Asphalt Road Repair
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for repairing asphalt roads, particularly but not exclusively to repairing longitudinal joins between adjacent wearing courses.
An asphalt road is constructed in layers for optimum load distribution, and allows the stresses and strains from the vehicles passing over head to be transmitted through the road structure, which then spread and lessen with depth. In order to achieve this, stronger and consequently more expensive materials are used in the upper levels, with relatively low strength materials being used in the lower layers. It is also important that a good bond is achieved between all of the layers to ensure the road structure acts as a single structural entity with good bearing capacity. The wearing course, or top layer of a road may consist of up to three asphalt layers - a surface course, a binder course and an asphalt base course - and together these constitute the top layer of the road structure and overlie a structural road base layer (which usually also comprises several layers).
There are a wide range of surface course specifications, and these wearing mixtures must be designed to have sufficient stability and durability to withstand the appropriate traffic loads and the detrimental effects of environmentally-induced stresses - such as air, water and temperature changes - without exhibiting cracking, rutting or other failure modes. Their usage also depends on specific requirements, local conditions and functional
characteristics, such as traffic levels, skid resistance, noise reduction and durability. In some cases, rapid drainage of surface water is desired, while in other cases the wearing course should be impermeable, to keep water out of the road structure.
The binder course is an intermediate layer. It is designed to reduce rutting and withstand the highest stresses that occur about 50-70 mm below the surface course layer. Binder mixtures typically use a large aggregate size (19-38 mm) with a corresponding lower asphalt binder content to produce a combination of stability and durability.
The asphalt base course mixtures have a maximum aggregate size (up to 75 mm) and an even lower asphalt binder content, providing adequate durability since this layer is not exposed to the environment.
In some roads the three asphalt courses may only comprise two layers, or even one; in the first case, the uppermost layer is referred to hereinafter as the surface course and the two layers together are the wearing course, in the second case there is only the surface course which constitutes the wearing course. Many roads are provided with several carriageways, or traffic lanes, each about 3 -4m in width, !n constructing such roads, the structural road base layer is often made in a single width extending over the entire width of the road. However, the wearing courses of these roads are often constructed to the width of the carriageway only, or traffic lane, by a paver (also known as a paver finisher, asphalt finisher or paving machine). The paver has an auger which places a stockpile of heated asphalt (a mixture of bitumen and aggregate) onto the road base layer in front of a screed which spreads the material over the width of the carriageway and provides initial compaction to leave a relatively smooth, uniform surface. The wearing course is then fully compacted by a road roller.
Where adjacent wearing courses abut there is a longitudinal joint which extends between them running in the direction of the road; this joint may be sealed with a strip of bitumen, rubber or similar compound. It also often delineates the boundary between adjacent traffic lanes, and so reflectors known as "cat's eyes" may be inserted into the wearing surface along this line, and it may also be partially covered by lane markings. These longitudinal joints are susceptible to fail well before the remainder of the wearing course for a variety of reasons such as the ingress of water and the action of frost, poorly formed or
cut joints, insufficient compaction of the wearing courses at their edges, poor matching of asphalt materials in adjacent wearing courses, inaccurate supply of materials when constructing the wearing courses and so on. Failure at these joints is often seen as cracks, widening and/or deepening to potholes to the depth of the wearing course along the line of the longitudinal joint, whilst the remainder of the wearing course, away from the longitudinal joint (more than about 0.3m transversely - any wider failure is usually a major fault which must be repaired immediately before the road and/or traffic is damaged severely) is still intact and has many years of useful life remaining. The extent of longitudinal joint failure normally varies along the length of the joint: some lengths of the joint may be severely damaged, whereas other extents of the joint may be only slightly damaged, or even in good repair.
