CA2042000A1 - Method and apparatus for repaving asphaltic pavement - Google Patents
Method and apparatus for repaving asphaltic pavementInfo
- Publication number
- CA2042000A1 CA2042000A1 CA 2042000 CA2042000A CA2042000A1 CA 2042000 A1 CA2042000 A1 CA 2042000A1 CA 2042000 CA2042000 CA 2042000 CA 2042000 A CA2042000 A CA 2042000A CA 2042000 A1 CA2042000 A1 CA 2042000A1
- Authority
- CA
- Canada
- Prior art keywords
- strip
- asphalt
- pavement
- asphaltic pavement
- heating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Abstract
ABSTRACT
An asphaltic pavement preconditioning machine to remove and grind up old asphalt so that it can be rejuvenated. The method and apparatus heats a strip of asphalt, grinds a first strip portion and moves the ground asphalt to a second strip portion leaving behind an exposed unruptured, unsoftened layer. Both the ground material and the previously heated unground asphalt in the second strip are then ground. The exposed hard asphalt in the first strip is heated, softened and then ground and moved onto the first strip portion. The heat from the ground asphalt lying over the centre strip portion softens the unground asphalt there which is subsequently ground together with the ground material and left for further processing. At least three heating and grinding steps are effected so that the depth of asphalt requiring softening by heat is approximately 1/2 to 5/8 inches and smoke emission is substantially lower than prior methods.
An asphaltic pavement preconditioning machine to remove and grind up old asphalt so that it can be rejuvenated. The method and apparatus heats a strip of asphalt, grinds a first strip portion and moves the ground asphalt to a second strip portion leaving behind an exposed unruptured, unsoftened layer. Both the ground material and the previously heated unground asphalt in the second strip are then ground. The exposed hard asphalt in the first strip is heated, softened and then ground and moved onto the first strip portion. The heat from the ground asphalt lying over the centre strip portion softens the unground asphalt there which is subsequently ground together with the ground material and left for further processing. At least three heating and grinding steps are effected so that the depth of asphalt requiring softening by heat is approximately 1/2 to 5/8 inches and smoke emission is substantially lower than prior methods.
Description
3 ~ ~
METHOD A~D APP~RATU~3 FOR REP~VING ~SPHl~LTIC P~VEMENT
BACKGROUND
The present application relates to a multi-stage apparatus and process for in-place recycling of asphaltic pavement without the need to remove the asphalt to a remote reconditioning plant and then return it for use in repavlng.
Single stage units which heat asphaltic pavement, rupture an upper layer of the surface, remove it from the road surface, pulverize it ancl then place it back on the road surface are ]cnown. Such units, however, can not recycle more than approximately the top inch of asphalt because of the difficulty in heating the asphalt to a greater depth. The time to heat asphalt to a given temperature at a given depth depends on the square of the depth. Thus, it takes four times as long to heat a 1/2 inch layer of asphalt to a given average temperature than it does to so heat a onr inch layer.
One early solution offered by U. S. Patent Number 4,545,700 issued October 8, ~9~5 to Yates was to employ a plurality of stages of heating and milling or grinding the heated asphalt. After each stage of heating and milling the ground asphalt is removed from the road surface either by windrowing the ground asphalt off to the sides of that portion of the road surface being processed or by windrowing it up onto spaced apart collection chutes along which the asphalt moves until it reaches the next milling stage. ~indrowing the yround asphalt to the side tends to contaminate the asphalt with dirt as well as getting in the way of oncoming traffic, depending on which side the asphalt is windrowed. The disclosure showing the material onto chutes is purely schematic as there is no practical way of holding the asphalt from spilling off of the sides or moving it along the surface of each of the chutes. In ~ ~.J ` ~
practice Yates Corp. used a conveyor to pick up the material from the roacl surface and carry it over the next stage of heaters. It is the latter conveyor which creates significant problems due not only to its cost and high maintenance requirements but also by the amount oE space it takes up. Due to the conveyors, ~ates was able to include only a limited lenyth oE heaters for each staye, otherwise his vehicle would have been excessively lony. Thus, he was able to heat and remove only about 1/4 inch of asphalt per staye for a total of one lnch for his four stage machine.
It is normally desirable to remove and recondition at least the top 1 1/2 inches of asphalt.
Canadian Patent Number 1,264,422 issued to Wiley and Rorison discloses a two stage process very similar to Yates which also uses a conveyor. The latter machine removes one inch per stage by employiny banks of infra red heaters on each of two separate vehicles, one vehicle being used for each stage of heating and milling. Even then in order to heat the asphalt sufficiently to soften it down to a depth of one inch and still be able to travel at about 20 feet per minute, the practical minimum, it is necessary to raise the temperature at the top surface of the asphalt to 600 to 700 degrees Fahrenheit. Such high temperatures burn the asphalt at the surface ancl create significant amounts of smoke. An additional problem in the Wiley et al.
method is the requirement of a conveyor in the second stage to carry the first stage ground material over the second stage heaters. It is the latter conveyor which limits the length of heaters possible in the second stage without the second stage vehicle being excessively long. Thus, even though the first inch of asphalt is heated marginally sufficiently, heating of the lower second inch by the second stage heaters is inadequate.
U. S. Patent Number 4,850,740 issued on July 25, - 3 - ~ 3~7 1989 to Wiley discloses a method which allows the conveyor to be eliminated altogether and to use a longer bank of heaters in the second s-tage machine. Wiley '740 utilizes the heated windrowed material to heat a central unground lower layer of aspha]t without the need for infra red heaters to heat that portion. Except for the first stage heater, such heaters are only required for the side strips from which the milled asphalt is windrowed. Both Wiley'740 and the Canadian Patent issued to Wiley disclose removing one inch per stage for a total of two inches. However, heating down to one inch requires either long heaters or relatively slow operation or both. Attempts to run the machines faster results in insufficient heating and a greater number of rock fractures which degrade the quality of the repaving.
Raising the temperature of the heaters causes burning of surface asphalt and results in the creation of unacceptably large amounts of smoke. There is at the present time considerable concern that such smoke is carcinogenic. There is, therefore, a need for a method and apparatus for repaving which produces substantially less smoke than known methods and machines and which can recondition down to at least two inches of depth while maintaining a speed of operation of twenty feet per minute or more.
