Patent Publication Number: US-2005122833-A1

Title: Process and equipment for producing concrete products having blended colors

Description:
FIELD OF THE INVENTION  
      The invention relates generally to the production of concrete products. More specifically, the invention relates to a production process in which one or more liquid pigments are blended into concrete so that the final product is not a uniform color, but has a variegated appearance that might be described as swirled, folded, or mottled. Most specifically, the invention relates to the production of such concrete products in a dry cast process. Concrete products to which the invention can be applied include, but are not limited to, architectural concrete blocks, concrete bricks, and concrete blocks that are suitable for use in landscaping applications, such as retaining wall blocks, pavers, and slabs.  
     BACKGROUND OF THE INVENTION  
      Concrete products can be produced without any coloring agents, in which case the resulting product will have a color dictated by the native colors of the raw materials, typically cement and aggregate, that have been used. The result is typically a shade of gray. It is possible to alter this gray color by introducing a coloring agent into the mixture. The coloring agent is typically a pigment, or a mixture of pigments, that will impart the desired color to the finished product.  
      There are a variety of known processes for making concrete products. In a wet cast system, a concrete mixture that contains sufficient water so that it flows readily is introduced into a closed mold. The mixture is allowed to harden in the mold, and the molded product is then stripped from the mold. In a dry cast system, a much drier concrete mixture is introduced into a mold. The concrete mixture is densified in the mold, and then removed from the mold before it has hardened. Because the concrete mixture is of a “low slump” or “no slump” nature, the molded product, if carefully handled, will retain its molded shape while it is transported to a curing area, where it will cure over a period of hours. This dry cast process is suitable for highly automated, mass production of a number of types of concrete products, including architectural concrete blocks, segmental retaining wall units, concrete bricks, slabs, and interlocking concrete pavers.  
      In recent years, it has become desirable to produce some of these products with variegated colors, rather than with uniform colors. The variegated color products will have two or more distinct colors visible in the finished product, with the colors folded, or swirled, or mottled in some fashion. This is a popular look in landscape products in particular, where the appearance of naturally-occurring, variegated colored stone is being sought. In this specification, the term “color blended” will be used to refer to such a variegated color appearance.  
      An example of a known dry cast concrete product production system  5  is illustrated in  FIG. 1 . The system  5  includes a mixer  6  in which a batch of the low slump concrete is mixed from known components. After mixing, the batch of uncured concrete is transported by a conveyor  7  to a surge hopper  8 , with the concrete being deposited into the hopper  8 . Uncured concrete is then metered from the hopper  8  onto a metering belt  9  which transports the metered amount of concrete to a production machine  10  which forms a plurality of concrete products from the concrete.  
      The production machine  10  includes a hopper  15  that receives the concrete from the metering belt  9 . The production machine  10 , as would be understood by a person having ordinary skill in the art, includes molds that are open at the top and bottom. A pallet is positioned below each mold to close the bottom of the mold, and the uncured concrete is delivered from the hopper  15  into each mold through the open top of the mold via one or more feed drawers. The uncured concrete is then densified and compacted by a combination of vibration and pressure. The mold is then stripped by a relative vertical movement of the mold and the pallet to remove the uncured concrete product from the mold. The uncured product is then transported to a location where it is cured. The production machinery needed to construct a system of this type is available from Besser Company of Alpena, Mich., as well as from a number of other sources, including Columbia Machine Company, Tiger Machine Company, Masa, Omag, Rikers, Hess, KVM, Zenith, and others. Batching and mixing equipment is available from a number of sources well known in the industry. Color pigments are available from a number of sources, including Bayer, Davis Color, and Hamburger Color Company.  
