The present invention relates to asphalt repair systems and in particular to systems useful in the repair of roads.

Asphalt deteriorates because of oxidation and the constant pounding of traffic, but it is the joints from old repairs that become the achilles heel as weather and water ingress and break up the seal and adjacent asphalt. Considerable sums of money are spent each year on routine maintenance and repair of carriages and footways, and the utility companies also spend large sums making effective repairs after their excavations. Furthermore, road repair causes significant inconvenience tσ trie public whilst roads are undergoing repair. Additionally, roads are generally deteriorating.

Bituminous wearing courses such as asphalt are typically composed of about 94% aggregate (gravel or sand) and about 6% bitumen binder. The bitumen binder generally contains hydrocarbons and has ionic properties, which serve to bind the sand and gravel particles together.

Wearing courses deteriorate through oxidation of the bituminous binder. It is believed that the oxidation process reduces the ionic properties of the bitumen, which in turn leads to release of the aggregate. The oxidised binder loses its flexibility and the surface shrinks and cracks. The effects of traffic and weather (temperature changes and moisture) speed up this process. After general release of material larger flaws appear which eventually turn into potholes.

The oxidisation process accelerates other damage to the wearing course and failure of joints especially from conventional reinstatements, around ironwork and on trenchwork.

The traditional method for the repair of damaged or aged asphalt and tarmacadam-wearing courses comprises the total removal of an area and its replacement with new asphalt. The damaged area and its surrounds may be removed by using noisy pneumatic or hydraulic hand held or machine mounted breakers. In this traditional method it is necessary to use expensive and very noisy diamond saws to pre-cut the area to minimise additional damage and to form a face to bond in the replacement material. The areas may also be removed by more modern methods known as cold planing that pulverizes the damaged asphalt. The area is then filled with new material that then needs to be compacted and sealed with overbanding or jointing sealant. The removed asphalt is then transported away for disposal that is normally for land-fill due to the limitations of current re-cycling systems.

These conventional methods are not ideal in respect of costs, safety, environment, sustainability and durability and the time taken for repair and levels of manpower required. Such methods are described in US-A-4534674 and DE 3906352 A1.

More recently Hot In-Place Recycling (HIR) techniques have been developed for the effective repair of potholes, cracks and sunken utility cuts in asphalt surfaces using an infrared heating process. The surface is heated and raked and a rejuvenation liquid is then applied so as to recycle the existing embrittled asphalt. This enables a substantial reduction in repair costs. A typical rejuvenating liquid for use in the method generally comprises maltenes.

The infrared HIR method comprises heating the damaged area with an infrared heating device; adding new material if required; raking together; applying a liquid that rejuvenates the original bitumen; and compacting the new combined material.

The HIR method can also include applying a topcoating liquid to the repaired area that seals and binds the repair, or applying a fine aggregate to provide skid resistance. The top coat may be applied for cosmetic purposes, for example to give a black appearance to the treated asphalt.

WO04/018774 describes an improved system for the repair of roads using a vehicle mounted infra red heating system. The present invention relates to improvements to such a system.

The present invention therefore provides an improved road heater system which can be used for the repair of roads.

The improved road heater system comprises one or more panels carrying a burner assembly to which are supplied a pre-mixture of combustible gas and air. The burner assembly preferably comprises a knitted metal fabric. The preferred fibers for these materials are produced from an alloy known as Fecralloy, which is an iron chromium alloy of preferred composition. Fe72.8/Cr22/AI 5/Y 0.1/Zr 0.1 and has excellent resistance to oxidation at elevated temperatures. Fecralloy fibers are knitted to form a 'mat' known as NIT which preferably covers the whole burner surface and edges of the panels or cassettes. As the NIT material expands under heat, the mat is welded at specific points across its surface to ensure a consistent output whilst in operation.

This knitted product is made from a yarn made from the Fecralloy (stainless steel alloy) metal fibres and is both flexible and durable. Although other materials may be used to produce infrared flame Ferroalloy is preferred due to durability, consistent performance and long life capability of NIT. Radiation from the surface of the panels originates from two sources: emissions from the heated surface and emissions from the hot combustion gases leaving the surface.

