Patent Abstract:
This invention relates to a novel seal coat process and equipment for applying the seal coat to improve the reliability of seal coat aggregate retention to the surface of the pavement by increasing the surface area of aggregate covered with binder and interlocking the aggregate with finer gradation material such as choke stone. It also relates to the use of lower amounts of asphalt binder, lower amounts of aggregate application, lower quality of aggregates, use of softer binders, and faster release to traffic times.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a surface treatment for a paved surface and the equipment for applying the asphalt binder and aggregate to accomplish this treatment. More specifically, the present invention is a seal coat process that uses substantially synchronous multiple applications of asphalt binder and aggregate in a single pass of the equipment over a road surface. 
     2. Description of the Related Art 
     Asphalt concrete deteriorates over time through the effects of air and water damaging the flexibility of asphalt cement and the bond of asphalt cement to the aggregate in the asphalt concrete mix. To delay the damaging effects of air and water, surface treatments are placed on top of asphalt concrete to seal the voids. This decreases the exposure of the asphalt binder in the asphalt concrete to air and water. 
     One of the most common and cost effective surface treatments is known as a chipseal. A chipseal involves spraying an asphalt binder (usually asphalt emulsion but can be asphalt cutbacks or hot asphalt cement) from a distributor truck onto the surface of the pavement. Soon after application of the asphalt binder to the road surface, aggregate is applied by a chip spreader vehicle. 
     While the most cost effective seal coat available, chipseals can have problems keeping the aggregate adhered to the road. Loose aggregate causes significant windshield damage, and many agencies have discontinued the use or restricted the use of chipseals to low traffic count roads. The main cause of premature aggregate loss is due to low embedment of the aggregate into the asphalt binder. There are multiple variables which contribute to low aggregate embedment including, but not limited to, irregular existing asphalt pavement texture, rock dimension changes, weather, delay in getting the rock applied to the asphalt binder, and traffic load. Another cause of low aggregate embedment is excess dirty fines coating the aggregate and not allowing it to adequately bond to the asphalt binder. 
     The obvious solution to aggregate loss in chipseals would be to increase the amount of asphalt binder applied to the existing pavement surface to increase embedment. However this approach creates a “bleeding” problem where the asphalt binder is pushed to the surface of the chipseal causing a rich asphalt surface. A “bleeding” or “flushing” chipseal deteriorates the aesthetics of the chipseal as well as potentially lowering the skid resistance of the finished chipseal. 
     Other attempts have been made to improve aggregate retention. The methods tried to date include precoating the aggregate with asphalt binder before shipping it to the construction site, applying choke stone after the chipseal is constructed to attempt to interlock the chipseal aggregate, and the use of fog seal applications several days after the chipseal is constructed to add extra asphalt to the surface. These approaches have shown improvement in aggregate retention. However, better methods of providing a surface treatment to a surface are still needed. 
     Also, paving vehicles for applying the asphalt binder and aggregate in a single pass of the vehicle have been employed, such as the paving vehicle which is the subject of U.S. Pat. No. 6,805,516 by James J. Barnat et al. and which is incorporated herein by reference. This patent teaches a roadway paving system and paving vehicle for applying a single layer of asphalt binder and thereafter applying a single layer of aggregate in a single pass with the paving vehicle in continuous fashion without driving on the freshly paved surface. By applying the aggregate to the layer of asphalt binder shortly after the binder is applied to the roadway, aggregate retention is improved. Also because both the binder layer and aggregate layer are applied in a single pass of the paving vehicle behind the rear wheels of the vehicle, the layers of binder and aggregate are not disturbed by the tires of the paving vehicle. 
     This type of paving vehicle needs to be continually supplied with binder and aggregate as it operates. Thus, specialized supply trucks, such as the one taught in U.S. Pat. No. 6,776,557 by James J. Barnat et al., are required to supply binder and aggregate to this type of paving vehicle as the paving vehicle is operating. The teachings of both U.S. Pat. No. 6,805,516 and U.S. Pat. No. 6,776,557 are incorporated herein by reference. 
     However, it would be desirable to be able to apply multiple layers of binder and aggregate in a single pass of a paving vehicle. Also, it would be desirable if the layers of binder thus applied could be of two different types of binder material. Further, it would be desirable if the layers of aggregate thus applied could be of two different types of aggregate material. The present invention addresses this need by providing a paving vehicle and supply truck and method for applying multiple layers of asphalt binder and aggregate in a single pass of the paving equipment over a roadway. 
     SUMMARY OF THE INVENTION 
     The present invention is a pavement surfacing process that uses substantially synchronous multiple applications of asphalt binder and aggregate. In the process of the present invention, normally a first portion or layer of the normal asphalt binder content is placed on the road surface, followed by application of aggregate, followed by a second portion or layer of asphalt binder being applied over the surface of the aggregate, followed by a second layer of aggregate in a substantially continuous fashion. The binder employed for the second layer may or may not be the same binder material used in the first layer. Normally the second layer of aggregate applied to the roadway is different from the first layer of aggregate, although it is possible to use the same type of aggregate for both first and second layers. Preferably, a finely graded material, choke stone, or sand is distributed over the second layer of binder as the second layer of aggregate, which helps to prevent the second layer of asphalt binder from being picked up by tires rolling over the surface. 
     Although the process of the present invention, normally applies a first layer of the binder, followed by first application of aggregate, followed by a second layer of binder, followed by a second layer of aggregate, it is not so limited. Instead, the process of the present invention can omit the first layer of binder and simply apply a first application of aggregate, followed by a single layer of binder, followed by a second layer of aggregate. 
     Having a significant percentage of the total asphalt binder sprayed on top of the aggregate in the second layer or as a single layer increases the surface area of the aggregate that is coated by asphalt. This increases aggregate retention, allows lower application rate of aggregate, and allows for potentially higher fines content aggregate. By using this process in a one step application, lower aggregate content than used in a normal one layer chipsealing process can be used. This allows for faster return of traffic to the treated surface. 
     Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is right side elevation view of a roadway paving system according to a preferred embodiment of the present invention comprising a roadway paving vehicle and a supply truck; 
         FIG. 2  is an enlarged isometric view of the roadway paving vehicle illustrated in  FIG. 1  taken from the left side of the paving vehicle; 
         FIG. 3  is a side elevation view of the roadway paving vehicle illustrated in  FIG. 2 ; 
         FIG. 4  is a top plan view of the roadway paving vehicle illustrated in  FIG. 2  with a partial schematic added to illustrate operational features of the vehicle and with the input hopper for the finely graded aggregate removed for clarity; 
         FIG. 5  is a rear end view of the roadway paving vehicle illustrated in  FIG. 2 ; 
         FIG. 6  is a rear end perspective view of the supply truck illustrated in  FIG. 1 , with the tailgate in a closed position; 
         FIG. 6   a  is a rear end perspective view of the supply truck illustrated in  FIG. 1 , with the tailgate in a closed position and showing the opposite side from what is shown in  FIG. 6 ; 
         FIG. 7  is the same rear end perspective view of the supply truck shown in  FIG. 6  but with the tailgate in an open position; 
         FIG. 8  is a cross-sectional view of the treated road surface of the present invention; and 
         FIG. 9  is a partial front view of the roadway paving vehicle illustrated in  FIG. 2  showing the two input hoppers. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and initially to  FIG. 1 , there is illustrated an improved surface treatment for a road surface. In a preferred embodiment of the present invention, the process of applying this surface treatment includes applying a portion of asphalt binder on a surface, then applying aggregate to the binder, and then applying the remaining asphalt binder so as to substantially cover the aggregate. A finely graded material then may be placed on the second layer of binder. 
     The asphalt binder may be an asphalt emulsion, asphalt cutback, liquid asphalt, molten bituminous material, hot asphalt cement, or another type of binder. Preferably, the asphalt binder is prepared as an asphalt emulsion. Most preferably, it is a polymer modified asphalt emulsion. Typically chipseal grade binders may be used, or alternatively, higher needle penetration asphalts may be used. Preferably, the binder can be an asphalt emulsion. More preferable, the asphalt emulsion is prepared as a cationic rapid set emulsion. Most preferably, the asphalt emulsion has a viscosity of at least about 50 Saybolt Furol seconds (SFS) at 50° C. The binder is applied at a rate in a sufficient amount to adhere the aggregate to the surface. Preferably, the binder is applied at a rate of about 0.1-1.0 gallons per square yard. For a particular size of aggregate, the rate of emulsion application can be up to approximately 20% by volume less than in a traditional chipsealing processes. 
     The aggregate can be any traditional aggregate made from limestone, granite, or other rock. It may be obtained from gravel or crushed stone. Typically, it will range in size from about 0.25-0.75 inches. Preferably, a maximum of 3% passes through a 200 mesh sieve. Preferably, a minimum of 80% is retained on a #4 sieve. It is further contemplated that the aggregate may, but need not, be precoated aggregate. The aggregate is applied at a rate of about 5-50 pounds per square yard, depending on the size of the aggregate. The rate of aggregate application can be up to approximately 30% by weight less than in traditional chipsealing processes. Typically, it will be at least about 20% less. This will amount to up to about 30% less aggregate by weight being used than used in a typical one layer chipseal process. 
     The remaining asphalt binder is applied as a second layer of binder. The total amount of binder used is proportional to the amount of aggregate applied in the first aggregate layer. It may, but need not have, the same composition as the first layer of binder. One or both layers may, but need not, be polymer modified. However, by providing a first binder and a second binder with different characteristics, surfaces that meet particular needs can be made. For example, the first layer of binder can have a higher needle penetration value than the second layer of binder. This could provide a soft layer that receives aggregate while still providing good structural support to receive traffic. 
     The total amount of binder used in the surface treatment of the present invention is substantially less than a traditional double chipsealing process. Preferably, less than 80% of the binder used when two layers of traditionally sized aggregate are applied is used in the present invention. Most preferably, the amount of asphalt used in both binder layers is no more than what is used in a single layer chipseal. The top layer of binder should be about 20-80% by volume of the total amount of binder used. Preferably, at least about 25% by volume of the total amount of binder used is on the top layer. Preferably, no more than about 60% by volume of the total binder used is on the top layer. More preferably, at least about 35% by volume of the total amount of binder used is on the top layer. Most preferably, the top layer of binder is about 45-55% by volume of the total amount of binder used. 
     It is desirable but not required to place a finely graded material on top of the second layer of binder. This layer can be used to blot excess asphalt, allowing for quicker return to traffic than treatments that have a top coating of aggregate (not finely graded) or binder. This helps to keep tires from disturbing the first layer of aggregate. Adding a layer of finely graded material on top of the second layer of binder also accelerates coalescence by absorbing moisture. If a finely graded choke stone or other finely graded aggregate is used, then this will be the second layer of aggregate applied. Preferably, a finely graded choke stone is placed on top of the second layer of binder. Alternatively, sand or other finely graded material may be used in place of choke stone. More specifically, the finely graded material should have at least about 50% passing through a ¼ inch sieve and a maximum of about 15% passing through 200 mesh. Preferably, at least about 75% of the finely graded material passes through a ¼ inch sieve, and most preferably, at least about 95% of the finely graded material passes through a ¼ inch sieve. If a finely graded choke stone or other finely graded aggregate is used, only a small amount of the total amount of aggregate used is a part of the second layer, unlike a traditional double chipseal. Typically, about 10-30% by weight aggregate of the total amount of aggregate is used in the final layer. Most preferably, about 15-20% by weight aggregate of the total amount of aggregate is used in the final layer. A finely graded material placed over the second layer of asphalt binder may help to reduce tires tracking in the asphalt binder. 
