EP0046827B1 - Procédé et appareil pour la production de béton d'asphalte - Google Patents

Procédé et appareil pour la production de béton d'asphalte Download PDF

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Publication number
EP0046827B1
EP0046827B1 EP19800302968 EP80302968A EP0046827B1 EP 0046827 B1 EP0046827 B1 EP 0046827B1 EP 19800302968 EP19800302968 EP 19800302968 EP 80302968 A EP80302968 A EP 80302968A EP 0046827 B1 EP0046827 B1 EP 0046827B1
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EP
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Prior art keywords
mixture
accordance
chamber
moisture content
moisture
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EP19800302968
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German (de)
English (en)
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EP0046827A1 (fr
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Paul E. Bracegirdle
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    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
    • E01C19/00—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving
    • E01C19/02—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving for preparing the materials
    • E01C19/10—Apparatus or plants for premixing or precoating aggregate or fillers with non-hydraulic binders, e.g. with bitumen, with resins, i.e. producing mixtures or coating aggregates otherwise than by penetrating or surface dressing; Apparatus for premixing non-hydraulic mixtures prior to placing or for reconditioning salvaged non-hydraulic compositions
    • E01C19/1013—Plant characterised by the mode of operation or the construction of the mixing apparatus; Mixing apparatus
    • E01C19/104—Mixing by means of movable members in a non-rotating mixing enclosure, e.g. stirrers
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
    • E01C19/00—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving
    • E01C19/02—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving for preparing the materials
    • E01C19/10—Apparatus or plants for premixing or precoating aggregate or fillers with non-hydraulic binders, e.g. with bitumen, with resins, i.e. producing mixtures or coating aggregates otherwise than by penetrating or surface dressing; Apparatus for premixing non-hydraulic mixtures prior to placing or for reconditioning salvaged non-hydraulic compositions
    • E01C19/1004—Reconditioning or reprocessing bituminous mixtures, e.g. salvaged paving, fresh patching mixtures grown unserviceable; Recycling salvaged bituminous mixtures; Apparatus for the in-plant recycling thereof
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
    • E01C19/00—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving
    • E01C19/02—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving for preparing the materials
    • E01C19/10—Apparatus or plants for premixing or precoating aggregate or fillers with non-hydraulic binders, e.g. with bitumen, with resins, i.e. producing mixtures or coating aggregates otherwise than by penetrating or surface dressing; Apparatus for premixing non-hydraulic mixtures prior to placing or for reconditioning salvaged non-hydraulic compositions
    • E01C19/1013—Plant characterised by the mode of operation or the construction of the mixing apparatus; Mixing apparatus
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
    • E01C19/00—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving
    • E01C19/02—Machines, tools or auxiliary devices for preparing or distributing paving materials, for working the placed materials, or for forming, consolidating, or finishing the paving for preparing the materials
    • E01C19/10—Apparatus or plants for premixing or precoating aggregate or fillers with non-hydraulic binders, e.g. with bitumen, with resins, i.e. producing mixtures or coating aggregates otherwise than by penetrating or surface dressing; Apparatus for premixing non-hydraulic mixtures prior to placing or for reconditioning salvaged non-hydraulic compositions
    • E01C19/1059—Controlling the operations; Devices solely for supplying or proportioning the ingredients

Definitions

  • the present invention relates to a process and apparatus for making asphalt concrete from aggregate, such as stone and sand, and binder material, such as asphalt cement. Other additives may be included.
  • Direct-fired processes generally are of two types. In one, aggregate is directly heated, as by a flame, and the heated aggregate is mixed with a binder to form the asphalt concrete. This is a batch process. In a second process, a continuous process, a mixture of aggregate and binder is directly heated, usually by an open flame burner. In indirect-fired processes, the mixture within a mixing apparatus is indirectly heated by means of a heat transfer fluid.
  • the prior art systems both the direct and indirect-fired systems, generally operate at high temperatures to produce an asphalt concrete product having a discharge temperature of about 121°-154°C (250°-310°F) and require large amounts of energy. None of the prior art systems reviewed above recognizes the energy value of moisture contained in the aggregate and/or binder used to make asphalt concrete. Instead of using the energy in the entrained moisture, the above prior art systems use more energy to drive off the moisture, typically about 20-50% of the energy used. There is no recognition that any particular amount of moisture in the final product results in a superior product, contrary to the present invention.
  • DE-B1-2848145 (corresponding to GB-A-2036574) discloses a process in which the mixing of moist aggregate and a hot bituminous binder take place under a pressure which is not less than the saturation pressure of water at the temperature of the mixture. After this mixing step, the pressure is reduced below atmospheric pressure in order to remove water and so dehydrate the mixture.
  • the heating is effected by direct action within a rotary mixing drum and the moisture content is not controlled after the dehydration step.
  • the use of direct hot gas heating also involves the possibility of entrainment of dust and other pollutants and contaminants.
  • DE-A1-2827608 (corresponding to AU-B-513429) also involves direct heating of the mixture within a rotary drum in which the ingredients are mixed under the action of the combustion products of a liquid fuel fed into the drum.
  • the bulk of the moisture is driven off from the drum with the effluent combustion products, desirably under a neutral, i.e. atmospheric or somewhat reduced pressure.
  • the present invention is based upon the discovery that the strength and specific gravity or density of hot mixed asphalt concrete can be increased by controlling the moisture content of the asphalt concrete during mixing within prescribed limits defined by the environmental conditions and the moisture content and absorption of the starting materials. Strength and density both affect the useful life and durability of asphalt concrete when used for its normal purposes, for example in highways, driveways, parking lots and the like.
  • the present invention overcomes the disadvantages of prior art processes and apparatus for making asphalt concrete.
  • apparatus for making asphalt concrete, comprising a mixing chamber having an inlet, an outlet and means within the chamber for indirectly heating a mixture of starting materials comprising aggregate and binder while moving the mixture through the chamber, which is characterized in that the inlet and outlet are selectively sealable so that the interior of the mixing chamber does not communicate with the atmosphere when sealed, and that moisture control means are provided for adjusting the moisture content of the mixture to a predetermined value by removing moisture from the mixture within the chamber in the form of water vapour when the moisture content is greater than the predetermined value until the moisture content equals the predetermined value, and/or by adding water to the mixture within the chamber when the moisture content is less than the predetermined value until the moisture content equals the predetermined value.
  • a process for making asphalt concrete is characterized by the following steps:
  • asphalt concrete of increased strength and density can be obtained at lower temperatures than heretofore possible.
