Synthesis and characterization of cement clinker using recycled pulverized oyster and scallop shell as limestone substitutes

Abstract

Developments in the aquaculture industry have increased the production of shellfish. However, the lack of a proper recycling method for discarded shells is resulting in marine environmental pollution. For the sustainable management of shellfish byproducts, pulverized oyster and scallop shell powder were used as major raw materials in cement-clinker production, replacing 100 wt% of limestone. The characteristics of the synthesized cement clinkers and hydrated cement pastes were analyzed via scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), strength tests, thermogravimetric analysis, isothermal calorimetry, and X-ray diffraction (XRD) with Rietveld refinement. The analysis results for the synthesized oyster-shell cement (OSC) and scallop-shell cement (SSC) were compared with those of limestone-based cement and commercial ordinary Portland cement (OPC). Anhydrous cement-clinker phases such as C3S, C2S, C(3)A, and C(4)AF were successfully formed in all the synthesized clinkers, similar to the OPC. Additionally, the OSC and SSC yielded the same main hydration products (CeSeH and portlandite) as the OPC, and the morphology of the hydration products in the OSC and SSC was very similar to that in the OPC. The results indicate that oyster and scallop shells are suitable substitutes for limestone as a raw material for cement.