In order to explore the toughening performance and failure mechanism of hollow slab beams strengthened with prestressed steel strand polyurethane cement composite, three test beams (L1–L3) were strengthened and one test beam (L0) was used as a comparison. The influence of different tensile stresses of steel strand and fiber additions on the flexural bearing capacity of the hollow slab beams, was studied. The cracking characteristics, load deflection relationship, ductility and strain of each test beam were compared and analyzed. The test results showed that the toughened material was well bonded to the hollow slab beam and the steel strand, which effectively inhibited the development of cracks in the test beams. The flexural bearing capacity of the strengthened test beams was significantly improved. The use of prestressed steel strand polyurethane cement composite material effectively improved the flexural bearing capacity of the test beams, and this reinforcement process can be further extended to engineering applications.

Polyurethane cement (PUC) is now commonly used in the reinforcement of old bridges, which exhibit various issues such as poor toughness, temperature-sensitive mechanical properties, and brittle failure. These problems can lead to the failure of the reinforcement effect of the PUC on old bridges in certain operating environments, leading to the collapse of such reinforced bridges. In order to alleviate these shortcomings, in this study, the toughness of PUC is improved by adding polyvinyl alcohol (PVA) fiber, carbon fiber, and steel fiber. In addition, we study the change law of the flexural strength of PUC between −40 °C and +40 °C. The control parameters evaluated are fiber type, fiber volume ratio, and temperature. A series of flexural tests and scanning electron microscope (SEM) test results show that the flexural strength first increases and then decreases with the increase in the volume-doping ratio of the three fibers. The optimum volume-mixing ratios of polyvinyl alcohol (PVA) fiber, carbon fiber, and steel fiber are 0.3%, 0.04% and 1%, respectively. Excessive addition of fiber will affect the operability and will adversely affect the mechanical properties. The flexural strength of both fiber-reinforced and control samples decreases with increasing temperature. Using the flexural test results, a two-factor (fiber content, temperature) BP neural network flexural strength prediction model is established. It is verified that the model is effective and accurate, and the experimental value and the predicted value are in good agreement.

In order to explore the construction technology of prestressed steel strand–polyurethane cement composites for strengthening hollow slab beams, two reinforced test beams (L1, L2) and one unreinforced test beam (L0) were subjected to flexural static load tests. The deflection, ductility, stiffness, strain, and bearing capacity of each test beam were used to summarize the influence of different reinforcement techniques on the flexural performance of hollow slab beams. Research shows the prestressed steel strand–polyurethane composite material was well-bonded to the hollow slab beam, which effectively inhibits the development of concrete cracks and delays the damage process of hollow slab beams, that the reinforcement effect of the test beam L1 under the reverse pouring process was remarkable, and the bending performance of the test beam L2 under the forward pouring process of the simulated real bridge was good, which was much better than that of the unreinforced beam L0. The use of tensile prestressed steel strands and forward casting of polyurethane–cement composite materials effectively improved the flexural bearing capacity of the test beams, and this reinforcement process can be further extended to engineering applications.