Effect of Sand Replacement on the Early-Age Strength Gain and Long-Term Corrosion-Resisting Characteristics of Fy Ash Concrete

Abstract

This is a report of the results of experiments carried out to evaluate compressive-strength development and corrosion-resisting characteristics of concrete mixtures in which fly ash was used as an admixture (an equal quantity of sand was replaced). Data were developed for fly ash additions of 0, 20, and 30 % and water-cement ratios of 0.35, 0.40, 0.45, and 0.50. The compressive strength was determined at 3, 7, 14, 28, 56, and 90 days. Concrete samples were partially immersed in a 5 % sodium chloride solution for a period of about 4 years, and corrosion-resisting characteristics of concrete were evaluated by monitoring the half-cell potential and measuring the corrosion rate of embedded steel bars using electrochemical techniques. Results show that addition of fly ash as an admixture increases the early-age compressive strength and long-term corrosion-resisting characteristics of concrete. The superior performance of these mixtures compared to plain concrete mixtures is attributable to the densification of the paste structure due to pozzolanic action between the fly ash and the calcium hydroxide liberated as a result of hydration of cement.