Abstract:
An elongated joint connects adjacent concrete sections, usually slabs, and remains below the top surface of the slabs during temperature fluctuations. The joint has a grooved top surface and an opposite keyed bottom, and two mirror image spaced apart sides. The top, bottom, and sides form a generally rectangular cross section. Within the joint, upright risers, flat braces, and angled knees provide stiffness to the joint yet allow bending to withstand expansion and contraction of adjacent slabs. The joint has a generally symmetrical cross section. Upon the sides and bottom, the joint has keys that connect the joint to adjacent slabs. The joint can also serve as formwork for concrete.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The collapsible expansion joint relates generally to pavement, and more specifically, to a joint extending the full depth of a slab and that remains below the top of the slab during lateral compression. 
         [0002]    Since the time of the Romans, owners and contractors have made structures of all kinds with concrete. Concrete has been made into walls that stand upright, slabs that lay flat, and structural members that connect walls and slabs. Because concrete requires a time to set and forms must be constructed, concrete structures are often assembled in sections. Adjacent sections of concrete meet at joints. 
         [0003]    Concrete also endures the elements and the environment, such as temperature and moisture. As with other materials, concrete expands and contracts as the ambient temperature rises and falls. At a joint, two sections of concrete expand towards each other in warmer temperatures and pull away from each other in colder temperatures. In hot temperatures, adjacent concrete sections abut upon a joint and may rise upwards creating a ridge. Such ridges can impede traffic upon slabs or crack walls. In cold temperatures, a joint widens between adjacent concrete sections allowing contaminants to fall within the joint. Then moisture introduced in a joint can damage adjacent concrete sections particularly in cold weather. In colder weather, moisture in a joint freezes and in doing so expands. When expanding, ice can split concrete and degrade a joint. Deicing compounds applied to concrete also infiltrate a joint under the action of moisture and chemically degrade the concrete over time. 
         [0004]    A common location for joints is in slabs, such as roads or driveways adjacent to walls. Roads are constructed by slabs of concrete placed to meet concrete setting criteria and the limits of construction schedules. Day by day, a contractor and its labor force form and place concrete in slabs that accumulate over a project into a road. Adjacent slabs have a joint between them that requires filling. The joints generally extend across the travel lanes of a road and along the centerline. The joints are filled to prevent introduction of moisture and contaminants therein and to permit expansion and contraction of the slabs. Where a driveway meets a wall, a slab encounters upright concrete. The slab and wall expand and contract perpendicular to each other. Often the slab expands into the wall causing the wall to tip and to crack and perhaps weaken structurally. A joint between the driveway and the wall allows the driveway to expand with less risk of cracking an adjacent wall. 
       DESCRIPTION OF THE PRIOR ART 
       [0005]    Presently, joints in concrete are filled with various materials. Contractors use wooden boards, fiberboard, epoxy, plastic, rubber, tar, asphalt and other resilient but compressible materials. These materials are placed into a gap, or joint, between adjacent concrete sections and the sections compress the materials when they expand. At high temperatures, the expanding sections may exude the compressible material upwards from the joint which vehicles bump over in summer. In extremely high temperatures, ridges form at joints that require chipping, sawing or other removal methods and then replacement. On the other hand, the materials may reopen a gap when the sections contract in colder temperatures. A reopened gap permits the entry of moisture and chemicals that degrade the concrete over time. In colder climates, snow plows scrape over joints and cause damage to them in various degrees. 
         [0006]    In some cases, joints are made by placing a board or other material in setting concrete. The board extends from the top into the slab for less than the full depth of the slab. During temperature fluctuations, the adjacent slabs expand and contract while flexing the concrete below the board. In time, the concrete below the board crumbles and the board sinks to expose the joint to moisture. 
         [0007]    The present invention overcomes the limitations of the prior art explained above. The present invention extends for the full depth of a joint in two adjacent concrete sections and connects to the sections to prevent the invention from rising upward or sinking downward between two sections. That is, the art of the present invention provides a full depth joint that does not erupt upwardly from the joint under the thermal expansion and contraction of concrete slabs. 
       SUMMARY OF THE INVENTION 
       [0008]    Generally, the present invention provides an elongated joint that connects to adjacent concrete sections, usually slabs, and that remains below the top surface of the slabs during temperature fluctuations of the slabs. The joint has a grooved top surface and an opposite keyed bottom, and two mirror image spaced apart sides. The top, bottom, and sides form a generally rectangular cross section. Within the joint, upright risers, flat braces, and angled knees provide stiffness to the joint yet allow bending to withstand expansion and contraction of adjacent slabs. The joint has a generally symmetrical cross section. Upon the sides and bottom, the joint has keys that connect the joint to adjacent slabs. 
