US 3767170 A
A concrete mixing truck complying with maximum permissible highway legal load limitations, a trailer towed by the truck, and pneumatic conveyor means to transfer from the trailer to the truck separated, premeasured ingredients for one or more subsequently mixed concrete batches. The trailer may also separately store cement for admixture with the other ingredients of the first batch within the mixing truck when the hauling distance is such that the concrete mixing time specifications would be exceeded if all of the ingredients of the first batch were added to the truck at the concrete plant. When the separately stored ingredients in the trailer are pneumatically conveyed into the mixing truck, the entire void region in the mixer is completely filled with cement blown in under pressure so that the cement is more uniformly dispersed and in a much shorter time than customary with present in-field concrete mixing apparatus.
Claims available in
Description (OCR text may contain errors)
Morgenstern Oct. 23, 1973 METHOD AND APPARATUS FOR MIXING AND TRANSPORTING CONCRETE  Inventor: Harold L. Morgenstern, Missoula,
 Assigneer The First National Bank of Missoula 22 Filed: Apr. 26, 1972 21 Appl. No.: 247,840
Related US. Application Data  Continuation-in-part of Ser. No. 162,947, July 15,
51 Int. Cl. 860p 3/16, B280 5/38, B286 5/42  Field at Search....l 259/148, 161,162, 259/163,'l64, 165, 168, 175, 176, 111,157,
8/1969 Taylor et al.
7 qt Montana, Missoula, Montana.
Primary Examiner-John Petrakes Assistant Examiner-Alan l. Cantor Attorney-George J. Neilan  ABSTRACT A concrete mixing truck complying with maximum permissible highway legal load limitations, a trailer towed by the truck, and pneumatic conveyor means to transfer from the trailer to the truck separated, premeasured ingredients for one or more subsequently mixed concrete batches. The trailer may also separately store cement for admixture with the other ingredients of the first batch within the mixing truck when the hauling distance is such that the concrete mixing time specifications would be exceeded if all of the ingredients of the first batch were added to the truck at the concrete plant. When the separately stored ingredients in the trailer are pneumatically conveyed into the mixing truck, the entire void region in the mixer is completely filled with cement blown in under pressure so that the cement is more uniformly dispersed and in a much shorter time than customary with present infield concrete mixing apparatus.
13 Claims, 5 Drawing Figures pmd Oct. 23, 1973 3 Sheets-Sheet I,
Patunled Oct. 23, 1973 3 Sheets-Shaet 2 Patanted Oct. 23, 1973 3 Sheats-$heet 5 METHOD AND APPARATUS FOR MIXING AND TRANSPORTING CONCRETE CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-impart of my copending application Ser. No. 162,947 filed July 15, 1971.
BACKGROUND OF THE INVENTION This invention relates to improvements in techniques and apparatus for transporting and mixing concrete. More particularly, the invention relates to the use of a concrete mixing truck in combination with one or more towed trailers each capable of carrying all of the ingredients of one or more batches of concrete. The invention is also concerned with adding the various ingredients for a concrete mix, especially cement, to a mixing truck under pneumatic pressure to achieve a very quick, uniform dispersion of the cement particles throughout the particles of the remaining ingredients of the batch whereby a more uniform concrete product is achieved than is presently obtainable by customary infield mixing procedures.
In the ready-mix concrete industry, there are limitations upon the quantity of concrete which may be transferred over public roads and in addition there are Furthermore, there is a limit to which the payload can be increased due to the spacing of the load transfer trailing wheels and the weight laws. Such attachments are commonly used, but in most states and all federal highways there is a maximum legal hauling capacity of 9 cubic yards of concrete for such arrangements. There are many of these devices in use but they are not very satisfactory because of the high initial cost, high maintenance cost, and the unstable attitude of the trailer and load in transit especially over rough terrain which is encountered at most job sites.
