Centrifuge Model Test on Bleeding of Fresh Concrete in Bored Piles

Bleeding in fresh concrete refers to the rise of excessive water as a result of sedimentation and consolidation of the aggregates. Moderate bleeding is often observed after the concrete is cast. Such bleeding is uniform and not detrimental to concrete quality. However, excessive bleeding, particularly localized bleeding, may leave channels in bored piles. Although the cross-sectional area of the channels is relatively small compared with the pile, the quality of bored piles suffers from excessive bleeding along channels and reinforcements. Some previous studies attributed this phenomenon to poor concrete design and handling, however, the mechanism of localized bleeding in bored piles remains rather vague. Centrifuge tests were carried out on model bored piles to study the bleeding behaviour of fresh concrete. The model piles are up to 47 cm in length and 20 cm in diameter. The tests were carried out in a beam centrifuge with an acceleration up to 120 g. The distribution of concrete pressure after casting was measured with a pressure pad. The pore water pressure was measured at three levels along the model pile. The volume of bleeding water and the overbreak were measured at the end of the tests.