Abstract:
A concrete batch mixing system and method are disclosed that enable the batch master to measure and control both the water and cementitious ingredient feeds in relation to each other so as to be able to blend the two ingredients in a known, selected, adjustable and repeatable manner, and to agglomerate these ingredients in a counter-rotating twin screw mixing apparatus for use in the preparation of batches of mixed concrete in a concrete batching process.

Description:
BACKGROUND OF THE INVENTION 
   I. Field of the Invention 
   The present invention relates generally to concrete batching operations and, particularly, to advances in equipment, and in a method of processing or batching the ingredients used to produce concrete mixes. Specifically, this invention encompasses a batching operation that includes a pre-mix system which measures and controls both the water and the cementitious material feeds in relation to each other so as to be able to blend these components in a known, selected, adjustable and repeatable manner that optimizes the water/cement ratio and therefore the production and strength of the concrete mixture for each mix design. The pre-mix system further includes a twin screw agglomerator pre-mixing unit for blending or pre-mixing these materials prior to combining them with aggregates in a drum of a transit mixer truck or other final mixing vessel. 
   II. Related Art 
   In a typical concrete batching operation, all the ingredients are pre-measured and then all the ingredients are transferred to a mobile concrete mixing truck for mixing and transport to job sites remote from the sources of the concrete ingredients. In some batching operations, all the ingredients may be transferred to a pre-mixer, which is a permanent part of the batching operation, before being transferred to a mobile concrete mixing truck or other receiving vehicle. 
   Pre-mixing of the water and cementitious materials prior to bringing them together with the aggregates is known to offer several advantages. These advantages include, but are not limited to:
         1. Increased concrete strength results from improved hydration of the cementitious materials.   2. Cost savings result from increased concrete strength when the concrete producer is supplying a strength based concrete.   3. Improved truck utilization is possible due to faster loading of agglomerated mixes into mobile concrete mixer trucks.   4. Better dust suppression is accomplished by elimination of the need to directly feed dry cementitious ingredients into mixer truck drums.   5. Generally cleaner mixer truck drums are seen, both inside and out, thereby simplifying clean out.   6. Material build-up on the back side of the truck mixer fins is reduced.   7. Both truck mixer head packs and cement balling in the load are eliminated.       

   In recent years, attempts have been made to design equipment that would pre-mix the water and cementitious materials as part of the batching process before combining them with the aggregates. Such devices have been only partially successful. 
   One such approach has employed vortex-type mixers. Vortex mixers in some ways resemble home blenders. They include a large open-face pump at the base of each unit and a drain valve at the base of the pump which is situated above a charging hopper of a transit mixing truck as a final mixing vessel. The cementitious materials, water and some of the admixtures are introduced into the top of the vortex mixer. The ingredients are blended and thereafter, the valve at the base of the pump is opened and the mixed materials are transferred to the mixer truck where they are combined with aggregates. However, these units are limited to mix designs where the water/cement ratios are relatively high: 0.38 or greater. This may be higher than allowable for mixes designed to achieve low water/cement ratios. When this occurs, additional dry cementitious material must be added, handled separately from the rest of the cementitious material that is being blended in the vortex mixer, and charged directly into a truck. This is inefficient and may result in dusting problems. 
   Another device that has been used is a mixing tube employing a single screw mixing auger. In the single screw mixing auger, cementitious materials can be delivered to the mixing auger by various known methods. A water injection manifold is used to introduce the liquid materials into the cementitious materials as they are being conveyed through and by the screw auger. This type of pre-mixing device has had limited success due to an inability to overcome a variety of shortcomings which include:
         1. Known units of this type have been unable to measure and control both the water and the cementitious material feeds in relation to each other so as to be able to blend these two in a known, selected, adjustable and repeatable manner.   2. The centrifugal action associated with the use of a single auger throws the materials being mixed outward and thereby forces the materials against and into water spray nozzles used to supply or infuse water into the mix causing them to plug and malfunction.   3. In addition, the action of the centrifugal force throwing the materials to the outside of the mixing tube results in incomplete mixing of the ingredients, as evidenced by the presence of streaks of dry cementitious material in the mix as it is discharged from the mixer.   4. Many single screw units experience a build-up of the mixed materials at the inlet where the cementitious materials and water begin to commingle due to insufficient baffling in this area.   5. Many single screw units also have difficulty mixing when the water/cement ratios are below 0.38.       

