Abstract:
A method and apparatus are provided for in situ rejuvenation of asphalt pavement. The apparatus and method provide for heating the underlying surface to form a preheated surface, passing a mill over the preheated surface and milling the preheated surface to loosen the preheated surface to a desired depth and discharging the milled material from opposite ends of the respective windrows of known breadth. Windrow height is measured as is rate of advance of the transport structure to determine a volume throughput. Rejuvenating fluid is added to each windrow at a dosage rate based on a desired weight percentage and the volume throughput. A mixer is passed over the windrows and receives the windrows through respective openings at either end thereof. The mixer also blends the rejuvenating fluid with the milled material and forms a blended mixture which is discharged from the mixer. The mixer may be a pug mill operated in an inverted arrangement utilizing the road surface as a bottom thereto.

Description:
[0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 09/592,398 filed Jun. 13, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to apparatus for in situ rejuvenation of asphalt pavement. More particularly this invention relates to a method and apparatus for mixing milled asphalt pavement and rejuvenating fluid in such rejuvenation.  
         BACKGROUND OF THE INVENTION  
         [0003]    Asphalt pavement consists essentially of an aggregate and sand mixture held together with a petroleum based binder, such as asphalt cement (ie. an “asphalt mix”). With continued exposure to sun, moisture, traffic, freezing and thawing, asphalt mix surfaces degrade. The degradation is principally in the binder, rather than the aggregate and sand mixture which makes up the bulk of the asphalt mix. Also, much of the degradation occurs within the top two or three inches of the surface.  
           [0004]    Traditionally, worn asphalt pavement was not restored but was instead torn up and replaced with new asphalt mix. This is a costly approach and creates a problem as to what to do with the torn up pavement. Accordingly, techniques and apparatus have been developed for restoring or rejuvenating the top few inches of an asphalt paved surface.  
           [0005]    A typical road resurfacing machine has a heater for heating and softening the asphalt pavement surface as it passes along the surface. Following the heater is a “rake” or “scarifier” which breaks up or “scarifies” the softened pavement. The scarified pavement is generally crushed or “milled”, blended with rejuvenating fluid and optionally additional sand or aggregate and redeposited. The redeposited material is spread out and rolled to create a rejuvenated surface comparable in quality to the original surface before degradation.  
           [0006]    In order to produce a rejuvenated surface of high quality, it is important to ensure that an appropriate amount of rejuvenating fluid is added. Generally, a core sample or several core samples are initially taken of the surface to be rejuvenated and a desired ratio of rejuvenating material to milled material is analytically determined.  
           [0007]    It is also important to thoroughly intermingle the milled material with the rejuvenating material, which will at least include a fluid but may also include additional sand and/or aggregate. In doing so it is important to maintain retention in the mixer while nevertheless maintaining volume throughput at a desired rate.  
           [0008]    It is an object of the present invention to provide a method and apparatus for thoroughly blending the milled material with at least the rejuvenating fluid and with any other rejuvenating materials.  
         SUMMARY OF THE INVENTION  
         [0009]    Improvements are provided in an asphalt pavement resurfacing machine having a transport structure, a heater mounted to the transport structure for heating an underlying asphalt pavement surface to form a heated surface, a mill mounted to the transport structure to follow the heater and grind the heated surface to form a milled material and to prepare the underlying surface to a preset depth, a rejuvenating fluid sprayer for introducing a rejuvenating fluid to the milled material and a mixer for blending the milled material with the rejuvenating fluid. According to the improvement, the mill is provided with at least two outlets of predetermined breadth. A respective height monitor is provided at each of the two outlets for determining the height of the milled material being discharged from each of the outlets. Respective forward facing inlets are provided into the mixer for receiving milled material from each outlet as the machine is advanced in a travel direction. A respective rejuvenating fluid sprayer is provided for spraying rejuvenating fluid on the milled material emanating from each outlet. The mixer may be a pug mill having a housing which has a downwardly facing bottom opening. The mixer may further have a plurality of paddles extending radially from a pug mill shaft mounted within the housing, rotatable with the shaft and orientated to blend the rejuvenating fluid with the milled material and to direct a blended material so formed toward at least one discharge outlet facing rearwardly relative to a travel direction of the resurfacing machine.  
           [0010]    Windrow guides may be provided between the mill and the mixer to maintain windrow breadth and to guide the windrows into the mixer.  
