Valorising bio-waste mussel shells in LC3 Systems: Hydration and mechanical performance

Abstract

Limestone calcined clay cement (LC³) is a promising low-carbon binder; however, intrinsic drawbacks, including the relatively low reactivity of calcite and decreased early strength, limit its ability to compensate for cement clinker reduction. In this study, mussel shell powder (MSP), derived from a widely available bio-waste, was investigated as a sustainable replacement for limestone in LC³ systems, offering a more reactive polymorph of aragonite. The results showed that, compared to LC³, MSP-based LC³ (m-LC³) exhibited a longer induction period due to the retardation effect of the organic matrix present in the MSP. However, it gradually released the more reactive aragonite phase in the alkaline environment, which facilitated the formation of greater amounts of hemicarboaluminate and monocarboaluminate at early hydration stages. This enhanced early strength by 130 % and 58 % at 1 day for m-LC³ without and with sulphate adjustment, respectively. At later stages, the portlandite concentration decreased due to the pozzolanic reaction with metakaolin, and the release of aragonite slowed down. As a result, m-LC³ showed slightly higher strength at 28 days. As a low-CO₂ binder, m-LC³ not only leverages a waste-derived source of metastable CaCO₃ but also demonstrates potential for large-scale performance improvements and carbon footprint reduction.