The repair of failed longitudinal joints is often carried out piecemeal, where the failure is particularly deep or wide and leaves a significant area of structural road base layer open to weathering and damage by passing traffic. This is partly because the varying extent of failure along the joint makes it quicker and easier to carry out patch repairs, which are usually made using only smaller, hand-operated machinery and with a large amount of manual input. Alternatively, repairs are carried out using similar machinery as was used in the initial construction of a wearing course, and over a width about the same as the original wearing course: firstly the surface is prepared for repair using a "cold planning" process, in which a rotating cylindrical roller with protrusions removes the wearing course. The roller is about the same width as the carriageway, and is rotated with such power that the wearing surface is broken up (with the aggregate itself being smashed, or pulverised) and removed (it cannot be re-used as the aggregate has been smashed and will no longer be of the specified size for the wearing course), leaving a structural road base layer the upper surface of which is scored by the protrusions - the score lines provide a "key" for the new wearing course to attach to - as the cold planning machine is driven along the road. There follows a paver which lays an entirely new wearing course as in the initial construction process, followed by a road roller. It will be appreciated that the former process is slow, and requires that the road be blocked either side of the part of the joint under repair, or the provision of temporary traffic controls to divert traffic onto a carriageway removed from the repair. The second process is also relatively slow, because the width of wearing course under repair is extensive and, as the different machines need room to manoeuvre and to be separately controlled and directed manually, this process also means that whilst the repair work is
taking place a significant part of the road is blocked. The patch repair method is particularly unlikely to match the material of the repair with that of the original wearing course, resulting in a repair which is almost as vulnerable to failure around its edges as the original longitudinal joint (and therefore has a life which is different from that of the wearing course), and which either stands proud of the original wearing surface or which is soon compacted into a shallow depression - each of which cause discomfort when driven over. The carriageway width repair method is less likely to result in a wearing surface which stands proud of, or below, the surrounding wearing course, however it effectively creates two new longitudinal joints along either side of the repair, and these joints are as susceptible to failure for the same reasons as was the original joint.
SUMMARY OF THE INVENTION
The present invention provides apparatus for repairing a longitudinal joint between adjoining asphalt road wearing courses, the apparatus comprising; a heater array for heating the surface of the asphalt wearing courses on both sides of the joint; a mixer for depositing bitumen and heated aggregate onto the heated surfaces, having agitators for mechanically disturbing the heated asphalt over a predetermined distance which extends transversely over the joint and to either side of it, and, for lifting at least some of the disturbed asphalt away from the wearing surface temporarily and for mixing the heated aggregate, bitumen and asphalt; and a screed for spreading and tamping the mixed heated aggregate, bitumen and asphalt, wherein the heater array, mixer and screed are arranged linearly and mounted to a single machine so as to pass over the wearing course in the order recited as the machine moves in a forward direction, and wherein the entire linear arrangement is disposed to one or other side of the machine.
Such an arrangement allows a single machine, which can be controlled and driven by a single operator, to drive along a longitudinal joint and to carry out most of the processes necessary to repair the joint in a single pass (the machine would be preceded by workmen removing any cat's eyes or the like, and followed by a road roller providing final compaction of the repair) in a much quicker and less obstructive method than either of the traditional methods of longitudinal repair. The location of the linear array to one or other side of the machine allows repairs to be carried out on a joint adjacent a kerb or other step joint whilst the apparatus is able to drive close to the kerb, thus blocking the minimum width of road;