It has also been proposed in the prior art to provide oversized mixer trucks with facilities to pull a trailer which is capable of hauling separate portions of the ingredients of a batch of concrete over a roadway without exceeding legal load limits, with the mixer truck having the capacity to mix all of the combined ingredients at the job site where the legal load limits do not apply. In this latter situation, the oversized truck and the trailer must travel partly empty in order to stay within the legal load limits and on the job site only a single batch of concrete can be mixed as contrasted with the present invention where two or three complete batches limitations upon the distance that concrete may be i plant which distance heretofore has been limited by mixing time specifications of the concrete. Overcoming or minimizing the influence of these two limiting factors upon the delivery of concrete will materially. improve the economics of construction due to decreasing labor costs as well as other costs per unit ofmixed concrete.
Truck travel on most of the highways of the United States are governed by laws regulating a maximum legal weight limit according to various formulas which relate weight to wheel spacing and the like. An ordinary concrete mixing truc'k under most weight laws can carry only a predetermined maximum amount of concrete in order to stay within the legal weight limit. In most states and on all federal highways standard mixing trucks range in capacity from 4 to 8 cubic yards of concrete. Also, it is common knowledge that the maximum legal load on federal highways and most state highways for presently operated mixing trucks limits the larger trucksto a payload of 7 cubic yards even though the g'xer may have the capacity of hauling 8 cubic yards.
are mixed in sequence. Therefore, very little gain is obtained by the use of the costly oversized equipment.
Another approach to increasing the payload is to utilize a semi-trailer with the mixer and the power unit for the mixer mounted on the semi-trailer. This provides two additional axles and increases the load capacity up to 12 cubic yards. This arrangement has proven unsatisfactory in commercial use for various reasons including that its size inhibits delivery of the concrete at the job site, and it cannot compete effectively with standard mixing trucks.
It is also known to carry the ingredients for a second batch of concrete in a trailer pulled by the concrete mixing truck which carries the first batch of concrete. This approach has not been commercially adapted. Heretofore it has taken a relatively long time to mix the second batch within the mixing truck after the first batch has been discharged. Furthermore, in some known art structures of this type it has been necessary to elevate the trailer in order to provide a means for transferring the second batch to the mixer.
In variousprior art structures, the devices for hauling the cement, aggregate, water, and other additives of an additional batch generally added so much weight to the hauling unit that the increase in useful payload is not very significant. Also, prior art approaches have required too much time and labor to transfer the second batch to the mixing truck.
In summation, heretofore there has been no successful auxiliary transporting unit to handle one or more complete additional batches of concrete that has proven economical. In addition, there is no known standard mixing truck which in most states and on all federal highways will handle more than seven cubic yards of concrete legally, other than a specially equipped trailer and mixer with an additional axle operated hydraulically which will carry nine cubic yards of concrete on federal highways and in most states.
SUMMARY OF THE INVENTION It is a primary object of the invention to provide a novel method and apparatus for economically achieving larger payloads of concrete mix while complying with present day highway standards, and to overcome transportation distance limitations inherent in concrete mixing time specifications.
The present invention utilizes an essentially standard concrete mixing truck which has been modified to tow one or more trailers each capable of handling one or more complete additional batches of concrete to thereby increase the total useful payload capacity of the unit well beyond that of a standard mixing truck. Each trailer is compartmented so that there are separate compartments containing the exact quantities of cement, aggregate, water and any other desired additives which when mixed together form an additional concrete batch. No field weighing or measuring of the quantities of the ingredients is required.
If the haulage time from the plant to the job site exceeds the time that the ingredients of the first batch may remain together, the trailer has provision to separately store the measured amount of cement required to complete the batch carried by the truck. For example, many projects require that the cement must remain separate from the water and aggregate unless the batch can be discharged within one hour after all the ingredients are mixed together. It has been known to haul the aggregate in the truck and then by techniques such as a cement screw, rubber bags, commonly known as roto-bags, or by merely breaking sacks of cement in the rear of the mixer to add the cement at the job site. These approaches have proven unsatisfactory since it takes considerable mixing to be sure that the cement is uniformly distributed throughout the batch.
