Effect of Mg 2+ and Sr 2+ on the transformation of vaterite in calcium carbonate cements

The effects of different aqueous concentrations of Mg2+ and Sr2+ on the transformation of vaterite (CaCO3) to aragonite and calcite at 60 °C are reported. X-ray diffraction was used to analyze the crystalline phases formed at different times. Sr2+ promotes the transformation of vaterite to aragonite, with high concentrations causing the formation of calcite and strontianite ((Sr0.5,Ca0.5)CO3). Mg2+ delays the vaterite to aragonite phase transformation and suppresses calcite nucleation. A solution containing 0.1 M Mg2+ and 0.1 M Sr2+ was optimal for transforming vaterite into stable aragonite. Mixing vaterite with this solution at low L/S ratio forms calcium carbonate cements that harden and develop strength by producing interlocking aragonite crystals. Calcium carbonate cement pastes formed at L/S = 0.6 had compressive strengths of ∼14 MPa at 7 days. The potential for using calcium carbonate cement pastes to manufacture construction boards and block-type products is discussed.