AU2006297059B2 - Method and apparatus for applying hot mix for tar sealed roads - Google Patents

Description

WO 2007/035982 PCT/AU2006/001373 TITLE: METHOD AND APPARATUS FOR APPLYING HOT MIX FOR TAR SEALED ROADS This invention relates to a method and apparatus for applying hot mix for tar sealed 5 roads BACKGROUND OF THE INVENTION 10 In conventional practice, the surfaces of tar-sealed roads are covered by a layer of material comprising a mix of what is known as "aggregate" and bitumen. (,when used in this specification, the term "mix" will refer to a mixture of these materials that is suitable for building and repairing roads, unless it is clear from the context that another meaning is intended). The aggregate comprises stone particles of various graded sizes. 15 If the mixing has been properly carried out, the stones are randomly dispersed in a matrix of the bitumen and the bitumen should be bonded to each stone and should cover as much of the surface of the stone as possible. It is of course nearly impossible to achieve such an ideal mix in practice but it is at least a goal that is aimed at 20 At the present time when a new tar-sealed road is being constructed, the mix is commonly prepared in bulk at a fixed facility remote from the road building site or by a large machine that is transported to, and temporarily set up, at the site. In either case the prepared mix is transferred to a machine that lays the mix down in a continuous layer that is as wide as the road being built. These techniques have been developed 25 over many decades in conjunction with advances in road building methods and machinery. The machines required for building new roads in this way are large and expensive. They are satisfactory for the construction of a new road but it would be impractical and .30 uneconomic to use them for small repairs such as potholes. The repair of potholes thus presents particular problems. Potholes are, by their nature, widely spaced apart and may be many kilometres away from a facility, of the kind discussed above, for preparing an aggregate/bitumen mix. The distance may be such that it is difficult or impossible to keep a mix that has been pre-prepared and transported to the site of a WO 2007/035982 PCT/AU2006/001373 2 pothole, at the correct temperature for use. The problem is exacerbated by the fact that only a small amount of material is required for each pothole. The bitumen and the aggregate are heated when preparing a mix. Bitumen does not 5 flow readily at ambient temperature, and it must be heated to enable it to form a good matrix for the aggregate. The aggregate is heated to drive off residual moisture but also to keep the mix fluent. It is well known that moisture interferes with the bond between the bitumen and the particles in the aggregate. The bitumen and the aggregate are usually preheated separately especially in the large scale plants of the type described 10 above used in the preparation of mix for making new roads. After being heated,'the bitumen and the aggregate are mixed together in a mixing vessel designed for the purpose. It is important that the mix should be at the right temperature (170-180*C) when it is 15 used. It is well established that there is an optimum temperature for good bonding between the aggregate particles and the bitumen. One of the most common causes of poor road construction or a poor repair is the use of a mix that has cooled down or that still contains moisture when it is applied, as this tends to disrupt the bonding. 20 The applicant is aware of several mobile machines that are used in the repair of potholes. Most of these comprise a truck- or trailer-mounted insulated vessel for holding a hot mix that has been preprepared and loaded into the vessel. The apparatus may be provided with a small heating device, fuelled by LPG or diesel oil, for keeping the mix hot. These machines are not able to heat a bitumen mix from cold to 1800 and 25 most of them do not have any mixing devices. The applicant is aware of two mobile machines that do have mixing devices. However, the applicant believes that the disadvantages associated with the use of these machines, the construction and operation of which are discussed below, are such that they have 30 not found widespread use. In any case, the applicant believes that the mix for repairing potholes is still most often prepared by methods that have been used for many years. In one such method, commonly used in less developed countries, the mix is prepared by hand at the site where the potholes occur. The aggregate and the bitumen and placed in a suitable receptacle that is heated, using a fire or other suitable heater. The heated mix WO 2007/035982 PCT/AU2006/001373 3 is then shovelled into a wheelbarrow or the like and taken to the pothole. In bigger jobs, the mix is prepared in a larger receptacle and loaded into a suitable truck for transport to the work site which may sometimes be perhaps 100 km distant. Here, it is tipped or hand shovelled into the potholes. In another method, the mix comprises 5 aggregate added to a proprietary material comprising a bitumen base and emulsifying additives which renders the material fluent at a much reduced temperature. The mix is at this reduced temperature when applied to the pothole. Both of these methods have their problems. It is practically impossible to mix the 10 materials properly by hand in the manner discussed above and the applicant believes that the use of cold mixes comprising proprietary materials of the type discussed above results in poor quality repairs. Nevertheless, they remain in widespread use notwithstanding the availability of mobile mixing machines of the.type mentioned above. 15 One of the mobile machines mentioned above comprises, in essence, three vessels mounted on a trailer chassis that can be hooked on to a truck or other towing vehicle. The aggregate is heated in one of the vessels and the bitumen is heated in the second vessel. The first and second vessels arc thus heating vessels. The heated materials are 20 transferred to the third vessel. This is a mixing vessel and in it the materials are mixed together by rotating paddles provided for the purpose. The mixing vessel is provided with a gate through which the mixed materials can be discharged by gravity into a wheelbarrow or the like. 25 One disadvantage of this machine is that the components that handle the bitumen, i.e. the heating vessel, the mixing vessel and the associated pump and pipework by which the heated bitumen is transferred to the mixing vessel, must be cleaned after each use of the machine. The cleaning operation can typically take an hour or even two. If the machine is not cleaned and the hot bitumen or hot mix has been allowed to cool in the 30 pump and pipework or the mixing vessel, it is very laborious and time consuming to clear them. Another disadvantage of this machine is that the heating vessel for the aggregate is of the type that comprises a cylindrical shell that is supported on rollers and rotates about WO 2007/035982 PCT/AU2006/001373 4 a horizontal axis. A measured quantity of aggregate is charged through an inlet aperture formed in a plate located at one end of the shell. The aggregate is heated as the shell rotates and is discharged through an outlet aperture formed in a second plate at the opposite end of the shell. Both of the apertures have gate-type closures to retain 5 the aggregate in the shell as it rotates. The shell is heated by burners that are located inside the shell above the aggregate. The outlet aperture is located adjacent the bottom of the shell to allow the aggregate to flow out of the shell by gravity. The inlet aperture is located well below the top of the shell. The heated moisture forms steam and, in the applicant's experience, it is difficult for the steam to exit the shell efficiently due to the 10 fact that the apertures are normally closed by the gates and are located below the top of the shell. The result is that the aggregate is often not properly dry when it leaves the shell or, at best, the aggregate must be held in the shell for longer than is necessary in order to ensure that it is properly dry., 15 In the second mobile machine known to the applicant, mentioned above, a truck is provided with a tipping body into which .a mix that has been preprepared is tipped. The floor of the body comprises two flat surfaces that run the length of the body and slope upwardly on each side of the fore-and-aft centreline of the floor. Two heater tubes and two rotating agitator shafts are mounted in the body, running the length thereof. The 20 shafts have screw-type flights that convey hot mix material that gravitates into their path in the fore-and-aft direction of the body and thus perform a mixing function. Hot gas from an LPG burner carried on the vehicle flows through the tubes. The body has an open top provided with covers. The body and the covers are insulated. An aperture is provided in the rear wall of the body. The hot mix is discharged through this 25 aperture when the body is tipped. This machine has three disadvantages. The heating arrangements are insufficient to heat a full load of mix from cold to I 80"C in any practical sense and it is thus again necessary to ensure that the vessel is cleaned before it is allowed to cool. Second, the 30 agitator shafts do not perform the mixing function with any great efficiency with the result that some parts of the mix are liable t6 be too cold and other parts too hot. A third disadvantage is that the bearings of the agitator shafts are liable to failure as a result of the stresses that they undergo due to the thermal expansion of the agitator shafts.

