Patent Publication Number: US-10760267-B2

Title: Method and mold for manufacturing an interlocking concrete retaining wall block

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 14/704,621, filed May 5, 2015, the contents of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to prefabricated interlocking concrete blocks. In particular, this invention relates to a mold and method for manufacturing prefabricated interlocking dry-cast concrete blocks. 
     BACKGROUND OF THE INVENTION 
     Interlocking concrete blocks are used for many outdoor construction applications, one of the most common being the construction of retaining walls. Interlocking concrete blocks are thus designed for durability, stability and aesthetic appeal. 
     One of the ways that aesthetic appeal is imparted to a structure formed from interlocking concrete blocks is to make the exposed face look as much as possible like natural stone, or some other architectural texture. While this is possible using existing methods of wet-casting concrete into textured, rubber molds, the present invention provides a new, innovative way to impart textures, designs, colours and/or special treatments (such as face-mixes, for example) to the exposed face of a retaining wall block using conventional dry-cast concrete machinery and methods. 
     Currently, dry-casting concrete blocks has many advantages over wet-casting concrete blocks from a production efficiency and economic point of view. In dry-casting, rigid steel molds are used to compress a “dry” mix of concrete into specific shapes (such as blocks or paving stones). Due to the minimal amount of water contained in the concrete mix, the blocks can be demolded almost immediately after they are compressed (molded). This allows the manufacturer to produce a layer of blocks in a matter of seconds, and immediately re-use the mold. 
     In comparison, wet-cast concrete blocks are created by pouring a wet, flowable concrete mix into non-rigid, malleable rubber mold. The concrete must be left to cure for a significant length of time (8-12 hrs) before the block can be demolded and the molds can be reused. As a result the cycle time is extremely long compared to dry-casting, the investment in the total number of rubber molds is significant, and the space requirements in the factory to store and manage these molds is significant. However, due to the pliable nature of the rubber molds, it is possible to imprint natural textures and detail in the concrete block. 
     Despite the benefits of dry-casting concrete from a manufacturing and production efficiency point of view, the nature of the rigid steel molds and machinery used in production is such that the “appearance” of the face of the block has been limited. The invention described herein provides a novel way to impart decorative facings to a dry-cast retaining wall blocks, while still being able to create interlocking structures on the top and bottom surface of the blocks. The interlocking mechanism allows for shear resistance and greater structural stability when used as resist lateral earth pressures typical to a segmental retaining wall. Furthermore, the invention orients the critical “height” dimension of the block in a way that ensures substantially perfect dimensional accuracy, and therefore substantially perfect horizontal wall alignment. 
     Conventionally, dry-cast blocks are created by casting dry-mix concrete in a mold, with the exposed face of one block joined to the exposed face of another block, and breaking the blocks apart along a score line. This results in an essentially random topography on each exposed face of the block pair, which produces a natural ‘look and feel’. 
     In a traditional mold box used for forming dry-cast concrete blocks the interior walls, which create the cavities that form the concrete blocks or other products, extend to the bottom of the mold box. As such, it is not possible to have a positive interlocking shape or protrusion since the mold box is extracted vertically from the concrete product. A positive protrusion on any interior mold wall would be an obstruction when the mold box is lifted vertically. In the case of interlocking concrete blocks in which a tongue extending along the top surface interlocks with a groove extending along the bottom surface, this essentially limits the blocks to being formed upright and in face-to-face pairs in the mold box, because the sides and rear faces are the only surfaces of the blocks that do not have a positive interlocking shape or protrusion. 
     For example,  FIGS. 1A to 1L  illustrate a typical molding process for a prior art interlocking concrete block  20 .  FIG. 1A  shows a prior art mold  10  with a mold box  12  and a floor comprising a mold insert  14  in position for casting. The mold insert  14  has a profile with projecting features  5   a  designed to form the interlocking structures on the bottom of the block  20  (in the embodiment shown recesses  5 ) and projecting features  6   a  forming break lines  6 , as shown in  FIG. 1B . After dry mix concrete has been fed into the mold  10 , shown in  FIG. 1C , a press head  15  is actuated to consolidate the concrete  1 . In the prior art blocks  20  shown the press head  15  also forms the top interlocking structures, ribs or “tongues”  4  complementary to the recesses  5 , and break lines  6 , as shown in  FIG. 1C . 
