MODULAR PRECAST WALL SYSTEM WITH MORTAR JOINTS

Abstract: A modular construction system (10) is provided, the preferred embodiment of which is directed toward the construction of structural walls (26). The construction system (10) employs precast wall units (12) and a variety of spacer/tensioning, spacer, tensioning, and extension assemblies (14, 16, 18 and 20). The wall units (12) contain a plurality of cavities (44) and are made of concrete with side walls (36) reinforced with prestressed tension wires (48). In the process of constructing a wall (26), the wall units (12) are stacked one upon the other onto threaded wall bars (24) that extend upwardly from a foundation (22). The spacer/tensioning assembly (14) and the spacer assembly (16) provide alignment during the stacking process and also create mortar joints (52). The spacer/tensioning assembly (14) and the tensioning assembly (18) are utilized in conjunction with the wall bars (24) to tension the wall units (12) onto a lower wall units (12) and the foundation (22). When stacked, the internal structure of the wall units (12) creates vertically and horizontally extending passages (85 and 86) into which grout (84) is poured to create a monolithic wall (26).

Description: MODULAR PRECAST WALL SYSTEM WITH MORTAR JOINTS U.S. Application Serial No. 08/335,059, entitled "MODULAR PRECAST CONSTRUCTION BLOCK SYSTEM' and filed on November 7, 1994 by Howard M. Franklin and Erik Garfinkel, is included in Appendix A and is hereby incorporated by reference in its entirety. TECHNICAL FIELD The present invention relates generally to the field of construction, and more particularly to a construction system employing precast block units for the construction of walls and other structures in which mortar joints are desired. BACKGROUND ART Shelter is a basic need, and human ingenuity has arrived at numerous and sophisticated methods and materials to meet this need. Among the many methods include those employing precast concrete units that are assembled to create a building or other structure. These methods encompass construction systems incorporating a wide range of precast unit designs that vary from the simple to the very complex. The most elementary precast unit designs are those used in basic, concrete masonry. While concrete masonry units (CMU's) may be designed for a variety of applications, they can result in structures that are structurally inferior to those created with larger, reinforced concrete units. Smaller CMU's can crack and chip as well. Construction with small CMU's also requires a specialized labor force. As a result, building methods utilizing CMU's can create high labor costs, and it can be difficult to find a qualified work crew. More sophisticated construction systems use concrete columns, beams, and foundation members to create a superstructure. A beam and column joining assembly is set forth in U.S. Patent No. 4,583,336, issued to Shelangoskie, et al. on April 22, 1986. U.S. Patent No. 5,103,613 issued to Satoru Kinoshita on April 14, 1992 teaches foundation members interconnected by a binding member having mortises therein for receiving tenons on the bottom of a column. U.S. Patent No. 4,124,963 issued to Taaayasu Higuchi on November 14, 1978 sets forth a precast unit for providing a footing for a building. While the above patents describe a superstructure they provide no teachings on the construction of walls or the like. In addition, the precast units of the inventions provide little flexibility for increasing structural integrity of the larger structure. Two U.S. Patents present precast units in which wall members are also employed. U.S. Patent No. 4,328,651 issued to Manuel Gutierrez on May 11, 1982 shows a system having a number of precast units including footing boxes, grade beams, roof beams and a wall panel. The Gutierrez system sets forth an intricate system of interconnecting parts. The intricacies of the design limit the flexibility of the system, however. The beams and wall panels described therein would have to be formed to custom lengths and heights in order to meet the needs of differing structures. In addition, the wall panels lack flexibility for increasing structural strength. The second patent is U.S. Patent No. 5,081,805 issued toM Omar A. Jazzar on January 21, 1992. This patent teaches precast units of half-story height that include steel reinforcements. The Jcizzar invention requires substantial lifting equipment, however, and is also limited in versatility. Furthermore, building designs departing from preformed dimensions require a second, expensive mold, or considerable custom work to arrive at the desired shape. Authors David A Sheppard and William R. Phillips illustrate unitary load-bearing or non- load-bearing precast panels in their book Plant-Cast Precast & Prestressed Concrete - A Design Guide. Third Edition, McGraw-Hill Inc., 1989, (see pages 311-13). The same book also illustrates the use of very large, precast, concrete "voided" bearing walls at page 340. The large bearing walls and precast panels, like those in the Gutierrez patent, must be custom formed and require large custom molds, a large site slab, and very large lifting equipment. In addition, the immense size of the walls makes them impractical for smaller construction projects. Illustrated in a commercial brochure of American ConForm Industries, Inc. (1993), is a modular construction system that employs stackable polystyrene units. Concrete is poured within the stacked units to create walls for different applications. The design of the units allows for the placement of reinforcing steel, but the units themselves are non-structural. Such a system suffers from a number of problems, including those inherent in having to pour large quantities of concrete, such as delays due to inclement weather conditions and the creation of clutter and debris at the work site. Moreover, strict engineering tolerances are difficult to obtain without skilled workers. To the inventors' knowledge, no building system employing preformed building units has been developed that provides versatility in design, can accommodate a variety of reinforcement designs for great structural strength, requires relatively small lifting equipment, allows for the rapid construction of buildings, and that does not suffer from the limitations of poured concrete systems. DISCLOSURE OF THE TNNENTION Accordingly, it is an object of the present invention to provide a construction system using precast units that can be used for the construction of a variety of building forms and designs. It is another object of the invention to provide a construction system that can be used to rapidly construct buildings while achieving a very high quality of construction and great structural strength. It is a further object to provide a construction system, using precast units, that can accommodate a wide range of reinforcement designs. It is yet another object to provide a construction system using precast units, which system allows for the introduction of conventional mortar joints. It is still a further object to provide a construction system that does not require a large amount of specialized erection equipment. It is yet another object to provide a construction system that does not require a crew having specialized skills. It is yet a further object to provide a construction system, using precast units, that includes alignment aids. It is still another object to provide a construction system using precast units which can be easily cut to size. It is still a further object of the present invention to provide a construction system that is cost effective for residential and light-commercial projects. Briefly, the preferred embodiment of the present invention is a modular construction system employing precast wall units and a variety of spacer, tensioning, and extension assemblies for the construction of walls. The wall units contain cavities and are made of concrete and reinforced with prestressed steel wires. In the process of constructing a wall, the wall units are stacked onto threaded wall bars that extend upwardly from a foundation, the wall bars being inserted into the cavities of the wall units. The stacking is performed with the aid of the spacer, tensioning, and extension assemblies. When stacked, the structure of the preferred wall units creates both vertically and horizontally extending passages within the resulting wall. Reinforcement rods or bundles of rods may be placed within both the vertical and horizontal passages. The tensioning assemblies utilize the vertically extending wall bars and the horizontally positioned reinforcement rods to tension the wall units onto lower wall units and onto the foundation. The extension assembly provides the capacity to extend the height of the wall bars and therefore the height to which the wall units may be stacked. Grout is poured within the vertical and horizontal passages of the stacked wall units to create a monolithic wall of great structural strength. The spacer assemblies provide spaces between wall units for conventional mortar joints and also assist in the alignment of the wall units during their stacking. One variety of spacer assembly provides a tensioning capability in addition to providing mortar joint spaces and assisting in alignment. This spacer assembly includes a bracket which spans most of the width of the wall unit and which has an aperture for receiving a wall bar. The bracket also includes upwardly and downwardly extending pairs of vertical alignment fins which are inserted within the side walls of the wall units to give a precise stacking of the wall units. The bracket is tensioned down onto a wall unit by torquing a nut onto the threaded wall bar and bracket. The bracket is hidden from view by the mortar joint since it does not extend the full width of the wall unit side walls. A second variety of spacer assembly provides mortar joint spaces and assists in alignment of the wall units. This spacer assembly includes two bracket halves removably joined together with a bolt. Each bracket half has an upwardly and downwardly extending alignment fin. The side walls of wall units are inserted between the alignment fins of the mated bracket assembly to give precision stacking. After completion of the wall, the outer bracket half is removed and a simple patch of mortar is applied to fill the void. The inner bracket half is then hidden from view. This spacer assembly may be modified to include a wall brace fin which extends perpendicularly outward from the outer bracket half and wall. The wall brace fin includes an aperture to which external bracing may be connected to provide support for the wall during its construction where necessary. An advantage of the present invention is that the construction system allows for a significantly more rapid and easy assemblage of walls and building forms than is possible by either conventional cast-in-place concrete or CMU construction methods. Another advantage of the invention is that the construction system provides for the building of structures with significantly more uniform and accurate dimensions than is possible by either conventional cast-in-place concrete or CMU construction methods. Yet another advantage is that the construction system allows for the introduction of more reinforcing material and therefore a greater structural strength than is possible with conventional CMU walls, with a strength that can approach that of a conventional cast-in-place concrete wall. A further advantage is that the construction system allows a wall to be engineered and built as a conventional CMU wall and with the convenience thereof. Yet a further advantage is that walls made with the construction system are significantly less water permeable than CMU construction methods. Still another advantage of the invention is that the construction system allows for engineers to utilize the sidewalls of precast wall units as part of the overall structural wall thickness in their calculations for CMU-built walls. Yet another advantage is that the precast units of the construction system may be stockpiled for immediate use. A further advantage is that the precast units of the invention may be stocked in varying sizes for a wide range of applications. Yet another advantage is that construction with the present invention may be carried out in inclement weather. Still another advantage is that the construction system can be implemented by smaller work crews than are typically employed. Yet a further advantage is that the construction system generates very little debris. A still further advantage is that the construction system of the present invention does not require a superstructure. These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention as described herein and as illustrated in the several