   As is the case of the vortex-type mixers, some facilities using these units must also make provisions to handle additional dry cementitious material separately from the pre-mixed cementitious material and supply it directly into a truck or other final mixer vessel. 
   Thus, there remains a definite need in the concrete batching field to provide a concrete batching facility that includes a pre-mix arrangement that provides an accurate system to measure and control both the water and other wetting agents and the cementitious material feeds in relation to each other so as to blend the ingredients in a known, predetermined and repeatable manner over a relative wide range of ratios of water (wetting agent) to dry ingredients. 
   SUMMARY OF THE INVENTION 
   By means of the present invention, there is provided a concrete batching system pre-mix arrangement that includes a controlled ingredient supply aspect to measure and control both wetting agent and cementitious ingredient feeds in relation to each other so as to achieve a blending of these ingredients in a known, predetermined, adjustable and repeatable manner that produces the desired water/cement ratio and therefore optimizes the production and strength of the concrete produced from the mixture for each mix design. 
   The term “cementitious” as used herein is defined to include Portland cement, fly ash and any other dry components, not including aggregate materials (sand and stone). The term “wetting agents” as used herein is defined to include water with or without other additive ingredients. 
   Central to the ingredient supply and pre-mixing systems of the concrete batching system of the invention is an enclosed twin screw pre-mixer agglomerator chamber which is fed the cementitious materials by a cement weigh batcher using a metering screw conveyor device and is fed one or more wetting or agglomerating agents via a liquid metering system which controls both rate and total amount of wetting agent for a batch. The metering system supplies a manifold which is provided with a plurality of spaced spray nozzles situated to infuse the liquid along a portion of the agglomerator mixing chamber. The pre-mixer agglomerator is designed to be charged with dry, cementitious ingredients at an inlet end and to discharge the agglomerated or blended materials at a discharge port during normal operation. 
   Mixing and material conveying in the pre-mixer agglomerator vessel is accomplished by a pair intermeshing, preferably counter-rotating, screw conveyors or augers mounted for rotation in the chamber. The augers are of varying pitch in which threads or flights of relatively fine pitch, which together act as baffles, at an input end control the feed rate to a central mixing section and also prevent material build up in that area. Coarser pitch threads provide a very aggressive and efficient kneading/squeezing mixing action and strongly convey the material through a central mixing section to specially designed discharge scoops or paddles that propel mixed material out through the discharge port or outlet at the bottom of a discharge end which is opposite to the inlet end. For the purposes of this specification, pitch is defined to mean the distance between successive convolutions of the thread of a screw conveyor or auger relative to the diameter of the screw conveyor or auger. The terms “screw conveyor” and “auger” are used interchangeably herein. 
   The supply system and the construction of the pre-mixer agglomerator vessel and the mixing screw conveyors or augers allows any water/cement ratio to be selected and apportioned and mixed in the pre-mixer agglomerator. The pre-mixer agglomerator chamber is provided with a discharge chute designed to discharge mixed material into a collecting hopper which, in turn, leads into the input or charging hopper of a mobile concrete mixing truck or other receiving final mixing vessel located beneath the collecting hopper. 
   The batching system is designed so that the aggregate material (generally sand and stone) is measured and provided separately and fed directly through the collecting hopper to the input hopper of the mobile mixing truck or other final mixing device and is not mixed in the agglomerator. 
   In a preferred embodiment, counter-rotating full auger flights are used in the twin screw compulsory mixer of the agglomerator-mixer and, as previously indicated, they are divided into three distinct sections. The first is an inlet or receiving section that includes a short section of twin shaft counter rotating screw segments of relatively narrow or reduced pitch (such as one-quarter pitch or one-third pitch) which results in relatively small inter-flight or successive convolution gaps to regulate the delivery of cementitious materials from the discharge of a metering screw pre-feeder to the receiving or input section of the pre-mixer agglomerator and eliminate build-up in this area. 
