A concrete contraction and expansion joint with a mechanism providing adjustable height, enabling fast, efficient pouring of concrete over layout surfaces, achieving accurate thickness and desired slope of the concrete slab. In a preferred embodiment, the concrete section joint assembly ( 35 ) is pre-formed by using longitudinal sections having a channel ( 37 ) for holding elastomeric material ( 42 ), with the section supported from its underside by shaped support units, each mounted on two threaded studs ( 24 ). A specially designed nut ( 28 ) threaded on each stud ( 24 ) provides height adjustability and by rotation raises or lowers the height of support unit sides. The height adjustment, provided from above the assembly, can be performed before concrete pouring is completed and an upper edge portion of the elastomeric material or the upper edges of the channel are visible with the concrete surface, providing a reference height and slope for the concrete surface. Another embodiment provides a surface level guide for mortar or plaster work in wall finishing.

FIELD OF THE INVENTION 
     The present invention relates to construction and building materials and methods and more particularly, to adjustable height concrete expansion joints enabling easy height adjustment for accurate leveling of concrete surfaces, and providing pre-fabricated joints for same. 
     BACKGROUND OF THE INVENTION 
     Concrete expansion joints are an essential component in the proper construction of many large concrete surfaces, such as floors, roofs, parking lots, roads, airport runways and the like. These joints enable expansion and contraction of the concrete or mortar surfaces based on surrounding temperatures, which reach hot and cold extremes, respectively, in summer and winter periods, and other factors including shifting of soil underneath the slabs. These joints are meant to eliminate the deterioration of the slab due to random cracks which otherwise form in the concrete. 
     As used herein the term “joints” applies equally to expansion and contraction joints. 
     In pouring concrete over a large surface and insuring that it spreads evenly, reference marks are needed to indicate the height of the concrete slab. In many cases where forms are used to define areas into which concrete is poured, flexible joint materials are placed into the grooves resulting when the forms are removed. A leveling string is stretched from a stud at the corners of the forms, and the stud is vertically adjustable by use of a nut, to provide the reference for pouring the concrete. This task requires much time and effort and still leaves irregularities in the concrete surface. 
     Existing methods of providing joints in concrete slabs include the method of saw cutting a groove for the joint in the solid concrete, and this requires specially designed diamond saw cutting blades, which have a very short useful life and are very expensive. In addition, there is a limiting time factor, since the sawcut must be performed within a short period after pouring the concrete. 
     In U.S. Pat. No. 4,050,206 to Utsuyama, an improved jointing material is disclosed for placement on a support assembly having an adjustable height to provide a reference surface. The support assembly comprises leg assemblies which are adjusted to the desired reference surface height, by bending the legs toward and away from each other. This adjustment is neither consistent nor convenient for all of the support assemblies. 
     A product commercially available from Thorbjorn Lund Sweden, known as Combiform, discloses a method of supporting a screed rail with a ground plate having adjustment screws to adjust the rail height. The adjusting screws are supported by a ground plate placed under the rail, so that these screws are at a low level, and once concrete is poured over these, no further adjustment is possible. This limits flexibility in construction. 
     U.S. Pat. No. 4,198,176 to Bentz discloses a concrete expansion joint forming structure in which a U-shaped metallic sheet holder supports an expansion joint. The holder is supported on a pair of chisel-shaped pegs driven into the ground before pouring concrete around the area to set the expansion joints. No height adjustment is described for the pegs once they are set. 
     U.S. Pat. No. 4,875,801 to Montrym discloses an expansion joint brace with ground pegs for setting the brace before pouring concrete. As before, no height adjustment is described for the pegs once they are set. 
     In U.S. Pat. No. 4,979,846 to Hill et al., there is disclosed a contraction joint for concrete linings in which a triangular-shaped section is placed with its apex protruding over a reference surface of concrete, but without a height adjustment. 
     Therefore, it would be desirable to provide a concrete joint which is also capable of height adjustment to establish a desired reference surface height for pouring concrete. 
     The reference surface height (thickness) problem also applies to the construction of walls, when it is necessary to straighten the wall surface or slope when applying mortar or during plastering, to achieve a thin layer, usually less than 2-3 cm, with a high degree of precision. 
