Process Description

The system, in principle, comprises one machine. It is a one-pass completed process, although in practice and where applicable, several machines can operate in echelon much the same as pavers do in appropriate circumstances.

The machine delivers water at infinitely controllable pressures through rotating nozzle jets that contact pavement surfaces up to 100 mm from the point of water discharge in a captive re-texturing tray, much like a screed.

Existing migrated binder or asphalt matrix fines are liberated and the used water and solid waste is recovered by a powerful vacuum leaving a clean, dry and immediately usable surface. There is no need for the temporary speed restrictions that are attendant to other surface-dressing processes.

The effect of our proprietary process, which has numerous other uses including porous asphalt maintenance cleaning, is to restore macro texture and improve skidding resistance. Texture depths of between 0.6 and 1.5 mm have been recorded as restored texture depth by our process. The degree of texture depth restoration materially depends upon the size of aggregate and the degree of binder migration and type of binder. Heavily fatted surfaces have been know to require more than one pass, although this is the exception rather than the rule.

The system operates at a minimum working width of 2.3 m and at rates of progress of between 0.8 and 1.5 km per hour. Outputs of 15,000 m² per day are frequently achieved. Porous asphalt carriageways have been treated at outputs of almost 10 kph with a 2.5-m working width.

Pavements suitable for the process

The system is capable of dealing with all types of surfacing materials including surface-dressed carriageways, macadams, SMA, HRA, concrete block paved pavements and PQ Concrete.

Provided that the pavement is not excessively rutted or cracked, to the extent that it would be more beneficial to seal it with a surface dressing or a similar surfacing medium, and that macro texture is low and skid resistance is marginal, then our process is an ideal option to consider. It is not only a proven process, but cost-effective too. Our rates are around 20% more competitive than premium surface dressing and mechanical re-texturing, the latter being ineffective on surface-dressed pavements anyway or any surface where macro texture is lacking.

The equipment we use is adept at removing impacted rubber deposits from runway touch-down zones paved in either concrete, porous friction course or grooved Marshall asphalt, without damaging the edges of the grooves in the latter surface. The process is so controllable that work can proceed between aircraft movements (off-peak) and the runway can be vacated within seconds of a command from the ATC. No potential F.O.D. (Foreign Object Debris) is left behind, and operational delays to airport operators are virtually nil.

The Operation

Sites are identified and inspected for QA purposes, and limits are agreed upon with the client's representative.

The machine is fully charged with clean water (6,000 l) at the outset of the working shift and once clearance is received from the ATC, the machine and support plant enters the runway under escort. As described above, work commences at the centre line and proceeds in one direction down the runway to the end of the TDZ or designated working area.

Support vehicles in attendance are a water bowser which provides clean water for the process and a vacuum tanker for used and waste water. Recharging and decanting takes about 10 minutes after each operational hour. The waste is taken to a liquid waste processing plant where the water is fully recycled. Solid waste is collected and taken to a landfill site. Our operations manager remains with the team on a full-time basis. The whole team moves around as a unit.

The process is "all-weather," but it is inadvisable to work in ambient temperatures at or below 0oC or in fog.

Normally, friction testing is carried out by our employee or an independent testing house. We can, however, offer an inspection, test and treatment package, if required. Tests are valid and accurate only if pre-treatment tests are carried out and post-treatment tests are done as soon as possible after operations have been completed.

Safety

The system and process are inherently safe. All high-pressure fittings are designed for safety factors of 1.5 times the maximum pump pressure. It is nonetheless wise to remain clear of the location of the high-pressure pump when operational. Its location is always pointed out to all visitors during an oral briefing upon arrival. Refer to our health and safety documentation and our risk assessment for hydrology processes for more detail.

Ecological Services Proprietary Process for Advanced Hydrology Surface Treatments

--------------------------------------------------------------------------------

PROCESS RISK ASSESSMENT

PROCESS DESCRIPTION

The process comprises the following elements:

i) Surface treatment machine
ii) Supervision
iii) Mobile traffic management (where required)
iv) Full traffic management including contra-flow or lane closures (where required)
v) Support vehicles, comprising a water bowser and a waste tanker

Risk is assessed on a scale of 1 to 10, where 1 represents minimum risk and 10 maximum risk including potential fatal consequences in extremis.

The following assessment considers the above elements individually and in situ and is, of necessity, comprehensive.

i) The machines we use are inherently safe by design, being purpose-built by a reputable manufacturer with over 35 years of experience in the use of hydrology. Nonetheless, accidents can still happen and we attempt to anticipate such potential incidents as follows:

a) Catastrophic failure of the high-water pressure system, including pump and fittings

To our knowledge, such an incident has never occurred. All elements of the system are designed to have a safety factor of 1.5 times the maximum working pressure built in. In addition, the majority of the parts of the system which could fail under pressure are enclosed in steel housings. In extremis, a part failing under pressure could cause FATAL injury, but for the above-noted reasons, we assess that risk as being 1.