figures of the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a fanciful isometric, cut-away view of the preferred embodiment of the present invention; Fig. 2 is a side view of a wall unit of the preferred embodiment; Fig. 3 is an end cross-sectional view through a cavity in a wall unit of the preferred embodiment; Fig. 4 is an end cross-sectional view through a cavity wall of a wall unit of the preferred embodiment; Fig. 5 is an exploded view of a wall bar extension assembly; Fig. 6 is an exploded view of a combination spacer/tensioning assembly; Fig. 7 is a cut-away, end cross-sectional view through the cavities of two stacked wall units of the preferred embodiment incorporating the combination spacer/tensioning assembly; Fig. 8 is a fragmentary side view of a grout-filled wall with wall unit side walls removed; Fig. 9 is an exploded view of a spacer assembly; Fig. 10 is a cut-away, end cross-sectional view through the cavities of two stacked wall units of the preferred embodiment incorporating a spacer assembly and a tensioning assembly; and Fig. 11 is an exploded view of a tensioning assembly. BEST MODE FOR CARRYING OUT THE INVENTION The preferred embodiment of the present invention is a modular construction system employing precast block units and providing for mortar joints between the block units. The construction system of the preferred embodiment is directed toward the creation of structural walls and is set forth in Fig. 1, where it is designated therein by the general reference character 10. Referring to Fig. 1 of the drawings, the construction system 10 is shown to include a number of wall units 12, a combination spacer/tensioning assembly 14, a spacer assembly 16, a modified spacer assembly 17, a tensioning assembly 18, and a wall bar extension assembly 20. A base structure or foundation 22 provides a number of upwardly projecting wall bars 24 that are received by the wall units 12. As illustrated in Fig. 1, the wall units 12 of the preferred embodiment are designed to be stacked, one on top of the other, to create a vertical wall 26. The structure of the wall units 12 is detailed in Figs. 2-4. As shown in the side elevational view of Fig. 2 and the end cross-sectional view of Fig. 3, the wall units 12 have a generally rectangular solid shape that includes a wall unit top surface 28, a wall unit bottom surface 30, two wall unit side surfaces 32, and two wall unit end surfaces 34. As indicated in the various figures, the wall unit side surfaces 32 are considerably longer than the wall unit end surfaces 34, typical wall unit 12 lengths and widths being on the order of 3.0 to 18.3 m (10 to 60 ft) and 20 to 30 cm (8 to 12 in) respectively. Typical wall unit 12 heights are on the order of 46 to 91 cm (18 to 36 in). The wall units 12 of the preferred embodiment 10 are precast, prestressed masonry forms composed of any of a variety of concrete mixes and additives depending on the strength required and the climate anticipated. In addition to various structural additives, the inclusion of color additives and waterproofing additives are contemplated as well. Furthermore, the wall units 12 may be provided with a variety of architectural finishes during the casting process (e.g., using a patterned form-liner, or adding aggregate). Commercially available insulation cores may be incorporated as well. Each integrally molded wall unit 12 has two rectangular, parallel, opposing wall unit side walls 36. The wall unit side walls 36 are joined by a number of cavity walls 38. As best illustrated in Figs. 1 and 4, the cavity walls 38 are peφendicular to, and integral with, the wall unit side walls 36. In the preferred embodiment of the construction system 10, a cavity wall top surface 40 and a cavity wall bottom surface 42 are each recessed approximately 15 cm (6.0 in) from the wall unit top and bottom surfaces (28 and 30) for reasons as will be explained later herein. The wall unit side walls 36 and cavity walls 38 of the preferred wall unit 12 have thicknesses of approximately 3.8-4.4 cm (1.5-1.8 in) and 5.1 cm (2.0 in) respectively, with center to center distances of approximately 30.5 cm (12 in) between cavity walls 38. Although not indicated in the drawings, the various interior surfaces of the wall units 12 have slight tapers which are introduced during the formation of the wall units 12 to allow for the easy removal of the patterns used to mold the wall units 12. The inclusion of such tapers or "drafts" is well- known in the art. The resulting structure comprised of wall unit side walls 36 and cavity walls 38 creates a number of vertically extending cavities 44 within the wall unit 12. As best shown in Figs. 1 and 3, each cavity 44 extends for the height of the wall unit 12, opening onto both the wall unit top surface 28 and the wall unit bottom surface 30. The molded design and incorporation of cavities 44 into the wall unit 12 provides for both structural integrity and a substantial reduction in weight for the wall unit 12. This reduced weight permits the rapid erection of walls 26 using lifting equipment of a relatively smaller size than would otherwise be possible. Contained within each wall unit 12 of the construction system 10 of the preferred embodiment is a reinforcement structure 46. The reinforcement structure 46 is illustrated in the partial cutaway view of Fig. 1 and the cross-sectional views of Figs. 3 and 4. The reinforcement structure 46 is comprised of three parallel tension wires 48 that are horizontally disposed within each wall unit side wall 36. The tension wires 48 are pre-tensioned and cast in place when the wall units 12 are formed. The tension wires 48 place the entire wall unit 12 under compression -co¬ upon formation, which adds to the structural integrity of the wall unit 12 and reduces undesirable cracking and spalding, especially during transit and handling. The preferred material for the tension wires 48 is high tensile strength steel of approximately 5 mm (0.2 in) in diameter or otherwise meeting industry-accepted requirements. Despite the presence of the tension wires 48, and although the wall units 12 are precast at a discrete length, each wall unit 12 can be quickly and easily cut on-site to fit any length as required. Any number and type of tension wires 48 might be utilized according to the desired strength of the wall unit 12. Additional methods of imparting increased strength to the wall unit 12 include, among others, the casting in place of mild steel ("rebar"), and the post-tensioning of a cable or wire fitted into a plastic sleeve that is itself cast in place. The preferred embodiment of the construction system 10 of the present invention contemplates the use of a variety of mortar spacing and wall tensioning methods and combinations thereof. When wall bars 24 are employed, as shown in Fig. 1, the combination spacer/tensioning assembly 14 and/or wall bar extension assembly 20 may be incoφorated to add structural strength, flexibility of design, and improve the speed and ease with which buildings can be constructed. The spacer/tensioning assembly 14 serves multiple functions, including providing a wall tensioning capability while also acting as a spacer to introduce and maintain spaces for mortar joints 52 between the wall unit top surface 28 of a lower wall unit 12 and the wall unit bottom surface 30 of a next higher wall unit 12. In addition to providing mortar spacing and adding structural integrity, the spacer/tensioning assembly 14 further allows for the wall units 12 to be securely attached to the foundation 22 without the need for additional bracing. The wall bar extension assembly 20 and combination spacer/tensioning assembly 14 are set forth in detail in Figs. 5-7. Fig. 5 shows an exploded view of the wall bar extension assembly 20 and an associated wall bar 24. The wall bar extension assembly 20 includes an extension bar 54 and a bar coupler 56. Both the wall bar 24 and the extension bar 54 are threaded, and each includes two bar ends 58. The bar coupler 56 includes a threaded coupler aperture 60 for simultaneously receiving the bar ends 58 of both the wall bar 24 and the extension bar 54. The wall bar extension assembly 20 provides, in essence, the capacity to vertically extend the wall bar 24. This aspect is advantageous in the event the wall units 12 must be stacked higher than the vertical height of the wall bars 24. By using the wall bar extension assembly 20, extension bars 54 may be added to as great a height as is necessary for the structure under construction. A preferred embodiment of the spacer/tensioning assembly 14 is set forth in detail in Figs. 6 and 7. As illustrated in the exploded view of Fig. 6, the spacer/tensioning assembly 14 of the construction system 10 includes a spacer/tensioning bracket 62, a tensioning washer 64, and a tensioning nut 66. The spacer/tensioning bracket 62 is integrally formed and includes a bar receiving aperture 68, two upper alignment fins 70, two lower alignment fins 72, and two spacer fins 74. Both pairs of upper and lower alignment fins (70 and 72) are present in parallel opposing fashion, with an upper alignment fin 70 and a lower alignment fin 72 being present in an identical vertical plane. Each spacer fin 74 projects horizontally outward from an upper and lower alignment fin (70 and 72) in a plane peφendicular to the aforementioned vertical plane. In the construction system 10 of the preferred embodiment (and in applications for which wall units 12 having a width of approximately 20 cm (8.0 in) are utilized), the spacer/tensioning bracket 62 will have an overall length of approximately 15 cm (6.0 in), with a width of approximately 5.1 cm (2.0 in). The preferred spacer fins 74, as will be explained below, have a thickness of approximately 0.95 cm (0.38 in). Referring now to both Fig. 6 and the cross-sectional view of Fig. 7, the spacer/tensioning bracket 62 fits over the wall bar 24 with the wall bar 24 passing through the bar receiving aperture 68 and with the lower alignment fins 72 being inserted between the interior surfaces 76 of opposing wall unit side walls 36. The tensioning washer 64 and tensioning nut 66 are subsequently threaded onto the wall bar 24 and can be tightened such that the spacer/tensioning bracket 62 exerts a downward force on the wall unit top surface 28 to thereby tension the wall unit 12 onto the foundation 22 or a wall unit 12 directly below. When a second wall unit 12 is stacked on top of the first wall unit 12, the upper alignment fins 70 are likewise inserted between the interior surfaces 76 of opposing wall unit side walls 36 of the upper wall unit 12. The spacer/tensioning bracket 62 thus forces the wall unit side walls 36 of the two wall units 12 to be in vertical alignment. The clearances between the upper and lower alignment fins (70 and 72) and the interior surfaces 76 of the wall unit side walls 36 are small so that precision stacking may be achieved. The spacer/tensioning assemblies 14 are typically incoφorated at increments of 3.0 to 4.6 m (10 to 15 ft) along the length of a wall unit 12. Also shown in Fig. 7, and indicated therein by dashed lines, are variations on the preferred embodiment in which notches 78a or 78b are incoφorated into the wall unit side walls 36. Notch 78a is a recess in the interior surface 76 of the wall unit side wall 36, while notch 78b is a vertical hollow in the wall unit top or bottom surfaces (28 or 30). Either of the recessed or hollowed notches (78a or 78b) can be precast or field-cut and both allow for simultaneous vertical and horizontal alignment of the wall units 12. (The spacer/tensioning bracket 62 would of course require a lengthening of the distance between opposing pairs of upper and lower alignment fins (70 and 72) in order to accommodate these variations.) In addition, it is contemplated that a bracket similar to spacer/tensioning bracket 62 could be employed, wherein the upper and lower alignment fins (70 and 72) are omitted to give a bracket that is essentially a flat plate having only the bar receiving aperture 68 and that functions in a spacer capacity only. This "bare" bracket could be used in conjunction with wall units 12 having notches similar to hollowed notch 78b, and into which a separate alignment fixture (e.g., a short metal bar) is placed, or with wall units 12 that are precast to include mating vertical protrusions and hollows in the wall unit top and bottom surfaces (28 and 30), or in some other way specifically shaped to aid in alignment and stacking. Continuing to refer to Fig. 7, the spacer fins 74 prevent the top and bottom surfaces (28 and 30) of stacked wall units 12 from making contact, thereby creating spaces for mortar joints 52. In practice, mortar 80 is applied during the stacking process, that is, an upper wall unit 12 is laid upon a fresh bed of mortar 80 