In the tensile stress for plain concrete exceeds the

In the past few decades, fibre reinforced concrete
(FRC) has evolved to a widely used construction material as an improvement or
alternative to the either plain or traditionally reinforced concrete.
Significant research has been done and a number of real projects have been completed
up to date. At present, steel fibre reinforced concrete is used worldwide in a
large field of applications.

Traditional
concrete is characterized by excellent load carrying capacity in compression
but also by brittle behaviour in tension. When the tensile stress for plain
concrete exceeds the tensile strength, cracks start to develop. Rapid propagation
of a single relatively small crack can often lead to tension failure. The
concept of employing fibres to improve the matrix characteristics is as old as
adding straw or horsehair to mud bricks in Babylonian and Egyptian times
(Naaman 2007). The fibre reinforcement allows to carry a considerable amount of
load after the cracking of matrix has occurred. The introduction of fibres into
concrete was originally intended to enhance the tensile strength of the
concrete matrix, by postponing the widening of micro-cracks. With early
research works, done by Romualdi & Mandel (1964), Shah & Rangan (1970,
1971), Aveston & Kelly (1973), Swamy et
al. (1974), Naaman & Shah (1975, 1976, 1979), Shah & Naaman (1976),
Hannant (1978), it became evident, that the addition of fibres significantly
increases the post cracking energy absorption or material toughness characteristics
of the brittle concrete, without significantly affecting the cracking strength
of the matrix.

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Fibre
reinforcement can provide an alternative to conventional steel bars in order to
improve the efficiency and working conditions on construction sites and for the
prefabricated structures. In some types of structures, such as slabs on grade,
foundations and walls, fibres can replace ordinary reinforcement completely. In
other structures, such as beams and suspended slabs, fibres can be used in
combination with ordinary or pre-stressed reinforcement. In both cases the
potential benefits are due to economic factors as well as to the improvement of
the working environment at the construction site.

From a
structural aspect, the main reason for adding fibres is to improve the fracture
characteristics and structural behaviour through the fibres ability to bridge
cracks. The mechanics of crack bridging influences both the serviceability and
ultimate limit states. The beneficial effect on the service load behaviour is
achieved with increased flexural stiffness and reduced crack width as well as
crack spacing propagation. The behaviour in the ultimate limit state is influenced
by increased load resistance and in the case of shear and punching failures,
the ductility of concrete (Shah & Rangan 1971, Grzybowski & Shah 1990,
Stang & Aarre 1992, Thomas and Ramaswamy 2007, Barros and Figueiras 1999,
di Prisco et al. 2009). However, the
addition of fibres has little effect on the behaviour of concrete before
cracking (ACI Committee 544 2008).

During the last few decades, a wide research has
been performed on material properties of FRC, both at fresh and hardened state.
Research on structural response of FRC elements was mainly developed during the
last twenty years (Rossi & Chanvillard 2000, RILEM TC 162-TDF 2002, di
Prisco et al. 2004, Reinhardt &
Naaman 2007, Gettu 2008). Despite the increased awareness in practice and research,
FRC has largely been limited to use in non-critical load bearing members, even
though significant potential exists for full or partial replacement of costly,
manually placed, steel bar reinforcement. One of the reasons for limited use of
fibre reinforced concrete in load-carrying structures seems to be the lack of
internationally accepted building codes for structural design of FRC elements.
This leads to the limited utilisation of FRC among engineers, even though a
number of design guidelines were recently developed (RILEM TC 162-TDF 2002,
JCI-S-002 2003, JCI-S-003 2007, CNR-DT204 2007, DBV 2007, EN14651 2007, ACI
Committee 544 2008, DAfStb-Richtlinie 2010, fib Model Code 2010). A more
general utilization of fibre reinforced concrete in structural concrete
structures requires more detailed design rules, combined with guidance
regarding the optimal choice of fibre types, concrete composition,
implementation rules and test methods