Wollastonite-based brushite cements are mainly used for refractory material applications, but they may also offer new prospects for the solidification/stabilization of hazardous wastes. Most studies on these binders have been focused on the characterization of the final products, on the associated microstructure or on the functional properties of the resulting materials. This work provides new insight into their setting and hardening process, by characterizing the evolution of both the liquid and solid phases with ongoing hydration.

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Wollastonite-based brushite cement are prepared by mixing wollastonite with a phosphoric acid solution containing metallic cations and boric acid. This work investigates simplified systems comprising wollastonite and H3PO4 solutions only, in order to clarify the influence of the H3PO4 concentration, Ca/P and l/s ratios (this latter parameter being correlated to the two others) on the setting and hardening process. At constant H3PO4 concentration, increasing the Ca/P ratio, and decreasing the l/s ratio, accelerates the early stages of hydration but limits its progress at 7 d. At high Ca/P ratio, more basic calcium orthophosphates form in addition to dicalcium phosphate. At constant l/s ratio, increasing the H3PO4 concentration in the range 7-10 mol.L-1 retards cement hydration, and inhibits the setting at concentrations  12 mol.L-1. A good compromise is obtained for H3PO4 concentrations between 9 and 10 mol.L-1 : hydration is not too fast and yields the maximum amount of dicalcium phosphate.