Hydration of clinkers doped with baryte with and without addition of gypsum

Abstract

The use of alternative fuels and raw materials in cement industry leads to the incorporation of some undesirable compounds into the clinker phases. One of them is barium oxide which influences the formation of clinker phases and related properties of the produced cement. Barium in clinker was already studied; the phase composition is changed depending on the amount of barium. However, detailed research focused on hydration properties of these clinkers and cements has not been carried out, yet. A clinker with barium oxide addition to raw meal was prepared. As a source of barium oxide, barium sulphate (baryte) was used in amount of 4% calculated to BaO in the clinker. Barium incorporated in clinker inhibits formation of alite; therefore, lime saturation factor was slightly reduced. Compared to barium carbonate—another source of barium oxide—barium sulphate influences the ratio of clinker phases less significantly. This clinker and a reference sample without barium were milled with and without addition of gypsum. Hydration of barium clinker and cement was examined by XRD in situ hydration and isothermal calorimetry. Hydration products were evaluated by means of thermogravimetric and differential thermal analysis. An increase in total heat of hydration can be seen in samples with barium. The heat is influenced by different hydration of clinker phases with incorporated barium, sulphates and by higher content of free CaO and C3A. According to XRD in situ hydration, hydration of samples with barium is suppressed, the amount of portlandite during the whole measurement is much higher in samples without barium.