     The steps in the prior art forming process are illustrated in  FIGS. 1D to 1L . The mold box  14  is positioned ( FIG. 1D ) beneath the press head  15  and the mold box  12  is placed on the mold insert  14  ( FIG. 1E ). Concrete  1  is fed into the mold  10  ( FIG. 1F ) and the press head  15  is actuated to consolidate the concrete and form the top surface  22  of the block  20  ( FIG. 1G ), then the press head  15  is retracted ( FIG. 1H ). The mold insert  14  can be removed immediately due to the zero slump concrete mix and the consolidation by the press head ( FIG. 1I ), and the mold box  12  lifted off of the slab of joined blocks  20  ( FIG. 1J ), leaving the unbroken slab of blocks  20  on a board or pallet (not shown). After the concrete has cured for at least 12 hours, blades  7  are forcibly applied to the break lines to split the individual blocks  20  from the slab ( FIG. 1K ). The exposed faces of the blocks  20  manufactured in this fashion have a “split block” finish, shown in  FIG. 1L , which has been an industry standard for over 25 years. 
     There are disadvantages to this manufacturing method. While the (complementary) topographies produced on the exposed faces by breaking the blocks apart looks natural, using this manufacturing method the manufacturer has no control over the final appearance of the exposed face of the block because the fracturing occurs randomly. This limits the profile of the exposed face, and occasionally blocks must be rejected because of over-breakage resulting in the exposed face having a damaged appearance. Also, the height of the concrete blocks is determined by the stroke of the press head, which is a moving part, and since the length of each stroke of the press head may be slightly different there is a commensurate variation in the heights of concrete blocks cast at different times. Furthermore, if a colour other than natural concrete is desired on the exposed face, the colour must be mixed into the entire volume of concrete so that the exposed face provides a uniform colour, which given the cost of some dyes can be very expensive. 
     One or more of the embodiments of the invention addresses one or more of these disadvantages. While embodiments of the invention are described in detail below, it will be appreciated that not every advantage of the present invention necessarily applies to every embodiment described or claimed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In drawings which illustrate an embodiment of the invention by way of example only: 
         FIGS. 1A to 1L  are views showing a typical molding process for a prior art interlocking concrete block. 
         FIG. 2  is a perspective view of an embodiment of a mold box according to the invention. 
         FIG. 3  is a plan view of the mold box of  FIG. 2 . 
         FIG. 4  is an end elevation of the mold box of  FIG. 2 . 
         FIG. 5  is a cross-section of the mold taken along the line  5 - 5  in  FIG. 3 . 
         FIG. 6  is a cross-section of the mold taken along the line  6 - 6  in  FIG. 3 . 
         FIG. 7  is a perspective view of an embodiment of a mold insert according to the invention. 
         FIG. 8  is a perspective view of the mold insert taken opposite  FIG. 7 . 
         FIG. 9  is a top plan view of the mold insert of  FIG. 7 . 
         FIG. 10  is a side elevation of the mold insert of  FIG. 7 . 
         FIG. 11  is a cross-section of the mold insert taken along the line  11 - 11  in  FIG. 9 . 
         FIG. 12  is a cross-section of the mold insert taken along the line  12 - 12  in  FIG. 9 . 
         FIG. 13  is a perspective view of the mold box being lowered onto the mold insert. 
         FIG. 14  is a perspective view of the mold box positioned on the mold insert for casting. 
         FIG. 15  is a cross-sectional end elevation of the mold insert in position in the mold box for casting. 
         FIG. 16  is an enlarged cross-sectional end elevation of an intermediate finger engaging a partition in the mold insert of  FIG. 7 . 
         FIG. 17  is an enlarged cross-sectional end elevation of the left-most finger in  FIG. 15  engaging the left side of the mold box. 
         FIG. 18  is an enlarged cross-sectional end elevation of the right-most finger in  FIG. 15  engaging the right side of the mold box. 
         FIGS. 19A to 19F  illustrate steps in the manufacture of concrete blocks according to an embodiment of the invention. 
         FIG. 20  is a perspective view of an interlocking retaining wall block produced by the mold and method of the invention. 
         FIG. 21  is a side elevation of the retaining wall block of  FIG. 20 . 
