Abstract:
A method for delivering a pre-weighed package comprising sand, aggregate and dry cement to a mixing site comprises the steps of preparing a first mixture comprising fine aggregate and course aggregate at an offsite plant. The first mixture is placed into a first storage compartment of a hopper and the load of dry cement is placed into a second storage compartment of the hopper. The hopper is transported to the mixing site, where the first mixture and the cement are discharged from the hopper and mixed to form a concrete slurry. The hopper comprises the first storage compartment and the second storage compartment, where there is a water tight dividing means separating the first storage compartment and the second storage compartment. The storage compartments have respective inlets and outlets for receiving and discharging the respective components.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a method and apparatus for delivery of concrete to a job site, and more particularly to a method and apparatus by which the dry components of a concrete mixture are prepared in pre-weighed packages at a cement plant, delivered to the job site in the apparatus, and thereafter the dry components are blended together, mixed with water, and used as needed or desired.  
         [0002]     The logistics of providing concrete for a construction project can be quite complicated. Concrete is a mixture of a “paste” and aggregate, where the aggregate is typically a blend of course aggregate (gravel) and fine aggregate (sand). The paste, composed of portland cement and water, coats the surface of the fine and coarse aggregates. The paste hardens and gains strength to form concrete, a rock-like mass. Concrete therefore has the trait of being plastic and malleable when newly mixed, but strong and durable when hardened. Other additives or “admixes” may be added to provide various properties to the concrete, including water reducer, accelerant, retardant, foaming agents, and other density control additives.  
         [0003]     Soon after the aggregate, water, and the cement are combined together as a slurry, the mixture starts to harden. During the chemical reaction of the cement with the water (i.e., hydration), a node forms on the surface of each cement particle. The node grows and expands until it links up with nodes from other cement particles or adheres to adjacent aggregates. This process results in the progressive stiffening and hardening of the slurry and the gradual development of strength in the slurry. Therefore, once the cement is placed into contact with water through the mixing of the slurry components, the concrete should be placed as desired before the slurry becomes too stiff to be properly placed.  
         [0004]     It is important that the proper ratios of course aggregate, fine aggregate, cement and water be used in preparing the concrete slurry. The concrete slurry must be sufficiently workable for proper placement in the construction application, yet the hardened concrete must possess the required durability and strength for the application. A mixture which does not have sufficient paste to fill the voids between the aggregate components will be difficult to place and will produce rough honey-combed surfaces and porous concrete. However, a mixture with excess paste will be smoother and easier to place, but it is subject to shrinkage and is more expensive. Therefore, the methods of providing concrete to a job site must maintain the proper proportions of each of the components of the concrete.  
         [0005]     There are generally three different known methods for providing concrete to a construction site. In the first method, pre-measured sacks of dry cement and aggregate are delivered to the job site, where the sack is opened and mixed with water to create the concrete slurry. This method has the advantage of allowing the slurry to be mixed shortly before placement, allowing substantial time for placement of the slurry before the concrete begins to stiffen. However, this method has the disadvantage of being costly and labor intensive. Individual sacks of dry concrete are more expensive than concrete purchased in bulk. In addition to the added expense for packaging and handling, the aggregate in sack concrete must have a very low moisture content to prevent the cement from prematurely hydrating within the sack. The sacks are heavy, difficult to handle, and must be individually opened and mixed. A 94 pound sack of dry concrete when mixed with approximately 6 gallons of water yields less than 5 cubic feet of concrete.  
         [0006]     It is to be appreciated that because a common cement truck holds 9.5 cubic yards of concrete slurry (i.e., approximately 256 cubic feet), one would have to mix over 50 individual sacks of cement to equal the volume of slurry delivered by a single cement truck. By way of example, a 4 inch thick 1800 square foot concrete pad requires over 22 cubic yards of concrete, requiring three cement trucks to deliver the concrete slurry. This same job would require mixing and placing approximately 120 sacks of cement. Because of these limitations, the sack method is generally limited to very small jobs.  
