Influence of calcium sulfate and calcium hydroxideon the hydration of calcium sulfoaluminate clinker

Summary: Calcium sulfoaluminate cements represent a low CO2-alternative to ordinary Portland cements. In order to better understand the hydration mechanisms of this type of binder, a commercially available calcium sulfoaluminate clinker was investigated that has been blended with different amounts of gypsum, anhydrite and portlandite. It was found that the hydration of the main hydraulic phase ye’elimite (C4A3S−) can be accelerated and controlled by the addition of calcium sulfate of sufficient reactivity. In the presence of gypsum or anhydrite, ettringite and Al(OH)3 form as hydration products. When the calcium sulfate is consumed, monosulfate forms instead of ettringite. The addition of calcium hydroxide leads to very rapid initial hydration reactions forming calcium aluminum hydrate C4AHx, which causes a very rapid setting of the binder. Compared to Portland cements, mortars based on calcium sulfoaluminate cements are able to reach higher compressive strengths up to 100 MPa after 28 days.

1 Introduction

The production of Portland cement clinker counts for about 5  % of the total man-made CO2-emissions. A promising low-CO2 alternative is the production of alternative clinkers based on calcium sulfoaluminate (C4A3S−) [1]. They can be made from calcium sulfate, limestone and bauxite at a temperature of about 1250 °C [2]. Compared to alite (1.80 g CO2 per ml of the cementing phase), calcium sulfoaluminate releases only 0.56 g CO2 per ml cementing phase [1]. In addition, this type of clinker can be ground easier compared to ordinary Portland cement. Depending on the raw meal...

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