INVESTIGATION OF HIGHLY SOLUBLE SULFATE CARRIERS IN RAPID SETTING CEMENT SYSTEMS

摘要

The reactivity of the sulfate carrier plays a major role in rapid hardening setting cement systems. In dependence of the sulfate availability at early times of hydration both, the aluminate and silicate reactions are influenced. In this investigation different amounts of α-bassanite were added to cement mixture. Its influence on the hydration mechanism was investigated by XRD and calorimetric methods. A rapid hardening cement mixture with a mixing ratio of 90 wt.% white cement (WC) and 10 wt.% calcium aluminate cement (CAC) was mixed with different amounts of α-bassanite. The cement powder was homogenized and equilibrated at 23 °C. For preparation of the pastes water was added to the cement (w/s value 0.5) and the sample was stirred by external stirring for one minute. The calorimetric investigations were carried out with an Erlanger heat flow calorimeter. The XRD measurements were carried out on a Bruker D8 X-ray diffractometer. Rheological measurements were carried out with an automated Gillmore needle (imeter/MSB, Augsburg, Germany). Rietveld refinement was performed for selected measurements using the structural models from ICSD of the cement phases. To achieve results of high quality, selective dissolutions of the cements were carried out. The residues were investigated by powder diffraction and the XRD patterns were fitted by refining the structural models. The refined parameters of the phases were implemented for the QXRD of the hydrating cement pastes. The investigations show the important role of the sulfate carrier on the early hydration of a WC/CAC cement mixtures. With an increasing amount of α-bassanite in the WC/CAC mixture, the ettringite formation during cement hydration is significantly influenced. The higher Ca2+ and SO4 2-availability at early times of hydration lead to a hindered ettringite formation over the first hours of hydration. In opposite, ettringite formation in systems without sulfate addition is almost finished ten minutes after the stirring process.