ICA_Feb 07.pdf - Roof & Facade

Transportation
The Advantages of Steel Fibre
Reinforced Concrete (SFRC)
The addition of steel fibres to concrete is an important step in research towards improving its properties. The
areas of potential use are expanding. For example, steel fibres not only offer a solution for the low-tensile
strength of concrete but give pseudo-ductile properties to brittle concrete. Finally, the steel fibres provide good
energy-absorption which, in turn, offers a technical solution to certain specific loading conditions.
FIBRE reinforced concrete is a composite material
whose bearing strength is determined by the
combination of its two constituent parts: the concrete
and the fibres.
P c
= P m
+ P f
This assumes there is a close interaction between the
two materials. Where a load is applied, this results in a
deformation. Depending on the composite’s state of
deformation of the composite, this interaction is
governed by (1) the ratio between the elasticity moduli
(n = E f
/E m
), (2) the transmission of the stress from the
concrete to the fibres, and (3) the uniformity of
distribution of the fibres.
Steel fibres with hooked ends maximise these
interaction fibres because the use of high-tensile drawn
steel wire and the anchored hooked ends of the fibres,
which make it possible to use the whole length of fibre
to transmit the maximum amount of force and to
prevent any splitting force from being exerted on the
concrete. Furthermore, a uniform distribution of fibres
in the concrete is obtained via the easy handling quality
of steel fibre bundles.
Reinforcement with steel fibres only show its full
value in the post-elastic deformation phase. The sudden
brittle failure of reinforced concrete is transformed into
slow, controlled crack propagation under the influences
of forces such as compression, tension, flexure, shear,
shrinkage and creep. The intrinsic qualities of using
steel fibres are fully revealed when they span hairline
cracks in the concrete and absorb the tensile forces
present. This process is related to the fibres’ hooks
which are fixed in the concrete and continues until a
high maximum pulling-out force is reached. To avoid
sudden failure of the concrete, the quality of the steel is
selected so that the breaking strength of the fibres is
only exceeded in exceptional cases.
In the case of further loading, the width of the crack
will increase due to the pulling-out of the fibre as the
hooks of the fibre undergo plastic deformation. This
plastic deformation under high tensile stresses is one
of the principle characteristics of steel fibres, and it
allows the steel fibre concrete to achieve a high degree
of toughness (ductility).
As applied to concrete tunnel linings, worldrenowned
expert on the subject of steel fibre reinforced
concrete Mr Ir. Marc Vandewalle stated in a presentation
in Singapore in 2006 sponsored by The Institute of
Engineers Australia that the technical advantages of
using steel fibre reinforced concrete (SFRC) include
homogenous distribution, multidirectional reinforcement,
excellent corrosion resistance, high-impact
resistance and excellent control of shrinkage cracks, thus
allowing for a more cost-effective and environmentallyfriendly
engineering solution than using the standard
reinforcement-cage alternative. ❏
About the Company
BEKAERT began as a small manufacturing
and trading company founded by Leo Leander
Bekaert in 1880 in the city of Zwevegem,
Belgium, which is still home to Bekaert’s head
office. Over the years, the company has grown
into an international wire and wire-related
products company, with manufacturing facilities
in Europe, North and South America, Asia, and
offices all over the world.
Bekaert employs close to 18,000 people
worldwide and has an annual sales volume of
nearly US$3 billion. Because there is still a strong
need for manufactured goods, particularly wire
products, Bekaert is expanding every year with
new products and technology to keep up with
world demand.
As a world leader in advanced metal
transformation and advanced materials and
coatings, Bekaert is also known in the concrete
industry as the manufacturer of premiumquality,
cold-drawn, hooked-end steel fibres
under the trade name Dramix ® which turns
concrete (a normally brittle material) into a
ductile one when added to a concrete mix. ❏
SFRC segmented tunnel linings
6 ICA Volume 1 Issue 1 2007