US1774649A - Method of making paving material - Google Patents

Description

Sept. 2, 1930. D. McK HEPBURN ET AL 1,774,649 METHOD oF MAKING PAVING MATERIAL Filed Sept. 28. 1929 Patented Sept. 2, 1930 f vUNTTED STATES PATENT OFFICE DONALD MCKNIGHT HEPBURN, OF PHILADELPHIA, AND SAMUEL SCHMUCKER SADTLER, F SPRINGFIELD TOWNSHIP, MONTGOMERY COUNTY, PENNSYLVANIA, ASSIGNORS TO AMIESITE ASPHALT COMPANY OF AMERICA, 0F CAMDEN, NEW

JERSEY, A CORPORATION OF NEW' JERSEY' METHOD 0F MAKING v:PAVING MATERIAL Application filed September 28, 1929. Serial No. 395,813.

The present invention relates to methods of or processes for mixing and drying materials suitable for the formation of layers or courses of roads or other pavements, and

more particularly to the methods of making road making materials wherein a mineral aggregate of stone or pebble or sand or fines or a mixture thereof is coated with a bituminous or similar binding material, and

particularly adapted to be Iaid' hot or cold, and compacted to form' a permanent course or layer of the roadway.

The objects of the present invention are to provide a method of coating a mineral aggregate suitable for the aggregate of bituminous roadways, at the quarry or gravel pit whence the aggregate is obtained, in order tomake necessary but a single handling of the aggregate to produce a road materia-l rg0 of aggregate coated with a bituminous or similar binder, which material can be stored until wanted for placement, wit-hout form-- ing an agglomerate, or which may be loaded, directly it is made, into railway cars or motor trucks for transportation to the place where it is to be used in road construction.

A further object of the invention is' to provide a proces in which relatively low grade oils, such as crde oil or fuel oil or 3o bunker oil are used as the binding and coating material), for mineral aggregates, such materials being usually sufficiently fluid, when hot, to obviate the use of a liqueier, and being applied usually to a hot aggregate.

Another object of-the invention is to provide for the continuous'treatment of an aggregate at the sand pit or quarry where a continuous stream of mineral aggregate is first subjected to heat in a current of hot 40 air to dry the aggregate and remove the dust therefrom, said stream being thereafter subjected to a continuous agitation or mixing process and treated first to a waterproofing material in liquid form and thereafter being treated with a hot bituminous binding building operation that the haulage thereto by a train or`truck is not excessive or prohibitive. e

A further objectl of the invention is to effect, in a single continuous and progressive treatment, the drying, dusting, water proong and coating with a suitable binding material, mineral aggregate suitable for the construction of roadways or other pavements', and at the same time to substantially increase the ductility of said binding ma terial. 4

A further object of the invention is to provide a paving material which will re.

quire the use of a minimum amount of binding material thereby providing a substantially non-skid surface of the roadway.

A A,further object of the invention is to provide a method whereby localstone, which may not be of the highest character, and even stones that are water-absorptive and relatively low in strength may be utilized, by subjecting the stone to a temperature sufficient to evaporate the water in a lstream of warm air and to thereafter impregnate the stone with a coating material which at atmospheric temperatures has viscosity and cohesiveness sufficient to firmly bind together the aggregate of a roadway and which is highly resistant to the wear of trac, and to water.

A further object is to provide a simple easily practiced process for continuously drying, waterproofing (when necessary or desirable) and coating with liquidasphalt or similar material a constantly progressing or flowing stream of mineral aggregate.

Further objects of the invention will appear in the specification and claims below.

Although the process or method of making a paving material forming this invention may be performed in a variety of ways or even by hand operations, Donald McKnight Hepburn, one of the present inventors has also invented an apparatus particularly adapted for the automatic practice of this improved process, said apparatus forming fin the subject-matter of a co-pending application, tiled by him August 10, 1929, nerial No. 384,998, and for the purpose of making clear the nature of the treatment to which the aggregate is subjected, and how the process may be performed commercially, but without limiting the practice of the process thereto, said apparatus is illustrated in the drawings forming a part of this application, to which reference will now be made.

