Patent Publication Number: US-2023151559-A1

Title: Concrete dowel placement method and apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 17/035,056, filed on Sep. 28, 2020, which claims the benefit of U.S. Application No. 62/990,902, filed on Mar. 17, 2020, the entire contents of which are expressly incorporated herein by reference. 
    
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable 
     BACKGROUND 
     The present disclosure relates generally to a method and apparatus for use in concrete construction, and is more specifically directed to a method and apparatus for placing slip dowels into horizontal concrete slabs. 
     In construction, a “cold joint” in concrete is a weakened interface between two sections of a generally horizontal concrete surface slab that harden at different times. Typically, a concrete surface is formed by pouring concrete into a form of a desired shape, finishing the concrete surface and allowing the concrete to harden within the form. When the area of the concrete surface becomes large, or for other reasons, it is sometimes desirable to form the concrete surface by pouring it piecewise in adjacent sections at different times, allowing each adjacent section to harden to some extent before the next adjacent section is poured and allowed to harden. The interface between a previously poured adjacent section of concrete and a more recently poured adjacent section is called a cold joint. 
     A cold joint in concrete is typically weaker under tension and under vertical loads than concrete that has been allowed to harden without any cold joints, and this weakness at the cold joint may cause problems after the concrete hardens. Due to this weakness, over time cold joints often become uneven or buckled due to thermal expansion and contraction of the concrete. Compaction of the underlaying soil caused by improper substrate preparation before pouring the concrete can also cause buckling or cracking at the cold joint as adjacent sections of the concrete shift vertically relative to one another. Further, too much water moisture may accumulate on the end face of the first concrete section before a second, adjacent concrete section is poured and hardens. If the accumulated water freezes, undesirable cracking in the concrete may occur due to ice expansion against the concrete. Also, in terms of aesthetics, cold joints often form a visual line at the interface of the two concrete sections, which is often undesirable. 
     To resist buckling, bulging, and vertical or horizontal displacement of adjacent concrete sections at the cold joint, it is common to insert long steel rods, known as “slip dowels,” into the edge portions of adjacent concrete sections so that the concrete sections may slide freely along one or more of the slip dowels. This ability to slide freely may allow linear expansion and contraction of the concrete sections in the plane of the concrete surface, while substantially maintaining the concrete in a common plane, thus preventing undesirable buckling, bulging, or unevenness at the cold joint. 
     To function properly, it is important to properly position the slip dowels within adjacent concrete sections. For instance, most slip dowels are placed in substantially parallel alignment relation to each other to allow the concrete sections to slide along the length of the slip dowels while resisting movement of the concrete in a direction orthogonal to that length. Thus, the purpose of placing the slip dowels is defeated when the dowels are not properly positioned in substantially parallel relation to each other because, in such a case, the concrete sections are not able to slide along the slip dowels. Further, nonparallel placement of slip dowels can cause cracking in the concrete as well as faulting, i.e., misalignment of the concrete sections at the cold joint. 
     In the prior art, the methods for installing slip dowels include drilling holes for the slip dowels into a side of a first adjacent concrete section after removing the concrete forms, or forming cavities in the side of the first adjacent concrete section into which the slip dowels are inserted after the concrete hardens and the concrete forms are removed. A second adjacent concrete section is then poured to embed the end of the dowel extending from the first concrete section. The concrete forms are often a finished, wooden 2×4 inch or 2×6 inch stud. Such studs are typically smaller than nominal size because finishing the studs to a smooth finish reduces the nominal size of the stud, so the concrete slabs formed with the finished studs is thinner than the nominal size of the stud. For road paving, the forms may be metal and 8 to 12 inches high, or higher. The depth and diameter of the individual holes are typically least twelve inches deep and typically have a diameter of approximately one-half to five-eighths of an inch for foot traffic, and ¾ to one inch diameter for vehicle traffic. 
     The methods and apparatus of the prior art have various disadvantages, including one or more of time consuming installation techniques, misalignment errors, requiring expensive inserts to form cavities for the dowels, requiring heavy inserts to form the cavities and requiring large inserts to form the cavities, and requiring expensive installation techniques, to name a few. There is thus a need for an improved method and apparatus that reduces installation time and expense, and uses less expensive components. Accordingly, there remains a need in the art for methods and/or systems for facilitating the proper placement of slip dowels, and methods for manufacturing such placement systems, which overcome the previously described deficiencies associated with prior art placement devices and systems. 
     BRIEF SUMMARY 
     The present disclosure is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 
     An improved concrete surface with a cold joint, a dowel slip system and a method for forming that surface are provided. Relatively thin baseplates having tubular projections are fastened to at least one first stud using fasteners extending part way into the first stud, with the first stud forming at least part of a periphery of a first concrete slab. When the first stud is removed the baseplates, projections and fasteners remain embedded in the first concrete slab. Slip dowels are inserted into each of the tubular projections through a hole in the baseplate aligned with the longitudinal axis of the tubular projection and a second concrete is then poured adjoining the first concrete slab. The second concrete embeds or entrains the slip dowels, backplates and projecting distal ends of the fasteners and when hardened to form the second concrete slab, forms a cold joint between the first and second concrete slabs. 
