Self-Consolidating High Performance Concrete – SCC – Self-Compacting & Highly Flowable Concrete

Stability and homogeneity of SCC are two key issues that influence the mechanical and durability performance of the material in its hardened state. Thus, concrete is required to have the ability to resist the segregation of aggregate throughout the mixing, transportation and casting process. Due to the high flowability of SCC, it is much more susceptible to stability problem than normal concrete. This hints that it is urgent to have a test method to evaluate segregation in the field.

Material stability has a two-fold meaning. Dynamic stability refers to the resistance of concrete to separation during movement (e.g. mixing, placement into the formwork). Static stability refers to the resistance of SCC to bleeding and segregation after the SCC is cast until it is hardened. Test methods to measure both the dynamic and static segregation resistance of SCC are needed.

Currently, the most commonly used methods to evaluate segregation resistance are the visual examination method, the column segregation test (ASTM C 1610), and the V-funnel method. In the visual examination method, segregation resistance is evaluated by observing the periphery of the concrete after the slump flow test. A visual stability index ranging from 0 to 3 is used to rate the SCC. The method evaluates segregation qualitatively and it relies on the experience of the examiner. In the column segregation method, the coarse aggregates are sieved from the concrete in the top and bottom section of a column after 15 minutes of casting. The percent of static segregation is then evaluated according to ASTM C 1610. The V-funnel method was firstly developed in Japan and consists of measuring the variation of flow times following different periods of resting after filling the SCC in the V-funnel. Again, this method does not give a quantitative evaluation of segregation. The penetration apparatus (PA) method was first introduced by Bui et al. to qualitatively evaluate the static segregation of SCC. The structure of the apparatus produced by ACBM is shown in Fig. 7.

Fig. 7 Penetration Apparatus

Fig. 8 Application of the penetration apparatus

The test can be combined with the L-box test. During the test, the PA is located on the top of the vertical leg of the L-box, and the penetration cylinder is then adjusted to just touch the upper surface of concrete (Fig. 8). After releasing the screw, the cylinder is allowed to penetrate freely into the concrete for 45 seconds. The final penetration depth can be recorded by reading the scale. It was found that a good segregation resistance of the tested SCC can be indicated by a penetration depth that was less than 7 mm.

Some of the other new testing methods that are under development at ACBM are discussed in the following sections.