Patent Publication Number: US-7585128-B2

Title: Method for adding foaming agents to pavement aggregate

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to road reconstruction equipment and, more particularly, to a method for depositing pavement reconditioning materials on a roadway. Since their debut in the late 1960s and early 1970s, asphalt milling machines have been considered one of the major innovations in road reconstruction. Asphalt milling machines were originally designed to remove a top layer of deteriorated asphalt so a new layer of asphalt could be overlaid on the exposed underlayer. The resulting pavement was superior to simply overlaying a new layer of asphalt directly onto the old and deteriorated asphalt. 
     One significant benefit of asphalt milling machines that has emerged modernly is the ability to break up asphalt into recyclable-sized fragments. As recycling of all types has become more popular, asphalt milling machines have similarly increased in popularity. 
     One core component of most modern asphalt milling machines is the cutting element. Most cutting elements incorporate numerous cutting teeth to cut or tear into the road surface. In cutting elements comprising a generally cylindrical drum, the rotational axis of the drum is frequently positioned parallel to the road surface and the drum is rotated while being driven along the road surface in a direction transverse to its axis of rotation. Conventional cutting drums mill the asphalt in an upward direction, or an “up-cut” direction. However, some cutting drums may permit “down-cutting” to control “slabbing,” and facilitate pulverizing and mixing. 
     Due to the abrasive nature of pavement, the cutting teeth traditionally wear out quickly and require frequent replacement. The replacement process may create significant downtime and hinder the overall efficiency of the milling process. Consequently, considerable effort has been expended to accelerate the replacement process and to increase the durability of the cutting teeth. Many newer cutting teeth, for example, are coupled to the cutting drum using various bolt-on housings to enable faster replacement. 
     U.S. patent application Ser. Nos. 11/164,947; 11/163,615; and 11/070,411 to Hall et al., which are all herein incorporated be reference for all that they contain, disclose systems to milling and repaving paved surfaces in situ. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect of the invention, a method for reconditioning a paved surface includes the steps of providing a vehicle adapted to traverse the paved surface; providing a layer of loose aggregate on a underlayer by degrading the paved surface with a degradation element attached to the vehicle; adding a foaming agent to the layer of loose aggregate on the underlayer; and coating a total aggregate surface area by mixing hot asphalt into the loose aggregate and allowing the foaming agent to expand the asphalt. The layer of pavement aggregate may be consistent with incorporation into a wearing surface, a road base, a road sub-base, a drive way, a parking lot or combinations thereof. The degradation element in the step of providing a layer of loose aggregate may comprise at least one vertical milling apparatus. 
     The foaming agent may comprise azodicarbonamide, inorganic carbonates, organic acids, polycarbonic acid, organic salts, inorganic oxides, zinc, potassium, water, glycerol, stearate, hydrocarbons, nucleating agents, antioxidants, pigments, fire-retardants, or combinations thereof. It may have a characteristic of having a foaming half-life of 5-180 seconds. The foaming agent may foam at its decomposition threshold, which may be between 200 to 350 degrees Fahrenheit. The step of mixing at least one foaming agent with the loose aggregate may occur at a temperature below the foaming agent&#39;s decomposition threshold. Hot asphalt may bond the layer of pavement aggregate to an underlayer of the paved surface. 
     The method may further include a step of softening the paved surface by heating it before the step of degrading the paved surface. The method may further comprise a step of compacting the aggregate while coating the total aggregate surface area. The method may further comprise a step of fogging the pavement surface and/or loose aggregate with foaming agent using a fogger attached to the vehicle. The method may further comprise a step of mixing at least one foaming agent with at least one other component before adding the resulting mixture to the loose aggregate. The other component may be selected from the group consisting of water, liquids, gases, polymers, clays, waxes, oil based substances, zeolites, and combinations thereof. 
     The foaming agent may be added to the pavement and/or loose aggregate by a dispenser. The foaming agent may be directed towards the loose aggregate by an opening of a channel attached to the vehicle that connects the opening to at least one supply of a foaming agent. The channel may be adapted to vibrate, rotate, shake, move, or oscillate. The opening of the channel may be protected by a superhard material. The opening may comprise a nozzle. The opening in the channel may be positioned below the surface of the loose aggregate while adding the foaming agent. 