     There is thus advantageously provided a concrete dowel placement system that includes one or more finished 2×4 or 4×6 studs having a stud length with opposing first and second side walls and opposing top and bottom edge walls. The system also includes a plurality of baseplates each having opposing front and back sides with a relatively thin thickness typically between 0.1 and 0.25 inches. The baseplates are preferably made of a polymer which does not split or crack when a fastener is forced through the baseplate. Each baseplate has an outer periphery which is located between the top and bottom edge walls of the stud and 0.5 inches or more from the top edge wall of the stud. One or more fasteners are preferably fasteners forced through each of different ones of the baseplates fasten the baseplate to the first side wall of the stud so the planar periphery cooperates with the first side wall of the stud to which the baseplate is fastened to form a seal that inhibits the entry of poured concrete between the baseplate and stud. Each fastener has a fastener length which extends into the stud a distance of at least ¼ inch and less than 1 inch. A separate tubular projection extends from each respective baseplate along a longitudinal axis that is substantially perpendicular to the front face of the baseplate from which the projection extends. Each tubular projection has a length of preferably between 4 to 9 inches with a closed distal end and a hollow interior configured to receive a cylindrical shaft having a diameter between 0.2 to 0.4 inches and preferably being 0.25 to 0.375 inches in diameter. 
     In further variations of this system, the three fasteners extend a distance of 0.3 to 0.5 inches into the stud and comprise nails or staples or both. The hollow interior may also be configured to receive a shaft 0.2 to 0.3 inches in diameter. Advantageously, the tubular projections have engagement features to better entrain the tubular projections in the concrete. The tubular projections may also be spaced at 18 inch intervals along the stud length. Further, there are advantageously only three staples holding each of the baseplates to the stud. 
     There is also provided an improved concrete surface having first and second concrete slabs joined by a cold joint. The is improved concrete surface includes a plurality of polymer baseplates embedded in the first concrete surface at intervals along the cold joint. Each baseplate has an outer periphery located at least 0.5 inches from a top surface of the first slab of concrete at the cold joint. Each baseplate also has a tubular projection extending perpendicular from the baseplate and into the first concrete slab. Each tubular projection has a length of 4 to 9 inches. Each baseplate also has multiple fasteners preferably at least three fasteners extending from the first concrete surface, through the baseplate and into the second concrete surface a distance of 0.2 to 1 inch with a head of each fastener embedded in the first concrete slab and distal ends of a further plurality of these fasteners embedded in the second concrete slab. The system also includes a plurality of straight, stainless steel or fiberglass slip dowels having first and second opposing ends and a length of preferably between 4 to 18 inches. The second end of each slip dowel is embedded in the second concrete slab while the first end extends into a different one of the tubular projections. Each slip dowel has a diameter of 0.2 to 0.4 inches, but preferably is either 0.25 or 0.375 diameter stainless steel and/or fiberglass, although other metal or non-metal dowels are contemplated. The sequence of steps in assembling or attaching the baseplate to the at least one concrete form and using it to form part of the periphery of the first concrete surface, can vary. 
     In further variations, the improved concrete surface has the slip dowels made of stainless steel with a diameter of 0.2 to 0.3 inches. The slip dowels may alternatively be made of fiberglass and have a diameter of 0.2 to 0.3 inches. Advantageously, the fasteners extend the through the baseplate and into the second concrete surface a distance of 0.25 to 0.6 inches. 
     There is also provided a method of forming a cold joint between adjoining sequentially formed first and second slabs of concrete. The method includes the steps of arranging a at least one stud to form at least a portion of a periphery of the first slab of concrete. The method also includes the step of fastening a plurality of baseplates to the at least one stud with a plurality of at least three separate fasteners forced through each respective baseplate and into the stud to which the baseplate is fastened. Each baseplate has opposing front and back sides with a thickness of between 0.015 and 0.25 inches. Each baseplate is made of a polymer which does not split or crack when each fastener is forced through the baseplate and into the stud. Each baseplate has an outer periphery which is located between a top and bottom edge wall of the stud and 0.5 inches or more from a top edge wall of the at least one stud. Each fastener has a fastener length which extends into the stud a distance of at least ¼ inch and less than 1 inch. Each baseplate has a tubular projection extending along a longitudinal axis that is substantially perpendicular to the front face of the baseplate from which the projection extends. Each tubular projection has a closed distal end and a hollow interior configured to receive a straight cylindrical shaft 0.2 to 0.4 inches in diameter through an opening in the baseplate. Each tubular projection has a length of 4 to 9 inches from the baseplate and has a sidewall thickness less than 0.1 inches. 
     The method includes pouring a first concrete area bounded partially by the at least one stud to entrain the plurality of baseplates and tubular projections. The poured first concrete is then leveled and finished to form the first concrete slab upon hardening of the first concrete, with the tubular projections extending into the first concrete slab. The method also includes removing the first plurality of studs, leaving the baseplates embedded in the first concrete slab along a first edge of the first concrete slab, with distal ends of the fasteners extending from the respective baseplates along that first edge of the first concrete slab. 