      Returning to  FIG. 1 , color blending has previously been achieved by preparing a batch of concrete of a first color and depositing a first colored concrete layer  11  in the hopper  8 , preparing a batch of concrete of a second color and depositing a second colored concrete layer  12  in hopper  8  on top of the first layer of concrete  11 , and, if a third color is desired, preparing a batch of concrete of a third color and depositing a third colored concrete layer  13  in hopper  8  on top of the second layer  12 . For example, the first layer  11  can be black concrete, the second layer  12  can be brown concrete, and the third layer  13  can be gray concrete. Blending of the three colors occurs within the hopper  8 , as the concrete is metered from the hopper  8  onto the metering belt  9 , on the metering belt  9  itself, and within the production machine  10  prior to being introduced into the molds.  
      A difficulty with this previous blending process is that the blending of the different colors, and the resulting color blended look of the concrete product, are not controllable. The initial amount of concrete that is metered from the hopper  8  onto the belt  9  is mostly a single color from the layer  11 . Therefore, concrete products made from the initial amount of concrete will have little or no color blending, and as a result, will have an appearance that is significantly different from concrete products that are formed from later metered amounts of concrete. These initial products are often discarded due to insufficient blending. In addition, the final amount of concrete from the hopper  8  is often primarily a single color from the layer  13 , so that products made from this final amount are also frequently discarded.  
      Further, the color blending that does occur in the hopper  8  and downstream from the hopper is random, as is the amount of each color contained in the concrete that is metered from the hopper  8  onto the belt  9 . Therefore, products produced from one metered amount of concrete may have one look, while products produced from another metered amount of concrete may have an entirely different look. This can be a problem when it is desired to achieve a somewhat consistent color blended appearance.  
      In addition, the design of the hopper  8  is such that the entire amount of concrete must be used up before new color layers  11 - 13  can be introduced. Therefore, if the decision is made to change the blended look of the products while concrete remains in the hopper  8 , it is generally necessary to use up the remaining concrete in the hopper, or discard the remaining concrete entirely. The need to use up all of the concrete in the hopper  8  also slows down production, since the mixer  6  must then form each new colored batch for introduction into the hopper  8 . While the hopper is being refilled, the production machine  10  may be standing idle waiting for filling to be complete and for new concrete to be metered from the hopper.  
      Moreover, due to the relatively long time the colors are in contact with each other, the colors can bleed together and produce areas on the resulting products having a color that is a mixture of two or more colors. This bleeding of colors can detract from the appearance of the product, by blurring the colors at the junctures between colors, which blurs the separation between colors in the resulting product.  
      Accordingly, there is a need for an improved process and equipment for producing color blended concrete products, in which there is more control of the resulting color blended appearance of the products, so that the appearance is generally repeatable, and at the same time reducing the amount of waste and reducing production down time.  
     SUMMARY OF THE INVENTION  
      The invention relates to a process and equipment for high speed, mass production of concrete products formed from concrete having one or more colors blended into the concrete. The concrete is preferably a multi-color blend that results in multi-colored concrete products. Preferably, the invention is used to produce concrete products that are suitable for use in landscaping applications, such as retaining wall blocks. The invention can also be used to produce color blended pavers, slabs, and bricks. The visible surfaces of a concrete product resulting from the multi-color blend have a variegated appearance which is generally repeatable, and which, in the case of landscape products, may simulate natural stone or rock.  
      With the present invention, the amount of each pigment added to the concrete to produce the multi-color blend is precisely controllable. As a result, a more consistent multi-color blend in the concrete can be achieved, so that the color blended appearance of the concrete products is more consistent and repeatable, and the production of one-color, or otherwise insufficiently color blended products, is reduced. The need to discard product due to insufficient color blending is therefore reduced. Further, the colors that are used in the multi-color blend can easily be changed, so that the resulting appearance of the visible surfaces of the concrete products can be readily altered.  
      In a preferred embodiment, liquid pigment is applied to concrete that is discharged from a hopper. Two or more different pigment colors are preferably applied onto the concrete by a spraying mechanism. The concrete then proceeds to a blending mechanism which blends the applied pigments into the concrete, resulting in a multi-color concrete blend. The concrete blend is then deposited into a hopper of a production machine, which forms one or more multi-color concrete products from the multi-color concrete blend.  
