A novel test to determine the workability of slipform concrete mixtures

Abstract

The science of rheology is not strictly applicable for low workability of slipform concrete mixtures because such mixtures are not fluids. However, the workability of slipform concrete mixtures can be assessed using the concepts behind describing rheological behaviour. Understanding the workability of a mixture is important for construction activities to achieve a successful pavement. Too dry a mixture may cause problems achieving sufficient consolidation, while too wet a mixture may result in edge slump. The novel workability test method (vibrating Kelly ball test or VKelly test) presented in this paper quantitatively assesses the responsiveness of a dry concrete mixture to vibration, as desired of a slipform paving mixture. The development process was carried out in three phases to achieve cost-effectiveness, portability, ability to assess critical performance parameters and repeatability. The three phases were assessing the sensitivity of the VKelly test to check whether it can signal variations between laboratory mixtures with a range of materials and proportions, evaluating the test in field applications at a number of construction sites and validating the test against the box test developed at Oklahoma State University. The VKelly test appears to be suitable for assessing a mixture's response to vibration (workability) with a low multiple operator variability. A unique parameter, the VKelly index, is introduced, and a mixture in the range of 2·0–3·0 cm/s1/2 seems to be suitable for slipform paving.