     It is further contemplated, as another aspect of the present invention that using a substantially synchronous process, 2 layers of binder and 2 layers of aggregate could be applied even if the second layer of aggregate was not finely graded. The present invention includes performing multiple chipsealing processes in less than 24 hours, preferably in less than 12 hours, and most preferably as a substantially synchronous and continuous process. 
     Another aspect of the present invention is a three layer substantially synchronous process that includes applying aggregate, followed by applying binder, followed by applying a layer of finely graded material. It is also contemplated to have a four layer synchronous process where additional binder is applied on top of the finely graded material layer. Still another aspect of the present invention involves applying binder, followed by aggregate, followed by finely graded material in a substantially synchronous process. 
     A treated road surface resulting from the process described above is another aspect of the present invention. A road surface having a preferred surface treatment of the present invention is shown in  FIG. 8  and is broadly designated by reference numeral  12 . This surface treatment includes applying a first layer of binder  14  on road surface  12 , a first layer of aggregate  16 , a second layer of binder  17 , and a second layer of finely graded aggregate or choke stone  19 . As illustrated in  FIG. 8 , second layer of binder  17  substantially covers aggregate  16 . When aggregate  16  is distributed on binder  14 , it is somewhat or partially imbedded in binder  14 . Additional binder  17  then substantially covers aggregate  16  so that the road surface is a layer of aggregate imbedded in binder. 
     In making the treated road surface of the present invention, the first layer of aggregate  16  should be placed on the first layer of binder  14  before it substantially coalesces. Preferably, the first layer of aggregate  16  is placed within about 2 hours of the application of the first layer of binder  14 . Most preferably, the first layer of aggregate  16  is placed within about 1 hour of the application of the first layer of binder  14 . Typically, the first layer of aggregate  16  is placed within less than a minute of the application of the first layer of binder  14 . In addition, the second layer of aggregate or other finely graded material  19  should be placed on the second layer of binder  17  before it substantially coalesces. Preferably, the second layer of aggregate or other finely graded material  19  is placed within about 2 hours of the application of the second layer of binder  17 . Most preferably, the second layer of aggregate  19  is placed within about 1 hour of the application of the second layer of binder  17 . Typically, the second layer of finely graded material  19  is placed within less than a minute of the application of the second layer of binder  17 . Preferably, the second layer of binder  17  and the second layer of aggregate  19  are placed prior to the first layer of binder  14  substantially coalescing. Preferably, the second layer of binder  17  is applied to the first layer of aggregate  16  within about 24 hours. Preferably, all of the layers  14 ,  16 ,  17  and  19  are placed within about 24 hours. More preferably, all of the layers  14 ,  16 ,  17  and  19  are placed within about 12 hours. Even more preferably, all of the layers  14 ,  16 ,  17  and  19  are placed within about 6 hours. Most preferably, all of the layers  14 ,  16 ,  17  and  19  are placed in a substantially continuous and synchronous process. 
     Preferably, 3 layers, namely, binder, aggregate and remaining binder, are placed in a substantially synchronous process where the sprays have non-intersecting trajectories. Most preferably, 4 layers, namely, binder, aggregate, remaining binder, and finely graded material are placed in a substantially synchronous process. 
     The substantially continuous and synchronous process of the present invention may be accomplished by using a single piece of equipment capable of applying all layers in a single pass in a substantially synchronous manner. Alternatively, multiple distribution vehicles may be used. Preferably, the single piece of equipment is a vehicle that includes 2 spray systems and 2 aggregate dispensing systems. Preferably, this vehicle includes spray systems with independent control of distribution of the first layer of binder and the second layer of binder. This independent control allows the ratio of the first binder layer to the second binder layer to be adjusted at any time or to be completely turned off. 
     For purposes of illustration, a preferred embodiment of the present invention is illustrated as an asphalt paving system  10  comprising a roadway paving vehicle  20  and a supply truck  22  as shown in  FIG. 1 . The roadway paving vehicle  20  applies asphalt binder  14 , aggregate material  16 , remaining binder  17 , and finely graded material  19  typically over an existing road surface  12 , such as a roadway, to surface treat the road surface  12 . It also could be used for new roadway surfaces or other road surfaces. The supply truck  22  carries two supplies of asphalt binder material  14  and  17 , aggregate material  16 , and finely graded material  19  for the purpose of refilling the roadway paving vehicle  20  with materials. In operation, the supply truck  22  links with the roadway paving vehicle  20  on the run. The phrase “on the run” means that the roadway paving vehicle  20  is moving forward and continuously dispensing asphalt binder materials  14  and  17 , aggregate material  16 , and finely graded material  19  while it is being refilled. This requires that the supply truck  22  be linked with the paving vehicle  20  so that the supply truck  22  and paving vehicle  20  can move together while the supply truck  22  is refilling the paving vehicle  20 . After the supply truck  22  is empty, the supply truck  22  is disconnected from the roadway paving vehicle  20  and then the roadway paving vehicle  20  can then be linked with another supply truck (not illustrated). 
     The paving system  10  is primarily used to surface treat an existing road surface  12  with a first asphalt binder layer  14 , an aggregate layer  16  spread on the top of the asphalt binder layer  14 , a second asphalt binder layer  17 , and a finely graded material layer  19 . The layers  14 ,  16 ,  17  and  19  combine to create a new surface over the road surface  12  that provides a water barrier or seal, improves the life-span of the surface, provides for improved vehicle traction, and can also provide a new wearable layer. Although this disclosure describes four layers  14 ,  16 ,  17  and  19 , it will be appreciated to those skilled in the art that once these layers  14 ,  16 ,  17  and  19  are deposited on a roadway surface, the layers typically combine integrally and are substantially indistinguishable from one another forming a single stratum of paving material. 