         [0007]     The second method of providing concrete to a construction site is perhaps the most commonly used. In this method, concrete slurry comprising aggregate, cement and water is placed into cement trucks at a cement plant, and the trucks thereafter deliver the slurry to the job site. There are several disadvantages of this method. The concrete slurry should be poured within 90 minutes from the time the cement and aggregate are mixed with water. Therefore, the distance of the job site from the cement plant can limit or prevent use of this method. If the truck is delayed by traffic or other reasons and the concrete slurry not placed within the required time window, the concrete slurry cannot be used and it becomes waste material. Not only is the concrete lost, but it must then also be transported to a proper disposal site.  
         [0008]     Typically, it is desired that concrete be delivered to the construction site first thing in the morning. Accordingly, demand for concrete at the cement plant is high in the early morning. A cement plant might have a capacity of loading 15 to 20 trucks per hour. Depending upon the demand, there may be congestion at the cement plant, with a large number of cement trucks idling and waiting for concrete. If a particular construction project has a large demand for concrete, the number of trucks required to deliver concrete can be large, consuming large amounts of fuel, and emitting pollutants.  
         [0009]     The third method of delivering concrete to a construction site is only practical for very large construction projects. This method is to set up a portable plant on the job site, with separate bulk storage for each of the concrete components. The components are thereafter weighed, blended and mixed on the job site as required for the construction. While this method has the advantage of providing concrete on an as-needed basis, it is prohibitively expensive except for large projects.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention is directed to an apparatus and method which meet the needs identified above for delivery of concrete to construction sites. A method for delivering a pre-weighed package comprising sand, aggregate and dry cement to a mixing site is disclosed. One embodiment of the method comprises the steps of preparing a first mixture comprising fine aggregate and course aggregate at an offsite plant. This first mixture is weighed. A load of dry cement is weighed. The first mixture is placed into a first storage compartment of a bulk transport apparatus (i.e. a hopper). The load of dry cement is placed into a second storage compartment of the bulk transport apparatus. The bulk transport apparatus is loaded onto transportation means with lifting means. The bulk transport apparatus is transported by the transportation means to the mixing site, which is at or convenient to the job site. The first mixture is discharged from the first storage means of the bulk transport apparatus into mixing means. Likewise, the dry cement is discharged from the second storage means of the bulk transport apparatus into the mixing means. The first mixture and cement are mixed with water to achieve the desired slurry properties and the concrete slurry is thereafter poured as desired.  
         [0011]     In this method, the bulk transport apparatus comprises the first storage compartment and the second storage compartment, where there is a water tight dividing means separating the first storage compartment and the second storage compartment. The first storage compartment has a first inlet for receiving the first mixture and a first outlet for discharging the first mixture. The second storage compartment has a second inlet for receiving the load of dry cement and a second outlet for discharging the load of dry cement. The bulk transport apparatus further comprises means for attachment of the apparatus to a lifting means.  
         [0012]     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a side view of one embodiment of the bulk transport apparatus.  
         [0014]      FIG. 2  is a front view of the embodiment of the bulk transport apparatus depicted in  FIG. 1 .  
         [0015]      FIG. 3  is a top view of the embodiment of the bulk transport apparatus depicted in  FIG. 1 .  
         [0016]      FIG. 4  is a cross-section taken along line  4 - 4  of  FIG. 2 .  
         [0017]      FIG. 5  shows the bulk transport apparatus loaded on a truck.  
         [0018]      FIG. 6  shows how the bulk transport apparatus may be lifted by a forklift. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0019]     Referring now specifically to the drawings,  FIGS. 1 through 6  show an embodiment  100  of the disclosed apparatus. This embodiment, hereinafter referred to as the hopper, comprises a shell  102  having an outside surface  104 , an inside surface  106 , a top  108  and a bottom  110 . As generally shown in the drawings, the shell  102  may be in the approximate shape of an inverted pyramid having a generally rectangular top  108  and bounded by opposite-facing and matching sides  112 . The sides  112  may taper inwardly as the sides  112  extend toward the bottom  110  as shown in  FIG. 2 . The back  114  of the shell may be substantially vertical as shown in  FIG. 1 , while the front  116  may taper inwardly as the front extends from the top  108  toward the bottom  110 . While many materials may be used for shell  102 , 3/16″ thick mild steel is an appropriate material. The hopper  100  may be constructed to hold different volumes of cement and aggregate, which typically will range from 3 to 5 cubic yards, or roughly a third to one half the volume of the commonly known cement truck.  