   This is followed by an agglomerating or mixing section which consists of an extended length in which the twin shaft counter rotating agglomerating segments have a pitch greater than that of the inlet section (such as one-half or two-thirds pitch). This insures that the material fed from the inlet section does not completely fill the cavity of the agglomerating section thereby promoting improved mixing. Metered wetting agents are introduced into this section from a pattern of spaced nozzles located in the top of the chamber. The third and final section is a discharge section that consists of a short section of counter-rotating paddles or flat-pitch scoops that serve to eject the blended materials out of the agglomerator. 
   The screw pre-feeder accurately regulates the feed rate of cementitious material to the agglomerator. It is preferably a variable speed feeder which also uses reduced pitch segments (such as one-half or one-third pitch) in conjunction with multiple (double or triple) segments to create a labyrinth that eliminates the tendency of the finely divided fluidized cementitious materials to flow around and through the feeder. If desired, the system may include a by-pass line to enable the direct feed of dry powdered cementitious material through the metering screw and the agglomerator section directly into the collecting hopper to the inlet hopper of a mobile mixing truck or other final mixing vessel. 
   While the preferred arrangement incorporates overlapping counter-rotating twin screws that produce more vigorous kneading/squeezing mixing, a further arrangement in which both overlapping screws rotate in the same direction is also contemplated and can be used if desired. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings wherein like numerals are utilized to depict like parts throughout the same: 
       FIG. 1   a  is a schematic elevational view depicting a typical concrete batching facility utilizing the mixing system of the invention; 
       FIG. 1   b  is a side view of the main cement silo and mixing facility of  FIG. 1   a  with parts removed for clarity; 
       FIG. 2   a  is an enlarged fragmentary schematic elevational view of a portion of the batching facility of  FIGS. 1   a  and  1   b  including the ingredient supply and pre-mixing systems of the invention; 
       FIG. 2   b  is a partial side view of components in  FIG. 2 ; 
       FIG. 3   a  is a schematic top view of one embodiment of a twin-screw agglomerator-mixer in accordance with the invention; 
       FIG. 3   b  is a schematic side elevational view of the agglomerator-mixer of  FIG. 3   a;    
       FIG. 3   c  is a schematic end view of the agglomerator-mixer of  FIGS. 3   a  and  3   b;    
       FIG. 4  is an enlarged representation of one embodiment of a pair of assembled counter-rotating intermeshed mixing screws suitable for use in the agglomerator-mixer of the embodiment of  FIGS. 3   a - 3   c;    
       FIG. 5  is a representation similar to  FIG. 4  featuring a pair of intermeshing mixing screws designed to rotate in the same direction; and 
       FIG. 6  is a control schematic for operating the premixing system of the invention including the ingredient supply aspect. 
   

   DETAILED DESCRIPTION 
   There follows a detailed description of certain embodiments which are presented as examples which capture the essence of the invention but these representations are in no way intended to be limiting with respect to the scope of the invention as it is contemplated that other embodiments using the concept will occur to those skilled in the art. For example, the concept may be used to treat other dry ingredients in other processes having flow and mixing characteristics commensurate with or similar to dry cementitious materials and wetting agents. 
     FIGS. 1   a  and  1   b  are elevational views of a portion of a concrete batching facility, generally represented by  20 , incorporating an agglomerator-mixer system in accordance with the present invention. The batching facility includes a primary Portland cement silo  22 , a second silo  24  which may also contain Portland cement or other finely divided dry cementitious ingredients such as fly ash, which are typically also included in concrete mixes. An aggregate bin as shown at  26  which may have compartments containing sand and coarse stone. 
