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Concrete In Australia : December 2013
Concrete in Australia Vol 39 No 4 47 of the concrete is recorded, as shown in Figure 11. It can be seen that the tip of the concrete reached the end of the horizontal box at about t=8s, which matches the test result (7.56s), indicating the CFD model is capable of simulating the TC flow behaviour very well. In addition to the concrete flow profiles and profile fractions, CFD method can provide many other features and information about the flow performance such as pressure, velocity and temperature at any time and any location. These successful simulations will certainly provide confidence to simulate the more complex process of concrete flow in real deep foundations under very harsh and “blind” conditions. Figure 12 shows the process of the concrete spreading which started from immediately after the slump cone is removed until the concrete stops moving. The maximum spread diameter is 410 mm, matching well with the test result (420 mm). 6.0 CONCLUSIONS Concrete for deep foundations (piles and retaining walls) is subjected to special environmentally harsh and demanding conditions. Additional hydraulic and hydrostatic pressures along the pile shaft together with challenging (blind) placement techniques call for the highest standards for concrete workability and stability. Advanced concrete test methods for workability (L-box and slump flow) and stability (filtration press) were introduced in the Recommended Practice “Tremie Concrete for Deep Foundations” in 2012. The application of these new performance based tests is not limited to tremie concrete requirements for deep foundations. The authors believe that its application can conveniently be extended to satisfy new challenging requirements for modern high performance concretes as well. A case study with CFA piles has demonstrated that the recommendations of the Recommended Practice booklet can be successfully used and extended to other piling techniques, improving the quality of the end product. CFD simulations were carried out showing evidence that modern concrete behaves like a non-Newtonian frictional viscoplastic Bingham-plastic fluid. The CFD simulations for slump and L-box tests demonstrated that the method is capable of shedding light on the “blind process” side of the deep foundation, as a powerful prediction tool. As a next step concrete behaviour inside deep foundation elements (piles or diaphragm walls) could be modeled using CFD to achieve a better understanding of the processes during the placement of concrete under fluid. Quality control, optimised ingredients and best operational procedures may be achieved by repeatedly simulating the process with different conditions and configurations to ensure high quality of the deep foundation. REFERENCES 1. Recommended Practice “Tremie Concrete for Deep Foundations”, Z17 first published September 2012, Concrete Institute of Australia. 2. Beckhaus, K., Larisch, M., Alehossein, H., Northey, S., Vanderstaay, L., Lucas, G. and Ney, P. “Introducing the Recommended Practice booklet for Tremie Concrete”, Proceedings, 25th Biennial Conference of the Concrete Institute of Australia, 12-14 October 2011, Perth, Australia. 3. Recommended Practice “SWC”, Z40 first published Sept. 2005, Concrete Institute of Australia. 4. Alehossein, Habib, Beckhaus, Karsten and Larisch, Martin (2012) Analysis of L-box tests for tremie pipe concrete. ACI Materials Journal, 109 3: 303-311. 5. Larisch, M., “Experience with high strength concrete for the foundation of a high rise building”, 9th Symposium on High Performance Concrete, 9-12th August 2011, Rotorua, New Zealand. 6. AS 1012 “Methods of Testing Concrete”, Standards Australia. 7. Kordts, S. and Breit W., “Assessment of the fresh concrete properties of self-compacting concrete”, Concrete Technology Reports 2001-2003 (Verein Deutscher Zementwerke e.V. Germany) 113-123. 8. Peiffer, H. and W. F. van Impe,. “Evaluation of the influence of pile execution parameters on the soil condition around the pile shaft of a PCS pile”. Proceedings of the 2nd International Geotechnical Figure 8: The addition of certain minerals can notably reduce the filtration liquid of a piling mix. Figure 9: Meshed geometrics of CFD models for the slump test and the L-box test. 41-48 Larisch.indd 47 41-48 Larisch.indd 47 25/11/13 3:58 PM 25/11/13 3:58 PM