covering the wall unit top surface 28 of a lower wall unit 12. Because the spacer fins 74 do not extend completely to the wall unit side surfaces 32, but rather are set back by approximately 2.5 cm (1.0 in), the spacer/tensioning bracket 62 is hidden from view by the mortar joint 52. For the first course of wall units 12 rising up from the foundation 22, standard construction shims (not shown) are inserted between the wall unit bottom surface 30 and the foundation 22 to insure that the resulting wall 26 is level and aligned. In addition, since a mortar joint 52 is also desired between the foundation 22 and the first course of wall units 12, a modified spacer/tensioning bracket 62 having no lower alignment fins 72 is employed at the base of the first course in order to provide spacing for the mortar joint 52. While the spacer/tensioning bracket 62 as depicted in the drawings is shown with the intermediary portion 82 of the spacer/tensioning bracket 62 lying between opposing pairs of upper and lower alignment fins (70 and 72) as being planar and plate-like, it is contemplated that this intermediary portion 82 may be specifically designed to assist in the flow of grout over and around the spacer/tensioning bracket 52 and throughout the wall 26. Thus, this intermediary portion 82 may be preferably formed with a downwardly-curving or other hydraulically engineered shape. For the construction of structures in which the Uniform Building Code (UBC) is controlling, the thickness of the spacer fins 74 will generally be 0.95 cm (0.38 in) or greater, because a mortar joint 52 of that thickness, under current UBC requirements, permits the thickness of the wall unit side walls 36 to be taken into account as part of the overall wall unit 12 thickness for puφoses of structural engineering calculations. For walls employing CMU's, the genre in which the wall units 12 of the preferred embodiment of the present invention are technically categorized, in which mortar 80 is not used, or in which mortar 80 is present in a thickness of less than 0.64 cm (0.25 in), structural wall thickness calculations must be limited to using the width of the (grout-filled) cavities 44 only, as measured between the interior surfaces 76 of opposing wall unit side walls 36. Thus, the inclusion of a sufficiently thick mortar joint 52 allows wall units 12 of a smaller width to be used than would otherwise be possible in the construction of walls using CMU's, reducing both the weight of the wall units 12 and construction costs. Moreover, the presence of mortar joints 52 allows a wall 26 to be engineered and built as a conventional CMU wall. It is contemplated, however, that UBC requirements may be revised and modified, in part because of the introduction onto the market of the wall units 12 of the present invention, to make it possible to meet certain structural requirements with the use of an adhesive other than mortar 80. For example, an epoxy or similar glue might be permitted to be employed to make an adhesive, water-tight joint between the wall unit top and bottom surfaces (28 and 30). As noted previously, and still referring to Fig. 7, in the preferred embodiment of the construction system 10, the cavity wall top and bottom surfaces (40 and 42) are each recessed from the wall unit top and bottom surfaces (28 and 30). Thus, when two wall units 12 are stacked one upon the other, in addition to a plurality of vertical passages 85 being formed, the cavity wall top surfaces 40 of the lower wall unit 12 and the cavity wall bottom surfaces 42 of the upper wall unit 12 combine together with interior surfaces 76 of opposing wall unit side walls 36 to create a horizontally disposed passage 86 that extends the length of the stacked wall units 12. Referring also to Fig. 8 now, the passage 86 permits grout 84 that is poured into the cavities 44 to flow between laterally adjacent cavities 44, thereby creating a wall 26 in which is contained a continuous cementitious skeleton 88. The passage 86 also allows for the placement of horizontal reinforcement rod or rebar 90 within the wall units 12. The cementitious skeleton 88, reinforced by rebar 90 (and wall bar 24), greatly increases the structural integrity of the resulting wall 24, although for some applications (and under certain building codes), grout 84 and/or reinforcement with rebar 90 may be unnecessary. (Although not shown, even greater reinforcement is possible by wrapping containment rings or ties around rebar 90 of more than one level of wall units 12.) It is also possible to create a passage similar to passage 86, and into which rebar 90 may likewise be placed, by recessing only the cavity wall top surfaces 40. However, the additional recessing of the cavity wall bottom surfaces 42 enables standard rigging equipment to be employed to grab hold and lift wall units 12 of any length without the need for special precast or field-installed lifting inserts. In the preferred wall units 12, all of the cavity wall bottom surfaces 42 are recessed so that if it is necessary to cut a wall unit 12 at any particular point, a cavity wall bottom surface 42 will always be present so that a hook of the rigging equipment may be positioned thereunder for lifting. The application of mortar 80 between the wall unit top and bottom surfaces (28 and 30), and the pouring of grout 84 into the cavities 44 and passages 86, provides a monolithic wall 26 of great structural strength. While in Fig. 8 a continuous cementitious skeleton 88 is shown, it is also contemplated that for certain applications, in which less structural strength is required, grout 84 might not be poured throughout the entire wall 26. For these lower strength applications, sleeves or similar partitioning devices (not shown) might be employed to prevent the grout 84 from entering the horizontal passages 86, thereby creating single vertical grout voids (i.e., contained vertical passages 85) wherein discrete concrete pillars or columns would be formed upon the pouring of the grout 84. These voids could similarly be permitted to remain empty, with grout 84 poured in neighboring vertical and horizontal passages (85 and 86). This latter application is useful where, for example, plumbing fixtures need to be installed or maintained. As indicated previously, in the construction system 10 of the preferred embodiment, the foundation 22 provides a number of vertically disposed reinforcing wall bars 24. Referring once again to Fig. 1, it is shown that the wall units 12 are stacked onto the foundation 22 with the wall bars 24 inserted through the cavities 44 within the wall units 12. While the incoφoration of wall bars 24 provides for walls 26 of increased strength, it is understood that walls 26 can also be built that do not have wall bars 24 by simply stacking the wall units 12 and introducing a mortar joint 52 with a spacing device that does not utilize a wall bar 24. Spacer assembly 16 may be employed in this regard. Moreover, spacer assembly 16 can also be employed in conjunction with the combination spacer/tensioning assembly 14 and/or the tensioning assembly 18, as shown in Fig.1. Referring now to the exploded view of Fig. 9, one preferred embodiment of the spacer assembly 16 is shown to include an inner bracket half 92, an outer bracket half 94, and a bracket bolt 96. The inner bracket half 92 includes inner bracket alignment fins 98 and an inner bracket spacer fin 100 that is peφendicular to the inner bracket alignment fins 98. The outer bracket half 94 similarly includes outer bracket alignment fins 102 and a peφendicular outer bracket spacer fin 104. The outer bracket spacer fin 104 is longer than the inner bracket spacer fin 100 (this is best seen in Fig. 10). The inner bracket spacer fin 100 is provided with a threaded, bolt receiving aperture 106, while the outer bracket spacer fin 104 has a non-threaded, bolt receiving aperture 108. Analogously to spacer/tensioning bracket 62, both sets of inner and outer bracket alignment fins (98 and 102) are present in parallel opposing fashion when the inner and outer bracket halves (92 and 94) are mated together with bracket bolt 96. The preferred inner and outer bracket spacer fins (100 and 104) have a thickness of approximately 0.95 cm (0.38 in) to allow for a mortar joint 52 of at least 0.64 cm (0.25 in) thickness. Referring now to the cross-sectional view of Fig. 10, in which is shown both a complete and a partial spacer assembly 16, the inner and outer bracket halves (92 and 94) are assembled together with the bracket bolt 96 and then positioned over a wall unit top surface 28 so that the inner and outer bracket alignment fins (98 and 102) straddle the wall unit side wall 36, the inner bracket half 92 being on the cavity 44 side of the wall unit 12. When a second wall unit 12 is stacked on top of the first wall unit 12, the wall unit side wall 36 of the upper wall unit 12 is likewise inserted into opposing inner and outer bracket alignment fins (98 and 102). The distance between opposing inner and outer bracket alignment fins (98 and 102) is just sufficient to allow insertion of the wall unit side walls 36, thus the wall unit side walls 36 of the two wall units 12 are forced into vertical alignment and precision stacking may be achieved. Once the wall units 12 have been stacked, mortared, and grouted, the bracket bolt 96 is removed together with the outer bracket half 94. The inner bracket half 92 is left in place (as shown at the left of the drawing) to maintain the desired spacing for the mortar joint 52. A simple patch of mortar 80 is applied to fill in the void in the mortar joint 52 remaining from removal of the outer bracket half 94. Thus, the inner bracket half 92 is hidden from view. Like the combination spacer/tensioning assembly 14, the spacer assemblies 16 (where used alone) are typically incorporated at increments of 4.6 m (10 to 15 ft) along the length of a wall unit 12. Notches similar to recessed and hollowed notches (78a and 78b) may also be utilized in conjunction with the spacer assembly 16, together with other automatic alignment methods as described previously for spacer/tensioning bracket 62. Although the spacer assembly 16 does not have the wall tensioning capability of the spacer/tensioning assembly 14, since it is designed to interact with only one of the wall unit side walls 36 at a time, the spacer assembly 16 is more flexible in other regards. Specifically, the inner and outer bracket alignment fins (98 and 102) of the mated spacer assembly 16 are able to straddle both a wall unit side wall 36 and a wall unit end wall 110. Thus, the spacer assembly 16 can be used to align not only the wall unit side walls 34, but also the wall unit end walls 110, unlike the spacer/tensioning bracket 62. Furthermore, as shown in Fig. 1, the outer bracket half 94 of the spacer assembly 16 may be modified to integrate a wall brace fin 112. In the modified spacer assembly, which is given the reference numeral 17 in the drawing, the wall brace fin 112 extends peφendicularly outward from the outer bracket half 94 and includes a wall brace fin aperture 114. The modified spacer assembly 17 may be used to assist in the bracing of a wall 26 during its construction when the height of the wall 26, or the prevailing wind conditions, are such that the use of external bracing is mandated to prevent the wall from leaning or falling over. External bracing 115, such as a rod or beam, may be conveniently attached to the wall brace fin 112 via either bolting or tying with a cable through the wall brace fin aperture 114. In addition, the wall brace fin 112 may be further employed to assist in the alignment of consecutive lengths of walls 26. The situation will often exist where it will be required that two or more walls 26 be placed end-to-end in order to construct a structure having a sufficiently long overall wall length. And even where it is possible to pre-cast wall units 12 of sufficient length for the particular application at hand, building code requirements may mandate that vertical "breaks" or joints be incoφorated at specific distances along the length of a wall 26 to help maintain the integrity of the wall 26. In either event, the modified spacer assembly 17 having the wall brace fin 112 can be used to assist in plumbing adjacent wall 26 sections. As with the unmodified version of the spacer assembly 16, the outer bracket half 94 (which incoφorates the wall brace fin 112) is removed after grouting of the wall and a simple patch of mortar 80 applied to fill the resulting void. The modified spacer assembly 17 may be placed anywhere along a horizontal mortar joint 52 to meet a wide range of job- specific requirements. It is also understood that the above-described embodiment of the spacer assembly 16 is only one of many possible embodiments. Another prominent example would be a