Accordingly, it is an object of the invention to provide an improved method and apparatus for recycling and repaving asphaltic pavement. It is a further object of the invention to provide a method and apparatus for repaving asphaltic pavement which produces less smoke than known machines and, at the same time, is capable of operating as fast or faster than known methods and machines.
~ 3 1 1 SUMMARY OF THE INVENTION
The present invention provides an asphaltic road surface repaving apparatus of a type that removes asphalt from the surface of the road, conditions it and reapplies it to the road surface as the apparatus progresses along the road. The apparatus includes first staye radiant heating means for heatiny a first layer of a strip of asphaltic pavement, firs-t rupturing means for rupturing asphalt in the first heated layer and windrowing the ruptured heated asphalt onto a remaining portion of the strip of the asphaltic pavement. Second stage radiant heating means heats an exposed second layer of asphaltic pavement in the remaining portion of the strip. That portion of a third layer of asphaltic pavement below the windrowed material is heated by conduction from the heated windrowed material. A third stage radiant heating means is provided for heating a third layer of exposed unruptured asphaltic pavement in a remaining portion of the strip.
Third rupturing means is also provided for rupturing the third layer of previously unruptured asphaltic pavement.
A repaver is used for levelling the ruptured asphaltic pavement over the strip and then rolling it to form finished pavement.
By simply windrowing ground material from one stage onto a selected strip of the road surface being processed and using the heat from the windrow to conductively heat the underlying unground road surface rather than picking up the windrow in a conveyor and radiantly heating the whole road surface being processed, the need to incorporate a conveyor at each stage is avoided. Moreover, by multiplying the number of stages to a-t least three, it is possible to reduce the thickness of road surface layer heated, ruptured and windrowed in each stage and therefore ~ 5 - ~?~
to reduce the temperature to which the surface of the road is raised to as low as 350 degrees Fahrenheit. The total depth of asphaltic pavement that is conditioned is at least 1 1/2 inches. The spaciny between the first, second and third rupturing means is such that heat from the heated, xuptured, windrowed asphaltic pavement in each of the windrows conducts downwardly into the underlying unruptured asphaltic pavement below the windrows to soften the latter prior to being ruptured by subsequent rupturing means.
~ dvantageously, the third rupturing means moves the ruptured asphaltic pavement onto the windrow portion of the strip. A fourth stage radiant heating means may be pro~ided after the third rupturing means for heating a fourth layer of exposed unruptured asphaltic pavement in the remaining portion of the strip and fourth rupturing means for rupturing the fourth layer of previously unruptured asphaltic pavement.
Preferably the method includes heating the entire road surface being processed until a preselected depth is softened, rupturing and windrowing the ground asphalt onto a centre strip portion. Next the two exposed side strip portions are heated until softened and ruptured. The ruptured asphalt then is moved onto the centre strip portion which separates the two side strip portions. The unground asphalt in the centre strip portion is ground and the two side strip portions are again heated to soften the asphalt therein. The softened asphalt in the two side strip portions is again ground and moved onto the centre strip portion. Finally the unground asphalt in the centre strip portion is ground and left for further processing.
The foregoing heating, rupturing and windrowing steps are repeated at least one more time until a depth of at least 1 1/2 inches have been removed from the road surface.
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The further processiny preferably includes mixing the ground asphalt in the centre s-trip portion with rejuvenant, pulverlzing it and then applying it to the pavement. Typically the time between moving ground asphalt onto the centre strip portlon and grinding it together with underlying unground asphalt is 1 to 1 1/2 minutes.
The utilization of a windrow to heat unruptured asphalt allows the elimination of a conveyor to carry ground asphalt up over the next: stage heaters. The elimination of the conveyor allows more heaters to be used in a given length of vehicles and, in fact, allows up to four stages of heating ancl grinding to be placed on two movable vehicles. Going from two to four stages reduces by 1/~ the amount of asphalt each stage must heat and rupture.
Such a reduction reduces the time to heat 1/2 inch by one-quarter that required to heat one inch. In practical terms the required heating can be accomplished by raising the surface temperature to as low as 350 degrees Fahrenheit and, because of the more thorough heating down to the 1/2 inch level, less rock fracturing of aggregate in the pavement occurs and correspondingly less wear on the grinders or millers takes place. Finally the lower surface temperatures produce no significant burning of the asphaltic pavement at the surface and hence produce little smoke and pollution.
B~IEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as other features and advantagQs thereof, will be best understood by reference to the detailed description which follows, read in conjunction with the accompanying drawings, wherein:
Figure 1 is a perspecti.ve view of a four stage process implementing a preferred embodiment of the invention;
Figure 2 is a plan vlew of a four stage apparatus for carrying out the method which shows banks of heating elements and grinders mountecl on two separate vehicles used to support them;
Figure 3 is a side elevation view O:e the first vehicle shown in Figure 2;
Figure ~ is a plan view of the rear vehicle and a conventional machine for mixing rejuvenant in with the ruptured asphalt if required, picking up the asphalt with a conveyor, optionally adding some virgin asphalt to the ruptured asphalt, levelling the mix of asphalt and rolling it; and Figure 5 is a rear elevation view of each vehicle showing the rear grinders.
DFTAILED DESCRIPTION WITH REFERENCE ~O ~HE DRAWING~
Referring to Figure 1 there is shown in perspective a four stage embodiment of the invention for processing asphaltic pavement. In all of the drawings like reference numbers refer to like parts. In the Fi.gure, the direction of travel is shown by the large arrow pointing generally to the bottom left hand corner. First the entire road surface being processed, which is -typically one lane of travel, is heated as shown at location 72 until the asphalt down to approximately 1/2 inches of depth is softened. The first 1/2 inch layer of asphalt is then milled or ground by grinders 36 and 37 immediately behind heated area 72 with grinders 36 simultaneously windrowing ground asphalt into the centre as shown by the arrows. The grinders may rotate either against the clirection Oe travel or with the direction of travel.