         FIG. 22  is a perspective view of a retaining wall utilizing interlocking concrete blocks produced by the mold and method of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a mold for and method of manufacturing an interlocking, Dry-Cast Concrete block  20  which has an exposed face to which fully controllable custom textures and profiles can be applied with a press head  15 , in some embodiments without removing the blocks  20  from the mold box. The exposed faces of the blocks  20  can also be coloured as desired, using a minimal amount of expensive concrete pigment in a face coat which can be as little as 10-15 mm thick. The height tolerance of each block  20  is determined by sturdy, fixed structures within the mold itself, rather than by a moving press head as in the prior art technique described above, and is therefore highly precise so that each block is substantially identical in height with all other blocks cast in the same mold. This is a major benefit for ease of installation compared to prior art systems. By changing the orientation of the blocks  20  within the mold, particularly with the exposed face  28  facing upwardly, the potential for changing the aesthetics of the exposed block face  28  is significantly increased. 
     The invention accomplishes this by providing, in a preferred embodiment, a mold  30  in which the interlocking concrete blocks are cast in an orientation such that their exposed faces  28  are at the top of the mold  30 . The blocks  20  are thus oriented such that the top surface  22  of one block  20  is adjacent to the bottom surface  24  of the block  20  beside it (except for the outermost blocks which are adjacent to the wall  34  of the mold box  32 ). The mold box  32  for a typical block configuration is thus deeper than a prior art mold box  12 , but commensurately smaller side-to-side so the footprint required for the casting process is reduced. Thus, interlocking concrete blocks  20  can be manufactured according to the method of the invention with a higher throughput for the same amount of floor space. 
     The applicants own co-pending U.S. patent application Ser. No. 14/093,710 filed Dec. 2, 2013 by Risi et al. for a Method and Mold For Manufacturing an Interlocking Concrete Block, which application is incorporated by reference herein in its entirety. 
     According to the present invention, the interior walls or ‘partitions’  42  within the mold box  30  do not extend to the bottom of the mold box  30 , but instead are aligned, and preferably mated in a positive interlock, with a set of profiled insert members  64  that are inserted into and withdrawn from the mold box  30  horizontally, and as such can form the positive interlocking structures  22   a ,  24   a  in the top and bottom surfaces  22 ,  24  of the block  20  without interfering with the vertical motion of the mold box  30 . The top and bottom surfaces  22 ,  24  of the retaining wall block  20  are thus formed by two separate pieces: in the front portion F of the block  20  they are formed by the partitions  42  (and, for the end blocks, rigid mold walls  34 ,  36 ), while in the interlocking portion I and rear portion R they are formed by the profiled insert members  64 . 
     As noted above, providing the exposed faces  28  of the interlocking concrete blocks  20  at the top of the mold  30  also allows for the application of a surface coat of face mix or another suitable, durable coating material to be applied while the blocks  20  are still in the mold  30 . The exposed faces  28  may be coloured as desired without having to colour the concrete used for the body of the interlocking concrete block  20 , and/or formed to any desired texture or profile. 
     The invention thus provides mold for manufacturing at least one interlocking concrete retaining wall block, the at least one block having a top surface having a transverse profile comprising at least one interlocking structure projecting from or recessed into the top surface, and a bottom surface having a transverse profile comprising at least one complementary interlocking structure projecting from or recessed into the bottom surface, the mold comprising: a mold box, comprising two side walls joined to end walls to define a mold cavity, a top face, and a substantially open bottom face, and partitions configured to define a space between adjacent blocks or a space between a block and a side of the mold box, extending substantially parallel to the side walls of the mold box substantially from the top face into the mold cavity, at least a longitudinal portion of at least some of the partitions being configured to form a first transverse portion of the profile of the top surface of one block or a first transverse portion of the profile of the bottom surface of an adjacent block, or both, wherein the first transverse portions do not include any undercut portion that would impede removal of the mold box in a substantially vertical direction; and at least one removable insert comprising insert members which, when positioned in the mold box beneath the partitions, extend substantially parallel to the side walls and are configured to occupy the space between adjacent blocks, or the space between a block and a side of the mold box, for forming a remaining transverse portion of the profile of the top surface of one block or a remaining transverse portion of the profile of the bottom surface of an adjacent block, or both, wherein the remaining transverse portions include at least one undercut portion; at least some of the insert members, when in position in the mold box for casting, having top surfaces being substantially in lateral alignment with respective bottom surfaces of at least some of the partitions, and at least one end of the mold box comprising openings through which the insert members can be inserted and retracted at least in a longitudinal direction. 
