53
july-august 2014
international
construction
MIXING TECHNOLOGY
Spin cycle
Asphalt
Asphalt provides even more challenges when it comes to mixing,
especially due to the rise in popularity of reclaimed asphalt
pavement (RAP) as a material..
Mixing asphalt and aggregate to make asphalt concrete (AC) is
all about temperature options. Hot mix asphalt concrete (HMA)
can see aggregates heated to as much as 150°C while the asphalt
is heated to just below boiling point, at 95°C. This is favoured
for high-traffic paving, such as highways and airport runways.
Warm mix asphalt concrete (WMA) is made by adding
zeolites, waxes, emulsions or water in the mixing process. This
is a more eco-friendly option as it uses less energy and produces
fewer emissions and carbon dioxide.
Mixing the asphalt with water and soap, before adding the
aggregate, produces cold mix asphalt concrete. Cold mix is most
often used as a patching material and on less busy roads.
US-based asphalt plant manufacturer Astec launched a number
of new product lines at the ConExpo-Con/Agg exhibition
earlier this year.
The manufacturer has increased the ability of its signature
Double Barrel drum dryer/mixer to handle RAP. The Double
Barrel HR includes enhancements to the drum which allows
use of up to 65% RAP. The company also offers its 100% RAP
plant – the RAP King.
Astec president Malcolm Swanson said, “The Double Barrel
HR is a key product in the Astec line. It fulfils a need for those
producers who already run high percentages of RAP and in
whose markets the trend toward running more RAP is expected
to increase.”
Astec also introduced its 120 tonne per hour Voyager plant.
The Voyager 120 has the ability to run up to 30% RAP and
offers a compact, highly portable design.
The Voyager 120 is built around a counter flow drum featuring
Astec v-fights. The v-flights provide greater uniformity of the
aggregate veil during the drying process, which results in better
heat transfer, a reduction of fuel use and increased productivity.
To enhance portability, a hydraulically driven swing out drag
and batcher can be set and ready to go in 10 minutes. Other
features include a reverse pulse baghouse, a control cab with
fully automated PLC controls, gravity take-up with direct
drive, air ride suspension and up to five cold feed bins and two
RAP bins.
On the rails
High output concrete train
N
urock’s cement mixers have proved an integral part in Network Rail’s North
West Electrification Project between Liverpool and Manchester, as the railways
operator installs 25 kV overhead power on the lines between the two cities.
The UK manufacturer created a bespoke High Output Concrete Train (HOCT) for the job.
Created from Nurock’s 7-m
3
truck mounted mobile concrete catching plant, the HOCT
was designed to comply with rail gauges and tunnel heights.
The HOCT carries sand, aggregate, cement and water in separate compartments,
mixing them on demand to reduce waste.
“The HOCT has just finished phase 2 of electrification works between Liverpool and
Manchester. It’s been operational for two years successfully supplying concrete six nights
a week,” explained Graham Jones, managing director of Nurock Mixers.
The Astec Double
Barrel HR allows
producers to use
up to 65% RAP
in mix
ADM’s AC tanks
are available
in vertical and
horizontal/
portable
configurations
>