           [0011]    The improved machine may further comprise a control and processing station which receives input from each height monitor and from a resurfacing machine speed monitor to determine a discharge rate of milled material from each outlet and cause each sprayer to dispense rejuvenating fluid on the milled material at a desired rate based on the discharge rate.  
           [0012]    A method is provided for asphalt paved road surface rejuvenation utilizing a structure having a heater, a mill and a mixer carried by a transport structure. The method comprises the steps of:  
           [0013]    i) passing the heater over the road surface to heat and soften the road surface and form a preheated surface;  
           [0014]    ii) passing the mill over the preheated surface and milling the preheated surface to loosen the preheated surface to a desired depth thus forming a milled material;  
           [0015]    iii) discharging the milled material from opposite ends of the mill in respective windrows of known breadth;  
           [0016]    iv) measuring windrow height and rate of advance of the transport structure;  
           [0017]    v) comparing the breadth in step (iii) with the height and rate of advance in step (iv) to determine volume throughput;  
           [0018]    vi) adding a rejuvenating fluid to each windrow at a dosage rate based on a desired weight percentage and the volume throughput;  
           [0019]    vii) passing the mixer over the windrows and receiving the windrows through respective openings in the mixer;  
           [0020]    viii) blending the rejuvenating fluid with the milled material in the mixer to form a blended mixture; and  
           [0021]    ix) discharging the blended mixture from the mixer.  
           [0022]    The mixer may be a pug mill extending transversely across the support structure and having sufficient breadth to capture the windrows simultaneously.  
           [0023]    The pug mill may be operated in an inverted arrangement in which an open face thereof is adjacent the surface to utilize the surface as a bottom thereto. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0024]    Preferred embodiments of the present invention are described below with reference to the accompanying drawings in which:  
         [0025]    [0025]FIG. 1 is a schematic representation of an asphalt resurfacing machine according to the present invention;  
         [0026]    [0026]FIG. 2 is an enlarged view of the rearward portion of the asphalt resurfacing machine of FIG. 1; and,  
         [0027]    [0027]FIG. 3 is an exploded view of a mixer according to the present invention;  
         [0028]    [0028]FIG. 4 is a schematic plan view from above of an alternate embodiment arrangement of the milling and mixing stages; and,  
         [0029]    [0029]FIG. 5 is a front elevation corresponding to FIG. 4. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]    An asphalt pavement resurfacing machine is generally indicated by reference  10  in FIG. 1. The resurfacing machine  10  travels in a path of travel indicated by arrow  12 . The resurfacing machine  10  has a transport structure  11  to which its various components are mounted. The transport structure  11  is basically a support frame having wheels or tracks  54 . A power plant  14  at the front of the transport structure  11  is provided to drive the apparatus and typically includes an engine and a hydraulic system.  
         [0031]    Behind the power plant  14  and also mounted on the transport structure  11  is a heater  16  which includes numerous burners and associated plumbing for heating an asphalt paved surface  18  upon which the resurfacing machine  10  travels. A propane (or other combustible fuel) tank  20  and a combustion blower  22  serve the burners in the heater  16 . The heater  16  directs heat at the asphalt surface  18  to cause softening of an upper part of the asphalt paved surface  18 .  
         [0032]    The softened surface  18  may be initially dislodged by a raking device, generally indicated by reference  30 , mounted to the transport structure  11 , and which follows the heater  16 . The raking device  30  has rakes which dislodge the heated surface  18 . The raking device  30  may include main rakes  32  and extension rakes  34 , the extension rakes  34  performing a similar function to the main rakes  32 , but to the outside edges. The main rakes  32  break up material around manholes where a main mill  36  behind the raking device  30  cannot run.  
         [0033]    The main mill  36  which is mounted to the transport structure  11  behind the raking device  30  grinds up the material dislodged by the rakes, levels the underlying surface and prepares the surface to a preset depth. Extension mills  38  ahead of the main mill  36  perform a similar function, but process outer material typically from  10  to  15  feet to each side of the resurfacing machine  10  and move it to a central part of the resurfacing machine  10  where it is subsequently processed by the main mill  36 .  
         [0034]    In some applications the apparatus may be operated without a raking device  30 , in which case the softened surface  18  will be directly ground by the main mill  36  and any extension mills  38 .  
         [0035]    A pug mill  100 , also mounted to the transport structure  11 , follows the main mill  36  and acts as a mixer for blending the processed material from the main mill  36  with rejuvenating fluid from a tank  42 . The pug mill  100  is described in more detail below.  