     The invention further provides a method of manufacturing a plurality of interlocking concrete retaining wall blocks each having a top surface having a transverse profile comprising at least one interlocking structure projecting from or recessed into the top surface and a bottom surface having a transverse profile comprising at least one complementary interlocking structure projecting from or recessed into the bottom surface, comprising the steps of: a. providing a mold box comprising two side walls joined to end walls to define a mold cavity, a top face, and a substantially open bottom face, and partitions configured to define a space between adjacent blocks or a space between a block and a side of the mold box, extending substantially parallel to the side walls of the mold box substantially from the top face into the mold cavity, at least a longitudinal portion of at least some of the partitions being configured to form a first transverse portion of the profile of the top surface of one block or a first transverse portion of the profile of the bottom surface of an adjacent block, or both, wherein the first transverse portions do not include any undercut portion that would impede removal of the mold box in a substantially vertical direction, and at least one removable insert comprising insert members which, when positioned in the mold box beneath the partitions, extend substantially parallel to the side walls and are configured to occupy the space between adjacent blocks, or the space between a block and a side of the mold box, for forming a remaining transverse portion of the profile of the top surface of one block or a remaining transverse portion of the profile of the bottom surface of an adjacent block, or both, wherein the remaining transverse portions include at least one undercut portion, b. inserting the insert members into the openings in the end of the mold box, such that top surfaces of at least some of the insert members are in substantially lateral alignment with respective bottom surfaces of at least some of the partitions; c. introducing concrete into the mold cavity; d. consolidating the concrete; e. in any order: i. removing the mold insert from the mold box, and ii. removing the formed blocks from the mold box. 
       FIGS. 2 to 18  illustrate by way of non-limiting example the various components of a mold  30  for manufacturing a plurality of interlocking concrete blocks  20  according to the invention. The interlocking blocks  20  are advantageously of the type having a top surface  22  with a transverse profile comprising at least one interlocking structure projecting from or recessed into the top surface  22 , in the embodiment shown a tongue  22   a , and a bottom surface  24  having a transverse profile comprising at least one complementary interlocking structure projecting from or recessed into the bottom surface  24 , in the embodiment shown a groove or recess  24   a  complementary to the tongue  22   a , as illustrated in  FIGS. 20 and 21 . 
     The projecting tongue  22   a  on the top  22  of the block  20  extends laterally (i.e. in the end-to-end direction), and the recess  24   a  complementary to the tongue  22   a  also extends laterally, providing a “tongue and groove interlock” which prevents one block  20  from shifting transversely relative to the block  20  immediately above or beneath in the wall structure, as best seen in  FIG. 22 . In the embodiment illustrated the interlocking structures  22   a ,  24   a  extend fully between the ends  26  of the block  20 , however it will be appreciated that the interlocking structures  22   a ,  24   a  may extend partially between the ends  26  of the block  20 . The precise length, height, shape and placement of the interlocking structures  22   a ,  24   a  is a matter of selection and is not limited by the particular embodiment illustrated. 
     In the preferred embodiment of the invention, the blocks  20  are oriented in the mold  30  such that the exposed face  28  of each block  20 , defined herein as the face of the block  20  that is intended to be visible in the finished structure (for example a retaining wall), is disposed in a plane generally parallel to the top face  40  of the mold  30 , preferably substantially flush with the top of the mold  30 . 
     The mold  30  comprises a mold box  32 , illustrated in  FIGS. 2 to 6 . In the example illustrated the mold box  32  comprises two end walls  34   a ,  34   b  joined to two side walls  36   a ,  36   b  to define a mold cavity  38 . The bottom face  50  of the mold box  32  may be substantially open, since the mold box  32  will form a container when placed on a wooden board or other planar surface during casting. The top face  40  is open between partitions  42  and between the partitions  42  and the side walls  36   a ,  36   b , which both allows for concrete to be poured evenly throughout the mold  30  and for the formation of the block faces  28 , as described below. 
