Abstract:
A void former or dowel sleeve adapted to be encapsulated in a hardened mass of concrete, which is collapsible upon the application of a tensile force longitudinally thereof to remove the void former from the concrete and provide a void for a load transferring dowel.

Description:
[0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 60/431,532 filed Dec. 6, 2002, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains to concrete construction, and more particularly to an apparatus for creating a void in a concrete slab. 
       BACKGROUND OF THE INVENTION 
       [0003]    The construction of various concrete surfaces is typically accomplished by forming a plurality of adjacent concrete slabs separated by expansion joints. When the concrete surfaces are used to support heavy loads, such as those surfaces used as aircraft runways, taxiways, and parking aprons, the heavy loads supported by the concrete surface may cause vertical movement of adjacent slabs. 
         [0004]    To control relative movement between adjacent slabs and more evenly distribute loads among the slabs, it is common to provide load bearing dowels which extend between adjacent slabs and across the expansion joints. Various methods of installing the dowels between joints have been used. 
         [0005]    According to a first, more or less conventional method, wet concrete is poured into a slab form and allowed to cure. The form is then removed and holes are drilled into the sides of the slab, generally parallel to an upper surface of the slab. After the holes have been drilled, first ends of the dowels are coated with an epoxy and inserted into the drilled holes. The opposite ends of the dowels extend outwardly from the slab into an area adjacent the slab, where additional concrete is poured to cover the outwardly extending ends of the dowels and thereby create an adjacent slab. 
         [0006]    U.S. Pat. No. 5,674,028 discloses a second, improved method of installing dowels between adjacent slabs. As seen in this patent, plastic sleeves are inserted into the edges of concrete slabs after the forms are removed, but while the concrete is still relatively plastic. After the concrete hardens, dowels are inserted into the sleeves with an end of each of the dowels projecting outwardly. Thereafter, an adjacent slab is poured, embedding the outwardly projecting ends of the dowels and completing the joint. 
         [0007]    Dowel placement sleeves are also described in U.S. Pat. Nos. 5,005,331; 5,216,862, and 5,487,249. In constructions of this type the sleeves are removed after the concrete is hardened. In the &#39;862 patent, for example, it is disclosed that a sleeve may be tapered to facilitate extraction. While this type of sleeve may be relatively easily removed from the void it creates after an initial longitudinal displacement of the sleeve has been effected, a significant amount of force may still be required to break the sleeve free from the cured concrete and obtain that initial displacement. 
         [0008]    The prior methods described above have various drawbacks. For example, drilling holes for receiving the dowels after the concrete has cured is a labor-intensive and time consuming process. Furthermore, without adequate controls, the holes drilled into the concrete may not be properly aligned with the top surface of the concrete slab or the edge into which the holes are drilled. Such misalignment may restrict relative movement between the slabs to a point which hinders performance of the expansion joint. While forming voids in the concrete by means of removable sleeves has advantages, it is often difficult, as noted above, to remove the sleeves from the concrete after the concrete slab has cured. 
         [0009]    There is thus a need for a device which may be used to form voids in concrete slabs while the concrete is in a plastic state and which overcomes various drawbacks of the prior art, such as those described above. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a void former or dowel sleeve that may be completely and easily removed from a concrete slab or the like after the concrete has hardened to provide an opening or void to receive a load-transmitting dowel. The void former or sleeve may either be inserted into an edge of a concrete slab or other structure after the form has been removed but while the concrete is in a plastic state, or attached to an inner surface of a form and the concrete poured over and around it. In either case, once the concrete has hardened, the void former or sleeve can be easily removed from the hardened concrete by simply imparting a tensile force to its outer end. This will cause the void former or sleeve to collapse inwardly upon itself, thereby reducing its diameter to a dimension substantially less than that of the void it has formed, and allowing it to be completely and easily removed from the hardened concrete slab or other structure. In accordance with the present invention this is accomplished by injection molding the void former or sleeve with a closed inner end and a flanged outer end, with the body of the void former or sleeve provided on its inner surface with a groove extending spirally about the inner wall of the void former or sleeve. The groove does not extend completely through the wall of the void former or sleeve, but stops just short of the outer surface. This provides a smooth outer surface and a thin bridge of material over the spiral groove. As a consequence, the void former or sleeve possesses sufficient rigidity for handling and placement, while at the same time, furnishing a readily rupturable section when exposed to the proper forces. More specifically, when it is desired to remove the void former or sleeve from a hardened concrete slab or the like, a tensile force, acting substantially longitudinally of the void former or sleeve, is applied to its flanged end. This tensile force is transmitted as a shear force normal to the thin web bridging the spiral groove and thereby permitting the void former or sleeve to be collapsed inwardly. 
         [0011]    In other words, the longitudinal tensile force applied to the outer end of the void former or sleeve, tends to elongate it. As a result, the void former or sleeve, tends to contract in diameter. This brings a shear force to bear transversely of the wall of the void former, rupturing the wall at its weakest point, and resulting in further contraction to a size permitting ready withdrawal from the slab. 
