing and two-way thawing makes the thawing rate 1.35 times that of the freezing rate, and this asymmetric characteristic is the key to understanding the mechanism of slope instability.

Aging of asphalt is a major cause of pavement distress. While regenerators restore aged asphalt, their mechanisms and efficacy differences remain unclear. This study quantified the repair effects of waste bio-oil (WBO) and mineral oil (MO) rejuvenators on aged asphalt binder using a comprehensive characterization approach. Conventional properties (penetration, softening point, ductility), functional groups (FT-IR), thermal stability (TG), differential scanning calorimetry (DSC), and dynamic shear rheology (DSR) were analyzed. Results reveal distinct mechanisms: WBO acts chemically via polar molecules, selectively reducing oxygen-containing groups and significantly improving ductility, while MO acts physically through light components that dilute viscosity, exhibiting weaker chemical repair. WBO-regenerated asphalt showed a lower thermal-oxidative peak temperature, superior low-temperature ductility, and enhanced high-temperature rheological performance (higher rutting factor, optimized viscoelasticity). These mechanistic differences—chemical restoration (WBO) versus physical replenishment (MO)—determine performance outcomes at the binder level. The findings provide a theoretical basis for regenerator selection in pavement engineering, highlighting WBO’s advantages for functional group restoration and balanced thermal rheological properties, supporting sustainable road development.

Permafrost, as a soil type under unique environmental conditions, has bearing characteristics that are highly susceptible to thermo-hydraulic environments. Rapid evaluation of the bearing characteristics of in situ permafrost at various depths in perennially frozen regions is a critical scientific issue urgently needing resolution in the road design and construction sectors in China. To address this, this study investigates the correlation between CPT parameters and laboratory mechanical indices under the combined effects of multiple factors in frozen sandy soils. By conducting both CPT and CBR tests on frozen sandy soils, the study analyzes the trends in changes in cone tip resistance (q_c) and CBR values under the influence of temperature (T), moisture content (ω), and compaction degree (K) and establishes a functional relationship between them. Based on the standard requirements for indoor CBR, an evaluation criterion using q_c for assessing the bearing capacity of frozen sandy soil is proposed. The results indicate that both CBR values and q_c increase initially and then stabilize as K increases. With decreasing temperature, both indices stabilize after an initial increase, with turning points at −3.1 °C for CBR values and −2.5 °C for q_c. As ω increases, both indices first increase and then stabilize, with a turning point at 40%ω. There is a robust linear relationship between the CBR values and q_c, with the ratio of predicted CBR values to actual values showing a histogram and log-normal distribution accounting for 81% and 51.3%, respectively, within a 20% accuracy level, indicating good predictive performance. Referring to the highway subgrade specifications for indoor CBR, a standard for evaluating the bearing capacity of frozen sandy soils using CPT technology is proposed. This study provides new insights for geological surveys in perennially frozen regions and a theoretical basis for the application of CPT technology in evaluating the bearing capacity of permafrost.

With rising global temperatures, roads in the permafrost regions of the Qinghai–Tibet Plateau are exhibiting issues such as subsidence, water accumulation alongside the roads and in their foundations, and ongoing permafrost degradation. Among these issues, water accumulation has emerged as a prominent challenge in road management. In this study, sodium-based-bentonite-modified cementitious waterproof grouting materials were prepared and utilized as functional barrier layers. The rheological properties, mechanical strength, flowability, and setting time of the materials were tested under different sodium bentonite dosages. The feasibility of the application of these materials was evaluated, accounting for the evolution of pressure, flow rate, and diffusion distance of permafrost subgrades over different time scales when the materials were applied as functional barrier layers. The results indicate that, when used as a functional barrier layer, the modified cement-based grouting material exhibits a fluidity that meets the upper limit of grouting requirements, with a controllable setting time. Both compressive strength and apparent viscosity rise with the addition of sodium-based bentonite (Na-bentonite). Notably, an appropriate viscosity range of 0.35–0.50 Pa·s was found to effectively resist groundwater erosion while satisfying the critical performance requirements for grouting applications, demonstrating excellent applicability. In the field grouting test, the effects of grouting pressure and flow rate over different time scales on soil cracking, spreading distance, and the crack-filling process were further analyzed. Based on these findings, a technical solution using a new type of subgrade treatment material (functional barrier layer) was proposed, providing a reference for related theoretical research and engineering practice.

Warm mix asphalt pavements can effectively reduce construction energy consumption and control environmental pollution compared to conventional asphalt pavements. However, there is no clear test standard for the evaluation of warm mix agents. The selection of a warm mix agent is easily influenced by subjective factors. Moreover, it is difficult to consider quantitative and qualitative factors such as technical indexes and the economy. A fuzzy hierarchical comprehensive evaluation model of warm mix agents is proposed based on fuzzy hierarchical analysis. Four types of indexes, namely, material properties, technical indexes, economy, and construction difficulty, were selected to construct the hierarchical structure of the target, guideline, and indicator layers. The influence weights of all factors were determined by the judgment matrix, and an affiliation judgment matrix was established at the same time. Finally, the comprehensive score of the warm mix agent modification effect was calculated. Three warm mix agents were selected for market research and indoor testing. And the evaluation model was applied to process the data. The calculation results show that the technical indicators have the greatest influence, with a weight proportion of 0.493; WM-2 had the best comprehensive evaluation, with a comprehensive score of 0.96, and its optimal mixing amount was 0.3%. The calculation results further verified the effectiveness of the fuzzy hierarchical comprehensive evaluation model of warm mix agents. Compared with the existing methods, the fuzzy-hierarchical-integrated evaluation model of warm mix agents has a more comprehensive evaluation scope, lower subjective factor bias, and more flexible application scenarios. It provides a more rigorous and convenient idea for the development and evaluation of different warm mix agents. In conclusion, the model has greater application value and popularization value.