     Referring to  FIGS. 2-5 , the roadway paving vehicle  20  comprises a frame or chassis  26  supported on wheels  28  and an engine  30 . For purposes of reference, the vehicle  20  includes front and rear ends generally indicated at  32 ,  34 . The vehicle  20  carries a first asphalt binder dispensing systems  36  that dispenses asphalt binder material  14 , a first aggregate material dispensing system  38  that dispenses aggregate material  16 , a second asphalt binder dispensing system  39  that dispenses binder  17 , and a finely graded material dispensing system  37  that dispenses finely grade material  19 . As generally shown in  FIGS. 1 and 3 , the asphalt binder dispensing systems  36  and  39  are separate from the aggregate material dispensing systems  38  and  37  such that asphalt binder materials  14  and  17  and aggregate materials  16  and  19  are not mixed in the vehicle  20  prior to the dispensing of the asphalt binder materials  14  and  17  and the aggregate materials  16  and  19  at the rear end  34  of the vehicle  20 . Thus, the aggregate material  16  and  19  is discharged without being mixed with asphalt binder  14  and  17  inside the vehicle  20 . By using a single vehicle  20  carrying both the asphalt binder dispensing systems  36  and  39  and the aggregate material dispensing systems  38  and  37 , the time and spacing between application of the asphalt binder material  14  and  17  and aggregate material  16  and  19  can be optimized for best chip embedment and retention. In addition, the dispensing areas of the asphalt binder dispensing systems  36  and  39  and the aggregate material dispensing systems  38  and  37  are all arranged at the rear end  34  of the vehicle  20  behind all of the supporting wheels  28  such that the wheels  28  do not roll over freshly laid first asphalt binder layer  14 , aggregate layer  16 , second asphalt binder layer  17 , and finely graded material layer  19 . This prevents the wheels  28  from picking up and throwing stones or damaging the fresh application and may allow less aggregate to be used. 
     In the disclosed embodiment, the first asphalt binder dispensing system  36  generally comprises a tank  40 , a spray bar  42 , an input pump  44 , an input conduit  46 , an output pump  48  and an output conduit  50 . The second asphalt binder dispensing system  39  also comprises a tank  41 , a spray bar  43 , an input pump  45 , an input conduit  47 , an output pump  49  and an output conduit  51 . The tanks  40  and  41  are supported between front and rear sets of wheel  28 , and each contains hot asphalt binder material  14  or  17 . The tanks  40  and  41  are sized large enough to provide a sufficient holding capacity for dispensing asphalt binder material  14  or  17  on a continuous basis between changes in supply trucks  22  without the need to stop, thereby avoiding flaws or bumps in the roadway surface. The output pumps  48  and  49  are fluidly connected to the tanks  40  and  41 , respectively, and the spray bars  42  and  43 , respectively, to pump asphalt binder material  14  and  17  to the spray bars  42  and  43 , to form sprayers. The particular disclosed pumps  48  and  49  are asphalt gear pumps which may both pump and meter asphalt binder material  14  or  17  directly. However, it will be appreciated that other pumps, such as tank pressurizing pumps could be used for example in conjunction with control valves, or other pumping schemes. 
     The spray bars  42  and  43  extend horizontally generally parallel to the roadway surface  12 . Referring to  FIGS. 3 , and  4 , the spray bar  42  is comprised of a plurality of nozzles  52  and a plurality of control valves  54  in series with the nozzles  52 . For clarity of illustration, not all control valves and nozzles or connections between control valves and nozzles are shown in  FIG. 4 . Each control valve  54  controls flow of asphalt binder material  14  to the individual nozzles  52 . The control valves  54  have open and closed states for allowing and preventing flow of asphalt binder material  14  to individual nozzles  52 . With this arrangement, the span or spray width of asphalt binder material  14  is selectively variable or modular and can be controlled or adjusted by shutting off selected control valves  54 . 
     The spray bar  42  also preferably includes extendible and retractable arms  56 , as best seen in  FIG. 4 . The arms  56  can extend beyond the normal width of the vehicle  20  so as to cover an entire roadway lane. The arms  56  can also retract to be within the normal width of the vehicle  20  for road transport. The extendible and retractable arms  56  are illustrated as the pivoting type, pivoting between raised and lowered positions, but it will be appreciated that horizontally extendible and retractable telescoping arms may also be utilized that extend horizontal with respect to the roadway  12 . 
     The details of spray bar  43  are not shown but it is contemplated that spray bar  43  could have the same or similar features as spray bar  42  with regard to spray nozzles and control valves. Spray bar  43  is also provided with extendible and retractable arms  56 ′, as best seen in  FIG. 4 . 
     The disclosed asphalt binder dispensing systems  36  and  39  also include refill systems comprised of the input conduits  46  and  47 , respectively, and the input pumps  44  and  45 , respectively, for pumping asphalt binder material  14  and  17  into the holding tanks  40  and  41 , respectively, as shown best in  FIGS. 3-4 . Preferably the input pumps  44  and  45  are gear pumps that work through suction rather than pressure to avoid pressurized lines that could otherwise rupture. The input conduits  46  and  47  fluidly connect to the holding tanks  40  and  41 , respectively, and extend vertically above a platform  58  of an operator station  60  on the vehicle  20  and terminate in hydraulic couplings  62  and  63 , respectively. The hydraulic couplings  62  and  63  are disposed at a convenient vertical height for ready and accessible connection to the asphalt binder supply of the supply truck  22  by the operator stationed on the vehicle&#39;s operator station  60 , as will become apparent when the supply truck  22  is discussed in more detail hereafter. The input conduits  46  and  47  preferably include swivel joints  64  and  65 , including ball joints or other rotatable joints, respectively, allowing rotation about the vertical axis to allow an operator to connect the hydraulic couplings  62  and  63  to the supply truck  22 . The input conduits  46  and  47  also extend vertically upwardly through the platform  58  in a centrally accessible location relative to conveyers  88 ,  89  discussed infra. 
