|In drilled shaft construction, the recent development of sophisticated techniques for integrity and load testing has lead to the ability to assess the quality of drilled shaft foundations in terms of integrity and load carrying capabilities after they have been cast. Although this ability has lead to better assessment of drilled shaft foundations, it has also given insight to problems that are associated with materials and construction practices that has lead to defects or less than optimal performance for drilled shaft foundations.
This study examines the more common problems associated with drilled shaft foundations to emphasize the importance of constructability in design and workability in the construction materials. The majority of these problems consist of the failure to adequately consider one or more of the following issues:
·Workability of concrete for the duration of the pour
·Compatibility of the highly congested rebar cages and concrete being placed
·Bleeding and segregation
The main purpose of this study is to evaluate the use of self-consolidating concrete (SCC) as a viable material to overcome these issues due to its high flowability, passing ability, resistance to segregation, and reduced bleeding. A laboratory study will examine the difference between ordinary drilled shaft concrete and self-consolidating concrete (SCC) for both fresh and hardened properties. The fresh properties include filling ability, passing ability, segregation resistance, workability over time, bleeding characteristics, and controlled setting, while the hardened properties include the comparison of the compressive strength, elastic modulus, drying shrinkage, and permeability.
The laboratory results for both the ordinary drilled shaft concrete (ODSC) and SCC mixtures were evaluated and compared. The results show that SCC can be used to address many of the problems associated with drilled shaft construction because of the inherent workability, passing ability, resistance to segregation, and reduced bleeding of this type of concrete. Furthermore, the data suggest that the use of SCC in drilled shaft applications can provide similar or improved hardened concrete properties, which includes the compressive strength, elastic modulus, drying shrinkage, and permeability. However, some potential concerns for this material in drilled shaft applications include the general and overall lack of experience and research, lack of standardized tests, lack of well-defined mixture proportioning, and larger changes in workability compared to ODSC mixtures.