Study of gypsum and phosphogypsum as a source of calcium sulfate in supersulfated cement (SSC) against sulfate attack

ABSTRACT

Supersulfated cement (SSC) is made with a small or almost no amount of clinker (responsible for the high release of CO2 into the atmosphere in the production of Portland cement - PC), and also for presenting good resistance in environments with high concentrations of sulfate. In this work, the length variation of the SSC samples (made from slag, gypsum or phosphogypsum as a calcium sulfate source), exposed to the sodium sulfate solution, as proposed in NBR 13583 (ABNT / 2014), comparing the results obtained with of the CP. The dimensional variation test showed that the PC sample showed the greatest expansion. Among the CSS samples, it was verified that the greatest expansion was observed in that containing phosphogypsum as a source of calcium sulfate. The microstructure analyzes (XRD, DSC and SEM) identified ettringite and gypsum as expansive phases in the PC samples, which justifies their greatest expansion among all. However, the greater expansion of SSC made with phosphogypsum was attributed to the longer time of formation of ettringite and not to the amount formed, but which would require more research.

Key-words
supersulfated cement; phosphogypsum; gypsum; sodium sulfate