Resistance of different types of concretes to cyclic sulfuric acid and sodium sulfate attack
An improvement in accelerated testing as a way of predicting durability was proposed in this study. Accordingly, the behavior of different concrete mixtures was examined in relation to a cyclic exposure to sulfuric acid and sodium sulfate solutions, recording the expansion and mass loss of the test specimens for about 5 years. Three different cements – i.e. Portland limestone, blast furnace slag and pozzolanic cement – were used, the latter two both with and without silica fume (SF), to prepare the concretes for the study. Scanning Electron Microscopy (SEM) and energy-dispersive X-ray analysis (EDX) were used to correlate the samples’ microstructure and deformation.The lowest expansion was obtained by mixtures containing silica fume, although they were more susceptible to corrosion in acid. After a dormant period when no expansion occurred, the Portland limestone cement and blast furnace slag cement exhibited a large expansion that began suddenly and increased at an almost constant rate. This expansion correlated with the presence of cracks filled with calcium sulfate crystals in the core of the concrete samples.For comparison, the expansion of concretes specimens left in a sodium sulfate solution was also measured. The dormant period in the two-step expansion process seen in the Portland limestone and blast furnace concretes was shorter in the cyclic testing in sulfate and sulfuric acid, which can be considered as a model of accelerated deterioration, than in the latter.