Abstract:
A method and apparatus for controlling the mixing of asphalt aggregate with rejuvenating materials in an asphalt rejuvenating machine. According to the method, milled aggregate is discharged in a windrow of fixed width, and windrow height is compared to rejuvenating machine speed to determine a volume rate of material being processed. A processor controller calculates a required amount of rejuvenating fluid addition based on the volume rate being processed and a desired proportion of rejuvenating fluid to aggregate. The processor controller controls a sprayer which directs rejuvenating fluid at some point along a zone extending from a milling apparatus to a mixer.

Description:
FIELD OF THE INVENTION 
     This invention relates to apparatus for in situ rejuvenation of asphalt pavement. More particularly this invention relates to a method and apparatus for controlling the mixing of milled aggregate and rejuvenating fluid in such rejuvenation. 
     BACKGROUND OF THE INVENTION 
     Asphalt pavement consists essentially of an aggregate and sand mixture held together with a petroleum based binder, such as tar. With continued exposure to sun, moisture, traffic, freezing and thawing, asphalt surfaces degrade. The degradation is principally in the binder, rather than the aggregate and sand mixture which makes up the bulk of the asphalt. Also, much of the degradation occurs within the top two or three inches of the surface. 
     Traditionally, worn asphalt pavement was not restored but instead was torn up and replaced with new asphalt. 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. 
     A typical road resurfacing apparatus has a heater for heating and softening the asphalt surface as it passes along the asphalt 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. 
     In order to produce a rejuvenated surface of high quality, it is important to ensure that an appropriate amount of rejuvenation 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 rejuvenation material to milled aggregate is analytically determined. Although the amount is relatively easy to determine, its control may prove difficult. Past asphalt rejuvenation machines have assumed a constant cutting or milling depth and a constant rate of machine travel in determining the rate of addition of rejuvenating fluid. 
     In practice, the machine speed may vary and as well, the depth of cut will generally vary because of surface irregularities and sloped surfaces. Accordingly, adding rejuvenation fluid at a rate based on constant speed and depth assumptions has produced rejuvenated surfaces with inconsistent properties. 
     It is an object of the present invention to provide a method and apparatus for more accurately controlling the mixing of asphalt aggregate with rejuvenating materials. 
     SUMMARY OF THE INVENTION 
     A method for controlling the mixing of asphalt aggregate with rejuvenating materials in an asphalt rejuvenating machine, said method comprising the steps of: 
     (i) dislodging a top layer of an asphalt paved surface; 
     (ii) passing a milling apparatus over the dislodged layer from step (i) to strip said top layer and break up the top layer of the asphalt paved surface to form a milled aggregate; 
     (iii) adding rejuvenating material to the milled aggregate; 
     (iv) transferring the milled aggregate to a mixer and blending the milled aggregate with said rejuvenating material to form a blended aggregate. 
     (v) discharging either the blended aggregate or the milled aggregate in a windrow of pre-determined width; 
     (vi) measuring the height of the windrow; 
     (vii) measuring a speed of travel of the asphalt rejuvenating machine; 
     (viii) comparing the height of the windrow with said speed and determining a volume rate of discharge from said mixer; 
     (ix) determining a desired rate of addition of the rejuvenating materials which corresponds to the volume rate of discharge and a pre-determined final composition; and, 
     (x) adjusting a rate of addition of the rejuvenating material in step (iii) to correspond to said desired rate of addition from step (ix). 
     An asphalt rejuvenating machine has a transport structure movable along an asphalt surface, a power plant mounted to the transport structure for providing motive force for the transport structure and a heater mounted to the transport structure for heating the asphalt surface. A rake mounted to the transport structure travels behind the heater for scarifying the asphalt surface to produce a scarified surface. A milling apparatus is mounted to the transport structure for milling the scarified surface to form a milled aggregate and to present the milled aggregate to a mixer. A rejuvenating fluid supply system is mounted to the transport structure for supplying rejuvenating fluid to the milled aggregate. The machine includes a mixer for blending the milled aggregate with the rejuvenating fluid and depositing a blended aggregate thus formed in a windrow of pre-determined width. The machine further includes a speed sensor for measuring the speed of travel of the transport structure and a height measuring device for measuring the height of the windrow. The machine further includes a comparator for comparing the speed of travel with the height to determine a volume rate of discharge of the blended aggregate. A controller associated with the rejuvenating fluid supply system is provided to vary a volume rate at which the rejuvenating fluid is added, based on the volume rate of discharge and the pre-determined final composition. 
