Performance of limestone cement concretes in chloride-sulfate environments at low temperature

摘要

Portland-limestone cement concretes were stored in two chloride-sulfate solutions, corresponding to exposure classes XS2, XA2 and XA3 specified by the standard BS EN 206:2013, at 5 +/- 1 degrees C. Their performance was evaluated in terms of the limestone content (15% or 35% w/w) of the cements used and the partial replacement of limestone cement with natural pozzolana, fly ash, blast-furnace slag or metakaolin. Sulfate attack was monitored through visual inspection of the specimens, mass measurements, compressive strength tests and X-ray diffraction analysis. The penetration of chloride ions was evaluated by determining total (acid-soluble) and free (water-soluble) chloride contents, as well as apparent chloride diffusion coefficients. Limestone cements favoured thaumasite sulfate attack and chloride accumulation in concrete compared to ordinary Portland cement. Mineral admixtures improved the concrete's durability against sulfate attack, inhibited chloride penetration and enhanced chloride binding. Fly ash, metakaolin and blast-furnace slag were more effective than natural pozzolana. Higher sulfate content of storage solutions promoted deterioration, and decreased chloride diffusion coefficients. The results obtained for concretes with mineral admixtures were competitive with those achieved when ordinary Portland cement was used.