After milling or grinding by the central grinder 37, the two exposed side strip portiorls 74 and 76 are heated radiantly down to àpproximately l/2 inch while the centre strip between is heated by the windrow of ground asphalt material 77. A second set of grinders 36 and 3~3 repeat the grinding processed as effected by the first stage oE grinders 36 and 37 and again windrow 79 heats the unground centre strip while side strips 91 and 93 are heated radiantly down to approxima-tely 1/2 inch. The latter heating and milliny steps are repeated twice more with windrows 81 and 84 again being used to heat unground centre strips while side strips are heated radiantly down to 1/2 inch. Finally, rejuvenant and possibly virgin asphalt may be added if desired as shown by arrow 86 and the ground asphalt and virgin asphalt, if any, mixed as shown by the arrows at 90 . The mixed material is then distributed evenly over the road by a screed 88 and then rolled.
Referring to Figures 2 there are shown in plan view a self-propelled vehicles 10 and 11. In Figure 3 there is shown in elevation vehicle 10. Vehicle 11 is identical except for heater bank 12 having no tunnel down the centre as do each of heater ban~s 13, 14 and 15 as seen in Figure 2. Vehicle 10 consists of a platform 25 supported by wheels 18 at a forward end thereof. Heater banks 12 and 14 are each formed by rows 50 of propane-fired, elongatsd, infra-red heaters 54 mounted on the underside of front and rear carriages 25 and 22, respectively. The heater banks 12, 13, 14 and 15 are arranged in side by side relationship _ 9 to extend across a strip of pavement to be heated. Spaces 52 and 53 are located be-tween the heater rows midway along banks 12, 13, 1~ and 15 although there are tunnels or gaps 21 and 23 extendiny longitudinally throuyh the centre of the banks 13, 14 and 15 which intercept the spaces 52 and 53 of vehicles 10 and 11. The latter spaces are present to allow the surface temperature of the heated asphaltic pavement to cool and the heat to transfer into the unruptured pavement before the next bank of heaters pass over.
Tunnels 21 and 23 in the heater banks overlie the central windrows 77, 79, 81 and 8~, and avoid heating the latter. At either side of spaces 52 and 53 there are located three elongated radiant heaters 56 designed to compensate for the lower heating effect at the edye of the bank of heaters 5~. Wheels 13 coupled to the front of each vehicle lO and 11 are remotely controlled through a micro processor uni.t (not shown) located at the rear of vehi.cles 10 and 11. Carriages 25 and 27 are attached by means of a pivotal joint 19 that permits articulation for allowing a small radius turn.
Carriage 25 is supported by front wheels 18 and, at the rear, by carriage 22. Carriage 22 is supported by forward wheels 27 and four rear wheels 26. Wheels 18, 27 and 26 can all be turned in response to remote control signals applied by operators at the rear of vehicles 10 and 11. The grinding units 36 and 37 corresponding to the first and second stages of heating and grinding, respectively, are located on vehicle 10 behind heater banks 12 and 13, respectively. Similarly, on vehicle 11, grinder units 36 and 37 are located behind third and fourth stage heater banks 1~ and 15, respectively. Each of gr~nder units 36 and 37 have two forward side grinders 39 and a central rearwardly disposed grinder 38. Grinder units 38 - 10 - ~ 4~ J ~
and 39 are supported by means of a V-brace member 32 which, in turn, is supported at screw connections 30 from a front beam 28 affixed to the frame 22 of each of vehicles 10 and 11. Rear yrinder units 3~ overlap slightly the interior edges of side grinders 39.
Figure ~ shows the rear vehicle 11 followed by a conventional repaver 100 having a pug mill mixer 102 at the front for mixing rejuvenant with the ruptured asphaltic pavement, a conveyor 104 for picking it up and transporting it to a bin 106 in which virgin asphalt may be mixed, followed by a screed 108 which levels the asphalt after it is deposited on the strip and finally a roller 110 for rolliny and compressing -the asphalt.
As shown in Figure 5, at the back of grinders 37 and 38 there are vertically oriented blades 40 and 42 which extend down to the level of -the cutting edges of grinders 36 and 38 and in operation exert slight pressure on the freshly ground pavement surface. As seen in Figure 5 there is an opening 41 in the centre of plate 42, the plate behind the rear grinder 38 of each grinding unit 37 to permit windrowed ground material to pass therethrough. By making the size of the opening 18 inches for a strip width of the pavement being processed of 12 feet and the height increasing from the front grinding unit 37 to the rearmost one, the windrow is contoured and compacted, thereby increasing the heat conductivity down through the windrow into the underlying unruptured layer.
The carriages 25 and 22 of vehicles 10 and 11 are each used to support a variety of different equipment required to operate the units such as a propane tanks 44, a container 46 to hold rejuvenant and pump unit 48.
In operation vehicle 11 follows closely behind by vehicles 10. A single operator operates each of vehicles lo with both operators located at the rear of their respective vehicles. The way in which these vehicles process and move the material has already been illuskrated in Figure 1. It is to be understood that the areas shown in Figure 1 are only a snapshot of an ongoing process which progresses forwardly as the vehicles move. The ground material 84 is pulverized a-t step 90 by a pugmill mixer (not shown). The mix material can then be further processed either by levelling it out with a screed 88 and then compacting it or, by picking up the ground material and directing it to a bin in which the old material is heated, mixed and spread over the pavement surface by a repaving machine of conventional design (not shown). The speed of the machines and spacing of the grinders 36 and 37 relative to the banks of heaters 12, 13, 14 and 15 is such that ground windrows 77, 79, 81 and 84 are left on the top of the surface of the centre strip where it is allowed to soak into the underlying unground material for a period of about one to one and one half minutes. This period has been found sufficient to soften approximately 1/2 inch of the unground underlying material sufficiently so that grinding of this material is facilitated. By only slightly increasing the depth of grinding it is possible to remove an additional 1/8 inches of material in each stage leading to an increased depth of recycling of 5/8 inch in all.
By confining the windrow to as small a width as possible given the volume of material removed and applying a slight amount of pressure to it as it passes through the hole in the central grinder back blade the heating effect on the unground centre strip in each stage is maximized.
