Synthesis and characterization of MgO- and SrO-doped cement: Mineralogical composition and polymorphism of cement clinker phases

Abstract

To investigate the role of trace alkaline earth group elements on the formation of cement clinker phases, cement clinkers doped with magnesium oxide (MgO) and strontium oxide (SrO) were synthesized at temperatures between 1200 and 1450 °C. The synthesized clinkers were characterized using X-ray powder diffraction (XRD) with Rietveld refinement, field-emission electron probe microanalysis (FE-EPMA), and compressive strength tests. The findings of this study demonstrate that the MgO content in the clinker phase leads to an increase in C3S-M3 and a decrease in C2S. Periclase appeared in the clinker with an increase in the MgO doping ratio. In contrast, SrO in the clinker phases promoted the transformation of C2S-α’ and C3S-M1 at elevated temperatures. As the SrO content increased, free CaO emerged and increased instead of SrO and Sr(OH)2 in the cement clinker system. FE-EPMA analysis revealed distinct distribution trends, with MgO preferentially concentrated in the order of C4AF-C3A-C3S-C2S, while SrO was concentrated in the order of C2S-C4AF-C3A-C3S. The grain size of C3S increased with increasing SrO doping ratio, in contrast, that of C3S with MgO doping decreased slightly. The elemental compositions of the cement clinker in calcium silicate indicated that Mg ions were predominantly incorporated into C3S, whereas Sr ions were preferentially substituted into C2S, replacing Ca ions and significantly influencing the polymorphism of clinker phases. The results for mechanical properties show that the compressive strength of undoped cement (PC) can be improved via appropriate SrO doping.