Fig. 1 is a side elevational view, partly in section, of the essential parts of a combined drying, dusting, heating, waterproofing and mixing machine, showing the mode of introducing the aggregate thereinto, of causing it to traverse the length thereof substantially in a continuous stream, and the manner of supplying fuel to the heater and waterproofing and coating material continuously to the aggregate, together with the mode of continuously introducing into the mixing portion of the apparatus, fines, sand and/or chemicals, suchas sulphur, for the purpose of increasing the viscosity of the binding material and to increase the thickness of the coatme.

lFig. 2 is a transverse cross-sectional view, on the line 2-2 of Fig. 1.

Fig. 3 is a transverse cross-sectional view looking in the opposite direction to that in Fig. 2 and taken on the line 3-3 of Fig. 1, and

Fig. 4 is a transverse cross-sectional view on the line 1 4 of Fig. 1.

The rotatable cylinder 1 is preferably composed of three alined sections, the upper section 1a comprising a heating chamber wherein the mineral aggregate is heated, dried and freed from dust; an intermediate section 1b wherein the aggregate is cooled and wherein the aggregate may be sprinkled with any suitable liquid, such as kerosene, rubber in solution or soap solution and. is herein termed the cooling and water-proofing section or chamber; and a mixing chamber 1c wherein hot binding material is added to the aggregate and the aggregate is continuously stirred and agitated for the purpose of thoroughly coating each piece of the aggregate with the binding material, and is herein termed the mixer section or chamber 1c.

The adjacent ends of the heating chamber 1a and of the intermediate section 1b are preferably spaced from each other and the gap therebetween is closed by a split ring 2, tightly yfitting over the said adjacent ends of said chambers and firmly clamped thereon by bolts 3 passing through the radial flanges 4 thereof. The adjacent ends of the waterproofing chamber l and the mixing chamber lc are similarly spaced apart and the gap therebetween is closed by a likey split ring 2 with flanges 4 and bolts 3 passing therethrough.

The rotatable cylinder 1 is preferably supported on a series of pairs of anti-friction rollers 5--5, and the cylinder 1 is provided with a plurality of circular tracks 2 one for each pair of rollers. The lower end of the mixer section 1c preferably fits loosely within a circular opening 7 through a side wall of a stationary housing 8 which is in communication with a centrifugal fan 9 arranged to impel a strong blast of air (at substantially atmospheric temperature in all but the section l?) through the entire length of the rotatable cylinder 1.

The housing 8 is also provided with a chute 10 adjacent the lower end of the mixer section 1C through which the material coming thereto from the lower end of the mixing chamber lc is delivered to a conveyer for storage or to a truck or car for transportation. Adjacent the upper end of the rotatable cylinder 1 is a bucket elevator 11 adapted to discharge its load into a hopper 12 having a chute 13 extending into the upper and otherwise open end of the heating section 1. Near the upper end of the heater section l;l is a toothed wheel or sprocket wheel 111 upon which runs a sprocket chain 15 connected to any suitable source of power for continuously rotating the cylinder 1. W'ithin its upper end, the intermediate section 1b is provided with a spider 16 rigidly secured thereto and provided at its center with two rings 17 concentric with the axis of the cylinder, and litting against the marginal edges of the opposite sides of a disk 18.