     The aggregate material dispensing system  38  comprises a storage hopper in the form of an input hopper  70  at the front end  32  of the vehicle  20  and an output hopper  72  at the rear end  34  of the vehicle. The aggregate material dispensing system  38  further includes a conveyer mechanism  74  extending diagonally for transporting aggregate material from the input hopper  70  to the output hopper  72 . 
     The hoppers  70 ,  72  are sized large enough to provide a sufficient holding capacity for dispensing aggregate material  16  on a continuous basis between changes in supply trucks  22  without the need to stop, thereby avoiding flaws or bumps in the roadway surface. The input hopper  70  may include extendible and retractable extension wings  76  that expand horizontally outward via a fluid powered cylinder outside the normal span of the vehicle  20  to increase the holding capacity of the input hopper  70  and retract within the normal span of the vehicle  20  for over the road transportation. In the disclosed embodiment, each of the wings  76  can be pivoted about hinges  77  by fluid powered cylinders  79  to provide the desired clearance. The disclosed embodiment also includes augers  78  disposed above the conveyer mechanism  74  and mounted between the input hopper  70  and a horizontal cross support  81  mounted to the chassis  26 . The augers  78  or other such spreaders can be operated to spread out the aggregate material in the input hopper  70  to more fully utilize the holding capacity of the input hopper  70  and wings  76 . 
     The output hopper  72  discharges aggregate material  16  through a discharge port  80  at the bottom thereof as shown best in  FIGS. 2 and 3 . The discharge port  80  is divided into separate adjacent sections by a plurality of gates  82  as schematically shown at the top of  FIG. 4 . For clarity of illustration, not all control valves and gates or connections between gates and control valves are shown in  FIG. 4 . The gates  82  have open and closed states for allowing and preventing discharge of aggregate material  16 . The overall span or width of the applied layer of aggregate material  16  is determined by the gates  82 , which can be opened and closed. More gates  82  can be opened to expand the span of discharged aggregate material  16  or closed to decrease the span of discharged aggregate material  16 . Thus the length or span of the discharge port  80  is selectively variable or modular to accommodate different application widths and changes in the width of the roadway surface  12 . In practice, the width of the discharged aggregate material  16  is typically equal to or just greater than the width of the discharged asphalt binder material  14 . Aggregate material  16  may be discharged in a forward direction, a rearward direction or in both directions through the discharge port  80 . The discharge port  80  may also be divided into multiple horizontally parallel sections with certain sections having a fixed output and other sections having a variable output. 
     The output hopper  72  is also divided into a pair of horizontally translatable dispensing bins  86 ,  87  disposed one in front of the other. The bins  86 ,  87  are contained within the normal span of the vehicle  20  for over the road transportation. However, the bins  86  and  87  expand through horizontal movement with respect to the roadway outside the span of the vehicle  20  to expand the overall length of the discharge port  80  sufficient to cover at least an entire lane of a roadway  12  and substantially equivalent to the length of the extended spray bar  42 . The dispensing bins  86 ,  87  and the spray bar  42  can be shifted from side to side or right or left for adjustment as necessary as an offset or off-center feature. 
     As the output hopper  72  may be divided into separate bins  86  and  87  as in the disclosed embodiment, similarly, the conveyer mechanism  74  may comprise separate conveyers in the preferred form of endless belt conveyers  88  and  89  controlled by motors  90  and  91 , respectively. Although belt conveyers  88  and  89  have been illustrated, it will be appreciated that other conveyer mechanisms could also be used, such as augers which may also have holding capacity for aggregate material if large enough. Each belt conveyer  88  and  89  feeds aggregate material  16  into the bins  86  and  87  through a guide chute  92 . Each conveyer  88  and  89  can feed aggregate material  16  in both bins  86  and  87 , or alternately, each conveyer  88  and  89  can be dedicated to one bin  86  or  87 . The diagonal arrangement of the conveyers  88  and  89  allows for room for the operator station  60  and platform  58  to be at a relatively high vertical height towards the front end  32  of the vehicle. At the front end  32 , the conveyers  88  and  89  have a relatively low vertical height. As the conveyers  88  and  89  extend rearward and upward, clearance is provided for the tanks  40  and  41  and engine  30  toward the center and rear end  34  of the vehicle  20  where the conveyers  88  and  89  are at a relatively high vertical height. 
     Referring also to  FIG. 9 , the finely graded material dispensing system  37  comprises a storage hopper in the form of an input hopper  71  at the front end  32  of the vehicle  20  and an output hopper  73  at the rear end  34  of the vehicle. The input hopper  71  may be a separate hopper from input hopper  70  which may be located beside or above input hopper  70  or may be simply formed by a partition within input hopper  70  to separate the contents of the two input hoppers  70  and  71 . 
     The finely graded material dispensing system  37  further includes a conveyer mechanism  75  extending diagonally for transporting finely graded material  19  from input hopper  71  to output hopper  73 . The details of the finely graded material dispensing system  37  are not shown, but it is contemplated that this dispensing system could include some or all of the features of aggregate material dispensing system  38  which has previously been described or may be any other type of aggregate moving device, such as for example an auger type conveyer shown in  FIG. 9 . 
     The first spray bar  42  is generally parallel to the discharge port  80  and spaced in front of the discharge port  80  a distance of between about 0.1 and about 10 feet. The second spray bar  43  is generally parallel to discharge port  80  and is spaced behind the discharge port a distance of about 0.1 to about 10 feet. The discharge port  83  of the finely graded material output hopper  73  is spaced a distance of between about 0.1 and about 10 feet behind second spray bar  43 . The roadway paving vehicle  20  applies asphalt binder material  14 , aggregate material  16 , additional asphalt binder material  17 , and finely graded material  19  at a maximum sustainable speed of between about 1 and about 15 miles per hour. During truck refilling, the speed of the vehicle  20  may slow. 
