Combined Effect of Water Reducer–Retarder and Variable Chloride-Based Accelerator Dosage on Rapid Repair Concrete Mixtures for Jointed Plain Concrete Pavement

Abstract

On-site addition of accelerator to rapid repair concrete mixtures can result in accidental overdose. Since these mixtures are designed to contain large accelerator dosages, an overdose will produce concrete with extremely high accelerator amounts, well above those recommended by the manufacturer. This study investigated the effect of calcium chloride–based accelerator dosage on the stresses and cracking behavior of realistic concrete mixtures that contain multiple chemical admixtures. The findings indicate the effect of accelerator dosage on increasing the temperature gradient in concrete leading to higher tensile stress generation with upward or downward curling. The effect is exacerbated when there is a simultaneous coincidental occurrence in the maximum of cement paste heat flow and ambient temperatures. The apparent activation energy determined through the heat of hydration or strength measurements shows a drop when chemical retarders are added, whereas for accelerators the effect appears to be dosage dependent. The results of compressive, tensile strength and elastic modulus testing indicate a decrease in the mechanical properties of concrete at high accelerator dosages. Accelerator overdose affects hydration kinetics by limiting the degree of hydration at high temperatures while accelerating the reaction at earlier times or lower temperatures. Modeling indicated that the negative effects of accelerator overdose can be reduced by lowering the concrete placement temperature and placing concrete during evening hours.