      The spraying mechanism preferably includes spray nozzles that are adjustable vertically in a direction toward and away from the concrete, as well as horizontally in a direction transverse to the direction of conveyance of the concrete. The spray pressure of the spray nozzles can also be adjusted. In addition, the blending mechanism preferably includes a pair of rotatable stirring mechanisms that have adjustable rotation speeds, and which are adjustable vertically in a direction toward and away from the concrete, as well as horizontally in a direction transverse to the direction of conveyance.  
      The settings of the nozzles, i.e. the positions of the nozzles relative to the concrete, and the spray pressure, and the settings of the stirring mechanisms, i.e. the positions of the stirring mechanisms relative to the concrete, and the rotation speeds, impact the blending of the pigments into the concrete. Changing any one of the settings changes the blending that occurs. However, once a desirable color blended appearance in a product has been achieved, the color blended appearance can be repeated by retaining the settings of the nozzles and the stirring mechanisms. Thus, a consistent multi-color appearance of the product can be achieved.  
      The process and equipment of the invention results in a reduction of concrete waste by eliminating the need to discard concrete from the hopper when a change in the multi-color appearance of the products is desired. The invention further results in a reduction in production stoppages, as the hopper can be filled with additional concrete as it runs low on concrete. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The patent or application file contains at least one drawing or photograph executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the United States Patent and Trademark Office upon request and payment of the necessary fee.  
       FIG. 1  is a schematic depiction of a known dry cast concrete product production system.  
       FIG. 2  is a schematic depiction of a dry cast concrete product production system according to the present invention.  
       FIG. 3  is a perspective view of the liquid pigment spray mechanism and the blending mechanism positioned relative to the concrete conveyor in the production system.  
       FIG. 4  is an elevated perspective view illustrating the liquid pigment spray mechanism and the blending mechanism position relative to the conveyor, viewed from the end of the conveyor.  
       FIG. 5  is a color photograph of a plurality of concrete blocks produced according to the invention and stacked into courses to form a wall. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Overview  
      The present invention provides a process for producing multi-color blended concrete products, as well as to a system and equipment utilized in implementing the process. As used in this specification, the term “concrete products” includes architectural concrete blocks that are assembled with mortar to build external walls, concrete bricks, modular concrete products that are suitable for use in landscaping applications, such as retaining wall blocks, concrete pavers, concrete slabs, and other concrete products.  
      The preferred application of the process, system and equipment is in the dry cast production of blocks that are used in landscaping applications, particularly retaining wall blocks that are designed to be stacked on top of one another in multiple courses to form a retaining wall, without the use of mortar.  
       FIG. 2  illustrates a dry cast production system  20  according to the present invention. The system  20  includes a hopper  22 , which comprises a mixer that mixes batches of concrete. The components used to form the concrete, and the ratios of the components, may vary depending upon the particular application, and the particular mix designs are within the ordinary skill in the art. The components are typically aggregates such as sand and gravel, cement and approximately 5% by weight of water. Other components, depending upon the application, may include pumice, quartzite, taconite, and other natural or man-made fillers, and chemicals to improve such properties as water resistance, cure strength, and the like. The concrete mixed in the mixer  22  may also contain color pigment(s) to color the concrete to a base color. The ratios of various ingredients and the types of materials can be selected within the skill of the art and are often chosen based on local availability of raw materials, technical requirements of the end products, and the type of production machine being used. The mixer itself may be of any known type presently used in the industry, including pan-type mixers and ribbon-type mixers. In a currently preferred embodiment, the mixer is of the pan-type.  
      After the concrete is mixed, the concrete batch is transported from the mixer  22  by an infeed conveyor  24  to a surge hopper  26  which holds the concrete. The surge hopper  26 , which is of conventional construction, includes a plurality of sidewalls and a bottom wall defining an interior volume. A discharge opening is formed adjacent the bottom of the hopper  26 , through which concrete is to be discharged from the hopper. The discharge opening is controlled by a gate. The gate controls or meters concrete from the hopper through the discharge opening and onto a conveyor  28  which preferably comprises a metering belt. The conveyor  28  then carries the concrete from the hopper  26  to a production machine  30  which includes a hopper  32  into which the concrete is deposited. The production machine  30  then forms a plurality of blocks from the concrete.  
