Sodium chloride effect on durability of ternary blended cement. Microstructural characterization and strength

Abstract

This work is a continuation of a previous durability study of ternary Portland cements (TPCs), containing thermally activated paper sludge and fly ash, in the main expansive salts present in the sea water. The same experimental methodology was applied in the present case, but with a sodium chloride solution. The study was carried out by testing the flexural strength of blended pastes immersed in sodium chloride (24,530ppm), and demineralised water as a reference, at 18°C over a period of 180days. The reaction mechanism of chloride ions with the paste was evaluated by scanning electron microscopy (SEM), porosity and pore-size distribution, and X-ray diffraction (XRD). The results showed that ternary blended cement was stable against chloride attack. The enhancement of mechanical properties was a result of the formation of non-expansive Friedel’s salt inside the pores and an alkaline activation of the pozzolanic reaction of the additions promoted by the ingress of chloride and secondary related reactions; accordingly, the microstructure was refined.