5 Although the mixing process is apparently simple, well-known techniques have been developed in order to achieve a good quality mix. For example, it is known that the quality of the mix can be improved by adding the particles of each size in sequence to a batch of aggregate that is being dried. Often the sequence is starts with the largest size 5 and progresses to the smallest size (which is, essentially, dust). The bitumen is best added after some of the dust has been added and the batch is properly dry. More dust can then be added to bring the mix to the right consistency. The sequence is also sometimes reversed. It is not possible, in a practical sense, to use these techniques with the mobile machines described above. 10 STATEMENTS OF TIE INVENTION According to the invention, there is provided apparatus for preparing a hot mix 15 comprising aggregate and bitumen, the apparatus comprising a vessel incorporating a mixing chamber arranged to receive aggregate and bitumen, means for mounting the vessel on a vehicle, heating means arranged to heat the aggregate and bitumen, and mixing means for mixing the aggregate and bitumen to form a hot mix, the vessel comprising a shell with a cross member located at what, in use, is the lower end of the 20 mixing chamber, and the mixing means comprising a rotor that can be rotatably mounted on the cross member for rotation about a rotational axis that is disposed longitudinally in the shell and is arranged to carry at least one mixing member that is disposed transversely to the rotational axis and, as the rotor rotates, describes a path that substantially spans the space between the rotor and the shell. 25 According to one aspect of the invention, the shell is of right-circular cylindrical shape and the rotational axis is coincident with the longitudinal axis of the shell. In another aspect of the invention, the shell is mounted on the vehicle in a vertical 30 disposition.