It is a significant feature of the present invention that the cement is introduced into the mixing drum pneumatically. The cement so introduced into the mixing truck, whether it be cement to complete the initial batch conveyed with the mixing truck or the cement for an additional batch, is thoroughly and uniformly distributed throughout the entire mixer using air at approximately 7 psig. Since the cement and other ingredients are introduced into the mixing tank in a extremely turbulent condition due to the air velocity and pressure, the cement is thoroughly mixed with the other ingredients within a short period of time, i.e., in the order of several minutes.
An exhaust-powered blower mounted on the exhaust duct of the trucks engine is the source of the pressurized air for the pneumatic conveying means. Since the cement is conveyed pneumatically, the cement compartments may be entirely emptied ensuring that all of the cement is introduced into the mixing drum. This is a distinct improvement over, for example, the use of a screw conveyor since the quantity remaining in the screws is unknown and the cement must be weighed at the discharge end. The invention is also far superior to other approaches such as the use of a conveyor belt or bucket line each of which may lead to the loss of portions of the ingredients while increasing the weight of the unit and thus reducing the payload, etc.
The aggregate may be transported from the trailer to the mixing drum on a conveyor belt, since there is not the same criticality about the exact amount of aggregate as there is with regard to the cement and water which are employed in smaller amounts.
The driver-operator of the truck can readily operate the controls for conveying ingredients from the trailer to the mixing drum without the assistance of additional labor. The additional batches of concrete may be conveyed from the trailer to the mixing truck, and the cement thoroughly mixed with the other ingredients in a very short period of time, for example, in about 10 minutes.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a somewhat schematic side elevational view of a concrete mixing truck and towed trailer in accordance with a presently preferred embodiment of the invention.
FIG. 2 is a plan view of the trailer of FIG. 1.
FIG. 3 is a schematic view of the high volume-low pressure air system employed in carrying out the invention.
FIG. 4 is a schematic view of the high pressure air system utilized in the embodiment of FIG. 1.
FIG. 5 is an elevational view on an enlarged scale of a portion of the apparatus of FIG. 1 illustrating the pneumatic conveying of cement into the trucks mixing drum.
DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings and more particularly to FIG. 1, reference numeral 1 designating a conventional concrete mixing truck of any appropriate size and capacity. The truck has a conventional mixing drum 3, a receiving hopper 4 which feeds materials into the drum, and a suitable discharge means such as a chute (not shown). A standard hydraulic pump 5 is connected to the engine or transmission of the truck and to dual hose connections 6 at the rear of the truck. An exhaust powered blower 7 such as a Schweitzer turboconveyor is mounted on the engine exhaust of the truck and has connecting conduits leading to a hose coupling 8 at the rear of the truck. The purpose of the hose connections 6 and the hose coupling 8 will be described hereinafter. The truck is also equipped with an air brake system, a standard trailer brake hose connection, and a trailer hitch 9 which allows pivotal movement about a vertical pivot.
A trailer generally designated by reference numeral 2 is attached at a pivot 11 to a towing tongue 10. The pivot 11 allows vertical swinging movement of the towing tongue from the operative towing position shown in full lines in FIG. 1 to the detached position shown in dash lines where the towing tongue is detached from hitch 9. The forward axle and wheels of the trailer pivot about a vertical axis for movement in the horizontal plane with the tongue 10, and the rear axles and wheels remain aligned with the trailer frame 12.