         [0020]     The shell  102  may be supported by various support members or structures attached to the outside surface  104  of the shell  102 . For example, as shown in the drawings, the shell may be cradled within support structure  118 . Support structure  118  comprises vertical legs  120  which are attached at the upper end of each vertical leg to cradle support  122 . Cradle support  122  engages and supports shell  102 . Cradle support  122  has openings  124  which are generally oriented outside of and parallel to sides  112 . As shown in  FIG. 6 , openings  124  are of a dimension to receive the forks  126  of a lifting means, such as a forklift  128 . Vertical legs  120  have feet  130  at the lower end of each leg to support the entire hopper  100 . This configuration of the hopper  100  allows the device to be lifted by a forklift  128  onto transportation means, such as a flat bed truck  132 , or alternatively, a railroad flat car or other conveyance for transportation to the desired job site. Alternatively, the hopper  100  may be lifted by a crane or boom, with lifting cables attached to lifting eyes  134 . The lifting eyes  134  may also be used in conjunction with tie-downs to secure the hopper  100  to the flat bed truck  132 .  
         [0021]     The hopper  100  comprises a first storage compartment  136  and a second storage compartment  138 , which are defined by a water tight dividing means, such as dividing wall  140 . The water tight dividing means keeps the fine and course aggregate separated from the cement, which is often necessary because the moisture content of the aggregate may be sufficiently high to initiate the hydration of the cement. The first storage compartment  136  is formed between the inside surface  106  of the shell  102  and dividing wall  140 . A first inlet  142  extends through the top  108  of the shell  102  providing access into the first compartment  136 . A first outlet  144  extending through the shell  102 , provides an outlet at the bottom  110  of the shell for materials stored within the first storage compartment  136 . The second storage compartment  138  is on the opposite side of dividing wall  140  from the first storage compartment  136 . A second inlet  146  extends through the top  108  of the shell  102  providing access into second storage compartment  138 . A second outlet  148  extends through shell  102 , providing an outlet at the bottom  110  of the shell for materials stored within the second storage compartment  138 . First inlet  142  and second inlet  146  may be respectively covered with first removable cover  150  and second removable cover  152 . However, while the drawings show first inlet  142  being covered with first removable cover  150 , it is to be appreciated that first inlet  142  does not necessarily require cover  150  and the first inlet may comprise the rectangular opening of top  108  excluding second inlet  146  and its supporting structure, thereby simplifying the loading of first storage compartment  136 . In this configuration, a cover may be fabricated which simply fits over the first inlet  142 . In common usage, first storage compartment  136  will be used to store a first mixture comprising a blend of fine aggregate and course aggregate. It may be most convenient to load the first storage compartment  136  through a first inlet  142  having a large cross-sectional area.  
         [0022]     For construction purposes, it may be advantageous for either the first storage compartment  136  or the second storage compartment  138  to comprise a vessel enclosed within shell  102 . For example, the drawings generally depict second storage compartment  138  as a vessel  154 . However, it is to be appreciated that the second storage compartment  138  may be formed simply by means of fabricating dividing wall  140  within shell  102 , thereby defining two separate compartments. As generally shown in the drawings, vessel  154  may be generally cylindrical in shape, and may be tapered or finneled at the bottom  156  of the vessel. As shown in the drawings, first outlet  144  and second outlet  148  may coincide, such that one of the outlets is defined by the annulus formed between the shell  102  and the other outlet. For example, as shown in the drawings, first outlet  144  may comprise the annulus between shell  102  and second outlet  148 .  