The invention also provides a process for repairing damaged asphalt comprising heating the damaged asphalt by means of an infra red heater comprising a panel having a knitted metal fabric which heats the asphalt through radiation from the fabric, raking or scarifying the asphalt, applying a rejuvenating composition comprising maltenes and an emulsifying agent, optionally adding aggregate to the asphalt and compacting the asphalt surface.

The gas/air pre-mixture is preferably supplied to the burners by a fan mix or atmospheric venturi system to enhance combustion at each of the panels. The use of the venturi system provides a balanced gas feed to the injector, with use of optimum the air supply. The venturi also provides the ability to generate a turbulent air/gas mixture to stabilize combustion on the Fecralloy NIT material which is particularly useful when repairing roads under adverse weather conditions.

The gas supply may be from a variety of products with Liquid Petroleum Gas (LPG) providing the ideal but not exclusive source. The LPG may be either Propane, or Butane or a combination of similar products. The gas supply can be delivered by conventional upright LPG gas cylinders, or preferably by a horizontal side clip liquid delivery cylinder which is particularly useful when used in combination within a purpose designed vaporizer system. If the LPG is provided by conventional vertically mounted gas delivery cylinders the volumes of gas required for this application can cause rapid freezing and this limits the operating temperatures. This can also substantially limit the amount of LPG delivered from the total bottle capacity. By using vaporisers from a liquid delivery system operating ambients can be very low indeed and by extracting liquid from the cylinders it is positive to totally deplete the cylinder capacity. Thus improving the efficiency of the operation. In a preferred design a vaporizer assembly and manifold are fed from two horizontally mounted liquid delivery cylinders mounted in the upper body of the heater assembly. By using liquid delivery systems extended operating periods can be achieved when compared to 'normal' gas delivery methods. The vaporizer assembly is preferably made from stainless steel. A preferred assembly of the present invention comprises of 4 panels or cassettes forming the center core of the infrared heater. Preferably the design of the control system, allowing for any or all of the panels to be powered. In a further preferment each panel is designed with its own ignition, pilot and monitoring system.

In operation the premixed air gas mixture is ignited on the NIT material surface with the injectors and venturi providing an optimum mix to generate an infrared emission of medium to long wave output directly on the surface of the NIT. This can be calculated on preset output to provide optimum infrared output to soften the asphaltic surfaces to be repaired without carbonizing the surface. The ignition can be activated by an initial spark generator powered from a transformer converting 12 volt to 11OVoIt to a pilot system that both carries the flame ioniser and activates the valve sequence that allows gas to be supplied to the required panel or panels.

Infrared penetration from medium to long wave can be selected by height of the assembly from the road surface and the operating time to achieve the required depth of operation.

The dimensions of each heater panel can be selected accordingly to the intended use. However, we prefer to use rectangular or square panels having sides of from 300mm to 1500mm particularly from 500mm to 1000mm. In a preferred system 4 panels are used each is 500mm x 500mm to form a center core measurement of 1 meter x 1 meter. Alternatively two panels each being 1000mm x 500 may be used to form a core of 1 metre x 1 meter. Fewer panels can be preferred since it reduces the number of valves and control functions required. However, the burner deck design and the NIT construction places no limit to the size of panels "Wings" can be added to the outer edges to form a combination that can generate a larger heating surface area . Any combinations of the preferred 2 or 4 panel system optionally with the outer wings can be activated to form a "patchwork pattern". The metal fibre burner mainly consists of-a steel housing with the metal fibre medium mounted on top. Distribution plates fed by a venturi system are used inside the housing to provide for the homogeneity of the combustion.

The assembly can easily be extended by adding an additional number of panels or cassettes fixed on one or more sides of the assembly as may be required according to the width of the surface to be repaired. The addition of these wings is simplistic in its mechanical design allowing for a range of other width and depth options and ultimate burner configuration.