     In one further variation, the method also includes inserting a slip dowel into each tubular projection through the hole in the baseplate, with each slip dowel advantageously having a diameter of 0.2 to 0.4. The dowels may be made of stainless steel or fiberglass and may have a length of 12-18 inches. Each tubular projection is advantageously configured to slidingly but tightly receive the slip dowel. This one further variation also includes pouring a second concrete to entrain the slip dowels and the distal ends of plurality fasteners, and then leveling and finishing the second concrete to form the second concrete slab upon hardening of the second concrete. 
     In further variations of either of the above methods, the slip dowels are preferably made of metal and preferably stainless steel and have a diameter of 0.2 to 0.3 inches. The slip dowels may alternatively be made of fiberglass or other resin/polymer material and have a diameter of 0.2 to 0.3 inches. Advantageously, the method includes using only multiple and preferably three fasteners to hold each baseplate to the at least one stud. Preferably, the fasteners have a length of 0.2 to 0.5 inches extending into the stud, projecting from the first concrete edge, and embedded in the second concrete surface. Advantageously, the fasteners are nails or staples. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which; 
         FIG.  1    is a front perspective view of two tubular projections each preferably having a textured exterior surface and extending from a baseplate stapled to a concrete form; 
         FIG.  2    is a rear perspective view of one of the tubular projections and baseplates of  FIG.  1   , without the concrete form; 
         FIG.  3    is a front view along the longitudinal axis of one of the tubular projections of  FIG.  1   ; 
         FIG.  4    is a front view along the longitudinal axis as in  FIG.  3   , but showing a circular baseplate on a larger concrete form; 
         FIG.  5    is a sectional view taken along section  5 - 5  of  FIG.  1   ; 
         FIG.  6    is the sectional view of  FIG.  5    showing the projection and baseplate embedded in a first concrete surface with the concrete form attached to the baseplate; 
         FIG.  7    is the sectional view of  FIG.  6    with the concrete form removed; 
         FIG.  8    is the sectional view of  FIG.  7    with a dowel inserted into the projection and a free end extending parallel to the exterior surface of the first concrete surface; and 
         FIG.  9    is the sectional view of  FIG.  8    with a second, adjacent concrete surface embedding what was the free end of the dowel of  FIG.  8   . 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, the following part numbers refer to the following parts throughout:  10 —tubular projection;  12 —concrete form;  13 —vertical side of form;  14 —baseplate;  15 —ground;  16 —fastener;  18 —engagement feature;  20 —distal end of projection;  22 —open proximal end of projection;  24 —opening in baseplate;  26 —first concrete;  30 —slip dowel; and  32 —second concrete. 
     Referring to  FIGS.  1 - 3  and  5 - 6   , a tubular projection  10  extends along a longitudinal axis perpendicular to the vertical side of a concrete form  12 . The inside of the projection  10  is preferably smooth with a uniform cross-section along all or almost all (i.e., 90%) of the axial length of the projection. The tubular projection extends perpendicularly from a baseplate  14  which is fastened to the flat, vertical side  13  of the concrete form  12  on the side of the form adjoining the concrete when it is poured into the form. Advantageously, a plurality of fasteners, such as staples  16 , tacks or short nails are used to fasten the baseplate  12  to the concrete form  12 . The projection  10  advantageously has one or more optional ribs or engagement features  18  on the exterior side of the projection  10  to better interlock with the concrete that is poured there-around to entrain the projection during use and reduce concrete cracking. The figures show the engagement feature  18  as a continuous helical rib  18  extending along and encircling the projection  10  like a single external thread. The tubular projection  10  advantageously has a closed distal end  20  and an open proximal end  22  which coincides with an opening  24  in the baseplate  14  providing access to the hollow interior of the tubular projection  10 . 
     The hollow interior of the projection  10  is preferably cylindrical, having a diameter sufficient to receive and allow axial motion of a dowel pin  30  ( FIGS.  8 - 9   ) having a diameter between 0.2 to 0.499 inches, and preferably a diameter of 0.2 to 0.3 inches, with a conventional standard sized diameter of ¼ inch to ⅜ inch believed preferable. The preferred diameter is ¼ inch or ⅜ inch. These diameters are subject to slight variation arising from manufacturing tolerances, which variation are typically less than 5%. The projection  10  preferably has a length of 4 to 9 inches, with a length of 4 to 6 inches preferred. 
     Referring to  FIGS.  3 - 4   , the baseplate  14  although being formed having any desired configuration advantageously has a rectangular shape of its outer periphery when the concrete form  12  is a 2×4 stud, and advantageously has a circular shape when the concrete form is a 2×6 stud, and in both configurations the tubular projection  10  extends from the center of the baseplate. The baseplate shapes may be used to help align the projections in approximately the same vertical plane, advantageously the midplane of the concrete slab formed by the concrete forms  12 , with preferably coincides with the midline along the length of the concrete forms  12 , or close thereto (i.e., within ½ to ¾ inch). The rectangular shape (which includes a square) allows a user to more easily center or align a plurality of projections  10  on the concrete form  12  by visually using the same distance from the top or bottom edge of the baseplate to the respective top or bottom of concrete form—the 2×4 stud. The user could also visually center the baseplate  14  by visually comparing the distance between the top and bottom of the concrete form and the adjacent, straight and parallel sides of the baseplate. 