         [0036]    Blended material  46  from the pug mill  100  is picked up by a scalping conveyor  44  which deposits the blended material  46  in a heated holding hopper  48 . The holding hopper  48  keeps the blended material  46  hot until it is needed. The holding hopper  48  may be filled through its top with material for start ups or if additional material is needed. The holding hopper  48  may also be dumped if required or at the end of a day&#39;s operation.  
         [0037]    A screed  50  follows the asphalt rejuvenating apparatus  10  and may be a unit such as typically found on an asphalt paver. The screed  50  lays, spreads and slightly compacts the blended material  46  for final rolling.  
         [0038]    A water system  52  may be provided to supply cooling water to the front and rear tires or tracks  54 .  
         [0039]    An operator  56  operates a control and processing station  58 . From initial core samples the amount of rejuvenating fluid, sand and aggregate required to bring the asphalt paved surface  18  up to a suitable specification can be determined. The operator  56  can input and monitor the amounts of rejuvenating fluid, sand and aggregate being added.  
         [0040]    A sand/aggregate bin  60  precedes the asphalt pavement resurfacing machine  10 . The sand/aggregate bin  60  may be attached to the apparatus  10  or attached to a separate machine (not shown) running in front thereof. Sand/aggregate is metered at a specific rate which is a function of ground speed and specification requirements.  
         [0041]    The mixer or “pug mill”  100  is shown in more detail in the exploded view of FIG. 3. The mixer  100  has a first stage  102  which includes a housing or “first stage shell”  104  which is substantially enclosed but for a downwardly facing bottom opening  106 . The first stage shell  104  also has an inlet opening  108  through a forward face thereof which faces in the travel direction  12  of the transport structure  11 and a rearwardly facing discharge outlet.  
         [0042]    The first stage  102  in use is placed in close proximity to the underlying surface to form a substantially enclosed chamber with the underlying surface acting as a bottom part of the first stage  102 . A hydraulic cylinder  120  and parallel bar linkage  122  in FIG. 2 mount the mixer  100  to the transport structure  11  and control the placement of the first stage  102 .  
         [0043]    A first stage shaft  110  is mounted to the first stage shell  104  for rotation about a first stage shaft axis  112  which extends transversely relative to the travel direction  12 . A plurality of paddles  114  extend from the first stage shaft  110  in a direction generally radial relative to the first stage shaft axis  112 . The paddles  114  are rotatable with the first stage shaft  110  to blend the milled material with the rejuvenating fluid. The paddles  114  are aligned to direct the blended material ( 46  in FIGS. 1 and 2) generally in the direction of arrows  116  toward a discharge outlet  118 . The discharge outlet  118  faces rearwardly relative to the travel direction  112  and the blended material  46  is discharged therefrom as the resurfacing machine  10  moves in the forward direction  12 .  
         [0044]    A rotator for rotating the first stage shaft  110  may take a variety of forms. For example, as illustrated in FIG. 2, a motor  121  may be mounted to the pug mill  102  and rotationally coupled to the first stage shaft  110  by a motor sprocket  123  mounted to the motor  121 , a first stage shaft sprocket  124  mounted to the first stage shaft  110  and a roller chain  126  extending therebetween. It will be appreciated by those skilled in driver apparatus for such machinery that the rotator could take a variety of other forms. For example, a direct gear drive may be used instead of the sprocket and chain drive illustrated, or the motor  120  could be directly coupled to the first stage shaft  110 .  
         [0045]    According to one embodiment, the blended material is not be immediately discharged from the first stage discharge outlet  118 , but rather is further blended in a second stage  130  which follows the first stage  102 . The second stage receives blended material from the first stage discharge outlet  118 . The second stage  130  has a downwardly opening second stage shell  132 , which may be integral with and extend from the first stage shell  104 . A second stage shaft  134  is mounted in the second stage shell  132  for rotation about a second stage shaft axis  136 .  
         [0046]    A plurality of paddles  138  extend generally radially from the second stage shaft  134  and are rotatable therewith to further blend the blended material  46 . The paddles  138  are oriented to direct the blended material  46  in the direction of arrows  140  toward the second stage discharge opening  142 .  
         [0047]    The second stage discharge opening  142  faces rearwardly relative to the travel direction  12 . The blended material is preferably discharged from the second stage discharge opening  142  in a windrow of fixed breadth determined by the breadth of the second stage discharge opening  142 .  
         [0048]    A rotator for rotating the second stage shaft  134  may, as illustrated in FIG. 2, be a second stage shaft sprocket  144  mounted to the second stage shaft  110  and about which the roller chain  126  extends.  
