Development of empirical models for chloride binding in cementitious systems containing admixed chlorides

The binding of admixed chlorides in the concrete can delay the corrosion of reinforcing steel and extend the service life of reinforced concrete structures. Although extensive research has been conducted to study the chloride binding capacity of cementitious systems subject to external chlorides, there is little information available on the chloride binding capacity of cementitious systems containing admixed chlorides. In this paper, the chloride binding capacity of several cementitious systems containing ordinary portland cement (OPC), Type C and F fly ashes, slag, and silica fume with different replacement levels is studied using acid-soluble, water-soluble, and pore-pressed testing procedures. In addition, the influence of water-to-binder ratio and admixed chloride levels on the percentages of bound chlorides is explored and discussed. The experimental results indicate that, on average, the concentration of pore-pressed chlorides is significantly lower than the concentration of water-soluble chlorides. Furthermore, the estimated bound chlorides using the pore-pressed chlorides are significantly higher than the bound chloride estimated using water-soluble chlorides. Results show that the Langmuir isotherm can be used to explain the relationship between free and bound chlorides in OPC paste samples containing admixed chlorides. Results of this study also suggest that chloride testing procedures can be very influential in quantifying the concentration of bound chlorides. Therefore, there is a need to standardize the process used for measuring the chlorides in cementitious systems for assessing chloride binding.