6 In one form of the invention, the rotor comprises a rotatable shaft and the apparatus comprises a bearing arrangement that is mounted on the cross member and in which an end of the shaft rotates. 5 In one aspect of the invention, the bearing arrangement comprises an opening such that material from the mixing chamber that passes between the shaft and the bearing arrangement can pass back into the mixing chamber. In one form of the invention, the apparatus comprises a drive arrangement for rotating the 10 rotor, the drive arrangement comprising a driven rotary member in which is formed a passage through which the rotor projects, the passage and the rotor being complementarily out-of-round so that the rotor is able to slide axially in the passage while being driven by the rotary member. 15 According to yet another aspect of the invention, the vessel is mounted so as to be stationary on the vehicle when the aggregate and bitumen are being heated and mixed. Advantageously, according to the invention, the vessel comprises a second chamber located adjacent the mixing chamber, the heating means being located in the second 20 chamber. It is envisaged that the vessel could be mounted on a vehicle that is self propelled or that is in the form of a trailer that is towed by second vehicle. The trailer would advantageously be provided with an engine or other means for powering the mixer and 25 tilting mechanism. The intended use of the apparatus has important effects on various aspects of its design. A vital feature of the apparatus is that it should be able to transport the mix from a locality at which the vessel is charged with the ingredients of the mix and the work site 30 where the mix is discharged. It is highly unlikely that the use of public roads could be avoided in this task and the size of both the vehicle and the vessel will be at WO 2007/035982 PCT/AU2006/001373 7 least partially determined by this, since the size of any vehicle that uses a public road is limited by regulation. Furthermore, the apparatus is intended primarily for use in repairing roads, rather than for building new roads, although a vehicle for the latter purpose is not necessarily excluded from the scope of the invention. Consequently, it is 5 highly desirable that the vehicle should be very manoeuvrable at the work site and this will also affect the size of the vehicle, the length of its wheelbase and the like. Furthermore, again because of the primary intended use of the vehicle, the heating means should advantageously be designed to heat the ingredients from the ambient to 10 the minimum mixing temperature in a reasonably short period of time that is affected at least partially by the time taken for the vehicle to transport the load from the locality at which the vessel is charged with the ingredients of the mix to the work site where the mix is discharged. The maximum kW output of the heater will therefore need to be relatively large, and this maximum will increase with the volume of the ingredients. 15 that the vessel is capable of holding. However, both the maximum heat output and the volume of ingredients will be limited by the size of the vehicle, as already noted. A detailed description is given below of a vessel mounted on a vehicle that are both considered, at the present time, to be of optimum size. The sizes given are merely 20 examples and there is no intention that the scope of the invention should be limited to a vehicle and vessel of these sizes. The vessel in the example is smaller than the maximum presently envisaged according to the invention or the maximum as determined by the parameters discussed above. One reason for this difference in sizes is that, as should be obvious, as the apparatus gets bigger, it also becomes more 25 expensive and less manoeuvrable. The size of the necessary heater also increases and it may become more difficult to provide a heater with sufficient output to heat the mix in a reasonable time. So the overall usefulness of a larger vehicle and vessel may be diminished. 30 The applicant believes that the road regulations in most countries would limit the volume of the vessel to about 8 cubic metres and that a heater for heating the charge in a vessel of this size would be of ti'e order of 200kW. In the example of the invention given below, the apparatus is provided with a gas heater with an output of about 75kW. This is considered sufficient to heat a mix having a volume of about 0.7 cubic WO 2007/035982 PCT/AU2006/001373 8 metres. Although not to be excluded from the scope of the invention, it is considered unlikely, at the present time, that apparatus constructed according to the precepts of the invention and requiring a heater of 200 kW output would be commercially or practically viable, at least for repair work on roads as opposed to the building of new 5 roads. At least one reason for this is that it is likely to be difficult and expensive to design a vehicle which would be practical to operate, and which would not be damaged by the heat radiated by an apparatus of this size It is also likely that apparatus that is constructed and used in accordance with the 10 present invention but that is of less than a certain capacity will be uneconomic to operate. For instance, an apparatus that is of smaller size than that described with reference to the drawings should not necessarily be excluded from the scope of the invention. 