purely internal spacer assembly of unitary construction essentially identical to the spacer/tensioning bracket 62, but without the bar receiving aperture 68. Of course, the spacer/tensioning brackets 62 may be used as is, with the bar receiving aperture 68 simply being ignored. All of the various embodiments of the spacer/tensioning bracket 62 and the spacer assembly 16 may be made of steel, plastic, or other structural material. As mentioned previously, the spacer assembly 16 may be used alone or in conjunction with the spacer/tensioning assembly 14. Where horizontal rebar 90 (and wall bar 24) is employed, the spacer assembly 16 and/or spacer/tensioning assembly 14 may also be used, as shown in Fig. 1, in conjunction with tensioning assembly 18. As illustrated in the exploded view of Fig. 11, the tensioning assembly 18 includes a rebar bracket 116, a tensioning washer 64, and -75- a tensioning nut 66. The rebar bracket 116 includes a wall bar receiving aperture 118 and a rebar receiving notch 120 which traverses the width or length of the rebar bracket bottom surface 122. Referring to both Fig. 11 and the cross-sectional view of Fig. 10, the rebar bracket 116 fits over the wall bar 24 with the wall bar 24 passing through the wall bar receiving aperture 118 and the rebar receiving notch 120 fitting onto the horizontal rebar 90. As indicated previously, the horizontal rebar 90 lies within passage 86. In the construction system 10 of the preferred embodiment, rebar guide notches 124 are precast or field-cut into the cavity wall top surfaces 40 to assist in the positioning ("registering") of the rebar 90 and to further increase the structural integrity of the resulting wall 26. The tensioning washer 64 and tensioning nut 66 are subsequently threaded onto the wall bar 24 and are tightened such that the rebar bracket 116 exerts a downward force on the wall unit 12 via the registered horizontal rebar 90, thereby tensioning the wall unit 12 onto the foundation 22 or a wall unit 12 directly below. The ability to employ the various combinations of the different spacer and tensioning assemblies (14, 16, 17 and 18) gives the construction system 10 of the preferred embodiment great versatility in application. While the above disclosure describes the use of the wall units 12 only in terms of vertical applications (i.e., the building of walls), the "wall" units 12 may just as easily be used in similar fashion for horizontal applications such as floors and decks (in which cases the wall unit side surfaces 32 would face upward and downward). Moreover, the nature of the wall units 12 is such that an individual wall unit 12 may be employed singularly to function as a beam. Applications include, among others, a beam for spanning an opening such as a large doorway, or a grade beam for a pier and grade-beam foundation. To use the wall unit 12 in the capacity of a beam, the wall unit 12 is conveniently placed upright on a flat piece of wood or similar surface and concrete is poured within the cavities 44. Typical beam applications require a large amount of reinforcement, and the recessed nature of the cavity walls 38 permits a larger amount of reinforcing steel and concrete to be added than is possible with existing CMU's. In addition to the preceding and above mentioned examples, it is to be understood that various other modifications and alterations with regard to the types of materials used, their method of joining and attachment, and the shapes, dimensions and orientations of the components as described may be made without departing from the invention. Accordingly, the above disclosure is not to be considered as limiting and the appended claims are to be inteφreted as encompassing the entire spirit and scope of the invention. INDUSTRIAL APPLICABILITY The modular precast construction block system 10 of the present invention is compatible with wall and foundation designs that would normally employ standard cast-in-place concrete walls. Implementation of the construction system 10 is simple compared to heretofore known methods capable of producing structures of comparable strength. Prior to delivery of the precast wall units 12, a layout crew sets wall lines. Using a relatively lightweight crane, wall units 12 are removed from the delivery truck and stacked over the wall bars 24, a bed of mortar 80 being laid down on the foundation first. Between the first course of wall units 12 and the foundation 22, structural shims are placed as needed, together with the modified spacer/tensioning brackets 62 having no lower alignment fins 72. In between each stacked wall unit 12, an installation crew places combination spacer/tensioning assemblies 14, spacer assemblies 16 and 17, extension assemblies 20, horizontal rebar 90, and/or tensioning assemblies 18 as needed. A bed of mortar 80 is also laid down. The wall units 12 are easily positioned atop one another because of the built-in alignment features of the various spacer assemblies 14, 16, and 17. As the wall 26 proceeds higher, the installation crew works atop a scissors lift, ladders, or scaffolding. Where necessary, external bracing 115 may be attached to the modified spacer assemblies 17. When stacking of the wall units 12 is complete, grout 84 is poured into the cavities 44 and the horizontal passages 86. Prior to pouring the grout 84, additional reinforcing steel may be placed into the vertically extending cavities 44, the structure of the wall units 12 allowing the resulting wall 26 to contain more reinforcing material than is possible with walls built using known CMU's. After the grout 84 has cured, any external bracing 115 and outer bracket halves 94 are removed and patches of mortar 80 applied. Unlike cast-in-place concrete methods, the construction system 10 is a very "clean" system. The present invention also completely eliminates the need to create forms on site. The inherent stability of structures created with the construction system 10 eliminates as well the need for a welded superstructure. The construction system 10 of the present invention is intended to be widely used in the construction industry as a quick, precise, cost effective and strength equivalent alternative to cast-in-place concrete structural elements. For these reasons and numerous others as set forth herein, it is expected that the industrial applicability and commercial utility of the present invention will be extensive and long lasting. MODULAR PRECAST CONSTRUCTION BLOCK SYSTEM TECHNICAL FIELD The present invention relates generally to the field of construction, and more particularly to construction systems implementing interconnecting precast forms to create buildings and other structures. BACKGROUND ART Shelter is a basic need, and human ingenuity has arrived at numerous sophisticated methods and materials to meets this need. Among the many methods are those using precast concrete units that are assembled to create a structure. These methods include construction systems incoφorating a wide range of precast unit design, from the simple design to the very complex. The most simple precast unit designs are those used in basic, concrete masonry. While concrete masonry units are easy to design, they can result in structures that are considered structurally inferior to those created with larger, reinforced concrete units. Smaller concrete masonry units can crack and chip as well. Working with small masonry units also requires a specialized labor force to implement. As a result, using such a building method can create high labor costs , and it can be difficult to find a qualified crew. More sophisticated construction systems use concrete columns, beams, and foundation member to create a superstructure. A beam and column joining assembly is set forth in U.S. Patent No. 4,583,336, issued to Shelangoskie et al. on April 22, 1986. A series of precast foundation elements are also present in the prior art. U.S. Patent No. 5,103,613 issued to Satoru Kinoshita on April 14, 1992 teaches foundation members interconnected by a binding member having mortises therein for receiving tenons on the bottom of a column. U.S. Patent No. 4, 124,963 issued to Tadayasu Higuchi on November 14, 1978 sets forth a precast unit for providing footing for a building. While the above patents describe a superstructure they provide no teachings on the construction of walls or the like. In addition, the precast units provide little flexibility in increasing structural integrity. Two U.S. Patents present precast units containing wall members. U.S. Patent No. 4,328,651 issued to Manuel Gutierrez dated May 11, 1982 presents a system having a number of precast units including footing boxes, grade beams, roof beams and a wall panel. The Gutierrez system sets forth an intricate system of interconnecting parts. The intricacies of design limit the flexibility of the system, however. The beams and wall panels would have to be formed to custom lengths and height in order to meet the needs of varying structures. In addition, the wall panels lack flexibility in increasing structural strength. The second patent is U.S. Patent No. 5,081,805 issued toM Omar A. Jazzar on January 21, 1992. This patent teaches precast units of half story height that include steel reinforcements. The Jazzar invention requires substantial lifting equipment, however, and is also limited in versatility. Building designs departing from the preformed dimensions require a second, expensive mold, or considerable custom work to arrive at the desired shape. Authors David A. Sheppard and William R Phillips illustrate unitary load-bearing or non- load-bearing precast panels in their book Plant-Cast Precast & Prestressed Concrete - A Design Guide. Third Edition, McGraw-Hill Inc., 1989, (see pages 311-13). The same book also illustrates the use of very large, precast, concrete "voided" bearing walls on page 340. The large bearing walls and precast panels, like those in the Gutierrez patent, must be custom formed, requiring large custom molds, a large site slab, and very large lifting equipment. In addition, the immense size of the walls makes them impractical for smaller construction projects. To the inventors' knowledge, no building system employing preformed members has been developed that provides versatility in design, can accommodate a variety of reinforcement designs, requires relatively small lifting equipment, and that provides for the rapid construction of buildings. DISCLOSURE OF INVENTION Accordingly, it is an object of the present invention to provide a construction system using preformed members that can be used to design a variety of building shapes. It is another object of the present invention to provide construction system using preformed members that can accommodate a wide range of reinforcement designs. It is still another object of the present invention to provide a construction system using preformed members that can rapidly construct buildings. It yet another object of the present invention to provide a construction system using preformed members that does not require a large amount of specialized erection equipment. It is still another object of the present invention to provide a construction system using preformed members that does not require a crew having specialized skills. It is yet another object of the present invention to provide a construction system using preformed members that includes built-in alignment aids. Still another object of the present invention is to provide a construction system using preformed members that is cost effective for residential and light-commercial projects. It is another object of the present invention to provide a construction system using preformed members with wall units that can be easily cut to size. Briefly, the preferred embodiment of the present invention is a modular precast horizontal construction block system including a foundation subsystem and a wall subsystem. The wall subsystem of the preferred embodiment includes precast, vertically stackable wall units, each having a number of vertical cavities. Once the wall units are stacked, the cavities can receive reinforcing grout, vertical reinforcement bars, or a combination of both. A shear tying assembly is provided for connecting horizontally adjacent wall units. Also included is a reinforcement bar extension assembly for increasing the vertical height of reinforcement bars, and a wall tensioning assembly for increasing the structural integrity of a wall created with the wall units and reinforcement bars. In the preferred embodiment, the wall units are designed to be stacked onto wall bars that extend upward from a foundation. Each wall unit is a generally rectangular solid with a number of vertical disposed in a row along the length of the wall unit. The wall units can be stacked with the reinforcement wall bars extending through