  • the use of lower temperatures results in the use of less energy and, accordingly, the same amount of asphalt concrete with increased strength and density can be obtained at a lower cost than at present.
  • the cost factor is significant, since energy costs will almost surely continue to rise in the future.
  • substantially zero pollutants are released to the atmosphere.
  • the term "substantially zero” means that the amount of pollutants released into the atmosphere in carrying out the present invention is sufficiently low as not to constitute a health problem. In other words, the amount of pollutants released into the atmosphere in carrying out the present invention is below the limits according to federal, state and local standards for asphalt concrete producing equipment and processes. It should be noted, however, that this condition exists when venting the vapour to atmosphere. When using the condenser, there are no atmospheric emissions at all.
  • Apparatus 10 may be installed outdoors, indoors, or on vehicle beds to provide for portability of the apparatus to various job sites.
  • the apparatus 10 includes a plurality of sources of aggregate such as a silo 12 for coarse aggregate, e.g., 19.1 to 9.5 mm (3/4 to 3/8 inch), a silo 14 for medium aggregate, e.g. 9.5 mm (3/8 inch) to 4 mesh, a silo 16 for fine aggregate, e.g. 3.8 to 0.075 mm (4 mesh to 200 mesh) and a silo 18 for very fine aggregate, e.g. 0.075 to 0.025 mm (200 to 600 mesh).
  • a silo 12 for coarse aggregate e.g., 19.1 to 9.5 mm (3/4 to 3/8 inch
  • a silo 14 for medium aggregate, e.g. 9.5 mm (3/8 inch) to 4 mesh
  • a silo 16 for fine aggregate e.g. 3.8 to 0.075 mm (4 mesh to 200 mesh
  • the aggregate can be any inert material, such as gravel, sand, shell, broken stone, blast furnace slag (the non-metallic product, consisting essentially of silicates and alumino-silicates of lime and other bases, which is formed simultaneously with iron in a blast furnace), or combinations thereof.
  • the sizes and types of the aggregates are merely for purposes of illustration, since specifications for a particular job usually dictate the particular size and type of aggregate.
  • the aggregate may be raw virgin aggregate or recycled aggregate obtained by crushing old paving material, such as roadways or parking area surfacing material. Recycled asphalt concrete aggregate will retain some hardened binder material which will be totally reclaimed. It may require the addition of new binder material and/or other additives known to those skilled in the art.
  • the aggregate should form 94% to 98% by weight of the final asphalt concrete product.
  • the silos 12, 14, 16 and 18 are illustrated as being supported on a frame 20.
  • Each silo is provided with a gravimetric or volumetric feeder 22 at its discharge point, for selectively controlling the amounts and rates of discharge of aggregate from the various silos.
  • Each feeder 22 deposits the-aggregate on to an endless conveyor belt 24 driven by any conventional motor and drive mechanism.
  • the conveyor belt 24 communicates with an inlet hopper 26.
  • the apparatus 10 includes a frame 21.
  • the frame 20 is at a higher elevation than the frame 21, since this minimizes the discrepancy in elevation between the feeders 22 and the inlet hopper 26.
  • a single frame or frames at the same elevation could be utilized.
  • Frames 20 and 21 may be fixed or portable, as when they are mounted on truck or trailer beds.
  • a mixing chamber 28 is supported by frame 21 and includes a heat exchanger-mixer for indirectly heating the asphalt concrete mixture.
  • Mixer 28 may include a hollow flight, hollow shaft screw conveyor-mixer as disclosed in the patents set forth hereinbefore within an insulated chamber or within a chamber having a double wall containing heat exchange material between the double walls.
  • the presently preferred heat exchanger-mixer is a twin shaft type wherein the shafts and their associated mixing blades or flights are internally heated so that the asphalt concrete is indirectly heated.
  • Suitable screw conveyors include, for example, those disclosed in U.S. Patent 3,020,025 of O'Mara, having mixing blades arranged in a discontinuous screw pattern, or those manufactured by The Bethlehem Corporation under the trademark Porcupine.
  • Mixer 28 includes a pair of hollow shafts 30 and 32 leading to hollow flights and/or mixing blades.
  • Shaft 30 is supported by bearings 29 and 31 and is driven by motor 34 coupled to the shaft by suitable gearing.
  • Shaft 32 is supported by bearings 33 and 35 and is driven by motor 36 coupled to the shaft by suitable gearing.
  • Motors 34 and 36 are secured to frame 21.
  • Other drive arrangements are possible and may be substituted for the drive arrangement disclosed herein.
  • Shafts 30 and 32 should be adapted to be driven in either a clockwise or counterclockwise direction.
  • shaft 30 should be driven clockwise and shaft 32 driven counterclockwise to cause the mixture to be propelled from the inlet end to the outlet end of mixing chamber 28.
  • shafts 30 and 32 both should be operated in a clockwise direction so that the mixture is caused to move in a generally elongated elliptical or reciprocal pattern between the inlet and outlet ends of mixing chamber 28.
  • inlet control 38 for introducing the aggregate into mixer 28.
  • inlet control 38 is a screw conveyor which carries sufficient aggregate and is so dimensioned that it effectively seals the interior of chamber 28 from the atmosphere.
  • inlet control 38 may comprise any type of valve capable of metering aggregate material and selectively sealing mixing chamber 28 from communication with the atmosphere.
  • Mixer 28 has an outlet control 40 which operates in the same manner as inlet control 38.
  • outlet control 40 must be able to allow the asphalt concrete product to be discharged from mixing chamber 28, and must be capable of selectively sealing the mixing chamber during mixing of the mixture.
  • Inlet control 38 and outlet control 40 may be of the same or different construction. As presently preferred, inlet control 38 and outlet control 40 are both variable speed screw conveyors within enclosed chambers.
  • the enclosed chamber for inlet control 38 communicates at one end with the bottom of hopper 26 and at its other end with the lefthand or inlet end of mixer 28.
  • the enclosure for outlet control 40 communicates at one end with the bottom portion of the righthand or outlet end of mixer 28 and at its other end with a receptacle, vehicle 41 or other means for transporting the asphalt concrete.
  • Control means 38 and 40 each should have a suitable sealing device, such as a valve, to selectively seal chamber 28 when no material is present in the screw conveyors.
  • inlet control 38 and outlet control 40 Any other control means may be used for inlet control 38 and outlet control 40, such as star valves, solenoid-operated valves, or the like.
  • star valves such as star valves, solenoid-operated valves, or the like.
