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

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 C(3)A over C2S. More in-depth analyses from density function theoretical simulations show that in C3S, C2S and C(3)A, the substitution occurs by replacing Ca while in C(4)AF, 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.

Automated summary

The systematic study on the existence form and doping behaviors of magnesium in ordinary Portland cement (OPC) clinker reveals that MgO incorporates into the clinker phases as substitutional solid solutions and periclase. The results also show a substitution preference in C3S and C(3)A over C2S, with different substitution mechanisms identified in different phases. The low solubility of magnesium in OPC clinker is determined by large structure distortions and sharp increase in formation energies with increasing MgO content.