It has been found that using the four stage machine maximum surface temperatures of as low as 350 degrees Fahrenheit is developed with a corresponding substantial ~ ~3 ~
reduction in emissions and a signiflcant increase in operating speed.
Although grinders or mlllers have been shown other means of rupturing the heated asphalt could be used.
Although a four s-tage heating and grindiny apparatus has been shown clearly t:hree stages or five or more stages are possible. However, three stages would be capable only of recycling a total of only 1 1/2 inches without significant overheating and cold yrinding or rupturing.
Following the hea-ting and rupturing stages the ruptured or ground asphaltic pavement rejuvenant may be mixed into the latter and then the ruptured asphaltic pavement is spread evenly over the strip being processed, levelled and rolled as is known in the art.
Accordingly, while this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. ~arious modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall with the true scope of the invention.
METHOD A~D APP~RATU~3 FOR REP~VING ~SPHl~LTIC P~VEMENT
BACKGROUND
The present application relates to a multi-stage apparatus and process for in-place recycling of asphaltic pavement without the need to remove the asphalt to a remote reconditioning plant and then return it for use in repavlng.
Single stage units which heat asphaltic pavement, rupture an upper layer of the surface, remove it from the road surface, pulverize it ancl then place it back on the road surface are ]cnown. Such units, however, can not recycle more than approximately the top inch of asphalt because of the difficulty in heating the asphalt to a greater depth. The time to heat asphalt to a given temperature at a given depth depends on the square of the depth. Thus, it takes four times as long to heat a 1/2 inch layer of asphalt to a given average temperature than it does to so heat a onr inch layer.
One early solution offered by U. S. Patent Number 4,545,700 issued October 8, ~9~5 to Yates was to employ a plurality of stages of heating and milling or grinding the heated asphalt. After each stage of heating and milling the ground asphalt is removed from the road surface either by windrowing the ground asphalt off to the sides of that portion of the road surface being processed or by windrowing it up onto spaced apart collection chutes along which the asphalt moves until it reaches the next milling stage. ~indrowing the yround asphalt to the side tends to contaminate the asphalt with dirt as well as getting in the way of oncoming traffic, depending on which side the asphalt is windrowed. The disclosure showing the material onto chutes is purely schematic as there is no practical way of holding the asphalt from spilling off of the sides or moving it along the surface of each of the chutes. In ~ ~.J ` ~
practice Yates Corp. used a conveyor to pick up the material from the roacl surface and carry it over the next stage of heaters. It is the latter conveyor which creates significant problems due not only to its cost and high maintenance requirements but also by the amount oE space it takes up. Due to the conveyors, ~ates was able to include only a limited lenyth oE heaters for each staye, otherwise his vehicle would have been excessively lony. Thus, he was able to heat and remove only about 1/4 inch of asphalt per staye for a total of one lnch for his four stage machine.
It is normally desirable to remove and recondition at least the top 1 1/2 inches of asphalt.
Canadian Patent Number 1,264,422 issued to Wiley and Rorison discloses a two stage process very similar to Yates which also uses a conveyor. The latter machine removes one inch per stage by employiny banks of infra red heaters on each of two separate vehicles, one vehicle being used for each stage of heating and milling. Even then in order to heat the asphalt sufficiently to soften it down to a depth of one inch and still be able to travel at about 20 feet per minute, the practical minimum, it is necessary to raise the temperature at the top surface of the asphalt to 600 to 700 degrees Fahrenheit. Such high temperatures burn the asphalt at the surface ancl create significant amounts of smoke. An additional problem in the Wiley et al.
method is the requirement of a conveyor in the second stage to carry the first stage ground material over the second stage heaters. It is the latter conveyor which limits the length of heaters possible in the second stage without the second stage vehicle being excessively long. Thus, even though the first inch of asphalt is heated marginally sufficiently, heating of the lower second inch by the second stage heaters is inadequate.
U. S. Patent Number 4,850,740 issued on July 25, - 3 - ~ 3~7 1989 to Wiley discloses a method which allows the conveyor to be eliminated altogether and to use a longer bank of heaters in the second s-tage machine. Wiley '740 utilizes the heated windrowed material to heat a central unground lower layer of aspha]t without the need for infra red heaters to heat that portion. Except for the first stage heater, such heaters are only required for the side strips from which the milled asphalt is windrowed. Both Wiley'740 and the Canadian Patent issued to Wiley disclose removing one inch per stage for a total of two inches. However, heating down to one inch requires either long heaters or relatively slow operation or both. Attempts to run the machines faster results in insufficient heating and a greater number of rock fractures which degrade the quality of the repaving.
Raising the temperature of the heaters causes burning of surface asphalt and results in the creation of unacceptably large amounts of smoke. There is at the present time considerable concern that such smoke is carcinogenic. There is, therefore, a need for a method and apparatus for repaving which produces substantially less smoke than known methods and machines and which can recondition down to at least two inches of depth while maintaining a speed of operation of twenty feet per minute or more.
Accordingly, it is an object of the invention to provide an improved method and apparatus for recycling and repaving asphaltic pavement. It is a further object of the invention to provide a method and apparatus for repaving asphaltic pavement which produces less smoke than known machines and, at the same time, is capable of operating as fast or faster than known methods and machines.
~ 3 1 1 SUMMARY OF THE INVENTION
The present invention provides an asphaltic road surface repaving apparatus of a type that removes asphalt from the surface of the road, conditions it and reapplies it to the road surface as the apparatus progresses along the road. The apparatus includes first staye radiant heating means for heatiny a first layer of a strip of asphaltic pavement, firs-t rupturing means for rupturing asphalt in the first heated layer and windrowing the ruptured heated asphalt onto a remaining portion of the strip of the asphaltic pavement. Second stage radiant heating means heats an exposed second layer of asphaltic pavement in the remaining portion of the strip. That portion of a third layer of asphaltic pavement below the windrowed material is heated by conduction from the heated windrowed material. A third stage radiant heating means is provided for heating a third layer of exposed unruptured asphaltic pavement in a remaining portion of the strip.
Third rupturing means is also provided for rupturing the third layer of previously unruptured asphaltic pavement.
A repaver is used for levelling the ruptured asphaltic pavement over the strip and then rolling it to form finished pavement.