  • Binder material which is mixed with the aggregate to form asphalt concrete is contained in tank 42, shown for purposes of illustration as being located on frame 21 at an elevation above the elevation of mixer 28. Binder material is pumped from tank 42 by means of pump 46 through conduit 44 and valve 48 into the mixer 28. Actuation of pump 46 may be controlled by a timer. The binder material may be added to the mixing chamber anywhere along the length of the chamber, but preferably, it is added near the inlet end as shown in Figure 1A.
  • the binder material may be any of the usual types of binder material used in making asphalt concrete. Suitable types include, for example, asphalt cement, asphalt cement-water emulsions having a typical amount of about 50-70 weight percent asphalt cement, sulfur-based binder, asphalt cement-sulfur mixtures, and the like. Typically, the type of binder material is determined by the job specifications for a particular project. The type of binder material is not as important as knowing the water content, if any, of the binder material. Generally, the binder material comprises about 2 to about 6% by weight of the asphalt concrete product.
  • Additives to prevent or minimize fouling of the apparatus, to wet the surface of virgin aggregate for more complete coverage by the binder material and/or to rejuvenate the recycled aggregate material may be added to mixing chamber 28.
  • such additives are added to the binder material in conduit 44 from storage tank 50 by means of pump 52. Actuation of pump 52 may be controlled by a timer.
  • Actuation of pump 52 may be controlled by a timer.
  • additives are added to the binder material, it is possible to eliminate another conduit connection to mixing chamber 28 which would have to be sealed.
  • an additional sealable connection may be used if desired and located substantially anywhere along the length of mixing chamber 28, but preferably near the inlet end.
  • Anti-fouling agents may also be added to the condenser system to be described hereinafter.
  • the additive should be metered into the binder material so that about 0.1 to about 2.0% of the additive based on the weight of the binder material is added to the mixer.
  • the final concentration for the additive should be about 0.002 to about 0.12% by weight based on the total product.
  • Triton X-100 is as an octylphenoxy- polyethoxyethanol.
  • Triton X-102 is octyl- phenoxypolyethoxyethanol containing 12-13 moles of ethylene oxide.
  • Triton X-207 is described as an oil-soluble nonionic alkylaryl polyether alcohol type of surfactant.
  • the heat exchanger-mixer is heated by means of a heat transfer fluid contained within the hollow shafts, flights and blades.
  • the fluid may be a gas, such as steam, or a liquid, such as hot oil or commercially available molten salt mixtures, such as a mixture of 53% KN0 3 , 40% NaN0 2 and 7% NaN0 3 , or the like. No novelty is claimed concerning the type of heat exchange fluid.
  • the heat exchange fluid is supplied to the mixing blades, paddles or flights through shafts 30 and 32.
  • Shafts 30 and 32 are connected by well known sealable rotary joints 60 and 62 which are connected to an inlet conduit 58 and a return conduit 64. Conduits 58 and 64 may contain various valves as appropriate.
  • Conduits 58 and 64 are connected at their other ends to a source 54 of the heat transfer fluid.
  • the fluid is pumped by pump 56 through conduit 58, rotary joints 60 and 62 and shafts 30 and 32 to the heat exchanger mixer.
  • the fluid is then returned through conduit 64 to source 54 where it is reheated in any manner.
  • the fluid may be heated, for example, by an oil burning heater, a gas burning heater, an electrical heater or solar heater. Suitable heating units are available from American Hydrotherm Corp., for example.
  • the temperature of the product at the outlet end of mixing chamber 28 is generally maintained between about 60°C (140°F) and about 150°C (302°F), preferably between about 93.3°C (200°F) and about 150°C (302°F) and most preferably between about 100°C (212°F) and about 121°C (250°F).
  • the heat exchanger-mixer apparatus may be used in a continuous manner, in a semi-continuous manner or in a batch manner.
  • a semi-continuous operation there is not a continuous discharge of product. Rather, the product can be retained in the mixing chamber and intermittently discharged into a number of con'" tainers, for example, vehicles.
  • a batch operation the entire contents of a single batch of mixture is completely discharged.
  • the asphalt concrete product When operating in a continuous manner, the asphalt concrete product is discharged from outlet control 40 onto a conveyor, not shown, which in turn may discharge the asphalt concrete into a storage silo, not shown, or into vehicle 41.
  • frame 21 is sufficiently high to allow vehicle 41 to park beneath outlet control 40 to be filled with the asphalt concrete product. It should be understood that this arrangement is merely for purposes of illustration and that a variety of alternative arrangements are possible. If desired, vehicle 41 may be parked on a weighing scale 43 to facilitate accurate control of the amount of asphalt concrete to be carried by the vehicle.
  • any excess moisture in the form of water vapor and/or other gases could be vented to the atmosphere through an appropriate bleed valve in the top portion of the mixing chamber.
  • a water vapor condensing system to be described hereinafter is preferred.
  • Water vapor and other gases evaporated from the asphalt concrete mixture within mixing chamber 28 are preferably removed therefrom and condensed in any convenient manner.
  • two alternative types of condensing systems are shown.
  • water evaporated from mixing chamber 28 is condensed in a condenser 66, shown as being air cooled by fan 67 driven by motor 69 and drive belt 71.
  • a suitable condenser is available from Happy Division of Therma Technology, Inc.
  • Other cooling means may be used to cool the condenser, including enclosed heat exchange fluids, and the like.
  • Mixing chamber 28 is connected to condenser 66 by conduits 68 and 72.
  • Valve 70 selectively seals chamber 28 from conduit 68.
  • Valve 76 selectively seals chamber 28 from conduit 72.
  • a pump 74 is adapted to pump water vapor and other gases through conduit 72 and is only required at final product temperatures less than 100°C in mixing chamber 28.
  • Optional pressure sensor 96 detects pressure in conduit 72 to check pressure drop in the conduit or to determine the amount of vacuum created by condenser to determine the amount of vacuum created by condenser 66 when the system is operating in a vacuum mode. It is preferred to allow the water vapor and other gases to be expelled from the mixing chamber by means of their own vapor pressure.
  • feed silos 12, 14, 16 and/or 18 as heat sinks into which a condensing coil may be located.
  • This has the advantage of using the feedstock aggregate to condense the water vapor and/or gases, thus reducing the cost of the apparatus by not requiring a separate condenser unit 66 and by serving to reclaim the otherwise lost energy in the water vapor.
  • the aggregate may be preheated by this procedure.