         [0009]    There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and that the present contribution to the art may be better appreciated. 
         [0010]    Further, the present invention also includes knees and a riser that stiffen the top for vehicle loads, rounded keys that reduce the requirement for vibration of setting concrete, and a raised key that permits lateral movement of the joint as adjacent slabs compress it. 
         [0011]    Numerous objects, features and advantages of the present invention will be readily apparent to those of ordinary skill in the art upon a reading of the following detailed description of the presently preferred, but nonetheless illustrative, embodiment of the present invention when taken in conjunction with the accompanying drawings. Before explaining the current embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
         [0012]    It is, therefore, the principal object of this invention to provide a collapsible expansion joint for concrete slabs that extends for the full slab depth and does not rise above the top of the slab. 
         [0013]    Another object of this invention is to provide a collapsible expansion joint that folds downward when compressed from the sides. 
         [0014]    Another object of this invention is to provide a collapsible expansion joint with a mechanical connection to adjacent concrete slabs that prevents the joint from rising upwards. 
         [0015]    Another object of this invention is to provide for a collapsible expansion joint with a bottom that folds upwards into the joint to prevent contacting the subgrade. 
         [0016]    Another object of this invention is to provide for a collapsible expansion joint with a low cost of manufacture so that the consuming contractors may obtain the joint. 
         [0017]    Lastly, it is an object to provide a collapsible expansion joint with a grooved top that folds downwards into the joint and that directs water and debris lengthwise off of the joint. 
         [0018]    These together with other objects of the invention, along with the various features of novelty that characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In referring to the drawings, 
           [0020]      FIG. 1  shows an isometric view of present invention installed between two slabs of pavement in accordance with the principles of the present invention; and, 
           [0021]      FIG. 2  describes an end view of the present invention showing the interior members before compression by adjacent slabs. 
       
    
    
       [0022]    The same reference numerals refer to the same parts throughout the various figures. 
       DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    The present art overcomes the prior art limitations by having a durable compressible joint secured between two slabs or a slab and a wall for the full depth of a slab with the slab resting upon a subgrade or lower foundation. For ease of description,  FIG. 1  shows the preferred embodiment of the collapsible expansion joint  1  emplaced between two slabs C. The joint may be used where two other concrete sections abut following the same principles and description herein provided for abutting slabs C. For sidewalks, driveways abutting garages, some runways, and roads, concrete is used as a durable pavement that resists the elements and turning vehicles, and has a long life span and low maintenance costs.  FIG. 1  shows two adjacent slabs as in a road. The slabs C have a depth and an expansion spacing as specified in the construction documents. The expansion spacing is occupied by the joint  1 . 
         [0024]    The joint  1  is generally an elongated hollow member with a cross section that appears somewhat rectangular. The joint can be made to any length by extrusion or other means. The length of the joint matches the length of the expansion spacing between the slabs. The expansion joint of the present invention has sufficient rigidity and stiffness to remain upright. The expansion joint also can serve as formwork for the placement of plastic concrete or other pavement materials, a straight edge for bull floating tools and other pavement finishing tools, and can support tools, personnel, and light equipment for other construction and maintenance activities. 
         [0025]    The description continues upon the cross section of the joint that is used throughout the length of the joint. In cross section, the joint has a top  2 , generally at the elevation of the surface of the adjacent slabs. The top has a centered groove  3  running the length of the joint. The groove  3  denotes the low part of the top and directs the halves  2   a  of the top to fold downwards when the joint is compressed by the expanding slabs. Opposite the top, the joint has a bottom  4 . The bottom has a raised center portion  5  that guides the bottom to fold upwards when the slabs expand. In folding upwards, the bottom limits pressing into the subgrade. Connecting the top and the bottom, two spaced apart and symmetric sides  6  abut the faces of the adjacent slabs. The sides are generally the longer portion of the rectangular joint cross section. The sides have a key  7 , here shown as concave, generally centered that permits concrete to enter within the outer shape or limits of the cross section. When that concrete sets, the key prevents removing the joint from between the slabs. Inside of the top, the sides, and the bottom, the joint has a web of internal members that stiffen and support the joint under various loads. 
