Structure and Properties of Lightweight Oyster Shell-based Geopolymers Prepared with Alkali Activation Method

The oyster cultivation in coastal areas of China produces a large number of oyster shells every year, whose resource utilization is related to environmental protection and sustainable development of industry. Lightweight oyster shell-based geopolymers were prepared by using oyster shell and fly ash as main raw materials, water glass and NaOH solution as composite activators, and H₂O₂ as the foaming agent. The effects of foaming agent, aluminum silicate fiber and calcium stearate on pore structure, apparent density, compressive strength and weathering properties of the oyster shell geopolymers were systematically studied. The pore structure and microstructure were analyzed by using XRD, FTIR, SEM and contact angle tester. It is found that apparent density and compressive strength of the geopolymer continue to decrease with increasing content of H₂O₂, but the strength increases first and then decreases. Apparent density, compressive strength and specific strength of the geopolymers increase first and then decrease with increasing content of aluminum silicate fiber, reaching the maximum values at 1.00%, which are 0.63 g·cm⁻³, 4.45 MPa and 6.98 kN·m·kg⁻¹, respectively. The addition of a small content of calcium stearate did not affect structure and compressive strength of the geopolymers, the weathering performance was significantly improved. When the content was 0.50%, the optimal weight loss and specific strength loss were 10.1% and 14.1%, respectively. This lightweight geopolymer is expected to be useful in sidewalk bricks and curb stones to realize the value-added utilization of oyster shells as resources.