15 The smallest and largest size of an apparatus that has commercial value will be determined by demand in the market place. BRIEF DESCRIPTION OF THE DRAWINGS 20 The invention is further discussed with reference to the accompanying drawings in which a vehicle for use in road repair is illustrated by way of example, and in which Figure 1 is a somewhat schematic side elevation, partly in section, of a vehicle 25 fitted with a vessel for preparing a road mix; Figure 2 is a plan view of the vehicle also partly in section of the vehicle shown in Figure 1; Figures 3 and 4 are enlarged sectional views of two bearing arrangements with which the vessel is provided; 30 Figure 5 is a view on arrows A-A in Figure 4; and Figure 6 is a view in elevation of a paddle arm In the description that follows, only those parts of the vehicle and vessel that are relevant to the present invention will be described in detail. Furthermore, the design WO 2007/035982 PCT/AU2006/001373 9 and construction of many parts of the vehicle and vessel are either known or would present no difficulty to those skilled in the art. In some cases, these parts are commercially available. Parts that are not shown in the drawings fall into these categories unless it appears otherwise from the context. 5 Referring to the drawings, there is shown a vehicle 10 having a pair of front wheels 12 and a pair of rear wheels 14. The vehicle is propelled by the front wheels and steered by the rear wheels. A vessel 16 is mounted on the front of the vehicle 10. The vehicle comprises a chassis or frame 18 on which is mounted an engine 20 housed in a bonnet 10 22. In the present example, the engine is a diesel engine of 34 h.p. The engine is located at the rear of the vehicle and is coupled to a hydraulic pump assembly 24. A seat 26 for the driver is mounted to one side of the engine. The driver thus sits at the rear of the vehicle, facing forward in an optimum position to view the operation of the vessel. As no cab is provided, the driver sits in the open, behind a steering wheel 28 15 supported by a bracket 30. The vehicle in this example is about 3.3 metres long and 2.0 metres wide. The vessel 16 comprises an inner steel shell 32 with a right circular cylindrical body and, at its upper end, a dome shaped cross member that will be referred to as the top 20 wall 36. A cylindrical outer shell 38 surrounds the inner shell with a space therebetween forming an annular passage 40 between the two shells. The shell 32 incorporates an upper chamber 42 that in use functions as a mixing chamber in which aggregate and bitumen are mixed together, as will be described. The upper chamber is separated from a second, lower, chamber 44 by a floor comprised of two dome shaped 25 cross members that will be referred to as cross walls 46, 48 located one above the other. Mixing means is the form of rotor comprising a paddle assembly 50 mounted on a shaft 60 is located in the upper chamber and heating means in the form, in this case, of a-gas ring 52 is located in the lower chamber, supported by a cross member 54. In the lower chamber, apertures 56 are formed in the wall of the shell 32. Via the annular 30 passage 40, the apertures connect the lower chamber to chimneys 58 spaced around the domed top 36. The paddle assembly 50 comprises a pair of mixing members in the form of paddle arms 50a, 50b. The paddle arms are mounted in alignment with each other on opposite WO 2007/035982 PCT/AU2006/001373 10 sides of the shaft 60, which is of square cross section. The shaft is disposed longitudinally the shell. The shaft is carried in bearing arrangements mounted on the upper cross wall 46 and in the top wall 36 respectively and rotates about a rotational axis X that is coincident with the longitudinal axis of the shell that, in the present 5 example, is vertical. The upper end 60a of the shaft projects through a drive arrangement 62 that, in this example, comprises a driven rotary member in the form of a gear wheel 66 driven by a worm. The worm is coupled to a hydraulic motor 70 driven, through suitable hydraulic 10 lines and controls to the pump assembly 24. The gear wheel 66 is integral with the outer race 72a of a roller bearing assembly 72 the inner race 72b of which is bolted to the floor of the gearbox housing 74. The gearbox in turn is bolted to the top of a pedestal assembly 36a that is mounted on the top wall 36 of the vessel. The outer race is bolted to a circular collar plate 76. The bearing assembly 72 and the collar plate are 15 parts of the upper bearing arrangement for the shaft 60. The collar plate is provided with a central passage 78 that is of square cross sectional shape of size complemental to the shaft 60 and such that, when the gear wheel rotates, the collar plate engages the shaft, forcing it to rotate also. However the shaft is also able to slide up and down in an axial direction in the passage 78. This is important as the shaft undergoes considerable 20 such axial movement up and down as the apparatus heats up and cools down. This axial movement is as much as 30 mm in the present example. It is not essential that the shaft 60 and the passage 78 be of square cross sectional shape but this shape is probably the most practical. Any suitable out-of-round shape could be used. 25 The lower end 60b of the shaft is machined so that it is round and is received in the lower bearing arrangement 64. This arrangement comprises a vertically disposed sleeve 80 that in use functions as a bearing bush for the lower end of the shaft. The sleeve is supported above the cross wall 46 on four legs 82 that are welded to the sleeve and to the- cross wall 46. The legs are equally spaced about the periphery of the 30 sleeve. There is thus a space 84 between the lower end of the sleeve and the cross wall and there are gaps 86 between each pair of the legs. Additionally, openings in the form of vertical slits 88 are formed in the lower end of the sleeve 80. These slits are open to the gaps 86 between the legs 82.

