Influence of minor ions on the stability and hydration rates of β-dicalcium silicate

The effects of Al3+, B3+, P5+, Fe3+, S6+, and K+ ions on the stability of the beta-phase and its hydration rate were studied in reactive dicalcium silicate (C2S, Ca2SiO4) synthesized using the Pechini process. In particular, the dependences of the phase stability and degree of hydration on the calcination temperature (i.e., particle size) and the concentration of the stabilizing ions were investigated. The phase evolution in doped C2S was determined using XRD, and the degree of hydration was estimated by the peak intensity ratio of the hydrates to the nonhydrates in Si-29 MAS NMR spectra. The stabilizing ability of the ions varied significantly, and the B3+ ions were quite effective in stabilizing the beta-phase over a wide range of doping concentrations. The hydration results indicated that differently stabilized beta-C2S hydrated at different rates, and Al3+- and B3+-doped C2S exhibited increased degree of hydration for all doping concentration ranges investigated. The effect of the doping concentration on degree of hydration was strongly dependent on the stabilizing ions.