     Partitions  42  are configured and spaced from one another and from the side walls  36   a ,  36   b  to define the space between adjacent blocks  20 , corresponding to the height H of the cast block  20  (indicated in  FIG. 20 ). Partitions  42  extend between the end walls  34   a ,  34   b  of the mold box  32 , substantially from the top face  40  (i.e. generally flush with the top face  40  of the mold box  32 ) partway into the mold cavity  38 . 
     The mold  30  can be divided up to make any length of block  20  and/or number of blocks  20  up to the maximum mold size (typically determined by the size of the vibrating machine that will be used to assist in the compaction of the concrete). In the embodiment illustrated the mold box  32  is designed to form 3 rows of 6 blocks  20  per row. Within each row a block  20  is oriented with its top surface  22  facing the bottom surface  24  of the next adjacent block  20 , while each row of blocks is disposed so that the blocks  20  are oriented end-to-end with the blocks  20  in the next adjacent row. To accomplish this, internal walls  44   a ,  44   b  are disposed extending between the side walls  36   a ,  36   b  of the mold box  32  and fully from the top face  40  to the bottom face  50  of the mold box  32  to completely separate the blocks  20  in one row from the blocks  20  in the adjacent row. As illustrated the internal walls  44   a ,  44   b  extend fully between the side walls  36   a ,  36   b  of the mold box and the partitions  42  are disposed between the walls  34   a  and  44   a ;  44   a  and  44   b ; and  44   b  and  34   b , which effectively creates three isolated mold cavities  38   a ,  38   b  and  38   c , respectively, within the mold box  32 . Any other suitable configuration is possible, including casting most of the components as an integral unit, as described below. 
     The partitions  42  are configured to form a portion of the transverse profile of the top surface  22  of one block  20  and a portion of the transverse profile of the bottom surface  24  of an adjacent block  20  in the mold  30 . In the embodiment shown, the partitions  42  form the top and bottom surfaces of the front portion F of the block  20  while the interlocking portion I and rear portion R of the block  20  (see  FIG. 21 ) are formed by a removable mold insert  60 , described in detail below. 
     The partitions  42  are accordingly provided on one side  42   a  with a profile that is a ‘negative’ of the transverse (face-to-rear) profile of the top surface  22  of the block  20  in the front portion F; and on the other side  42   b  with a profile that is a ‘negative’ of the transverse profile of the bottom surface  24  of the block  20  in the front portion F. In the embodiment shown, for example, the partitions  42  are provided on side  42   a  with a planar profile corresponding to the planar profile of the top surface  22  of the block  20  in the front portion F, extending from the block face  28  up to but not including the tongue  22   a ; while the other side  42   b  of the partition  42  is provided with a profile corresponding to the planar profile of the bottom surface  24  of the block  20  in the front portion F, extending from the block face  28  up to but not including the groove  24   a.    
     The sides  36   a ,  36   b  of the mold box  32  are each provided with a profile corresponding to the bottom and top surfaces of the front portion F of the block  20 , respectively. Specifically, the upper portion of side  36   a  is provided with a planar profile corresponding to the planar profile of the bottom surface  24  of the block  20  in the front portion F, extending from the block face  28  up to but not including the tongue  22   a , and the upper portion of side  36   b  is provided with a profile corresponding to the planar profile of the top surface  22  of the block  20  in the front portion F, extending from the block face  28  up to but not including the groove  24   a . The sides  36   a ,  36   b  are formed thicker than the partitions  42 , in order to accommodate the mold insert  60  (as described below) while still being strong and rigid enough top offer the concrete containment functionality of the mold box  32  without swelling or distorting under the weight of the concrete. 
     The mold insert  60 , illustrated in  FIGS. 7 to 12 , comprises a series of insert members  64 . In the preferred embodiment the insert members  64  are connected together at one end by a connecting bar  62 , for convenience, which may be provided with holes  62   a  for ease of grasping and manipulation by a user. In the embodiment shown insert members  64  are configured to define the space between the interlocking portions I and rear portions R of adjacent blocks  20 , in the embodiment shown extending from the rear face  29  of the block  20  up to and including the front edges of the tongue  22   a  and recess  24   a . Thus, in the embodiment shown the insert members  64  form the remainder of the transverse profiles of the top and bottom surfaces  22 ,  24  of the interlocking retaining wall block  20  which are not formed by the partitions  42  and side walls  36   a ,  36   b , as best seen in  FIG. 16 . 
