Marble wastes recycling: Design and synthesis of low-temperature calcium silicate hydrate under various CaO:SiO2 ratio and alkalinity

Marble sludge wastes (MSW) are investigated as solid precursors 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 the oven at 100°C for 24 h 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 CSH(I) at 100°C through pozzolanic reactions. The increase of the alkalinity of the solution improves 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 CSH into the final matrix. The precursor with CaO:SiO2 = 1 seems to promote C-S-H(I) with more monomers while 2CaO:SiO2 and 3CaO:SiO2 resulted in orthosilicate chains and interlayer respectively. The high reactivity and fine particles (diametre < 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 binder and concrete seed, refractory precursors, hydroceramics, insulating matrices, filtration and catalysis.