the vertical cavities. If the wall bar is not of sufficient height, the reinforcement bar extension assembly can connect an extension bar to the end of a wall bar to extend the reinforcement bar structure. To increase wall stability and assist in the aligning the wall units, in the preferred embodiment, the bottom surface of each wall unit includes a downward extending key portions. Correspondingly, the top surface of each wall unit includes a channel of complementary shape to the key portion. The channel-key arrangement enables the wall units to be vertically aligned with one another when stacked. Grout is added to selected cavities to increase structural strength., if desired. In the preferred embodiment, a unique scaffolding assembly is provided that is particularly adapted to mate with, and be deployed along walls created with the wall units. The foundation subsystem of the preferred embodiment provides precast "T" spread footing type components, precast grade beam components, precast pier components, and precast vertical columns. In the preferred embodiment, the "T" footing components are shaped at a variety of angles that enable the "T" footing components to be joined together to create a variety of angled corners and tee joints. The "T" footing components are further designed to overlap onto one another by one "T" footing component providing an overlap portion, and a second component providing a ledge portion. The grade beam components are similar in design to the T footing components , being angled so as to be capable of forming a variety of angled connections. The grade beam components each include a number of vertical holes for receiving reinforcing bars provided by conventional cast-in-place foundations, or precast components of the present invention. The pier components are provided for concentrated load points in a foundation, and the column components provide for raised vertical load points. All the precast components of the foundation subsystem can be cast with vertical wall bars set therein. An advantage of the present invention is that it provides a construction system using preformed members wherein the preformed members may be stockpiled and cut and used as needed. A further advantage of the present invention is that it provides a construction system using preformed members that are quickly and easily assembled to create structures. Yet another advantage of the present invention is that it provides a construction system using preformed members of consistent, accurate dimensions. Still another advantage of the present invention is that it provides a construction system using preformed members that can be deployed in inclement weather. Yet another advantage of the present invention is that it provides a construction system using preformed members that include stock sizes that can cover a wide range of load requirements. Still another advantage of the present invention is that it provides a construction system using preformed members that can erect structures using smaller crews. Another advantage of the present invention is that it provides a construction system using an easily deployed, custom scaffold assembly. Yet another advantage of the present invention is that is provides a construction system using preformed member that generates very little debris. Still another advantage of the present invention is that it provides a construction system using preformed members that does not require a superstructure. These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the several figures of the drawing. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a fanciful isometric, cut away view of the preferred embodiment of the present invention; Fig. 2 is a side view of a wall unit of the preferred embodiment; Fig. 3 is an end cross sectional view of a cavity in a wall unit of the preferred embodiment; Fig. 4 is an end cross sectional view of a cavity wall of the preferred embodiment; Fig. 5 is a side cross sectional view of two wall units joined by a shear connecting bar connection of the preferred embodiment; Fig. 6 is an exploded view of a wall bar and wall bar extension assembly of the preferred embodiment; Fig. 7 is an exploded view of the wall tensioning assembly of the preferred embodiment; Fig. 8 is a side cross sectional view of a wall built with the preferred embodiment; Fig. 9 is an end cross sectional view of an alternate wall unit; Fig. 10 is a side cross sectional view of a grade beam application of the wall unit of the preferred embodiment; Fig. 11 is a partially cut away isometric view of the "T" footing members of the preferred embodiment; Figs. 12A-12C are top plan views of three examples of "T" footing member pairs of the preferred embodiment; Fig. 13 is a partially cut away isometric view of the grade beam members of the preferred embodiment; Figs. 14A-14C are top plan views of three examples of grade beam member pairs of the preferred embodiment; and Fig. 15 is a partially cut away isometric view of a pier member and a column member of the preferred embodiment. BEST MODE FOR CARRYING OUT INVENTION The best presently known mode for carrying out the invention is a modular precast construction block system and is set forth in Fig. 1 and designated by the general reference character 10. The preferred embodiment 10 includes a variety of different precast building blocks adapted to interconnect with each other in a variety of configurations allowing for a versatile range of building designs. The preferred embodiment 10 includes elements aimed at creating building walls and/or foundations. As shown in Fig. 1, the preferred embodiment 10 can be conceptualized as having two subsystems, a wall subsystem 12 and a foundation subsystem 14. In the preferred embodiment 10, the wall subsystem 12 includes the necessary components to create vertical structures. It is noted that the foundation subsystem 14 includes components to create a variety of foundation designs, and Fig. 1 illustrates only one type of foundation component. Additional aspects of the various foundation subsystem 14 components will be discussed at a later point herein. The wall subsystem 12 of the preferred embodiment 10 is set forth in detail in Figs. 1-8. Referring now to Fig. 1, the wall subsystem 12 of the preferred embodiment 10 is shown to include a number of wall units 16, a shear connecting bar assembly 18, a wall bar extension assembly 20, and a wall tensioning assembly 22. As illustrated in Fig. 1, the foundation subsystem 14 provides a number of upwardly projecting wall bars 24 that are received by the wall subsystem 12. As illustrated in Fig. 1, the wall units 16 of the preferred embodiment 10 are designed to be stacked, one on top of each other, to create vertical, structural walls 26. The wall unit 16 of the preferred embodiment 10 is set forth in detail in Figs. 2-4. As shown in the side elevational view of Fig. 2 and the end cross sectional view of Fig. 3, the wall units 16 have a generally rectangular solid shape that includes a wall unit top surface 28, a wall unit bottom surface 30, two wall unit side surfaces 32, and two wall unit end surfaces 34. As shown in the various figures, the wall unit side surfaces 32 are considerably longer than the wall unit end surfaces 34. Each wall unit 16 is an integral molded structure having two rectangular, parallel, opposing wall unit side walls 36. The wall unit side walls 36 are joined by a number of cavity walls 38. As best illustrated in Figs. 1 and 4, the cavity walls 38 are peφendicular to, and integral with, the wall unit side walls 36. The resulting structure creates a number of vertically extending cavities 40 within the wall unit 16. As best shown in Fig. 3, each cavity 40 extends all the way through the wall unit 16, opening into both the wall unit bottom surface 30 and the wall unit top surface 28. The molded design of the wall unit 16 provides structural integrity while at the same time, due to the cavities 40, reduces the weight of the wall unit 16. Reduced weight allows for rapid erection of vertical walls 26 structures with only relatively small lifting equipment. In the preferred embodiment 10 each wall unit 16 is precast at a discrete length but can be quickly and easily cut "on site" to fit any length requirement. In the preferred embodiment 10, the wall units 16 are specifically shaped to aid in alignment and stacking. As shown in Figs. 1, 3 and 4, the wall unit top surfaces 28 include a horizontally disposed alignment channel 42. The alignment channel 42 of the preferred embodiment 10 is formed by identical, downward indentations 44 in each of the cavity walls 38. As is best illustrated in Figs. 3 and 4, each of the indentations 44 includes two sloped channel sides 46 and a channel bottom 48. Corresponding to the indentation 44 in each cavity wall 38 is a key portion 50 that extends below the wall unit side walls 36. The key portion 50 has a complementary shape to the indentation 44, having two sloped key sides 52 and a key bottom 54. As is best illustrated in Fig. 1, when stacked, the key portions 50 of one wall unit 16 fit within the indentations 44 of the wall unit 16 below. Because each wall unit 16 is precast from a precision mold in a controlled process, the tolerances of critical features in the wall unit 16 shape, such as the indentations 44 and the key portions 50, are maintained, which ensures repeatable, precision stacking of consecutive wall units 16. Within each wall unit 16 of the preferred embodiment 10 is a reinforcement structure 56. The reinforcement structure 56 is illustrated in the partial cutaway view of Fig. 1 and the cross sectional views of Figs. 3 and 4. Disposed within each wall unit side wall 36 are three parallel, horizontal tension cables 58. The tension cables 58 are pretensioned and cast in place when the wall units 16 are formed. The tension cables 58 place the entire wall unit 16 under tension when formed, which adds to the structural integrity of the wall unit 16 and reduces undesirable cracking and spalding. In addition to the tensioning cables 58, the reinforcement structure 56 of the preferred embodiment 10 also employs reinforcing stirrups 60. Each stirrup 60 is disposed within a cavity wall 38 and wraps around the tension cables 58. The tension cables 58 and stirrups 60 of the preferred embodiment 10 are constructed of steel. One skilled in the art would recognize that the number and type of tensioning cables 58 and stirrups 60 can vary according to desired wall unit 16 strength and material. It would also be recognized that while the preferred embodiment 10 includes the reinforcement structure 56, such a design is not critical to the invention 10. Wall units 16 without tensioning cables 50 and/or stirrups 52 may be employed where appropriate for the load and structural requirements of the application. In the preferred embodiment 10 the wall units 16 are composed of fiber-reinforced mesh concrete mix. One skilled in the art would arrive at a number of variations in the material used to create the wall units 16 according to required strength and anticipated climate. The present inventors anticipate including, in addition to structural additives, color additives and/or water proofing additives. Of course, it is understood that wateφroofing and coloring could be surface applied as well. As illustrated in Fig. 1, and best set forth in the cross sectional view of Fig. 5, horizontally adjacent wall units 16 of the preferred embodiment 10 are connected via the shear connecting bar assembly 18. The shear connecting bar assembly 18 includes two tie notches 62, a tie bar 64, and a cavity fill 66. As best shown in Fig. 5, the tie notches 62 are set within opposing joining walls 68. In the example illustrated in Figs. 1 and 5, the joining walls 68 are the adjacent side wall 36 and cavity wall 38 of adjoining wall units 16. As the wall units 16 are abutted against one another, the tie notches 62 are aligned and the tie bar 64 disposed within the tie notches 62. As best shown in Fig. 5, the tie bar 64 has an inverted "U" shape with two vertical tie portions 70 joined by a horizontal tie portion 72. The tie bar 64 is arranged with the horizontal tie portion 72 set within the tie notches 62 and the vertical tie portions 70 extending downward into adjacent cavities 40. The adjacent cavities 40 are subsequently filled with the cavity fill 66 which completes the shear connecting bar assembly 18. In the preferred embodiment 10 it is intended for the tie notches 62 to be cut into the appropriate locations on adjoining wall units 16 at the construction site. It is understood however, that such a feature could be incoφorated into the precast process to provide for wall units 16 formed with integral tie notches 62. While the views of Figs. 1 and 5 illustrate the shear connecting bar assembly