     The circular shape of the circular baseplate  14  allows a reduction in the material used to form the baseplate, while still allowing the user to visually locate the baseplate  14  and projection  10  at the same midplane location as the rectangular shaped baseplate. A user may visually locate the circular baseplate  14  to have the same distance between the top (or bottom) of the concrete form, and preferably to visually locate the circular baseplate to have an equal distance between the top and bottom of the baseplate and the respective top and bottom of the concrete form. 
     Preferably the thickness of the baseplate  14  is relatively thin, i.e. preferably between 1/64 of an inch to ¼ of an inch to reduce material costs and enable conventional staples/nails to easily penetrate the baseplate during installation to the 2×4 or 2×6 concrete form as described below. 
     Referring to  FIGS.  1  and  3 - 7   , the baseplate  14  is fastened to one of the concrete forms  12  by plural conventional fasteners  16 , with the baseplate having a flat surface adjoining the concrete form  12  so the tubular projection  10  is held by the baseplate substantially perpendicular to the vertical side  13  of the concrete form  12 . As used herein, “substantially perpendicular” includes angular variations of 10° and less. Advantageously, at least two and preferably three fasteners  16  surround or encircle the juncture of the projection  10  and baseplate  14 . Advantageously, the baseplate  14  is stapled by fasteners  16  which are driven through the baseplate  14  and a short distance (i.e., 0.2 to 0.6 inches) into the concrete form  12 , with the fasteners advantageously extending ¼ to ½ inches past the baseplate and into the concrete form  12 , and preferably extending ⅜ inches into the concrete form. Fasteners extending a distance of 0.2 to 1 inch are believed usable, but the longer lengths make it more difficult to strip the concrete forms from the embedded fasteners. 
     The fasteners  16  preferably comprise conventional staples which can be quickly applied from above the concrete forms  12  using conventional mechanical/pneumatic or electric staplers. However, conventional nails may be additionally utilized preferably utilizing a conventional nail gun (not shown). 
     The fasteners  16  extend into and are entrained in the second poured concrete  32  as it hardens to further hold the projection  10  and baseplate  14  in position, and to provide a small, localized interlock across the cold joint formed between the adjoining edges of the first and second concrete slabs  26 ,  32  when the slabs harden. The short length of the fasteners  16  and the small cross-sectional size or diameter of the fasteners  16  are such that the fasteners do not initiate or propagate cracks in the first or second concrete slabs  26 ,  32  when the slabs harden or thereafter. Further, the short length of the fasteners  16  are selected so the length does not extend much beyond half of the lateral thickness of the concrete form  12  when the baseplates  14  are fastened to the concrete form or stud  12 . Longer fasteners and fasteners with larger cross-section sizes make removal of the concrete form or stud  12  more difficult and also can leave the fasteners bent or curved to differing amounts because the concrete forms are typically removed by moving a first end of the form laterally away from the first concrete  26  and pivoting that first end about an opposing second end of the form with the result that the fasteners adjacent the first end of the form are straight or fairly straight, but the fasteners toward the second end of the form may be curved—depending how the studs  12  are removed. Curved fasteners  16  entrained in the second concrete  32  will resist relative movement of the first and second hardened concrete slabs  26 ,  32  along an axis parallel to the slip dowel  30  of the projection and baseplate to which the fasteners are connected, and that resistance of movement is believed to present a risk of crack initiation or spalling. Further, the fasteners  16  are made of metal, typically iron, steel or stainless steel and the thermal expansion of the metal fasteners is much greater than that of the concrete  26 ,  32 . By keeping the size of the fastener cross-section small as described, and by reducing the length, it is believed that potential cracking and spalling from the thermal expansion of the fasteners is reduced. 
     Thus, the fasteners  16  are preferably long enough in length, and large enough in cross-sectional size or diameter so that the baseplate and projection are held securely to the concrete form  12  for pouring of the concrete, but are small enough in length and cross-section to allow easy manual separation from the concrete form  12  after the first concrete  26  hardens with the separation occurring so the protruding portion of the fasteners are substantially straight and parallel to the axis of projection  10 . The fasteners  16  are also selected so they extend a short enough distance into the second concrete  32  that they provide some concrete interlock around the baseplate  14  while not extending far enough into the second concrete  32  or having a large enough cross-section that they may cause or contribute to cracking or spalling at the fastener locations as the concrete slabs  26 ,  32  move along the length of the projections  10  and slip dowels  30 , or as the concrete slabs expand and contract with temperature changes that can exceed 100° F. 
     The second concrete  32  entrains the baseplates  14  to the extent that the baseplates extend beyond the edge of the first concrete  26  as may occur if the baseplate is deformed during removal of the concrete form  12  after the first concrete  26  hardens. The second concrete  32  entrains any deformed baseplate  14  and enters any opening or recess or pocket in the baseplate that faces the edge of the second concrete  32  after the concrete form  12  is removed. The tight fit, but slip fit, between the hollow inside of the tubular projection  10  and the slip dowel  30  is small enough that while some cement may enter the inside of the projection, the amount of any such cement is small enough that it does not prevent relative movement of the slip dowel  30  inside the tubular projection  10 . 
