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 CxS (x = 1, 2, 3) and CSH at 100C through pozzolanic reactions. The increase of the alkalinity of the solution improved the silica dissolution and enhances the formation of CxS and CSH up to 2N. Further increase of the alkalinity affected the silica polymerization, the particle size and the concentration of CxS 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.
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