further, the machine may be configured so as to carry out the repair safely whichever side of the road the joint is on (i.e. the linear array can be disposed so that the apparatus can carry out the repair whilst the apparatus is driven in a direction which faces towards or away from the oncoming traffic, whichever is deemed most safe). Preferably the predetermined distance is significantly less than the width of a road wearing course, or carriageway, such as less than about 1m. This allows the heater array, mixer and screed to be mounted to a single machine, which can be steered relatively easily along the joint under repair. The entire linear arrangement is conveniently disposed on one or other side of the machine, so reducing the amount of road width which is blocked while repair is underway to not much more than the width of the machine; this arrangement also allows the repair of longitudinal joints which are close to the edge of a road, and/or close to a kerb, without heating unnecessarily areas of road which are distant from the joint. Because the width of the repair is less than about lm, a smaller road roller may be used, as there is less width of repair to compact. The agitators may be even narrower, about 0.2m in width for example; because the heater array heats the wearing course sufficiently to soften the asphalt, the agitator which disturbs the wearing course above and on either side of the joint does not have to be operated with the same power as a conventional cold planing device. Instead, it merely combs through the softened wearing course, causing the asphalt to crumble but not breaking or smashing the individual pieces of aggregate; this is advantageous, because this disturbed asphalt can then be re-used in the repair process, thus avoiding wasteful use of repair material. Mixing of the disturbed asphalt and the sprayed bitumen is assisted by the lifting of some of this material away from the wearing course by a significant distance before it is allowed to fall back onto it. The agitators may be cylindrical rollers with teeth or protrusions which are shaped, configured and/or disposed so as to disturb, lift and/or mix material as appropriate. Because the majority of the failures along the length of the longitudinal joint are usually quite minor in extent, the agitators need be no more than about 0.2m wide. To deal with more extensive joint failures, the rollers may be mounted so as to be reciprocable transversely to the linear arrangement and to the joint by up to 0.6m in total, thus allowing the apparatus to repair more extensive joint failures. The heater array may comprise several separate heater modules, which may be removably mountable on rolling frames which may be mounted to the front of the machine and to one or other side to form a linear array. This allows the heating apparatus to extend sufficiently and heat the road surface enough while the apparatus can move forwards more
quickly than in conventional arrangements. Rolling frames may be attached to the machine and to each other, and have wheels which may be independently steerable so as to be able to guide the heaters along parts of the longitudinal joint which are not straight (around bends in the road, for example). The heaters are not subjected to the same stresses in use as are the agitators, so the heaters may be demountable (for easy and rapid deployment to either side of the machine or disassembly and storage on the machine), however the mixer is preferably mounted securely to the chassis or frame of the machine.
The mixer may comprise, in the direction of forward direction of the machine in use, a bitumen spray for depositing heated bitumen onto the wearing course, a first agitator for disturbing and lifting the heated asphalt and mixing it with the heated bitumen, a delivery channel for depositing heated aggregate onto the wearing course behind the first agitator and a second agitator for mixing the aggregate with the heated bitumen and the disturbed heated asphalt. The provision of two agitators, rather than one device which agitates the material as is sometimes used in conventional devices, enables more thorough mixing of the new material with the loosened material. Such a mixer can be relatively small, as it need essentially comprise only a frame which is sufficiently robust to hold the agitators in use, a bitumen spray jet ahead of the first agitator and a duct for delivering aggregate between the first and second agitators. There may also be a duct for blowing fibres such as glass fibres onto the wearing course between the first and second agitators, for applications where the specification requires that the repair be strengthened by such fibres.
The invention also provides a process for repairing a longitudinal joint between adjoining asphalt road wearing courses, the process comprising the successive steps of: a) applying heat to the surface of the asphalt wearing courses over a predetermined distance extending transversely over the joint to raise the temperature of a first predetermined depth of asphalt to a predetermined temperature; b) spraying heated bitumen onto the heated surface; c) agitating the asphalt wearing courses over a predetermined distance either side of the joint so as mechanically to disturb the asphalt to a second predetermined depth and to lift at least some of disturbed asphalt away from the wearing courses and at least partially to mix the heated bitumen with the disturbed asphalt; d) adding heated aggregate onto the at least partially mixed disturbed asphalt and heated bitumen; e) agitating the heated aggregate, bitumen and the disturbed asphalt to mix them together, and f) spreading and tamping the mixed aggregate and disturbed asphalt above and on either side