     The baseplate  14  advantageously has no fastener holes preformed in the baseplate for the staples or for the fasteners  16  so that the shafts of the fasteners  16  are forced through the material of the baseplate and create their own hole through the baseplate. A plurality of projections  10  and their baseplates  14  are fastened to the concrete form  12  with the projections  10  preferably located in the same general plane at or preferably within one inch of the midplane of the planned concrete slab for a 2×4 concrete form  12  or stud, and within two inches of the midplane of the planned concrete slab for a 2×6 concrete form or stud. Three fasteners  16  are believed suitable to hold the baseplate  14  to the concrete form  12 , with the three fasteners located about 120° apart, with one fastener at the top center of the baseplate. The use of “about” in reference to the fastener spacing is with respect to the longitudinal axis along the centerline of the projection  10 , and encompasses a variation of 20 degrees either direction from the equidistant position achieved by the preferred 120° spacing. Advantageously, the three fasteners  16  are located with at least one fastener above the horizontal plane through the centerline along the length of the projection  10  and at least two fasteners  16  below that plane. But other arrangements may be used, including one fastener on a first side of a vertical plane through the centerline of the projection  10  and two fasteners on an opposing, second side of that vertical plane. As will be recognized by locating the fasteners in such a manner, the fasteners can be quickly applied from above the concrete forms using a conventional staple or nail gun (not shown). 
     The rectangular baseplate  14  allows multiple, i.e., preferably three fasteners  16  to be manually driven through the baseplate  14  by a worker kneeling over the stud and projection when the stud is on the ground (or other surface on which the concrete is poured) and the sides  13  of the studs or concrete forms  12  are vertical, and a fastener  16  through each corner of the baseplate extending into the stud forming the concrete form  12  provides for a sturdy connection that aligns the projection  10  perpendicular to the side  13  of the stud and that inhibits entry of the concrete between the baseplate and the stud as may block or hinder access to the hollow projection  10 . Three staples or fasteners may be similarly applied easily to a circular baseplate  14 . 
     As shown in  FIGS.  5 - 6   , after the projection  10  and baseplate  14  are fastened to the concrete form  12 , uncured first concrete  26  is poured into the forms  12  to entrain the projections  10 . The exterior surface of the first concrete  26  is finished while the concrete is still wet and pliable enough to be altered. The exterior surface of the first concrete  26  is typically finished flat with the top surface of the concrete form  12  or parallel to that top surface of the form  12 . 
     Referring to  FIG.  7   , the wet first concrete  26  flows around the engagement features  18  on the projection  10  to interlock with the first concrete  26  as it hardens. When the concrete hardens, the hardened first concrete  26  interlock with the engagement features  18  to restrain movement of the projection  10  along the length of the projection  10 . The wet first concrete  26  also flows around the edges and inward facing portion of the baseplate  12 . But the baseplate  12  has a flat back that is fastened to the flat side of the concrete form  12  so no concrete flows between the baseplate and the concrete form. 
     When the concrete hardens sufficiently to support a person&#39;s weight without deformation, or as otherwise specified by the concrete requirements, the concrete forms  12  are removed, i.e., stripped from the first concrete  26 . As the projections  10  and periphery of the baseplates  12  are embedded in the first concrete  26  and as the projections and baseplates are permanently connected, the projections and base plates remain embedded in the first concrete  26  when the form is removed. The fasteners  16  also remain embedded in the first concrete  26  and project outward from the vertical surface of the concrete slab. 
     A slip dowel  30  is then inserted into the hollow inside of each tubular projection  10 . The slip dowel  30  is preferably a fiberglass or stainless steel rod, 0.2 to 0.499 inch diameter, and preferably ¼ or ⅜ inch diameter. The slip dowel material and diameter are preferably selected so each slip dowel has or provides a shear stress of 6000 psi. The slip dowel  30  is preferably cylindrical in shape, but other cross-sectional shapes may be used, including rectangular (which includes square shapes), hexagonal and oval shapes. The slip dowel  30  has a length of 12 to 18 inches and is inserted until an end of the dowel  30  hits the closed end  20  of the now embedded projection  10 , with the installer preferably moving the dowel  30  outward, away from the closed end a movement distance, preferably a distance of 0.2 to 1 inches, with a movement distance of ¼ to ½ inch preferred. That leaves a length of the slip dowel  30  extending outward from the vertical side of the hardened first concrete  26  and a slight space between the interior end of the slip dowel and the closed end of the projection  10 . An extending length of 6 to 9 inches is preferred, preferably about half the length of the dowel (i.e., within an inch of the center). 
     If the slip dowel  30  makes contact with the closed end of the projection  10 , then thermal expansion of the dowel may be sufficient to create internal pressure on the concrete  26 ,  32  embedding the slip dowel, and may lead to cracking or buckling of the concrete. Thus, a slight space of 0.2 to 0.5 inches is preferred to exist between the closed end  20  of the projection  10  and the adjacent end of the slip dowel inserted into the projection, with the space being sufficient so that thermal expansion does not cause the slip dowel  30  to contact the closed end  20 . The short gap or space can help prevent undesirable pressure between adjoining concrete sections that may be caused by the slip dowel  30  pressing against the end of the projection  10  when the concrete expands. Such pressure can potentially expedite undesirable weakening of the concrete. 
