Multi-scale characteristics of eco-friendly marine binder using coral waste

On islands far away from the mainland, the raw materials for concrete production are often more difficult to obtain. Converting the coral waste generated during the island construction process into a marine binder is an eco-friendly strategy. This research explores the multi-scale characteristics of cement paste mixed with coral powder (CP) from the nano-scale to the macro-scale for the first time, and the environmental benefits of the mixture are evaluated. The results indicated that although the strength of the cement paste decreases with the increase of CP content, incorporating 10% CP can improve the early-age strength of the sample and make its 28-d compressive strength reach 93.5% of the reference group. Meanwhile, incorporating CP can significantly reduce the autogenous shrinkage of the mixture, and the 7-d shrinkage value of the CP30 mixture is only 56.7% of the control group. The results of nanoindentation show that although the incorporation of CP reduces the hydration product and increases the pore phase of the cement paste, a small amount of CP (10%) can increase its C-S-H content and reduce the unhydrated phase content. In addition, CP reacts with calcium trialuminate to form monocarbonate in 28 d, which inhibits the conversion of ettringite to monosulphate. Therefore, using an appropriate amount of coral waste to prepare the binder can not only alleviate the pressure of ocean transportation of raw materials, but also reduce the cracking risk caused by the shrinkage. • Waste coral powder and cement were used to produce eco-friendly binder. • The multi-scale characteristics of the novel marine binder were tested. • The influence mechanism of CP on cement paste was explored.