     To accommodate different vehicle speeds, different application rates, and different widths and thickness of the layers  14 ,  16 ,  17  and  19  of asphalt binder and aggregate, the paving vehicle  20  includes an electronic controller  84 , either as an integral controller or as several separate controllers, in electrical communication with the control valves  54 , the output pumps  48  and  49 , and the gates  82 , as schematically indicated in  FIG. 4 . The electronic controller  84  is responsive to vehicle speed determined by a speed sensor  96  and other operator input. The electronic controller  84  controls these components to set an application rate and width for each asphalt binder material  14  and  17 , the aggregate material  16 , and finely graded material  19  from one of many of the various application rates and widths available. As the vehicle speed changes, the electronic controller  84  automatically compensates accordingly to produce uniform application. 
     To better prevent spilling of material  14 ,  16 ,  17 , and  19  during supply truck  22  refilling operations, the roadway paving vehicle  20  also includes a mechanical coupling hook attachment  98  at the front end  32  that releasably couples to a cross bar  120  at the rear end  132  of the supply truck  22 , as can be seen in  FIGS. 1 ,  3 ,  4 ,  6 ,  6   a  and  7 . This better ensures proper spacing between the roadway paving vehicle  20  and the supply truck  22 . The truck  22  also preferably includes a truck spring impact mechanism  170  to absorb impact when the speeds of the truck  22  and roadway paving vehicle  20  are being synchronized when linking the truck  22  and paving vehicle  20  without stopping the forward progression of the chipsealing operation. The truck spring impact mechanism  170  allows the cross bar  120  to move forwardly against the action of a spring. 
     The roadway paving vehicle  20  similarly includes a vehicle spring impact mechanism  93  associated with the mechanical coupling hook attachment  98  for also absorbing impact. The vehicle spring impact mechanism  93  allows the hook attachment  98  to move rearward against the action of a spring. Although spring impact mechanisms  93  and  170  are illustrated, it will be appreciated that other shock absorbers may be used including silicon packing or other resilient members. 
     Turning in greater detail to the supply truck  22  with reference to  FIGS. 1 and 6 ,  6   a , and  7 , the supply truck  22  is shown in the form of an over-the-road tractor  122  and a detachable live bottom trailer  124 , although a unitary truck can also be used. The truck  22  includes a trailer chassis  126  supported on wheels  128  and extending longitudinally between front and rear ends  130 ,  132 . The chassis  126  supports an elongated supply hopper  134  for holding aggregate material having a discharge region  136  at the rear end  132 . The supply hopper  134  may hold traditionally sized aggregate for the first aggregate layer  16 , finely graded material for the top layer  19 , or combinations thereof with partitions in hopper  134  to keep the fines  19  from mixing with the coarse aggregate  16 . A conveyer mechanism  138  in the supply hopper  134  can convey aggregate material  16  or  19  toward the discharge region  136 . 
     Although only one conveyer mechanism  138  is illustrated, it may be desirable to have a second conveyer mechanism. The second conveyer mechanism may be similar in design to the first conveyer mechanism  138  or may be of any suitable design, such as an augur type conveyer. If two conveyer mechanisms  138  are provided, the first conveyer mechanism  138  would be employed to convey aggregate material  16  into input hopper  70  on the paving vehicle  20  and the second conveyer mechanism would be employed to convey finely graded material  19  into input hopper  71  on the paving vehicle  20 . 
     Referring back to the drawings of the supply truck  22 , a tailgate  140  closes the discharge region  136  of the supply hopper  134  to prevent material  16  and  19  from escaping and opens rearward to allow for material  16  and  19  to be discharged. 
     The supply truck  22  is also equipped with a first supply tank  142  containing asphalt binder material  14 , as shown in  FIG. 6 , and optionally a second supply tank  143  containing a second type of asphalt binder material  17 , as shown in  FIG. 6   a . Optionally, the second supply tank  143  can contain the same type of asphalt binder material  14  as contained in the first supply tank  142  if it is desired to apply only one type of asphalt binder material  14  to a roadway. 
     When the supply truck  22  and roadway paving vehicle  20  are linked together, aggregate material  16  can be transferred from the supply truck  22  to the input hopper  70  through the discharge region  136  and/or finely graded material  19  can be transferred from the supply truck  22  to the input hopper  71 . The tailgate  140  is comprised of horizontally outwardly pivoting doors  144  and  146  that control and direct the discharge of aggregate material  16  and  19  from the supply hopper  134  of the truck  22 . Further details of the outwardly pivoting doors are described in U.S. Pat. No. 6,386,818 by Michael F. Reed, the entire disclosure of which is hereby incorporated by reference. Suffice it to say that the doors  144  and  146  pivot rearward and away from each other to open the discharge region  136  and forwardly and toward each other to close the discharge region  136 . 
     The supply truck  22  is illustrated as the “live bottom” type with the conveyer mechanism  138  comprising an endless belt  148  entrained around sprockets and driven by motor  150 . The motor  150  has a variable speed such that the discharge rate of aggregate material  16  or finely graded material  19  is controllable. It is an aspect of the invention that the speed of motor  150  and therefore the conveyer mechanism  138  is controlled at the operator station  60  on the roadway paving vehicle  20 . In the disclosed embodiment, this is accomplished with electronic control modules  152  of the supply truck  22  that extend to the paving vehicle  22 . The control modules  152  are in electrical communication with the motor  150 . In this manner, the refill rate of aggregate material  16  into the input hopper  70  and the refill rate of finely graded material  19  into input hopper  71  are controlled from the roadway paving vehicle  20 . The operator of the paving vehicle  20  can control refilling and prevent an overfill condition as the input hoppers  70  and  71  are in clear sight of the operator of the paving vehicle  20  from the operator station  60  of the paving vehicle  20 . 