of the surface of the joint, this being carried out in a continuous process along the line of the longitudinal joint. The predetermined distance may preferably be significantly less than the width of a road wearing course, or carriageway, such as im or less. This is significant because it permits the process to be carried out by apparatus mounted on a single machine, The agitators may comprise cylindrical rollers having surface protrusions, so that step c) and/or step e) may be carried out by rotating the rollers with sufficient speed and/or power to disturb the asphalt wearing course and to mix the heated aggregate, bitumen and the disturbed asphalt but not so vigorously as to break the aggregate in the wearing course in step c) or, in step e) that aggregate or the aggregate added in step d). Because the agitators may be operated at a relatively low speed/power compared to the rollers used in cold planning, the forward speed of the machine can be significantly increased, up to about 1200-1400m per day, compared to repair methods which use cold planning and repair a substantial width of wearing surface (i.e. about the width of the carriageway), which achieve about 700m per day, or manual repairs which only achieve about 50m per day; the process according to the invention allows repairs to be carried out even more quickly compared to patch repairing (our prototype machine allows up to about 1200-1400m of longitudinal joint to be repaired per day), thus minimising disruption to road users. A further advantage of the invention is that it permits the repair to be of exactly the same specification as the original wearing course; this is achieved firstly by re-use of at least part of the original asphalt, and secondly by using aggregate in step d) of the same specification as in the original wearing course and by adding that aggregate, and the bitumen in step b), in similar proportions as were used in the original wearing course. This means that, rather than repairing a failed single joint with a repair which has two edges which each form joints which are as susceptible to early failure as the original joint, the repair is effectively a seamless joint of uniform material specification the same as that of the original wearing course specification overlying the original longitudinal joint and knitted seamlessly to the wearing course on either side of the repair (which has also been heated by the machine). The rollers may be driven so as to contra-rotate; with such an arrangement the first roller breaks up the wearing course and begins the mixing of the disturbed asphalt and the bitumen as some of these materials are carried up and over the roller and deposited in front of the second roller. The second roller then combs through these materials and the newly-deposited aggregate, mixing them thoroughly across the width of the second roller and staring to level the surface ahead of the screed.
The second predetermined depth may be less than the first predetermined depth, which is normally about 50mm. This allows sufficient heat to be applied to permeate most or all of the wearing course, whilst only the asphalt wearing course is disturbed; the underlying structural road base layer may be heated, so as to weaken the adhesion of the wearing course thereto, but preferably that underlying layer is not disturbed. Consequently, the second predetermined depth may be approximately the same as, or slightly less than, the depth of the asphalt surface course of the wearing courses either side of the joint, normally a little less than about 50mm.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example, and with reference to the accompanying figures, in which:
Figure 1 is an illustrative side view of an apparatus in accordance with the invention;
Figure 2 is a schematic plan view of the apparatus of Figure 1 in the process of repairing a longitudinal joint; Figure 3 is a schematic plan view of a mixer forming part of the apparatus of Figure
Figure 4 is a perspective view of a heater forming part of the apparatus of Figure 1. DETAILED DESCRIPTION OF THE EMBODIMENTS
Figure 1 shows a longitudinal joint repair machine 10 having a cab 12 (containing a driver's seat, driving controls and controls for the various devices forming part of the repair apparatus) and arranged to be driven forward ly, when in use for repair, in the direction of the arrow F. There are shown 4 heaters 1, 2, 3, 4 arranged in a linear array in the direction F (although we prefer to use more heaters, 8 in our prototype, only four are shown for illustration); the heaters are further described below, in connection with Figure 4. Each heater is supported by at least two hanging supports 16 (for clarity only one is referred in the drawing, at the front of heater 3, and those for heater 4 are omitted to allow the large rear wheel of the machine to be seen); the hanging supports 16 depend from either a hanging beam 18 which is a secured to the chassis of the machine 10, or from rolling frames 20. Each rolling frame 20 is removably attached to the front of the machine, either directly