Within the cylinder 1 and extending practically axially thereof from the lower end thereof to theupper end of the intermediate section 1b is a series of' pipes, the lower ends of which may be and preferably are within the stationary housing 8 and extend through the lower wall thereof. Extending through the disk 18 is the fuel pipe 19, the upper end of which is provided with a burner Q0 projecting forwardly substantially axially of and at the lower end of the heating chamber 1n. This fuel p'ipe 19 is provided with a valve 21 by means of which the flow of fuel oil to the burner may be regulated and controlled. Extending substantially parallel to the fuel lll() pipe 19 is a pipe 22 by meansl of'which air under substantial pressure is conducted to the burner to aid in the combustion of the fuel. This air pipe 22, also extending through the lower wall of the housing 8 is preferably provided with a controlling valve 23. lVhen fuel is admitted through the pipe 19 to the burner 2() and ignited and supplied with air from the air pipe 22 and from the fan 9, a hot flare flame or blast is projected forwardly from the burner 20 and substantially fills the chamber 1c.

Also passing through the disk 18 is a pipe 24 extending into the housing 8 and thence downwardly through the lower wall of the housing 8 where it is provided with a controlling valve 25. The upper end of this pipe 24 is provided with a series of perforations 26 through which any suitable liquid may be sprayed onto the stream of aggregate delivered thereto from the heating chamber 1a, as will'be referred to again below.

The fourth pipe 27 of the group of pipes or tubes is preferably well above the bottom of the cylinder 1 and may terminate at its upper end short ofthe disk 18. In the drawings, the upper end of said pipe 27 isshown as suspended by a hanger or clamp 28 from the pipe 24 and terminating at the point where the perforations 26 in the pipe 24 begin. Said tube or pipe 27, after extending into the housing 8 andt-hence downwardly through the bottom thereof is also preferably provided with a hand operated valve 29.' It is through this pipe 27 that the coating and binding material for the aggregate is conducted into the mixing chamber 1c and discharged through the perforations upon the aggregate under agitation therein. Within the forward part of the housing 16 is a strut or bracket 31 in which the pipes 19, 22, 24 and 27 are rigidly mounted and held together. rl`hus the group of pipes is rigidly supported substantially axially of the cylinder 1 in the spider 16 and bracket 31, and the spider is free to rotate around the stationary disk 18 when the cylinder 1 is rotated.

The -heating chamber 1fL is preferably provided on the inner surface thereof with a series of troughs 32 preferably disposed parallel to the axis of the cylinder. `When the cylinder is rotated in the direction of the arrow 33 (Fig. 2) these lifting troughs lill with aggregate and lift it to a point near the top of the cylinder whence it falls back t-o the bottom side of the cylinder and transversely through the flame from the burner 20 and transverselythrough the blast of air coming from the fan 9 and heated by said flame.

The interior surface of the mixer section or chamber 1c is provided with a plurality of series of stirrer blades 34, the blades of each series being preferably@ disposed in al circle on the interior of the section 1, and inclined at substantially 45 to the direction of their rotative path. Were the inner surface of the section 1c to be laid out flat, in development, the blades in any series would be parallel to each other, and those of the ad-A jacent series would be parallel to each other and would make angles of 90 with the blades in the series first above mentioned. These series of rings of stirrer blades 34 preferably extend for substantially the full lengthv of the mixing section 1. e o

Within the cylinder 1, and over the pipes 19, 22, 24 and 27, is preferably mounted a a y guard plate or shield or roof 35 of sheet metal supported on any of the said pipes and the walls of which diverge sharply downwardly so that any of the coated stones which may stick to the stirrer blades 34 and drop therefrom when the blades are in their highest position during the rotation of the cylinder, and strike said roof, will not adhere thereto or accumulate thereon.

On the housing 8 is preferably mounted a hopper 36, the bottom of which is preferably provided with a feed screw 37 for the purpose of delivering steadily from the hopper 36 any fine solid materials which are needed or desired in the mixture under treatment in the mixing chamber 1. The feed end of the screw 37 communicates with a chute 38 extending downwardly therefrom into the lowcr end of the mixer chamber 1c and well above. the lowest portion of the cylinder section 1', so that it is clear of the stream of material under treatment in said section 1.

In carrying out the improved process of this application with the apparatus above described, thefuel oil from the fuel pipe 19 is ignited at the burner 20 and air under pressure is supplied through the air pipe 22. The fan 9 impels a blastof air at atmospheric temperature through the mixer section. 1c and the intermediate section'1b but 20. The cylinder 1 is constantly `rotated by the chain 15 driving the sprocket wheel 14.

