عنوان مقاله [English]
The aim of this study is to investigate effects of incorporating low ratios of different nanosilica types on concrete resistivity against bars corrosion embedded in high-performance concrete (HPC). Three ratios of water to binder is considered in the experiment, very low, low and moderate ratio equal to 0.25, 0.30 and 0.35 respectively were used. In addition to implementing different ratios of w/b, different types of nanosilica were applied, a coarser and a finer one, respectively with specific surface area of 200 and 380 . Moreover, two low ratios of nanosilica 0.75 and 1.50 percent were considered to replace with cement according to previous studies. Compressive strength test, electrical resistivity and non-destructive ultrasonic test were conducted in this study. In addition, the workability of the mixtures was kept constant by adjusting the superplasticizer.
Although, due to high activity of nanosilica, the performance of different types and different ratios of nanosilica was variable, but it was significant that nanosilica with lower specific surface area was performed much better than the control specimen and the specimen with finer one. It should be noticed that due to very much fine size of pyrogenic nanosilica used in this study, it was highly agglomerated. So by using a high shear speed mixer, nanosilica was mixed with partial mixture water. It is shown that lower water to binder ratio had more compressive strength and also more electrical resistivity was addressed which indicate more durability due to lower water to binder ratios. It is also noticeable that using nanosilica in mixtures, made the HPC more durable and increased compressive strength. Coarser grade of nanosilica sounded better durability characteristics and also showed more corrosion resistivity based on ACI222r01. As a result, lower water to binder ratio mixtures with higher replacement of cement (1.5%) with coarser nanosilica (lower specific surface area) had the most compressive strength, electrical resistivity and non-destructive ultrasonic pulse velocity, and indicated the best concrete resistivity against corrosion of deformed bars.