The development of tailings in concrete technology is not only conducive to the realization of the goal of reducing carbon emissions, but also conducive to the inhibition the occurrence of shortages of sand and gravel supplies. In this study, graphite tailings were used to replace sand in the range of 0~100%, and the mechanical mechanism of graphite tailings concrete was examined through compressive and flexural tests. The mechanical experimental results were evaluated and verified based on concrete macroscopic failure appearance, mesoscopic failure appearance, and physical characteristics of graphite tailings. The results revealed that the concrete strength increases first and then decreases with the increase of the graphite tailings content. Compared to GT00 (GT00 is a specimen with a graphite tailings content of 0%, and so on), GT10~GT60 exhibited better mechanical properties, of which 30% was recommended as the optimal replacement rate. The mechanical properties of GT10 and GT20 had an upward trend, and GT30 had low spalling, with aggregate fragmentation found on the fracture surface. GT30 showed the best resistance to bending and deformation. The mechanical properties of GT40~GT60 had a downward trend. When the graphite tailings content was higher than 70%, the interface defects of the aggregate matrix increased, thus making it easier for cracks to propagate along the interface. Furthermore, the mechanism of graphite tailings replacing sand verified the test results from different perspectives, which provides new analysis ideas for other tailings in environment-friendly concrete.

As impacted by environmental concerns and the demand for high-strength concrete, novel ideas of the development of eco-efficient, steel fiber-reinforced concrete have been proposed. In this study, the aim is to develop a type of eco-efficient steel fiber-reinforced concrete with graphite tailings and steel fiber. Steel fibers act as a type of concrete toughening material, and graphite tailings serve as a partially alternated aggregate to sand. Mechanical properties exhibited by the concrete are assessed based on different volume fractions of graphite tailings (i.e., 0%, 10% and 20%). The concrete mixture proportion is determined in accordance with the theory of particle densely packing, and the concrete mechanical properties are more specifically studied by performing compressive and flexural tests. As indicated by the results, the maximal mixed bulk density of graphite tailings at different grades is greater than that of sand, so concrete with graphite tailings exhibits higher compressive strength. For the content of graphite tailings, the addition of graphite tailings impacts the interfacial adhesion between aggregates and cementing matrix, thereby inhibiting bifurcation and convergence of cracks. However, excessive mixing of graphite tailings would decrease the specimen’s effective water-to-binder ratio (W/B), thereby adversely affecting the internal structure of the concrete. The amount of graphite tailings impacts the distribution of steel fibers at the concrete interface, which could be the most conducive to the distribution of steel fibers under the graphite tailings’ content of 10%. This study demonstrates that graphite tailings and steel fibers are feasible to prepare eco-efficient, steel fiber-reinforced concrete.

Polyurethane cement composite is a new organic–inorganic composite material with high strength, corrosion resistance, and fast curing. It is a complement and alternative to traditional cement materials. The flexural properties of polyurethane cement composites are the basic mechanical index of the material. In order to study the flexural properties under different temperature loads, a molecular model was established, the chemical reaction process of polyurethane cement and the temperature response mechanism was analyzed, and the preparation process of polyurethane cement was proposed. Then, bending tests were carried out in strain-controlled mode to obtain the specimens’ bending strength and stiffness modulus under different temperature loads. The test results showed that the tensile strength of polyurethane cement decreased first, then increased, and finally decreased with the increase in temperature, while the bending stiffness modulus decreased with the increase in temperature. Combined with the theoretical derivation, the damage mode of the samples under different temperature loads was analyzed, and the “L-type” damage strain curve was obtained. The results showed that the proposed theory could effectively explain the mechanism of action and flexural properties of polyurethane cement composites under temperature loading, which is a significant improvement to the application of polyurethane cement composites in practical engineering.

Stone arch bridge is an important type in the early bridge construction process because of its beautiful shape, material saving and economic rationality. However, stone material will deteriorate after long-term operation, which results in a decrease in strength and bearing capacity of stone arch bridge. The vehicle load is increasing at the same time. Therefore, accurate evaluation of bearing capacity of stone arch bridge is essential to ensure safety. In this article, a three-span open-spandrel stone arch bridge was taken as research object. Firstly, the bridge damages were investigated and analyzed in detail, and bridge service state was evaluated. Then, based on the evaluation results of disease damages and considering stone material deterioration, a refined finite element model of stone arch bridge was established to analyze bending moment, axial force, strain and deformation. Finally, static load test was carried out to test vertical deformation and stress of arch ring, horizontal displacement of pier, settlement of foundation and development of cracks. The results show that static load test is the most accurate method for evaluating bearing capacity of stone arch bridge. The evaluation accuracy of finite element model based on material correction is in the middle, and the evaluation accuracy of disease damage assessment is the worst. In practical work, bearing capacity of stone arch bridge can be evaluated by combining the three methods with high accuracy and comprehensive results.