  • a suitable arrangement is shown, for example, in U.S. Patent 2,519,148 of McShea, however, the condensing arrangement need not be so complex. Generally, it will be sufficient if the arrangement is as shown schematically in dotted lines in Figures 1A and 1B.
  • Conduit 73 may lead to or be integrally formed with a condenser coil 75 in hopper 18.
  • Condenser coil 75 may be integrally formed with or attached to a conduit 77 for controlling the flow of the condensate.
  • Condenser coil 75 is shown as being located in hopper 18 only for purposes of illustration. Other condenser coils in other hoppers 12, 14 and/or 16 or even inlet hopper 26 may be attached to conduits 73 and 77 in a series or parallel connection. Any suitable valving may be incorporated into the hopper condenser system as desired.
  • the condensate comprising mostly water, is removed from condenser 66 or 75 through conduit 78 or 77, respectively, and flows into storage tank 80.
  • a flow sensor 79 is used to determine the amount of condensate flowing from condenser 66 or 75 to tank 80.
  • Any hydrocarbons or undesirable materials present in the condensate may be removed, if desired, from the condensed water by conventional devices before the water enters storage tank 80.
  • a typical device suitable for use in removing hydrocarbons from the condensed water is the "BilgeMaster" separator available from National Marine Service, Inc.
  • the trace hydrocarbons or other condensed materials may be reclaimed and/or discarded, if desired, in accordance with standard procedures.
  • a test of the condensate from asphalt concrete made in a laboratory apparatus according to the present invention has indicated that the condensate complies with current discharge standards.
  • Storage tank 80 may be equipped with a standard level control, drain pipe and water inlet, all of which are conventional and are not shown in the drawings. Water from tank 80 may be recycled into mixing chamber 28 by being pumped by pump 82 through conduit 84 and valve 86 into inlet control 38. It is not necessary that conduit 84 lead into inlet control 38. Instead, if desired, valved conduit 84 can connect directly with mixing chamber 28 anywhere along its length, but preferably near its inlet end. The water may be preheated prior to being introduced into chamber 28 by the excess heat from the heater 54 or by heat from the vapor condensing system. Information in the form of electrical signals is generated by sensor devices, such as moisture sensors, pressure sensors, flow sensors and temperature sensors. Such sensor devices or transducers are conventional and are readily commercially available.
  • a moisture sensor 88 is used to determine the moisture content of the aggregate in inlet hopper 26.
  • a temperature sensor 92 is used to determine the temperature of the asphalt concrete mixture in mixing chamber 28. Temperature sensor 92 is preferably located in a side portion of mixing chamber 28 so as to accurately sense the temperature of the asphalt concrete mixture.
  • a pressure sensor 94 is used to determine the pressure within mixing chamber 28. Pressure sensor 94 should be located in the top of mixing chamber 28 above the level of the mixture therewithin.
  • the proper amounts of aggregate according to a particular job mix formula are discharged from silos 12, 14, 16 and 18 by means of feeders 22 onto conveyor 24.
  • the aggregate is then deposited into inlet hopper 26. There, the moisture of the aggregate is determined by means of moisture sensor 88.
  • Inlet control 38 meters a specified amount of aggregate into chamber 28.
  • Binder material from tank 42, with or without additives from tank 50, is also introduced into mixing chamber 28.
  • the aggregate and binder material are introduced into mixing chamber 28 when the heat exchanger-mixer is in operation.
  • the rate of addition of materials is controlled so as to be co-ordinated with the mixing rate of the asphalt concrete mixer and the outlet control device.
  • mixing chamber 28 two generalized conditions concerning temperature and pressure can exist.
  • the temperature will be greater than, equal to, or less than 100°C (212°F) and the pressure will be greater than, equal to, or less than atmospheric pressure. These conditions are sensed by temperature sensor 92 and pressure sensor 94. Since the amount of material within mixing chamber 28 can be a readily controlled constant amount, the volume within mixing chamber 28 is substantially constant. Accordingly, pressure and temperature are the variables, rather than only temperature as in all the prior art.
  • the pressure within mixing chamber 28 generally will be atmospheric. Assuming that the job mix formula calls for a moisture content in the final asphalt concrete product of, say, 2%, and the moisture content of the aggregate in inlet hopper 26 is, say, 3.5%, (and assuming that no other sources of water are added), it will be necessary to remove 1.5% water to achieve the specified moisture content in the final product.
  • percent and % mean percent by weight based on the total weight of the material under discussion.
  • moisture content 3.5%
  • the moisture in the aggregate is 3.5% by weight of the total weight of the moisture plus the aggregate.
  • valve 76 is opened and pump 74 is actuated to cause the vapor to be removed from chamber 28 through conduit 72 into condenser 66 or through conduit 73 to condenser coil 75. After condensation, any uncondensed gases may be returned to mixing chamber 28 through conduit 68 and valve 70. If desired, valve 70 can remain closed and no uncondensed gases will be recycled. This would create a vacuum operation that would reduce the vaporizing temperature of the moisture.
  • a positive vapor pressure will exist in chamber 28.
  • the magnitude of the positive pressure is determined by pressure sensor 94.
  • pressure sensor 94 When the temperature, and hence, the pressure, in chamber 28 is sufficient to overcome the pressure existing in conduit 68 or 73 and the tortuous path of the conduits within condenser 66 or condenser coil 75, a signal will be sent to close valve 70 and open valve 76. With valve 76 open, the hot, pressurized water vapor migrates to the cold source represented by condenser 66 or condenser coil 75 so as to reach an equilibrium temperature and to reduce the pressure. Thus, the water vapor and other gases will enter into conduit 72 or conduit 73 and flow through condenser 66 or condenser coil 75 because of the vapor pressure within chamber 28. The water condensed from the vapor is collected in storage tank 80.
  • the water can be added to mixing chamber 28 by being pumped from storage tank 80 by pump 82 through conduit 84, valve 86 and inlet control 38.
  • the moisture sensor 88 detects that the aggregate has a moisture content below the desired design moisture level, such as less than 2% from the prior example, a proportional control system using pump 82 will make up the difference by adding the correct amount of water.
  • a control system integrates the information from moisture sensor 88, temperature sensor 92, flow sensor 79 and pressure sensor 94. Based on the signals from these sensors, the control system opens and closes valves 70, 76 and 86 at the proper time, controls inlet control 38 and outlet control 40, controls the speed of the mixing blades and controls the operation of pumps 74 and 82. In this manner, and as primarily determined by the moisture content of the starting materials, the moisture content of the asphalt concrete mixture and final product can be controlled at some point between about 0.1 and about 10%, and preferably at some point between about 1 and about 4%.
