Evaluation of Self-Consolidating Concrete for Drilled Shaft Applications at Lumber River Bridge Project, South Carolina

Case studies have shown that when conventional concrete mixtures are used in congested drilled shafts, lack of adequate workability or flow between reinforcing bars may lead to trapped laitance or segregation between the inside and outside of the reinforcing cage. Due to its flow-ability and resistance to segregation, self-consolidating concrete (SCC) was evaluated as a viable material to overcome this problem. Several 1.8-m (6-ft) diameter drilled shafts were constructed using SCC as part of a field trial during the Lumber River Bridge Project, South Carolina. Identical shafts were constructed with SCC and a high slump gravel-aggregate concrete mixture typically used in coastal South Carolina. Both mixtures were observed to have excellent workability characteristics. Observations of the hardened concrete from exhumed drilled shafts indicate that generally good performance can be achieved in difficult construction conditions (congested cage, tremie placement, and lengthy placement times) if highly workable concrete is used. Some imperfections in the concrete were observed, even under these closely monitored conditions, and some degree of imperfection in this type of construction appears to be practically unavoidable. The imperfections observed in these field trials were detected by crosshole sonic logging, but they do not appear to have significant adverse consequences for foundation performance. On the basis of results of this project, it is concluded that SCC may be feasible for use in congested drilled shaft applications.