By simply windrowing ground material from one stage onto a selected strip of the road surface being processed and using the heat from the windrow to conductively heat the underlying unground road surface rather than picking up the windrow in a conveyor and radiantly heating the whole road surface being processed, the need to incorporate a conveyor at each stage is avoided. Moreover, by multiplying the number of stages to a-t least three, it is possible to reduce the thickness of road surface layer heated, ruptured and windrowed in each stage and therefore ~ 5 - ~?~
to reduce the temperature to which the surface of the road is raised to as low as 350 degrees Fahrenheit. The total depth of asphaltic pavement that is conditioned is at least 1 1/2 inches. The spaciny between the first, second and third rupturing means is such that heat from the heated, xuptured, windrowed asphaltic pavement in each of the windrows conducts downwardly into the underlying unruptured asphaltic pavement below the windrows to soften the latter prior to being ruptured by subsequent rupturing means.
~ dvantageously, the third rupturing means moves the ruptured asphaltic pavement onto the windrow portion of the strip. A fourth stage radiant heating means may be pro~ided after the third rupturing means for heating a fourth layer of exposed unruptured asphaltic pavement in the remaining portion of the strip and fourth rupturing means for rupturing the fourth layer of previously unruptured asphaltic pavement.
Preferably the method includes heating the entire road surface being processed until a preselected depth is softened, rupturing and windrowing the ground asphalt onto a centre strip portion. Next the two exposed side strip portions are heated until softened and ruptured. The ruptured asphalt then is moved onto the centre strip portion which separates the two side strip portions. The unground asphalt in the centre strip portion is ground and the two side strip portions are again heated to soften the asphalt therein. The softened asphalt in the two side strip portions is again ground and moved onto the centre strip portion. Finally the unground asphalt in the centre strip portion is ground and left for further processing.
The foregoing heating, rupturing and windrowing steps are repeated at least one more time until a depth of at least 1 1/2 inches have been removed from the road surface.
~ 6 ~ d ~
The further processiny preferably includes mixing the ground asphalt in the centre s-trip portion with rejuvenant, pulverlzing it and then applying it to the pavement. Typically the time between moving ground asphalt onto the centre strip portlon and grinding it together with underlying unground asphalt is 1 to 1 1/2 minutes.
The utilization of a windrow to heat unruptured asphalt allows the elimination of a conveyor to carry ground asphalt up over the next: stage heaters. The elimination of the conveyor allows more heaters to be used in a given length of vehicles and, in fact, allows up to four stages of heating ancl grinding to be placed on two movable vehicles. Going from two to four stages reduces by 1/~ the amount of asphalt each stage must heat and rupture.
Such a reduction reduces the time to heat 1/2 inch by one-quarter that required to heat one inch. In practical terms the required heating can be accomplished by raising the surface temperature to as low as 350 degrees Fahrenheit and, because of the more thorough heating down to the 1/2 inch level, less rock fracturing of aggregate in the pavement occurs and correspondingly less wear on the grinders or millers takes place. Finally the lower surface temperatures produce no significant burning of the asphaltic pavement at the surface and hence produce little smoke and pollution.
B~IEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as other features and advantagQs thereof, will be best understood by reference to the detailed description which follows, read in conjunction with the accompanying drawings, wherein:
Figure 1 is a perspecti.ve view of a four stage process implementing a preferred embodiment of the invention;
Figure 2 is a plan vlew of a four stage apparatus for carrying out the method which shows banks of heating elements and grinders mountecl on two separate vehicles used to support them;
Figure 3 is a side elevation view O:e the first vehicle shown in Figure 2;
Figure ~ is a plan view of the rear vehicle and a conventional machine for mixing rejuvenant in with the ruptured asphalt if required, picking up the asphalt with a conveyor, optionally adding some virgin asphalt to the ruptured asphalt, levelling the mix of asphalt and rolling it; and Figure 5 is a rear elevation view of each vehicle showing the rear grinders.
DFTAILED DESCRIPTION WITH REFERENCE ~O ~HE DRAWING~
Referring to Figure 1 there is shown in perspective a four stage embodiment of the invention for processing asphaltic pavement. In all of the drawings like reference numbers refer to like parts. In the Fi.gure, the direction of travel is shown by the large arrow pointing generally to the bottom left hand corner. First the entire road surface being processed, which is -typically one lane of travel, is heated as shown at location 72 until the asphalt down to approximately 1/2 inches of depth is softened. The first 1/2 inch layer of asphalt is then milled or ground by grinders 36 and 37 immediately behind heated area 72 with grinders 36 simultaneously windrowing ground asphalt into the centre as shown by the arrows. The grinders may rotate either against the clirection Oe travel or with the direction of travel.
After milling or grinding by the central grinder 37, the two exposed side strip portiorls 74 and 76 are heated radiantly down to àpproximately l/2 inch while the centre strip between is heated by the windrow of ground asphalt material 77. A second set of grinders 36 and 3~3 repeat the grinding processed as effected by the first stage oE grinders 36 and 37 and again windrow 79 heats the unground centre strip while side strips 91 and 93 are heated radiantly down to approxima-tely 1/2 inch. The latter heating and milliny steps are repeated twice more with windrows 81 and 84 again being used to heat unground centre strips while side strips are heated radiantly down to 1/2 inch. Finally, rejuvenant and possibly virgin asphalt may be added if desired as shown by arrow 86 and the ground asphalt and virgin asphalt, if any, mixed as shown by the arrows at 90 . The mixed material is then distributed evenly over the road by a screed 88 and then rolled.
Referring to Figures 2 there are shown in plan view a self-propelled vehicles 10 and 11. In Figure 3 there is shown in elevation vehicle 10. Vehicle 11 is identical except for heater bank 12 having no tunnel down the centre as do each of heater ban~s 13, 14 and 15 as seen in Figure 2. Vehicle 10 consists of a platform 25 supported by wheels 18 at a forward end thereof. Heater banks 12 and 14 are each formed by rows 50 of propane-fired, elongatsd, infra-red heaters 54 mounted on the underside of front and rear carriages 25 and 22, respectively. The heater banks 12, 13, 14 and 15 are arranged in side by side relationship _ 9 to extend across a strip of pavement to be heated. Spaces 52 and 53 are located be-tween the heater rows midway along banks 12, 13, 1~ and 15 although there are tunnels or gaps 21 and 23 extendiny longitudinally throuyh the centre of the banks 13, 14 and 15 which intercept the spaces 52 and 53 of vehicles 10 and 11. The latter spaces are present to allow the surface temperature of the heated asphaltic pavement to cool and the heat to transfer into the unruptured pavement before the next bank of heaters pass over.