  • This example is directed to an asphalt concrete composition made from raw virgin aggregate.
  • the following ingredients were used in the indicated proportions to make a 47.7 kg sample mixture.
  • the aggregate and filler. are weighed and placed in a sealed vessel so that a 5% composite moisture content as determined by ASTM C136 testing procedure would be retained.
  • the asphalt cement is mixed with the surfactant and the liquid mixture is preheated to 140°C.
  • the aggregate and filler are introduced into the heat exchanger-mixer with its blades turning and then the heated asphalt cement and surfactant are added into the mixing chamber.
  • the heat exchanger mixer is then sealed, except that an outlet is connected to a tee fitting.
  • a pressure gauge is connected to one end of the tee fitting and an "EPA Method 5" particulate testing filter, followed by a condenser, is connected to the other end of the tee fitting.
  • the asphalt concrete mixer is heated using steam at 1.034x10 6 N/m 2 gauge (150 p.s.i.g.) at a temperature of 185°C.
  • the temperature of the sample mixture rises from room temperature to 100°C within 2 minutes. If hot oil at a temperature of about 343°C were used, the time for raising the mixture from ambient temperature to 100°C would be reduced by about two-thirds or to about 40 seconds.
  • the mixture remains at around 100°C for 5 minutes during which free water is evaporated.
  • Several batches are made and water is evaporated from the mixture at various vapor pressures and temperatures. Over a period of 5 more minutes, the temperature rises to 150°C and the vapor pressure becomes virtually 0 after substantially all of the water evaporates.
  • a vapour pressure of about 6,895 N/m 2 gauge (1 p.s.i.g.) is required to cause the free hot water vapour in the mixing chamber to migrate to the cooler condenser as a function of condenser design.
  • the asphalt concrete product is removed from the mixing chamber and formed into 1.25 kg samples for testing as described hereinafter.
  • This example is for a product containing recycled asphalt concrete.
  • the recycled asphalt concrete was obtained from a deteriorated New Jersey Department of Transportation highway wearing course.
  • the recycled asphalt concrete was crushed and found to have the following size particles as determined by the method of ASTM C136: 98.8% passed through a sieve having openings of 12.7 mm (1/2 inch), 95.9% passed through a sieve having openings of 9.5 mm (3/8 inch), 64.8% passed through a 4.8 mm (No. 4) U.S. sieve, 45.3% passed through a 2.4 mm (No. 8) U.S. sieve, 21.7% passed through a 0.3 mm (No. 50) U.S. sieve and 7.4% passed through a 0.75 mm (No. 200) U.S. sieve.
  • the amount of asphalt cement contained in the recycled asphalt concrete was determined in accordance with the method of ASTM D2172 in conjunction with the specific gravity test method of ASTM D2726 and the compaction specification, stability and flow test procedure of ASTM D1559. Using these test methods, blending the recycled material with the stone aggregate, the new asphalt cement and the surfactant, the recoverable asphalt cement content in the recycled road material was determined to be 6% of the recycled material. Thus, the total asphalt cement in the mixture is 5.58%.
  • the process for making asphalt concrete from a mixture of recycled asphalt concrete, new aggregate and asphalt cement is basically the same as the process set forth in Example 1.
  • the new asphalt cement and surfactant are mixed together and preheated to 140°C.
  • the recycled asphalt concrete and the aggregate are added to the heat exchanger-mixer along with the new asphalt cement-surfactant mixture.
  • the heat exchanger-mixer is then sealed in the same manner as Example 1 and the free water removed under its own vapor pressure.
  • the temperatures and times set forth in Example 1 with respect to asphalt concrete made from virgin starting materials also apply to the present example. During heating of the asphalt concrete product, 1.25 kg samples were removed for testing as set forth hereinafter.
  • Samples of the various test specimens were prepared promptly after discharge of the product from the mixing apparatus. "Marshall Specimens" were prepared in accordance with ASTM D1559. A thermometer was used to check the temperature of the discharged asphalt concrete product. The temperature of the speciment prepared from the sample of the asphalt concrete product was taken just prior to compaction. The time period from discharge of the product sample from the mixing chamber until compaction of the samples at each level was 3 to 10 minutes. No meaningful drop in temperature from discharge to compaction was noted.
  • the specific gravity of the specimens was determined in accordance with the procedure of ASTM D2726 and plotted to form the graphs of Figures 3 and 5. Stability of the specimens was measured in accordance with the procedure of ASTM D1559 at various compaction temperatures and plotted to form the graphs of Figures 4 and 6.
  • the symbol A represents data with respect to samples of a product prepared in accordance with the present invention.
  • the symbol 0 represents data with respect to samples made in accordance with the present invention, but after the moisture content purposefully retained in the product of the present invention had been baked off by placing the product in an oven at atmospheric pressure and baking at 140°C for 1 hour.
  • the specimens for the data represented by 0 were molded at decreasing temperatures, rather than increasing temperatures as was the case for the data represented by A.
  • the symbol 0 represents data with respect to specimens prepared from asphalt concrete made in accordance with the prior art.
  • the same starting materials in substantially the same proportions were used as in Examples 1 and 2, with the exception that no surfactant was used for the samples made in accordance with the prior art method.
  • the prior art method was to heat the aggregate to about 138-160°C (280-320°F). The heated aggregate was placed in an unsealed mixer and the asphalt cement, preheated to 140°C, was added to the heated aggregate in the mixer. The mixture was mixed until the asphalt concrete product was uniform and 1.25 kg specimens were molded as with the products of Examples 1 and 2.
  • the line A-E-F-D illustrates how the specific gravity varies with the compaction temperature for specimens prepared from the product made in Example 1 according to the present invention.
  • the line A-B-C-D illustrates how the specific gravity varies with the compaction temperature for specimens prepared from asphalt concrete made in accordance with the prior art method.
  • point E the specific gravity of the product made according to the present invention below 100°C
  • point F the specific gravity of the product made in accordance with the prior art process
  • the specific gravity of the product according to the present invention is significantly greater at 104.4°C (220°F) than the specific gravity of the prior art product. See point F compared to point B in Figure 3.
  • a point F the product made in accordance with the present invention contains the optimum moisture content for the particular job mix formula, namely 2.0% at 104.4°C (220°F).
  • the moisture content had been reduced to 2% by controlled evaporation as determined by measuring the amount of water condensed.
