Abstract
Reinforcing steel corrosion, caused by chloride ingress into concrete, is the leading cause of reinforced concrete deterioration. One of the main findings in the literature for reducing chloride ingress is the improvement of the durability characteristics of concrete by the addition of supplementary cementitious materials (SCMs) and/or chemical agents to concrete mixtures. In this study, standard ASTM tests—such as rapid chloride permeability (RCPT), bulk diffusion and sorptivity tests—were used to measure concrete properties such as porosity, sorptivity, salt diffusion, and permeability. Eight different mixtures, prepared with different SCMs and corrosion inhibitors, were tested. Apparent and effective chloride diffusion coefficients were calculated using bound chloride isotherms and time-dependent decrease in diffusion. Diffusion coefficients decreased with time, especially with the addition of SCMs and corrosion inhibitors. The apparent diffusion coefficient calculated using the error function was slightly lower than the effective diffusion coefficient; however, there was a linear trend between the two. The formation factor was found to correlate with the effective diffusion coefficient. The results of the laboratory tests were compared and benchmarked to their counterparts in the marine exposure site in the Arabian Gulf in order to identify laboratory key tests to predict concrete durability. The overall performance of concrete containing SCMs, especially fly ash, were the best among the other mixtures in the laboratory and the field.
Highlights
Corrosion of reinforcing steel is the most common cause of reinforced concrete deterioration [1,2].While the high pH environment of concrete normally protects reinforcing steel from corrosion, presence of chlorides at high rates in pore solutions, which reduces alkalinity, or at the steel–concrete interface can initiate corrosion
This study examines on the ability of concrete electrical test methods to quantify concrete transport properties, with special focus on the utility of the formation factor
The concrete formation factor was calculated from rapid chloride permeability (RCPT) data collected during the first hour of the test and the pore solution conductivity was calculated using the NIST pore solution conductivity calculator
Summary
Corrosion of reinforcing steel is the most common cause of reinforced concrete deterioration [1,2]. The diffusion coefficient in Equation (1) accounts for the rate at which chloride ions can diffuse through the concrete pores. The apparent diffusion coefficient can be fit to experimental data obtained from bulk concrete diffusion tests such as ASTM C1556 without having to measure the chloride binding or separate out the two effects. One of the best ways to protect concrete reinforcing steel from corrosion and increase the service life is to reduce the concrete porosity and permeability [4,12,13]. Concrete permeability and diffusivity can be reduced by the use of supplementary cementitious materials (SCMs) such as slag cement, fly ash, or silica fume or use of a lower water-to-cementitious materials ratio (w/c) [14,15,16,17]. Formation factor was compared to concrete absorption and effective diffusion coefficient for concrete tested in the laboratory. Laboratory-measured values were compared to performance of concrete samples from the same mixtures exposed to seawater at an outdoor field exposure site [51] to validate the test method performance, especially the formation factor, to predict concrete durability
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