As best seen in FIG. 2, three separate air tight cement storage hoppers l3, l4 and 15 are mounted at the front of the trailer. The hopper 13 may carry a premeasured amount of the cement to complete the initial batch in the truck 1 when the truck-trailer combination is used in a long haul situation in which the entire initial batch could not remain that long in the mixer without deleterious results. In situations where the plant is near the job site and the cement may be added to the batch in the truck at the plant, the hopper 13 would be empty. Directly behind the cement storage hoppers are two covered gravel storage bins 16 and 17, which contain measured aggregate for two additional concrete batches. Beneath the lower rear sloping wall of the bin 17 there are three water tanks l8, l9 and 20. The tanks 18 and 19 contain measured amounts of water for use in making the two additional batches of concrete, and the tank 20 contains water to be used as needed at the job site, for example, for cleaning purposes. The water for the initial batch of concrete in drum 3 is added to the drum before the truck leaves the batch plant. If other concrete additives are required, air entraining ad ditives are carried with the aggregate in bins 16 and 17, and accelerating agents and dispersing agents are added to the water, each in measured amounts, based upon the size of the respective batch of which it is a part.
it will be appreciated that the trailer is usually unhitched while a batch of concrete is discharged from the mixing drum at the job site.
Assuming that the drum 3 has been emptied of the first batch of concrete, the truck is backed up to the trailer. Then a second batch of concrete is introduced into the drum 3 employing a belt conveyor 35 to convey aggregate from bin 16 into receiving hopper 4, a water hose 53, and a pneumatic conveyor tube 22 which has a flexible discharge end 48 which is inserted through a tubular sleeve 49 in hopper 4 into the rear of the drum 3 to transport the measured amount of cement in cement hopper 14 to the mixing drum. As will be discussed hereafter, the engine of truck 1 is utilized as the basic power source for conveyor 45 and also for transporting the water and cement to the mixing tank from the trailer. i
FIG. 3 illustrates somewhat diagramatically a high volume, low pressure air system utilized in carrying out the invention. The blower 7 on one side exhausts the engine exhaust gases in duct 60 and on the other side draws in and compresses atmospheric air in duct 62. By way of example only, a suitable air blower is available as the Schwitzer 3TC Turboconveyor Kit from the Schwitzer Division of Wallace-Murray Corp. and specifications are available to select an appropriate size air blower for any diesel engine. It is not intended to limit the invention to the use of any particular blower. ln duct 62 there is a control valve 64, a guage 66, a pressure relief valve 68, and a petcock 70 by which the operator may control the pressure of the air. With valve 64 open, and when it is intended to convey cement from hopper 13 to the mixing drum, valve 72 is opened so that air flows through duct 74 and check valve 76 into the upper region of hopper 13. At the same time, a small amount of air is bled off through conduit 78 and introduced through an air pad 82 to aerate the cement in hopper l3. Discharge valve 80 which may be a flapper valve is opened, and the cement is forced out by the air pressure into a pneumatic conveyor tube 22, which conveys the cement to the mixing drum 3 in order to mix this cement with the other ingredients of the initial batch which have been carried in the mixing drum. A vibrator 30 attached to the bottom of hopper 13 assists in loosening any clogged material and the operator can tell by the sound when the hopper is empty.,
in like fashion, when additional batches of concrete are to be added to the mixing drum, air is introduced into the top of hopper 14 via valve 84 and conduit 86 so that the cement is discharge through discharge valve 88 to the pneumatic conveyor 22. Subsequently, hopper may be discharged by passing air through valve 90, conduit 92 and check valve 76 into the top of hopper 15 to force cement through discharge valve 94 into the pneumatic conveyor tube 22.
Contemporaneously with supplying cement from hopper 14 to the mixing drum, water and aggregate are also introduced into the mixing drum. The water is introduced by bleeding off a portion of the low pressure air through duct 96 and check valve 98 into the top of the water tank 18 to force water out through discharge valve 100 into water supply hose 53 in which there is a control valve 102. Similarly, when preparing a second additional batch of concrete utilizing the cement in hopper 15, a portion of the air is passed through duct 96, duct 104 and valve 106 into the upper region of the water tank 19 so the water is passed out through valve 108 and through the water supply hose 53. In like fashion, the water in tank 20 which is used for cleaning purposes or the like, is emptied from the tank by passing air through ducts 96 and 110 and valve 112 into the upper region of the tank 20 so that water passes through valve 114 from whence it may either flow entirely through the hose 53 or it may be drawn off through petcock 116.
