The Deep Foundations Institute (DFI) and European Federation of Foundation Contractors (EFFC) have released a free download of their recent Best Practice Guide to Tremie Concrete for Deep Foundations. The publication stems from initial efforts of the joint DFI and EFFC Concrete Task Group, established in 2014 to study common problems in drilled shafts and diaphragm walls constructed using tremie methods.
The task group recognized the potential for improving project quality and cost effectiveness by remedying tremie concrete practice, members identifying significant issues related to the use of mixes with insufficient workability, stability or robustness; poor specifications; and, inadequate testing procedures. The rapid evolution of concrete technology has promoted the use of modern mixes with five components—cement, additions, aggregates, chemical admixtures and water—which often have characteristics that differ significantly from traditional cement, aggregate and water formulations.
Guide to Tremie Concrete authors also cite a) trends favoring higher strength concrete classes and lower water/cement ratio mixes, each hinging on admixtures to compensate for reduced workability and address often competing demands for workability in the fresh state and setting time; b) how current testing methods have not evolved at comparable pace to allow results to reflect more complex mixes’ rheological properties; and, c) tendencies to base acceptance on slump or flow table test results.
In addition to presenting design considerations surrounding mix design and rheology, reinforcement detailing and concrete cover, Guide to Tremie Concrete proposes changes to common specification methods and test procedures. It likewise highlights factors to minimize risk related to concrete workmanship and quality, and potential conflicts between contracted parties.
A follow-on research and development project is proceeding this year under Technical University of Munich and the Missouri University of Science & Technology, Rolla. It includes desk studies plus laboratory and field tests in the U.S. and Europe. A second edition of the guide will incorporate subsequent study results and recommend appropriate acceptance criteria and testing protocols.