     After a slip dowel  30  is placed inside each of the projections  10 , then a second wet concrete  32  is poured into a set of forms adjoining the first concrete  26 , to form a second concrete slab. The second concrete  32  entrains the previously exposed end of the slip dowel  30  and the distal ends of the fasteners  16  extending beyond the back of the baseplate  14 . If the distal ends of the fasteners are not bent over, they extend about 0.2 to 0.8 inches into the second concrete  32  and provide further concrete interlock between the first and second concrete slabs  26 ,  32  along the length of the fasteners. The exposed surface of the second concrete  32  is finished while pliable, and usually finished to create a continuous exterior surface with the first concrete  26 . After the second concrete  32  hardens, the concrete form  12  or forms for that second concrete are removed. 
     The projection  10  may be temporarily fastened to the slip dowel  30  by friction or by other means of temporary attachment, such as low strength adhesives or other adhesives applied over a small area so that a small force of under 5 or 10 pounds can cause relative axial movement between the projection and slip dowel. One of ordinary skill in the art will appreciate that the fit between each slip dowel  30  and its corresponding projection  10  is tight enough and sealed enough so that it is unlikely that pourable concrete can leak into the inside of the projection  10  and into the space between the projection and the slip dowel inserted into the projection when the concrete is poured and the slab hardens. Concrete leaking into the interior of the projections can negatively impact one of the functions of the concrete dowel system, which is to allow slip dowels  30  to slide freely within the projections  10 . Further, the fasteners  16  holding the baseplate  14  and projection  10  to the concrete form  12  is strong enough such that the pouring of the concrete does not break or disrupt the connection and cause misalignment of one or more of the projections  10 . 
     As the concrete  26 ,  32  expand and contract, the slip dowels  30  move along the length of their respective projections to allow movement along the longitudinal axes of the projections, which axes and projections are aligned in the same plane. As a weight moves horizontally across the joint from the first concrete  26  to the second concrete  32  (e.g., a person walking, or a light vehicle), the slip dowels  30  interlocked with the concrete distribute that vertical load across the juncture of the concrete and into the adjacent first and second concrete in which the slip dowels and projections are entrained. 
     By using small diameter slip dowels  30 , the weight of the dowels that must be supported in position by the baseplates  14  is reduced sufficiently so that the baseplates  14  may hold the projections  10  in a sufficiently perpendicular position relative to the vertical side  13  of the concrete forms  12  to avoid cracking of the concrete  26 ,  32  when the concrete expands and contracts and when vertical loads traverse the joints between adjoining concrete slabs  26 ,  32 . By selecting the thickness and size of the baseplate  14  to support this reduced weight of the slip dowel  30 , the baseplate may be more quickly fastened to the concrete forms  12  and be less costly to fabricate than in the prior art. An installer may use a conventional hammer stapler to drive a two-pronged staple of fastener  16  through the baseplate  14  and into the wooden stud of the concrete form  12  with each swing of the hammer stapler. That provides for much faster installation that in the prior art. 9/16 wide crown staples are believed suitable. Finish nails with lengths of 0.5 to 1 inch and diameters of 0.05 to 0.1 inches are believed suitable for the fasteners  16 , as is a 2d penny nail, finish nail, casing nail, box nail or brad. As used herein, a reference to a nail includes these various types of nails, tacks and brads. A 2d penny nail is believed to have a diameter of 0.07 inches, and staples with the same diameters or cross-sectional areas on each of the prongs or legs of the staples are believed suitable. As used herein, a staple is considered as one fastener even though it has two prongs. It is contemplated that irrespective of the particular type of fastener being used, it will be installed using a conventional staple or nail gun for quick installation. 
     The fasteners  16  and baseplate  14  remain embedded in the concrete so there is a vertical separation surface on the slab of first concrete  26 . There are no large voids in the edge of the first concrete formed by a removable baseplate as in the prior art, and there is no need to pry any broken pieces of a removable baseplate out of the concrete as in the prior art. The fasteners  16  are short in length and small in diameter so little force restrains the separation of the concrete form  14  from the hardened first concrete  26  as the form  14  is stripped away from the edge of the hardened slab of the first concrete  26 . The tips of the fasteners  16  project from the vertical side of the hardened slab of first concrete when the form  14  is removed. But the fasteners  16  are short in length, small in diameter, are easily bent sideways so the temporarily exposed fastener tips do not easily penetrate the boots worn by construction workers. The tips of the fasteners are exposed only for the short time between removing the form  14  and pouring the adjacent or adjoining second concrete  32 . Thus, the time needed to install and remove the projections  10  and forms  12  is reduced. Further, the exposed tips of fasteners  16  are easily bent sideways so a worker with a hammer, club or steel-toed shoe can quickly bend them sideways or downward to further reduce any potential adverse contact with the exposed fastener tips. 