     In one aspect of the invention, a method comprises the steps of providing a vehicle adapted to traverse an area comprising a layer of pavement aggregate, wherein the vehicle comprises a first channel that precedes a second channel in the direction of motion of the vehicle, and wherein the first channel is in communication with at least one supply of foaming agent and the second channel is in communication with at least one supply of hot asphalt; positioning the first channel and the second channel so that at least a portion of each channel is disposed within the layer; adding the foaming agent into the layer from an opening in the first channel positioned below the surface of the layer; and adding hot asphalt into the layer from an opening in the second channel positioned below the surface of the layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating an embodiment of a pavement recycling machine. 
         FIG. 2  is a cross-sectional view of an embodiment of a pavement recycling machine reconditioning a road surface. 
         FIG. 3  is a cross-sectional view of an embodiment of a mixture of paving materials in the process of reconditioning a road surface. 
         FIG. 4  is a cross-sectional view of an embodiment of a fogger depositing foaming agent onto paving materials. 
         FIG. 5  is a cross-sectional view of an embodiment of an injector. 
         FIG. 6  is a cross-sectional view of another embodiment of a pavement recycling machine reconditioning a road surface. 
         FIG. 7  is a perspective view of an embodiment of pavement recycling tools on a recycling machine. 
         FIG. 8  is a flowchart illustrating an embodiment of a method of reconditioning a paved surface. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT 
     In this application, “pavement” or “paved surface” refers to any artificial, wear-resistant surface that facilitates vehicular, pedestrian, or other form of traffic. Pavement may include composites containing oil, tar, tarmac, macadam, tarmacadam, asphalt, asphaltum, pitch, bitumen, minerals, rocks, pebbles, gravel, polymeric materials, sand, polyester fibers, Portland cement, petrochemical binders, or the like. Likewise, reconditioning materials refer to any of various binders, oils, and resins, and foaming agents including bitumen, Celogen 780, azodicarbonamide, zinc, potassium, water, glycerol, stearate, hydrocarbons, nucleating agents, antioxidants, pigments, fire-retardants, surfactant, polymeric materials, emulsions, asphalt, tar, cement, oil, pitch, maltenes, zeolite, wax, or the like. Reference to aggregates refers to rock, crushed rock, gravel, sand, slag, soil, cinders, minerals, or other course materials, and may include both new aggregates and aggregates reclaimed from an existing roadway. Likewise, the term “degrade” or “degradation” is used in this application to mean milling, grinding, cutting, ripping apart, tearing apart, or otherwise taking or pulling apart a pavement material into smaller constituent pieces. 
     Referring to  FIG. 1 , in selected embodiments, a pavement recycling machine  100  may include a shroud  104 , covering various internal components of the pavement recycling machine  100 , a frame  105 , and a translation mechanism  106  such as tracks, wheels, or the like, to translate or move the machine  100 , such translation mechanisms being well known to those skilled in the art. The pavement recycling machine  100  may also include means  107  for adjusting the elevation and slope of the frame  105  relative to the translation mechanism  106  to adjust for varying elevations, slopes, and contours of the underlying road surface. 
     In selected embodiments, to facilitate degradation of a swath of pavement wider than the pavement recycling machine  100 , the recycling machine  100  may include two or more support assemblies  108   a ,  108   b  that are capable of extending beyond the outer edge of the pavement recycling machine  100 . Because the support assemblies  108   a ,  108   b  may be as wide as the vehicle itself, the extended support assemblies  108   a ,  108   b  may sweep over a width approximately twice the vehicle width  102 . 
     To extend the support assemblies  108   a ,  108   b  beyond the outer edge of the pavement recycling machine  100 , each of the support assemblies  108   a ,  108   b  may include actuators  112 , such as hydraulic cylinders, pneumatic cylinders, or other mechanical devices known to those of skill in the art, to move the assemblies  108   a ,  108   b  to each side of the machine  100 . Each support assembly  108   a ,  108   b  may also include a rake to level, smooth, and mix pavement aggregates, including new aggregates and reclaimed aggregates generated by pavement degradation tools. 
