The Civil Engineering Contractor July 2018 | Page 20

ON SITE
In preparation for the new asphalt layer, the road is milled to create a better, rougher bonding surface.
vehicle, which transfers the asphalt to
the asphalt paver.
A paver is used to distribute, shape,
and partially compact the layer of
asphalt on the surface of the road. As
the paver passes over the prepared
road area, the feeder conveyors move
the asphalt to the rear of the paver,
while the distribution augers push the
asphalt outward to the desired width.
The screed then levels the layer of
asphalt and partially compacts it to
the desired shape, after which a heavy,
steel-wheeled roller follows the paver
to further compact the asphalt to the
desired thickness.
“Hand labour also ensures that the
joins are even, and the depth correct
before rolling,” Van Rensburg adds.
Using a manual depth measure for
spot checks and relying on pre-set
electronic levelling beams on the
paver, the desired asphalt thickness is
achieved. Smith adds, “There is also
an international roughness index (IRI)
specification, which determines the
texture of the road surface to ensure
vehicle traction and good rideability,
measured with a laser, which picks up
any irregularities on the road surface.
The specifications are so strict that
should the IRI not meet spec, the
layer is removed, at significant cost.”
“The results of this are heavily
dependent on the feeder and the
equipment we use,” Van Rensburg
20 - CEC July 2018
states, adding, “So far, we have had
excellent results as we use only the
best machines.”
Once the asphalt is laid, compacted,
and cooled down, it is only a matter
of a couple of hours before the section
can be reopened to the traffic, as the
surface sets within a short time.
Wirtgen Group’s Vögele range was
chosen for the project, comprising
the Super 1803-2 paver and the MT
3000-2 offset Power Feeder, with a
whopping R14-million-plus price tag.
In response to asking whether
removed asphalt can be recycled, Smith
says, “National Asphalt does recycling
mixes comprising between 20 and
40%; it’s just that it isn’t popular in
South Africa yet, whereas overseas
they use up to 100% recycled mix.”
Smith maintains that the company has
laid some test sections that will take a
couple of years to assess quality.
Challenges
Executed along a high traffic volume
section of the freeway brings its own
challenges, the biggest being that the
traffic must continue to flow, despite
the roadworks. This vehicle stream
must be diverted when a lane is
resurfaced, with workers cordoning
off the specific lane, in the face of
oncoming traffic.
The restricted working hours have
also impacted the project, which is
“The SMA for the Proefplaas
project consists of 10mm,
7.1mm aggregate and
crusher dust with binder
content specified at 6.5%.”
Neels Smith, National Asphalt
only permitted to work between
09:00 and 15:00 on weekdays and
07:00 to 14:00 on Saturdays, with
absolutely no work undertaken
during public holidays, including
all foreseeable statutory declared
election days. “We also have to be off
the road the day before and after the
Easter weekend, as well as the days of
school-term closure,” adds Francois
van Wyk, KPMM site agent.
“The heavy rain we have had over
the past few weeks has also impacted
productivity,” Van Wyk adds, saying
that to date, 18 days have been lost
owing to weather.
With bitumen a main component of
asphalt, Smith points out that supply
can be problematic, more so when
refineries are undergoing maintenance
“or shut down unexpectedly”, he says.
The commodity is expensive as it is
directly related to the current oil
price. However, Smith explains, the
project caters for this fluctuation in
its commercial clauses.