UHP Water Cutter

Richard Shaw and Greg Slaughter

Techlink would like to thank Richard Shaw, Greg Slaughter and the experts at Fulton Hogan Ltd, for their contributions to this case study.

Introduction

Flushing of bitumen is a major problem on many New Zealand roads. It occurs where bitumen rises through the road producing a shiny black surface. Roads flushed with bitumen are dangerous to road users as they cause vehicle hydroplaning, and reduced traction and skid resistance. Flushing is a serious concern for the roading engineer.

Flushed road surfaces are usually the result of wear and tear by vehicles or the result of some defect in the underlying pavement. Flushed surfaces can also be caused by poor construction techniques such as too much bitumen applied during surfacing.

Traditional methods of removing bitumen are not always effective and are not environmentally sound. Fulton Hogan has developed an Ultra High Pressure (UHP) Water Cutter which they believe is the most effective and environmentally responsible road maintenance tool for the treatment of flushed bitumen currently available in New Zealand, if not anywhere (Conceptual statement).

An Opportunity

Fulton Hogan was aware that traditional methods of treating flushed bitumen were far from environmentally acceptable. Traditional methods consist of either resealing over the problem areas or burning off the excess bitumen. Both sealing and burning have large operational and environmental costs.

Environmental Comparison of Alternative Techniques (pdf)

Fulton Hogan's Environmental Policy

Feedback from Regional Councils' consultation processes identified the unacceptability of road burning. The smoke smells bad and was found to cause damage to crops. Road burning was also considered wasteful of resources. Regional Councils now require road burning to have resource consent or have prohibited it.

Following the restrictions on road burning, Fulton Hogan consulted stakeholders such as Regional Councils and Transit New Zealand, regarding the use of Water Cutting technology. It was generally agreed that discharging water and bitumen onto the roadside was also unacceptable.

A team of Fulton Hogan staff led by Richard Shaw a mechanical engineer, developed the original idea for the Water Cutter after seeing similar equipment being used for paint removal. UHP Water Cutters had been developed overseas to replace environmentally unfriendly sandblasting paint removal techniques. Steve Grave, Fulton Hogan Canterbury Regional Manager, Garry Wells, Fulton Hogan Canterbury Specialist Plant Manager, and Gary Casey, Fulton Hogan Canterbury Surfacing Manager, contributed to the development of each of the three Water Cutters Fulton Hogan currently operates. Each Water Cutter is an improvement on the one before. Innovations are made and trialled and proven concepts are funded allowing further innovation.

COP Brief development

Risk Assessment of the Water Cutter

Early in the development of the Water Cutter it was identified that a number of operational and environmental risks needed to be addressed before it could be considered economically and environmentally acceptable.

The Australian/New Zealand standard for risk management (AS/NZS 4360:1999) provides a structured framework for considering risk under the following headings.

• Establish the Context
• Identify the Risks
• Analyse the Risks
• Evaluate the Risks
• Treat the Risks

Fulton Hogan's R&D Group uses these key elements to assess new initiatives such as the Water Cutter.

The main areas of initial concern regarding the development of a Water Cutter were:

• Disposal of the waste product
• Fuel consumption
• Maintaining the integrity of the road surface
• Operator safety

The major environmental risks were the disposal of the waste product and minimising fuel consumption.

Management of the Waste

The Vehicle

UHP water cutting equipment is available from a range of suppliers who have developed the technology over many years. However a search of suppliers of UHP equipment with experience in using this technology for bitumen removal was unsuccessful so Fulton Hogan developed this specialist equipment.

Although these water jets are energy intensive and effective at removing the excess bitumen from the road surface, this energy dissipates very quickly and does not have a detrimental effect on the bitumen that anchors the aggregate in place.

UHP Water Cutting should not to be confused with water blasting. This method of road maintenance can harm road surfaces because it uses large volumes of water which can cause chipseal to break-up. Water-blasting also creates large amounts of water/bitumen slurry waste that requires disposal.

Development

The Water Cutting process has evolved from the initial trial phase with the 'two truck' system to a single truck mounted system. The third machine produced has been optimised to make the operation as efficient as possible.

Two major changes have been made:

• Firstly, the slave engine to drive the vacuum recovery fan has been removed and one engine now meets the demands of both the water pumping, deckblaster operation and the vacuum recovery. This minimises the fuel use and reduces unnecessary weight.
• Secondly, optimised axle loads have created the ability to carry a full day's supply of water to the site and a full day's worth of recovered product away. This dramatically improves the efficiency of the whole operation by eliminating the need to travel to and from disposal sites during the day.

The truck mounted machine is self contained and involves the following major components: fresh water and recovered product tanks, a diesel engine, two hydraulically operated UHP reciprocating plunger water pumps, an electronic control system, an umbilical self propelled deckblaster (like a rotary lawnmower) that contains the revolving spraybar, and the vacuum recovery system.

The recovered product tank on the truck has been optimised to cope with the difficult material removed from the road surface. The recovered product contains approximately 20% bitumen, which coagulates and settles in the tank. The tank design is a tipping body with an exceptionally steep tipping angle and a large hydraulically operated rear door. The seal for this door has been carefully designed to provide a watertight seal even with 8,500 litres of water and recovered product on board. The tank is constructed of stainless steel.

The recovered product is inert and non-hazardous and every effort has been put into the design and construction of the deckblaster, recovery system and recovered product tank to ensure that all material is removed from the road surface and that this material is efficiently contained until the disposal site is reached.

Output

Compared with traditional methods of excess bitumen removal, UHP Water Cutting has the following advantages:

• Excess (flushed) bitumen is completely removed from the upper surfaces of the embedded stone in a chip sealed surface (the predominant surfacing on New Zealand roads).
• The combination of low water volume and ultra high pressure minimises the likelihood of penetrating the seal membrane and damage to the road surface.
• The microtexture of the stone surface is restored to near the "as-crushed" state and the effects of polishing under traffic are largely removed (New Zealand patent application 517062).
• Minimal chip loss occurs. The energy of the water stream is finely focussed so that it does not dislodge the chip.
• The process is very environmentally friendly. All waste produced during water cutting is immediately sucked from the surface leaving it completely clean and ready for traffic. Relatively small volumes of waste is produced which can be easily disposed of or recycled. Very low volumes of water are used, and there are no emissions as in burning. Solid bitumen collected within the unit's recovered material tank is 100% recyclable.
• The unique umbilical system allows the operator to target only the specific areas that need treatment. The system provides manoeuvrability, minimal overlapping and the ability to square off the ends of areas for a professional finish.

Other uses for the Water Cutter

Although the Water Cutter has been primarily developed for the restoration of chip sealed surfaces further development has expanded the scope of operations to include:

• Texturising asphaltic concrete and concrete surfaces.
• Revitalisation of Open Graded Porous Asphalt (OGPA) surfaces.
• Removal of spillages from road surfaces.
• Rubber removal from airport runways.
• Cleaning of large floor areas in commercial premises.

Conclusion

A patent (517062) for the Water Cutter has been applied for. It's environmental and functional design is unique in New Zealand. Fulton Hogan is proud to have developed this environmentally and commercially successful technology.