     Therefore, it would also be desirable to provide a surface level guide for mortar or plaster work in wall finishing. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a principal object of the present invention to overcome the disadvantages of prior art concrete expansion joints and provide a concrete expansion joint with a simple mechanism providing adjustable height, enabling faster, more efficient pouring of concrete over large layout surfaces, to achieve accurate thickness and desired slope of the concrete slab. 
     It is another object of the invention to provide a surface level guide for mortar or plaster work in wall finishing. 
     In accordance with a preferred embodiment of the present invention, there is provided an adjustable height concrete section joint assembly for placement prior to pouring a concrete slab surface, comprising: 
     section means extending longitudinally and being shaped for holding a flexible material; and 
     means for supporting said section means at an adjustable height, said height adjustment being provided before completion of pouring of concrete, such that an upper edge portion of said section means is visible at the concrete slab surface, providing it with a desired reference height and slope. 
     In a preferred embodiment, the concrete section joint assembly is pre-formed by use of longitudinal sections having a channel formed therein for holding elastomeric material, with the section supported from its underside by shaped support units. Each support unit is supported on a pair of threaded studs, by a specially designed nut threaded on each stud, so as to be adjustable in height. The nut has formed therein a groove into which an omega-shaped retaining spring can be inserted, to support each side of the unit. Rotation of the nut raises or lowers the height of each support unit side. 
     The height adjustment is provided from above the assembly and can be performed before completion of pouring the concrete, such that an upper edge portion of the elastomeric material or the upper edges of the channel are visible even with the concrete surface, providing a desired reference height and slope for the concrete surface. 
     This embodiment using elastomeric material provides a joint meant to eliminate the random cracks which form in the concrete. 
     In an alternative embodiment, the section is replaced by a rail means that extends longitudinally and is formed with a protruding inverted U-shaped middle rib with a flexible rib covering the inverted U-shaped middle rib. The rail means is supported from its underside on a pair of threaded studs, by the specially designed nut threaded on each stud, so as to be adjustable in height. 
     The rail means is intended to form weakness lines which guide the cracks which form in the concrete, and to provide a very accurate reference level for leveling the concrete slab surface during pouring. 
     The present invention is designed to allow access to the specially designed nut from above the support assembly, to allow the height and slope adjustment to be performed before and during the pouring of concrete, thus allowing greater freedom in achieving the correct adjustment, while saving set-up costs. 
     The inventive technique eliminates the need to saw the joint in the concrete, as with prior art methods, since the joint is ready before the concrete is poured. 
     In yet another alternative embodiment, the concrete expansion joint assembly section is formed from a protruding rib-like structure whose two sides are slightly open on its underside, and provided with horizontal wings extending from both sides and integral to them, the whole forming an inverted, longitudinal T-shaped profile. The assembly section is supported from its underside by a flat support unit, a suitable number of such units being appropriately spaced along the axis of the joint assembly section. The support unit is provided with pre-cut foldable tabs which, when folded over the horizontal wing surfaces of the assembly section, secure the support unit to the section. Each support unit is itself supported on a pair of threaded studs integrally formed with a raised base structure. The studs are provided with a specially-designed nut threaded on each stud, so as to be adjustable in height. The nut has formed therein a groove into which an omega-shaped retaining spring can be inserted, to support each side of the support unit. Rotation of the nut raises or lowers the height of each support unit side for leveling and aligning the joint section. As in the previously-described embodiment, the height adjustment is provided from above the assembly section and can be performed before completion of pouring the concrete, such that an upper edge portion of the section is visible even with the concrete surface to be poured, providing a desired reference height and slope for the finished concrete surface. 
     In another alternative embodiment, the invention provides a surface level guide for mortar or plaster work in wall finishing, comprising a rail having a protruding inverted U-shaped middle rib integrally formed with horizontal flanges, which are formed with a plurality of spaced apart mounting holes, designed to allow permanent or removable mounting of the rail. 
    
    
     Other features and advantages of the invention will become apparent from the following drawings and description. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention with regard to the embodiments thereof, reference is made to the accompanying drawings, in which like numerals designate corresponding elements or sections throughout, and in which: 
     FIGS. 1 a-d  illustrate, respectively, perspective and side views of a preferred embodiment of an adjustable height concrete section joint constructed and operated in accordance with the principles of the present invention; 
     FIGS. 2 a-c ;  3   a-c ;  4   a-c ; and  5   a-c  each illustrate perspective, front and side views of various alternative embodiments of a novel concrete contraction joint, each featuring a different form and assembly. 