     In the disclosed embodiment, the electronic control modules  152  are actually part of the supply truck  22 . Specifically, the electronic control modules  152  are carried by the tailgate  140  of the supply truck  22  and extend rearward to the operator station  60  on the roadway paving vehicle  20  when the tailgate  140  opens rearward. More specifically, the electronic control modules  152  are carried on the end of support arms  154  affixed to the outwardly pivoting doors  144  and  146 . The support arms  154  extend diagonally and upwardly positioning the electronic control modules  152  above the doors  144  and  146  so that when the doors  144  and  146  extend rearward, the electronic control modules  152  extend to the operator station  60  for ready access and use by an operator on the roadway paving vehicle  20 . 
     Asphalt binder material  14  and  17  is transferred from the supply truck  22  to the roadway paving vehicle  20  via transfer conduits in the form of flexible transfer hoses  156  and  157 . The flexible transfer hoses  156  and  157  have one end connected to the supply tanks  142  and  143 , respectively, and the other end terminating in hydraulic couplings  158  and  159 , respectively. When the tailgate  140  extends rearward, the flexible transfer hoses  156  and  157  and hydraulic couplings  158  and  159  also extend rearward to the operator station  60  for attachment with asphalt binder dispensing systems  36  and  39 , respectively, of the roadway paving vehicle  20 . In the disclosed embodiment, the transfer hoses  156  and  157  are supported by their associated support arm  154  and they extend beyond the end of the arm  154  to provide flexible end portions  160  and  161  for easy manipulation. The end portion  160  may be latched to the truck supply hopper  134  for transport. The transfer hoses  156  and  157  extend diagonally and upwardly generally parallel with support arms  154  being secured thereto by cables or chains  162 . When the doors  144  and  146  extend rearward to open the discharge region  136 , the transfer hoses  156  and  157  extend rearward to the operator station  60  for connection to the vertically extending input conduits  46  and  47 , respectively. The hydraulic couplings  158  and  159  fluidly connect in a detachable manner to the hydraulic couplings  62  and  63 , respectively, provided on the input conduits  46  and  47  of the roadway paving vehicle  20 . Once connected, the input pumps  44  and  45  are operable to transfer asphalt binder  14  and  17  from the supply truck  22  to the paving vehicle  20  to refill the tanks  40  and  41 , respectively. 
     A further aspect disclosed herein is that supply tanks  142  and  143  are disposed vertically beneath the conveyer mechanism  138  and the hopper  134  and between the front wheel set  164  and the rear wheel set  168  of the supply truck  22 . The tops of the supply tanks  142  and  143  are mounted directly to the chassis  126  with brackets  169 . This achieves a low center of gravity for the truck  22 , particularly when the tanks  142  and  143  are full, and allows for a wider supply hopper  134  as opposed to use of side mounting tanks that would be mounted onto the side walls of the supply hopper  134 . 
     In operation, the roadway paving vehicle  20  discharges asphalt binder material  14  and  17  and aggregate material  16  and  19  over the roadway  12  to surface treat the roadway surface. Specifically, the output pump  48  transfers asphalt binder material  14  from the tank  40  to the first spray bar  42  and out through the nozzles  52  to form the first asphalt binder layer  14 . The output hopper  72  discharges aggregate material  16  through discharge port  80  to form an aggregate layer  16  over the asphalt binder layer  14 . Output pump  49  pumps asphalt binder material  17  from tank  41  to the second spray bar  43 , which distributes a second asphalt binder layer  17  over the aggregate layer  16 . Then, output hopper  73  distributes finely graded material layer  19  on top of the second asphalt binder layer  17 . 
     During operation, various retractable arms  56 , control valves  54  and gates  82  can be selectively closed or opened in order to set the width or change the width of the surface treatment operation. This can be done without stopping the vehicle  20 . In the event that the vehicle  20  incurs a change in speed, the electronic controller  84  can proportionally control the application flow rates of asphalt binder material  14  and  17  and aggregate material  16  and  19  to maintain uniform thickness of the layers  14 ,  16 ,  17  and  19 . The flow rate of asphalt binder material  14  and  17  can be controlled by adjusting the speed of pumps  48  and  49  or the degree of opening of the control valves  54  in the spray bars  42  and  43 , or both. The flow rate of aggregate material  16  from hopper  72  can be controlled by adjusting the degree of opening of the gates  82 . Likewise, the flow of finely graded material  19  from hopper  73  can also be adjusted. The flow rates of aggregate material  16 , finely graded material  19  and asphalt binder  14  and  17  may, but need not, be closely linked so as to increase and decrease in unison in order to maintain uniformity of the new treated surface formed from the operation of the present invention. 
     During operation, the roadway paving vehicle  20  uses its own internal supply of asphalt binder material  14  and  17  contained in the tanks  40  and  41 . In addition, the conveyers  88  and  89  transport aggregate material  16  from the input hopper  70  to the output hopper  72 , and conveyer  75  transports finely graded material  19  from input hopper  71  to output hopper  73 . Eventually, the supplies of asphalt binder material  14  and  17 , of aggregate material  16 , and of finely graded material  19  contained in the vehicle  20  begin to run out. The supply truck  22  which carries a supply of both asphalt binder material  14  and  17  and aggregate materials  16  and  19  serves to refill these supplies for the roadway paving vehicle  22 . 
