A comparison of the performance of various synthetic gypsums in plant trials during the manufacturing of OPC clinker

This paper compares the plant performances of various synthetic gypsums used as set regulators in cement. The decision about the suitability of a specific gypsum was based on measurements and comparisons of the specific areas (Blaine), initial setting time (min), final setting time (h), SO3 content and compressive strength of the OPC clinker mixed with it. The results from the trials run with synthetic gypsum that was wet milled and treated with milk of lime showed no significant difference in compressive strengths at all ages, but a delay of approximately 35% in initial and 50% in final setting times occurred. Gypsum from a Tioxide plant can be successfully used as set retarders for OPC cement if the handling problems can be solved. In this case, no significant difference in either initial or final setting times or the compressive strengths, were observed. The ultrasonically treated phosphogypsum displayed a large variability of 50% or more in final and initial setting times, as well as compressive strengths at all ages, and is unsuccessful in rendering the gypsum usable as a set retarder for OPC cement. (C) 2004 Elsevier Ltd. All rights reserved.