Use of inorganic setting retarders in cement industry

The majority of cement plants in Greece mainly use natural gypsum to prevent rapid cement setting. The partial or total replacement of gypsum by materials, which contain calcium sulfate, has been instigated by two facts. Firstly, the increasing availability of low-cost by-products containing calcium sulfate and secondly, the prospect that, in the near future, the quarries will mine rock that is a mixture of gypsum and anhydrite. The aim of this paper is to discuss results from laboratory and industrial scale trials where calcium sulfate bearing materials (CSBM) such as natural gypsum, anhydrite and FGD gypsum have been used in various proportions in the cement production. The operational parameters and conditions of the cement mill during the industrial trials and the profile of the calcium sulfate hydrated forms in the produced cement are examined. The addition of FGD gypsum increases setting time without affecting compressive strength profile. The degree of dehydration of the dihydrated calcium sulfate regulates setting and strength performance of the cement partially replaced with either anhydrite or FGD gypsum.