      As shown schematically in  FIG. 2 , a liquid pigment spray mechanism  40  is positioned between the surge hopper  26  and the hopper  32 . The spray mechanism  40  is designed to apply one or more liquid pigments to the concrete on the conveyor  28  as the concrete is being transported by the conveyor  28  to the production machine  30 . In the preferred embodiment, the spray mechanism  40  applies two or more differently colored liquid pigments to the concrete. The description hereinafter will discuss the application of two differently colored pigments to the concrete. However, a single liquid pigment color or more than two could be applied to the concrete, if desired.  
       FIG. 2  also schematically illustrates a blending mechanism  42  positioned between the spray mechanism  40  and the hopper  32  of the production machine  30 . After the liquid pigments are applied to the concrete, the conveyor  28  delivers the concrete to the blending mechanism  42  which blends the liquid pigments into the concrete to produce a multi-color concrete blend. The concrete blend is then deposited into the hopper  32  of the production machine  30 . One or more multi-color blocks are then produced from the multi-color blend.  
      With reference to  FIG. 3 , the spray mechanism  40  comprises a support bar  44  that extends between, and is connected to, a pair of longitudinal frame elements  46 ,  48 . The frame elements  46 ,  48 , together with transverse frame element  50  at the end of the frame elements  46 ,  48 , form a portion of a frame  52  that is mounted in relation to the conveyor  28  so as to support the spray mechanism  40  and the blending mechanism  42 .  
      A pair of spray nozzles  54 ,  56  are mounted at spaced locations on the support bar  44 . Each color to be added to the concrete requires a separate spray nozzle. Therefore, for two pigment colors, at least two spray nozzles  54 ,  56  are used; for three pigment colors, at least three spray nozzles would be used; etc. There could also be more than one spray nozzle for each pigment color.  
      The spray nozzles  54 ,  56  point downward toward the conveyor  28  for spraying liquid pigments onto the concrete that is discharged from the hopper  26  onto the conveyor. The pigments are preferably sprayed onto portions of the upper surface of the concrete on the conveyor  28  as the concrete is transported by the conveyor toward the production machine  30 . Because the nozzles  54 ,  56  are spaced apart from each other, the respective pigment colors from each nozzle will be applied to different portions of the concrete.  
      The spraying of pigment onto the concrete can be continuous, so that the pigment is applied to the upper surface of the entire concrete portion. Alternatively, spraying can be intermittent, in which case pigment will be applied to spaced portions of the upper surface of the concrete. In addition, the spray nozzles  54 ,  56  can operate simultaneously, in which case different colors are applied simultaneously, or in alternating fashion, in which case a first pigment color is applied, then a second pigment color is applied, then the first pigment color is again applied, etc. Numerous sequences of pigment application are possible within the scope of the invention. The specific spraying sequence chosen will impact the resulting concrete color blend and the concrete products produced therefrom. In the preferred embodiment, the spraying is continuous, and the spray nozzles are operated simultaneously.  
      Each spray nozzle  54 ,  56  is connected to a source of liquid pigment  58 ,  60  by flow lines  62 ,  64 . In the preferred embodiment, the pigment is SPR 9000 series color available from Hamburger Color Company of King of Prussia, Pa. Included in each flow line  62 ,  64  is a pump  66  that pumps liquid pigment from the source  58 ,  60  to the spray nozzles  54 ,  56 . The pump  66  is preferably an air driven pump with a regulator to allow adjustment of the delivery pressure of the pigment. It is believed that the delivery pressure of the pigment impacts the blending of the concrete and the resulting appearance of the concrete products. Delivery pressures of between about 40 psi and about 100 psi have been tested successfully. However, other delivery pressures could be used, depending upon the desired product appearance. The ratio of the amount of pigment to the amount of concrete to which it is applied, i.e. the color loading, is between about 1% to about 10%. For example, about 37.5 lbs. of pigment added to about 1250 lbs of concrete, providing a color loading of about 3%, has achieved satisfactory results.  