     The rejuvenating fluid supply system may include a rejuvenating fluid tank, a sprayer for spraying the rejuvenating fluid on the milled aggregate, a pump fluidly communicating with the rejuvenating fluid tank and the sprayer for delivering the rejuvenating fluid from the tank to the sprayer, and a flow meter for determining a volume flow rate of the rejuvenating fluid. 
     The speed sensor may be mounted on an axle of the transport structure. 
     The mixer or the milling apparatus may have a discharge opening with a guide for determining the pre-determined width of the windrow, and a levelling device which rides along a top surface of the windrow. 
     The comparator may be part of a central processor unit which receives input from the speed sensor, the height measuring device, an operator control panel and the fluid flow meter. The central processor unit may also act as the controller by sending an output to the pump. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention are described below with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic representation of an asphalt rejuvenating machine according to the present invention; 
     FIG. 2 is a schematic representation of the components of an asphalt rejuvenating machine according to the present invention which relate to a method for the controlling of the mixing of asphalt aggregate according to the present invention; 
     FIG. 3 is a perspective view illustrating a height measuring device according to the present invention; 
     FIG. 4 is a perspective view of an alternate embodiment of a height measuring device according to the present invention; 
     FIG. 5 is a perspective view of another alternate embodiment of a height measuring device according to the present invention; and, 
     FIG. 6 is a perspective View of yet another alternate embodiment of a height measuring device according to the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     An asphalt rejuvenating apparatus is generally indicated by reference  10  in FIG.  1 . The rejuvenating machine  10  travels in a path of travel indicated by arrow  12 . The rejuvenating 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. 
     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 surface  18  upon which the rejuvenating apparatus  10  travels. A propane (or other combustible fuel) tank  20  and a combustion blower  22  would typically be provided. The heater  16  directs heat at the asphalt surface  18  to cause softening of an upper part of the asphalt surface  18 . 
     The softened asphalt surface  18  is 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 asphalt 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. 
     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 rejuvenating apparatus  10  and move it to a central part of the rejuvenating apparatus  10  where it is subsequently processed by the main mill  36 . 
     A pug mill  40 , 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 . Blended material  46  from the pug mill  40  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. 
     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. 
     A water system  52  may be provided to supply cooling water to the front and rear tires or tracks  54 . 
     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 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. 
     A sand/aggregate bin  60  precedes the asphalt rejuvenating apparatus  10 . The sand/aggregate bin  60  may be attached to the asphalt rejuvenating 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. 
     The rejuvenating fluid is supplied by a rejuvenating fluid supply system generally indicated by reference  100  in FIG.  2 . The rejuvenating fluid supply system  100  includes the rejuvenating fluid supply tank  42  and further includes a sprayer  102 , a pump  104  for delivering rejuvenating fluid from the supply tank  42  to the sprayer  102  and a flow meter  106  for measuring a volume flow rate of the rejuvenating fluid. 
     The sprayer  102  may be located at the main mill  38 , between the main mill  38  and the pug mill  40  or at the pug mill  40 . The sprayer  102  delivers rejuvenating fluid to the milled aggregate for final blending with the milled aggregate in the pug mill  40 . 
     A speed sensor  108  is mounted to an axle  110 , typically a drive axle of the transport structure  11  in FIG.  1 . The speed sensor measures the speed of the transport structure  11  and sends a signal to a central processing unit  112  which is part of the control and processing station  58 . 
