The Effect of Titanium Dioxide on the Structure and Reactivity of Ferrite

Minor constituents can have a major impact on the structure and reactivity of Portland cement and Calcium Sul- foaluminate cement. An important example of this is the effect of titanium dioxide on the reactivity of the ferrite phase, the end member of which is brownmillerite. The effect of TiO2 on ferrite reactivity was investigated by forming the pure end member from reagent grade materials and adding in TiO2 at the dosages 0%, 0.5% 1.6% 2.6% and 3.6% by weight. The powders were mixed and pressed into pellets, preheated to 800 °C and then fired at 1350 °C for 30 minutes. The brownmillerite was milled for 1 hour and characterized by X-ray diffraction, energy- dispersive X-ray spectroscopy, isothermal calorimeter and thermogravimetric analysis. The addition of TiO2 was expressed in the principle XRD peak with values of TiO2 greater than 1.6% shifting it to higher d-spacing. For TiO2 greater than 1.6% the hydration and subsequent set time was found to be retarded, from only a few minutes for the materials with no TiO2 to approximately 5 to 6 hours. The addition of very low levels of TiO2 (0.5%) appeared to slightly increase the set time of the brownmillerite over the pure end member. The rate of strength development of mortar cubes also varied significantly with the higher TiO2 samples (i.e. 2.6 and 3.6%) having lower one-day strengths but much higher (by up to twice) at 7 and 28 days. It was demonstrated that the behavior of brownmillerite as a cementitious material was greatly affected by relatively small dosages of TiO2 indicating the importance of even low levels of minor components in the Portland cement and Calcium Sulfoaluminate cement.