Fresh Concrete Testing And Co-ordination Than The Study Of The Design Method And Its Application In The Design Of Self-compacting Concrete

On the basis of study of the concepts and testing methods of concrete workability and concrete mix design, the present work is concentrated on the following three aspects: Firstly, the improvement of two workability testing methods, i.e. slump flow apparatus and U-type workability device for flowability of concrete, has been conducted. The purposes of the improvement is (1) to enlarge the testing range of workability from high down to low workability mixes, (2) to simulate the practical conditions of concreting such as vibration and the presence of reinforcing bars and (3) to obtain more information needed to evaluate workability properties apart from flowability, for example, stability and compactability. The capabilities of the devices developed have been proved satisfactory by preliminary experimental tests. Secondly, the method of concrete mix design has been studied. The concept of filling-voids of densely packed aggregates has been adopted but the differences of the present work from previously published ones lies in the filling materials. Mortar instead of cement paste is used. By controlling the workability of fresh mortar and the amount of mortar needed to fill the voids and separate the coarse aggregates, the designed workability of concrete is easily and simply obtained under the condition that the strength of concrete is controlled by WIC ratio. Two important parameters are put forward. One is Q, the ratio of voids content of coarse aggregates to the volume of mortar. The other is R, the ratio of voids content of fine aggregates to paste volume. At last, based on the improved workability devices and concrete mix design method, self-compacting high performance concrete has been proportioned and experimentally studied. The results indicate that both the design method and devices are effective, practical and useful.