The Civil Engineering Contractor February 2019 | Page 28

TECHNOLOGY
the plant produces a physical sample
of that design to prove it can actually
be manufactured at the plant. That
sample is then tested, and if it again
passes the prescribed tests, a paving
trial is conducted on the road. The
contractor will thereafter pave for
two or three days, performing trial
tests during that time, which may
require further tweaking of the
design based on actual performance.
“We are currently moving
over to an entirely new bitumen
specification and asphalt mix design
process, which is performance based
and is being driven by the industry.
The current bitumen specification
covers a number of empirical tests,
mainly for viscosity at different
temperatures. These tests are done
before and after short-term ageing
and although they give an indication
of ageing that takes place during the
asphalt mixing and paving process,
they do not cater for prediction of
long-term ageing that happens on
the road,” Marais explains.
“The new performance grade
(PG)
specification
classifies
bitumen in different temperature
grades relating to the maximum
and minimum expected pavement
temperatures, as well as traffic
class to which the asphalt will be
subjected. The new PG specification
does not only look at the viscosity of
the binder and the effect of short-
term ageing, but also incorporates
a long-term ageing process — using
the pressure ageing vessel (PAV) —
26 | CEC February 2019
which simulates three to 10 years of
ageing on the road. The testing that
is performed on the aged bitumen
also tests the response of the
binder to repeated stresses applied
in the dynamic shear rheometer
(DSR) as well as low-temperature
performance in the bending beam
rheometer (BBR).”
Dave Bennet, general manager of
National Asphalt plant in Pretoria
North, says: “The current asphalt
mix requirements are not suited to
handle these high traffic volumes
and in future, all product will have
to be supplied with a performance
guarantee of a minimum of five years.
For this reason, the consistency of
the asphalt mix component will be
even more critical.”
Concrete manufacturers are in
the process of lobbying for more
roads to be constructed using
concrete. This may be a hard
sell given that a new innovative
asphalt mixture developed in
France (EME) using a harder
binder grade has been earmarked
to replace concrete pavements.
“This product is not just cheaper
than concrete but is rendering
similar stiffness values as
concrete with the advantage of
flexibility. The production and
turnaround times are also much
quicker than concrete; therefore,
curing time delays are no longer
needed, which in turn reduces
the construction period by 70%,”
says Bennett.
Advantages of equipment
One of the major contributors to
road rehabilitation efficiency, is
the sophistication of the equipment
used. Paul Heslop, MD of Rhino
Excavator Hammers, explains
that the state of the construction
industry means Rhino does more
work operating its equipment on
civils sites and mines than on
selling its excavators and hammers.
“We normally put hammers onto
road building equipment for the
secondary breaking after blasting.
We also provide an alternative
to blasting on quarries, which
is our major connection to road
building.”
Marc Beer, Baseline Civil
Contractors’ plant director, says:
“As we speak, there is a fair
amount of new work coming out
in both the public and private
sector, and we feel we’ve
geared up in terms of advanced
new equipment to meet these
challenges and above all, provide
our clients with a better product
than our competitors.”
It is the more sophisticated
equipment that sets the company
apart and gives it a technological
edge, he claims. “With much
of the new work in both road
construction and rehabilitation
on offer, tender specifications
demand that certain specialised
equipment be used to ultimately
create a better and longer-lasting
road surface,” Beer adds. nn
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