Comparative Flexural Toughness Evaluation of Steel Fibre-Reinforced Concrete

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Comparative Flexural Toughness Evaluation of Steel Fibre-Reinforced Concrete Swathy Manohar1



Shakeel Ahmad Waseem2 • Bhupinder Singh3

Received: 4 February 2020 / Accepted: 31 August 2020 Ó The Institution of Engineers (India) 2020

Abstract A comparative appraisal of the protocols recommended in the ASTM and Japanese standards for evaluation of flexural toughness of three concrete grades reinforced with steel hooked-end fibres is presented. Target 28-day cube compressive strengths of the three concrete grades were 25 MPa, 35 MPa and 45 MPa and the fibres having an aspect ratio of 80 were used at volume fractions of 0%, 0.13%, 0.19%, 0.25%, 0.31% and 0.38%. Testing for toughness was carried out in the form of displacementcontrolled four-point bend tests on prismatic specimens of size 150 mm 9 150 mm 9 700 mm and stable load–deflection behaviour was obtained only when fibre dosage was at least 0.25%. For fibre volume fractions of 0.25% and more, the toughness parameters obtained from the ASTM and the Japanese standard were comparable. From the results of the comparative study, it is recommended that for an Indian standard, if the toughness characterisation is to be done, then equivalent flexural strength should be considered as the parameter over residual strength. In addition, ‘equivalent flexural strength ratio is also to be considered, since it represents the load retaining capacity & Swathy Manohar [email protected] Shakeel Ahmad Waseem [email protected] Bhupinder Singh [email protected] 1

Department of Civil Engineering, Indian Institute of Technology Madras, ChennaiTamil Nadu, 600 036, India

2

Department of Civil Engineering, National Institute of Technology Srinagar, Hazratbal 190006, India

3

Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India

of the specimen after the peak load. Nevertheless, equivalent flexural strength is the average flexural strength up to the specified deflection limit which does not specify any post-peak behaviour, hence need not be a characterising parameter for understanding fibre performance in concrete. Keywords Fibre-reinforced concrete  Fibre volume fraction  Toughness  Flexural strength  Equivalent flexural strength

Introduction It is well established that inclusion of steel and polymeric fibres improves crack control, toughness, impact resistance and the fatigue characteristics of concrete [1–4]. In slabs on grade, and in pavements and tunnel linings, etc., where moments and shears may be relatively small, steel fibres are increasingly being used as the primary reinforcement [5]. In such applications, fibres can provide significant post-cracking strength due to their bridging action across cracks and due to the moment redistribution, which can occur after the first crack. Due to their pull-out failure mode, fibres will prevent a catastrophic loss of load-carrying capacity and thus contribute to toughness of the material [6, 7]. In this context, it is desirable to char

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