Abstract:
End-of-life tyres are a disposal problem resulting from the large volumes produced worldwide
every year. Waste tyres are difficult to manage because of their sheer volume and the potential
impacts on human health and environment. These discarded tyres, currently stockpiled and
dumped in the open, are a source of fire hazards and provide a prolific breeding ground for
mosquitoes and other pests.
The use of waste tyre shreds as fill material in geotechnical applications can help to mitigate the
waste tyre disposal problems. Specifically, when tyre shreds are used as lightweight fill material
in the construction of highway embankments, a considerable volume of waste tyres is consumed.
With regard to this, an investigation into tyre shreds mixed with sandy soils of South Africa was
undertaken to assess the shear strength behaviour of the sand-tyre shred composite and to
propose an alternative use of the scrap tyres produced every year.
A series of shear strength tests were performed using a large-scale direct shear box on the
mixtures composed of tyre shreds with two relative sizes, i.e. 10-15 mm and 50-60 mm sizes,
combined separately with Cape Flats and Klipheuwel sands. The shear strength tests started
from unreinforced material (control tests) followed by those on tyre shreds-sand composites at
different shred dosages such as 10, 20, 30, 40 and 50% by dry weight, ending on pure tyre
shreds. The results showed that this inclusion generally improved the shear strength of sand. The
angle of friction reached its maximum at 10% tyre shred content and reduced for increased shred
content in the mixtures. The cohesion was improved for dosage up to 30%, then decreased at
higher concentrations. Despite the shred size in the composite, a concentration of 30% by dry
weight was considered as optimum shred content to reinforce granular soils of South Africa, but
the long shreds showed better improvement compared to the small tyre pieces.
Based on the findings of this study, the use of lightweight tyre shreds sand composite material
was recommended in the construction of road embankments and the guidelines to be followed
were proposed. Because of the complexity in the preparation of the mixture based on density, the
optimum shred dosage by weight was converted into volume ratio and this corresponded to 55%
shred content by volume which can easily be used on site. For workability and simplicity of
quantity measurements in the field, 50% tyre shred content by dry volume was suggested in the
proposed guidelines to be mixed with sand in the preparation of embankment material.
