Meeting to provide concrete evidence
SCI Construction Materials
Group: Fibres in Cementitious Materials
London, 18 November 2004
 How
can steel fibres and polypropylene be used in concrete to
prevent explosive fire damage in tunnels? What problems occur
when using low quality fibre concretes, and what is the correct
use of fibres in concrete?
Peter Shuttleworth of Arup Consulting Engineers, Michael
Grantham, immediate past Chairman of SCI’s Construction
Materials Group, and Bruce Perry of Grace Construction Products
will discuss these issues at a half day meeting on 18 November
2004.
Significant benefits in the performance of concrete can be
imparted by adding polypropylene fibres; they reduce the formation
of plastic shrinkage and settlement cracks by increasing the
tensile strain capacity of plastic concrete. This reduction
or elimination of plastic cracks enables the concrete to develop
its optimum long-term integrity. Polypropylene fibres enhance
the toughness and impact resistance of pavement slabs. Unlike
welded wire fabric, polypropylene fibres cannot be misplaced
in concrete and do not rust.
However, the secret to using them correctly is to ensure
that the concrete is of adequate quality. Recently several
high-profile cases have occurred where polypropylene fibre-reinforced
concrete was employed for external heavy duty paving for warehouse
yards. Such yards are subject to the likelihood of freeze-thaw
damage and to the scrubbing action of multi wheeled, heavy-duty
articulated lorries. This is a very severe environment for
concrete to withstand. The concrete used in the cases examined
was of too low a quality to perform adequately under these
aggressive conditions. In one case, the concrete broke up
and cracked and in another caused major problems with surface
‘dusting’, leaving behind a concrete still liable
to freeze-thaw problems in future years.
The manufacturers of the fibres are promoting polypropylene
as a substitute for air-entrained concrete, and when tested
by the standard freeze-thaw test procedure, the concrete can
perform well, providing it has an adequate cement content
and a low enough water-to-cement ratio. However, international
research suggests that fibres are not an effective substitute
for air entrainment.
The afternoon will be of interest to engineers and concrete
technologists, and also logistics warehouse owners who may
face potential problems with concrete yards. To quote the
warehouse owner of one of the problem sites: ‘I never
thought I would have to understand concrete technology in
this job, but I am beginning to appreciate its importance,
even to me!’
For more information on the event, please visit our web page
(see links on sidebar) or contact Katherine Simpson, T: +44
(0)20 7598 1566, F: +44 (0)20 7235 7743, E: katherine.simpson@soci.org.
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