Effects of ferrite concentration on synthesis, hydration and mechanical properties of alite-calcium sulfoaluminate-ferrite cements

Low- to high-iron alite-calcium sulfoaluminate-ferrite clinkers were designed through new compositional parameters and synthesized. Clinker compositions were optimized through different firing regimes and verified through characterization methods, such as free lime determination, X-ray diffraction (XRD)/Rietveld, and scanning electron microscopy/energy-dispersive spectroscopy methods. Clinkers with 5–45% of ferrite (C4AF) were produced at a temperature of 1275–1325 °C for a dwell time of 60 min, with the incorporation of fluxes and mineralizers. The hydration processes and the mechanical properties were studied by calorimetry, XRD, thermogravimetry, and compressive strength analyses. The more ferrite that was present in a clinker, the lower the compressive strength, which was mainly due to the unreacted ferrite still present even after six months. Additions of triisopropanolamine to these compositions caused the ferrite to entirely react within seven days, allowing the incorporation of larger amounts of calcium sulfates to produce ettringite, and exhibiting equivalent compressive strengths to compositions with less calcium sulfates.