     Under the shroud  104 , the pavement recycling machine  100  may include an engine and hydraulic pumps for powering the translation mechanism  106 , the support assemblies  108   a ,  108   b , the pavement degradation tools, or other components. Likewise, the pavement recycling machine  100  may include a tank  124  for storing hydraulic fluid, a fuel tank  126 , a tank  128  for storing a first supply of reconditioning materials such as asphalt, bitumen, oil, tar, or the like, another tank  130  for storing a second supply of reconditioning material, such as a foaming agent, and a hopper  132  for storing aggregate such as gravel, rock, sand, pebbles, macadam, concrete, or the like. 
     Referring now to  FIG. 2 , the support assemblies  108   a ,  108   b  may include banks of pavement degradation tools  110  that rotate about an axis substantially normal to a plane defined by a paved surface. Each of these pavement degradation tools  110  may be used to degrade a paved surface in a direction substantially normal to their axes of rotation. The pavement degradation tools may comprise diamond. As a pavement recycling machine  100  moves forward in the direction of the arrow it may progressively degrade an asphalt surface  204  into loose pavement aggregate  174 . A fogger  203  may add a foaming agent  209  to the layer loose aggregate  174  during or after it passes through the pavement degradation tools  110  to create an aggregate-foaming agent mixture  207 . Although in the present embodiment the foaming agent  209  is added by a fogger  203 , other types of dispenser may add the foaming agent  209  in a manner consistent with the present invention. A rake  114  may penetrate into and further blend the mixture  207 . In some embodiments, the rake  114  may move side-to-side, front-to-back, in a circular pattern, vibrate, or the like to aid in mixing the aggregate  174  with the foaming agent  209 . As illustrated, the rake  114  may comprise multiple injectors  118 . In selected embodiments, each of the injectors  118  may be independently extended and retracted. This feature may allow selected injectors to be retracted to avoid obstacles such as manholes, grates, or other obstacles in the roadway. 
     In certain embodiments, each of the injectors  118  may be hollow to accommodate a flow of pavement reconditioning materials for deposit on a road surface. Pavement reconditioning materials may include, for example, foaming agent, asphalt, bitumen, tar, oil, water, combinations thereof, or other suitable materials, resins, and binding agents. In the present embodiment the foaming agent  209  is mixed into the loose aggregate  174  during the process of degradation. Subsequently, hot asphalt is added to the aggregate-foaming agent mixture  207  through one or more channels  118  to activate the foaming agent  209  and create a foaming mixture  208 . Reconditioning materials may be mixed with various aggregates  174 , including new aggregates and reclaimed aggregates generated by the pavement degradation tools  110 . One feature of the present invention is that pavement reconditioning materials may be added to a layer of aggregate  174  below the surface of the layer. At least one injector  118  may comprise a special diamond tip that allows it to drag against surface of an underlayer  205  while injecting reconditioning materials into the layer. Staggered injectors  118  may contribute to a complete distribution of injected materials into the layer of loose aggregate  174 . Additionally, injectors  118  positioned close to the surface of the underlayer may extrude hot asphalt that may serve to bond the underlayer  205  and the reconditioned pavement aggregate. 
     In certain embodiments, each support assembly  108   a ,  108   b  may include a screed  201  and a bank of one or more tampers  122 . The screed  201  may be used to level the foaming mixture  208  and prepare it for compaction by a tamper  122  or other discrete elements such as vibratory rollers, and/or vibratory sleds. Once compacted, the new pavement  202  may be finished and sealed to provide protection against the elements, and tests on the pavement  202  may be performed to collect feedback on the recycling process. Like the injectors  118 , the tampers  122  may, in certain embodiments, be independently extendable and retractable. In some embodiments of the invention a heater  220  may heat the road surface prior to degradation. This is believed to both decrease the wear on the degradation elements by softening the road surface, and to conserve the size of components of pavement aggregate  174 . 
