Using oyster-shell foamed bricks to neutralize the acidity of recycled rainwater

• Optimum calcining condition for oyster shells was 650 °C for 1 h.
• Oyster shells gradually changed from CaCO3 to CaO as temperature rising.
• The fresh oyster-shell foamed bricks offered good workability and high porosity.
• The harden oyster-shell foamed bricks performed good neutralization efficiency.

To neutralize the acidity of recycled rainwater, oyster shells were calcined, hydrated and foamed by adding cement and foaming agent to produce oyster-shell foamed bricks (OSFBs). Experimental results demonstrate that natural oyster shells could not provide an alkali environment with sufficient metal powders for oyster-shell powder to foam, thus creating a need for additional alkali agent or calcined oyster shells. The pH of oyster shells was positively related to calcining temperature, and the optimum calcining condition was 650 °C for 1 h. The fresh OSFBs offered good workability and high porosity. Meanwhile, the 7-day and 28-day compressive strength ratios of OSFBs significantly exceeded those of normal cement paste. Through the dynamic neutralization experiments, it demonstrated that OSFB would reach the optimum condition to perform the highest neutralization efficiency when the liquid–solid ratio was 1000, the weight ratio of cement to oyster-shell was 1:5, and the foaming agent amount was 0.5% of cement.