The sulfate resistance of various cementitious binders according to different performance indicators at Nordic countries conditions

Abstract The sulfate resistance of moderate C 3 A Portland and Portland limestone cements (respectively PC and PLC) and their mixes with fly ash (FA) was monitored according to five performance indicators: changes in length, in mass, in strength, in ultrasonic pulse velocity and in appearance. Mortar samples (40 × 40 × 160 mm) were immersed in sodium sulfate solution (16 g/l of SO 4 2− ) for up to 12 months at ambient +20 °C conditions and more common for Nordic countries +7 °C conditions. The water/binder ratio in mortars was 0.6, pre-curing period before immersion of mortar samples in sodium sulfate solution was 28 days in water at +20 °C. Research results demonstrated that rating of sulfate resistance using different indicators is not simple and depends on the binder type and exposure temperature. The deterioration of mortar samples in sulfate environment can occur without noticeable expansion. Firstly surface degradation begins and then deterioration throughout the sample volume (loss in strength, decrease of UPV) occurs. The signs of deterioration occur quicker at +7 °C. Research results have showed that a significant positive effect of partial replacement of cement by FA for both PC and PLC was observed only at 20 °C. At +7 °C this effect is much weaker for normal hardening PC and there is almost no effect for rapid hardening PLC.