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8/3/2019 Bitumen Sprayer
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6 QUEENSLAND ROADS Edition No 5 March 2008
INNOVATIVE BITUMEN SPRAYER
Daren Mott
Sealing Manager, Fulton Hogan
AbstractThe innovative Multispray® bitumen sprayer has
been developed which can control the application
rates of bitumen in a vehicle’s wheel paths to enhance
seal life and improve safety through improved skid
resistance.
The new sprayer has twin telescoping spray bars with
two sets of spray nozzles on each bar. The computer
controlled sprayer can produce detailed spray reports
for quality control.
IntroductionAlmost exclusively, sealed roads in Queensland are line
marked which channels traffic into lanes. The rolling
and compaction effect of channelised traffic causes
accelerated wear to the road pavement which varies
in extent across the width of the road laneway. High
vehicle tyre loads and traffic volumes greatly influence
this damaging effect. In highly trafficked areas,
the binder in a spray seal may bleed up around the
aggregate reducing the macro texture. Other effects that
may occur in these conditions are rutting and heavingof the pavement. This can result in a reduction in skid
resistance and a reduction in effective seal life.
Figure 1. Bitumen sprayers – from old to new
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In problem areas treatment often requires the
application of different rates of binder across the
pavement. This is just one of the areas where the new
technology Multispray® bitumen sprayer (Figure 1),
has efficiency gains over existing technology sprayers.
The Multispray® bitumen sprayer has been specifically
designed to apply binder at different rates across the
pavement.
BackgroundBitumen sprayers operate by pumping hot bitumen
(≈ 175oC) from an insulated tank to a spray bar
where it is discharged through a number of nozzles.
Austroads have standardised on the use of Copley1
bitumen nozzles. The bitumen pump is typicallya positive displacement helical gear pump. By
controlling the rotational speed of the pump, the
volume of bitumen pumped is controlled. Prior to
spraying, the hot bitumen is circulated through the
pipe work and spray bar back to the tank to ensure the
nozzles and control cocks/valves are heated so that
any residual bitumen is adequately softened to allow
satisfactory operation of the cocks and nozzles.
The spray nozzles are operated at their rated flow rate
to ensure that the fan pattern and flow distribution
is consistent. The spray from the nozzles is
typically at a 30o angle to the spray bar with the fans
overlapping. At any point along the spray bar, the
pavement is covered by four separate spray nozzles
(ends excluded) (Figure 2). At each end is a special
unsymmetrical nozzle which sprays more on one
side of the fan than on the other. With all nozzles
spraying at their rated capacity, the application rate is
controlled by varying the sprayer road speed. For a
heavy application the sprayer travels at a slow speed
and for a lighter application the sprayer travels at a
faster speed.
The basic design concept behind the pump-type
bitumen sprayer has not changed markedly since its
inception. However, the manner in which the pump
is driven and controlled has changed markedly, as
described below:
The early sprayers had a separate auxiliary•engine at the rear of the sprayer. These were
highly mechanistic machines and required an
operator to pull levers, monitor pressure gauges
and control pump revolutions from a platformat the rear of the sprayer (1). Depending on
prevailing wind conditions, the operator could be
engulfed in bitumen and kerosene fumes
The next innovation was the replacement of •the rear auxiliary engine with a hydraulic drive
system. There was no longer a need for an
operator at the rear of the sprayer. The variable
output hydraulic pumps on these early machines
were usually driven from the front of the main
engine via a hole cut in the truck radiator. The
hydraulic pump protruded beyond the front bumper bar and was protected by a heavy metal
guard. The hydraulic pump supplied pressurised
oil to a fixed displacement hydraulic motor which
in turn drove the bitumen pump.
The hydraulic pump was later driven from an•engine power take off.
Figure 2. Conventional spray bar spray patterns
1 A E Copley Enterprises Pty Ltd, Melbourne
3 0 °
End nozzle(heavier toward outside)
Inverted plan view
Spray distribution
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8 QUEENSLAND ROADS Edition No 5 March 2008
2 Cut back bitumen can contain up to 50% kerosene.
The integration of electronics into the variable•output hydraulic pump design permitted the
hydraulic pump output flow rate to be controlled
electronically.
Compressed air actuated spray nozzles in•conjunction with electronic circuitry allowed
individual spray nozzles to be manually selected
by the sprayer operator. The bitumen flow rate
was automatically adjusted by the electronics to
maintain the preset application rate.
A further development was the fitting of twin spray• bars.
Operational shortcomings of aconventional sprayer
A conventional single bar bitumen sprayer applies
a uniform rate of binder across the width of the
pavement. This method of application often delivers
too much binder to the areas where the traffic is
concentrated and too little to the lower trafficked areas.
This can result in compromise which may reduce
surface quality and seal life which equates directly to
maintenance expenditure. Hence the seal design in
these instances is a compromise and may not provide
an optimal solution. This problem can be overcome bymultiple runs of the bitumen sprayer; however, there
are operational and cost issues with this practice.
Existing bitumen sprayers on the market have fixed
spray bars usually with a 1m taper bar on the driver
side of the truck. The taper bar is a fixed width spray
bar extension with air actuated spray nozzles which
can be controlled by the operator to vary the spraying
width. The spray bar remains extended out from the
sprayer even though the spray width has been reduced.
This extended spray bar often protrudes out beyond theedge of the works, which presents problems such as:
the possibility this extension could hit a person or •road furniture such as guide posts or guard rails
traffic cones may have to be moved to allow for the•extension
the bar may hit an object and break off (as they•are designed to break instead of bend). Apart
from the job delays and cost, this could pose a
safety issue or an environmental issue if sprayingcutback bitumen2.
