Publication of new guidance is expected to improve characterisation of fresh concrete and aims to eliminate issues of using advanced concrete mixes placed by tremies for deep foundation applications.
The second edition of the Guide to Tremie Concrete for Deep Foundations is the result of a joint project by the European Federation of Foundation Contractors – of which the UK’s Federation of Piling Specialists is a member – and the US-based Deep Foundations Institute.
The organisations formed the 20-strong Concrete Task Force to develop the guide in 2014 following a joint review of problems in bored piles and diaphragm walls cast using tremie methods. The work has been supported by 10 academic partners from across Europe and more than 30 industrial partners to bring together existing knowledge and best practice into one document.
“The guide is a comprehensive collection of all aspects dealing with the placement of tremie concrete in deep foundations,” said Concrete Task Force chairman Karsten Beckhaus, who also head of the materials group at Bauer Spezialtiefbau. “The guide will contribute to better specification and supply of better concrete, as well as better execution of concrete placement that is specifically adapted to the task.”
The first document was published in 2016 to present best practice but the latest version brings this together with research and development commissioned as part of development of the guide.
The guide addresses design consideration including concrete rheology, concrete mix design, reinforcement detailing, concrete cover and best practice for concrete placement. The guide also presents a review of methods to test the as-built elements and advice on identification and interpretation of the results.
According to Beckhaus, one of the biggest advances included in the guide is the potential for numerical modelling to better asses the risks. “The engineering assessment presented in the guide is not new but brings best practice together and emphasises that there can never ever be just one single set of performance values to accept a concrete for placement,” he said. “The new guide presents ranges for target values from which engineers can select specific target values that consider the complexity and relevance to the structure being built.”
The first edition of the guide contained requirements for support fluids due to the impact of these materials on the quality and integrity of the final product, however, this section has been removed from the second edition. Instead a new Support Fluid Guide is being planned and is expected to be published next year.
The EEFC and DFI have said that it is hoped that the guide will provide information for use in future European and US standards.