WO 2007/035982 PCT/AU2006/001373 11 In use, material from the aggregate and bitumen that is being mixed in the mixing chamber migrates, principally under the force of gravity, between the lower end 60b of the shaft and the sleeve 80. It has been found that this material has a tendency to build up in the sleeve and, in the absence of means to prevent it, eventually causes the shaft 5 to seize. The build up is prevented by the presence of the space 84 and the slits 88 which function as openings through which the material is able to exit the sleeve through the gaps 86 and back into the mixing chamber. In the present example the diameter of the lower end of the shaft is about 58 mm and 10 the internal diameter of the sleeve 80 is about 61 mm. There is thus considerable clearance therebetween. This is necessary to accommodate the considerable changes in size of the components due to thermal expansion and contraction. It has been found in practice that, at it's centre, the cross wall 46 is typically lifted by about 30 m due to thennal expansion as it heats up to working temperature. 15 The paddle arms 50a, 50b that are similar to each other and only one is described in detail. The arm 50a is fabricated from a steel plate 98, tapered inwardly from its inner end to its outer end and- reinforced by a rib 100 that is welded to the approximate centre of the face 102 of the plate and runs along the entire length thereof. At its inner 20 end, the plate 98 is welded to an upstanding rectangular mounting plate 104 with boltholes drilled in each corner. The paddle arms are mounted on the shaft 60 by means of bolts 108 that pass through the holes and clamp the respective mounting plates against opposite faces of the shaft. Two upstanding paddle plates 11 Ga, 11 0b of approximately trapezoidal shape are welded to the face' 112 of the plate 98. Wearing 25 shoes 114 may be welded to the lower edges of the respective paddle plates. The width of each paddle plate is about a quarter of the length of the plate 98. The paddle plates 10 Oa, 110b on the arm 50a are mounted on the plate 98 with a space 116 between them approximately equal to the width of each paddle plate. The paddle plate I 10a is mounted at the outer end of the plate 98. The space 118 between the paddle plate 110b 30 and the mounting plate 104 is thus again approximately equal to the width of each paddle plate. The paddle arm 50b is substantially similar to th'e paddle arm 50a with the exception of the positioning of the paddle plates. While the paddle plates of the arm 50b are also WO 2007/035982 PCT/AU2006/001373 12 mounted with a space 1 16a between them approximately equal to the width of each paddle plate, the inner paddle plate of the arm 50b is located close to the mounting plate 104 of that arm. The result of this arrangement is that, when the shaft 60 is rotated, the paddle plates between them sweep the entire diameter of the shell 32 and 5 the cross wall 46. The paddle plates are shaped and mounted on the arms 50a, 50b in such positions that the wearing shoes are located close to, and parallel with, the domed upper cross wall 46. The outer ends of the paddle arms are located close to the inner face of the shell 32. 10 As the rotor rotates, each paddle arm thus sweeps through a path that substantially spans the space between rotor and the shell 32. Furthermore, the path swept by the paddle arms jointly is substantially coincident with the upper surface of shell floor. The tops of the paddle plates are located close to the top of a full load of aggregate in the mixing chamber. Virtually all of the load is thus subject to the mixing action of the 15 paddle assembly during each revolution of the rotor and the mixing action is thus highly efficient. This action is most efficient when the shell is right circular cylindrical. A shell of this shape is also likely to be the most economical to produce. However, shells of other shapes are not necessarily excluded from the scope of the invention. A shell of square shape could also conceivably be used. In this case, the path swept by 20 the paddle arms would best span the smallest space between the rotor and each vertical wall of the shell. This space would extend between the rotor and the centre of the vertical wall. An aperture in the form of a manhole 120 is provided at the fronL of the domed top 25 wall 36. Aggregate and lumps of bitumen in solid condition are shovelled into the upper chamber through this manhole, as will be described. Discharge means are provided in the form, in the present example, of a closable aperture or manhole 122 is provided low down at the front of the shell, adjacent the 30 upper cross wall 46. The manhole is closed by a manually operated, guillotine type gate 124. A chute 126 is mounted adjacent the manhole 122. When the aggregate and bitumen have been properly mixed and heated to the correct temperature in the upper chamber, the mix can be discharged through the manhole and onto the chute.

