Epoxy resin adhesive for pavement is often insufficient in flexibility and toughness. Therefore, a new type of toughening agent was prepared to overcome this shortcoming. To achieve the best toughening effect of a self-made toughening agent on an epoxy resin adhesive, its ratio to the epoxy resin needs to be optimally selected. A curing agent, a toughening agent, and an accelerator dosage were chosen as independent variables. The epoxy resin’s adhesive tensile strength, elongation at break, flexural strength, and flexural deflection were used as response values to establish a single-objective prediction model of epoxy resin mechanical property indexes. Response surface methodology (RSM) was used to determine the single-objective optimal ratio and analyze the effect of factor interaction on epoxy resin adhesive’s performance indexes. Based on principal component analysis (PCA), multi-objective optimization was performed using gray relational analysis (GRA) to construct a second-order regression prediction model between the ratio and gray relational grade (GRG) to determine the optimal ratio and to validate it. The results showed that the multi-objective optimization using response surface methodology and gray relational analysis (RSM-GRA) was more effective than the single-objective optimization model. The optimal ratio of epoxy resin adhesive was 100 parts of epoxy resin, 160.7 parts curing agent, 16.1 parts toughening agent, and 3.0 parts accelerator. The measured tensile strength was 10.75 MPa, elongation at break was 23.54%, the bending strength was 6.16 MPa, and the bending deflection was 7.15 mm. RSM-GRA has excellent accuracy for epoxy resin adhesive ratio optimization and can provide a reference for the epoxy resin system ratio optimization design of complex components.

Waste tires can be ground as crumb rubber (CR) and incorporated into asphalt pavement for efficient resource utilization. However, due to its thermodynamic incompatibility with asphalt, CR cannot be uniformly dispersed in the asphalt mix. In order to address this issue, pretreating the CR with desulfurization is a common way to restore some of the properties of natural rubber. The main technique of desulfurization and degradation is dynamic desulfurization, requiring a high temperature that may lead to asphalt fires, aging, and the volatilization of light substances, generating toxic gases and resulting in environmental pollution. Therefore, a green and low-temperature controlled desulfurization technology is proposed in this study to exploit the maximum potential of CR desulfurization and obtain high-solubility “liquid waste rubber” (LWR) close to the ultimate regeneration level. In this work, LWR-modified asphalt (LRMA) with superior low-temperature performance and processability, stable storage, and less susceptibility to segregation was developed. Nevertheless, its rutting and deformation resistance deteriorated at high temperatures. The results showed that the proposed CR-desulfurization technology could produce LWR with 76.9% solubility at a low temperature of 160 °C, which is close to or even better than the finished products produced at the preparation temperature of TB technology, i.e., 220–280 °C.

Recycled crumb rubber (RCR) is considered a reliable asphalt modifier and a solution to the problem of scrap tyre recycling. RCR-modified asphalt (RCRMA) typically has good low-temperature performance and storage stability. However, the pre-treatment of crumb rubber (CR) impairs its physical properties, resulting in poor high-temperature performance, which limits the industrial application of RCRMA. In this study, low-density polyethylene (LDPE) composite RCR was used to modify asphalt, and LDPE/RCR-composite-modified asphalt (L-RCRMA) was produced to compensate for the deficiencies in the high-temperature performance of RCRMA. The comprehensive physical properties of L-RCRMA were elucidated using tests such as the conventional properties, rotational viscosity, and rheological tests. The results showed that the incorporation of LDPE improved the high-temperature stability and rutting resistance of the asphalt, but an excessive amount of LDPE impaired the low-temperature performance and storage stability of L-RCRMA. Therefore, it is necessary to control the amount of LDPE to balance the performance of the asphalt. On this basis, we recommend a dosage of 20% for RCR and 1.5% for LDPE.