     Preferably the foaming agent  209  foams at a specific decomposition temperature threshold. This would allow the foaming agent to begin to foam only upon injection of a material at or above that temperature threshold, such as hot asphalt. By injecting hot asphalt into the aggregate-foaming agent mixture  207 , the foaming action is believed to help the asphalt to coat the total surface area of the loose aggregate  174  as foamed material rises to the surface. The foaming agent  209  may comprise azodicarbonamide or other chemical foaming agents, zinc, potassium, water, glycerol, stearate, hydrocarbons, nucleating agents, antioxidants, pigments, fire-retardants, or combinations thereof Preferably the foaming agent  209  is Celogen 780 or a similar material, and is activated by hot asphalt. In some embodiments a wax such as Sasobit® may be incorporated into the reconditioning materials to lower the viscosity of the reconditioning material and aggregate mixture. At lower temperatures below its melting point the wax may freeze and afford additional mechanical strength to the new pavement  202 . 
     The foaming mixture  208  is believed to have a significantly reduced viscosity compared to the aggregate-foaming agent mixture  207 , which may allow the reconditioning materials to be more easily mixed with the aggregate  174 . The foaming mixture  208  may also expand to saturate and permeate the aggregate  174 . The resulting “foamed asphalt,” may provide several significant advantages when performing in situ, pavement recycling. For example, it is reported that some foamed asphalt may increase the shear strength of the resulting paved surface, while reducing its susceptibility to moisture. The strength of foamed asphalt may approach that of cemented materials, while being more flexible and fatigue resistant than cemented materials. 
     Furthermore, when performing cold or warm mix processes, this foaming technique may allow the foaming agent to be mixed with a wider variety of aggregates. Foamed asphalt may also require less binder and water than other methods of cold mixing, which reduces binder and transportation costs. Foamed asphalt can also be compacted and used immediately upon deposit to the road surface, thereby saving time and money. Furthermore, this technique conserves energy because only the asphalt requires heating; the aggregates may be mixed while cold or damp. In the preferred embodiment, the asphalt is heated to between 200 to 350 degrees Fahrenheit prior to adding it to the aggregate-foaming agent mixture  207 . 
     Other advantages include reported environmental benefits. The foaming technique reduces environmental harm that may occur from the evaporation of volatiles from the asphalt mix because curing generally does not release volatiles into the environment. According to some reports, foamed asphalt may also be stockpiled without binder runoff or leeching. Foamed asphalt may be deposited in adverse weather conditions, such as cold temperatures or light rain, without changing the characteristics or quality of the material. 
     Referring now to  FIG. 3 , an enlarged cross-sectional view of aggregate mixtures is shown. A pavement recycling machine moves in the direction of motion  305 . Loose aggregate  174  is shown resulting from the action of degradation elements  110 . A foaming agent  209  is added and mixed into the loose aggregate, preferably during the process of degradation. The resulting aggregate-foaming agent mixture  207  may foam only once activated by a hot asphalt  210 , or another hot reconditioning material As previously mentioned, a rake  114  may comprise multiple injectors  118 . The injectors  118  may extrude hot asphalt  210  or other hot reconditioning materials. The injectors  118  may extend from the rake  114  to varying depths in the layer of aggregate  174 . With injectors  118  at different depths, the hot asphalt may flow out and distribute throughout the layer of loose aggregate  174 . The injectors  118  may be raised and lowered as specific circumstances may require. In some embodiments a nozzle may fog or spray fresh reconditioning materials onto the surface of the foaming mixture  208  to ensure adequate surface coating. In some embodiments the injectors  118  may comprise sensors that detect the amount of reconditioning materials being dispersed into the aggregate  174  and appropriate settings on the height and flow of the injectors  118  and nozzle may be adjusted accordingly to obtain maximum efficiency. 
     In some embodiments the foaming agent  209  may be mixed with another component from another source. In some embodiments the foaming agent  209  may be Celogen 780 or another similar substance. The other component may be selected from the group consisting of water, liquids, gases, polymers, clays, waxes, oil based substances, zeolites, and combinations thereof. In some embodiments a fogger may pre-treat the paved surface or loose aggregate with a rejuvenating fog. As the pavement recycling machine  100  moves forward, a rejuvenating fog may comprise a mixture of maltenes and serve a number of purposes. For example, the rejuvenating fog may wet the aggregate  174  to allow better adhesion to additional reconditioning material that may be added later, act as a dust suppressant, and restore maltene content in the original aggregate  174  that may have been lost due to wear and tear on the road. 