WO 2007/035982 PCT/AU2006/001373 13 The heater 52 is a two ringed gas burner fed from twin gas cylinders 128 through suitable hoses. In the present example, the heat output of the burner is of the order of 75 kW, as already noted. The domed shape helps to prevent thermal distortion of the cross walls 46, 48. Notwithstanding the domed shape, in the absence of the lower cross 5 wall 48, the heat from the burner would be likely to overheat the upper cross wall 46, causing it to distort. The two cross walls are located close together in order to maximise heat transfer and the presence of the lower cross wall 48 helps to spread the heaL and avoid hot spots in the upper cross wall 46. 10 A layer 130 of suitable insulating material is placed around the outside of the shell 38 to reduce heat loss. The insulating material is held in place and protected by a steel shell 132. The hot gases from the burner pass through the apertures 56 in the shell 32 and out through the chimneys 58 via the annular passage 40. These gases heat the wall of the shell 32 and the heat is transferred to the mix in the upper chamber. 15 The vessel 16 is mounted on the frame 18 so as to be capable of tilting forward about a hinged connection 134 located at the front edge of the frame. The tilting is brought about by a hydraulic ram 136. The lower end of the ram is mounted 6n the frame through a pin seated between trunnions 138 welded to the frame. The upper end of the 20 ram is similarly mounted on the vessel through a pin seated between trunnions 140 welded to the shell 38. The ram is actuated by the driver through suitable controls, not shown. As should be clear, the vessel remains stationary on the frame while the aggregate and bitumen are being heated and mixed. 25 A safety barrier may be mounted on the front of the vehicle, surrounding the front of the vessel 16. The barrier comprises a series of steel stanchions 144 welded to the frame 18 at their lower ends and carrying rails 146 welded to their upper ends. The barrier is intended primarily to prevent damage to the vessel in the event that the vehicle collides with objects around a work place. One example of such an object is 30 the back of a delivery vehicle that carries aggregate and/or raw bitumen. It would often be convenient to shovel the aggregate or bitumen directly into the vessel from the delivery vehicle and the two vehicles would be brought together for the purpose.

