Coral aggregate concrete: Numerical description of physical, chemical and morphological properties of coral aggregate

With the increasing development of oceanic resources, coral aggregate concrete has wide potentials in the construction of islands and reefs, as well as the flood embankment, road and airport in coastal areas. However, the complex particle composition of coral aggregates, shape, surface structure and pores lead to unusual microstructure, workability, mechanical property and durability of resulting concrete. In this paper, the physical and chemical characteristics of coral aggregates are studied, and the particle shape features are analyzed. Quantitative parameters such as sphericity (psi), angular number (AN), and index of aggregate particle shape and texture (IAPST) are used to characterize the features of aggregates. An indicator, namely texture index (77), is proposed to characterize the surface microstructure of coral aggregate. The results show that the coral aggregates with rough surface and porous interior have unique tree-shaped and rod-shaped particles and the former accounts for 41.3% of the total weight. Coral aggregates have typical 'concave hole' characteristic, porosity of 48.2-55.6% and > 12% water absorption. The average sphericity and AN of coral aggregate are 0.5-0.6 and 27.5-30.3, respectively. At the same particle size, the psi of natural limestone aggregates is significantly larger than that of coral aggregates. The AN of coral aggregates is 2.4-3.0 times larger than that of limestone aggregates at a single grain size. At the same single-grain level, the IAPST of coral aggregates and natural limestone aggregates are between 31.6-34.3 and 18.6-19.6, respectively. The TI of the coral aggregates of 4.75-16 mm and 16-31.5 mm are 16.2 and 15.9, while the limestone aggregates are only 1.22 and 1.17, respectively. Compared with IAPST, the use of TI is more suitable to characterize the 'concave hole' feature of coral aggregate.