Self-compacting concrete (SCC) was first developed in Japan in 1988 to reduce labor in the placement of concrete, by eliminating or reducing the need for vibration to achieve consolidation [1]. Therefore, the main property that defines SCC is high workability in attaining consolidation and specified hardened properties.
Workability is defined either qualitatively as the ease of placement or quantitatively by rheological parameters [2]. The most commonly used test to determine workability in practice is the slump cone test. Either the vertical slump distance or the horizontal spread of the concrete can be measured. The most common rheological parameters, used to qualify workability, are the yield stress and plastic viscosity as defined by the Bingham equation [3]. In some cases, it was found that the Herschel-Bulkley (HB) equation was better suited to describe the flow [4]. This equation leads to the calculation of three parameters, a yield stress and two other parameters that cannot be associated with a physical entity. A linear approximation of the HB curve was introduced by F. de Larrard et al. [4] to define a plastic viscosity, but as this is another approximation, it was decided for this study to use the Bingham equation to calculate yield stress and plastic viscosity. The knowledge of the two parameters, yield stress and viscosity, allows a quantitative description of the workability.
A highly flowable concrete is not necessarily self compacting, because SCC should not only flow under its own weight but should also fill the entire form and achieve uniform consolidation without segregation. One type of SCC is used in structures with closely spaced reinforcing bars and should be able to flow through and completely fill the form without vibration. This characteristic of SCC is called the filling capacity. Several tests were designed to measure the filling capacity of concrete but none became a standard. The most widely used of these tests is the U-flow test [5]. The U-flow test is used to determine if the concrete mixtures qualified as SCC mixtures. To determine the factors that influence the flow of SCC, it is important to examine the behavior of the concrete in the simulated field tests (U-flow) and to compare with simpler and fundamental tests, such as slump and V-flow.
In this paper, rheological properties of the concrete mixtures were measured using two rheometers, the IBB 1 [6] and the BTRHEOM 1 [7] instruments. The flow of 13 concrete mixtures was determined using standard tests, slump and slump spread, the U-flow and the V-flow tests, which were designed for highly flowable concrete mixtures. The values obtained from these tests were compared and used to define of this type of SCC. A "workability box" [6], described later, was used to frame the parameters of yield stress and viscosity that results in SCC.