Investigation of mechanical characterization and damage evolution of coral reef sand concrete using in-situ CT and digital volume correlation techniques

Coral reef sand concrete (CRSC) plays an indispensable role in island reef projects, but limited knowledge of its damage poses safety and stability concerns for coral reef sand concrete structures. Therefore, the in-situ computed tomography (CT) is employed to investigate the strength and deformation, and pore structure evolution of coral reef sand concrete under uniaxial load. Additionally, the crack propagation and three-dimensional strain field evolution under different stress states are revealed by the digital volume correlation (DVC) techniques. The results demonstrate that when the stress is below 35.79 MPa, the porosity gradually decreases as the stress increases. However, when the stress exceeds 35.79 MPa, the local porosity increases with the rising stress, and the porosity at 39.89 MPa is higher than the initial porosity. Moreover, stresses evidently concentrate at areas of local maximum porosity, resulting in the initiation and development of cracks in those regions. During the failure process, CRSC experiences splitting damage firstly caused by longitudinal cracks, followed by the extension of these cracks into oblique cracks, resulting in shear damage. Coral aggregate is the weak phase in CRSC, exhibiting transgranular fractures. Additionally, CRSC exhibits significant strain in the pores and coral aggregates, leading to crack development along the direction of the pores or coral aggregates. Therefore, this study offers a deeper understanding of the damage mechanisms of CRSC, providing theoretical support for its further research and practical application in far-sea projects.