Preparation, Strengthening and Efflorescence Performance of Geopolymers from Oyster Shell Powder by Using Autoclave Curing

This study developed a geopolymer using oyster shells via autoclave processing. By synergistically optimizing material composition and curing methods, both mechanical properties and durability were enhanced. Waste oyster shells (OS) and coal fly ash (CFA) at a mass ratio of 9:1 were adopted as raw materials, the combination of alkali activation with pre-curing and autoclave processing significantly promoted the gel densification and eliminated microcracks. Incorporation of 0.15% graphene oxide (GO) accelerated the dissolution of alkaline earth metals via oxygen-containing functional groups on GO, promoting the polycondensation of Si—O—Al networks. Experimental results reveal that the geopolymer cured at ambient temperature (25 °C) for 3 days attains a compressive strength of 55.35 MPa, a bulk density of 1.70 g/cm³, and a stable porosity of 35.98%. Under weathering condition, Ca²⁺ leached from oyster shells reacts with carbonate ions (CO₃²⁻) to form precipitated calcium carbonate that blocks pores, thereby achieving nanoscale reconstruction of pore structures. Compared with conventional curing protocols, this method enhances the efflorescence resistance of geopolymers by 20.1%. By integrating high-value utilization of solid waste, accelerated autoclave hardening, and efflorescence-induced self-healing, this system offers a strategy for developing novel gel materials featuring low-carbon properties and environmental durability.