Comportamento frente à ação de cloretos de concretos compostos com adições minerais submetidos a diferentes períodos de cura

Abstract

This study aimed to investigate the effect of chlorides on the behavior of concrete compositions with mineral additions, especially the rice husk ash, that were wet cured for 3, 7 and 28 days. The performance of samples with substitutions of 10%, 20% and 30% of rice husk ash (RHA) for cement b/w was compared with samples with 50% blast furnace slag (BFS), 35% fly ash (FA) and plain cement (REF no additions). The water/binder (w/b) ratios used were 0.35, 0.50 and 0.65. Chloride permeability at 91 days was determined by measuring the total electrical charge passed according to ASTM C1202 (Rapid Chloride Pentration Test) and the chloride diffusion coefficient was measured according to EPCANP (AASHTO T259 90-day Ponding Test). Results show a reduction in chloride penetration for lower w/b ratios. The same is observed when cement is substituted with mineral additions and when the curing period is extended. Mixtures with RHA and FA appear to be more susceptible to the curing conditions than those with BFS. This suggests that the detrimental effects of the reduction in the concentration of aluminates in the binder (reduced chloride retention capacity) caused by the addition of ash can be offset by increased curing periods. For concrete samples of equal compressive strength values, those with BFS showed the lowest chloride diffusion coefficients with samples with 30% RHA showing the lowest charge passed values. Compressive strength values for samples with RHA were equal to or greater than those of the reference sample in all conditions of the test, and the samples with 20% substitutions showed the best performance. Statistical analysis showed that the correlations between the variables in the study are not valid when concrete samples with different mineral additions are investigated. However, within the same type of binder there are sound correlations between compressive strength vs. charge passed values and diffusion coefficient vs. charge passed (determination coefficients between 0.85 and 1.00).