Mechanical properties and failure mechanism of concrete-granite composite specimens under compression load

Concrete-rock composite structures represent a distinct category in engineering structures. The interplay between concrete and rock entities is of great significance in engineering research, especially concerning the stability of concrete-rock foundations. Recently, numerous compression tests have been conducted to investigate the interplay between concrete and rock, but the influence of interface inclination angle and concrete component percentage on the mechanical properties and failure mechanisms under biaxial compression loading conditions has not been addressed by previous studies. Therefore, the main objective of this study is to systematically investigate the mechanical response of CGCSs under compression loads and different combination modes (concrete component percentage and interface inclination angle). In this study, high-precision digital images were used to characterize the spatial distribution of mineral and material components in granite and concrete specimens, respectively. By employing digital image processing (DIP) technologies along with the numerical simulation code (RFPA2D), numerical models capable of reflecting the meso-structures inside concrete-granite composite specimens (CGCSs) were reconstructed for the first time. The results indicate that these numerical models realistically reproduce the mechanical properties and failure characteristics of CGCSs, and four kinds of failure modes have been observed for different combination modes of CGCSs under compression load. There was a critical concrete component percentage, below which the peak strength of CGCSs surpassed that of the concrete specimen and above which the opposite trend was observed. Moreover, the peak strength of CGCSs was lower than that of the concrete specimen when the interface inclination angle ranged from 30 degrees to 60 degrees, with the opposite trend observed for other angles. Due to the lateral constraints, the peak strength and elastic modulus of CGCSs exhibit a positive correlation with confining pressure under different combination modes. The peak strength and elastic modulus of CGCSs exhibit a negative correlation with the concrete component percentage. As the interface inclination angle increases, the peak strength and elastic modulus of CGCSs initially decrease and then stabilize. These numerical results provide valuable insight into the mechanical properties and failure mechanisms of CGCSs under different combination modes and complex loading conditions.