     The length of the exposed tips of fasteners  16  are short enough that while they are entrained in both the first and second concrete  26 ,  32 , the fasteners  16  are believed small enough, especially relative to the aggregate size typically used with the described concrete forms  12 , so the fastener tips are believed not to cause any cracks to propagate to the exterior surface of the adjoining concrete slabs under temperature changes and as vertical loads pass over the joint between adjoining first and second concrete slabs. 
     There is thus advantageously provided a method and apparatus for more quickly installing a interlock system of slip dowels  30  and hollow projections for receiving those dowels, in adjacent slabs of concrete  26 ,  32 . The interlock system has the projections  10  aligned sufficiently perpendicular with the concrete forms  12  and slip dowels  30  so that adjoining first and slabs of concrete  26 ,  32  do not crack under the temperate variations or under the vertical load variations for which such slabs are conventionally designed. 
     Several of the parts are described in more detail below. The projection&#39;s opening  24  is advantageously the same size as is the interior of the tubular projection  10 , but to make it easier to insert the slip dowel  30  into the inside of the tubular projection, the opening  24  could be slightly larger in cross-sectional dimension (i.e., 5% to 20%) than the hollow interior dimension of the tubular projection and tapered like a funnel. Any tapered length is advantageously short and preferably 0.25 to 0.5 inches long as measured from the side of the baseplate  14  adjoining the concrete form  12  during use. Advantageously, both opposing ends of the slip dowel  30  are not square, and are instead rounded and preferably chamfered at 30°-45° for a short length of an eighth of an inch or less, to make insertion into the inside of the projection  10  easier and to allow either end of the slip dowel to be inserted into the projection. 
     The distal end  20  of projection  10  advantageously has a rounded or chamfered external end. The avoidance of sharp corners is believed to reduce potential cracking locations. The closed end  20  of the projection  10  may be integrally formed with the projection  10 , or may be achieved by fastening an end cap over the distal end of the tubular projection. Such an end cap may comprise a piece of duct tape or construction tape, a cap, a plug, a piece of film, or any blockade that is either permanently affixed or removably attached to the distal end of the projection  10 . 
     The tubular projection  10  is advantageously made of a polymer material as is the baseplate  14 . Advantageously, the baseplate  14  and tubular projection  10  are integrally molded in a single pour injection molding process to form a unitary, simultaneously molded structure, so the open proximal end  22  of the projection  10  is the same as the opening  24  in the baseplate. The tubular projection  10  could be formed separately with its longitudinal axis centered on and the projection fastened around the opening  24  in the baseplate  14 , as by welding or spin welding, or less desirably by adhesives, by nesting the projection inside an encircling cylindrical flange on the baseplate, or other fastening mechanisms. 
     The projection  10  into which the slip dowel  30  is sheathed may have any cross-sectional shape, although advantageously the cross-sectional shapes for the projection and dowel are the same. Circular-cross-sectional shapes are preferable, with just enough space between the slip dowel  30  and the inner wall of the sheathing projection  10  to allow easy insertion by the installers and to allow movement during use that does not cause or propagate cracking. A spacing of 1 to 10 thousandths of an inch between the outer surface of the slip dowel  30  and abutting interior surface of the projection  10  is believed suitable with a spacing of 2 to 5 thousandths of an inch preferred when the parts are both aligned on the longitudinal centerline of the projection. If the spacing is too large then the slip dowel embedded in the second concrete  32  can shift position a greater distance before the dowel engages the tubular projection  10  in the first concrete  26  to interlock the adjoining concrete slabs. A smaller spacing provides a tighter interlock and greater strength. This spacing is affected by variations in the thickness of the sidewall of the tubular projection  10 , which affects the diameter or cross-sectional size of the hollow interior of the projection  10 . The sidewall thickness may vary depending on molding conditions and tolerances and the materials being molded. The sidewall of the tubular projection  10  advantageously has a thickness less than 0.1 inches and preferably less than 0.05 inches. 
     In use, gravity will cause the slip dowel to rest on and be slid along the bottom of the interior of the tubular projection  10 . The inside of the tubular projection  10  need not be a smooth cylinder as the projection may have engagement features to better entrain the projection  10  in the concrete and the wall thickness of the tubular projection may be substantially uniform (subject to molding variations) resulting in portions of the projection&#39;s tubular wall that exceed the desired spacing for short (under 0.2 inches) portions of the length of the tubular projection  10 . But the walls of the tubular projection  10  are sufficiently continuous along the length of the projection to support the slip dowel  30  substantially continuously along the length of the tubular projection  10  with the desired spacing. As used in this spacing context, the term “substantially continuously” refers to the desired spacing every 0.2 inches along at least 80% of the length of the tubular projection The ends of the dowel  30  can be rounded, tapered or otherwise configured to facilitate inserting the dowel into the inside of the projection  10 . This spacing of one to ten thousands to support the slip dowel substantially continuously along the length of the tubular projection  10  allows the slip dowel to fit tightly but slidingly inside the tubular projection. 
     The projection  10  is shown with a single, helical wound engagement feature  18 . A variety of configurations may be used for the engagement features  18 , including an intermittent, helical would rib, and radial ribs encircling the projections&#39; circumference in a continuous or intermittent manner. A plurality of wavy ridges and intervening valleys as found on rebar or structural reinforcing rods are also believed suitable. Engagement features extending outward from the longitudinal axis of the protrusion a radial distance sufficient to form a protrusion height of 1/16 to ⅛ inch above the generally cylindrical outer surface of the projection  18  are believed preferable. The engagement features advantageously have no sharp corners as may give rise to stress concentrations and induce cracking in the concrete. The engagement feature  18  on the projection  10  is believed desirable, but is optional. 