   Silo  24  is provided with a bottom discharge gate system  28  that is connected through gate valve  30  to a covered conveyor  32  which, in turn, discharges into a covered cement weigh batcher at  34  through a chute  36 . In a similar manner (and as best seen in  FIGS. 2   a  and  2   b ), silo  22  is provided with a discharge valve system  38 ,  39  and chute  40  which also discharge into weigh batcher  34 . Suitable dust filtering equipment is provided for both silos to minimize losses during charging and discharging operations. One such filter venting system is illustrated and described in U.S. Pat. No. 6,638,394, which is incorporated herein by reference to any extent necessary. Such devices are known and have been used in accordance with the charging and discharging dusting materials from storage silos; and this aspect, while important to dust reduction in batch plants, does not form a part of the present invention. Filter venting housings are shown at  48  and  50  in  FIGS. 1   a  and  1   b.    
   The silos  22  and  24  are elevated and suitably supported on heavy steel support structures  42  and  44 . A surge tank  52  is used to supply water to be mixed with the dry ingredients from the silos  22  and  24 , as will be described. A collecting hopper system is shown at  54  which receives aggregates and pre-mixed cementitious material to load into a mobile mixing truck  56  via a charging hopper  58 . 
   The aggregate bin  26  is further divided into sections addressed by mechanized swiveling loading chute  60  as at  62 ,  64  and  66 . Chute  60  is fed normally by conveyor (not shown) which discharges material through a receiving vessel  68  and can be rotated to address any of the sections which may optionally contain sand or different sizes of coarse stone or other aggregates. The bin sections  62 ,  64  and  66  are provided with discharge gates  70 ,  72  and  74 , to discharge the aggregates into a weigh hopper  76  to be discharged through gate  77  on to a loading belt conveyor  78  equipped with belt rollers  80 . Belt conveyor  78  carries and discharges material into the collecting hopper  54  for direct loading into vehicle  56  where final concrete mixing occurs. The aggregate bin is also supported in an elevated disposition by a heavy structural steel support framework  82  which may be fixed to the adjacent support structure  42  to add stability to the system. A facility such as schematically shown in  FIGS. 1   a  and  1   b  may be a permanent facility or one susceptible of being transported to different locations after being collapsed into a plurality of transportable components. 
     FIGS. 2   a  and  2   b  represent enlarged fragmentary schematic views of a portion of the batching facility of  FIGS. 1   a  and  1   b  including the ingredient supply and pre-mixer agglomerator systems of the invention. The system weigh batcher  34  is connected to the input of an enclosed variable speed metering screw or auger feed system or pre-feeder  90  driven by a computer-controlled variable speed motor  92 . Known amounts of material are fed from the cement weigh batcher  34  via connecting tube  94 , suitably valved by gate valve  96 . The metering screw conveyor or pre-feeder  90  regulates the feed rate of dry cementitious ingredients supplied to a twin screw pre-mixer agglomerator  100  driven by a motor  102  suitably coupled in a conventional manner to a gear speed reducer system  106 , as by a belt drive (not shown). Speed reducer  106  is designed to drive a pair of high torque enmeshing screws (known as a twin screw or twin auger system) in a counter rotating fashion at a designated constant speed. The speed reducer  106  is suitably coupled to the twin screws of the pre-mixer agglomerator  100  by a pair of output coupling devices, one of which is shown at  104 . The twin screws are most efficient if designed to operate in a counter-rotating fashion (but may be designed to rotate in the same direction. 
   Pre-feeder  90  further includes a first or normal metered feed or discharge outlet as shown at  108  which may contain an outlet shutoff valve (not shown) and which is connected by flexible conduit or chute  110  to a first inlet  152  in the pre-mixer agglomerator  100  utilized for charging dry ingredients from the metering screw of pre-feeder  90  into the pre-mixer agglomerator  100  to be mixed. This is further known as the inlet or feed end of the pre-mixer agglomerator. A further discharge arrangement  114  is provided in the metering screw  90  positioned directly below the inlet from the cement batcher suitably valved at  116  and which is connected by a flexible conduit  118  with a second or by-pass inlet  156  which is located in the pre-mixer agglomerator  100  at a point directly above discharge port  154  of the pre-mixer agglomerator with chute  157  for mixed ingredients or direct feed so that dry ingredients from the cement batcher  34  alternatively on occasion can be fed directly into the hopper  54  by-passing the metering screw system  90  and the pre-mixer agglomerator  100 . More detailed aspects of the twin shaft counter-rotating agglomerating screw conveyor embodiments are discussed below. 