     At least one end wall  34   a  of the mold box  32  provides insert member openings  65  into which the insert members  64  are respectively received. The spacing between openings  65  matches the spacing between insert members  64 , which is one advantage of connecting the insert members  64  together at a preset spacing, for example by a rigid connecting bar  62 . The rigid connecting bar  62  also serves to maintain the insert members  64  in precise parallel alignment both when assembling the mold  30  for casting and when pouring the concrete. The insert members  64  could alternatively be connected in groups, or could be provided as separate unconnected members  64  for example by providing both ends  34   a ,  34   b  insert member openings  65  to hold the insert members  64  in parallel alignment. However, the embodiment shown is also advantageous both for the speed at which the mold insert  60  can be inserted into and retracted from the mold  30 , and for the ability to automate these processes. 
     Ideally the profiles of the insert member openings  65  would be designed to closely match the cross-sectional profiles of the insert members  64 , providing a seal in the assembled mold  30  that substantially prevents concrete from seeping out of the openings  65  when the mold insert  60  is in position in the mold  30 . However, in the preferred embodiment the mold box  32  is capable of being lifted up off of and lowered down onto the mold insert  60  in a vertical direction, to facilitate an automated transition between casting cycles, as described below. Since the insert members  64  each include an undercut area  64 ′ and a projection  64 ″ (with the exception of the insert members  64   a ,  64   b  at each side wall  36   a ,  36   b , which respectively include only one of the projection  64 ″ or undercut  64 ′), the openings  65  in the end wall  36   a  of the mold box  32  must be a uniform width that is wider than the thickness of each insert member  64 , so as not interfere with the lowering of the mold box  32  onto the insert members  64  in each casting cycle. As a result, when the mold  30  is assembled a gap remains in the end wall  36   a  of the mold box at the undercut portion  64 ′ and beneath the projection  64 ″ of the insert member  64 . In order to prevent the seepage of the concrete mix out of the end wall  34   a  through these gaps, the portion of the length of the insert members  64  which will nest within the thickness of the wall  34   a  when the mold is assembled for casting are filled by filler blocks  66   a  and  66   b , best seen in  FIGS. 8 and 12 , which close these gaps when the mold insert  60  is in the casting position in the mold box  32 . The filler blocks  66   a ,  66   b  should preferably be formed in such a way that the concrete material does not stick to or accumulate around the filler blocks  64   a ,  66   b , and the filler blocks  66   a ,  66   b  do not affect the surfaces of finished block  20 , so in the preferred embodiment the inner edges of the filler blocks  64   a ,  66   b  extend flush to the inner wall of the mold box  32 . 
     In an alternative embodiment (not shown), the openings  65  in the end walls  36  can be formed to match the profile of the insert members  64 , including the undercut portions, and the concrete will be retained within the mold cavity  38  solely because of the close fit of the openings  65  around the insert members  64 . In this embodiment the mold insert  60  must be both inserted into and withdrawn from the mold box  32  horizontally, and the mold box  32  therefore cannot be lowered vertically onto the mold insert  60  for casting which makes automation somewhat more complex. 
     It will be appreciated that the insert members  64  extend fully between the end walls  34   a ,  34   b  of the mold box  32  in the embodiment illustrated because the tongues  22   a  and recesses  24   a  extend fully end-to-end across the blocks  20 . Embodiments in which the interlocking structures do not extend fully between the ends  26  the blocks  20  are possible, for example where the insert members  64  extend only partway into the mold cavity  38 , and fall within the scope of the invention. In either case, at the distal end  60 ′ of the mold insert  60  the bottom edge of each insert member  64  advantageously merges into the distal edge of the insert member  64  along a curve, as best seen in  FIG. 10 , to act like the runner of a sleigh allowing the mold insert  60  to glide over the board or palette as the mold insert  60  is inserted into the mold box  32 . 
     As illustrated in  FIGS. 15 and 16 , in the preferred embodiment the top surface of each insert member  64  is keyed to mate with the congruent bottom surface of each partition  42  (or optionally in the case of the end insert members  64   a ,  64   b , to a ledge  37   a  or  37   b  respectively formed in the side wall  36   a  or  36   b ). This ensures that in the assembled mold  30  the insert members  64  are retained against lateral shifting during casting, and that the top and bottom surface  22   a ,  24   a  of the block are level at the front portion F and rear portion R of the block  20  and lie in the same plane. 
