Strength and Structure of Concrete Cast in Deep Forms

摘要

The report gives a summary of the results of a series of investigations of the strength and the structure of concrete members cast in deep forms. Large differences were observed between the strength of concrete cores obtained from the walls, and the strength of control specimens. The strength of cores from the top was lower than the strength of control specimens, and this difference increased with the strength of concrete. The effect of adverse curing was larger for control specimens, and for the concrete of a lower strength. A significant improvement in the strength of concrete in a wall, particularly in its top part, was obtained by delayed revibration, combined with a static loading on top of the wall. For studying the causes for the variations in the strength of concrete, studies of sedimentation and the structure of concrete cast in deep forms were carried out, using some nuclear and radiographic techniques. These studies showed that the sedimentation and the resultant increase in water-cement ratio in the top accounts for a small fraction of the observed difference in strength, and other factors, such as the effect of micro-cracking etc., also contribute to the difference between the strength at the top and the bottom. (Author)