     FIGS. 3   a - 3   c  depict one embodiment or form of an pre-mixer agglomerator  100  in accordance with the invention which includes a housing, generally at  150 , a first top inlet opening  152  located toward one end of the top of the pre-mixer agglomerator  100  and a discharge opening  154  located on the bottom toward the opposite end of the pre-mixer agglomerator from the inlet opening  152  such that intended mixing takes place therebetween. The by-pass discharge arrangement  114  is aligned with the by-pass inlet opening  156  to allow straight through feed of dry ingredients as discussed above. 
   As will also be discussed with regard to the several example embodiments of twin-screw or twin-auger conveyors, the pre-mixer agglomerator  100  is designed to pre-mix and blend the cementitious ingredients and the liquid ingredients in a known, selected, adjustable and repeatable wetting agent/cement ratio that optimizes the desired production and strength of the concrete of the mixture for each mix design. The pre-mixer agglomerator  100  is characterized functionally by three sections, namely, an inlet metering section  158 , a mixing section  160  and a discharge section  162 . Water or wetting agent infusion nozzle locations are shown at  130  in  FIG. 3   a . They may be conventional spray nozzles (not shown) and are preferably limited to the mixing section, as will be discussed. 
   A pair of generally parallel intermeshing twin screw conveyors  164  and  166  having corresponding steel shafts  168  and  170  are mounted for rotation within the housings  172  and  174  using suitable corresponding bearings  176 ,  178 ,  180  and  182 . Shafts  168  and  170  are coupled to a suitable drive mechanism with intermeshing gears (not shown) so that the intermeshing screw conveyors  164  and  166  coordinate to counter-rotate at the same speed. 
   The water or wetting agent supply system includes four basic components. These include surge tank  52  which preferably is designed to hold enough water to produce a minimum of 1½ batches of concrete or about 300 gallons (1272 liters). A means of refilling the surge tank (not shown) is provided with sufficient capacity to refill the surge tank  52  by the time the next batch is to be started. The system further includes a pump  120  of sufficient capacity to deliver liquid wetting agent (normally water with or without additives) to the agglomerator  100 . A liquid wetting agent flow control valve  122  is provided and is one that is programmable with linear flow characteristics together with a computerized control system ( FIG. 6 ) so that the flow can be controlled as necessary to obtain the correct feed rate to the agglomerator so as to be coordinated with the flow rate of dry ingredients over a range of flow rates. Valves  123  and  125  are also provided in the wetting agent supply system of the agglomerating mixer  100 . Valve  123  is in the line to the spray nozzle system of the pre-mixer agglomerator  100  and valve  125  is a by-pass valve to allow direct infusion of wetting agents into chute  54  by-passing the pre-mixer agglomerator  100 . 
   A water meter  124 , which is provided with both digital and analog outputs, is also provided to measure the wetting agent supplied in two ways. The first output from the water meter is a discrete digital output which preferably produces one electronic impulse per gallon of liquid wetting agent being delivered to the agglomerator. These impulses are counted by a controlling computer or CPU ( 500  in  FIG. 6 ). When the total amount of water required for the batch in process is reached, the flow control valves  122 ,  123  and  125  are closed by the computer ending supply for that batch. The second output is a continuous analog output which is proportional to the rate at which the liquid wetting agent is flowing through the meter  124 . The computer uses this output to control the setting of the water flow control valve  122  in such a manner as to deliver the liquid wetting agent to the pre-mixer agglomerator  100  at the specified ratio to the cementitious materials that are being delivered at the same time to the agglomerator by the screw feeder. 
