Sodium sulphate effect on the mineralogy of ternary blended cements elaborated with activated paper sludge and fly ash

摘要

This paper presents an exhaustive study about the identification and evolution of the mineralogicaludhydrated phases of ternary Portland cements (TPC), containing thermally activated clay wasteud(paper sludge) and fly ash, exposed to sodium sulphate salt up to 180 days. The repercussion of theseudmineralogical changes on the microstructure and strength properties is also discussed in this work.udThe reaction mechanisms of sulphate ion with the paste was carried out through a microstructureudstudy, which included the use of scanning electron microscopy (SEM), porosity and pore-size distributionudand X-ray diffraction (XRD). The results showed that ternary Portland cement was stable against sodiumudsulphate attack at the conditions here studied. The enhancement of flexural strength was a result of theudformation of non-expansive ettringite inside the pores and an alkaline activation of the pozzolanicudreaction of additions promoted by the ingress of sulphate and secondary related reactions. Accordingly,udthe microstructure was strongly refined.