Sustainable road surfacing using Rubber Modified Asphalt with secondary steel slag aggregate

Hill Top, London Borough of Barnet

Rubber modified asphalt with recycled tyres





Location type




The challenge

This wide, tree lined street in the
London Borough of Barnet, required
a new surface course. There is a bus
route along the entire length, and
it is subject to on street parking by
local residents and parents whose
children attend the local infant and
junior school. The client required an
asphalt material that would deliver
long lasting durability but were also
looking for a more sustainable and
lower carbon solution to help meet
their climate change commitments.
The new surface course would also
need to be installed with minimal
disruption to residents and road users.
After discussions held during a visit to
Tarmac’s nearby Harper Lane asphalt
plant between the client and the term
maintenance contractor Tarmac Kier
JV and Tarmac’s Technical Product
Support Manager, Tarmac’s new
Rubber Modified Asphalt was selected. 

Our solution

Tarmac’s Rubber Modified SMA
incorporates recycled rubber from
end-of life and uses warm mix asphalt
technology to achieve a lower carbon
footprint, typically 8% lower than the
equivalent conventional SMA.
The use of recycled rubber crumb in
the mix helps to avoid export of waste
car tyres, incorporating approximately
500 tyres per kilometre of road. The
chosen surface would use 35mm of
10mm Rubber Modified SMA 40/60
PSV 60 incorporating steel slag
aggregate with rubber crumb added
in place of fibres and warm mix binder.
Steel slag aggregate, sourced from
Tarmac’s facility at the steel works
in Port Talbot, South Wales and
transferred to London by rail, also
helped to reduce embodied carbon,
as is classed as zero CO2 rated.
Approximately 85% of all the materials
in the asphalt were recycled or classed
as secondary. As well as reducing
carbon emissions, warm mix asphalts
also offer proven gains in productivity.
Requiring less time to reach trafficking
temperatures, they allow more work to
be completed within a given operating
window. This enables fast, efficient
resurfacing with reduced road closures
and disruption to traffic. 

Results and benefits

Once the old surface was planed out,
240 tonnes of Rubber Modified SMA
was supplied and successfully laid
by TKJV’s surfacing team in a single
shift. Although the program allowed
two days for the resurfacing work,
using a warm mix asphalt enabled
it to be completed in a single day.
It also helped to reduce fumes and
air pollution on this residential street
while work was taking place. The new
hard wearing, low texture surface
offers excellent deformation and
rutting resistance to help withstand
the bus traffic and on street parking. It
also offered an improved ride quality
and visual appearance. As well as
reducing disruption to road users, the
shorter programme time helped to
reduce costs from traffic management
charges and reduce risk to highway
maintenance teams.
The client was impressed with the
results of this collaborative working
between the term maintenance team
and materials supplier which allowed
them to benefit from this innovative
“This is the future of road resurfacing
in Barnet…. Materials technology in
road resurfacing has moved forward
and really significant improvements in
the sustainability of road resurfacing
is being achieved with our new joint
venture contractor and Tarmac’s
material skills”
Councillor Peter Zinkin, Barnet London
Borough Council

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Sustainable road surfacing in the London Borough of Barnet

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