Tunnels 21 and 23 in the heater banks overlie the central windrows 77, 79, 81 and 8~, and avoid heating the latter. At either side of spaces 52 and 53 there are located three elongated radiant heaters 56 designed to compensate for the lower heating effect at the edye of the bank of heaters 5~. Wheels 13 coupled to the front of each vehicle lO and 11 are remotely controlled through a micro processor uni.t (not shown) located at the rear of vehi.cles 10 and 11. Carriages 25 and 27 are attached by means of a pivotal joint 19 that permits articulation for allowing a small radius turn.
Carriage 25 is supported by front wheels 18 and, at the rear, by carriage 22. Carriage 22 is supported by forward wheels 27 and four rear wheels 26. Wheels 18, 27 and 26 can all be turned in response to remote control signals applied by operators at the rear of vehicles 10 and 11. The grinding units 36 and 37 corresponding to the first and second stages of heating and grinding, respectively, are located on vehicle 10 behind heater banks 12 and 13, respectively. Similarly, on vehicle 11, grinder units 36 and 37 are located behind third and fourth stage heater banks 1~ and 15, respectively. Each of gr~nder units 36 and 37 have two forward side grinders 39 and a central rearwardly disposed grinder 38. Grinder units 38 - 10 - ~ 4~ J ~
and 39 are supported by means of a V-brace member 32 which, in turn, is supported at screw connections 30 from a front beam 28 affixed to the frame 22 of each of vehicles 10 and 11. Rear yrinder units 3~ overlap slightly the interior edges of side grinders 39.
Figure ~ shows the rear vehicle 11 followed by a conventional repaver 100 having a pug mill mixer 102 at the front for mixing rejuvenant with the ruptured asphaltic pavement, a conveyor 104 for picking it up and transporting it to a bin 106 in which virgin asphalt may be mixed, followed by a screed 108 which levels the asphalt after it is deposited on the strip and finally a roller 110 for rolliny and compressing -the asphalt.
As shown in Figure 5, at the back of grinders 37 and 38 there are vertically oriented blades 40 and 42 which extend down to the level of -the cutting edges of grinders 36 and 38 and in operation exert slight pressure on the freshly ground pavement surface. As seen in Figure 5 there is an opening 41 in the centre of plate 42, the plate behind the rear grinder 38 of each grinding unit 37 to permit windrowed ground material to pass therethrough. By making the size of the opening 18 inches for a strip width of the pavement being processed of 12 feet and the height increasing from the front grinding unit 37 to the rearmost one, the windrow is contoured and compacted, thereby increasing the heat conductivity down through the windrow into the underlying unruptured layer.
The carriages 25 and 22 of vehicles 10 and 11 are each used to support a variety of different equipment required to operate the units such as a propane tanks 44, a container 46 to hold rejuvenant and pump unit 48.
In operation vehicle 11 follows closely behind by vehicles 10. A single operator operates each of vehicles lo with both operators located at the rear of their respective vehicles. The way in which these vehicles process and move the material has already been illuskrated in Figure 1. It is to be understood that the areas shown in Figure 1 are only a snapshot of an ongoing process which progresses forwardly as the vehicles move. The ground material 84 is pulverized a-t step 90 by a pugmill mixer (not shown). The mix material can then be further processed either by levelling it out with a screed 88 and then compacting it or, by picking up the ground material and directing it to a bin in which the old material is heated, mixed and spread over the pavement surface by a repaving machine of conventional design (not shown). The speed of the machines and spacing of the grinders 36 and 37 relative to the banks of heaters 12, 13, 14 and 15 is such that ground windrows 77, 79, 81 and 84 are left on the top of the surface of the centre strip where it is allowed to soak into the underlying unground material for a period of about one to one and one half minutes. This period has been found sufficient to soften approximately 1/2 inch of the unground underlying material sufficiently so that grinding of this material is facilitated. By only slightly increasing the depth of grinding it is possible to remove an additional 1/8 inches of material in each stage leading to an increased depth of recycling of 5/8 inch in all.
By confining the windrow to as small a width as possible given the volume of material removed and applying a slight amount of pressure to it as it passes through the hole in the central grinder back blade the heating effect on the unground centre strip in each stage is maximized.
It has been found that using the four stage machine maximum surface temperatures of as low as 350 degrees Fahrenheit is developed with a corresponding substantial ~ ~3 ~
reduction in emissions and a signiflcant increase in operating speed.
Although grinders or mlllers have been shown other means of rupturing the heated asphalt could be used.
Although a four s-tage heating and grindiny apparatus has been shown clearly t:hree stages or five or more stages are possible. However, three stages would be capable only of recycling a total of only 1 1/2 inches without significant overheating and cold yrinding or rupturing.
Following the hea-ting and rupturing stages the ruptured or ground asphaltic pavement rejuvenant may be mixed into the latter and then the ruptured asphaltic pavement is spread evenly over the strip being processed, levelled and rolled as is known in the art.
Accordingly, while this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. ~arious modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall with the true scope of the invention.