     In order to determine an accurate rate at which rejuvenating fluid should be added, the asphalt rejuvenating machine  10  continually monitors the throughput of milled material. The volume throughput can be determined by multiplying the cross-sectional area of milled aggregate or blended aggregate emanating from the main mill  38  or pug mill  40  by the speed of the transport structure  11 . To facilitate the measuring of the cross-sectional area, the main mill  38  or pug mill  40  may be provided with a discharge opening  114  having guides  116  a pre-determined distance apart. The guides  116  cause the milled or blended aggregate to be discharged in a windrow  120  of substantially constant width W. 
     If the width is a known constant, the only variable that needs to be measured to determine cross-sectional area of the windrow  120  is its height H. Accordingly, a height measuring device  122  is provided for measuring the height H of the windrow  120 . Various height measuring devices  122  may be used. FIGS. 3 through 6 show representative examples. 
     In the FIG. 3 variant a “shoe”  124  substantially spans the breadth of the discharge opening  114  and levels the windrow  120  as it rides upon the windrow  120 . The shoe  124  has a base  126  which inclines upwardly toward a front end  128  thereof. A parallel bar linkage  130  mounts the shoe  124  to the main mill  38  or pug mill  40 . Although this is likely the most convenient mounting location this should not be interpreted restrictively. For example, a separate mounting bracket might be used extending from the transport structure  11 . 
     A height transponder  132  is mounted to the parallel bar linkage  130  to send an electronic signal to the central processing unit  112  in response to vertical movement of the shoe  124  which is indicative of windrow height. A counterweight  134  may also be provided to reduce the downward force exerted by Palo the shoe  124 . 
     FIGS. 4 through 6 illustrate alternate embodiments for a height measuring device  122  which are similar in that they utilize a flap  136  extending across the discharge opening  114  as a levelling device instead of the shoe  124 . The flaps  136  are mounted so as to be pivotable about an axis  138  extending across the discharge opening  114  in a direction transverse to the travel direction of the asphalt rejuvenating machine. 
     In the FIG. 4 embodiment, the height sensor is an angular displacement transducer  140  which senses the angular position of the flap  136  and sends an electronic signal to the central processing unit  112  in FIG. 2 (not shown in FIGS. 3 through 6) indicative of windrow height H. 
     The FIG. 5 embodiment is very similar to the FIG. 4 embodiment except that it uses a linear displacement transducer  142  rather than the angular displacement transducer  140  of the FIG. 4 embodiment. 
     The FIG. 6 embodiment also has a flap  136  but utilizes an ultrasonic (ie., sound speed) or laser (ie., light speed) depth sensor  143  rather than a displacement sensor and targets the windrow  120  itself rather than the flap  136  or shoe  124 . The depth sensor  143  sends a signal to the central processing unit  112  indicative of windrow height H. 
     As will be apparent to persons skilled in apparatus for measuring depth or heights, various arrangements are possible and the above described embodiments should only be considered as a representative sample. For example, an ultrasonic or laser transducer could be mounted directly to the transport structure  11  or used instead of the transponder  132  in the FIG. 3 embodiment. 
     The central processor unit  112  acts as a comparator which receives input from the height measuring device, an operator control panel  144  and the fluid flow meter  104 . The central processor unit  112  also acts as a controller by sending an output to a flow regulator  146  which may be associated with the flow meter  106 , to regulate the flow of rejuvenating fluid provided by the pump  104  to the sprayer  102 . 
     It will be apparent to those skilled in flow regulation devices that various flow regulator arrangements could be used. For example, a pump may be used having a proportional motor or a valve or pressure regulator could be used in combination with a flow meter. Basically any combination of devices which pump rejuvenating fluid, measure fluid flow and provide feedback to control the flow are candidates. 
     The operator control panel  144  may be arranged as desired however it should preferably include a display for actual rejuvenating fluid flow  146 , a display for desired rejuvenating fluid flow  148  and an operator input set point display and adjustment control  150 . 
     The above description is intended in an illustrative rather than a restrictive sense. Variations, examples of which are suggested above, may be apparent to persons skilled in such equipment and methods without departing from the spirit and scope of the invention as defined by the claims set out below.