The effect of interface on the strength characteristics and fracture mechanism of the coral reef limestone-concrete combination specimen

Biological and biochemical geneses bring complex structures to coral reef limestone (CRL), leading to pronounced anisotropy and heterogeneity. The stress field concentration induced by pore structure introduces a considerable dispersion in mechanical parameters and reduce the strength of CRL significantly. The CRL-C specimens were made using coral reef limestone to conduct uniaxial compression tests with loading rate of 0.002 mm/s, revealing the controlling mechanism of interface inclination angle for the strength of CRL-C specimens. The experiment results shows that the peak strength, peak strain, and modulus of elasticity of the combination all tend to lessen and then grow with increasing the interfacial inclination angle. The achieved results indicate that the tensile damage occurs in specimens with 0°, 15°, and 90° inclination angles, whereas the tension-shear stress damage takes place for specimens with 30° inclination angle. In turn, the shear damage occurs along the interface for specimens with 45°, 60°, and 75° inclination angles. The strength of combination specimens underwent the shear failure is noticeably smaller than that of the combination specimens damaged across the interface. Additionally, the cement mortar at the interface has a remarkable reinforcing effect on the interface strength, and the CRL-C interface possesses the highest cohesion and a lower internal friction angle compared to terrestrial rocks. Simultaneously, the parameters of the CRL-C specimens in the single-interface model are appropriately determined based on the interface strength. The inclination range of the combination specimen damaged along the interface is 35.58°<α < 85.83°. The predicted strength parameters based on the Coulomb model and the single-interface model provide a solid reference for the engineering design of CRL-C.