Claims (15)
1. A multi-stage, movable, asphaltic pavement conditioning apparatus for use in re-conditioning asphaltic pavement, comprising:
(a) a first stage radiant heating means for heating a first layer of a strip of asphaltic pavement to a more softened condition;
(b) first rupturing means for rupturing heated asphaltic pavement in the first layer of the strip and moving the ruptured, heated asphaltic pavement to a windrow portion of the strip to form a windrow thereon, and leaving a remaining portion of the strip with exposed, unheated asphaltic pavement;
(c) a second stage radiant heating means for heating a second layer of exposed unruptured asphaltic pavement in the remaining portion of the strip to a softened condition;
(d) second rupturing means for rupturing the second layer of previously unruptured asphaltic pavement and moving the ruptured asphaltic pavement to the windrow portion of the strip to form a windrow thereon;
(e) third stage radiant heating means for heating a third layer of exposed unruptured asphaltic pavement in the remaining portion of the strip to a softened condition;
(f) third rupturing means for rupturing the third layer of previously unruptured asphaltic pavement; and (g) means for levelling the ruptured asphaltic pavement over the strip and rolling it to form finished pavement;
wherein the total depth of asphaltic pavement that is conditioned is at least approximately 1 1/2 inches and the spacing between the first, second and third rupturing means is such that heat from the heated, ruptured, windrowed asphaltic pavement in each of the windrows conducts downwardly into the underlying unruptured asphaltic pavement below the windrows to soften the latter prior to being ruptured by subsequent rupturing means.
(a) a first stage radiant heating means for heating a first layer of a strip of asphaltic pavement to a more softened condition;
(b) first rupturing means for rupturing heated asphaltic pavement in the first layer of the strip and moving the ruptured, heated asphaltic pavement to a windrow portion of the strip to form a windrow thereon, and leaving a remaining portion of the strip with exposed, unheated asphaltic pavement;
(c) a second stage radiant heating means for heating a second layer of exposed unruptured asphaltic pavement in the remaining portion of the strip to a softened condition;
(d) second rupturing means for rupturing the second layer of previously unruptured asphaltic pavement and moving the ruptured asphaltic pavement to the windrow portion of the strip to form a windrow thereon;
(e) third stage radiant heating means for heating a third layer of exposed unruptured asphaltic pavement in the remaining portion of the strip to a softened condition;
(f) third rupturing means for rupturing the third layer of previously unruptured asphaltic pavement; and (g) means for levelling the ruptured asphaltic pavement over the strip and rolling it to form finished pavement;
wherein the total depth of asphaltic pavement that is conditioned is at least approximately 1 1/2 inches and the spacing between the first, second and third rupturing means is such that heat from the heated, ruptured, windrowed asphaltic pavement in each of the windrows conducts downwardly into the underlying unruptured asphaltic pavement below the windrows to soften the latter prior to being ruptured by subsequent rupturing means.
2. A multi-stage, movable, asphaltic pavement conditioning apparatus for use in re-conditioning asphaltic pavement, comprising:
(a) a first stage radiant heating means for heating a first layer of a strip of asphaltic pavement to a more softened condition;
(b) first rupturing means for rupturing heated asphaltic pavement in first layer of the strip and moving the ruptured, heated asphaltic pavement to a central, windrow portion of the strip to form a windrow thereon, and leaving two side strip portions of exposed unruptured asphaltic pavement separated by the windrow;
(c) a second stage radiant heating means for heating a second layer of exposed unruptured asphaltic pavement in the side strip portions of the strip to a softened condition;
(d) second rupturing means for rupturing the second layer of previously unruptured asphaltic pavement and moving the ruptured asphaltic pavement to the windrow portion of the strip to form a windrow thereon;
(e) third stage radiant heating means for heating a third layer of exposed unruptured asphaltic pavement in the side strip portions of the strip to a softened condition;
(f) third rupturing means for rupturing the third layer of previously unruptured asphaltic pavement and moving the ruptured asphaltic pavement to the windrow portion of the strip to form a windrow thereon;
(g) fourth stage radiant heating means for heating a fourth layer of exposed unruptured asphaltic pavement in the side strip portions of the strip to a softened condition;
(h) fourth rupturing means for rupturing the fourth layer of previously unruptured asphaltic pavement; and (i) means for levelling the ruptured asphaltic pavement over the strip and rolling it to form finished pavement;
wherein the total depth of asphaltic pavement that is conditioned is at least approximately 1 1/2 inches and the spacing between the first, second, third and fourth rupturing means is such that heat from the heated, ruptured, windrowed asphaltic pavement in each of the windrows conducts downwardly into the underlying unruptured asphaltic pavement below the windrows to soften the pavement prior to being ruptured by subsequent rupturing means.
(a) a first stage radiant heating means for heating a first layer of a strip of asphaltic pavement to a more softened condition;
(b) first rupturing means for rupturing heated asphaltic pavement in first layer of the strip and moving the ruptured, heated asphaltic pavement to a central, windrow portion of the strip to form a windrow thereon, and leaving two side strip portions of exposed unruptured asphaltic pavement separated by the windrow;
(c) a second stage radiant heating means for heating a second layer of exposed unruptured asphaltic pavement in the side strip portions of the strip to a softened condition;
(d) second rupturing means for rupturing the second layer of previously unruptured asphaltic pavement and moving the ruptured asphaltic pavement to the windrow portion of the strip to form a windrow thereon;
(e) third stage radiant heating means for heating a third layer of exposed unruptured asphaltic pavement in the side strip portions of the strip to a softened condition;
(f) third rupturing means for rupturing the third layer of previously unruptured asphaltic pavement and moving the ruptured asphaltic pavement to the windrow portion of the strip to form a windrow thereon;
(g) fourth stage radiant heating means for heating a fourth layer of exposed unruptured asphaltic pavement in the side strip portions of the strip to a softened condition;
(h) fourth rupturing means for rupturing the fourth layer of previously unruptured asphaltic pavement; and (i) means for levelling the ruptured asphaltic pavement over the strip and rolling it to form finished pavement;
wherein the total depth of asphaltic pavement that is conditioned is at least approximately 1 1/2 inches and the spacing between the first, second, third and fourth rupturing means is such that heat from the heated, ruptured, windrowed asphaltic pavement in each of the windrows conducts downwardly into the underlying unruptured asphaltic pavement below the windrows to soften the pavement prior to being ruptured by subsequent rupturing means.
3. A machine according to claims 1 or 2, wherein each of said rupturing means includes a grinder having a rotating portion with a plurality of protuberances spaced over the surface thereof and a vertical blade immediately behind said rotating portion and supported by a common frame with said rotating portion, said vertical blade normally contacting the pavement and having a central opening for compacting and shaping the windrows.