As seen in FIG. 3, provision is made for venting the tops of the hoppers 13, 14 and 15 through vent line 118 and valve 120. Similarly the water tanks may be vented through line 122 and valve 124.
Relief valve 68 maintains the air pressure in range of 7 to 10 psig which is sufficient to move the cement and to force the water to the drum 3 but is not so high as to cause excessive dust or to put a strain on the hoppers or the water tanks. By blowing cement into the mixing drum, the mixing process is accelerated because the entire load of aggregate and water receives the cement uniformly as opposed for example, to the situation in which the cement is merely dumped into the rear of the mixing drum and must be worked forward by rotation of the entire mass within the drum.
FIG. 4 illustrates schematically the use of high pressure air supplied by the air brake system of truck 1 for the purpose of actuating the vibrators on the cement tanks and the gravel bins, and controlling the discharge gates at the bottom of the gravel bin and the water tank discharge valves. An air pressure tank 122 stores 'air at a pressure of about 100 1 10 psi from which high pressure air may be passed through duct 124 to header conduit 126. With regard to the vibrators, one vibrator is associated with each of the three cement tanks, and the two gravel bins. Push valves 128, 130, 132, 134, and 136 respectively regulate the flow of high pressure air to the five vibrators 30 34.
The opening and closing of discharge gates 25 and 26 at the bottom of the gravel bins l6 and 17 is also regulated by the high pressure air system. To regulate gate 25, air is passed through conduit 138, and a valve 140 so that air may be supplied through line 142 to the chamber of pneumatic piston system 144 which is operatively connected at the free end of the piston to gate 25. Line 146 communicating with the chamber on the other side of the piston head and vent 148 at valve 140 are used to exhaust air from the system, and by changing the position of valve 140 may be employed to move the piston in the other direction to close the gate as is well understood in the art. The opening and closing of gate 26 is similarly accomplished and since the mechanisms are substantially the same, the same reference numerals are employed as in the connection with the opening and closings of gate 25.
The means for opening and closing the discharge valves 100, 108, and 114 at the bottom of the water tanks 1%, 19 and 20, are also a series of three substantially identical, pneumatic piston systems for adjusting the valve positions and each include a disc control valve 150 and a pneumatic piston 152.
The belt conveyor 35 which receives aggregate from the gravel bins I6, 17 upon opening of the respective gates 25 or 26, may be driven in any suitable fashion, preferably by a hydraulic motor (not shown) which is connected to the hydraulic pump on the truck 1. This hydraulic system may also be used to actuate a telescoping piston cylinder (not shown) to raise and lower the towing tongue 10.
The operator may control the entire operation of conveying of the materials carried by the trailer to the mixing drum and allied functions from'a control panel where all necessary gauges, guages, control valves, and levers are clear of movinG parts and within easy reach. In addition to the safety features enumerated above, the apparatus may include additional safetY features such as relief valves throughout the system, both automatic and manual, and both the truck and trailer have conventional safety features as prescribed by state and federal safety regulations.