     In the embodiment shown there is a small gap (e.g. 1 mm) left between the top surface of the insert member  64  and the bottom surface of the partition  42  (exaggerated for purposes of illustration on  FIG. 16 ). This allows the insert members to slide in and out of the mold box  32 , leaving only a small burr along the front of the tongue  22   a  that sits inside a void in the tongue  22   a  and thus will not become an obstruction when stacking the blocks  20  in a wall. Accordingly, in the preferred embodiment the top surface of each insert member  64  is provided with the projection, for example a laterally convex profile as shown, and the bottom surface of each partition  42  is provided with the congruent mating recess, so as to preclude any accumulation of casting material on the top of the insert members  64 . However, other structural configurations that laterally interlock the insert members  64  to the partitions  42  can be used to effect the same result and are contemplated within the invention. 
     In the operation of the embodiment illustrated, the mold insert  60  is positioned on a planar surface, for example a floor, or a board or palette (not shown). The mold box  32  is disposed above the mold insert  60  as shown in  FIG. 13 , by aligning insert members  64  with their respective openings  65  in the end wall  34   a  of the mold box  32 , until the mold box  32  is seated on the board (operatively associated with a vibrating machine, as is well known) which closes the open bottom face  50  of the mold box  32  in the casting position shown in  FIG. 14 . Concrete having the desired slump, preferably “dry” concrete for quick-setting purposes, is poured into the mold  30  generally evenly until the level of concrete substantially reaches the top face  40 . 
       FIGS. 19A to 19F  illustrate the face forming process. A press (not shown) is disposed over the mold  30 , as shown in  FIG. 19A , and the press head  15  is activated, as shown in  FIG. 19B , to consolidate the concrete and, if desired, impart a texture and/or profile to the exposed faces  28  of the blocks  20  which is determined by the configuration and surface characteristics of the press head  15 . The press head  15  is retracted, as shown in  FIG. 19C . In the preferred embodiment the mold insert  60  is removed by drawing the mold insert  60  out of the end  34   a  of the mold box  32 , as shown in  FIG. 19D . Because of the uniform transverse profile of the blocks along the lateral extent of each block  20 , the mold insert  60  can be removed laterally from the mold box  32  substantially unimpeded by the interlocking structures formed on the concrete blocks  20 . 
     The mold box  32  can then be lifted off of the newly formed blocks  20 , as shown in  FIG. 19E . Because there is no positive interlock between the partitions  42  and the front portions F of the blocks  20 , the mold box  32  can be lifted off of the concrete blocks  20  without obstruction. The front portion F of each block  20  formed by the partitions  42  (and on the ends, side walls  36   a ,  36   b  of the mold box  32 ) is selected so that no portion of the top  22  or bottom  24  of the block interlocks in a vertical direction with the partitions  42 . The result is a course of blocks  20  standing on the board face-up, as shown in  FIG. 19F . The newly formed blocks  20  can then be pushed together and stood upright (i.e. top surfaces  22  up), to be placed on a skid for shipping. 
     It is advantageous to slide the mold insert  60  out from under the newly formed blocks  20  while the mold box  32  is still in position holding the blocks  20  in place. Alternatively, the mold box  32  can be lifted first and the blocks  20  held in position by other means as the mold insert  60  is drawn out from underneath the blocks. 
     The components of the mold  30  may be formed from steel or any other suitable material. The components of the mold box  32  may be bolted together, welded or affixed by any other suitable means. Some components of the mold box  32  may be cast integrally using conventional metal casting techniques; for example, in the embodiment illustrated the side walls  36   a ,  36  can optionally be formed integrally with the internal walls  44   a ,  44   b  and partitions  42  (for example, top-down) and the end walls  34   a ,  34   b  formed separately and subsequently bolted or otherwise affixed to the side walls  36   a ,  36   b.    
     The embodiment illustrated is dimensioned to cast three concrete blocks  20  per row, which blocks  20  may be of varying lengths. However, the mold  30  can be designed to cast fewer or more concrete blocks  20  as desired, the components of the mold  30  being provided with thicknesses suitable for withstanding the weight of the concrete without deforming during casting. It will be appreciated that since the components of the mold box  32  and mold insert  60  combine to form parallel surfaces, increased accuracy of mold construction and manufacturing may be required. 