         [0012]    The features and objectives of the present invention will become more readily apparent from the following Detailed Description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention. 
           [0014]      FIG. 1  is a perspective view of an exemplary concrete dowel void former, according to the present invention; 
           [0015]      FIG. 2  is a partial cross-sectional view of the void former of  FIG. 1 , taken along line  2 - 2 ; 
           [0016]      FIG. 2A  is a partial cross-sectional view similar to  FIG. 2 , depicting another embodiment of the void former; and 
           [0017]      FIGS. 3A-3B  are cross-sectional views depicting operation of the void former. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring to  FIG. 1 , there is shown an exemplary concrete dowel void former  10  of the present invention. The void former  10  has an elongate tubular body  12  with a first, open end  14  and a second, closed end  16 . The second end  16  of the body  12  may be tapered to facilitate insertion of the void former  10  into a slab of plastic concrete. The body  12  comprises a body wall  18  having an inner surface  20  and an outer surface  22 . An interior cavity  24  extends along the body  12  between the first and second ends  14 ,  16 . A spiral groove  32  is formed in the inner surface  20  of body wall  18  and extends from the first end  14  toward the second end  16 . In the exemplary embodiment shown, groove  32  extends around the circumference of the body  12  in a helical fashion, defining adjacent spiral-wound portions  12   a ,  12   b ,  12   c  of the body  12 , between successive turns of the groove  32 . 
         [0019]    Referring to  FIG. 2 , there is shown a partial section of the void former  10  illustrating the groove  32  formed in the inner wall  20  of body wall  18 . In the exemplary embodiment shown, groove  32  is defined as a v-shaped cross section formed into the inner surface  20  of the body wall  18 , but it will be understood that groove  32  may have other shapes and configurations. In an exemplary embodiment, groove  32  is formed from the inner surface  20  toward the outer surface  22 , but does not completely extend through the thickness of body wall  18 . Advantageously, a thin web of material  34  is retained between the groove  32  and the outer surface  22  to provide rigidity to the body  12 . In another embodiment, shown in  FIG. 2A , the groove  32  is formed from the outer surface  22  toward the inner surface  20 . 
         [0020]    Advantageously, groove  32  permits the void former  10  to collapse inward when a tensile or torsional force is applied to the first end  14  of the body  12 . This collapsing action of void former  10  may be best understood with reference to  FIGS. 3A-3B . Specifically, when a tensile force is applied to first end  14  of void former  10  while void former  10  is otherwise gripped within a void in a concrete slab  36 , adjacent spiral-wound portions  12   a ,  12   b ,  12   c  of the body  12  defined by groove  32  become separated as body  12  assumes an increasingly elongated shape under the tensile force. As body  12  increases in length, it also undergoes a reduction in outer diameter whereby outer surface  22  is urged in a direction away from the concrete wall defining the void formed in the concrete slab  36 . 
         [0021]    When groove  32  does not extend fully through body wall  18  and a tensile force is applied to the first end  14 , the configuration of the spiral groove  32  creates shearing forces in a direction transverse to the thin web of material  34 . Advantageously, the thickness of the web  34  between the groove  32  and outer surface  22  may be configured such that the shear forces rupture the web  34  when a desired tensile force is applied to the first end  14  of the body  12 . After the web  34  has ruptured, the unrestrained groove  32  facilitates collapsing of the body  12  inward to make removal of the void former  10  easier. Because void former  10  can collapse inwardly to facilitate removal from cured concrete, the outer surface  22  of the body  12  can be formed without a taper along its length so that substantially cylindrical voids may be formed in the slab. 
         [0022]    Void former  10  further includes a flange  26  disposed at the first end  14 . Flange  26  extends in a generally radially outward direction from the body  12  and circumscribes a portion of the first end  14 . In the exemplary embodiment shown, a notch  28  in the flange  26  is located proximate outer terminus of groove  32 , with side edges  29   a ,  29   b  lying on opposite sides of the terminus of the groove  32 . Flange  26  may be provided with additional notches or apertures  30  configured to receive fasteners (not shown) for securing void former  10  to a concrete form, or to facilitate grasping flange  26  to thereby apply a tensile force and/or torque to first end  14 . 
         [0023]    In use, void former  10  may be used to create voids in concrete slabs for receiving dowels. In this regard, a series of void formers  10  may be secured to an inner surface of a concrete form to face inward of an area for receiving poured, wet concrete. The poured concrete surrounds the void former  10 . Once the concrete has cured, the forms may be removed and the void formers, still attached to the form, will be withdrawn from the slab as described above, to expose the voids. 
         [0024]    In another exemplary embodiment, void former  10  may be inserted into a concrete preformed concrete slab, while the concrete is still in a plastic state. After the concrete has cured, void former  10  may be removed as described above to expose the void. A dowel may then be inserted into the void and concrete poured into an adjacent area to create an adjacent slab. 
         [0025]    While the present invention has been illustrated by the description of the various embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of Applicant&#39;s general inventive concept.