The aggregate in form of stone 'or sand or gravel as it comes from the` quarry, Crusher or pit is continuously dropped from the elevator 11 into the hopper 12 and thence is delivered to the heating chamber 1a. By the rotation of the cylinder the 'aggregate is continuously lifted up one side of the heating chamber 1a by the troughs 32 until it reaches a point near` the top of the cylinder whence itis spilled out or dropped from the said troughs or lifters and falls transversely through the flame and through the current of air to the botto-m of kthe `chamber 1a. This lifting and dropping of the aggregate in inder performs twor functions, (1') theyaggregate is heated to a temperature suflicient to evaporate the water contained therein, and

(2) any dust mixed with the aggregate is blown away and the aggregate is thereby cleaned. The inclination of the axis of the rotating cylinder 1 elfects, by gravity, slow progression or travel of the aggregate through its path in the cylinder in a direction contrary to/that of the blast of air supplied thereto from the fan 9. The aggre-1 gate thus progresses by gravity to the lower end of the heater section and except in the heating section 1a where a part of it is raining through the flame and blast of air, it flows as a stream over the split ring 2 and between the spokes or arms of the spider 16 into and through the second portion of its path which is through the intermediate section 1b and over the second smooth split ring 2. Immediately after the aggregate passes the burner 20 it meets the cool air impelled through the sections 1 and 1" from the fan 9 and moves in a direction contrary thereto. Thus the heated aggregate and the coating, after its application thereto", are also sub stantially cooled during their travel through the section 1C.

When the material with which the aggregate is to be coated is too thick and viscous even when heated to be easily mixed with the aggregate or to evenly coat the same, to the aggregate in the second stage or portion of its travel in'its path through the cylinder is added a liqueh'er of the bituminous material with which the aggregate isA to be coated, such as kerosene or naphtha or any other liquefier which may also contain other ingredients. Such liquefiers or mixtures or solutions are conveyed to the intermediate section 1b through the pipe 24 and are sprayed or yotherwise discharge onto the aggregate therein and flowing therethrough by gravity, through the perforations 26 at the upperend of the pipe. ordinarily at atmospheric temperatures, and hence also contribute to the rapid cooling of the aggregate coming from the chamber 1a.

Having thus been cooled in its travel between the drying or heating chamber 1a and the mixing chamber 1c, the stream of aggregate enters the third or last portion of its path by flowing into the upper end of the mixer or chamber 1C. Immediately `upon leaving the intermediate section l the aggregate passes under the upper end of the spray or jet pipe Q7 which is supplied with a liquid binding material preferably heated to the proper temperature dependent upon the character of the binder used, and thereafter throughout its travel through the cylinder Such liquids, when used, are' the split rings 2 2. On the side of the cylinder 1c it slides from one stirrer blade to a stirrer blade in the next concentric ring of stirrer blades, working back and forth from one blade to the next and at the same Ytime slowly progressing by gravity through the length of the mixing chamber 1c until it reaches the lower end thereof.

Shortly prior to the time when the mixing and coating of the aggregate has been completed in the mixer section l, a relatively small quantity of lines or sand, either alone or mixed with other naterials, such as lime and/or sulphur, is added thereto for the purpose of obtaining a thicker coating on the individual pieces of aggregate, a more even distribution of the coating material on the individual pieces, and imparting toughness or hardness or increased viscosity and cohesion to the binding material. The fine material is continuously added to the aggregate flowing through the last stage or portion of its travel or path through the cylinder 1, being fed from the hopper 36 by the screw 37 and delivered to the aggregate in the mixing section 1 as a continuous stream running down through the end of the chute 3S. rlhe blast from the fan 9 will prevent the material from being deposited directly below the lower end of the chute 38, vbecause it is finely comminuted and dust-like. These small particles so added will be blown by the blast of air some way upwardly toward the upper end of the mixing chamber 1c before it comes to rest on the aggregate being agitated there in, particularly if the lower end of the chute 38 be spaced a substantial distance above the upper surface of the aggregate under treatment in the mixing chamber 1c.

