Effects of Withholding Mixing Water and Retempering on Properties of Concrete

The effects of withholding mixing water at initial batching followed by retempering of the mix at the jobsite on the properties of the concrete produced for highway applications was examined in an experimental program. Additionally, the effects of redosage with water above and beyond that called for in the specified mix design was examined. Tests were performed to determine the effects on slump, air content, unit weight, compressive strength, flexural strength, abrasion resistance, and freeze thaw resistance. The effects of varying the withholding amount, withholding time, and cement content on the fresh and hardened concrete properties mentioned above were examined. The concrete examined was produced at a ready mixed concrete facility in order to duplicate as closely as possible job site conditions arising in typical concrete construction. The results of the study show that significant detrimental effects occur when mixing water is withheld and concrete is retempered at a later time. Slump, air content, abrasion resistance, and freeze thaw resistance are all adversely affected. The effects were found to vary with variations in both withholding time and cement content. The strength was not affected when water was withheld and concrete was retempered, but a reduction in strength accompanied an increase in water cement ratio above design values at redosage. The properties changed lead to concrete of reduced quality and questionable performance (A).