Mechanical properties determine the use of two-component polyurethane materials. The compatibility of two components in the polyether polyol-MDI molecular system greatly influences the formation of mechanical properties in polyurethane materials. In this paper, we studied and evaluated the compatibility and mechanical properties of two-component polyurethane at multiple scales by combining molecular dynamics simulation with macroscopic experiments, which is an important guideline for synthesizing and preparing two-component polyurethanes. We evaluated the stability of the two-component polyurethane system by calculating the solubility parameter, binding energy, and diffusion coefficient at four temperatures with three isocyanate contents. The Perl scripting language obtained the mechanical properties of the MDI-polyether polyol system. The MD calculation results show that the solubility parameter of two-component polyurethane negatively correlated with temperature, and the intermolecular binding energy and MDI diffusion coefficient positively correlated with temperature. When the mass ratio of polyether polyol to isocyanate was 1:0.6, the solubility parameter difference between the two was 1.43 (J/cm³)^1/2, the intermolecular binding energy was 531.68 kcal/mol, and the two-component system was more stable. A macroscopic direct tensile test was employed to assess the polyurethane elastomers’ tensile properties. Our results show that the tensile strength of polyurethane elastomers increased with the increase in isocyanate content and decrease in temperature. Furthermore, the elongation at the break decreased, and the modulus increased, which is consistent with the law of molecular simulation.

In this paper, the rib beam bridge slabs were taken as the research object. Static load and fatigue tests were carried out on the benchmark bridge slabs to determine the ultimate load capacity and fatigue life of the bridge slabs. Then, the bridge slab was pre-damaged and reinforced with polyurethane concrete. A fatigue test was carried out on the reinforced bridge slab to study the fatigue performance. Based on the damage theory, the fatigue damage reinforcement finite element models of the bridge slabs under different damage degrees were established. The fatigue performance of the reinforced bridge slabs was systematically studied. The results show that the fatigue damage of the reinforced bridge slab developed in stages. Compared to the unreinforced bridge slab, the fatigue damage of the reinforced bridge slab was significantly reduced at each stage. According to the least square method and numerical analysis results, a residual-bearing-capacity model including damage degree and fatigue cycles of the reinforced bridge slabs is proposed, which can be used as a reference in bridge slab reinforcement design.

In order to study the residual bearing capacity of the carriageway slab of a reinforced concrete rib beam bridge after fatigue damage, a double T-beam carriageway slab model with a high degree of symmetry was designed and fatigue tests were carried out. Based on the fatigue cumulative damage theory, the fatigue residual strength equation of concrete was improved and a constitutive fatigue model of a steel bar and concrete with arbitrary loading times was established. Because the carriageway slabs are highly symmetrical, we used a ratio of length to width and a ratio of width to height to express the dimensional changes in the carriageway slabs. Abaqus general analysis program was used to create a symmetrical T-beams model and analyze the influence of the fatigue load level, the ratio of width to height of the roadway slab, and the ratio of length to width on the remaining bearing capacity of the roadway slab. Finally, the 1stOpt fitting software was employed to fit the roadway slab’s residual bearing capacity evaluation model. The fatigue test results show that the fatigue failure form of the roadway slab is punching failure, and the development law of fatigue damage can be divided into three stages, accounting for 6.25%, 56.25%, and 37.5% of the total fatigue life. The finite element analysis results showed that the length–width ratio of the roadway slab is positively correlated with its relative residual bearing capacity, and the residual bearing capacity of the two-way slab is higher than that of the one-way slab. The fatigue load level and the aspect ratio of width to height are negatively correlated with their relative residual bearing capacity.