Vhen the coated aggregate leaves the lower end of the mixer section 1C it falls into the chute 10 and thence is carried away for storage by a continuous` conveyer, or is delivered into cars or trucks for transportation to the place where the roadway is being made.

Thus is provided a process or iretliod of continuously treating a mineral aggregate by forming it into a stream and moving it continuously by gravity through a predetermined path in a direction opposite to that of a blast of air driven thereover, and by subjecting the aggregate during the first portion of i its4 trav'el to a drying and dusting action in a flame and in a hot blast of air to evaporate the water contained therein therefrom and then continuously delivering said aggregate as a moving stream to a mixing chamber wherein there is continuously added coating material while the aggregate is kept under constant agitation, and finally, shortly prior to the 'time when said aggregate travels through the last portion or stage of its path and at a time too late in the mixing operation to permit of the formation into balls or masses of aggregate, adding lines and/or sulphur and/or other dry materials which increase the thickness of the coating and renders the bituminous material better suited for road making purposes.

klln making a 'paving material designed to be laid cold and compacted of the type known in the trade as Amiesite, the aggregate for a course of the road which is delivered from the elevator 11 to the upper end of the cylinder 1 is a graded aggregate. The heat to which it is subjected in the drying and heating section 1a is sufficient to evaporate any water contained therein, but the aggregate itself is not heated to such a degree that in the intermediate section 1b its temperature may not be readily reduced by the cool air blowing thereover to at or about 90 F. In passing through the intermediate section or portion of its path, a liqueer, such as kerosene or other slightly Volatile oilslalone or admiXed with other ingredients is sprayed thereon continuousl through the perforations 25 in the lique er pipe 24, the quantity being substantially from one to one and a half gallons for each ton of aggregate passing therethrough. y

When the aggregate iows from the intermediate section or portion of its path into the nal portion of its course, it Hows under the pipe 27 and substantially so long as the material is passing through said chamber, asphalt having a penetration at atmospheric temperatures ofD from to 100, but heated to a temperature of from 250 to 300 F. is

delivered to the aggregate in the mixing chamber and for substantially the entire time that the aggregate is flowing through said section 1. At the same time the aggregate is subjected to a vigorous agitation due to the rotation of the cylinder and the action of the blades 34. The quantity of as.- phalt delivered to a ton of aggregate passing a given point within the chamber will vary considerably, depending upon the size of the aggregate and the quality of the as` phalt, but generally, for a ton of aggregate which will pass through a quarter inch mesh. screen, the quantity of asphalt is from 8O tov 100 pounds or 4 to 6% or 7% of the weight of the aggregate. As the aggregate Hows to a point near the end4 of its-path of travel,

vsands or tines, from 5to 10% of the weight of the aggregate, are continuously .delivered to the ag regate under treatment inthe mixing cham er and is at a point sufficiently far up into the chamber to insure `the thorough mixing thereof with the aggre- `gate as 1t is acted upon by the blades at the lower end of the mixing chamber 1c. The aggregate thus coated and prepared falls through the chute 18 asa completely coated aggregateready for placement or storage.I

This process is also applicable to the making of a paving material which is to be laid hot, and wherein an asphaltic material havlvery little asphaltic materialremains.

intermediate section 1b and the lower end of ing a penetration index of 50, for instance, at atmosphericv temperatures, is used. In making this type of paving, the aggregate is heated to temperatures which are considerably higher than those used in making the cold laid avement above described, and it is prefera le to heat the asphaltic cement to be applied thereto to a temperature lof from 350 to 400 F. As soon as the coating is completed, the material should be placed upon the roadway and compacted hot for if the coated aggregate were allowed to cool be-A fore placement, the pieces of aggregate would rigidly cohere to each other and would require re-heating for placementfupon the road.