     Referring now to  FIG. 4 , the pavement degradation tools  110 , may spin in opposing directions, thereby helping to mix the foaming agent  209  into the aggregate  174  recovered from the degradation of the original pavement surface  204 . The pavement degradation tools  110  may move side to side as the pavement recycling machine moves forward into the original pavement surface  204 . Each tool  110  may also be able to move up and down individually to avoid obstacles such as manholes. Although the present embodiment depicts a fogger  203  dispensing the foaming agent  209 , embodiments of the invention may comprise one or more of various kinds of dispensers. 
     Referring now to  FIG. 5 , an injector  118  may comprise a first channel  134  in communication with the supply of foaming agent or hot asphalt provided by the duct  138 . The outside diameter of the first channel may slide inside a second channel  136  thereby transmitting the supply of pavement reconditioning materials into the second channel  136 . In certain embodiments, the first channel  134  may remain relatively fixed with respect to the housing  116 , while the second channel  136  may extend and retract (downward in the illustrated embodiment) with respect to the first channel  134  and the rake  114 . A seal may be provided between the first channel  134  and the second channel  136  to prevent leakage of reconditioning materials where the two channels  134 ,  136  interface. 
     A blocking element  144  may be coupled to the second channel  136 . In the illustrated embodiment, the blocking element  144  has a conical shape although other shapes are possible and within the scope of the invention. The second channel  136  may slide upward with respect to the first channel  134 , the blocking element  144  may contact a seat  146  coupled to the first channel  134 . The blocking element  144  and the seat  146  together form a valve  144 ,  146 . Upon contacting the seat  146 , the blocking element  144  seals off the first channel  134 , thereby cutting off the flow of reconditioning materials. Thus, when the injector  118  is retracted (i.e., slid upward), the flow of pavement reconditioning materials is cut off. Conversely, when the injector  118  is extended, the valve  144 ,  146  opens and re-initiates the flow of reconditioning materials. As shown, the blocking element  144  may include one or more passageways  148  to accommodate a flow of pavement reconditioning materials when the valve  144 ,  146  is open. These passageways  148  may connect to an opening  150  for depositing the pavement reconditioning materials on a road surface. 
     A hardened tip  152  may be coupled to the second channel  136  to provide added durability to the injector  118  and to resist the abrasive effects of pavement materials (i.e., rock, gravel, concrete, etc.) in the road surface. For example, in certain embodiments, the hardened tip  152  may be coated with diamond, boron nitride, cemented metal carbide, or combinations mixtures, or alloys thereof, to provide added durability. A hardened tip may also reduce wear and/or corrosion. 
     In some embodiments of the present invention, a nozzle may be fitted within the opening  150  for depositing the pavement reconditioning materials on a road surface. The nozzle may increase the pressure exerted on the pavement reconditioning materials as they exit the opening  150 . The nozzle may also increase the temperature and pressure of the pavement reconditioning material immediately before the reconditioning material exits the opening  150 , which may allow reconditioning material to be heated to a higher temperature before they are deposited. The nozzle may also comprise a particular pattern which may help deposit the reconditioning material in a specific desired manner. Individual injectors  118  may comprise a nozzle with a different pattern such that the injectors near the end of the swath of pavement may deposit the reconditioning material differently than the injectors that are positioned near the middle of the same swath of pavement. 
     To extend and retract the injector  118 , a piston  154  may be coupled to the second channel  136  and slide with respect to the first channel  134 . The first channel  134  may slide through a bore in the piston  154 . The rake  114  may comprise a chamber  156  to accommodate the travel of the piston  154 . In certain embodiments, the piston  154  may be driven by hydraulic fluid supplied under pressure to the chamber  156 , although it is contemplated that pressurized air or other fluids could also be used. In one embodiment, hydraulic fluid may be supplied to the chamber  156  through a pair of passageways  158 ,  160  in the rake  114 . Hydraulic fluid supplied under pressure through a first passageway  158  may exert force on a first surface  162  of the piston  154 , while hydraulic fluid supplied under pressure through a second passageway  160  may exert force on a second surface  164  of the piston  154 . Because the second channel  136  may connect to one end of the piston  154 , the area of the first surface  162  may be larger than the area of the second surface  164 . Thus, by applying equal hydraulic pressure to each of the first and second surfaces  162 ,  164 , the piston  154  will be urged downward due to the greater area of the surface  162 . 