  • line D-C-B-G illustrates how the specific gravity varies with the compaction temperature for specimens prepared from asphalt concrete made in accordance with the present invention, but after all of the water contained in the product has been evaporated.
  • the purpose of this procedure is to demonstrate that the moisture, rather than the surfactant of the asphalt concrete product prepared in accordance with the present invention is responsible for its increased specific gravity compared to the product made in accordance with the prior art method.
  • the data supports this conclusion.
  • the specific gravity of the product made in accordance with the present invention but containing no moisture varies with the compaction temperature curve in a manner very similar to that for the product prepared according to the prior art method.
  • the surfactant is not believed to have a significant effect on the specific gravity of the product.
  • the purpose of the surfactant is to enhance the mixing of the liquid and solid ingredients.
  • Figure 4 is a graph illustrating how the stability varies with the compaction temperature of the same products referred to with respect to Figure 3.
  • Line A-F-G-E represents the data for the product made in accordance with Example 1.
  • Line E-C-H represents data for the same product after the moisture had been substantially completely evaporated.
  • Line A-B-C-D-E represents data for a product made in accordance with the prior art method wherein no effort was made to control the moisture content of the product.
  • the stability of the sample is a measure of its strength, and, indirectly, its durability. As expected, the stability data corresponds to the specific gravity data. Thus, asphalt concrete having a higher specific gravity generally has fewer air voids, generally has a larger number of pores filled with asphalt cement and therefore, it has greater stability and strength than the same product with a lower specific gravity.
  • the test for these characteristics was made in accordance with the procedures of ASTM C127, ASTM C128, ASTM D2726 and ASTM D1559.
  • Figure 4 illustrates that a product with significantly greater stability may be attained in accordance with the present invention when compared to products prepared in accordance with the prior art.
  • the points in the vicinity of the letter C with respect to the product made from the prior art method and the product made in accordance with the present invention but having the moisture evaporated show a stability of about 544 kg (1200 pounds).
  • the product made in accordance with the present invention has a stability of about 669 kg (1475 pounds) at the same compaction temperature (point G).
  • point G compaction temperature
  • the product made in accordance with the prior art does not achieve this degree of stability until about 119°C (246°F). Again, the data support the conclusion that a superior product can be made at a lower temperature according to the present invention.
  • Figure 5 illustrates how specific gravity varies with the compaction temperature of a product made in accordance with Example 2, of the product made in accordance with Example 2 but having had the moisture evaporated therefrom, and of a product made from the same type and proportion of recycled and virgin components as Example 2, but made in accordance with the prior art methods.
  • Line B-C represents data with respect to specimens made according to the prior art process.
  • Line C-A represents data with respect to specimens made in accordance with the present invention, but after all moisture had been evaporated from them.
  • Line D-E represents data with respect to a product made in accordance with Example 2, which uses a substantial portion of recycled asphalt concrete.
  • the specific gravity of the product made in accordance with the present invention is greater than the specific gravity at corresponding compaction temperatures of the other two products.
  • a product made in accordance with the prior art would have to be compacted at 115.6°C (240°F). Again, this clearly indicates that significant energy and cost savings are available by making the product in accordance with the present invention.
  • the line C-A illustrates that the moisture, not the surfactant, in the product of the present invention is responsible for its increased specific gravity.
  • Figure 6 is a graph of the data which illustrates how stability varies with compaction temperature for the same products described with respect to Figure 5.
  • the data plotted on the graph in Figure 6 clearly indicates that at a given temperature, the stability, and therefore, strength, of a product made in accordance with the present invention is greater than the strength of a product made in accordance with the prior art or of a product made in accordance with the present invention but where the water has been evaporated.
  • the product made in accordance with the present invention has a stability of about 757.5 kg (1670 pounds) whereas the other products have a stability of about 671.3 kg (1480 pounds).
  • the prior art product and the product whose water was evaporated do not attain the strength at 104.4°C of the product made in accordance with the present invention until they are compacted at 117°C (242.5°F).
  • optimum moisture content is defined as the amount of moisture in asphalt concrete which will impart the maximum specific gravity and stability to the asphalt concrete at the lowest temperature at which the asphalt concrete will have the maximum specific gravity and stability.
  • the amount of water or moisture to be evaporated from the asphalt concrete can be controlled by controlling the vapor pressure within the mixing chamber.
  • Figure 7 illustrates the relationship between specific gravity and vapor pressure for a specific asphalt concrete made in accordance with Example 1.
  • a batch of asphalt concrete was made as set forth in Example 1, but the temperature was maintained at an average temperature of 116°C (240.8°F). This temperature was chosen so that the vapor pressure of the water vapor evaporated from the asphalt concrete in the mixing chamber would be as high as about 68,948 N/m 2 gauge (10 p.s.i.g.), the maximum limit for vapour pressure of water at that temperature.
  • Point E of Figure 7 corresponds to a product having a vapour pressure of about 68,948 N/m 2 gauge (10 p.s.i.g.) because the valve was completely closed. All moisture was therefore retained in the product of point E of Figure 7.
  • the specific gravity of point E of Figure 7 corresponds to the specific gravity of point E of Figure 3.
  • the underlying result of making asphalt concrete in accordance with the present invention is that a product can be produced having the same quality at a lower temperature than possible with prior art processes with a reduction in fuel consumption and corresponding cost savings. While the prior art seems concerned with evaporating all available moisture, the present invention is based on the premise that an optimum moisture content of about 0.1 to about 10% in the final product is beneficial. It is believed that the potential thermal energy of the moisture in the virgin aggregate (1% to 4% typically) represents about 20% to about 50% of the thermal energy within the asphalt concrete mixture. In the prior art processes, this potential energy is wasted and more energy is consumed in evaporating this moisture. In the present invention, energy is conserved and used to achieve an equal quality product at a lower temperature.
  • mixing chamber 28 contains two "Porcupine" heat exchange mixing screw assemblies from The Bethlehem Corp., with each screw having a diameter of 1.2 m (4 feet) and a length of 7.2 m (24 feet).
  • the mixture volume within mixing chamber 28 is about 11.33 m 3 (400 cubic feet).
  • a typical uncompacted density of an asphalt concrete mixture is about 1922 kg/m 3 (120 pounds per cubic foot). Accordingly, if the mixing chamber were completely full, it could hold 21.8 metric tons (24 short tons) of asphalt concrete. It will be assumed that mixing chamber 28 will be 90% full during operation, giving a capacity of about 20 metric tons (22 short tons) of asphalt concrete.