The process is also applicable to the use of binding and coating materials, the base of which is alcheap low grade oil, such as fuel oil, bunker oil, sludge or waste products from refining processes and in which Such binding materials comprise a cheap low grade oil combined at relatively high temperatures with sulphur, e. g'. 6% of the weight of the oil)l and preferably one ory more of the metallic salts of the fatty acids (as for example, aluminum stearate, 1/2 of 1% of the weight of the oil).

A paving cement of this character once compounded behaves like and in fact great ly resembles the asphalts used in road making. At 250 to 300o F. it is" very fluid and may be used in the process above describedy as a substitute for the asphalt. At atmospheric temperatures, its coherence, ductility, hardness and toughness compalevery favorably with the asphalts ordinarily used in` road construction.

But in using these materials as binders, in this process a liquefier is usually unnecessary, and it is preferable that the aggregate 'be heated to such a temperature that at the time it reaches the lower end of the mixing chamber its temperature shall be a little higher than that ofthe binding material discharged thereon from the fuel feed pipe 27. The cooling of the aggregate by the current of air between the upper end-of the the mixing section 1c should therefore be 115 avoided or reduced as much as possible by reducing the volumeof theair discharged over the stream of aggregate to the minimuniV required for removing the moisture and dust from the aggregate, or by heating. the air prior to its delivery to the-fahrer prior to its discharge from the fan into the lower end of the section 1.

Having thus described our invention, what we claim 'and desire to protect by Letters Patent ofthe United States is: l

1. The method of continuously making a bituminous paving material, which consists in causing a substantially continuous stream of mineral aggregate to ow gravitationally slowly through a predetermined path, and continuously impelling a strong current of air from the atmosphere over and parallel to said stream throughout the length of said path and in a direction opposite to that ot' said stream ot aggregate, heating said current of air in its flow over the first portion of said path of said aggregate and vigorously agitating said aggregate in said first portion of said path in said current of hot ai'r to heat and dry said aggregate and separate dust therefrom, reducing the temperature of the heated aggregate in its How through the remainder by said path of said current of air -flowing thereover vand transerring by said current of air the heat of said cooling aggregate to the aggregate then in said first portion of said path, and continuously discharging hot bituminous binding material over and continuously agitating said stream of aggregate during its travel through said last portion of' its path.

2. The method of continuously making a bituminous paving material, which consists in causing a substantially continuous stream of mineral aggregate toflow gravitationally slowly through a predetermined path, and continuously impelling a strong current of air from the atmosphere over and parallel to said stream throughout the length of said path and in a direction opposite to that of said stream of aggregate, heating said current of air in its flow over the first portion of said path of said aggregate, and continuously liftng and dropping said aggregate in said first portion ot said path through said current of hot air to heat and dry said aggregate and separate dust therefrom, reducing the temperature of the heated aggregate in its How through the remainder of said path of said current of air fiowing thereover and transferring by said current of air the heat of said cooling aggregate to the aggregate then in said first portion of said path, and continuously discharging hot bituminous binding material over and continuously agitating said stream of aggregate during its travel through said last portion of its path.

3. The method of continuously making bituminous paving material, which consists in causing a substantially continuous stream of mineral aggregate to flow gravitationally slowly through a predetermined path, and continuously impelling a strong current of air from the atmosphere over and parallel to said stream throughout the length of said path and in a direction opposite to that of said stream of aggregate, heating said current of air in its flow over the first portion of said path of said aggregate and, vigorously agitating said aggregate in said first portion of said path in said current of hot air to heat and dry said aggregate and separate dust therefrom, reducing the temperature of the heated aggregate in its flow through the remainder of said path of said current of air flowing thereover and transferring by said current of air the heat of said cooling aggregate to the aggregate then in said first portion of said path, continuously discharging hot bituminous binding material over and continuously agitating said stream of aggregate during its travel through said last portion ol its path, and continuously delivering to said stream ot' aggregate, shortly before said aggregate reaches the end of said path, a.' relatively small quantity of finely divided mineral'matter.

