Influence of the calcination temperature of phosphogypsum on the performance of supersulfated cements

Supersulfated cements (SSCs) are binders comprising mostly of granulated blast-furnace slag and calcium sulfate. In this study, phosphogypsum was used as source of calcium sulfate and the influence of its solubility (availability) on the properties of SSC was investigated. Mixtures were tested using 10 and 20% phosphogypsum calcined at either 350 or 650 degrees C, which were more or less soluble, respectively. The largest ettringite formations were verified in samples with greater calcium sulfate availability (20%, calcined at 350 degrees C), however, the highest compressive strength was not reported at this condition. The calcination temperature of 350 degrees C was shown to be only adequate for cements with lower calcium sulfate content. In mixtures with 20% calcium sulfate the compressive strength was low and related to the intense formation of secondary gypsum. In this study, the unavailability of calcium sulfate was preferable to high availability. The conversion of ettringite into monosulfate did not unduly influence the behavior of the SSCs. (C) 2020 Elsevier Ltd. All rights reserved.