When the conventional spray bar extensions are folded
upward in the vertical position, the spray nozzles
face directly outward. When hot bitumen is being
circulated through the spray bar with the extensions in
the vertical position, a dangerous situation arises if the
spray nozzles open unintentionally.
When the sprayer is stationary in bar circulate mode
with the extension bars down, the extensions arevulnerable to being hit by surrounding equipment
or traffic. While the sprayer manoeuvres into the
spraying position with the extension bars down, the
spray bar is highly susceptible to damage.
Features of Multispray® bitumen sprayer
Fulton Hogan's Multispray® bitumen sprayer is
a revolutionary solution for slowing the surface
deterioration of spray sealed pavements. Spray
seal surfaces deteriorate at different rates acrossthe width of the lane as a result of varying traffic
wear. Multispray® provides an innovative solution
for binder imbalance that minimisesthe potential for
bleeding in the wheel paths.
Historically, deterioration of spray sealed pavements
is particularly evident where the vehicle wheel path
is concentrated and consequently the binder rises to
the surface causing maintenance and safety concerns.
Multispray® provides a long lasting solution that
improves the safety and longevity of spray seal pavements by applying binder at varying rates
transversely on the pavement, with less binder sprayed
in highly trafficked areas. For optimum results this
process should be used from the first seal as this
assists in preventing future maintenance problems
such as flushing.
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Figure 3. Example of a flushed seal
On pavements that are already subject to flushing
and/or stripping of the aggregate, using varying
binder rates can reduce the impact that the reseal willhave on the existing seal (Figure 3). This is achieved
by designing the reseal specific to the problem areas
such as wheel paths.
Multispray's® variable transverse application rate
capability is used in conjunction with a telescoping
spray bar and a touch screen computer system to
control and customise the amount of binder applied
to the pavement.
The telescopic spray bar consists of two spray bar sections which move independently of each other,
and each section is fitted with both high and low
flow nozzles (Figures 4, 5).
By using the touch screen system, the operator can select
areas of 70, 80, 90 or 100% of the base application rate
across the full width of the spray bar. The onboardcomputer management system will automatically select
the appropriate nozzle combinations to achieve the
desired profile (Figure 6).
While spraying at variable rates, the spray width is able
to be adjusted from 0.6m to 5m in width during the run.
This means that a precise spray width can be selected for
any width of pavement. There is no unused portion of
the bar to act as a hazard or restrict traffic and other road
users, particularly around pedestrian islands.
The system has full data logging capabilities and clients
can be provided with detailed spray sheets for the project.
Advantages of Multispray®
The Multispray® bitumen sprayer provides many distinct
advantages including:
prevents/minimises flushing or aggregate loss by•applying the appropriate amount of binder for each
point across the width of the lane in a single pass.
This improves the economic life of the seal and
safety for road users
has the ability to have a preset second programme•which permits a change to the primary application
rate during the spray run without stopping
a solution for seals with existing flushing in the•wheel path as they can be sprayed with varying
rates of binder in the one pass; providing time
efficiency, improved quality at longitudinal joints and
minimising disruption to road usersimproves safety when spraying as the telescopic bar •is adjusted to the required width allowing work to
occur around fixtures such as poles and curbs, while
providing safer traffic control
improved production efficiencies in the sealing• programme
maximises the seal and pavement economic life as•the Multispray® reduces the excessive bitumen build
up or bleeding
reduces wastage of non-renewable resources.•
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Figure 4. Plan view of telescoping spray bars
Both spray bars
High flow nozzles
Low flow nozzles
Figure 5. Telescoping spray bars
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Shoulder
Wheel pathWheel path
90%
80%
70%
100% 100% 100%
90% 90%
80% 80%90%
High flow nozzles
Low flow nozzles
Low flow nozzles
High flow nozzles
Figure 6. Spray rate profiles
Figure 7. Onboard spray computer with touch screen
Application of Multispray®
After a detailed assessment of the pavement texture,
an optimised seal design is developed which takes into
consideration both high and low trafficked areas (2)
and existing surface textures. Using this seal design,
the operator enters the required spray rates into thesystem using the touch screen (Figure 7). Up to five
different spray patterns can be entered, allowing for
varied wheel path widths and varied rates as required.
The continuous spraying of binder reduces stop-start
joints and improves the quality of seal. As an example;
in one spray pass 1.2 l/m² of binder could be sprayed in
the wheel paths, 1.4 l/m² between the wheel paths and
1.7 l/m² on the shoulder.
The computer system also allows the telescopic bar to
operate while in variable mode to ensure the sprayer
covers a range of areas in a single pass. Each spray
nozzle is operated pneumatically and the computer
system reviews and controls each and every nozzle on a
30 millisecond cycle.
The spray profiles always maintain their positions relative
to the sprayer wheel track independently of the spray
bar's position. This is important as the desired position of
the lean areas will vary laterally with respect to the road
centreline. Typically, this would occur on bends where
vehicles wander transversely towards the inside curveradius. While spraying, the operator simply aligns the
sprayer tyres with the low texture fatty areas. The spray
bar is extended or retracted to maintain its alignment
with the seal edge and centreline. The wheel path areas
always maintain their relativity to the sprayer while the
remainder of the spray profile is adjusted automatically.
Conclusion
The Multispray® bitumen sprayer represents the next
generation of innovation in sprayed seal technology.The sprayer is safer and delivers more control over the
delivered spray rates. The sprayer produces a higher
quality surface with improved seal life which equates
directly to cost savings and improved safety.
References
Queensland Roads1. Vol 1, No 1, June 1962
Pidwerbesky B D, Waters J C.2. Preventing and
solving chipseal problems using a transverse variableapplication sprayer . 22nd ARRB Conference –
Research into Practice, Canberra, Australia. 2006