Effect of silica fume and micro fiber additives on sulfates and carbonation process in concrete

In this study, the effect of carbonation and sulfates on micro-fine cement called DMFC-800 cement, micro fibers-added and silica fume-added concrete was investigated. Silica fume was substituted with 0%, 5%, 10% and 15% by mass of DMFC-800 and 600 grams per cubic meter micro fiber additive was used. Eight groups concrete mixture of based on C25/30 class concrete were poured in 150x150x150 mm cube molds with 4 groups of micro fiber and 4 groups of non-micro fiber additive. Accelerated carbonation test method was applied in carbonation experiment. For this purpose, concrete samples were stored in condensed CO2 gas for 28 and 56 days. The concrete samples were subjected to the effect of outer sulfate at concentrations of 2% sodium sulfate and 2% magnesium sulfate for 28 and 90 days. After the curing ages, the samples were removed from the curing environment and experiments were carried out. According to the results of the experiment, silica fume and micro fiber additive had a positive effect on the reduction of carbonation. Carbonation resistance was found in the samples with a maximum of 10% and 15% silica fume, while the least carbonation resistance was observed in the samples without silica fume and micro fiber additive. Silica fume and micro fiber increased the concrete resistance against sodium sulfate attack. The maximum compressive strength of the concretes, which were exposed to sodium sulfate concentration for 28 days, was observed in concretes containing micro fiber and 10%, 15% of silica fume and the least compressive strength was seen in concretes without micro fiber and silica fume. However, as the ratio of silica fume increased, the resistance of the concrete against magnesium sulfate attack decreased. The highest compressive strength of the concretes, which were kept in 28 days magnesium sulfate concentration, was observed in the concrete which contains micro fiber and free of silica fume and the least compressive strength was observed in concrete which containing micro fiber and 10%, 15% of silica fume. The compressive strength of all concrete groups, which were kept in the sulfate solutions for 90 days, increased slightly compared to 28 days.