Understanding the setting and hardening process of wollastonite-based brushite cement. Part 1: Influence of the Ca/P ratio and H3PO4 concentration of the mixing solution

Abstract

Wollastonite-based brushite cement is 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.