Optimization of Concrete Mixture Design and Cover Thickness for Reinforced Concrete Members under Chloride Exposure

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Title: Optimization of Concrete Mixture Design and Cover Thickness for Reinforced Concrete Members under Chloride Exposure

Author(s): Saeid A. Alghamdi, Shamsad Ahmad, and Adamu Lawan

Publication: Materials Journal

Volume: 113

Issue: 5

Appears on pages(s): 589-598

Keywords: chloride-induced reinforcement corrosion; corrosion current density; cover thickness; mixture design; optimization; reinforced concrete; service life

Date: 9/1/2016

Abstract:
This paper presents a methodology proposed based on experimental and analytical procedures for optimizing concrete mixture design parameters and concrete cover thickness to achieve specified service life of a reinforced concrete (RC) member subjected to severe chloride exposure conditions. To explain utility of the suggested methodology, an experimental work was conducted consisting of preparation, chloride exposure, and corrosion testing of RC specimens. Test specimens were decided based on an experimental design considering various key factors that included three major concrete mixture parameters with their three levels (27 mixtures), three concrete cover thicknesses, and three chloride exposures, making 243 combinations. Three replicates of each combination resulted in a total number of 729 test specimens that were allowed to corrode for a period of approximately 4 years under exposure to chloride solutions. Reinforcing bars were then extracted from specimens to determine the weight loss due to corrosion using the gravimetric method. The weight loss value for each specimen was converted into equivalent corrosion current density Icorr using Faraday’s law. The Icorr data were then analyzed statistically using Analysis of Variance (ANOVA) to study the effects of each factor on reinforcement corrosion rate. A customized regression model for Icorr was obtained to determine optimum levels of concrete mixture parameters and concrete cover thickness corresponding to Icorr,min for a specified chloride exposure. A procedure to calculate the service life against corrosion damage using Icorr,min was explained, which would help to ensure that a targeted service life is achieved.