Although the operation of the apparatus is believed obvious from the above description, the following brief summary of the sequence of steps to be followed will be given. In a short haul situation where the critical mixing time for the poured concrete is not a problem, i.e., the cement for the initial batch may be added to the mixing drum at the batch plant; the driver backs truck 1 into a batch plant and all the ingredients for a maximum legal load of concrete are added to the mixing drum 3. The trailer is then hitched to the truck and backed into position so that aggregate bins 16, 17, cement hoppers 14, 15, and water compartments 18, 19 and 20 each may be loaded with their measured respective ingredients for one or two additional concrete batches. The cement hopper 13 remains empty since the cement for the first batch is already in the mixing drum. The driver then drives to the job site and unhitches the trailer. After delivery of the first batch of concrete in the truck, the truck is backed up over the lowered end of tongue as shown in dotted lines in FIG. 1, and the receiving hopper 4 is located under the discharge end 54 of the belt conveyor 35. The flexible discharge end 48 of the pneumatic cement conveyor is then inserted through pipe 49 in hopper 4. The driver then connects the hydraulic hoses on the trailer to the connections 6 at the rear of the truck 1, reconnects the trailer brake hose, and connects the blower 7 to the trailer via blower hose coupling 8 at the rear of the truck. The driver then activates the mixing drum 3, hydraulic pump 5, and the blower 7 and sets the trucks throttle at a suitable setting. Stepping to the control panel on the trailer, the driver checks the various gauges and then opens the main air valve 64 aerating the cement hoppers and pressurizing the water compartments. Then the following four steps are accomplished in sequence.
1. The drive for belt conveyor 35 is activated and set at the desired speed, the discharge gate 25 at the bottom of gravel bin 16 is opened employing the high pressure air system, described above in connection with FIG. 4 so that the gravel is conveyed to the mixing drum 3.
2. Water is transferred from tank 18 to the mixing drum 3 by opening the control valve 150 for the high pressure air which via pneumatic cylinder 152 opens the discharge valve 110 at the bottom of tank 18 and allows the water to be forced through hose 53 into the mixing drum.
3. Air flow through the pneumatic conveyor 22 for the cement is started by opening valve 71, and the cement hopper 14 is now pressurized by opening valve 84.
4. The air flow through valve 71 is adjusted to about 7 psi and upon opening discharge valve 82 the cement is conveyed to the drum 3.
The vibrator associated with hopper 14 is actuated and the operator can tell by sound when hopper 14 is empty. Opening and closing valve 84 after the hopper 14 is believed empty helps move any remaining cement due to the reversals in the air flow.
The air flow through conveyor 22 is continued for a few minutes after all of the ingredients are in the drum 3 in order to insure a complete mixing of the ingredients which results in obtaining a more uniform concrete final product than has been achieved heretofore with in-field mixing techniques.
After the second batch has been discharged from the mixing drum, it will be appreciated that a further batch of concrete may be prepared employing the aggregate in bin 17, the cement in hopper l5 and the water in tank 19 by essentially repeating the sequence of operations referred to above.
In a long haul situation in which the travel time from the cement plant to the job site exceeds mixing time specifications, the procedure is the same as for the short haul situation with the exception that the cement for the first batch of concrete is placed in cement hopper 13 on trailer 2 rather than with the other ingredients for the first batch in the mixing drum. In this case, the cement from hopper 13 is added to the mixing drum upon arrival at the job site via the pneumatic conveyor 22.
By use of the above described apparatus and method, it will be seen that provision has been made to substantially increase the useful payload while complying with the applicable highway standards in a relatively simple and efficient manner.
While a presently preferred embodiment of the invention has been shown and described with particularity, it should be appreciated that various changes and modifications may be resorted to and may readily suggest themselves to those of ordinary skill in the art upon being apprised of the present invention. It is intended to encompass all such changes and modifications as fall within the scope and spirit of the appended claims.
What is claimed is:
l. A method for transporting and mixing concrete comprising introducing into a mixing drum of a concrete mixing truck a first batch of concrete ingredients minus the cement ingredient of the first batch, introducing the cement ingredient of the first batch and ingredients for a second batch of concrete into separate containers on a wheeled trailer adapted to be drawn behind the truck, moving both concrete batches with the truck and trailer to ajob site, conveying the cement ingredient of the first batch from the trailer to the mixing drum, mixing the first batch of concrete and delivering the same at a job site, thereafter conveying all of the separated ingredients for the second batch of the concrete from the trailer to the mixing drum, and mixing and delivering the second batch of concrete at a job site.