joining two peφendicular wall units 16 it is understood that the shear connecting bar assembly 18 may also be used for connecting wall units 16 arranged end-to-end or at angles other than ninety degrees. Along the same lines, the wall unit end surfaces 34 can be prefabricated at a variety of angles to add to versatility in structure design. As mentioned previously, in the preferred embodiment 10, the foundation subsystem 14 provides a number of vertically disposed reinforcing wall bars 24. Referring once again to Fig. 1, it is shown that the wall units 16 are stacked onto foundation subsystem 14 with the wall bars 24 threaded through the cavities 40 within the wall units 16. While the incoφoration of wall bars 24 provides for walls 26 of increased strength, it is understood that walls 26 can also be built that do not have wall bars 24 by simply stacking the wall units 16. When the wall units 16 are stacked structural integrity can be increased by filling selected cavities 40 with grout 75. It is understood that when the wall units 16 are vertically stacked, the cavities 40 of wall units 16 can be aligned, allowing the grout 75 to stretch the entire vertical length of the wall 26. When wall bars 24 are employed, as shown in Fig. 1, the wall tensioning assembly 22 and/or wall bar extension assembly 20 can be provided to add structural strength, flexibility to design, and to improve the speed and ease in which buildings can be constructed. The wall bar extension assembly 20 and wall tensioning assembly 22 are set forth in detail in Figs. 6-8. Fig. 6, which is a blown up portion of Fig. 1, sets forth an exploded view of the wall bar extension assembly 20 and an associated wall bar 24. The wall bar extension assembly 20 includes an extension bar 74 and a bar coupler 76. Both the wall bar 24 and the extension bar 74 are shown to be threaded, and each includes two bar ends 78. The bar coupler 76 includes a threaded coupler aperture 80 for receiving the bar ends 78 of both the wall bar 24 and the extension bar 74. The wall bar extension subassembly 20 is intended to, in essence, provide a vertical expansion to the wall bar 24. This aspect is advantageous in the event the wall units 16 must be stacked higher than the total vertical height of the wall bars 24. By using the wall bar extension assembly 20 extension bars 74 may be added to as great a height as is required for the anticipated structure. In addition to adding structural integrity, the wall tensioning assembly 22 allows for the wall units 16 to be securely attached to the foundation subsystem 14 without additional bracing. As illustrated in the exploded view of Fig. 7, the wall tensioning assembly 72 of the preferred embodiment 10 includes an anchor plate 82, an anchor washer 84, and an anchor nut 86. The wall tensioning assembly also includes anchor notches 88 set within the wall unit 16. The wall tensioning assembly 22 as shown in Fig. 7 to be used in conjunction with an extension bar 74. It is understood that the design of the tensioning assembly 22 is equally applicable for use with a wall bar 24. The extension bar 74 is shown extending through an anchor cavity 90 within in the wall unit 16. The anchor cavity 90 is essentially identical to the other cavities 40, varying only in the inclusion of the anchor notches 88. The anchor plate 82 includes a bar receiving aperture 92, and two shaped anchoring ends 94. The anchoring ends 94 are designed to mate with the anchor notches 88 within the wall unit 16. The anchor plate 82 fits over the extension bar 74 with the extension bar 74 passing through the bar receiving aperture 92 and the anchor ends 94 mating with the anchor notches 88. The anchor washer 84 and anchor nut 86 are subsequently threaded onto the extension bar 74 and can be tightened to tension the wall unit 16 in a downward direction onto the foundation subsystem 14 or a wall unit 16 directly below. The bar receiving aperture 92 of the preferred embodiment 10 is slot shaped, which has been found by the inventors to facilitate the placement of the anchor plate 82 by creating a wider area for the extension bar 74 to fit within. The anchor notches 88 of the preferred embodiment 10 are precast into the wall units 16 at selected cavities 40 to create anchor cavities 90. While the preferred embodiment 10 sets forth an anchor plate 82 and corresponding anchor notches 88 of particular shape, it is understood that one skilled the art could arrive at a number of equivalent structures and the particular shape of the preferred embodiment 10 should not be considered limiting. Referring now to the cross sectional view of Fig. 8, the wall bar extension assembly 20 and wall tensioning assembly 22 are shown in assembled form. Fig. 8 illustrates three wall units 16 vertically stacked, including a bottom wall unit 16 A, a middle wall unit 16B and a top wall unit 16C. As set forth in the figure, the wall bar 24 extends upward, only halfway through the middle wall unit 16B. By employing the wall bar extension assembly 22, the extension rod 74 can be added to extend through the remaining portion of the middle wall unit 16B and the entire top wall unit 16C. While Fig. 8 illustrates a wall bar 24 of a particular vertical height, it is understood that the particular length of the wall bars 24 is not critical. Wall bars 24 and extension bars 74 can be cut, and extension bars 74 added until the desired vertical height is achieved. Fig. 8 also shows three wall tensioning assemblies (22A, 22B and 22C), one for each wall unit (16A, 16B and 16C). The wall tensioning assemblies (1 A, 16B and 16C) are illustrated in the assembled position. As mentioned previously, the tensioning effect provides structural integrity to the wall 26 and therefor, no additional bracing is required, as is necessary in prior art systems. While the example of Fig. 8 sets forth a wall tensioning assembly 22 for each wall unit 16, it is understood that fewer or greater numbers wall tensioning assemblies 22 can be employed per wall 26. As just one example, a wall 26 could employ only one wall tensioning assembly 22 in the very top most wall unit 16C. As shown in Figs. 1, 3-5 and 8, in the preferred embodiment 10 it is anticipated that selected wall units 16 can be produced with covering faces 96 attached thereto for decorative effects. As is best shown in Figs. 3 and 4, each covering face 96 is a composite structure having a decorative layer 98 and an insulation layer 100. As illustrated in Fig. 8, the covering faces 96 are secured to the wall units 16 by a number of panel tie connectors 102. The decorative layer 98 allows any number of architectural finishes to be applied to the wall units 16 adding versatility to the aesthetic appearance of structures created with the preferred embodiment 10. The insulation layer 100 ensures that differences in thermal expansion between the decorative layer 98 and the insulation layer 100 will not result in stress fractures in the decorative layer 98. One skilled in the art would recognize that covering faces 96 do not have to be multilayered, and that side surfaces 32 of the wall units 16 themselves could be molded with various patterns and colors as desired. It is anticipated that covering faces 96 can also be formed with beveled edges to allow for wall units 16 joined at 90 degree or some other angular relationship. One skilled in the art would recognize that the wall units 16 could be precast with any variety of prior art hardware attachment designs for providing an attachment point for lifting cranes. Just one such example would be an anchor and recess plug combination. Fig. 9 illustrates an alternate wall unit design, designated as 916. The alternate wall unit is very similar to the wall unit 16 of the preferred embodiment 10, and to that extent those elements of the alternate wall unit 916 which are identical to those appearing in the preferred embodiment 10 will be referred to by a reference number incoφorating the original reference number with an initial digit "9". Fig. 9 presents a side cross sectional view of the alternate wall unit 916. Like that of the preferred embodiment 10, the alternate wall unit 916 includes two wall unit side walls 936 joined by integral, peφendicular wall unit cavity walls 938, creating a number of cavities 940 within the wall unit 916. The alternate wall unit 916 departs from the preferred embodiment 10 in the shape of the wall unit side walls 936 which creates cavities 940 having non-vertical walls. As illustrated in Fig. 9, the side cross sectional aspect of the wall unit side walls 936 of the alternate wall unit 916 are not rectangular, as in that of the preferred embodiment 10, and instead includes opposed, negatively sloped cavity faces 104. The inventors have found this arrangement presents a unique advantage in hoisting procedures for the wall units 916. The negative slope of the cavity faces 104 allows for an expanding hoisting member to be inserted into one or more of the cavities 940, expand and engage the sloped cavity faces 104, allowing the wall units 916 to be hoisted thereby. The hoisting advantages of the alternate wall unit 916 eliminates the needs for complex rigging, or cast-in-place hoisting attachments. Referring once again to the preferred embodiment 10 set forth in Fig. 8, it is shown that the wall subsystem 12 of the preferred embodiment 10 includes a scaffold assembly 106 that is particularly adapted to work with the wall units 16 of the preferred embodiment 10. As illustrated in cross section in Fig. 8, the scaffold assembly 106 includes a number of frame members 108 and safety wire 110. Each frame member 108 is a rigid, integral structure that includes an overhang portion 114, a support portion 116, and a railing portion 118. The overhang portion 114 is shaped to curve over and snugly engage the top most wall unit 16C of the wall 26 created with the precast construction block system of the present invention 10. The support portion 116 extends away from the frame member 108, peφendicularly to the wall 26. As shown in Fig. 8, the railing portion 118 extends upward from the support portion 116, ' opposite from the overhang portion 114. In the preferred embodiment 10, the frame members 108 are disposed in a row, at set intervals, along the entire wall 26. Because the row of support portions 116 do not, in themselves, provide adequate footing, a number of planks 120 are overlaid on the row of support portions 116, creating a solid flooring to support crew members. A protective enclosure is provided by the safety wire 110 strung between adjacent railing portions 118. The unique design of the scaffold assembly 106 of the preferred embodiment 10, eliminates the need for erecting conventional scaffolding, which is extremely time consuming. Referring once again to Fig. 1, it is recalled that in the preferred embodiment 10, the wall subsystem 12 rests upon, and interconnects with the foundation subsystem 14. It is understood that it is not necessary for the wall subsystem 12 to be used only with the foundation subsystem 14 provided by the preferred embodiment 10. Any foundation providing level, load bearing elements can be used, including cast-in-place foundations. If desired, cast in place foundations can be formed with wall bars 24. In the preferred embodiment 10, the spaces between the wall units 16 and the foundation subsystem 14 are filled by a bed of structural shim and mortar. It is noted that structural shim and mortar could also be used between vertically stacked wall units 16. As this method is well known in the art it will not be set forth in detail herein. Referring to Fig. 10, a foundation application of the wall subsystem 12 is set forth. Fig. 10 illustrates the use of a wall unit 16 as a foundation grade beam. As set forth in the figure, the wall unit 16 is situated upon two cast-in-place foundation piers 122 formed within the ground 124. Each of the cast-in-place foundation piers 122 was formed with a wall bar 24 in place. The wall bar 24 is received by the cavities 40 within the wall unit 16. The cavity 40 of the wall unit 16 that receives the wall bar 24 is filled with grout 75. The wall unit 16 can then be the load bearing element for more wall units 16, or if desired, support walls created from conventional methods and components. While the wall unit 16 of Fig. 10 is secured to the cast-in-place foundation piers 122 by grout 75 and wall bars 24, the wall tensioning assembly 22 could also be used in this application. Thus, although the present invention 10 can be conceptualized as including a wall subsystem 12 and a foundation subsystem 14, components of the wall subsystem 12 can be used to in the creation of foundations. As set forth in Fig. 1, the modular precast construction block system of the present invention, in the preferred embodiment 10, includes a