  • each screw has an area of 0.16 m 3 (1.77 square feet) and, assuming the advance rate of material through the screws is 15 cm (0.5 feet) per revolution, each screw will carry 0.025 m 3 (0.885 cubic feet) of material per revolution.
  • the outlet control screw conveyor To remove 2 m 3 (70 cubic feet) of asphalt concrete per minute from the mixing chamber, the outlet control screw conveyor must rotate at a rate that compensates for the additional volume of the binder, such as 79.1 rpm for continuous operation. In semicontinuous operation, the outlet control screw conveyor operates at 110% of the rate of the speed for continuous operation to allow for build-up of product in the mixing chamber during the time it takes to move another vehicle or other container under the outlet. This assumes that the outlet screw conveyor has the same dimensions and advance rate as the inlet screw conveyor and that it runs completely full to provide an airlock. Standard linear control devices can control the speed of the inlet screw conveyor, the rate of addition of asphalt cement and other additives, the heat exchanger-mixer speed and the outlet control screw conveyor speed.
  • the temperature of the asphalt concrete mixer within mixing chamber 28 will generally be heated at between about 176.6°C (350°F) and 454.4°C (850°F).
  • the aggregate Upon entering the mixing chamber, the aggregate will have a temperature of about 21.1°C (70°F) and will have a vapour pressure of 0 N/m 2 gauge.
  • the products At the outlet end, the products will have a temperature between 93.3°C (200°F) and 148.9°C (300°F).
  • the maximum saturated vapour pressure in the mixing chamber will be about 1.79x10 5 N/m 2 gauge (26 p.s.i.g.) when the apparatus operates in the continuous or semicontinuous mode.
  • the maximum saturated vapour pressure attainable would be 3.59 N/m 2 gauge (52 p.s.i.g.) in the batch mode.

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Claims (26)

1. Appareil pour fabriquer du béton d'asphalte, comprenant une chambre de mélange (28) ayant une entrée (26, 38), une sortie (40) et des moyens (30, 32) logés dans la chambre (28) pour chauffer indirectement un mélange de matières de départ comprenant un agrégat et un liant tout en déplaçant le mélange à travers la chambre (28), caractérisé en ce que l'entre (26, 38) et la sortie (40) peuvent être sélectivement obturées hermétiquement de manière que l'intérieur de la chambre de mélange (28) ne communique pas avec l'atmosphère lorsqu'elles sont obturées hermétiquement et que des moyens de réglage de l'humidité (76, 88, 92, 94) sont prévus pour ajuster la teneur en humidité du mélange à une valeur prédéterminée en éliminant de l'humidité du mélange logé dans la chambre (28) sous la forme de vapeur d'eau lorsque la teneur en humidité est plus grande que la valeur prédéterminée, jusqu'à ce que la teneur en humidité soit égale à la valeur prédéterminée.
2. Appareil pour fabrique du béton d'asphalte, comprenant une chambre de mélange (28) ayant une entrée (26, 38), une sortie (40) et des moyens (30, 32) logés dans la chambre (28) pour chauffer indirectement un mélange de matières de départ comprenant un agrégat et un liant, tout en déplaçant le mélange à travers la chambre (28), caractérisé en ce que l'entrée (26, 38) et la sortie (40) peuvent être sélectivement obturées hermétiquement de manière que l'intérieur de la chambre de mélange (28) ne communique pas avec l'atmosphère lorsqu'elles sont obturées hermétiquement et que des moyens (86, 88, 92, 94) de réglage de l'humidité sont prévus pour ajuster la teneur en humidité du mélange à une valeur prédéterminée en ajoutant de l'eau au mélange contenu dans la chambre (28) lorsque la teneur en humidité est inférieure à la valeur prédéterminée, jusqu'à ce que la teneur en humidité soit égale à la valeur prédéterminée.
3. Appareil pour fabrique du béton d'asphalte, comprenant une chambre de mélange (28) ayant une entrée (26, 38) une sortie (40) et des moyens (30, 32) contenus dans la chambre (28) pour chauffer indirectement un mélange de matières de départ comprenant un agrégat et un liant tout en déplaçant le mélange à travers la chambre (28), caractérisé en ce que l'entrée (26, 38) et la sortie (40) pouvent être sélectivement obturées hermétiquement de manière que l'intérieur de la chambre de mélange de communique pas avec l'atmosphère lorsqu'elles sont obturées hermétiquement, et que des moyens (76, 86, 88, 92, 94) de réglage de l'humidité sont prévus pour ajuster la teneur en humidité du mélange à une valeur prédéterminée, ces moyens comprenant des moyens (76, 88, 92, 94) permettant d'éliminer de l'humidité du mélange contenu dans la chambre (28) sous la forme de vapeur d'eau lorsque la teneur en humidité est supérieure à la valeur prédéterminée, jusqu'à ce que la teneur en humidité soit égale à la valeur prédéterminée, et des moyens (86, 88, 92, 94) permettant d'ajouter de l'eau au mélange contenu dans la chambre (28) lorsque la teneur en humidité est inférieure à la valeur prédéterminée, jusqu'à ce que la teneur en humidité soit égale à la valeur prédéterminée.
4. Appareil selon la revendication 1, 2 ou 3, caractérisé en outre en ce que les moyens de réglage de l'humidité (76, 86, 88, 92, 94) comprennent des moyens (88) permettant de capter la teneur en humidité de l'agrégat avant qu'il ne soit mélangé au liant, des moyens (Fig. 8 à 20) permettant de comparer la teneur en humidité de l'agrégat avec la valeur prédéterminée, et des moyens permettant d'activer les moyens de réglage de l'humidité.
5. Appareil selon la revendication 1, 2 ou 3, caractérisé en ce que les moyens de réglage de l'humidité (76, 86, 88, 92, 94) comprennent des moyens permettant de capter le débit d'introduction de l'agrégat dans la chambre (28), des moyens permettant de capter le débit d'introduction de l'eau dans la chambre (28), des moyens (Fig. 8 à 20) permettant de comparer le débit d'introduction de l'agrégat et le débit de l'eau à un débit d'introduction de l'agrégat et un débit d'eau indicatifs de la valeur prédéterminée de la teneur en humidité, et des moyens permettant d'activer les moyens de réglage de l'humidité.
6. Appareil selon la revendication 1 ou 3, ou la revendication 4 ou 5, dépendant d'une de ces dernières, dans lequel un condenseur (66, 75) est prévu pour condenser la vapeur d'eau et un conduit (68, 72, 73, 77) relie le condenseur (66, 75) à la chambre (28).