2. A method according to claim 1, further comprising pneumatically conveying the cement of both batches to the mixing drum.
3. A method according to claim 2, further comprising introducing low pressure air used to pneumatically convey the cement into the mixing drum to assist in dis persing the cement throughout the other ingredients of the other respective batch in the mixing drum.
4. A method of transporting and mixing concrete comprising loading into separate compartments on a trailer the ingredients for a batch of concrete, towing the trailer behind a concrete mixing truck having a mixing drum to a job site, discharging a first batch of concrete from said mixing drum, conveying the separated ingredients carried on the trailer to the mixing drum to form a second batch of concrete using an air stream to convey the cement ingredient from the trailer to the mixing drum, introducing a low pressure air stream directly into the mixing drum to assist in dispersing the cement throughout the other'ingredients of the batch to facilitate mixing thereof, and delivering the mixed second batch at a job site.
5. A method according to claim 4, further comprising delivering water forming one of the ingredients of the second batch from the trailer to the mixing drum by introducing air pressure into a container containing the water.
6. Apparatus for transporting and mixing concrete comprising a mobile concrete mixer, a wheeled trailer having means for connection to said mixer, at least one aggregate bin on the trailer for storing a measured amount of concrete aggregates, said mixer being adapted to be charged with a first batchof concrete less the cement ingredient of the first batch, at least a pair of cement hoppers on the trailer, each containing a measured quantity of cement for a predetermined concrete batch, and conveyor means on the trailer for conveying from one cement hopper to said mobile concrete mixer the cement ingredient of a first batch, and upon discharge of said first batch, for subsequently conveying the contents of an aggregate bin and of another cement hopper to said mobile concrete mixer for use in preparing a second batch of concrete.
7. Apparatus according to claim 6, wherein said conveying means comprise an inclined endless conveyor element extending forwardly of the trailer and having an elevated discharge end for delivering aggregate from each aggregate bin to said mobile concrete mixer, and
pneumatic conveyor means for delivering cement from said cement hoppers to said mixer.
8. Apparatus according to claim 7, wherein said pneumatic conveyor means is attached to said inclined endless conveyor and is elevatable therewith.
9. Apparatus according to claim 8, further comprising a blower element operatively connected to an exhaust duct for an engine of the mobile concrete mixer to supply pressurized air to said pneumatic conveyor means.
10. Apparatus for transporting and mixing concrete comprising in combination a concrete mixing truck having a mixing drum, and a wheeled trailer having means to connect the trailer to said truck, at least one aggregate bin on the trailer for storing a measured amount of concrete aggregate, at least two cement hoppers on the trailer each adapted to contain a measured quantity of cement, at least one water tank on the trailer for containing a measured amount of water, first conveyor means extending from beneath a discharge opening of each aggregate bin forwardly of the trailer and having an elevated discharge end for delivering aggregate to said mixing drum, pneumatic conveyor means for delivering cement from each cement hopper to said mixing drum, said pneumatic conveying means having a discharge end extending into said mixing drum to supply pressurized air into said mixing drum.
11. Apparatus according to claim 10, further comprising a blower powered by exhaust gases from the engine of said truck to produce low pressure air for use in said pneumatic conveyor means, and means to introduce a portion of said low pressure air into the top of each of said cement bins to force the cement into said pneumatic conveying means.
12. Apparatus according to claim 10, further comprising a discharge gate associated with each aggregate bin, a discharge valve associated with each water tank, and means for supplying high pressure air from the brake system of said truck for use in actuating each discharge gate and each water tank discharge valve.
13. Apparatus according to claim 10, further comprising a pair of aggregate bins positioned adjacent to each other on the trailer, one of said aggregate bins having a sloping rear wall, and a plurality of water tanks positioned adjacent to said sloping rear wall, and wherein said pneumatic conveyor means is attached to said first conveyor means and elevatable therewith.