Distinct-layer casting of SCC: The mechanical consequences of thixotropy

It is demonstrated in this paper that thixotropic behavior of Self Compacting Concrete (SCC) may induce, in specific conditions, distinct-layer casting of the material that can generate lowered mechanical resistances in the final structure. First, the distinct-layer casting phenomenon is defined and described along with its potential consequences. Then, experimental results obtained for various SCC show that there exists a critical delay between layers casting above which separated layers are created in the element and generate losses of mechanical strength. This critical delay depends strongly on the thixotropic behavior of the SCC, the thickness of the layers and on the roughness of the interface between the two layers. Finally, an analytical method allowing for a rough prediction of this critical delay is proposed. (C) 2007 Elsevier Ltd. All rights reserved.