Synthesis and Characterization of Calcium Silicate Hydrate from Oyster Shell and De-Aluminated Metakaolin Based Sodium Silicate Via Sol Gel Precipitation Method at Ambient Temperature

This study employed a facile sol-gel precipitation method to synthesize calcium silicate hydrate (CSH) at room temperature using oyster shell-derived calcium nitrate and de-aluminated metakaolin-derived sodium silicate as sustainable precursors. The evolution of CSH gel from an initial stoichiometric Ca/Si molar ratio of 0.68 into crystalline phases was investigated over different aging periods (1, 3, 7, and 14 days). The microstructural characteristics of the synthesized CSH were comprehensively analyzed using Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), energy-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). XRF analysis revealed a progressive increase in Ca/Si ratio from 0.63 (Day 1) to 0.88 (Day 14), indicating enhanced calcium incorporation during aging. FTIR spectra confirmed the formation of hydrated silicates through characteristic functional groups (O–H, Si–O, and Si– O(Ca)), with band intensity evolution suggesting increased silicate chain polymerization over time. XRD patterns confirmed tobermorite-like crystalline phases at extended aging periods, correlating with improved structural ordering. TGA analysis revealed distinct thermal decomposition profiles attributed to adsorbed water loss, CSH phase dehydration, and decarbonation. SEM micrographs of 14-day aged CSH exhibited dense, fibrous morphology characteristic of well- developed CSH phases, while EDX analysis confirmed silicon and calcium as the predominant elements, corroborating XRF findings. Prolonged aging enhanced crystallinity, calcium content, and polymerization degree, aligning with properties reported for high-performance cementitious materials. These results demonstrated the viability of utilizing oyster shells and de-aluminated metakaolin as eco-friendly precursors for CSH synthesis. This study highlights the potential for valorizing dealuminated metakaolin and oyster shells into advanced materials for sustainable construction applications; and offers promising pathway for reducing environmental wastes while contributing to greener construction material development. Future research should focus on optimizing synthesis parameters and evaluating the mechanical and durability properties of CSH in composite systems.