Studies on the evaluation of permeability and corrosion resisting characteristics of Portland pozzolan concrete

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Saudi Digital Library
The service conditions of Eastern Saudi Arabia necessitate the production of concrete which is dense and impervious, so that it inhibits penetration of salts which are effective in setting up corrosion of rebars and chemical deterioration of hardened cement paste. Pozzolan is considered a potential admixture. This investigation evaluated the effect of using pozzolan on the permeability, porosity and general quality of concrete made with typical local aggregates consisting of finely graded sands and crushed limestone. I varied possolan substitution from 0 to 40% and water cement ratio in the range of 0.35 to 0.55. The performance of pozzolans from four different sources was also evaluated. The effects of hydration reaction of pozzolan on the properties of concrete was studied for one year, by measuring water permability, porosity, pulse-velocity and compressive strength. Accelerated corrosion tests were carried out in the laboratory to determine the effectiveness of pozzolan in inhabiting rebar corrosion. Exposure-site tests were carried out to evaluate the corrosion resistance characteristics of pozzolan concrete made with salt contaminate mixing water. The exposure-site samples were monitored to determine the time to cracking. Carbonation depth, weight loss of rebars, and pH were measured after 11 months. Results show that 20% fly ash improves the general quality of concrete. Pozzolan concretes show better performance than straight portland cement concrete in terms of resistance against rebar corrosion. Pozzolan concrete contaminated with salts do not show any noticeable aggravation, in rebar corrosion due to the presence of fly ash. Reaction between fly ash and calcium hydroxide (Ca(OH)$sb2$) of the hydrated cement paste does not reduce pH below that observed for the no-fly ash concretes. Carbonation depths of about 1.0 cm were observed in 11 months of exposure. The best performance was exhibited by French fly ash. (Abstract shortened by UMI.)