مهندسی عمران شریف (Feb 2021)
INVESTIGATING THE EFFECTS OF USING PYROGENIC NANOSILICA IN HIGH-PERFORMANCE CONCRETE ON CONCRETE RESISTIVITY AGAINST REBAR CORROSION
Abstract
The main objective of the present study is to investigate the effects of incorporating the low ratios of different Nanosilica types on concrete resistivity against bars corrosion embedded in High-Performance Concrete (HPC). Three ratios of water to binder are considered in the experiment: very low, low, and moderate ratios equal to 0.25, 0.30, and 0.35, respectively. 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 areas of 200 and 380 . Moreover, two low ratios of nanosilica 0.75\% and 1.50\% 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 the performance of different types and ratios of nanosilica were variable due to its great activity, it was significant that nanosilica with a lower specific surface area outperformed 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. Thus, by using a high shear speed mixer, nanosilica was mixed with partial mixture water. It was shown that a lower water-to-binder ratio had more compressive strength and also, more electrical resistivity was addressed indicating more durability due to lower water-to-binder ratios. It was also noticeable that using nanosilica in mixtures made the HPC more durable and increased compressive strength. Nanosilica of Coarser grade sounded quite better in terms of durability characteristics and also, showed more corrosion resistivity based on ACI222r01. As a result, mixtures of lower water-to-binder ratio 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, indicating the best concrete resistivity against corrosion of deformed bars.
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