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Characterisation of the toughness of fibre reinforced concrete - Revisited in the Indian context
Published in
2014
Volume: 88
   
Issue: 2
Pages: 8 - 23
Abstract
Increased use of fibre reinforced concrete (FRC) in India has resulted in the urgent need to standardise testing and characterisation. The current paper addresses the different available techniques and gives pre-normative suggestions for toughness characterisation. The use of an unnotched beam test is advocated here considering the dearth of laboratories for performing more sophisticated tests and the use of FRC being by-and-large restricted to slabs-on-grade and other non-structural applications. In this study, different types of steel fibres were incorporated in a typical M35 concrete used in India in flooring applications. Flexural tests were conducted to obtain the load-deflection curves and determine various toughness parameters, viz., flexural strength, equivalent flexural strength, equivalent flexural strength ratio and residual strength. The load-deflection curves of FRC with undulated fibres differed significantly from those with straight hookedended fibres in that the concrete failure often occurred with significant crack branching and spalling. The tests indicate no significant change in compressive strength due to addition of fibres while the flexural strength of FRC is slightly higher than that of plain concrete emphasising the need for determining the flexural strength by testing rather than using values from empirical equations or from tests of plain concrete. Specifically, the results illustrate that hooked-ended fibres do not influence the behaviour until after the peak and are more efficient in improving toughness, especially at larger deflections resulting in higher equivalent flexural strengths, in comparison with the undulated fibres. As expected, the higher aspect ratio and higher dosage of steel fibres impart more toughness to the concrete. It is shown that different combinations of fibre type and dosage can yield similar equivalent flexural strength ratios (Re,n) and different fibres at same dosage can have different Re,n values. It was observed, in general, that the variability of flexural strength is much higher than that of the compressive strength and that the variation of results is lower for straight hooked-ended fibres. The scatter in the residual strengths is much higher than that in the equivalent flexural strength, which results in a relatively lower characteristic value for the former in comparison to the latter at similar deflections. Based on the study, recommendations have been made for consideration in an Indian test standard.
About the journal
JournalIndian Concrete Journal
ISSN00194565
Open AccessNo