Crumb rubber concrete (CRC) has emerged as a sustainable solution to the environmental challenges posed by rubber waste. This study introduces an advanced mixed-random-aggregate mesoscale model for CRC based on the Base Force Element Method (BFEM) and the complementary energy principle. The model incorporates different rubber substitution ratios (0%–30%), rubber particle sizes (2 mm and 4 mm), and specimen dimensions (edge lengths of 100, 150, and 300 mm). These parameters are considered to investigate their effects on the mechanical properties and failure mechanisms of CRC. Accordingly, the numerical results include stress–strain responses, elastic modulus, and damage progression patterns. The results indicate that increasing rubber content leads to a pronounced reduction in both tensile and compressive strengths. This drop occurs mainly because rubber particles have a much lower elastic modulus. Thus, they represent stress concentrators and weak points, which accelerate the sample failure. Moreover, for the same replacement ratio, CRC with smaller rubber particles (2 mm) exhibits lower strength than CRC with larger particles (4 mm). This reduction occurs because the finer particles create more interfacial areas, introducing more sites for defect initiation and micro-cracks. In addition, increasing specimen size is associated with reduced strength and elastic modulus, highlighting size-dependent phenomena in CRC. The numerical predictions show good agreement with experimental results reported in the literature.

The mechanical properties and failure mechanism of lightweight aggregate concrete (LWAC) is a hot topic in the engineering field, and the relationship between its microstructure and macroscopic mechanical properties is also a frontier research topic in the academic field. In this study, the image processing technology is used to establish a micro-structure model of lightweight aggregate concrete. Through the information extraction and processing of the section image of actual light aggregate concrete specimens, the mesostructural model of light aggregate concrete with real aggregate characteristics is established. The numerical simulation of uniaxial tensile test, uniaxial compression test and three-point bending test of lightweight aggregate concrete are carried out using a new finite element method-the base force element method respectively. Firstly, the image processing technology is used to produce beam specimens, uniaxial compression specimens and uniaxial tensile specimens of light aggregate concrete, which can better simulate the aggregate shape and random distribution of real light aggregate concrete. Secondly, the three-point bending test is numerically simulated. Thirdly, the uniaxial compression specimen generated by image processing technology is numerically simulated. Fourth, the uniaxial tensile specimen generated by image processing technology is numerically simulated. The mechanical behavior and damage mode of the specimen during loading were analyzed. The results of numerical simulation are compared and analyzed with those of relevant experiments. The feasibility and correctness of the micromodel established in this study for analyzing the micromechanics of lightweight aggregate concrete materials are verified. Image processing technology has a broad application prospect in the field of concrete mesoscopic damage analysis.