SubscribeEach of these methods is discussed in detail below, taking into account their various attributes.
The most common methods of pavement retexturing are:
- High Water Pressure,
- Ultra High Water Pressure (TrackJet),
- Chemical,
- Shot Blasting,
- Mechanical Process.
High Pressure Water blasting (HPW)
Rubber is removed by means of rotary devices that move along the surface as it cleans. This is done utilising up to 30 gallons of water per minute at pressures of between 100 to 1,000 bar. The water that penetrates the surface effectively cleaning rubber deposits creates an hydraulic effect. This helps to increase the frictional values and surface texture of the pavement. A combined suction part or a sweeper that picks up the rubber debris during its operations usually accompanies it. This allows for the pavement to be easily and quickly returned to operations and is especially advantageous in airport operations where time constraints and short possession time is common.
Benefits of using this technique are:
- The speed at which rubber is removed (1,200 m² per hour are claimed).
- The cost efficiency of the process (water is generally provided).
- The improved friction characteristics of the pavement due to penetration of the water and the removal of rubber.
- The ease of getting off the runway in the event of an emergency.
- Its usage is independent of weather and can be operated in cold, damp wintry conditions.
Disadvantages are:
- Noise from the operation requires the wearing of hearing protection.
- Eye protection should also be worn in the vicinity of the machine while in operation.
- Appropriate disposal of waste material is required.
- Does loosen surface matrix encouraging the loss of fine materials.
- Cleaning rate is 70% with one run.
- Heavily damages certain asphalt types like antiskid.
- Damages grooves and pavement surfaces over time (8 years).
- Damages sealing.
- Cannot be used to clean AGL.
HPW is most effective on sprayed seals and asphalts that show loss of texture due to flushed bitumen. This results in safer operating conditions for pavements (SPEIDAL, 2002).
TrackJet (Ultra High-Pressure Water blasting)
The TrackJet, an Ultra High-Pressure Water blasting machine developed by Bernd Weigel in Germany, is widely used at BAA airports and other leading airports in Europe, as well as European highways for retexturing and paint marker removal.
Through its modern technology of retexturing, this machine has consistently removed 100% of rubber build-up and pavement markings from pavements without touching the pavement micro or macro texture. It utilises a nozzle system that is truck mounted, applying very little water at very high pressure through a unique computer-controlled system.
This enables an environmentally friendly and most effective maintenance for all kind of surfaces. Cost savings through increasing rubber removal intervals without damaging or destroying the aggregates on the pavement surface result in an increased pavement life. (Ian Coats: BAA Gatwick Field Study 2004/2005).
Benefits of this technology are:
- Optimum treatment with care of pavement surface.
- Reduces direct and indirect renovation cost by prolonging cleaning and resurfacing cycles.
- Applicable to all kinds of surfaces; for example asphalt, anti-skid, petro-grip and concrete.
- Best possible friction values, therefore prolongs the time interval till next cleaning.
- High environmental compatibility is reached due to very low water consumption and very low eroded road/runway substance volume.
- No damage to grooving, runway lighting systems, marker paints and joint sealing.
- Clearing out of expansion joints.
- Only needs one personnel to operate.
- The ease of getting off the runway in the event of an emergency; runway can be evacuated in 3 minutes leaving the working area tidy and surface like new.
- Its usage is independent of weather and can be operated in cold, damp wintry conditions or warm temperatures (2 to 40 degrees centigrade).
- High environmental care due to extremely low water and fuel consumption; the TrackJet works with clean water without chemical adhesives and requires only 10 to 20% of the water and 30% of the fuel HPW systems normally require.
- Low expenses with waste removal, because no chemical is used to separate the rubber waste from waste water.
This system is also universally suitable for cleaning sealing joints, concrete renovation, cleaning of steel and concrete areas, apron areas and oil spill removal.
Disadvantage of systems:
- Appropriate disposal of waste material is required.
- Some airport staff claim that up to 800 m² per hour cleaning (but 100% rubber removed) is too little.
Chemicals
Environmentally friendly chemicals have been developed that are safe and effective in cleaning rubber from contaminated surfaces. This is done by spraying the chemicals onto the pavement surface and then scrubbing, brushing and working them into the rubber deposit over several hours. The chemicals break down the polymerised rubber into a soft jelly like substance.
The substance is then flushed off the runway by water blasting when the process is completed. During this process, the runway cannot be reopened until the process is completed due to the runway surface being slippery.