(as in that holding heater 2) or indirectly via the front of a preceding rolling frame (as in that holding heater 1), and has wheels (not shown) to support the weight of the heater and so as to avoid the strains which a cantilevered arrangement would otherwise place on the attachments between frames and between the frame and the machine. At the rear of the machine 10 is a conventional heated screed 22. Between the rearmost heater 4 and the screed 24 is a mixer 26 (described further below in connection with Figure 3, but illustrated in Figure 1 by two circles representing two cylindrical roller agitators in end view), which is fed with aggregate from a conventional hot material hotbox 28, which in turn is supplied with gas for heating the aggregate from an on-board gas supply 30, The machine 10 is adapted to carry the heaters and the rolling frames when these are demounted from the front of the machine, as shown generally at 34,
Figure 2 shows the machine 10 schematically from above, in the process of repairing a longitudinal joint 36 extending between the hard shoulder 40 and the first, or inside, lane 42 of a three lane motorway (there is a middle lane 44 and an outer lane 46, there being similar longitudinal joints between each of these, as indicated by the dotted lines, and on the outside of the outside lane 46 there is a barrier 48 between the two opposing carriageways), Also on the machine 10 there is a bitumen supply 50 which feeds bitumen to the mixer 26 via the hotbox 28 in known fashion. The line of the joint behind the machine 10 is indicated at 52, though in practice this line would be very indistinct, because repairs in accordance with the invention produce an essentially seamless join, and there is a road roller 54 which compacts the repaired joint in the conventional manner, figure 3 shows schematically in plan view the mixer 26; this consists of a frame 60 which has journals to support for first and second shafts 62, 64 to rotate about axes A, A' respectively (as shown by the curved arrows), and which carry first and second cylindrical agitator rollers 66, 68 respectively. The curved surface of each roller 66, 68 is provided with protrusions 70 (for clarity only 2 are shown, in the form of conical studs, however the protrusions can be of any form which is suitable for the purposes of disturbing and lifting the heated asphalt (carried out by roller 66) and for mixing (roller 68)). In use, the mixer is driven along the longitudinal joint being repaired in the direction of arrow F - the asphalt over and either side of the joint having been heated by the preceding heater array. Heated bitumen is sprayed from a slot-style spray jet (not shown) onto the road surface 72 in
advance of the first roller 66; the jet allows for bitumen emulsion (polymer modified, cationic or anionic) to be introduced as required. The bituminous material needs to be heated to a temperature of eighty degrees centigrade or higher. This is achieved using a conventional electrically powered immersion prong fitted into the centre of the bitumen supply tank 50. The flow of bitumen to the jet is controlled via a hydraulically driven positive displacement pump (not shown) adjacent to the heated bitumen tank 50. The speed of flow of bitumen is controlled by increasing or decreasing the hydraulic oil pressure feeding the pump.
As the machine 10 progresses forwards, the first roller 66 disturbs or scarifies the wearing course either side of the joint and also mixes the sprayed bitumen with the disturbed material to an extent. The first roller 66 rotates in the opposite direction to the direction of movement of the wheels of the machine 10 so that, as the machine moves forward, the teeth 70 break up the wearing course and lift some of the disturbed asphalt and the sprayed bitumen up and over the roller, which further mixes the disturbed asphalt material with the heated bitumen. The materials which are carried Over the roller 66 are then deposited back onto the road surface (the materials do not adhere to the roller 66 or the teeth 70 because they are at a sufficiently elevated temperature). Next, a conventional auger (not shown) supplies heated aggregate from the hotbox 28 to the road surface 74 between the first 66 and second roller 68 (which are about 0.24m apart and about 0.2m in width), and as the machine continues moving forwardly the second roller 69 mixes the disturbed asphalt, the bitumen and the newly-supplied aggregate; we prefer that the second roller 69 is driven so as to contra-rotate relative to the first roller 66, as this promotes better mixing and also helps level the mixture of heated materials in advance of the screed 22. The rotation and movement of both rollers are independently governed by hydraulic motors, mounted to the chassis of the machine 10 via hydraulic hoses. As is known, a flowmeter controls the resultant speed of rotation of each roller by increasing or decreasing the flow of hydraulic oil to the motor. The mixer 26 is secured to the chassis of the machine, so as to withstand the stresses resulting from operation of the rollers 66, 68; however, the frame 60 may be mounted so as to be movable reciprocally as indicated by the arrows R (or the shafts 62, 64 may be movable within the frame 60 journals in the same direction), so that the rollers can operate over a greater width (up to about 0.2m either side). It is preferred that the frame 60 reciprocates, because it takes with it the bitumen spray jet and the aggregate feed so that these are equally spread over the width of the repair.
