Interdependence of passing ability, dilatancy and wet packing density of concrete

Abstract

Concrete should be flowable and cohesive to possess high passing ability. Adding superplasticizer solely cannot increase the passing ability of concrete monotonically because it decreases segregation stability (i.e. cohesiveness). Decreasing the maximum aggregates size can improve passing ability but it undesirably narrows the grading of aggregates and decreases flowability. To improve passing ability while keeping similar aggregates’ size, the concurrent limits of flowability and segregation should extend. In this paper, it will be shown that the enhanced passing ability of concrete having similar size of aggregates is the consequence of improved wet packing density (WPD). It is because when concrete passes through narrow gap of rebars, the flow velocity increases while depth decreases that cause a steeper velocity profile and a larger shear rate in the flow. Since superplasticized concrete is a dilatant fluid, there will be a jump in viscosity and increase in head loss when it passes through gap that impacts the passing ability. As concluded in authors’ previous studies that the WPD of cement powder paste or mortar could be negatively correlated to its dilatancy, the authors will in this paper show that the WPD of concrete can be positively correlated to its passing ability. The paper thus provides a new insight into the interdependence amongst passing ability, dilatancy and WPD of concrete.