The debris cannot be swept up using conventional sweepers since the chemicals will react with the rubber seals within the sweeper. Even though the debris is considered to be biodegradable, the chemical is not and as a result, the usual method of clean up is: flush the soapy residue off the pavement surface onto the surrounding soil after completion of works.
Over time, the debris accumulates and may eventually cause an environmental problem requiring remediation. The cost of chemical removal is usually double the cost of HPW and TrackJet due to the cost of the chemicals ((SPEIDAL, 2002).
Benefits of this method are:
- Rubber is cleaned at the same rate as HPW.
- Iit softens and removes polymerised rubber.
- The work can be accomplished using airfield staff and equipment.
Disadvantages are:
- Once the process begins, the pavement/runway must remain closed until clean up is complete.
- It is expensive in comparison to HPW and TrackJet.
- Poses an environmental problem due to chemicals not being biodegradable over time.
- Time taken for process to be completed.
- Requires more than one personal to carry out process.
- Reacts with rubber seals in conventional sweepers and on runways.
- Large amount of effluent needed to be disposed of.
High Velocity Impact Removal or Shot Blasting
Propelling abrasive particles onto the runway surface that blast the contaminant from the pavement surface using Shot-blasting. The operation is environmentally clean since it is self.
contained and the equipment can be adjusted to produce the desired surface texture result. On a non-grooved surface it collects the abrasive particles, loose contaminants and dust from the runway surface. The steel is then recycled for re-use. The primary reason using this method is for paint removal and the resurfacing and retexturing of pavement surfaces and not necessarily the removal of rubber deposits (SPEIDAL, 2002).
Benefits are:
- It retextures pavement and removes rubber deposit in excess of 1,000 m² per hour.
- Retexturing is done by removing a thin layer of the pavement and coincidentally removing rubber deposits as well.
- The equipment is truck-mounted and can easily be removed from the runway (like HPW and TrackJet) in case of an emergency landing.
- The equipment cleans the surface while working.
Disadvantages are:
- Expensive to mobilise.
- Overall cost is expensive.
- Noise and vision hazards due to operation process of machine.
- Care is required to carry out machine operation.
- FOD hazard on airfields where steel shot becomes semi-embedded into the surface and then dislodged later in time.
Mechanical Removal (Grinding or Milling)
Mechanical Removal is generally carried out either by grinding or milling. Like shot blasting, the primary reason for the machine is not the removal of rubber from pavement surface.
It is most effective in removing rough patches on highways and profiling high spots on pavements. It also removes rubber deposits as its process is carried out (SPEIDAL, 2002).
Benefits are:
- Removes high areas such as bumps on pavement surfaces or at joints where slabs have shifted or faulted.
- Mills asphalt surface for preparation of overlaying.
- Improves pavement surface friction characteristics by removing a thin surface layer.
Disadvantages:
- Can cause micro-cracking of the structure leading to accelerated aging of the surface.
- Damages surface texture.
Comparative Analysis of Retexturing Methods
The table below is a comparative analysis of the different attributes associated with each type of retexturing method.
In comparing the different methods of retexturing against key operative variables it can be deduced that the specific requirements of the user will determine which method suites them best.
In table 1, HPW is used as the basic method from which the other methods were measured against using several different factors.
Table 1 Comparative analysis of Retexturing Methods
| Technology | Cost per m² | 100 % Rubber Removal area | No. of staff used | Environment impact | Pavement vacuation time | Pavement retexturing ability | Safety/Noise | Speed of 100 % Cleaning |
| Chemicals | + | - | + | + | - | - | - | - |
| HPW | = | - | + | + | = | - | = | - |
| Shot Blasting | + | - | + | = | - | - | - | - |
| Mechanical Removal | + | - | + | = | - | - | - | - |
| TrackJet Technology | = | = | = | = | = | = | = | = |
Key to table: comparison of all technologies against TrackJet UHPW
= approximately the same like UHPW,
+ greater/more than UHPW
- less than UHPW
For cost, rubber removal, speed of cleaning, and pavement retexturing the TrackJet has a distinct advantage and equals HPW in the other factors. For pavement retexturing it should be noted that depending on the surface type whether asphalt or concrete there are advantages in using specific methods.
Shot blasting is more effective on concrete than it is on asphalt pavements. TrackJet is the only technology that removes paint markings without any damage to the texture below.