As is conventional, the repaired wearing course is then spread and tampered by the heated screed as the machine 10 continues moving forward, and then compacted finally by the road roller 54,
Figure 4 shows one of the heaters 1 (the others are similar) from Figure 1 in greater detail. The heater 1 (measuring about 2m x lm x 0.5m) has attachments 8 for releasable attachment to hangers 16, and contains a computer controlled gas feed utilising a ferrochrome alloy as a medium to pulse heat into the road surface. This pulsing method causes the asphalt to maintain a constant heat and therefore allows a systematic and controlled heat environment to be created across the treatment area.
The machine 10 moves forward at a variable speed to achieve the optimum temperature for the material content of the area to be treated. This is achieved across a lm wide area of the treatment patch. Screed end temperatures are dependent on the road surface temperatures and moisture content at the time of applying the process. The temperature achieved adjusts the forward motion of the machine. The process is controlled by monitoring the wearing course surface temperature along the heating train. Additionally, the temperatures of the bitumen to be sprayed and of the aggregate in the hotbox are monitored. This information is received by an on board computer which indicates to the operator what adjustments are required in forward speed of the machine 10 (which is mainly determined by the temperatures sensed immediately behind heater 4 and the agitator 26) and the output temperatures of the individual heaters (which are mainly determined by the nature of the wearing course and the depth to which it needs to be heated to effect the repair). Each individual heater 1, 2, 3, 4 is coupled to a temperature sensor continually giving a reading in degrees centigrade of the output of the unit. This is monitored by a central computer which can increase or decrease the heater outputs in degrees centigrade by increasing or decreasing the flow of LPG from the supply 30 to the heater.
It will of course be understood that many variations may be made to the above- described embodiment without departing from the scope of the present invention. For example, the invention has been described in connection with longitudinal joints in roads, however the invention is applicable to any asphalt surface having generally linear joints, such as runways, joins where trenches have been cut in roadways for the purpose of
accessing services under the road (such as water, gas or electricity services) and the like. The invention has been described for the repair of joints between adjacent wearing courses, but it will be apparent to those skilled in the art that it could also be used at the edge of a single wearing course, such as the edge of a roadway, or between a roadway and a kerb, As mentioned above, the heaters forming the linear array may be mounted to either side of the machine; it is not envisaged that the mixer may be easily movable, because It has to be securely mounted to the machine chassis to withstand the stresses resulting from operation of the agitator rollers, and to make the mixer reciprocate the full width of the machine may require excessive supporting structure; we prefer, if the machine is to be used for repairing on either side, to provide two mixers, one on either side. As mentioned above, provision may be made to supply glass fibres to be mixed in with the repair. Glass fibre spools are stored on the machine 10, and may be fed into a cutting device via a stainless steel hollow feed pipe to cut the fibres to the specified length. The cutters are switched on or of using an air feed from the on-board compressor, and the cut fibres are fed to a blower for adding to the mixture at 74. We have described how a reciprocating mechanism could enable 0.2m rollers to repair a greater width (up to about 0.6m, the maximum distance being limited by the width of the heaters); those skilled in the art will understand that the mixer frame 60 could be made wider, so as to accommodate rollers of different widths. In addition to the control process described above, the apparatus could be equipped with a GPS system to ensure that the machine accurately follows the longitudinal joint along its length. The protrusions 70 preferably extend far enough from the cylindrical surface of the rollers to carry out their function (e.g. if they are to disturb or comb the surface to a depth of 50mm then they should be at least 50mm in length; the protrusions may be fitted releasably to the rollers (e.g. screwed into threads in the roller) so that they may be easily changed when then become worn, or exchanged for protrusions of a different size and/or shape. Furthermore, where different variations or alternative arrangements are described above, it should be understood that embodiments of the invention may incorporate such variations and/or alternatives in any suitable combination.