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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



QUEENSLAND ROADS Edition No 5 March 2008

7

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




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.




9

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.•




Figure 4. Plan view of telescoping spray bars

Both spray bars

High flow nozzles

Low flow nozzles

Figure 5. Telescoping spray bars




11

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

bitumen sprayer

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