Beneficial use of limestone filler with calcium sulphoaluminate cement

The present study compares the cement hydration process and the mortar properties of samples containing calcium sulphoaluminate clinker and gypsum combined with quartz filler or limestone filler. Two different calcium sulphoaluminate clinker to gypsum mass ratios are tested, 5.26 and 2.50, at 20 °C and at 5 °C. Cement hydration is studied by isothermal calorimetry, X-ray diffraction and thermogravimetry on cement pastes containing filler. Setting time, strength development and volume stability are measured on mortar samples containing additional sand. The results show that the use of limestone filler instead of quartz filler modifies the cement hydration process and is beneficial for the mortar properties at 20 °C and at 5 °C. It accelerates the early hydration of the cement, thus shortening the initial setting time. After some days, the calcite from the limestone filler leads to the formation of hemicarbonate, which tends to stabilize ettringite and to minimize the formation of monosulphoaluminate. This efficiently increases the strength of the mortars containing limestone filler rather than quartz filler.