The evolution of the microstructure and mechanical properties of coral aggregate mortar under uniaxial compression using ultrasonic analysis

Abstract

This study investigated the compression behavior of coral aggregate mortar (CAM) under uniaxial loading using ultrasonic pulse velocity measurements. Silica sand mortar (SSM) was used for comparison. The results indicated that the compressive strength of the CAM was slightly higher than that of the SSM prepared with similar-sized silica sand. Numerous open pores in the porous structure of the coral aggregate provided water reservoirs for internal curing, enhancing the solid structure and improving the compressive strength. Since the grain strength is related to the grain size, which decreased with decreasing grain size, the compressive strength of the CAM decreased with an increase in the size of the coral aggregate. The ultrasonic wave velocities were stable around 4200 m/s for the P-wave and 2100 m/s for the S-wave before fracturing and dropping sharply due to the brittle failure of the SSM and the CAM. The compression behavior of the CAM and the SSM could be divided into five stages. The cumulative voltage energy indicated that the microcrack evolution of the two mortars was significantly different. Intergranular and transgranular crack propagation occurred in the CAM and depended on the particle strength and number of internal pores of the coral aggregate. We discuss in detail the mechanism between the cementitious materials and the pores of the coral sand mortar. The results can provide a reference for improving the strength of coral sand cement-based materials.