One of the environmental problems causing concern in the world today is the black pollution caused by the accumulation of waste rubber resources. Relevant experimental studies have proved that rubber concrete can help solve the black pollution problem caused by waste rubber tires, but it is undeniable that rubber particles will reduce the mechanical properties of concrete. To this end, many studies on the modification of rubberized concrete have been carried out, and this paper summarizes these studies, considering compressive strength, durability performance and insulation performance. The results show that chemical pretreatments, such as sodium hydroxide, can significantly improve the adhesion between rubber particles and cement matrixes. Mineral powder admixtures, such as silica fume and fiber admixtures, e.g., PP fibers, can improve the compressive strength of rubber concrete.

Expanded polystyrene (EPS) concrete is commonly used as the core material of commercial sandwich panels (CSPs). It is environmentally friendly and lightweight but has poor strength. Adding fibers can improve the microstructure of EPS concrete and reduce the weakening effect of EPS beads on the mechanical properties of concrete. An orthogonal experimental design (OED) was used in this paper to analyze the influence of length and content of polypropylene fiber (PF), glass fiber (GF), and carbon fiber (CF) on the physical and mechanical properties and micromorphology of EPS concrete. Among them, CFs have the most apparent impact on concrete and produce the most significant improvements in all properties. According to the requirements of the flexural performance of CSPs, the splitting tensile strength was taken as the optimization index, and the predicted optimal combination (OC) of EPS concrete with fibers was selected. The variations in the material properties, mechanical properties, and microstructure with age were analyzed. The results show that with increasing age, the dry density, compressive strength, and splitting tensile strength of concrete are markedly improved relative to those of the CSP core material and the control case (CC), and even the degree of hydration is improved.

With an emphasis on environmental protection and the sustainable development of resources, the reuse of waste concrete has long been a research hotspot, and the study of WCP is the key to improving the efficiency of waste concrete utilization. In this study, in which we reviewed the relevant literature at home and abroad in recent years, we first used Citespace software to visualize and analyze the research on the reuse and activation methods of WCP in recent years. In this paper, we explain the characteristics of WCP and the influence of different activation methods on the activity index of WCP. We summarize the mechanical properties and working properties of WCP mortar products, and finally, the optimal activation method of WCP and the optimal amount of WCP in mortar preparation are analyzed. In addition, some problems in the current research are determined.

In order to solve the problem of black pollution in the 21st century, a new type of rubber ceramsite concrete was prepared by pulverizing waste rubber tires into granules and adding aggregate to the ceramsite concrete. In order to reduce the weakening of mechanical properties of rubber, basalt fiber was used to modify the rubber. In this study, the compressive strength and splitting tensile strength of concrete specimens at days 3 and 28 were measured, the variation rule of compressive strength was explained based on the appearance of the microstructure, and the internal porosity of cubic specimens was characterized by the water absorption size. At the same time, an ultrasonic wave velocity test was used to test the uniformity and pore distribution of the block. The results showed that, with the increase in the rubber content, the compressive strength of rubber ceramsite concrete increases first and then decreases. The addition of basalt fiber can improve the compressive strength of the concrete. Water absorption is negatively correlated with compressive strength. Porosity is also negatively correlated with ultrasonic wave velocity. The basalt fiber length has no significant effect on the splitting tensile strength.

Ceramsite particles are an important component of lightweight ceramsite concrete wall panels, and the density of the aggregate is much lower than the density of the slurry. It is generally accepted that there are inhomogeneities in the distribution of ceramsite particles in wall panels. Ceramsite concrete wallboard material is a research hotspot in the field of fabricated building materials at home and abroad; however, there is no effective way to quantify their inhomogeneity. Based on the application of image recognition technology in concrete homogeneity, a method to quantitatively evaluate the distribution of light aggregates in wall panels was developed. Three commercial lightweight vitrified concrete wall panels were cut into 324 cubes. The four cut surfaces of each specimen were photographed to analyze the proportion of ceramsite particle area, while the density, ultrasonic pulse velocity, and compressive strength of the specimens were tested. The results demonstrated that the image analysis method could effectively describe the homogeneity of the panels. The proportion of particle area of aggregate in the section of the cube had a strong correlation with the compressive strength, ultrasonic pulse velocity, and density, and there was an obvious linear relationship with the height of the plate where the cube was located. Based on this, the correlation equations of the proportion of particle area of aggregate, density, ultrasonic pulse velocity, compressive strength, and the height where the specimen was located were proposed. The quantitative parameters of the relevant properties of the wall panels were also obtained: the maximum difference between the proportion of particle area of the aggregate was 24%, the maximum difference between the density at the top and bottom of the wall panels was 115 kg/m³, and the maximum difference in the strength reached 5 MPa.