     Referring now to  FIG. 6 , another embodiment of a pavement recycling machine  100  is disclosed, in which a degradation drum  610  is used. The degradation drum  610  may comprise cutting surfaces that may comprise diamond, cubic boron nitride, silicon carbide, tungsten, carbide, hard metals, and combinations thereof. As the recycling machine  100  moves in the direction indicated by the arrow, a heater  220  may heat the original paved surface  204  in order to loosen the pavement  204  and to preserve the original size of the aggregate  174 . A dispenser  620  may be connected to a reservoir  630  of foaming agent  209  or pavement reconditioning materials. The dispenser  620  or an element within the dispenser  620  may spin, thereby projecting the foaming agent  209  towards the degradation drum  610  and the newly loosened aggregate  174 . This process is believed to mix the loose aggregate  174  with the foaming agent  209  during the process of degradation, thereby efficiently producing a mixture of aggregate and foaming agent. 
     A spray nozzle  640  may be disposed on the rake  114 , and may be connected to a supply of hot asphalt  210  or another hot pavement reconditioning material. In some embodiments of the invention the spray nozzle  640  may be disposed on the pavement recycling machine  100  but not on the rake  114 . Although the present embodiment depicts a spray nozzle  640  pointed straight down at the aggregate  174 , the spray nozzle  640  may be directed at an angle or towards the degradation element  610 . It is believed that in some embodiments that foaming may occur as the spray nozzle  640  directs foaming agent towards the rotating degradation drum  610 . 
     In some embodiments a channel  118  may extend from the rake  114  and into the aggregate  174 . The channel  118  may comprise an opening through which it may extrude hot asphalt  210  or other pavement reconditioning materials. The opening may be disposed close to a surface of the sublayer  205 . The channel may comprise fins  650  and may spin or vibrate. It is believed that the presence of fins  650  and spinning or vibratory motion may help to mix the aggregate  174  and may help to form a layer of foaming aggregate  208 . As previously described a screed  201  may level the foaming aggregate  208  and prepare it for compaction. The present embodiment discloses a roller  660  used to compact the foaming aggregate  208 . Once compacted, the foaming aggregate  208  may form a layer of new pavement  202 . The new pavement  202  may be finished and sealed to provide protection against the elements, and tests on the pavement  202  may be performed to collect feedback on the recycling process. 
     Referring now to  FIG. 7 , a perspective view of another embodiment of a recycling machine  100  is disclosed. The present embodiment employs a plurality of dispensers  620  and a plurality of spray nozzles  640 , consistent with the dispenser  620  and spray nozzle  640  disclosed in  FIG. 6 . In the present embodiment the plurality of dispensers  620  and the plurality of spray nozzles  640  are incorporated into a recycling machine  100  which also comprises degradation elements  110  and tampers  122  consistent with the those disclosed in  FIG. 2 . Although specific combinations of degradation elements, foaming agent dispensers, nozzles, and channels have been described in this application any combination of these components may be consistent with the present invention. 
     Referring now to  FIG. 8 , as previously mentioned, the asphalt recycling process described in the previous figures may be characterized by a method  800  for reconditioning a paved surface. The method  800  includes a step  810  of providing a vehicle adapted to traverse the paved surface. The method further includes a step  820  of providing a layer of loose aggregate on an underlayer by degrading the paved surface with a degradation element attached to the vehicle and a step  830  of adding a foaming agent to the layer of loose aggregate on the underlayer. The method comprises a subsequent step  840  of coating a total aggregate surface area by mixing hot asphalt into the loose aggregate and allowing the foaming agent to expand the asphalt. The method  800  may comprise a finishing step  850  of compacting the aggregate. Final steps may also be taken such as sealing and finishing the roadway and collecting data on the finished roadway. Although specific steps of the method  800  are shown, this may not be construed to indicate that other steps may not be compatible with and inclusive into the method shown. 
     Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.