WO 2007/035982 PCT/AU2006/001373 14 The vehicle is obviously provided with the controls necessary for its operation. These controls would include a temperature gauge, visible from the driver's seat, for checking the temperature of the mix; and a regulator for controlling the flow of gas to the burner. 5 In use, stocks of raw bitumen and stones for aggregate are brought to a convenient place in the vicinity of where there are potholes in a tar-sealed road. For practical purposes, raw bitumen is solid at ambient temperature and the bitumen in the stock is broken into lumps that can pass through the manhole 120. The stones should 10 advantageously, but not essentially, be graded according to their size and left in separate stockpiles. All this is well known to experienced operators. The vehicle 10 illustrated in the drawings has a maximum travelling speed of about 12 km/h. This would be one of the factors that would determine how far away the stockpiles can be from the furthest pot hole that must be repaired. If the travelling speed renders the 15 working range of the vehicle unacceptably low, the vehicle 10 can be carried to the work place on the back of a truck or trailer capable of a higher speed. An alternative example of an apparatus according to the invention would be a vessel similar to the vessel 16 mounted directly on a vehicle in the form of a trailer that is towed by a second vehicle. This second vehicle could be a commercially available truck and 20 would usually be capable of a much higher speed than 12 km/h. The vehicle 10 is taken to the stockpiles where, in one method of use, first the aggregate is loaded into the upper chamber 42 through the manhole 120, while the mixer 50 is rotating and the burner lit. An experienced operator will know the 25 sequence in which the material should loaded. This has been discussed above. Such an operator will also know how long mixing and heating of the aggregate should be continued. Mixing is continued until the mixed aggregate is dry and has been brought up to the correct temperature. At this stage lumps of solid bitumen, conveniently at ambient temperature, are loaded by hand through the manhole 120. When the bitumen 30 has melted and is well mixed with the aggregate, a further small quantity of dust may be added to bring the mix to the correct consistency for use. It should be stressed that, instead of loading one grade of aggregate after the other, it is possible to use a premixed composition of several aggregate sizes and dust and then WO 2007/035982 PCT/AU2006/001373 15 add the bitumen. It is also possible, instead of adding the bitumen in solid (cold) form, it can be added in preheated, liquid form. It is an advantageous feature of the present invention that the manhole 120 is located 5 close to the top of the vessel. This enables substantially all of the moisture driven off the aggregate to escape to atmosphere as efficiently and quickly as possible. This feature is made possible by the fact that the vessel is stationary in use. Based on these parameters, the vessel and the shaft are most suitably vertically, or at least uprightly, disposed. 10 The mixer 50 continues to rotate while the vehicle is driven or taken to a selected one of the potholes to be repaired. The burner remains lit to keep the mix at the correct temperature. At the work site, the driver manoeuvres the vehicle so that the chute 126 is over the selected pothole and actuates the ram 136 to tilt the vessel 16 upwards and 15 forwards about the hinge 134. A second operator lifts the gate 124 to allow the required amount of hot mix to flow out of the vessel and over the chute from where it is deposited in the pothole. The driver returns the vessel to the upright position and backs the vehicle away from the pothole. The hot mix in the selected pothole is worked in known manner to complete the repair. 20 In the present example, the internal diameter of the shell 32 is 126 cm. The vertical distance between the upper cross plate 40 and the domed top 36 is 75 cm, and the distance from the bottom of the shell to the upper cross plate 40 is 30 cm. These dimensions are taken at the centre of the shell. The volume of the upper chamber 36 is 25 thus about 930 litres. This is sufficient for a charge of about 700 litres of aggregate and bitumen. The width of the annular passage 40 is 30 mm and the distance between the shell 38 and the shell 132 is 60 mm. The wall thicknesses of the shells 32, 38 and 132 are 6, 3 and I mm respe3ctively. The overall diameter of the vessel is thus about. 156 cm. This is less than the maximum width of the vehicle 10. The highest point on the 30 vehicle, with the vessel mounted in place, is at the top of the vessel and is about 203 cm above the road surface. The vehicle is thus well within the height.and width limits for vehicles to be allowed on the public roads of most countries without a special permit.

