Characterisation of Toughness and Post-cracking Behaviour of Fibre Reinforced Concrete

The macro plastic fibres do not have obvious effects on the compressive strength of concrete (de Oliveira and Castro-Gomes 2011), but they can effectively improve the toughness and post-cracking performance of concrete (Fraternali et al. 2011). Therefore, a good characterisation of the toughness and post-cracking behaviour is of scientific and technological importance for the macro plastic fibre reinforced concrete.

The toughness of fibre reinforced concrete materials can be considered as their energy absorption capacity. It is conventionally characterised by the area under the load-deflection curve obtained experimentally. Various testing methods, such as tensile, compressive and flexural tests, have been developed to study the energy absorption and toughness of the fibre reinforced concrete. The most straightforward way to characterise a material regarding its post-cracking behaviour in tension is by performing uniaxial tension tests under closed-loop displacement control (de Montaignac et al. 2012). However, such test procedure is complicated to carry out as compared to bending tests, and requires equipment that is not generally available. Using the flexural tests to characterise the toughness has been widely adopted and become the most popular, since the tests are easy to be operated and can simulate most of engineering situations. Therefore, various kinds of flexural toughness tests have been developed, and are of common use in different parts of the world.

No Australian standards exist at present to determine toughness and post-cracking performance of fibre reinforced concrete. Most of the available European and American standards and guidelines recommend the use of unnotched beam specimens subjected to four-point loading, such as ACI Committee 544 (544 1988), ASTM C1018 (ASTM 1997), ASTM C1399 (ASTM 2011a), and ASTM C1609 (ASTM 2011b). Load versus mid-span deflection curves are used in these standards to study the toughness of fibre reinforced concrete. Load-crack opening diagrams are recommend by some standards, including ASTM E1290 (ASTM 2008b) and BS EN 14651 (BSI 2007), through a three-point bending test on a notched specimen. ASTM C1550 (ASTM 2012) suggests testing the toughness on a concrete round panel instead of a beam. Other standards, such as JSCE-G551 (JSCE 2005a), JSCE-G552 (JSCE 2005b), and RILEM TC162-TDF (RILEM 2002) are also used to evaluate the toughness of fibre reinforced concrete. Facing with such a large amount of standards and guidelines, it is important to choose appropriate testing methods to characterise the toughness and post-cracking behaviour of macro plastic fibre reinforced concrete.

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