         [0049]    Rejuvenating fluid may be added at various points in the resurfacing process. Preferably rejuvenating fluid should be added to the milled material prior to its entering the pug mill  100 . This may be accomplished by adding rejuvenating fluid at or before the main mill  36  or ahead of the pug mill inlet  108 . The latter arrangement is illustrated in FIG. 3 which shows a spray bar  150  for directing rejuvenating fluid at or ahead of the pug mill inlet  108 .  
         [0050]    An alternate embodiment of the present invention is illustrated in FIGS. 4 and 5. According to the alternate embodiment, a main mill  236  is configured to discharge milled material through respective outlets  270  and  272  at opposite ends thereof in respective windrows  274  and  276 . The outlets  270  and  272  are of known width and a respective ultrasonic scanner or other measuring device  278  and  280  is mounted to a convenient location such as the transport structure  11  or the mill  236  to monitor the height of the windrows  274  and  276 . Windrow height data is sent to the control and processing station  58  which also monitors the speed of the resurfacing machine to calculate, preferably for each of the windrows  274  and  276 , the volume discharge rate and the requisite addition of rejuvenating fluid.  
         [0051]    Test results suggest that the measuring devices  278  and  280  are preferably radar devices such as the SITRANS LR 400 (TM) produced by Siemens Corporation. The SITRANS LR 400 utilizes 24 GHz radar for level measurement of solids or liquids. Radar measuring units appear to be more accurate than ultrasonic scanners and less prone to failure than potentiometer-based devices.  
         [0052]    As the main mill  236  in the alternate embodiment has two outlets  270  and  272 , a correspondingly designed pug mill  200  is required. The pug mill  200  is a single stage design having a single long pug mill shaft  210  mounted within a pug mill shell or, housing  204 . The pug mill housing has respective inlet openings  208  and  209  at opposite ends thereof aligned with the outlets  270  and  272  of the main mill  236 . The inlet openings  208  and  209  receive the windrows  274  and  276  respectively.  
         [0053]    In order to maintain the breadth of the windrows  278  and  280 , windrow guides  290  may be provided which extend from opposite sides of the outlets  270  and  272  of the main mill  236 . Corresponding guides  292  may be provided which extend from the inlet openings  208  and  209  of the pug mill  200 . Preferably one of the windrow guides  290  and  292  will be metal, and the other an elastarmeric material such as rubber to maintain a reasonably good seal therebetween. The windrow guides  290  and  292  assist both in maintaining a constant windrow breadth and in ensuring that the entire windrow is directed into the pug mill  200 . Maintaining the breadth enhances the accuracy of the volume throughput measurement based on the height measurement.  
         [0054]    Paddles  214  extend radially from the pug mill shaft  210  to blend the milled material with rejuvenating fluid. Preferably the rejuvenating fluid is sprayed on the windrows  274  and  276  in metered amounts by the sprayers  250  as calculated by the control and processing station  58 . The blended material is directed by the paddles  214  for discharge through a rearwardly facing discharge opening  242 .  
         [0055]    An advantage of adding rejuvenating fluid after milling is that the dislodged road surface has a further opportunity to cool which has the benefit of reducing the amount of smoke generated by the resurfacing machine  10 . Additionally, providing two windrows of material from the main mill  236  can significantly increase production rate by a factor of about two (2).  
         [0056]    A further advantage of the alternate embodiment of FIGS. 4 and 5 is enhanced response time (or reduced lag). Monitoring throughput of milled material at about the same point as the addition of rejuvenating fluid permits quick response and a high level of accuracy. In the first embodiment described above, a delay or lag of at least four (4) to five (5) feet would occur between the monitoring of volume throughput and the addition of rejuvenating fluid. While this is still a vast improvement over earlier systems, it does generate some error in uneven surfaces when fluctuations in the pug mill output may not coincide with fluctuations in the amount of surface being milled.  
         [0057]    As in the first embodiment described above having a two stage pug mill  100 , the shell  204  of the long single stage pug mill  200  is substantially enclosed but for a downwardly facing bottom opening  206 , the inlet openings  208  and  209  and the discharge opening  242 . The bottom opening  206  in use would be held in close proximity to the underlying surface for the underlying surface  18  to act as a bottom of the pug mill  200 .  
         [0058]    The above description is intended in an illustrative rather than a restrictive sense. Variations to the specific embodiments described may be apparent to those skilled in such apparatus and processes without departing from the spirit and scope of the invention as defined by the claims set out below.