foundation subsystem 14 in addition to the wall subsystem 12. Like the wall subsystem 12, the foundation subsystem 14 provides a wide variety of precast foundation members that are used according to the type of foundation desired. The various components of the foundation subsystem 14 of the preferred embodiment 10, are set forth in detail in Figs. 11-15 and are shown to include "T" footing members 126, pier members 128, grade beam members 130, and column members 132. Fig. 1 illustrates a continuous spread footing foundation design 134 composed of the "T" footing members 126 which are best set forth in Figs. 11 and 12A-12C. The "T H footing members 126 are precast, integral units each having a T foot base portion 136 and an upward extending T foot anchor portion 138. Each "T" footing member 126 terminates in two shaped T foot ends 140. The T foot base portion 136 is wider than the T foot anchor portion 138 giving the "T" footing members 126 an inverted T end cross sectional aspect. The shape of the "T" footing member creates opposing T foot ledges 142. The T foot ends 142 are best described by referring to Fig. 12. As shown in the figure the "T" footing members 126 are precast with complementary shaped T foot ends 140 where one "T" footing member 126 would include a foot end overlap 144 that matches the T foot ledge 142 of a corresponding T" footing member 126. In addition, the T foot ends 140 can be angled. Figs. 1, 11 12A each illustrate a 90-degree- comer footing pair 146. shaped to create a ninety degree comer in the continuous spread footing foundation design 134. One skilled in the art would recognize that this basic design can include any number of angled pairs. Just a few of the possible examples are set forth in the various figures. Fig. 1, in addition to illustrating a 90-degree-corner footing pair 146, also illustrates a 90-degree-tee-joint footing pair 148. Two additional variations are set forth in Figs. 12B and 12C, which illustrate a 135-degree-corner footing pair 150 and a 45-degree-tee-joint footing pair 152, respectively. In the preferred embodiment 10, the "T" footing members 126 are precast in left and right 45 degree, and 90 degree shaped T foot ends 140. As is best set forth in Fig. 11, the "T" footing members 126 of the preferred embodiment 10 also include cast in place wall bars 24 and connecting apertures 154 which extend through the T foot anchor portion 138. The internal design of the "T" footing members is best described by referring to the cutaway view of Fig. 11. Like the wall units 16 of the wall subsystem 12, the "T" footing members 126 of the preferred embodiment 10, include tensions cables 58 and stirrups 60 to provide additional structural integrity to the "T" footing members 126. As in the case of the wall units 16, the tension cables 58 and stirrups 60 can be omitted from the precasting process if desired. As illustrated in Figs. 1, 11 and 12, "T" footing members 126 of the preferred embodiment 10, are joined by a connecting assembly 156. The connecting assembly 156 is best described in conjunction with Fig. 11. The connecting assembly 156 includes connecting plates 158, connecting bolts 160, and connecting nuts 162. Each connecting plate 158 is pre-shaped to match the angle of the "T" footing members 126 to be joined. Each connecting plate 158 includes a number of bolt apertures 164 that are formed so as to be aligned with the connecting apertures 154 of the "T" footing members. The connecting bolts 160 are threaded through the bolt apertures 164 and corresponding connecting apertures 154. The connecting bolts 160 secure the connecting plate 158 to the "T" footing members 126, and consequently secure the "T" footing members 126 together. As would be clear to one skilled in the art, the connector apertures 154 and connector plates 158 can be shaped for "T" footing member 126 connections of various angles. Just three such examples are illustrated in Figs. 12A-12C. One skilled in the art would recognize that the connecting assembly could include threaded studs that are cast within the "T" footing members and thus eliminate the need for connector apertures 154 and connector bolts 160. It is understood that while used only for the "T" footing members 126 in the preferred embodiment 10, the connecting assembly 156 could also be used to join other precast components of the present invention 10, including the wall units 16 of the wall subsystem 12. The grade beam members 130 of the foundation subsystem 14 are illustrated in Figs. 13 and 14. The grade beam members 130 are adapted to be used in combination with cast-in-place- foundation piers 122, similar to the foundation design employing wall units 16 set forth in Fig. 10. As illustrated in Fig. 13, the grade beam members 130 are generally rectangular solid structures having a number of vertical beam rod apertures 166 therethrough. The vertical beam rod apertures 166 serve as receptacles for upward extending wall bars 24 that are precast into the cast-in-place foundation piers 122. The beam rod apertures 166 are filled with grout 75 to secure the grade beam members 130 to the cast in place foundation piers 122. Very similar to the "T" footing members 126, the grade beam members 130 each have two grade beam ends 168 which can be angled to create angled beam pairs. The views of Figs. 13 and 14A illustrate a 90- degree-corner beam pair 170. A 135-degree-corner beam pair 172 is illustrated in the top plan view of Fig. 14B, and a 45-degree-tee beam pair 174 is illustrated in Fig. 14C. It is noted that, like the "T" footing members 126, any variety of angled connections can be formed. It is further noted that like the wall units 16 and "T" footing members 126, the grade beam members 130 can be formed with horizontal connector apertures 154 and be joined by a connector assembly 156. Fig. 15 illustrates in detail, the pier member 128 and the column member 132 of the foundation subsystem 14. In the partially cut away isometric view, the column member 132 is depicted as attached to, and extending upward from, the pier member 128. It is understood that both the pier member 128 and the column member 132 can be used with the other members of the foundation subsystem 14, as well as with conventional foundation designs. The combination of pier member 129 and column member 132 in Fig. 15 is intended for illustrative puφoses only. The pier member 128 of the preferred embodiment 10 is an integral, precast structure that includes a pier base portion 176 and a generally cubic pier anchor portion 178. The pier anchor portion 178 extends upward from, and is smaller than, the pier base portion 176. As shown in the cut away view, the pier member 128 of the preferred embodiment is reinforced with a pier reinforcement bar 179 which is cast in place for added strength. Also cast in place upon formation, is a vertically disposed wall bar 24 serving the same function as the wall bars 24 of the other precast foundation members. The column member 132 of the preferred embodiment 10, is a vertically disposed rectangular solid structure, having four column sides 180 a column top 182 and a column bottom 184. Running vertically through the column member 132 is a column rod aperture 186 that opens into the column top 182 and column bottom 184. The column rod aperture 186 is adapted to receive a reinforcement bar (the wall bar 24 of the pier member 128 in Fig. 15) and subsequently be filled with grout 75. Precast within the column member 132 are vertically disposed prestressed tension cables 58. The column member 132 provides an elevated load bearing point for structure designs, and is particularly adapted for structures built on steep slopes. While the column member 132 has a rectangular solid shape, it is understood that cylindrical or other shaped column members 132 can be precast and utilized in the preferred embodiment 10. Various modifications may be made to the invention without altering its value or scope. All of the above are only some of the examples of available embodiments of the present invention. Those skilled in the art will readily observe that numerous other modifications and alterations may be made without departing from the spirit and scope of the invention. Accordingly, the above disclosure is not intended as limiting and the appended claims are to be inteφreted as encompassing the entire scope of the invention. INDUSTRIAL APPLICABILITY The modular precast construction block system 10 of the present invention is intended to be widely used in the construction industry as a quick, precise, cost effective alternative to cast-in-place structural elements. The precast wall units 16, "T" footing members 126, pier members 128, grade beam members 130, and column members 132 are each interchangeable and ' compatible with standard wall, and/or foundation designs. The wall units 16 of the preferred embodiment 10 are intended to be produced in standard sixty foot lengths, and cut on site to smaller lengths if necessary. The wall units 16 are also intended to be produced in standard heights of 18", 24" and 30". Typical widths will correspond to a standard cast in place wall thickness of 8", 10" or 12". The intended sizes of the wall units are particularly advantageous in that they are long enough to create large structures, yet do not require an on site slab necessary for large cast on-site systems. The reduced weight of the components and relatively small lifting equipment required for deployment result in a system that does not require a minimum site size. The wall subsystem 12 or the foundation subsystem 14 can be employed together, or separately. The wall subsystem 12 is intended to be used for a number of applications, including foundation designs. The inventors consider the wall subsystem 12 particularly adaptable in the construction of underground parking structures, basements, retaining walls, building walls, sound walls, and fences. Just a few of the foundation applications of the wall subsystem 12 are stems/spread footing foundation designs, and as grade beams in pier/grade beams foundation designs. When the wall units 16 are disposed sideways, that is with the wall unit side surfaces 32 facing upward and downward, the wall subsystem 12 can also be used to create a floor. The wall units 16 are also adaptable for use in individual applications, as a span beam and or wall opening beam. In the preferred embodiment 10 of the present invention he precast members of the foundation subsystem 14 and wall subsystem 12 can be stockpiled for immediate use or produced parallel with the construction job so as to provide a "just-in-time" production method. When the various precast members are stockpiled, the preferred embodiment 10 can be immediately ready for any construction applications requiring immediate response, dispensing with the coordination between materials suppliers and specialized crew members that are required for conventional construction methods. When stockpiled there is no need to create new concrete molds, reducing the initial capital required for any particular job. When used in a "just-in-time" supply method, the preferred embodiment 10 is a cost effective, extremely efficient construction system 10 that eliminates waste caused by suφlus production. The present invention is intended to be used during all times of the year. Because no concrete pouring is required, inclement weather does not have an impact on the modular precast construction block system 10. In addition, unlike cast-in-place methods, the preferred embodiment 10 is a very "clean" system, as no poured concrete is required. The present invention also completely eliminates the need to create forms on site. The elimination of the custom materials and labor necessary for on site forms provides additional cost savings. The modular precast construction block system of the present invention 10 may be utilized in any application where cast in place walls or other structures are used. It provides for decreased construction time and requires curing only when grout 75 or other cavity fill 66 is required. The inherent stability of structures created with the present invention eliminates the need for a welded superstructure. Thus, as buildings are erected with the present system 10 the specialized labor force and specialized inspection required for other construction systems can be avoided with the present invention. Since the modular precast construction block system 10 of the present invention may be readily constructed and may be adapted for a wide range of construction applications, it is expected that it will be acceptable in the industry as an effective alternative present methods. For these and other reasons, it is expected that the utility and industrial applicability of the invention will be both significant in scope and long-lasting in duration.