      A valve  68  in each flow line  62 ,  64  controls the flow of pigment to the spray nozzles  54 ,  56 . The valves  68  are controlled in a known manner to result in the continuous, intermittent, simultaneous, and/or alternating application of pigment discussed above.  
      Each spray nozzle  54 ,  56  is also mounted so as to be adjustable along the length of the support bar  44 . This allows adjustment of the spray nozzles  54 ,  56  in a direction transverse to the transport direction of the conveyor  28 , which results in a change in the locations on the surface of the metered concrete where the pigments are applied. The spray nozzles  54 ,  56  are also preferably mounted so as to be adjustable toward and away from the conveyor  28 . It is believed that the position of the spray nozzles  54 ,  56  relative to the concrete, both horizontally and vertically, also impacts the blending of the concrete and the resulting appearance of the concrete products.  
      After the metered concrete is transported by the conveyor  28  under the spray mechanism  40 , the concrete enters the blending mechanism  42  which blends the pigments into the concrete. The blending mechanism  42 , as best shown in  FIGS. 3 and 4 , comprises at least one, and preferably two, stirring mechanisms  80 . The stirring mechanisms  80  are illustrated as being generally in-line with each other. The stirring mechanisms  80  are identical, except for the preferred direction of rotation of each, as will be discussed below. Therefore, only one stirring mechanism will be described in detail, it being understood that the other stirring mechanism is the same.  
      With reference to  FIGS. 3 and 4 , the stirring mechanism  80  comprises a stir paddle  82  connected to a shaft  84  which is in driving engagement with a variable speed drive motor  86 . The drive motor  86  is preferably a hydraulic motor. A valve is used to control fluid flow to the hydraulic motor, thereby controlling the rotation speed of the stir paddle. A color coded flow control valve, model EF30S Easy Read available from Deltrol Corporation, can be used. However, other variable speed drive motor types could be used, including an electric motor. The drive motor  86  is designed to rotate the paddle  82  as the concrete is transported by the conveyor  28 . As the concrete approaches each stirring mechanism  80 , the concrete is stirred by the paddle  82 , which blends or stirs the pigments into the concrete. The paddle  82 , which is adjustable vertically relative to the conveyor  28  as discussed below, is positioned such that it is able to contact the concrete during rotation.  
      The stir mechanism  80  is mounted above the conveyor  28  on a transverse support bar  88  that extends between, and is attached to, the frame elements  46 ,  48 . In addition, a vertical support element  90  is supported on, and extends upwardly from, the support bar  88 , and a support block  92 , disposed between the drive motor  86  and the shaft  84 , is mounted to the support element  90 .  
      As shown in  FIG. 3 , the support bar  88  includes an elongated adjustment slot  94  that extends transverse to the direction of the conveyor  28 . The slot  94  permits adjustment of the support element  90 , and thus adjustment of the stirring mechanism  80 , in a horizontal or transverse direction relative to the conveyor  28 . In addition, the support element  90  includes an elongated adjustment slot  96  that extends vertically relative to the conveyor  28 . The slot  96  permits adjustment of the support block  92 , and thus adjustment of the stirring mechanism  80 , in a vertical direction relative to the conveyor  28 .  
      Both the vertical and horizontal positions of the stirring mechanism  80  are believed to have an impact on the blending of the pigments into the concrete. By adjusting the horizontal and vertical positions of the stirring mechanism  80 , the location of the stirring mechanism relative to the concrete is altered, which alters the resulting blending of the pigment into the concrete and the resulting appearance of the blocks. The particular vertical and horizontal positions chosen will be dependent upon the desired appearance of the blocks.  
      The speed of rotation of the paddle  82  also impacts the blending that occurs. The use of a variable speed motor  86  permits the speed of rotation to be changed, thereby changing the blending that results. Thus, the rotation speed can be selected based upon the desired appearance of the blocks.  
