Evaluation of using oyster shell as a complete replacement for aggregate to make eco-friendly concrete

The objective of this study is to investigate the feasibility of using oyster shells (OS) as a complete replacement for concrete aggregate, which provides a way to make eco-friendly concrete for the recycling of waste OS and the conservation of natural resources. In this study, the mineral composition of OS was analysed, and a series of experiments were carried out to investigate the effects of curing water, mineral admixtures, and steel fiber (STF) incorporation on the strength of all-OS aggregate concrete (AOSAC), and scanning electron microscopy (SEM) and the finite element method (FEM) were used to investigate the microstructure and meso-mechanical properties of AOSAC. In the FEM simulation, it was found that the main cracks of AOSAC under compression damage develop obliquely from the top and bottom corner to the interior, forming a double inverted triangle region on the surface, and the concrete outside the region quits working. The sequence of damage was observed in the internal slices of the model as interface transition zone (ITZ), OS aggregate, and mortar. In the tests, it was found that seawater curing introduces additional hydration reactions that leads to cracking within the concrete due to the generation of expansive hydrates resulting in reduced strength. The incorporation of fly ash (FA) can alleviate this problem and inhibit the generation of expansion hydrates. The incorporation of STF equivalent to 0.5% by volume results in the maximum increase in the strength of AOSAC, and the AOSAC developed was found to be fully strong enough for structural engineering purposes.