Polyurethane grouting materials, a type of expansible grout, has played a significant role in the rehabilitation of public infrastructures, such as lifting the slab in a road and reinforcing the broken wall rocks in a tunnel. Due to the unique expansion characteristic of polyurethane materials induced by the chemical reaction, its diffusion mechanism in rock fracture is rather complicated. Based on a numerical method presented in a previous paper, the diffusion law of expansible grout in a single fracture is studied considering the time-varying density and viscosity of the grout tested by experiments. The grout diffusion radius, pressure distribution and velocity field are calculated by the numerical model combining the finite volume method (FVM) and volume-of-fluid (VOF) method. Taking the gel time into account, the characteristics of flow field distribution during the grout movement process are investigated on five different cases and the influences of grouting quantity and fracture aperture on grout diffusion behavior are analyzed, which can reveal some diffusion law of expansible grout in a single water-free fracture.

Polyurethane grouting material (polymer) has been widely used in rock mass fracture grouting. The previous test of polymer slurry grouting in planar fracture did not consider the influence of temperature; therefore, in this paper, a test of polymer slurry grouting in planar fracture was firstly conducted in order to explore the diffusion characteristics of polymer slurry. The results show that the preheating temperature of polymer slurry has a great influence on the diffusion of slurry in fractures, which should be considered in the research of polymer fracture grouting. In addition, the slurry temperature is related to the chemical reaction of the polymer itself. However, the existing polymer fracture grouting models ignore the influence of temperature and the chemical reaction of the polymer slurry itself, which lack the rationality to reveal the diffusion behavior of the polymer slurry in fracture. Therefore, in this paper, a chemical reaction-fluid dynamic (CF) model was established. In addition, the Particle Swarm Optimization (PSO) algorithm was used to obtain the chemical reaction kinetic parameters of the polymer slurry. Based on the CF model, the diffusion characteristics of the polymer slurry during the fracture diffusion process were calculated. The applicability of the CF model was verified by comparing the experimental data with the calculated results. Finally, the influence of polymer preheating temperature and ambient temperature on slurry fracture grouting behavior was explored by the CF model. The research in this article provides some theoretical reference for the design of grouting parameters in fracture grouting engineering.

Polyurethane polymer grouting material has been effectively applied and promoted in the repair of road damages in nonfrozen areas. However, this material undergoes an exothermic reaction in the curing stage, which can cause a thermal disturbance in the frozen soil subgrade. To minimize the influence of the thermal disturbance of the polyurethane polymer grouting material in the repair of the frozen soil subgrade, an experiment was conducted to reduce the heat of the curing reaction under the influence of different proportions of a foaming agent, high-boiling point solvent, catalyst, and prepolymer. According to these test results, a proportioning scheme for the low exothermic polymer grouting material was formulated. The results indicated that the curing reaction temperature threshold of the polyurethane polymer grouting material was negatively related to the proportion of physical foaming agent (HCFC-141b) and high-boiling point solvent and positively related to the proportion of water weight. In the three stages of rapid temperature rise, slow temperature rise, and constant temperature, the rate of the temperature rise of the low exothermic polymer grouting material was lower than that of the common polymer, and the curing temperature threshold was 30.34 lower at a value of 101C. At a density of 80kg/m³, the compressive strength and tensile strength of the low heat release polymer grouting material were lower than those of the common polymer grouting material, thereby ensuring the excellent performance of polyurethane foam and providing a theoretical reference for the rapid repair of frozen soil roadbed diseases.

The rapid detection of asphalt content in asphalt mixture is of great significance to the quality evaluation of asphalt pavement. Based on the dielectric properties of an asphalt mixture, the prediction model of asphalt content is deduced theoretically using three types of dielectric models: Lichtenecker‐Rother (L‐R) model, Rayleigh model, and Bottcher equation. Under the condition of laboratory mixing at room temperature (about 20–25°C), a dielectric test of asphalt mixture is conducted to verify the applicability of the model. The test results indicate that the dielectric constant of the asphalt mixture is inversely proportional to the asphalt content and directly proportional to the aggregate size of the mixture. Among the models, the Rayleigh model has a wide range of applications and exhibits a high accuracy, with an average relative error of only 1.86%. The results provide a theoretical basis for the nondestructive testing of asphalt pavements using ground‐penetrating radar.

This study aims to address the problem that loose damage of the pavement base course cannot currently be quantitatively identified, and thus the classification and recognition of the extent of looseness mainly rely on empirical judgments. Based on the finite‐difference time‐domain (FDTD) method, a backpropagation (BP) neural network identification method for loose damage of a semirigid base is presented. The FDTD method is used to simulate a semirigid base road model numerically with different degrees of looseness, and the eigenvalue parameters for recognition of the presence and extent of the looseness of the base layer are obtained. Then, a BP neural network identification method is used to classify and identify the loose damage of the base course. The results show that the classification and recognition of simulated electromagnetic waves have an accuracy of over 90%; the classification and recognition of radar data from an actual project have a recognition accuracy of over 80%. The good agreement between the classification and recognition results for the simulated data and measured data verifies the feasibility of the classification and recognition method, which can provide a new method for the use of ground‐penetrating radar to detect loose damage and the extent of looseness in the base.