      Returning now to  FIGS. 3 and 4 , the paddle  82  comprises a rigid bar  98  that is connected to the drive shaft  84  and which extends substantially the entire length of the paddle  82 . Rubber plates  100 ,  102  are fixed to the bar  98  and extend a distance below the bar  98  to form a generally continuous rubber plate extending beneath the bar  98 . The rubber that is used to form the plates  100 ,  102  is preferably rigid enough to enable the paddle  82  to stir concrete when rotated, yet soft enough to prevent damage to the conveyor  28  in the event the paddle  82  comes into contact with the conveyor.  
      The length of the paddle  82  is preferably sufficient to allow the paddle to extend across almost the entire width of the conveyor  28 , yet allow room for horizontal adjustment of the stirring mechanism. For example, on a conveyor that is about 14.0 inches wide, a paddle length of about 12.0 inches, has been tested successfully. Because of the length of the paddle, almost the entire width of the concrete on the conveyor  28  is impacted by the rotation of the paddle.  
      The preferred embodiment of the blending mechanism  42  has been described as utilizing a pair of stirring mechanisms  80 . However, other blending mechanisms could be used to blend the pigments into the concrete.  
      To maintain the concrete on the conveyor  28  as the stirring mechanism  80  stirs the concrete, the frame  52  is provided with skirt elements  104  that project downwardly from the frame elements  46 ,  48 . When the frame  52  is mounted in position, the bottom edges of the skirt elements  104  are positioned closely adjacent the top surface of the conveyor  28 , as illustrated in  FIG. 3 , in order to maintain concrete on the conveyor as the concrete proceeds through the stirring mechanisms. A bottom edge portion  106  of each skirt element  104  is formed of rubber to prevent damage to the conveyor  28  in the event the skirt elements come into contact with the conveyor.  
      As discussed above, the stirring mechanisms  80  are identical, except for their preferred direction of rotation. The direction of rotation also impacts the blending of the pigment into the concrete. The stirring mechanisms  80  preferably rotate in opposite directions, as shown by the arrows in  FIG. 3 . However, a different multi-color appearance on a resulting product can be achieved by rotating the stirring mechanisms  80  in the same direction. Further, the direction of rotation of the stirring mechanisms could be periodically reversed.  
      After the concrete is conveyed through the blending mechanism  42 , a gap  108  between the end of the conveyor  28  and the frame element  50  permits the multi-color concrete blend to be deposited into the hopper  32  of the production machine  30 .  
      A preferred sequence of preparing a multi-color concrete blend for use by the production machine  30  will now be described. This sequence assumes that there is a sufficient amount of concrete in the hopper  26  to be discharged to the hopper  32 . The hopper  32  contains a probe which senses when the production machine  30  is running low on concrete and can accept additional concrete. When the concrete in the hopper  32  is low, the probe sends a signal to the hopper  26 . The conveyor  28  is then started and the hopper  26  starts discharging concrete onto the conveyor. Spraying of the pigments commences as soon as the conveyor starts, and spraying continues as long as the conveyor is operating.  
      Once the hopper  26  has discharged enough concrete to refill the hopper  32 , the hopper gate is closed, thereby preventing further concrete discharge, and the conveyor is stopped. Spraying ends as soon as the conveyor stops. If desired, the starting and stopping of spraying can operate on time delays, based upon the opening and closing of the hopper gate, and the speed of the conveyor  28 . Alternatively, a sensor can be provided adjacent the spraying mechanism  40  for sensing the leading and trailing ends of the metered concrete portion, thereby controlling operation of the spray mechanism.  
      Therefore, the concrete in the hopper  26  can be continuously replenished as needed, without having to stop production to fill the hopper  26 . Further, when a decision is made to change the multi-color blended appearance of the blocks, this can be accomplished without having to empty the hopper  26 .  
      After the pigments are applied to the concrete, the concrete proceeds through the two stirring mechanisms  80  which blend the pigments into the concrete. After blending, the multi-color concrete blend is then deposited into the hopper  32 .  
