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Concrete In Australia : December 2013
Concrete in Australia Vol 39 No 4 35 high rise tower. The pour was done early in 2010 at an ambient temperature 12–15 °C. The mix design details are in Table 10 for the 50 MPa concrete class. The raft had a strength class of 50 MPa (C50R90) to achieve characteristic strength at 90 days with a dimension of diameter of121manddepthof6m. The challenges addressed together with production of a high class LF-SCC was heat of hydration control and completion of the raft in approximately 60 hours with no bleeding and segregation. Almost 450 truck mixers were used with concrete being supplied from eight concrete plants and placed with the help of 18 pumps. The concrete which had a mixing time of 45s at the plant had initial flow of 550 mm (measured at plant) and flow at site (~2 hours) was measured at 500 mm. The admixture used was again a PCE based tailor-made high range water reducer aimed at achieving a good balance between yield (flow) and plastic viscosity. Typical strength progression is given in Table 11. 5.0 CONCLUSIONS LF-SCC addresses the needs of the ready mix concrete industry and projects where more than 80% of the concrete produced is between strength classes 25–40 MPa. This type of concrete goes into structures that are not heavily reinforced (everyday RCC structures). This eliminates the extra costs related to fines (material, silos, handling, logistics, etc.) and reduces the binder content for the required strength class. This means less cement or more supplementary cement materials, which helps in enhancing durability. The innovative viscosity modifying admixture is now available in most Asia Pacific markets and is poised to be a breakthrough for increasing the use of self-compacting concrete in the construction industry, as it offers multiple benefits to the various stake holders. This innovative technology helps in achieving: • optimum yield value and plastic viscosity • superior homogeneity of the mix • minimum energy dissipation • minimisation of paste volume • quantitative benefits in savings for labour, plant and time. ACKNOWLEDGEMENTS The authors gratefully acknowledge the stakeholders in the various examples mentioned in the paper. Without their active support such an innovation would have been impossible to implement on a commercial scale. REFERENCES 1. Okamura, H.; Ouchi, M., “Self Compacting Concrete”, Journal of Advanced Concrete Technology, Vol. 1, No. 1, 5–15 April 2003, Japan Concrete Institute. 2. BIBM, CEMBUREAU, EFCA, EFNARC, ERMCO joint publication “The European Guidelines for Self- Compacting Concrete, Specification, Production and Use”, May 2005. 3. ACI Committee 237, “Self-consolidating Concrete (ACI 237R-04), American Concrete Institute Farmington Hills, MI., 2007. 4. Skarendahl. A .; Billberg. P., “Report rep035 : Casting of Self Compacting Concrete - Final Report of RILEM TC 188-CSC”, Pages 1–26, ISBN: 2-35158-001 -X, 2006. 5. Kar, N; Kiat-Huat, S., Kluegge, J. “A New Dimension in Self Compacting Concrete (SCC): Smart Dynamic Construction”, 16–18 August 2009, 34th Conference on Oour World in Concrete & Structures: Singapore. 6. Kar, N; Feng, Q., “Low fines Self Compacting Concrete (SCC)”, New Zealand Concrete Industry Conference, Aug 2011, Rotorua, NZ, Technical Papers (TR47). Figure 13: Raft (aerial view). Figure 14: LF SCC in progress. Figure 15: Night concrete. 29-35 Kar.indd 35 29-35 Kar.indd 35 25/11/13 2:56 PM 25/11/13 2:56 PM