   Thus, the desired water feed rate can be set in a controlling computer or CPU  500  in proportion to the feed rate that has been set for dry cementitious ingredients being delivered to the agglomerator by the pre-feeder  90 . The computer  500  then uses feedback from the analog output of the water meter to set the position of the water control valve to maintain the water flow called for by the computer in the specified ratio to the cementitious ingredients being delivered to the pre-mixer agglomerator. As indicated above, when the total amount of water necessary to complete the batch has been delivered, the central processor  500  will cause the valve  122  and also valves  123  and  125  to close. The meter  124  is connected to a manifold  126  which is located on the pre-mixer agglomerator  100  and contains an array of spray nozzles or jets as at  130  for adding desired amounts of water to the pre-mixer agglomerator for mixing with the dry cementitious ingredients. 
   The intermeshing, counter-rotating mixing screw conveyors of  FIG. 4  may be designated  240 , and including screw conveyors  200  and  202 , are divided into three basic sections, these include an inlet section  242  characterized by a fine pitch section of the intermeshing screw conveyors in which the distance between intermeshing flights  173  is at a minimum. This is followed by a mixing section  244 . This provides a coarse interpitch section which accomplishes an aggressive kneading/squeezing mixing with the flights  208  intermeshing. This is followed by an outlet/discharge section  246  which employs paddles  248 . 
   With respect to the counter-rotating twin screw conveyors themselves, of course, it is apparent that they can be constructed to enmesh as either top converging or bottom converging combinations. In this regard, the preferred arrangement for optimum mixing in the pre-mixer agglomerator of the present invention involves configuring the twin screw conveyors as an arrangement where the flights rotate to converge together at the top so that material is slung down and away from the water inlet openings and, at the discharge end, toward the outlet. It should be noted, however, that the mixing efficiency itself is essentially equivalent either using a top or bottom converging arrangement. The advantage of the top converging arrangement, as stated, includes both prevention of buildup around the water inlet jets  130  and improved discharge of mixed materials. 
   In addition, as seen in  FIGS. 3   b - 3   c , the sides of the pre-mixer agglomerator housing can be bottom hinged as at  184  and  186  ( FIG. 3   b ) and  188  ( FIG. 3   c ) for easy access to the screw conveyors for cleaning. 
     FIG. 5  is a top view of an intermeshed mixer system  250  twin parallel screw conveyors similar to that of  FIG. 4  but disclosing an arrangement in which both of the screw conveyors  200  rotate in the same direction. Illustrated at right hand, this arrangement utilizes two identically pitched screw conveyors, (i.e., both left hand or right hand). 
   The arrangements in  FIGS. 4 and 5  will both accomplish mixing, however, the mixing that takes place in configuration  4  will be more efficient because in counter-rotating embodiments the ingredients are forced to be combined in a kneading or squeezing action in passing between the parallel intermeshing screw conveyors whereas in the case where the shafts rotate in the same direction, the material is passed between the parallel screw conveyors in opposite directions and is not forced together through the intermeshing flights. 
   Pre-mixer agglomerators in accordance with the invention, generally, are designed to operate at constant speed (although that speed can be varied if desired). The twin shaft rotating screw conveyors are specially designed for blending cementitious or other finely divided dry materials (usually Portland cement and fly ash) with liquid materials (usually water and various chemical additives) to form a pre-mixed material with a water/cement ratio that is generally designed to optimize the production and the strength of concrete produced from the mixture. The pre-mix is later combined with coarse aggregates (usually stone and sand) in the production of Portland cement concrete. 
   According to an aspect of the invention, as indicated in the description of representative types of twin-screw mixers, the agglomerator has been characterized as being generally divided into three distinct sections. These include an inlet section which consists of a short section of twin shaft counter rotating screw feeder segments of relatively fine or reduced pitch (such as from about one-half pitch to about one-fourth pitch) to regulate the delivery of cementitious materials from the discharge of the pre-feeder to the mixing section of the agglomerator. The mixing or agglomerating section consists of an extended section of twin shaft counter rotating agglomerating segments with a pitch greater than that of the inlet section (such as from about one-half pitch to about two-thirds pitch). 
