• Qin, Johnny
• Dux, Peter
• Alehossein, Habib
• Larisch, Martin
• Dao, Vinh

Abstract

High quality concrete for deep foundations needs to meet particular performance criteria to achieve the required workability (plastic flow-ability) and stability (resistance to bleeding). Workability is normally measured by the concrete slump test and most concrete specifications, codes and standards mainly rely on this test alone. The slump test alone is not a reliable method to determine workability, although it can reasonably indicate the consistency of a fresh concrete mix. Stability requirements to control concrete bleeding and aggregate segregations are usually not part of the current specifications and no standard test methods are recommended. For instance, it is highly important to consider the pressure effects from the hydraulic head and self weight of the concrete on the fresh concrete at the base of deep foundations causing potential risks of bleeding and other associated stability and quality issues. Concrete for deep foundations must have excellent workability criteria and sufficient resistance against bleeding to guarantee a non-defective end-product. Over the past decade, concrete technology has changed considerably and the test methods recommended by the current codes and standards need to be adjusted to reflect the technological progress demands. The paper highlights the new requirements, particularly the introduction of performance based testing criteria as recommended in the Recommended Practice “Tremie Concrete for Deep Foundations” published by the Concrete Institute of Australia in 2012. Concrete viscosity and plastic yield are the two important characterization parameters to be considered. A case study will demonstrate how these characteristics can be achieved by applying the newly introduced performance tests. The new testing criteria have been recommended to meet the progressive demands of modern concrete technology for deep foundations and – as a next step, for the entire concrete industry. To prove capability of numerical methods to mimic the complex process of concrete behaviour, CFD modeling has been used to simulate the laboratory tests. These simulations demonstrate that the behavior of a highly workable concrete is similar to a non-Newtonian frictional plastic-viscous fluid. The simulation results match the test results well, providing good confidence to extend the application of the CFD simulation tool to the process of flow and placement of fresh concrete in deep foundations.

Topics

• impedance spectroscopy
• polymer
• simulation
• viscosity