THE CL- OH- RATIO IN CHLORIDE-CONTAMINATED CONCRETE - A MOST IMPORTANT CRITERION/

Chloride-contaminated concretes were produced either by admiring sodiu m chloride with original mixes or as a result of exposure to external sodium chloride solutions. Free chloride and hydroxyl ion concentratio ns in the pore solutions of the concretes were determined. It was foun d that the value of free chloride content by itself cannot provide a m eaningful indication of the susceptibility of the reinforcement to chl oride-initiated corrosion. The ratio of free chloride to hydroxyl ion concentrations in the pore solution and differentiation between admire d and externally applied chloride are found to be factors that must be known if indicative values to predict corrosion are sought. Charts gi ving safe regions of Cl-/OH- values for various concretes are suggeste d. The use of a superplasticizer in concrete making was found to incre ase the concentration of free chloride and to raise the value of Cl-/O H- ratio in all the concretes tested. The use of fly ash was found ben eficial in immobilizing the chloride ions in non-superplasticized conc rete. However, in concrete made with a superplasticizer the inclusion of fly ash was found to cause a greater release of chloride ions into the pore solution.