Effects of admixtures on the mechanical characteristics and microstructure of coral aggregate mortar

Coral mortar is often used to reinforce building foundations in island-reef engineering. To en-hance the mechanical characteristics of coral aggregate mortar, and hence facilitate the develop-ment of ocean engineering, this paper studies the influences of silica fume (SF), metakaolin (MK), blast furnace slag (BFS) and fly ash (FA) on the workability, uniaxial compression process and mi-crostructure of coral aggregate mortar (CAM). Ultrasonic pulse velocimetry is used to investigate the effects of various additives on ultrasonic propagation speed and cumulative voltage energy (CVE). The microstructure and hydration products of different CAMs are analyzed using scanning electron microscopy. Experimental results show that silica fume is more effective than blast fur-nace slag and fly ash in improving density and water retention of CAM. Silica fume can promote the consumption of calcium hydroxide crystals and the formation of calcium silicate hydrate, thus improving the compressive strength of CAM. There is a good correlation between S-wave ve-locity and elastic modulus in CAM. The CVE of the P-wave in CAM with external admixture is sig-nificantly higher than that in ordinary CAM. Addition of blast furnace slag and fly ash makes the CVE of the ultrasonic wave in CAM decrease earlier and faster. The results provide a guide for the improvement of the strength of CAM.