Evaluating the effect of retarder on cement hydration and setting delay under hot weather curing condition using non-destructive methods

Abstract

Hot weather concreting has gained significant attention in recent years due to the increasing annual mean temperature. The accelerated hydration process under high temperature curing conditions can lead to premature hydration products, therefore, retarding admixtures are recommended to control the setting time. Various non-destructive methods were analyzed to estimate the setting time of cement-based materials. However, the evaluation of delayed cement hydration with added retarding admixtures has not been reported. This study aims to monitor the two non-destructive methods, electrical resistivity and ultrasonic pulse velocity, during the initial 24 h in cement pastes with added calcium lignosulfonate, the most common retarder. The setting time of cement pastes, cured at temperatures of 20, 30, and 40 ℃, was evaluated based on the rise time of these non-destructive measurements. Further, the effect of added retarder on the setting delay in cement paste was discussed and compared with the Vicat needle test. The results of X-ray diffraction and thermogravimetric analysis at the rising time of electrical resistivity revealed that the use of the retarding admixture induces delayed hydration reaction of C₃S, C₂S, and C₃A, key hydration products influencing the setting delay.