Experimental and numerical studies on the improvements in mechanical properties of coral aggregates concrete through aggregates strengthening method

To simultaneously improve the strength, deformability, and durability of coral aggregate concrete (CAC), a systematic strengthening program of coral coarse aggregate (CCA) was proposed, and the properties of the strengthened coral aggregate concrete (SCAC) under compression were investigated in this study. For the same, nine groups of 351 concrete specimens were fabricated by condersidering two parameters: CCA strengthening methods (cement paste coated CCA (CPCC) and cement dry-powder coated CCA (CDCC) methods) and strengthening factors (cement-coarse aggregate ratio (c/ca) and water-cement ratio (w/c) of the coating materials). The mechanical mechanism and macro-properties of SCAC were investigated using a novel test system combined with numerical analyses, which included a compression test, digital image correlation measurement, scanning electron microscopy and ABAQUS simulation. The properties and microstructure of CCA were observed to be efficiently enhanced through strengthening, causing a maximum increase of 24.75 % and 110.76 % in compressive strength and energy dissipation capacity of SCAC, respectively, in comparison to CAC. The ductility of SCAC was found to almost the same as that of ordinary concrete after using CPCC due to the improved interfacial transition zones, optimised particle structure and strong aggregates. The strength and deformability of SCAC changed with the variations in the strengthening method and its critical factors. Generally, the peak strain and strength of SCAC adopting CPCC were 6.2 % and 6.48 % greater than the specimens with CDCC, respectively. The splitting strength and ultimate strain of SCAC first increased and then decreased with increasing in strengthening factors, i.e., w/c of the coating materials, and the maximum enhancement in the ultimate strain was 58.16 %. Compared to CAC, the descending branch and curvature of the stress-strain curve of SCAC were significantly improved due to the changes in the crack propagation in concrete and plastic deformation. The typical influences of the characteristics of the strengthened CCA on the mechanism were also studied through numerical simulations, which indicated that the ductility and strength increased with increasing strength of the coating of aggregates. Finally, an analytical stress-strain model of SCAC that considered the effects of strengthening variables was proposed, which provides a basis for the actual application of SCAC structures. •The properties of CAC were