Probing the exact form and doping preference of magnesium in ordinary Portland cement clinker phases: A study from experiments and DFT simulations

Highlights: • The doping behaviors of Mg in OPC clinker phases were systematically studied. • About 1.3 wt% MgO enter OPC clinker phases by forming substitutional solid solutions. • In the 4 composed minerals, C₃S, C₃A and C₄AF can host more Mg ions than C₂S. • Mg ions prefer to replace Ca in C₃S, C₂S and C₃A while replace Fe and Ca in C₄AF. • Both the large structure distortions and formation energies governs the low solubility. A systematic study was performed to learn the exact existence form and doping behaviors of magnesium in ordinary Portland cement (OPC) clinker. Our results show that about 1.3 wt% MgO incorporates into OPC clinker phases by forming substitutional solid solutions while excess Mg accumulate and exist as periclase. Results from Rietveld refinement present a substitution preference in C₃S and C₃A over C₂S. More in-depth analyses from density function theoretical simulations show that in C₃S, C₂S and C₃A, the substitution occurs by replacing Ca while in C₄AF, it probably occurs by substituting Fe and Ca ions. The large structure distortions and sharp increase in formation energies with increasing MgO determines its low solubility. This work provides a clear understanding of the existence states and the intrinsic mechanism governing doping behaviors of Mg, thus should be very important in guiding the synthesis of OPC clinker by utilizing high-Mg limestone.