Exploring the Working Characteristics, Shrinkage Behavior, Mechanical Properties, and Underlying Mechanisms of Eco-Friendly Coral Mortar

With the continuous advancement of marine engineering and coral reef construction, the construction process of using coral reefs and sand as aggregate to make concrete or mortar came into being. Therefore, this study delves into the impact of aggregate type, water–cement ratio ($\mathrm{W}/\mathrm{C}$), and sand–cement ratio ($\mathrm{S}/\mathrm{C}$) on the workability, shrinkage, and mechanical properties of mortar. Simultaneously, it uses microscopic techniques to elucidate the mechanisms underlying the impact of aggregate type, $\mathrm{W}/\mathrm{C}$, and $\mathrm{S}/\mathrm{C}$ on mortar performance. The results demonstrate that the $\mathrm{S}/\mathrm{C}$ of coral mortar should be controlled at 1.5–2. The self-shrinkage and drying shrinkage values of coral mortar decrease progressively with higher $\mathrm{S}/\mathrm{C}$ and increase with increasing $\mathrm{W}/\mathrm{C}$. Coral mortar exhibits a smaller self-shrinkage than ordinary mortar. Unlike self-shrinkage, the early drying shrinkage of coral mortar is less than that of ordinary mortar. However, as time progresses, the drying shrinkage of coral mortar becomes notably greater than that of ordinary mortar. The flexural and compressive strengths of coral mortar are inferior to those of ordinary mortar. Coral mortar experiences transcrystalline fracture, in contrast to the intergranular failure observed in ordinary mortar. Moreover, strength exhibits a quadratic power function correlation with the $\mathrm{S}/\mathrm{C}$ and a negative linear correlation with the $\mathrm{W}/\mathrm{C}$. In addition, the construction technology for coral mortar differs from that of ordinary mortar.