Evaluation of industrial by-products for the control of setting time of cements
In this paper we present the results of investigations into the possibility of substituting sulfate bearing materials for natural gypsum as setting retarder in Portland cement (PC). The effects on setting and mechanical properties of phosphogypsum (GFS) and nitrogypsum (GNL) added in ratios 2, 4, 6, 8 and 10 mass-% to PC of different specific surfaces (Sp 1 = 3680 cm 2 g -1 and Sp 2 = 4110cm 2 g -1 ) were studied and compared with a PC containing natural gypsum. The results obtained for setting and compressive strength show that GFS and GNL may be used instead of natural gypsum. Similar results were obtained for two different grades of clinker fineness, so there is no need to grind clinker to the specific surface <3800 cm 2 /g. The cement of lower specific surface (Sp 1 ) made with GFS and GNL set faster compared with cement made with natural gypsum. The final setting time for cement with GFS and GNLforthe higher specific surface (Sp 2 ) was longerthan that obtained with cement made with natural gypsum.