     FIG. 6 is a front view of another alternative embodiment of the inventive expansion joint, featuring an inverted bracket; 
     FIGS. 7 a-d  each illustrate perspective, front and side views of an alternative embodiment of a novel concrete expansion joint, featuring a dowel bar reinforcing arrangement; 
     FIG. 8 is a top view of a curved expansion joint layout constructed using the inventive expansion joint assembly; 
     FIGS. 9-10 are respectively, perspective and front views of another alternative embodiment of the novel expansion joint; 
     FIG. 11 is a front view of another alternative embodiment of the expansion joint, featuring an inverted holder having substantially parallel vertical sides; 
     FIGS. 12-13 show front and side views of the alternative embodiment of FIG. 11 in a mounting arrangement; and 
     FIGS. 14-16 show, respectively, top, side and elevation views of an alternative embodiment used as a surface level guide. 
     FIGS. 17 a-c  show a perspective, top and side view, respectively, of an alternative embodiment featuring a joint assembly section secured to a flat support unit by pre-cut foldable tabs integrally-formed from the support unit; 
     FIG. 17 d  shows the adjustable mounting assembly for the flat support unit with the tabs folded securely over the wings of the assembly section and the support unit firmly anchored by threaded mounting studs integral to a raised base, and held in place by nuts and retaining springs of the type described for prior embodiments. 
     FIG. 18 shows a top view of the template used to form the flat support unit, including the arrangement of holes to accommodate threaded mounting studs and the pre-cut tabs which are used to secure the section to the adjustable support unit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1 a-d , there are illustrated, respectively, perspective and front views of an adjustable height concrete section joint assembly  10  constructed and operated in accordance with the principles of the present invention. Assembly  10  comprises a rail  12  having a protruding inverted U-shaped middle rib  14  and side walls  16  integrally formed with horizontal flanges  18 , which are formed with a plurality of spaced apart mounting holes  20 . A base  22  is formed integrally with a pair of threaded mounting studs  24  extending perpendicular thereto, and base  22  is formed with anchoring holes  26 . 
     In accordance with the principles of the present invention, joint assembly  10  is provided with a specially-designed threaded nut  28  which is formed with a groove, into which an omega-shaped retaining spring  30  can be inserted. Spring  30  serves to hold the rail  12  at the vertical height on stud  24  to which threaded nut  28  is adjusted. The simple adjustment is performed from above joint assembly  10 . 
     As shown in FIG. 1 b , base  22  is seated on a platform  32  and securely attached thereto by a pair of pins  34  which are driven into platform  32 . Before concrete is poured over platform  32 , the height of rail  12  can be adjusted, as shown in FIG. 1 c , so that rib covering  14  is at the desired height for the concrete surface FIG. 1 c  shows an alternate mounting arrangement for base  22  on platform  32 , by use of molly-type anchors and bolts  36 . 
     In FIG. 1 d , platform  32  is shown as a pre-cast concrete base, and the concrete section joint assembly  10  is shown after the concrete has been poured over platform  32 , in a procedure known as topping its surface  33 . The support assembly comprises two mounting studs only, with their lower portion covered with shrink wrap plastic which serves to stabilize the studs in the pre-cast concrete. When topping concrete is poured over the entire assembly  10 , rib covering  14  is visible flush with the topping layer. 
     In FIGS. 2 a-c , there are shown perspective, front and side views of an alternative embodiment of the inventive concrete expansion joint assembly  35 , in which U-shaped rail  12  is replaced by a longitudinal section formed with a channel  37  and flanges  38  which have mounting holes  40  formed therein. An elastomeric material  42  constitutes the expansion joint itself, which is seated in channel  37 . As with joint assembly  10 , the alternative joint assembly  35  is provided with specially-designed threaded nut  28  into which spring  30  is inserted to hold the channel  37  at the vertical height to which threaded nut  28  is adjusted on studs  24 , which are supported by a raised base  44 . 
     Before concrete is poured over base  44 , the height of channel  37  can be adjusted to fix the top edge of material  42  at the desired height for the concrete surface. This adjustment provides a reference level for use in pouring concrete. 