4. A machine according to claim 2, wherein each of said rupturing means includes a pair of spaced apart side grinders and a rear grinder disposed rearwardly of said side grinders, said grinders having a rotating portion with a plurality of spaced apart protuberances uniformly disposed over the surface of the rolling portion and a vertical blade behind the rotating portion which normally contacts the pavement, wherein the blades behind the rear grinders have an opening to permit passage of the windrows, the opening being sized to compact and shape the windrows.
5. A machine according to claims 1 or 2 wherein the width of said windrow is less than 2 feet.
6. A machine according to claim 2, wherein said first, second, third, and fourth stage radiant heating means are banks of infra red heaters suspended above the pavement and substantially parallel thereto.
7. A machine according to claim 6, wherein said heating banks are separated by gaps which permit cooling of the top surface of asphaltic pavement being heated before a next bank of heaters passes over and allows heat to conduct into the underlying layer of unruptured asphaltic pavement and including heating sections on either end of the space between banks to compensate for the reduced heating effect at the end of said banks of heaters.
8. A method of reconditioning asphaltic pavement, comprising:
(a) heating a strip of asphaltic pavement until it is softened;
(b) grinding a first strip portion of softened asphalt of said strip;
(c) moving the ground asphalt to an adjacent unground strip portion of said strip;
(d) grinding both ground asphalt and unground asphalt of said adjacent strip portion;
(e) heating exposed unheated asphalt in said first strip until it is softened;
(f) grinding softened asphalt in said first strip portion and moving it onto said adjacent strip portion;
(g) grinding both previously ground and unground asphalt in said adjacent strip portion at a time after the second grinding step sufficiently long so that heat from said ground, previously heated asphalt soaks into underlying unground asphalt and softens it sufficiently to be ground;
(h) repeating steps (e), (f) and (g) as often as necessary until a predetermined depth of asphalt has been removed; and (i) mixing said ground asphalt with rejuvenant and reapplying it to the pavement.
(a) heating a strip of asphaltic pavement until it is softened;
(b) grinding a first strip portion of softened asphalt of said strip;
(c) moving the ground asphalt to an adjacent unground strip portion of said strip;
(d) grinding both ground asphalt and unground asphalt of said adjacent strip portion;
(e) heating exposed unheated asphalt in said first strip until it is softened;
(f) grinding softened asphalt in said first strip portion and moving it onto said adjacent strip portion;
(g) grinding both previously ground and unground asphalt in said adjacent strip portion at a time after the second grinding step sufficiently long so that heat from said ground, previously heated asphalt soaks into underlying unground asphalt and softens it sufficiently to be ground;
(h) repeating steps (e), (f) and (g) as often as necessary until a predetermined depth of asphalt has been removed; and (i) mixing said ground asphalt with rejuvenant and reapplying it to the pavement.
9. A method according to claim 8, wherein said heating steps include exposing a section of said asphaltic strip to successive spaced apart banks of infra red heaters until it becomes softened.
10. A method of preparing asphaltic pavement for repaving, comprising:
(a) heating a strip of asphaltic pavement until it is softened;
(b) grinding two side strip portions of said strip and moving the ground asphalt onto an underground centre strip portion separating said side strip portions;
(c) grinding previously ground and unground asphalt of said centre strip portion;
(d) heating asphalt in said side strips exposed by said grinding step until it is softened;
(e) grinding softened asphalt in said two side strip portions and moving it onto the centre strip portion;
(f) grinding previously ground and unground asphalt in said centre strip at a time sufficiently long after step (c) so that heat from the heated ground asphalt conducts into underlying unground asphalt in said centre strip portion so that the latter is softened;
(g) repeating steps (d), (e) and (f) until at least approximately 1 1/2 inches of asphaltic pavement have been removed; and (h) mixing and reapplying the ground asphalt to the strip surface.
(a) heating a strip of asphaltic pavement until it is softened;
(b) grinding two side strip portions of said strip and moving the ground asphalt onto an underground centre strip portion separating said side strip portions;
(c) grinding previously ground and unground asphalt of said centre strip portion;
(d) heating asphalt in said side strips exposed by said grinding step until it is softened;
(e) grinding softened asphalt in said two side strip portions and moving it onto the centre strip portion;
(f) grinding previously ground and unground asphalt in said centre strip at a time sufficiently long after step (c) so that heat from the heated ground asphalt conducts into underlying unground asphalt in said centre strip portion so that the latter is softened;
(g) repeating steps (d), (e) and (f) until at least approximately 1 1/2 inches of asphaltic pavement have been removed; and (h) mixing and reapplying the ground asphalt to the strip surface.
11. A method according to claim 10, further including mixing the ground asphalt with a reconditioning agent, heating it, pulverizing, spreading and compacting the ground asphalt over said strip.
12. A method according to claim 10, wherein said grinding and moving steps are done simultaneously.
13. A method according to claim 10 wherein the time between successive grinding of both ground and unground asphalt in the centre strip is 1 to 1 1/2 minutes.
14. A method according to claim 10, wherein said heating steps include providing a heat soaking period between applications of radiant heating by providing a gap in banks of radiant heaters so that the asphalt surface does not overheat.
15. A method according to claim 10, including heating side sections of said gap between heaters to compensate for a reduced heating effect at the sides.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2042000 CA2042000A1 (en) | 1991-05-07 | 1991-05-07 | Method and apparatus for repaving asphaltic pavement |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2042000 CA2042000A1 (en) | 1991-05-07 | 1991-05-07 | Method and apparatus for repaving asphaltic pavement |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2042000A1 true CA2042000A1 (en) | 1992-11-08 |
Family
ID=4147561
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2042000 Abandoned CA2042000A1 (en) | 1991-05-07 | 1991-05-07 | Method and apparatus for repaving asphaltic pavement |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2042000A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2008006208A1 (en) * | 2006-07-14 | 2008-01-17 | Pat Wiley | Process for the rejuvenation of asphalt road surfaces |
-
1991
- 1991-05-07 CA CA 2042000 patent/CA2042000A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2008006208A1 (en) * | 2006-07-14 | 2008-01-17 | Pat Wiley | Process for the rejuvenation of asphalt road surfaces |
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