WO 2007/035982 PCT/AU2006/001373 16 The manhole 120 for filling the vessel is about 177 cm above the ground and the manhole 122 through which the mix is discharged is about 73 cm above the ground. There is no serious disadvantage in allowing any mix remaining in the mixing 5 chamber when a job is completed to coot and become solid as the mix can be made fluent again simply by heating. There is no pump or pipework to be cleaned at the end of a shift and, if necessary, the mixing chamber can easily be cleared by working through the manholes. 10 It may be noted that the machines constructed according to the precepts of the invention can be used to heat bitumen only or bitumen mixed with quarry dust in a certain percentage to repair, fill or seal cracks in the bitumen layer, of roads to prevent water from destabilizing the roadbase. The same machines can also be used to seal roofs, expansion gaps in concrete roads and slabs. 15 It is not intended that -recognised mechanical equivalents of and/or modifications of and/or improvements to any matter described and/or illustrated herein should be excluded from the scope of a patent granted in pursuance of any application of which this specification forms a part or that claims the priority thereof or that the scope of 20 any such patent should be limited by such matter further than is necessary to distinguish inventive matter disclosed herein from the prior art.

Claims (9)

1. Apparatus for preparing a hot mix comprising aggregate and bitumen, the apparatus 5 comprising a vessel incorporating a mixing chamber arranged to receive aggregate and bitumen, means for mounting the vessel on a vehicle, heating means arranged to heat the aggregate and bitumen, and mixing means for mixing the aggregate and bitumen to form a hot mix, the vessel comprising a shell with a cross member located at what, in use, is the lower end of the mixing chamber, and the mixing means comprising a rotor that can 10 be rotatably mounted on the cross member for rotation about a rotational axis that is disposed longitudinally in the shell and is arranged to carry at least one mixing member that is disposed transversely to the rotational axis and, as the rotor rotates, describes a path that substantially spans the space between the rotor and the shell. 15

2. Apparatus according to claim 1, in which the shell is of right-circular cylindrical shape and the rotational axis is coincident with the longitudinal axis of the shell.

3. 20 Apparatus according to claim 1 or claim 2, in which the shell is mounted on the vehicle in a vertical disposition.

4. Apparatus according to any one of claims I to 3, in which the cross member is dome 25 shaped.

5. Apparatus according to claim 4, in which the rotor comprises a rotatable shaft and the apparatus comprises a bearing arrangement that is mounted on the cross member and in 30 which an end of the shaft rotates. 18

6. Apparatus according to claim 5, in which the bearing arrangement comprises an opening such that material from the mixing chamber that passes between the shafn and the bearing arrangement can pass back into the mixing chamber. 5

7. Apparatus according to any one of claims 1 to 6, comprising a drive arrangement for rotating the rotor, the drive arrangement comprising a driven rotary member in which is formed a passage through which the rotor projects, the passage and the rotor being 10 complementarily out-of-round so that the rotor is able to slide axially in the passage while being driven by the rotary member.

8. Apparatus according to any one of claims 1 to 7, in which the vessel is mounted so as to 15 be stationary on the vehicle when the aggregate and bitumen are being heated and mixed.

9. Apparatus according to any one of claims 1 to 8, in which the vessel comprises a second chamber located adjacent the mixing chamber, the heating means being located in the 20 second chamber.