The heating system of the present invention may be used to provide improved equipment for performing the Infrared HIR techniques described above. Accordingly, in a further embodiment the invention provides a single vehicle road repair system wherein the means for supplying infrared heat to the surface to be repaired, is the system of the present invention combined with means for storing and supplying hot new asphalt, means for storing and supplying a rejuvenation liquid, and means for storage and supply of gas for heating.

The vehicle may be a truck, fitted at the rear with an infrared heater system according to the present invention, in a preferred embodiment the heater system is adapted to be moved towards and away from the surface to be repaired. The vehicle could be provided with a hot box that contains replacement asphalt if required, an adjacent tank containing rejuvenation liquid which may use the hotbox residual heat to maintain a good working temperature, and preferably a pump and lance for delivery of the liquid to the desired location. In a preferred embodiment a small waste container may be provided. A secure area is preferably provided for hand tools and other equipment such as traffic control signs, rakes and other equipment. A tow bar may be fitted for towing a trailer-mounted compaction roller.

In another embodiment the vehicle may be a tractor backhoe or wheeled or skid-steer loader to which the equipment may be quickly installed or removed. The attachment that forms the infrared heater of the present invention may be fixed to the dipper arm (of a backhoe loader) or the front loader quick change system (of a skid steer) so that it may be moved towards and away from the surface to be repaired. A separate attachment may be fitted to the rear of the vehicle containing a hot box for new asphalt, an adjoining tank for rejuvenation liquid that uses the hotbox residual heat to maintain a good working temperature, and a spray lance for its application to the raked area. With this system the area to be repaired may be heated with the vehicle which is then moved quickly away to a suitable position, the heated area is then raked so that the rejuvenating liquid may be delivered to the prepared surface of the area being repaired, prior to compaction.

Such attachments for tractor. backhoe vehicles are a part of the present invention. The invention therefore provides more efficient, compact and lightweight equipment that enables faster, quieter and more economic method of repair of a wearing course using HIR techniques.

The heating of the damaged area to be repaired may be carried out using the heaters of the present invention tailored to suit the size and shape of the area to be repaired. Typically the heating needs may be to depths of 10 mm to 100 mm from the surface. The average temperature of the heated material should generally not exceed 2000C and may be from 50 to 2000C, preferably 100 to 2000C. As with all carbon structures heat increases oxidation, but since the infrared output of the infrared attachment is selective at its medium wave output it does not induce burning (which would destroy the binder's asphaltenes permanently). The heating time may vary according to its structure and dependant upon the surface temperature, wind chill factor and whether the surface is damp, but may for example be from 5 to 20 minutes, typically 6 to 8 minutes.

Once heated, the damaged area may be raked or scarified to mix the highly oxidised top surface with the less oxidised sub-strata. This also increases the surface area of the mix. Care must be taken to leave an outer perimeter of the heated area unraked to allow development of an efficient bonded joint when compacted.

A rejuvenating liquid may then be applied preferably using a lance provided on the vehicle. Typically the composition of the rejuvenating liquid comprises rejuvenating oils high in aromatics with high levels of polar compounds. The oils in the rejuvenating liquid are preferably emulsified with cationic slow set emulsifiers at higher than normal levels to ensure not only a very storable and stable emulsion but also to aid in a slow cure and break time.

The rejuvenating liquid preferably contains from 30 to 80 parts by weight in total of a heavy paraffin distillation solvent extract and a heavy naphthenic distillate solvent extract, from 10 to 60 parts by weight of water, and from 1 to 5 parts by weight of the emulsifier. More preferably, the liquid comprises from 60 to 65 parts by weight in total of the heavy paraffinic distillate solvent extract and the heavy naphthenic distillate solvent extract, from 30 to 35 parts by weight of water and from 1 to 5 parts by weight of the emulsifier.

