The Deep Foundations Institute (DFI) and the European Federation of Foundation Contractors (EFFC) have released a free download of the recently published Best Practice Guide to Tremie Concrete for Deep Foundations.
The guide is the result of the initial study efforts of the joint DFI and EFFC Concrete Task Group, which was established in 2014 to study common problems in drilled shafts and diaphragm walls constructed using tremie methods. The project is supported by EFFC and DFI members, and funded in part by the DFI Committee Project Fund. Dr.-Ing. Karsten Beckhaus of Bauer Spezialtiefbau, Germany, chairs the task group, supported by Chris Harnan of Ceecom, U.K. The North American representatives of the task group are Peter Faust of Malcolm Drilling and Dr. Dan Brown of Dan Brown and Associates.
The Concrete Task Group recognized the potential for improving project quality and cost effectiveness by remedying tremie concrete practices. It identified significant issues related to the use of concrete mixes with insufficient workability, stability or robustness; poor concrete specifications; and inadequate testing procedures. The rapid evolution of concrete technology promoted the use of modern mixes with five components — cement, additions, aggregates, (chemical) admixtures and water — which often have characteristics that differ significantly from older three component mixes — cement, aggregates and water. Also, recent trends favoring higher strength classes and lower water/cement ratios, result in greater dependence on admixtures to compensate for reduced workability and to meet the (often competing) demands for workability in the fresh state and setting time. Current testing methods have not evolved at the same pace to allow results to reflect the rheological properties of these more complex mixes. Slump or flow table tests are commonly used as the only acceptance test for fresh concrete.
The primary purpose of the Best Practice Guide to Tremie Concrete for Deep Foundations is to present design considerations (concrete rheology, mix design, reinforcement detailing, concrete cover, etc.) and best practices for tremie concrete placement for drilled shafts and diaphragm walls that promote construction of high quality elements. In addition, the guide proposes changes to the methods used commonly to specify concrete mixes and the procedures to test them. It highlights important considerations to minimize risk related to concrete workmanship and quality, and potential conflicts between contracted parties.
A follow-on research and development project, also funded by the sponsors of this guide, is being conducted by Technical University of Munich in conjunction with the Missouri University of Science and Technology. This project includes desk studies, laboratory testing and onsite testing at project sites in Europe and the U.S. The research work will be completed in 2016. A second edition of the guide will be published that incorporates the results of this subsequent study and recommends appropriate acceptance criteria and testing protocols.
The guide is available for free download.