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The flexural tensile strength of concrete is measured in accordance with BS EN 14651: 2005, Test method for metallic fibered concrete – Measuring the flexural tensile strength (limit of proportionality (LOP), residual). This consists of a notched beam specimen tested under a central line load. The test determines the Limit of Proportionality and also the residual (post-cracking) tensile strength at various specified values of the opening of the preformed crack, namely 0.5, 1.5, 2.5 and 3.5mm, thus defining the falling branch of the load-deflection curve.
It should be noted that there are other beam tests used to determine the post-cracking behaviour of fibre reinforced concrete. Of these tests, the most common is probably the Japanese SF4 test. In this case the beam is subjected to four-point loading. The ‘equivalent flexural strength’ (or Re,3 value) is calculated from the average load up to a deflection of 3mm. Re,3 is widely used in the plastic design of ground-supported slabs.
Acknowledgement: The Concrete Society
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