New material may be needed if it is required to level the patch to be repaired, i.e., the amount of material that has been worn out of the surface. The material may also assist in knitting of the joint. On hot rolled asphalt, precoated chippings are added and compacted into the surface to give road texture. The material is generally raked level and then compacted either by a vibrating roller or compaction plate. A topcoat of a sealer/binder may also be applied, or a dusting of fine aggregate (e.g. aluminum silicate) may be added to ensure good initial skid resistance. Once the surface has cooled and hardened, normally for a minimum of one hour, it is capable of accepting traffic. The benefits of the system of the present invention are that they have a long operating life and are extremely safe in use due to it being flashback-, splash- and shock-resistant and their ability to withstand very high temperatures. The flexible burner design has excellent control capabilities and single NOX and CO ratings. Combustion and infrared emissions are unaffected by moisture, accidental fuel spillage or mechanical stress. In addition the burner systems of the present invention provided efficient fuel utilization and fast heat up and cool down properties.

The advantages to using the road repair apparatus of the present invention over traditional methods are: 1. Reduced asphalt costs since only material lost as a result of the damage is added: in the conventional method it is also necessary to replace material that is removed from around and beneath the damaged area. Substantial cost savings arise due to avoiding the need to transport the removed asphalt to land fill with its additional charges.

2. The resulting repair is fully bonded with the existing material by means of heat fusion. This eliminates or reduces the problems of joint failures and the problem of 'cold shock' that occurs in the conventional method when hot sealant or new material is added to cold asphalt to join the new material to the old material. There is no pre-cutting of an edge to the old surface, no need for any kind of overbanding or joint sealing (notoriously short-lived), and no mixing of materials with different expansion and contraction rates next to each other. Furthermore, when the application of the topcoating is included in the method of the invention, the surface is further bonded.

3. By recycling the existing surface there is far less new material used, the process is very quiet, and its speed enables the roads to be opened up far more quickly than would normally be the case. Due to the lack of noise, roads may be repaired at night while traffic is at its lightest with less disturbance to residents.

4. This method of repair also eliminates the problems of 'white finger' caused by pneumatic and hydraulic hand held breakers, which is a major problem to the construction industry, causing added costs to all concerned. 5. Some 94% of the wearing course is rock or sand and has an extremely long lifetime of many decades. Of the 6% of the wearing course that is binder, only a small fraction is degraded and the remainder (the predominant compounds being asphaltenes) has a very long life span. By replacing only the fraction of the aromatic oil component that is lost, the total combined method of the invention is highly efficient in material terms, and as a result effectively recreates the hydrocarbon chain.

The invention is illustrated by reference to the accompanying drawings in which:

Figure 1 shows an assembly according to the present invention comprising four panels 1 , 2, 3 and 4 mounted on a frame 5 provided wheels of which only two (6 and 7) are shown. The frame can be raised or lowered to adjust proximity to the road surface to be heated. Each panel is fitted with a venturi tube 8, 9, 10 and 11 for the supply of a mixture of combustible gas and air (from cylinders not shown). The panels 1 , 2, 3 and 4 each have a knitted metal fabric (not shown) into which combustible gas and air is passed via feed pipes 12.

Figure 2 shows a schematic representation of the apparatus of Figure 1 and the venturitubes, 8, 9, 10 and 11 are fed by feed pipes 12 through which is supplied the combustible gas and air to the panels 1 , 2, 3 and 4.

Figure 3 is a top elevation of the assembly shown in Figure 1 showing how the panels 1 , 2, 3 and 4 are assembled.

Figure 4 is an end view of the assembly shown in Figure 1 showing the ends 13 and 14 of the Fecralloy knitted fabrics fitted to panels 1 and 2.

Figure 5 shows a Fecralloy knitted fabric a piece of which is fitted to the underside of each of the panels 1 , 2, 3 and 4.

In the of the roads using the heater systems illustrated, the damaged area to be repaired is heated by the infrared system, the area is then raked and the pump may then be activated to deliver the rejuvenating liquid. The mix of heated original asphalt plus new material if required may then be further raked before being compacted by a vibrating roller or compaction plate. Once leveled to the original surface profile the repaired road is ready to accept traffic.