7. Appareil selon la revendication 6, dans lequel l'agrégat est contenu dans un ou plusieurs silos (12, 14, 16, 18) et le condenseur (75) passe à travers au moins l'un des silos (18).
8. Appareil selon la revendication 6 ou 7, caractérisé en outre en ce qu'une première conduite (72) munie d'une vanne (76), relie la chambre de mélange (28) au condenseur (66, 75), une deuxième conduite (68) munie d'une vanne (70) relie le condenseur (66, 75) à la chambre de mélange (28) pour renvoyer le gaz à la chambre (28), un réservoir (80) servant à stocker l'eau condensée par le condenseur (66, 75) est relié à ce dernier par une troisième conduite (78) munie d'une vanne, et une autre conduite (84) relie le réservoir (80) à la chambre de mélange (28) pour introduire de l'eau dans la chambre (28).
9. Appareil selon la revendication 8, caractérisé en outre en ce que les moyens de réglage de l'humidité (76, 78, 86, 88, 94) comprennent des moyens (79) permettant de capter le débit d'eau condensée passant dans la troisième conduite (78) munie d'une vanne, des moyens (Fig. 8 à 20) permettant de comparer le débit à un débit prédéterminé indicatif de la valeur prédéterminée de la teneur en humidité et des moyens permettant d'activer les moyens de réglage de l'humidité.
10. Appareil selon l'une quelconque des revendications précédentes, qui est transportable.
11. Appareil selon l'une quelconque des revendications précédentes qui est agencé pour fonctionner suivant un mode discontinu (Fig. 9), semi-continu (Fig. 13) ou continu (Fig. 19).
12. Appareil selon l'une quelconque des revendications précédentes dans lequel l'entrée (26, 38) et la sortie (40) comprennent des transporteurs à vis obturables (38, 40).
13. Appareil selon l'une quelconque des revendications précédentes dans lequel au moins un transporteur à vis à palette creuse et à arbre creux contenant un fluide d'échange de chaleur est contenu dans la chambre de mélange (28).
14. Appareil selon l'une quelconque des revendications précédentes caractérisé en outre en ce que les moyens de réglage de l'humidité (76, 78, 86, 88, 94) comprennent des moyens (94) permettant de capter la pression de vapeur du mélange contenu dans la chambre (28), des moyens (Fig. 8 à 20) permettant de comparer cette pression de vapeur à une pression prédéterminée indicatrice de la valeur prédéterminée de la teneur en humidité, et des moyens permettant d'activer les moyens de réglage de l'humidité.
15. Appareil suivant l'une quelconque des revendications précédentes, caractérisé en outre en ce que les moyens de réglage de l'humidité (76, 78, 86, 88, 94) comprennent des moyens (92) pour capter la température du mélange à l'intérieur de la chambre, des moyens (Fig. 8 à 20) pour comparer la température à une température prédeterminée, indicatrice de la valeur prédéterminée de la teneur en humidité, et des moyens pour activer les moyens de réglage de l'humidité.
16. Appareil selon l'une quelconque des revendications précédentes, caractérisé en outre en ce que les moyens de réglage de l'humidité (76, 78, 86, 88, 94) comprennent des moyens (Fig. 8 à 20) permettant de capter le débit d'introduction des matières de départ et de l'eau éventuelle dans la chambre, des moyens permettant de capter la vitesse du mouvement du mélange dans la chambre, des moyens permettant de capteur de lébit de déchargement du mélange de la chambre, des moyens permettant de comparer les débits d'introduction, vitesses de mouvement et débits de déchargement à des débits d'introduction, vitesses de mouvement et débits de déchargement indicatifs de la valeur prédéterminée de la teneur en humidité, et des moyens permettant d'activer les moyens de réglage de l'humidité.
17. Un procédé de fabrication de béton d'asphalte, caractérisé par les phases suivantes: a) enfermer hermétiquement sélectivement un mélange de matières de départ comprenant de l'agrégat et du liant de telle façon que le mélange ne communique pas avec l'atmosphère; (b) malaxer et chauffer indirectement le mélange alors qu'il est ainsi enfermé hermétiquement; c) ajuster la teneur en humidité du mélange à une valeur prédéterminée, soit en éliminant de l'humidité du mélange sous la forme de vapeur d'eau lorsque la teneur en humidité est supérieure à la valeur prédéterminée, jusqu'à ce que la teneur en humidité soit égale à al valeur prédéterminée, soit en ajoutant de l'eau au mélange lorsque la teneur en humidité est inférieure à la valeur prédéterminée, jusqu'à ce que la teneur en humidité soit égale à la valeur prédéterminée.
18. Un procédé selon la revendication 17, caractérisé en outre en ce qu'on détecte la teneur en humidité des matières avant de les mélanger et de les chauffer indirectement.
19. Un procédé selon la revendication 17 ou 18, dans lequel la matière liante est un ciment d'asphalte, une émulsion de ciment d'asphalte- eau, du soufre ou un mélange de ces substances.
20. Un procédé selon la revendication 17,18 ou 19, dans lequel l'agrégat est un agrégat vierge brut, un agrégat recyclé ou un mélange de ces agrégats.
21. Un procédé selon une quelconque des revendications 17 à 20, caractérisé en outre en ce qu'on chauffe le mélange à une température finale comprise dans l'intervalle de 60 à 150°C.
22. Un procédé selon une quelconque des revendications 17 à 21, caractérisé en outre en ce qu'on ajuste la teneur en humidité du mélange à une valeur comprise dans l'intervalle de 0,1% à 10%.
23. Un procédé selon une quelconque des revendications 17 à 22, caractérisé en ce qu'on chauffe le mélange à une température de plus de 100°C et en ce qu'on élimine l'humidité du mélange sous la forme de vapeur d'eau sous l'effet de la pression de vapeur de ce dernier.
24. Un procédé selon une quelconque des revendications 17 à 23, dans lequel la vapeur d'eau extraite du mélange est condensée.
25. Un procédé selon la revendication 24, dans lequel on recycle les gaz au mélange après avoir condensé la vapeur d'eau.
26. Un procédé selon l'une quelconque des revendications 17 à 25, dans lequel on ajoute un tensio-actif au mélange.
EP19800302968 1980-08-27 1980-08-27 Procédé et appareil pour la production de béton d'asphalte Expired EP0046827B1 (fr)

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EP0046827B1 true EP0046827B1 (fr) 1985-04-03

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