     In FIGS. 3 a-c , there are shown perspective, front and side views of another alternative embodiment of the inventive concrete expansion joint assembly  45 , in which longitudinal channel  37  is replaced by a channel  46  for holding elastomeric material  42 . In this example, the height dimension of elastomeric material  42  is greater than shown in FIGS.  2   a-c , such that the expansion joint extends to a greater depth. Channel  46  is supported by a flanged support bracket  48  having a narrow width. A plurality of spaced apart brackets  48  are placed along the expansion joint overall length. Again, the alternative joint assembly  45  is provided with specially-designed threaded nuts  28 , which allow vertical height adjustment on threaded studs  26 . 
     In FIGS. 4 a-c , there are shown perspective, front and side views of yet a further alternative embodiment of the inventive concrete expansion joint assembly  55 . In this embodiment, longitudinal channel  46  is replaced by a shaped channel  56  for holding elastomeric materials  58 . The shape of channel  56  is similar to that of a dual thickness saw cut. 
     Channel  56  has slanted top edges  59  which are bent to shape the edges of the concrete slab poured over the assembly, so that the concrete under these edges hardens in the shape of a beveled edge. The channel  56  is supported by a flanged support bracket  60 , which is also shaped like channel  56 , and has a narrow width. A plurality of spaced apart brackets  60  are placed along the expansion joint overall length. As before, specially-designed threaded nuts  28  enable height adjustment on threaded studs  24 . 
     The beveled edge shape of the concrete slab can also be obtained by providing the elastomeric material with an upper edge shaped with slanted edges (FIG.  7 ), like the shape of channel  56 . 
     FIGS. 5 a-c  illustrate another variation of the concrete expansion joint assembly, using adjustable height support brackets  62  to support a shaped holder  63  with a different cross-section, in which thick elastomeric material  64  is seated. 
     FIG. 6 is a front view of another alternative embodiment of the inventive expansion joint assembly  70 , featuring an inverted holder  72  for holding the elastomeric material  42 . The holder  72  is shaped so as to support the elastomeric material above the top of studs  24 . The resulting dimension X between the top edge of elastomeric material  42  and the horizontal edge of holder  72  provides a greater distance between the top of the concrete surface and the top of studs  24 . This is important in certain applications, for greater strength. 
     FIGS. 7 a-d  each illustrate perspective, front and side views of the FIG. 5 a  embodiment of the novel concrete expansion joint, featuring a dowel bar reinforcing arrangement. The elastomeric material  64  is seated in holder  63 , covering polyethylene foam material  79  placed within holder  63 . In FIG. 7 b , the front view shows a dowel bar  80  supported by a pair of hollow cylinders  82  each of which is slid over a threaded stud  24 , with a hollow ring  84  (FIG. 7 d ) welded onto each cylinder  82 , through which the dowel bar passes. The dowel bar arrangement is useful where the design of the concrete provided requires it. Any suitable arrangement may be used to fix the dowel bar position using the mounting studs  24 . 
     FIGS. 7 b-c  show the elastomeric material  64  with either a straight top edge (FIG. 7 b ) or a slanted edge (FIG. 7 c ), with the concrete slab edges being formed with the appropriate shape. 
     FIG. 8 is a top view of a curved expansion joint layout constructed with elastomeric material  42  using the inventive expansion joint assembly, with individual support brackets  48  placed at spaced apart locations and oriented according to the desired layout. 
     FIGS. 9-10 show respectively, perspective and front views of an alternative embodiment of the expansion joint, featuring an inverted T-shaped profile  90 . Elastomeric material  42  is seated on top of profile  90  which has its side walls  92  substantially closed one against the other, in a 0-20 degree range. This profile forms a deep expansion joint, from 15 to 80 mm. The height adjustment system is as described per FIG.  1 . 
     In FIG. 11, there is shown a front view of another alternative embodiment of the expansion/contraction joint, in which elastomeric joint material  42  is held in place in an inverted holder  94  having substantially parallel vertical side walls  95  integrally formed with horizontal flanges  18 . This part of holder  94  has no holes formed in side walls  95 , thus trapping air in the space  96  between walls  95  and preventing the entry of concrete therein. The trapped air provides side pressure flexibility, so as to develop a line of weakness. The contraction of the concrete causes cracking to occur only underneath this line, and by allowing for “squeezing”, the joint allows the concrete slab to expand. 