         [0023]     While first outlet  144  may be simply sealed with a plate, screwable cap or other sealing means, alternatively a first valve means may be used to allow for material to flow from the first storage compartment  136  through the first outlet  144  to the outside of the hopper  100 . For example, as shown in  FIGS. 1 and 2 , first outlet  144  may be closed by gate  158  which may be disposed across first outlet  144  to contain materials within the first storage compartment  136 , and pivotally retracted to allow materials to flow through the first outlet. While gate  158  may be operated manually, alternatively, as further shown in  FIGS. 1 and 2 , a first actuation means  160  may be used in conjunction with gate  158  to open and close the valve. The actuation means is an actuator of the type generally known in the art, which may be activated either pneumatically or hydraulicly. The air or hydraulic power source for the actuation means is of the type generally known in the art.  
         [0024]     Likewise, second outlet  148  may comprise a second valve means to allow material to flow from the second storage compartment  138  through the second outlet  148  to the outside of the hopper  100 .  
         [0025]     For example, as shown schematically in  FIGS. 1 and 2 , second outlet  148  may be closed by butterfly valve  162 , which may be rotated to either an open or closed position. Butterfly valve  162  may used in conjunction with a second actuation means  164  to either open or close the valve. The actuation means is of the type generally known in the art, and may be activated either pneumatically or hydraulicly. The air or hydraulic power source for the actuation means is of the type generally known in the art.  
         [0026]     The hopper  100  may further comprise means for vibrating different components of the apparatus.  FIG. 1  shows vibrating unit  166  attached to vessel  154 , although it should be appreciated that the same vibrating unit could be attached to various portions of shell  102  so as to vibrate the first storage compartment  136  or second storage compartment  138  in order to assist unloading of materials contained within either of the storage compartments. The vibrating unit may be of the pneumatic variety, such as those available from the ARNOLD COMPANY of Trenton, Ill.  
         [0027]     The hopper may also comprise weigh document storage means, such as lock box  168 , which may be attached to either the outside surface of the shell  102  or to the support structure  118 . The purpose of the document storage means is to store weigh documents which are prepared when the apparatus is loaded with the desired cement and aggregate components, where the respective weights of each component are determined at the cement plant and recorded on the documents. These documents thereafter accompany the concrete package contained within the hopper to the job site, where the documents may be referred to for control purposes and for determining the volume of water required for mixing the concrete slurry.  
         [0028]     A method for delivering a pre-weighed package for mixing concrete at a job site is realized using the hopper  100  described above. The pre-weighed package, which is prepared at the cement plant, comprises fine aggregate, course aggregate and dry cement. A first mixture is prepared which comprises a blend of fine aggregate and course aggregate. This first mixture is weighed and placed into one of the storage compartments of the hopper  100 . For purposes of describing the method, it will be assumed that the first mixture is placed within the first storage compartment  136 , although the second storage compartment  138  could also be used for storing the first mixture. A load of dry cement is weighed and placed within the other storage compartment of the hopper  100 , which is assumed, for purposes of this example, to be the second storage compartment  138 . The hopper is loaded onto transportation means, such as a flatbed truck  132 , or a railroad flat car for delivery to the mixing site. A lifting means, such as forklift  128 , is used to lift the hopper  100  onto the transportation means. It is to be appreciated that, depending upon the configuration of the cement plant, that the hopper  100  may be loaded either before or after it is loaded with the first mixture and/or the cement.  
         [0029]     Once loading of the hopper  100  has been completed and weigh documents generated, the hopper is transported to a mixing site, which should be conveniently located to the site where the mixed concrete is required. Mixing means, such a conventional cement mixing trucks or mixers may be used to receive the first mixture and cement from the hopper, which may be lifted by forklift  128  or other lifting means such that the first outlet  144  and second outlet  148  are positioned to discharge the first mixture and cement into the mixing means.  
         [0030]     Various admix may either be blended in with the first mixture at the cement plant when the first mixture is loaded into the hopper. Alternatively, the admix may be added with the mixing water to the first mixture and the cement. The admix may comprise any one or a combination of the following substances: water reducer, water replacer, accelerant, retardant, extender, shrinkage reducer, air entrainer, strengthener, and porosity reducer.  
         [0031]     While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. For example, the size, shape, and/or material of the various components may be changed as desired. Thus the scope of the invention should not be limited by the specific structures disclosed. Instead the true scope of the invention should be determined by the following claims.