     Advantageously, it is not necessary to back up a supply truck  22  as the supply truck  22  can be parked in front of the roadway paving vehicle  20  until the roadway paving vehicle  20  catches up with the stationary supply truck  22 . The supply truck  22  then releasably couples with the roadway paving vehicle  20  while the roadway paving vehicle  20  continues to move forward and continues to discharge asphalt binder material  14  and  17  and aggregate material  16  and  19 . This on the run coupling advantageously prevents bumps or flaws in the chipsealed roadway. Once coupled, the tailgate doors  144  open to allow aggregate material  16  and  19  from the truck hopper  134  to refill the input hoppers  70  and  71 . When the doors  144  open, the transfer conduits  156  and  157  also automatically extends rearward toward the roadway paving vehicle  20 . An operator on the roadway paving vehicle  20  can then couple the transfer conduits  156  and  157  to the input conduits  46  and  47 . An operator can selectively operate the input pumps  44  and  45  to suction asphalt binder material  14  and  17  from the truck supply tanks  142  and  143 , respectively, to refill the tanks  40  and  41 , respectively, of the roadway paving vehicle  20 . Opening of the doors  144  also extends the control modules  152  rearward to the roadway paving vehicle  20 . An operator on the roadway paving vehicle  20  can use the control modules  152  to control the truck conveyers  148  and  149  and therefore the refilling rate of the input hopper  70  and input hopper  71 . Conveyer  149  delivers aggregate to input hopper  71 . As shown in the drawings, conveyer  149  is an auger type system that can be moved rearward to position the conveyer  149  over the input hopper  71  and then can be moved forward to allow the doors  144  to once again be closed. 
     After the supply truck  22  is empty, the roadway paving vehicle  20  can be decoupled from the supply truck  22  and linked with a second supply truck that is identical or similar to the first with a new supply of materials  14 ,  16 ,  17 , and  19 . This also can be done without stopping thereby providing a continuous operation. In practice, fixed location supply stations are often a far distance from the work area and therefore several supply trucks  22  are typically used. 
     Several additional advantages of the disclosed embodiment can be realized. One advantage is that in many circumstances the roadway  12  can receive traffic in less than four hours after surface treating, thereby minimizing traffic disturbance. The roadway paving vehicle  20  and supply truck  22  can also occupy one roadway lane, if desired, during surface treatment operations, thereby also minimizing traffic disturbance. The dimensions of the vehicle  20  and supply truck  22  are sized to be contained within a roadway. The surface treatment process can also operate with a greater viscosity range of asphalt binder material  14  and  17 . This advantage can be realized due to the fact that aggregate material  16 , additional binder  17 , and finely graded material  19  can be discharged over the asphalt binder material  14  more quickly in a controlled manner. 
     The disclosed embodiment can achieve an application rate of about 10-900 square yards per minute, up to 24 tons per minute of aggregate  16  and  19  feed and about 10-400 gallons per minute of asphalt binder material  14  and  17 . The roadway paving vehicle  20  can store between about 1 and 100 tons (and preferably between 30 and 25 tons, and even more preferably between 10 and 13 tons) of aggregate material  16  and  19  and has a total maximum tank holding capacity of binder  14  and  17  of 15,000 gallons (preferably a maximum of 2,000 gallons and even more preferably a maximum of 1,000 gallons). Yet a further advantage is that all of the vehicles  20  and trucks  22  of the disclosed embodiment are moving forward during surface treatment operations. This is in contrast to prior systems where the asphalt dispensing vehicle moved forwardly while the chip spreader moved in reverse to prevent wheels from rolling over asphalt binder material. Another advantage is that all of the layers, namely, layers  14 ,  16 ,  17  and  19  can be applied in a substantially synchronous process. 
     Successful retention of the aggregate  16  and  19  is dependent on the existing surface texture, aggregate dimensions, weather, and traffic conditions. Each of these affect the surface area of the aggregate  16  and  19  covered with asphalt binder  14  and  17 . However, these variables are difficult to quantify. The advantage of the invention is that it significantly reduces the effect of these variables by putting some of the binder  17  on top of the aggregate  16  for better surface area bonding, minimizing the effect of existing surface texture, aggregate dimension, and aggregate cleanliness. 
     The application process of the present invention increases the surface area of the aggregate  16  and  19  covered with asphalt binder  14  and  17 . Increasing the surface area of the aggregate  16  and  19  covered with asphalt binder  14  and  17  minimizes the effect of pavement surface texture, aggregate dimensions, and weather by making more contact points on the aggregate  16  and  19  covered with asphalt binder  14  and  17 . 
     If the second application of asphalt binder  17  on top of the aggregate  16  is at least about 35% by volume of the total asphalt binder  14  and  17  applied in the chipseal process, the total application rate of binder  14  and  17  and aggregate  16  and  19  can each be as much as about 30% lower, and usually at least about 15% lower, than conventional chipsealing processes. The following table is an example of the advantages of the process of the invention compared with conventional processes: 
                                                   TABLE 1                       Quantity of Aggregate   Quantity of Asphalt       Nominal   Pounds/Square Yard   (gal/square yard)            Aggregate Size   Conventional   Invention   Conventional   Invention               ½″   25-30   16-22   0.45   0.35       ⅜″   20-25   13-18   0.35   0.25                    
Note that, in general, when using larger aggregate, application rates of both binder and aggregate increase. Excess fines on the aggregate  16  are less of an issue with the process of the present invention. This is advantageous because this will require less washing of the aggregate  16  before it is used.
 
     The process of the present invention is especially advantageous for higher traffic areas where the road stays closed until all layers  14 ,  16 ,  17  and  19  have been applied. By using a quicker and possibly a substantially synchronous and continuous process and increasing coalescence rates with finely graded material  19  such as choke stone, the treated road surface can be released to traffic sooner. 
     By using less aggregate  16  and/or covering the aggregate  16  with remaining binder  17 , less loose aggregate  16  remains. This is advantageous because it may reduce the need for the freshly treated surface to be swept. Having less loose material also reduces windshield and other vehicle damage. 
     In summary, the process of the present invention significantly improves aggregate retention. It also provides lower overall asphalt binder content and allows quicker return to traffic. Preferably, traffic is able to be on the newly treated road surface within an hour. Still further, softer asphalt can be used for longer life without causing bleeding conditions. 
     From the foregoing it will be seen that this invention is one well adapted to attain all ends and objectives herein-above set forth, together with the other advantages which are obvious and which are inherent to the invention. 
     While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for the purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.

Technology Classification (CPC): 4