     FIGS. 12-13 show front and side views of the alternative embodiment of FIG. 11 in a mounting arrangement similar to that of FIG. 10, on raised platform  44 . 
     Referring now to FIGS. 14-16, there are shown, respectively, top, side and elevation views of an alternative embodiment used as a surface level guide  100  for mortar or plaster work in wall finishing. Guide  100  is provided as an inverted U-shaped rib  102  having integrally formed flanges  104  which are formed with a plurality of holes  106 , and a plurality of keyhole-shaped holes  108 , in a spaced apart pattern. 
     The surface level guide  100  is installed on a wall  101  which is to receive an internal or external layer of plaster, by mounting the rib  102  with its flanges  104  on screws  110 . The spaced apart intervals of guide  100  are defined by the working space needed to smooth the plaster using a screed, or by the wall construction plan which defines the separate sections of the wall. 
     The spacing between the rib  102  and the wall, or its height above the floor, is adjustable by use of screws  110  which are threaded into wall anchors  112 , mounted on the wall, or used as floor anchors. Under the head of each of the screws  110  is a one-way retaining ring  114 , similar in function to the omega-shaped retaining spring  30  which is shown in previous illustrations, designed to hold the flanges  104  fixed in position on screws  110 . 
     The mounting of horizontal flanges  104  on screws  110  can be permanent or removable. If permanent, screws  110  are placed through small holes  106 , and rings  114  used to retain the flanges  104  in position. If removable, each screw  110  has a ring  114  locked in advance under its head, and flanges  104  are placed over screw  110  using the larger portion of keyhole  108 , and pushed to lock it in position under the narrow keyhole  108  portion. 
     Once the plaster has already been smoothed over the wall surface and allowed to partially dry, the guide  100  can be removed from the wall. This is achieved by sliding it towards the larger keyhole  108  portion, and lifting it off the wall. The remaining empty groove can be filled in with fresh plaster. 
     Referring now to FIGS. 17 a, b , and  c , there are shown respectively, perspective, top, and side views of an alternative embodiment of the concrete expansion joint assembly section comprised of an adjustable flat support unit  118  secured, by pre-cut foldable tabs  116 , to an inverted T-shaped section  90 . As can be seen from FIG. 17 a , the section may be provided with a plurality of spaced-apart holes  20  which are generally used for mounting, but in this embodiment merely allow for additional channels for the poured concrete to flow freely around section  90  since in this embodiment, support unit  118  is used for the actual adjustable mounting system. Alternatively, as shown in FIG. 17 d , section  90  may be provided without mounting holes as these are not essential to this embodiment. 
     In FIG. 17 d , the inverted T-shaped section  90  is shown secured to support unit  118  by the tabs  116  which are folded over the horizontal wings  18  of section  90 . Support unit  118  is anchored to a raised base  22  formed integrally with a pair of threaded mounting studs  24  extending perpendicular thereto, and base  22  is formed with anchoring holes  26  to secure it to the bed where the concrete is to be poured, using any method known to the art. 
     In accordance with the principles of the present invention, the threaded mounting studs  24  are provided with specially-designed threaded nut  28  into which an omega-shaped retaining spring  30  can be inserted. Spring  30  serves to hold support unit  118  at the vertical height on stud  24  to which threaded nut  28  is adjusted. The adjustment can be done in a simple manner from above the concrete joint assembly section  90 . 
     FIG. 18 shows support unit  118  in the form of a flat template which is provided in the embodiment of FIG.  17  and showing the position of mounting holes  20  and the position of tabs  116  before folding. 
     In summary, the inventive concrete expansion joint assembly allows height adjustment before and during the pouring of concrete, thus allowing greater freedom in achieving the correct height adjustment, while saving set-up costs. The inventive technique eliminates the need to saw the joint in the concrete, as with prior art methods, since the joint is ready before the concrete is poured. 
     In the case of mortar or plaster work in wall finishing, the present invention allows the surface of a wall to be accurately leveled and smoothed by passing a screed over the exposed edge of the adjustable height surface guide mounted on the wall in accordance with the present invention. The guide can be either removed after the surface has partially dried, or left permanently fixed which may be useful to decoratively mark separate wall sections. 
     Having described the invention with regard to certain specific embodiments, it is to be understood that the description is not meant as a limitation, since further modifications may now present themselves to those skilled in the art, and it is intended to cover such modifications as fall within the scope of the appended claims.