4. The method of making a bituminous paving material which consists in causing a substantially continuous stream ot mineral aggregate to flow gravitationally slowly through a predetermined path and continuously impelling a strong current of air from the atmosphere over and parallel to said stream throughout the length of said path and in a direction opposite to that of said stream of aggregate, heating said current 0f air in its flow over the first portion of said path of said aggregate and vigorously agitating said aggregate in said first portion of said path in said current of hot air to heat and dry the aggregate and to separate dust therefrom, reducing the temperature of the hot aggregate in its flow through the remainder of its said path by said current of air flowing thereover and transferring by said current of air the heat of said cooling aggregate to the aggregate then in said first portion ot said path, continuously discharging a liquid liquefier on said aggregate as it travels through the intermediate portion of its path, and continuously discharging hot bituminous binding material over and continually agitating said stream of aggregate during its travel through the last portion ot its path.

5. The method of making a bituminous paving material, which consists in causing a substantially continuous stream of mineral aggregate to flow gravitationally slowly through a predetermined path and continuously impelling a strong current ot air from the atmosphere over and parallel to said stream throughout the length of said path and in a direction opposite to that of said stream of aggregate, heating said current of air in its iiow over the first portion of said path of said aggregate and vigorously agitating said aggregate in said first-portion of' said path in said current of hot air to heat and dry the aggregate and to separate dust therefrom, reducing the temperature of the hot aggregate in its flow through the remainder of its said path by said current of air flowing thereover and transferring by said current of air the heat of said cooling aggregate to the aggregate then in said first portion of said path, continuously discharging a liquid liquefier on said aggregate. as it travels through the interlUO mediate portion of its path, continuously discharging hot bituminous binding material over and continuously agitating said stream of aggregate during its travel through the last portion of its path, and continuously delivering to said stream of aggregate, shortly before said aggregate reaches the end of said path,\a relatively small quantity of finely divided material.

6. The method of continuously making a paving material which consists in causing a substantially continuous stream of mineral aggregate to flow gravitationally slowly through a path and continually impelling a current of air over and parallel to said stream in a direction opposite tothat of said stream of aggregate, heating andthoroughly agitating said aggregate during its travel through the first portion or stage of its said path to dry said aggregate and to remove dust therefrom and continuously discharging on said aggregate during the latter portion or stage of its said path a hot fuel-oil binding composition which is freely fluid when hotand which is of asphaltic consistency at atmospheric temperatures, and thoroughly agitating and mixing said aggregate therewith dur- 'ing the said latter portion or stage of said path.

7. The method of continuously making a paving material which consists in causing a substantially continuous stream of mineral aggregate to How gravitationally slowly through a path and continuously impelling a current of air over` and parallel to said stream in a direction opposite to that of said stream ofaggregate, heating and thoroughly agitating said aggregate duringv its travel through the irst portion or stage of its said path to dry said aggregate and to remove dust theree from and continuously discharging on said aggregate during the latter portion or stage of its said path a hot fuel-oil binding composition-which is freely Huid when hot and which is of asphaltic consistency at atmospheric temperatures, and thoroughly agitating and mixing said aggregate therewith dur.- ing the said latter portion of said path, the

temperature of said aggregate being preferably higher than that of said hot binding composition added thereto.

8. The method of continuously making a bituminous paving material, which ,consists in causing a substantially continuous stream of mineral aggregate to iow slowly through a predetermined path, andcontinuously impelling astrong current of air from the at` mosphere over and parallel to snaid stream throughout the length of said path, heating said current of air in its flow over the rst portion of said path of'said aggregate and vigorously agitating said aggregate in said lirst portion of said path in said current of hot air to heat and dry said aggregate and separate dust therefrom, reducing the temlao'

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