Marble Wastes Recycling: Design and Synthesis of Low-Temperature Calcium Silicate Hydrate Under Various CaO:SiO 2 Ratio and Alkalinity

Abstract

Marble sludge wastes (MSW) are investigated as solid precursor for the production of low-temperature calcium silicate hydrate (CSH). Calcined powder of MSW is ball-milled with rice husk ash (RHA) and the slurries are treated in oven at 100C for 24 hours in a context where water evaporation is minimized. The initial CaO:SiO₂ molar ratio varies from 1 to 3 (CS, C₂S and C₃S) and the solution used for the preparation of the calcium silicate hydrate presents NaOH with concentration of 0, 1, 2 and 3 N. FTIR, XRD, Particle size distribution, BET surface area and Environmental Scanning Electron Microscope (ESEM) permitted to confirm the formation of C_xS (x = 1, 2, 3) and CSH at 100̊C through pozzolanic reactions. The increase of the alkalinity of the solution improved the silica dissolution and enhances the formation of C_xS and CSH up to 2N. Further increase of the alkalinity affected the silica polymerization, the particle size and the concentration of C_xS and CSH into the final matrix. Precursor with CaO:SiO₂ = 1 seem to promote more monomers while 2CaO:SiO₂ and 3CaO:SiO₂ resulted in orthosilicate chains and interlayer respectively. The high reactivity and fine particles (ϕ < 32 nm) of CSH obtained appeared promising for the design of low-cost, environmentally-friendly and sustainable binders as well as others engineering applications including refractory precursors, hydroceramics, insulating matrices, filtration and catalysis.