As an additional safety device, we insist upon oral briefing of visitors to our sites. This includes showing people where these systems are situated and advising them to remain clear of the high-pressure system whilst operational.

b) Other injuries potentially possible due to high water pressure

The re-texturing or surface treatment tray/screed is the point at which water at high pressure is imparted to the pavement surface through rotating jet nozzles. The rotating arms spin at up to 1000 RPM and often we use fine cutting jets in our treatments. The whole system is very adequately enclosed in sturdy steel housing and it operates close to the pavement surface so even a boot could not be inadvertently inserted under it.

The only perceptible risk to health is if someone insisted upon placing their hand or fingers into the system. If they succeeded in so doing, severe injury would result almost certainly, including non-surgical amputation. There would be no possibility of recovering amputated parts due to the vacuum recovery system which would instantly transport such materials to the waste collecting tank.

We perceive that the likelihood of such an incident to be potentia remota and assess the risk attendant thereto as 1. We believe it right to flag up the potential of the incident for these purposes, however.

c) Other injury risks

There is a risk of personnel or visitors being run over by the vehicle whilst operational or manoeuvring. To the extent that we perceive this risk to be 5–6 and while it is likely to be due to the misadventure of the individual concerned, we mitigate such risk by vigilant site supervision, the fitting and regular checking of reversing horns, the fitting of a rear-mounted closed-circuit television device so that the operator can see in wide angle if anyone is behind him, and reversing under traffic management. By using all these measures, we believe the risk as assessed is reduced to 2.

ii) Our site managers are experienced and fully trained in managing the process. They are equipped with mobile telephones, first-aid kits, and safety clothing and footwear. Estate-car transport is provided to carry all necessary support equipment and welfare facilities for the operatives. It is not practical to provide toilet or canteen facilities on remote locations and therefore this form of transport is used in such situations. The risk to the health and safety of workers is about the same as for any other similar road surfacing agent, and we assess this as 3–4. To minimize risks, all necessary equipment is provided and safety clothing is regularly changed so that it is clean and affords maximum visibility. We do not encourage long working hours, a typical day being 6 to 10 hours, 5 days per week.

iii) Mobile traffic management requires two trained operatives controlling two-way traffic by way of Stop/Go boards aided by two-way radio. We usually subcontract this function to well-known and reputable specialist traffic management companies. We assess the risk to the health and safety of traffic management operatives as being 8–10, as the occupation is inherently dangerous. It is not possible to make this occupation risk-free, but every opportunity and discipline should be employed to mitigate risk. Our site manager closely liaises with the traffic management foreman and we have a system whereby the latter has the final word as to whether a site is safe or not in which to operate a mobile traffic management set-up. This situation normally arises in poor weather or poor visibility conditions. In our experience, the system works very well in practice. Notwithstanding the steps we take to mitigate risk, the assessment remains high, as one can never predict the behaviour of motorists.

iv) Category A or B traffic management systems are safer to work within, but obviously dangerous to install. We never carry out such work, as we insist in the contract that this function be performed by our client or his employees. In the event that we were, however, bound in contract to install and maintain lane closures or contra-flow systems, our policy would be to employ either the client's own traffic management contractor or our own specialist. A similar risk assessment applies as in iii) above: 8–10.

v) Specialist support vehicles are employed for the functions of bringing fresh water and removing waste. We subcontract out these functions and accordingly the safety systems of these specialists apply. So far as the filling of fresh water is concerned, where possible we perform this function in a sanitized area, thus the overall risk to personnel is around 2. However, where we have to perform this in situ under traffic management, then accordingly the risk must be higher, around 4. The collection of waste is performed by enclosed umbilical hoses and vacuuming.

The waste management operative will be fully briefed upon the nature of the waste liquid and will act accordingly. The waste is not classified as special or of high-hazard bitumen and the oil content is less than 1% by volume. Similar risk assessments apply here as to the water filling function.

Concluding Comments

By virtue of the design of our equipment and our operating systems, this proprietary system is a very safe form of pavement treatment. It is faster in terms of achieving a finished product than surface dressing or other traditional forms of surfacing, and no latent safety problems are left behind post-treatment, such as loose chippings. Our process is also significantly safer and more environmentally friendly than certain competing processes. We assess the overall risk pertaining to our process, giving due consideration to personnel, visitors and motorists alike, as being 1–4. The higher figure would apply to sites with difficult topography, visibility or speed of traffic.