Reactive belite stabilization mechanisms by boron-bearing dopants

Belite-rich cements hold promise for reduced energy consumption and CO2 emissions, but their use is hindered by the slow hydration rates of ordinary belites. This drawback may be overcome by activation of belite by doping. Here, the doping mechanism of B and Na/B in belites is reported. For B-doping, three solid solutions have been tested: Ca2-x/2□x/2(SiO4)1-x(BO3)x, Ca2(SiO4)1-x(BO3)xOx/2 and Ca2-xBx(SiO4)1-x(BO4)x. The experimental results support the substitution of silicate groups by tetrahedral borate groups with the concomitant substitution of calcium by boron for charge compensation, Ca2-xBx(SiO4)1-x(BO4)x. Otherwise, the coupled Na/B-doping of belite has also been investigated and Ca2-xNax(SiO4)1-x(BO3)x series is confirmed to exist for a large range of x values. Along this series, α'H-C2S is the main phase (for x ≥ 0.10) and is single phase for x = 0.25. Finally, a new structural description for borax doping in belite has been developed for α'H-Ca1.85Na0.15(SiO4)0.85(BO3)0.15, which fits better borax activated belite cements in Rietveld mineralogical analysis.