Claims: * IN THE CLAIMS What is claimed is: 1. A modular construction system comprising: a plurality of block units, each said block unit being precast of concrete, each said block unit having a length, a width, a height, a top surface and a bottom surface, the length being substantially greater than the width, each said block unit further having end walls, a pair of side walls extending the length of each said block unit, and a plurality of cavity walls disposed between the pair of side walls and integral therewith, each side wall having a width and containing a reinforcement structure, each cavity wall having a height and a top surface, at least one cavity wall having a height that is less than the height of said block units, the cavity walls and the pair of side walls defining a plurality of cavities, said block units being arranged with the bottom surface of a first said block unit opposing the top surface of a second said block unit, the cavity walls of the arranged said block units defining a plurality of first passages extending the height of said block units and one or more second passages extending longitudinally between two or more cavities; and spacer means for providing a joint space between the top and bottom surfaces of said block units for placement of bonding material. 2. The construction system of claim 1 wherein the reinforcement structure is at least one longitudinally disposed, prestressed reinforcement wire. 3. The construction system of claim 1 wherein at least one of the first and second passages is filled with cementitious material. 4. The construction system of claim 1 further including a reinforcing bar extending froπr a base structure and into the cavities of one or more said block units. 5. The construction system of claim 4 wherein the reinforcing bar is threaded and further including a threaded extension bar and a threaded coupler, the coupler threadably engaging the reinforcing bar and the extension bar and creating an extended reinforcing bar thereby. 6. The construction system of claim 4 further including tensioning means. 7. The construction system of claim 6 wherein the reinforcing bar is threaded and wherein the spacer means and tensioning means are integral and include a bracket and a nut, the bracket having a length and a thickness, the length being sufficient to span the distance between the pair of side walls, the thickness providing the cementitious joint space, the bracket further having an aperture through which the reinforcing bar is received, the nut threadibly engaging the reinforcing bar, torquing force being applied to the nut to tension the bracket onto the top surface of a first said block unit and thereby tension the first said block unit onto a second said block unit or the base structure. 8. The construction system of claim 7 wherein the bracket further includes alignment fins, the alignment fins insertably fitting in close relation between the pairs of side walls of said block units and aligning said block units thereby. 9. The construction system of claim 8 wherein the bracket has the feature of being aerodynamically shaped. 10. The construction system of claim 6 wherein the reinforcing bar is threaded and further including a reinforcing rod longitudinally disposed within the second passage and lying on the top surface of the cavity walls of a first said block unit and wherein the tensioning means includes a bracket and a nut, the bracket having a notch into which the reinforcing rod is received, the bracket further having an aperture through which the reinforcing bar is received, the nut threadibly engaging the reinforcing bar, torquing force being applied to the nut to tension the bracket onto the reinforcing rod and thereby tension the first said block unit onto a second said block unit or the base structure. 11. The construction system of claim 10 further including the cavity walls having notches in the top surfaces thereof for receiving the reinforcing rod in predetermined alignment. 12. The construction system of claim 1 further including a reinforcing rod longitudinally disposed within the second passage and the cavity walls further having notches in the top surfaces thereof for receiving the reinforcing rod in predetermined alignment. 13. The construction system of claim 1 further including alignment means for aligning said block units. 14. The construction system of claim 13 wherein the alignment means and the spacer means are integral and include an inner bracket half and an outer bracket half removably joined together, the inner bracket half and the outer bracket half each having alignment fins and a spacer fin, the spacer fin providing the cementitious joint space, the side walls or the end walls of two said block units insertably fitting in close relation between the alignment fins and aligning said block units thereby . 15. The construction system of claim 14 wherein the outer bracket half further includes a brace fin for assisting in bracing and aligning said block units. 16. The construction system of claim 13 wherein the alignment means includes at least one of said side walls and said end walls having a notch, and further includes a fixture, the fixture being mateably received by the notch. 17. A spacing and registration system for use in stacking a first stackable construction unit on a second stackable construction unit, each said unit having end walls, opposing side walls and an interior cavity, with cavity members formed within said cavity and structurally extending intermediate said opposing side walls, said side walls having a discrete thickness and further having top and bottom surfaces, said cavity members being recessed from at least one of said top and bottom surfaces, the system comprising: one or more spacer means for placement on a top surface of at least one said side wall of said second stackable construction unit, each said spacer means including spacer fin means for occluding at least a portion of the associated top surface, such that, upon stacking, the bottom surface of said first stackable construction unit rests on the spacer fin means and a gap is formed intermediate the opposing top surface of said second stackable construction unit and the bottom surface of said first stackable construction unit, said spacer means having a small longitudinal dimension with respect to said construction units, such that a greater extent of the mortar gap is situated in locations where no said spacer means is placed than in locations where a said spacer means is placed; and bonding material for placement at least in the gap, so as to bond said stackable construction units together. 18. The spacing and registration system of claim 17 wherein: each said spacer means further includes at least one alignment fin, peφendicular to the spacer fin means, for interfacing with said side walls or said end walls to maintain lateral alignment between said first and said second stackable construction units. 19. The spacing and registration system of claim 18 wherein the spacer fin means has an extent sufficient to span the distance between said opposing side walls. 20. The spacing and registration system of claim 18 wherein the spacer fin means includes a first member and a second member, the first member and the second member being matably joined together, the second member being removable after said construction units are stacked. 21. The spacing and registration system of claim 20 wherein the second member includes wall brace fin means. 22. A method for building a structural wall comprising the steps of: (a) providing a plurality of elongated, precast concrete wall units, the wall units having a plurality of vertically disposed cavities, the wall units further having side walls containing prestressed reinforcing wires, the cavities being formed by the side walls and a plurality of recessed cavity walls integral with the side walls; (b) providing a foundation having a plurality of vertically extending, threaded wall bars; (c) placing a wall unit over the wall bars such that the wall bars extend through the cavities; (d) laying reinforcing rods on top of the cavity walls; (e) tensioning the wall unit onto the foundation or a lower wall unit with tensioning means that utilizes the wall bars and the reinforcing rods; (f) placing spacing means on top of the wall unit; (g) laying down a bed of mortar on top of the wall unit; (h) repeating steps (c)-(e), the stacked wall units creating a plurality of vertically and horizontally extending passages within the wall; and (i) pouring grout within the vertically and horizontally extending passages to create a monolithic wall. 23. A construction system for making a wall comprising: a plurality of wall units formed of precast concrete, each said wall unit having a top surface and a bottom surface and a pair of vertically disposed, opposing side walls, each side wall containing at least one prestressed reinforcing wire, each said wall unit further having a plurality of vertically disposed cavity walls integral with the side walls, the cavity walls being recessed from the top and bottom surfaces of said wall units, said wall units being vertically stacked to create a wall, said wall units having the feature of creating a plurality of contiguous vertically and horizontally extending grout receiving passages when stacked; and spacer means for providing a joint space between the top and bottom surfaces of said block units for placement of bonding material. 24. A construction building block system comprising: a plurality of stackable block units, each said block unit being precast of cementitious material, each said block unit having a length, a width, and a height, the length being substantially greater than the width, each said block unit further having a pair of side walls extending the length of each said block unit, and a plurality of cavity walls disposed between the pair of side walls and integral therewith, each side wall containing at least one pre-tensioned reinforcement wire to impart a prestressed character to each said block unit, the cavity walls and the pair of side walls defining a plurality of cavities. 25. The system of claim 24 wherein selected ones of the cavities are filled with grout. 26. The system of claim 24 further including each cavity wall having a height, the height of at least one cavity wall being less than the height of a said block unit for creating at least one horizontally extending passage when two said block units are stacked one upon the other. 27. The system of claim 24 further including at least one reinforcing stirrup precast within each said block unit and wrapping around said pre-tensioned reinforcement wires. 28. The system of claim 24 further including a plurality of vertically disposed reinforcement rods extending through the cavities of the stacked said block units. 29. The system of claim 28 further including an anchor system including a plurality of shaped notches within at least one of the pair of side walls and cavity walls, at least one horizontally disposed anchor plate, and tensioning means, the anchor plate being shaped to fit within the shaped notches and including a rod channel for receiving one of the reinforcement rods, the tensioning means forcing the anchor plate downward into the shaped notches. 30. The system of claim 24 further including each said block unit having a top surface and a bottom surface, the top surface having a top topology and the bottom surface having a bottom topology, the bottom topology being complimentary to the top topology such that said block units are vertically aligned when stacked. 31. The system of claim 24 further including each said block unit having a first side surface and a second side surface, and wherein at least one of the side surfaces includes a decorative design thereon. IN THE CLAIMS What is claimed is: 1. A building system, comprising: a plurality of precast wall units of a rectangular solid shape including a length, a width, and a height, the length being substantially greater than the height, each said wall unit including a vertically disposed first side wall, a vertically disposed second side wall, and a plurality of vertically disposed cavity walls, the side walls extending the length of the wall unit and the cavity walls defining the width of the wall unit, the cavity walls being integral with, and joining the side walls, the cavity walls and the side walls defining a plurality of wall cavities, said precast wall units being vertically stacked to create a vertical wall. 2. The building system of claim 1 wherein: selected wall cavities are filled with grout for added structural integrity. 3. The building system of claim 1 wherein: the side walls of each said precast wall unit includes a plurality of horizontally disposed, prestressed reinforcement rods. 4. The building system of claim 3 further including: at least one stirrup bar disposed within said precast wall unit, the stirrup bar disposed perpendicularly to the prestressed reinforcement rods, each one of the stirrup bars being a rectangular wrapped structure passing through one of the cavity walls around the prestressed reinforcement rods. 5. The building system of claim 1 further including: a plurality of vertically disposed reinforcement rods extending through the cavity walls of the stacked precast wall units. 6. The building system of claim 5 wherein: at least one of the reinforced rods includes a plurality of vertically disposed, threaded structural rods connected by a threaded coupling. 7. The building system of claim 5 further including: an anchor system including a plurality of shaped notches within at least one wall cavity of at least one precast wall unit, at least one horizontally disposed anchor plate, and tensioning means, the anchor plate being shaped to fit within shaped notches and including a rod channel for receiving one of the reinforcement rods, the tensioning means forcing the anchor plate downward into the shaped notches. 8. The building system of claim 5 further wherein: at least one reinforced rod extends upward from a foundation member. 9. The building system of claim 1 wherein: at least one pair of adjacent the cavity walls of horizontally adjacent, precast wall units are joined by shear connecting bar means. 10. The building system of claim 9 wherein: the shear connecting bar means includes a tie channel set within adjacent precast wall units and a shear tie, the shear tie having an inverted u-shape with two downward extending legs joined by a bridge portion, the bridge portion being disposed within the tie channel. 11. The building system of claim 1 further including: a scaffolding subassembly including a plurality of rigid scaffold members, each said scaffold member having an overhang portion for wrapping over the vertical wall and a crew portion connected to the overhang portion, the crew portion including a horizontal floor portion. 12. A precast vertical building block, comprising: a plurality of block members, each said block member having a top surface, a bottom surface, a first side surface, a second side surface, a first end surface and a second end surface, and a plurality of vertical cavities extending through the block member between the side surfaces, each vertical cavity opening into the top surface and the bottom surface, the block member including a plurality of prestressed cables precast therein, the prestressed cables disposed parallel to the side surfaces. 13. The precast vertical building block of claim 12 wherein: the top surface of each said block member has a horizontally disposed downwardly extending trough therein and the bottom surface has a downwardly projecting key portion, the trough of one said block member being shaped to receive the key portion of another block member thereon. 14. The building system of claim 13 wherein: the portions of block member separating adjacent vertical cavities are cavity walls, and the trough is defined by identical, downwardly extending notches in the cavity walls and the key portion is formed by downward extensions of the cavity walls. 15. The building system of claim 12 wherein: at least one of the side surfaces includes a decorative design thereon. 16. The building system of claim 15 wherein: the decorative design is formed by a covering face, the covering face including a decorative facing and an insulation layer attached to at least one of the side surfaces of said block member by a plurality of ties, the insulation layer being intermediate the decorative facing and the side surface. 17. A construction system, comprising: a reinforcing bar assembly having at least one vertically extending reinforcing bar, the reinforcing bar having an anchored lower end and a bar width; and a plurality of vertically stackable precast wall sections having at least one vertically disposed aperture for receiving said reinforcing bar assembly, the aperture being substantially larger than the bar width. 18. The construction system of claim 17 wherein: said reinforcing bar assembly includes a wall tensioning subassembly having at least one plate member and a tightening member, the plate member being adapted to engage one said wall section, the tightening member engaging one of the reinforcing bars and applying downward force on the plate member. 19. The building system of claim 17 wherein: each said wall section has a top surface with a top topology and a bottom surface with a bottom topology, the bottom topology being complementary to the top topology such that said wall sections are vertically aligned when stacked. 20. The building system of claim 17 wherein: each said wall section has at least one prestressed structural member precast therein.

Inventors: FRANKLIN HOWARD M, GARFINKEL ERIK, FRANKLIN, HOWARD, M., GARFINKEL, ERIK
Applicants: MEGAWALL CORP, MEGAWALL CORPORATION
Application year: 1995
Main classification: E04B2
IPC codes: E04B2