         [0026]    The cross section of the collapsible expansion joint is shown in more detail with  FIG. 2 . The joint has a top  2 , generally horizontal in an installed joint. The top has two halves  2   a  that descend and extend towards the center of the top. The halves meet at the groove  3  that runs for the length of the joint. The groove is lower than the corners where the top meets the sides  6 . Opposite the top, the joint has the bottom. The bottom has two outer portions  4 , sloped downwardly and generally parallel to the top that have a raised key  5  centered therebetween. The raised key  5  is centered upon the bottom of the joint and has a concave shape, generally upwardly, as shown in  FIG. 2 . In an alternate embodiment, the raised key  5  is a chevron shape, upwardly pointing, with straight members, as shown in  FIG. 1 . The raised key allows the bottom to rise upwards when adjacent slabs expand into the joint during high temperatures. Spanning between the top and the bottom, the joint has two symmetric and spaced apart sides  6 . Each side has two outer portions  6   a  located proximate to the top and the bottom respectively. The outer portions are generally coplanar and perpendicular to the top. Centered between the outer portions, the side  6  has a key  7  that extends into the joint in a generally concave shape. The key has the same thickness as the outer portions  6   a.  Each key  7  allows concrete to set within the sides and prevent the joint from rising above adjacent slabs. Within the perimeter of the joint, internal members span between the top, the sides, and the bottom for a stiff but compressible joint. 
         [0027]    The internal members are generally symmetric though offset designs of the internal members are possible. Here in  FIG. 2 , the internal members begin with the first riser  8 . The riser has an narrow elongated shape that extends from the intersection of the raised key  5  with the bottom  4 . The riser extends substantially vertical, generally perpendicular to a half  2   a  of the top  2 , and into the height of the key  7 . Above the first riser, a second riser  8   a  continues in a narrow elongated shape from the first riser, also substantially vertical, generally perpendicular to a half. The second riser stops at the height of the upper end of the key  7 . 
         [0028]    From the key  7 , a first brace  9  extends radially into the joint and is generally parallel to a half and perpendicular to the first riser. The first brace has a narrow elongated shape having a similar thickness as the first riser  8 . The first brace continues through the intersection of the first riser and the second riser into the center of the joint. Parallel to and spaced above the first brace, a second brace  9   a  extends from the upper end of the key  7  where it intersects the outer portion  6   a  into the joint generally parallel to the first brace. The second brace also has a similar thickness to the first brace. The second brace ends at a generally perpendicular angle to the second riser  8   a.  Inside of where the half  2   a  intersects with the upper outer portion  6   a,  a first knee brace  10  spans at an angle to the vertical from the outer portion to the half. Here the first knee brace spans from the intersection of the second brace  9   a  with the outer portion up and inward to the half  2 . Parallel and inward from the first knee brace, a second knee brace  10   a  spans from the intersection of the second riser with the second brace at an angle to the vertical. The second knee brace ends at the centerline of the joint. Where the second knee brace ends, a third riser  9   b  extends upwards to the top  2  generally beneath the groove  3 . As the joint is symmetric, each left and right half of the joint has a first riser, second riser, first brace, second brace, first knee brace, and a second knee brace, while having a third riser shared between the left and right halves of the joint. Generally, the internal members each have the same thickness as shown in  FIG. 2 . 
         [0029]    During use, the internal members respond to forces applied to the joint while preventing complete collapse of the joint. When a vertical load, such as a wheel load, is applied to the top, the halves fold downwards thus lowering the third riser, second knee brace, and first knee brace. Upon contact with the outer portions  6   a,  the first knee braces and second knee braces stiffen the top. Meanwhile, the vertical load continues downward through the second knee braces and into the second riser and into the first riser. The first riser then transmits a portion of the vertical load to the raise key  5  and into the subgrade. When the adjacent slabs expand into the joint, the horizontal loads are applied to the sides. The sides transfer those loads into the outer portions, the first braces  9 , the second braces  9   a,  the first knee brace  10 , and a half  2 . Under those loads, the raised key  5  moves upwards into the joint as the bottom sections, as at  4 , move inwards, the first brace folds downward at the centerline of the joint. The second brace  9   a  also moves inward which raises the second knee brace and the third riser to stiffen the top. When lower temperatures cause the adjacent slabs to pull away from each other, the joint returns to its normal shape pulled outwards by the key. The joint supports vehicle loads in warm and cold weather using the internal members cooperating with the top, the bottom, and the sides of the present invention. 
         [0030]    From the aforementioned description, a collapsible expansion joint has been described. The joint is uniquely capable of supporting loads while having a hollow construction and remaining in position between adjacent slabs using keys. The collapsible expansion joint and its various components may be manufactured from many materials including but not limited to polymers, EPDM, rugged plastics, textiles, ferrous and non-ferrous metals and their alloys, and composites. 
         [0031]    As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. Therefore, the claims include such equivalent constructions insofar as they do not depart from the spirit and the scope of the present invention.