      The multi-color concrete blend in the hopper  32  is used to produce one or more blocks in the production machine  30 . To produce blocks, a pallet is positioned below a retaining wall block mold, having an open top and bottom, in the production machine  30  to close the open bottom of the mold. The mold cavity can be designed to produce a workpiece that comprises a pair of blocks molded in face to face arrangement, with the workpiece being split after it is cured along the line of intersection of the faces to produce two blocks.  
      The multi-color blended concrete is delivered from the hopper  32  into the mold through the open top of the mold via one or more feed drawers. The concrete is then densified and compacted by a combination of vibration and pressure. The mold is then stripped by a relative vertical movement of the mold and the pallet to remove the uncured workpiece from the mold. A discussion of a retaining wall block mold that can be used with the present invention, along with a discussion of the block molding process, can be found in U.S. Pat. No. 5,827,015, which is incorporated herein by reference.  
      The uncured workpiece is then transported away to be cured, after which the workpiece is split in known manner to produce two blocks. Splitting mechanisms are known in the art. An example of a splitting mechanism that could be used with the invention includes U.S. Pat. No. 6,321,740, which is incorporated herein by reference.  
       FIG. 5  is a color photograph of a portion of a wall  150  that is constructed from a plurality of multi-color concrete blocks  152  produced using the process and equipment of the present invention. Each block  152  includes a split front face that results from a splitting operation that occurs on a workpiece that comprises two of the blocks formed face to face as discussed above.  
      The blocks  152  illustrated in  FIG. 5  were produced from a multi-color blended concrete comprising white colored base concrete to which was added red and black pigments. The following settings were used: 
          1) for the stirring mechanism  80  closest to the hopper  26 , the motor  86  was driven at about 8 rpm on the blue setting of the Deltrol Corp. EF30S Easy Read color coded flow control valve, the paddle was rotated in a counterclockwise direction, and the stirring mechanism was shifted in the slot  94  as far to the right as possible when viewing  FIG. 4 ;     2) for the stirring mechanism  80  closest to the hopper  32 , the motor  86  was driven at about 102 rpm on the purple setting of the Deltrol Corp. EF30S Easy Read color coded flow control valve, the paddle was rotated in a clockwise direction, and the stirring mechanism was shifted in the slot  94  as far to the left as possible when viewing  FIG. 4 ;     3) for each stirring mechanism, the paddle was positioned so that its bottom edge was positioned closely adjacent the surface of the conveyor  28 ; and     4) the black pigment was sprayed onto the concrete at a pressure of 60 psi, and the red pigment was sprayed onto the concrete at a pressure of 40 psi.        

      The motor speeds were obtained at a hydraulic pressure of 400 psi using a vicker&#39;s piston pump with an adjustabe compensator.  
      By keeping the same nozzle and stirring mechanism settings, the blending of the pigments into the concrete can be consistently repeated, and a consistent appearance of the blocks can be achieved. If a different appearance is desired, one or more of the settings can be changed, thereby changing the blending that occurs, and changing the resulting appearance of the multi-color block.  
      The shape of the block  152  can take many forms, depending upon the intended end use of the block. For example, the block  152  can include converging side walls, and an integral locator/shear flange(s) formed on the top and/or bottom face of the block. U.S. Pat. No. 5,827,015 discloses examples of blocks that could be formed utilizing the process and equipment of the present invention.  
      In the preferred embodiment, the system  20  includes a mixer that prepares concrete that is deposited into the hopper  26 , with the concrete then being fed into the hopper  32  of the production machine  30 . However, other configurations of the system are possible. For example, the infeed conveyor  24  from the mixer could deposit mixed concrete directly into the hopper of the production machine. In this case, the surge hopper  26  would not be used and the mixer would function as the surge hopper. In such a system, a spray mechanism  40 ′ and a blending mechanism  42 ′, similar to the spray mechanism  40  and the blending mechanism  42 , would be positioned above the conveyor  24 , as shown in dashed lines in  FIG. 2 , and the conveyor  24  would discharge into the hopper of the production machine.  
      The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.