Steel fibres from waste tyres to concrete : testing, modelling and design.

The disposal of waste tyres and steel fibres from tyres is a serious worldwide
environmental problem. This thesis examines the use of steel fibres extracted from
waste tyres as reinforcement for concrete. Previous attempts to use such fibres with
concrete ended up in balling of the fibres and wasting of the concrete.
Four concrete mixes using three different types of fibres (from shredded tyres, from
pyrolysis and commercially available fibres) were developed. An optimisation
procedure was used to maximise the amount of fibre used whilst maintaining a
reasonable degree of workability.
Single and double sided pull-out tests were developed to determine the anchoring
characteristics of fibres. Double-sided tests with multi-fibres were found to be the
most reliable. The anchoring characteristics of tyre fibres were found to be as good
as for commercially available fibres. Critical fibres lengths were determined for the
different fibres used. A simple fibre pull-out model is proposed.
Flexural toughness tests were developed and optimised based on the ASTM and
Japanese standards. The crack development, neutral axis depth and characteristic
length were examined in detail. An examination of the RILEM 0-£ model has shown
that the model can overestimate the flexural capacity of Steel Fibre Reinforced
Concrete (FRC).
New 0-£ models were derived by adopting inverse analysis techniques on results
from flexural tests on notched beams. These models when used with Finite Element
Analysis (FEA) can predict the behaviour of the tested prisms accurately. For design
purposes the models have been simplified. Parametric studies led to design equations
which predict the design moment by using a fibre parameter (relating to length and
bond) and the fibre amount by weight. The design equations are applied in several
applications including the design of slabs on grade. The results compare favourably
with existing design guidelines.
Finally, slabs for drainage covers were designed and tested, demonstrating that fibres
from tyres can be used for industrial applications.