Multiscale study on the effect of Seashell powder on rheology, hydration and strength development of cement paste

Abstract

With the potential to reduce CO₂ emissions, natural resources depletion, and the impact on the environment, Seashell powder (SP) presents a promising replacement for cement. To promote the utilization of SP in cement-based materials, a comprehensive understanding of its performance as a cement replacement is essential. This research examines the impact of SP on the rheology, hydration, microstructure and strength development of cement pastes across nano to macro scales. At the nano-scale, zeta potential tests were employed to explore the interaction between ions and SP in a simulated pore solution of cement paste. At the micro-scale, various techniques including Atomic Force Microscope, scanning electron microscopy, X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy and mercury intrusion porosimetry were used to characterize inter-particle force, chemical composition, the morphology of hydration products, pore structure and interface properties. At the macro-scale, the impact of SP on rheological behavior, hydration heat and compressive strength of cement pastes was investigated. Results indicate that reducing inter-particle correlation forces means increasing repulsive forces between particles. However, while the electrical repulsion between SP and cement particles improves rheology, its smaller particle size and sharp edges counteract this effect. Meanwhile, the exceptional Ca²⁺ adsorption capacity of SP particles promotes the growth and adhesion of calcium silicate hydrate (C-S-H) on its surface, thereby enhancing the degree of cement hydration and interface strength. The addition of SP, with its small size and superior nucleation effect, refines the pore structure and contributes to the high strength of cement paste.