Setting reaction of a olivine-based Mg-phosphate cement

The cementitious properties of natural Mg-rich olivine when reacted with a phosphoric acid solution are investigated, as a function of acid concentration and liquid/solid mass ratio. The obtained cements are composed of residual olivine crystals and amorphous silica nanoparticles dispersed in a dense and compact newberyite (MgHPO 4 ∙3H 2 O) matrix. The latter was mostly formed by packed micrometric tabular crystals, although evidence of the presence of a fraction of amorphous MgHPO 4 was also found. Water content in the raw mix was observed to play a pivotal role on the reaction pathway, either promoting porosity or hindering the crystallization of the products. Up to 57 % of olivine reactivity, whose dissolution was promoted by the curing temperature (60 °C) and low pH, was achieved. All in all, these results indicate that the industrial mineral olivine may serve a viable source of Mg for the production of phosphate cements. • Mg-olivine is tested for the first time as raw material in the production of MPC. • The cements are made of amorphous silica dispersed in a dense newberyite matrix. • The precipitated Mg-phosphates are mostly crystalline. • Water plays a pivotal role in defining the reaction pathways. • Up to 75 MPa of compressive strength is reached.