Model for Predicting Dosage of Superplasticizer for Slump Recovery of Fresh Concrete

Abstract

This paper aimed to propose a method to estimate the amount of superplasticizer redosing for concrete slump recovery using a type-F naphthalene-based superplasticizer for solving a problem of slump loss. This was achieved by developing equations for calculating the amount of the second dose of superplasticizer needed to recover the concrete slump to its initial values. Fresh concrete properties of OPC concrete having paste volume to void volume ratios of 1.1-1.3, and water to cement ratios in the range of 0.40 to 0.67 and naphthalene-based superplasticizer dosages between 0.25% and 1.6% were tested for initial slump and slump loss at 30-minute interval until 1.5 hours. The concrete mixtures showed slump losses ranging from 10% to 90% and then were redosed to recover their slump back to their initial values. Test results showed that slower slump loss was detected for the mixture with a higher initial dosage of the superplasticizer. The necessary redose of superplasticizer was influenced mainly by water to cement ratio and concrete paste content. The mixture with a lower water to cement ratio and lower paste content needs a larger second dosage of superplasticizer for redosing.