   The pitch of the mixing section is made greater than that of the inlet section to ensure that the material conveyed from the inlet section does not completely fill the cavity of the mixing section. This ensures that there is sufficient empty space in the flights of the mixing or blending section to promote aggressive kneading/squeezing mixing of the cementitious ingredients and the liquids into a pre-programmed blend ratio of fully mixed material. The discharge section includes a short section of twin shaft, preferably counter-rotating scoops or paddles to help eject the blended materials out of the vessel. 
   Wetting agents are preferably not applied in the inlet or outlet sections to avoid undesirable buildup of materials at the inlet end of the conveyors. Clogging and material buildup has long been a problem with single screw systems which continually throw material radially away from the screw in all directions. It should also be noted with regard to single screw systems that mixing is less efficient and streaks of dry cementitious material occur generally throughout the mixture indicating a non-uniformity in combining ingredients. 
   Likewise, according to another aspect of the invention, the metering screw pre-feeder  90  is provided with reduced pitch segments (such as one-half or one-third pitch) in conjunction with multiple (double or triple) segments to create a labyrinth that eliminates the tendency of fluidized cementitious materials to flow around and through the feeder in an uncontrolled manner. This solves previous problems associated with attempts to use a screw pre-feeder to closely meter or regulate the feed rate of cementitious materials to a mixing or blending unit due to the fluidized nature of cementitious materials when flowing from one container such as a weigh hopper to another such as screw feeder making measurement regulation difficult. 
   As indicated, the most preferred arrangement of the design of the agglomerator employs intermeshing counter-rotating screws and imparts a very aggressive kneading/squeezing mixing action and strongly conveys the material through the mixing chamber and out of the outlet. As a result, it is capable of thoroughly mixing and conveying any ratio of water to dry powder materials making it possible to determine and control any selected, and preferably an optimum, water/cement ratio for each mix design and to operate the pre-mixer agglomerator at this ratio. 
   Components for operating the system are shown in  FIG. 6 . The system may be controlled by a central processing unit (CPU) microprocessor  500 . The parameters of the current batch are entered and the CPU is programmed at  502 . After all the ingredients for the present batch have been pre-measured the CPU will activate the agglomerator mixer motor  102  at  510 . The water pump  120  will be activated at  512  and the water control valve  122  will be positioned at  514  to deliver the programmed water feed to the manifold  126 . Thereafter the cement batcher valve  96  is opened at  516  and the metering screw  90  is set at  518  to the speed/feed that has been set in the CPU for that batch. The CPU will continuously monitor the feed rate of the cement by sensing weight change in weigh batcher  34  at  508  and the feed rate of the water at  504  and will adjust the position of the water feed valve  122  at  514  to maintain the water/cement ratio that has been programmed in the CPU for that batch. 
   After all the cementitious ingredients have been emptied from the cement batcher, metering screw and agglomerator the water feed will continue until the total amount of water called for has been delivered, as determined by the digital water input from  506 , at which time the CPU will close the water valves  122 ,  123  and  125  at  514 ,  520  and  522  and turn off the water pump  120  at  512 . This serves to flush the mixing and outlet sections of the agglomerator and to clean the spray nozzles. Control lines for water valves  123  and  125 , which may be solenoids, are shown at  520  and  522 . 
   In addition, if desired, the agglomerator can be by-passed with material directed from the weigh batcher through the screw-metering device into the inlet hopper of a mobile cement mixer directly through a connecting tube (not shown) by by-passing the metering device through a by-pass gate  116  through the outlet section of the agglomerator and directly into the collecting hopper  54  and into the inlet hopper  58  of a transit mixer truck. Valve  125 , of course, can be used for direct injection of wetting agents. 
   The pre-mixer agglomerator augers or screw conveyors themselves may be constructed of any suitable materials including metals and non-metals and combinations thereof. Thus, the screw flights may be steel, steel coated with a polyamide material such as a nylon material or a polyurethane material or the like. They may be molded to the shafts using a relatively stiff composite elastomer material. It is desired that the flights resist abrasive wear and remain easily cleaned. 
   This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.