     It will be appreciated that although the blocks  20  are illustrated as oriented in the same direction in the mold  30 , because of the versatility in providing profiles on the insert members  62  the blocks  20  can be oriented in the mold  30  in different directions, for example some facing tongue-to-tongue and others oriented tongue-to-groove as shown. 
     Different types of interlocking structures may be formed using the mold  30  of the invention. However, because the blocks  20  are cast in a face-up orientation in the mold  30  and the concrete used is preferably is dry cast—i.e. has a low slump (water content), preferably the minimum amount of water required to make the concrete flow when cast but become free standing within 5 seconds of being compacted, there are factors that make the particular tongue-and-groove interlocking configuration illustrated advantageous. The dry cast concrete must be able to flow fully into any undercut structure, essentially any structure disposed beneath an outcropping, for example surfaces  67 ″ and  68 ′ which respectively form the rear surface of the groove  24   a  and the front surface of the tongue  22   a , as shown in  FIG. 16 . Undercut regions of the interlocking portion I are therefore preferably designed to strike a balance between creating a reasonably strong and stable interlock and ensuring substantial compaction in the area beneath each undercut. 
     Thus, the tongue  22   a  may be formed asymmetrically in cross-section, as in the embodiment shown in which the front surface of the tongue  22   a  is formed at a shallower angle than the rear surface of the tongue  22   a , respectively by surface  68 ′ of the insert member  64  which is at a shallower angle than the surface  68 ″ that forms the rear surface of the tongue  22   a . The rear surface of the tongue  22   a  is the “locking” side, creating the shear resistance between the top surface  22  of a lower block  20  and the bottom surface  24  of the upper block  20  resting on the lower block  20 , so for a more positive interlock it is desirable to have the rear surface of the tongue  22   a  inclined as steeply as possible from the horizontal. Depending on the board machine, concrete mix, and the pre-vibration and main vibration applied to the mold during the casting process, the inclination of the rear surface of the tongue  22   a  may range from between 30 to 45 degrees from the vertical. Testing and experience indicates that this angle allows compaction efforts above to transfer the pre-set concrete mixture into the undercut regions, albeit potentially to a lesser extent than the remaining regions within the mold  30 . This also has the advantage of rendering the tongue  22   a  self-supporting immediately follow extraction from the mold  30 , when the concrete is in an uncured state. The shallow front angle of the tongue  22   a  reduces the amount of material required to form the tongue  22   a , and thus its weight, to ensure that when the cast block  20  is standing vertically in an uncured state the tongue  22   a  remains intact and does not slump or distort. 
     The rear surface of the tongue  22   a  is formed at a significantly steeper angle by surface  68 ″ than the front surface of the tongue  22   a , in order to ensure a positive, stable interlock. At the same time the projection  64 ″, which will form the groove  24   a  in the finished block  20 , surface  67 ″ forming the rear surface of the groove  24   a  must complement the angle of the rear surface  68 ″ of the undercut  64 ′, and is thus formed steep enough to serve as a corbel (for example as indicated above 30 to 45 degrees) while still allowing the undercut portion beneath the projection  64 ″ to fill fully with concrete during casting. 
     It will be appreciated that the particular portions of the block  20  which may be formed by the respective partitions  42  and insert members  64  may differ from those that are illustrated herein solely by way of example of a preferred embodiment. 
     Although in the embodiment illustrated the projecting and undercut portions  22   a ,  24   a  of the top and bottom surfaces  22 ,  24  (i.e. the tongue  22   a  and groove  22   b  in the embodiment shown) are formed by the removable insert  60 , it will be appreciated that it is possible to extend the partitions  42  down on one side to form the front portion of the tongue structure  22   a , and/or for the insert members  64  to form part of the front portion F of the block  20 , without affecting the operation of the invention. 
     Various embodiments of the present invention having been thus described in detail by way of example, it will be apparent to those skilled in the art that variations and modifications may be made without departing from the invention. For example, although less advantageous than the preferred embodiments, the blocks  20  could be formed in the mold with their exposed faces  28  at the bottom of the mold while still providing some advantages of the invention. The invention includes all such variations and modifications as fall within the scope of the appended claims.