     Engagement features  18  may optionally be provided on a portion of the free end of the slip dowel  30  which is embedded in the concrete  32 . Any such engagement feature on the free end of the slip dowel does not extend into the projection  10  so as to inhibit free movement of the slip dowel along the length of the projection  10  into which the dowel is inserted or sheathed during use. 
     The concrete form  12  is advantageously a 2×4 or 2×6 wooden stud, and preferably finished studs. The finished studs have cross-sectional dimensions about 0.5 inches smaller than the unfinished or rough cut stud dimension in the long dimension, and about ⅜ inches smaller in the shorter dimension. A finished 2×4 typically has a cross-section of 1⅝×3½ inches, and a finished 2×6 typically has a cross-section of 1⅝×5½ inches. 
     The rectangular baseplate  14  advantageously has sides 2 to 2.5 inches long each side, with a thickness of 0.03 to 0.25 inches and preferably between 1/64 and ¼ inch when made of polypropylene or other suitable plastic or polymer that does not split or crack when the fastener is driven through the baseplate and into the form in a single strike of a hammer or hammer stapler. A baseplate made of polypropylene having a thickness of 1/64 to ¼ inch is believed suitable, with a thickness of 1/64 to 3/16 preferred. Thicknesses of 0.015 to 0.3 inches are believed suitable with ranges of 0.015 to 0.3 inches more preferred. Other polymer materials that allow fastener  16  to be driven manually through the baseplate by a single hammer blow or a manual hammer stapler, without cracking or breaking, are believed suitable. 
     Advantageously, the square baseplate  14  allows placement on the form  12  with the upper edge of the baseplate located at least 0.5 inches from the top of the form  12 . A circular baseplate  14  advantageously has a diameter of 2-2.5 inches. The circular baseplate may be positioned closer to the top of the form  12  because it does not have an extended length extending parallel to the top of the form and thus the intervening concrete  26  is stronger and less susceptible to cracking induced by the baseplate. While rectangular and circular baseplates are preferred, other shapes can be used, with plates having four to eight flat sides believed preferable, and with plates having circular or oval curved outer peripheries believed suitable. 
     The fasteners  16  advantageously have a length of 0.2 to 0.7 inches, with lengths of ¼ to 9/16 inches preferred, and a length of about 0.4 inches (give or take 0.05) preferred. 9/16, wide crown staples are believed suitable. The shaft thickness is sufficient to allow full installation of the fastener in one swing of a manual installation tool, such as a hammer or hammer stapler, with the fastener head against the baseplate. Electric or air powered staplers may be used but are not believed as desirable as mechanical hammer staplers. Advantageously, three or more fasteners  16  are used, one toward the top of the baseplate  14 , partially above the projection  10 , and one on each opposing side of the projection. The fasteners are long enough to hold the baseplate and projection in position, but short enough that the concrete form  12   
     The slip dowel  30  is preferably a smooth steel rod, but it is contemplated that the slip dowel  30  may be made of aluminum, iron, stainless steel, fiberglass or any other suitable metal or metal alloy or material strong enough to endure longitudinal or vertical compression and expansion forces that may occur between sections of concrete without bending enough to crack the concrete. AR-Glass, R-Glass, S2 Glass fiber and Z-Glass are various fibers and fiberglass believed suitable for use as slip dowels. Further, the entire outer surface of the slip dowel  30  need not be smooth. For example, a length portion of the slip dowel  30  intended for entrainment in the wet concrete may include a ribbed outer surface, similar to the outer surface of typical re-bar, or include other features on the outer surface such that the slip dowel is unsmooth such that when entrained in concrete that hardens, the unsmooth features will inhibit the slip dowel from movement along its axis. 
     The ability for the slip dowels  30  to slide freely within the sheaths formed by projection  12  allows the interface between the first concrete  26  and the second concrete  32  to remain aligned, thus preventing faulting, i.e., undesirable skewing of the hardened first concrete section  26  and the second hardened concrete section  32  at the cold joint betw 3 en those concrete sections. Skewing at the cold joint may damage the concrete, weaken the concrete, or result in undesirable aesthetics. 
     In use, the ground is leveled and prepared by any tamping, addition of sand or other steps appropriate to the particular pour. One or more concrete forms  12  are arranged around the periphery of the planned pour and fastened to the ground, usually by stakes. At least one concrete form  12  is used, as sometimes adjacent slabs of concrete or other structures provide the forms that define the periphery of the concrete slab. Structural steel reinforcing or rebar is placed as desired within the area of the pour inside the concrete forms. The rebar is typically arranged in a rectangular gridwork with regular spacings between the rebar crossings. The spacing and thickness of the rebar and the slab thickness depend on the loads expected to be carried by the concrete. 
     The projections  10  are fastened to the concrete forms  12  by passing fasteners  16  through baseplate  12  and into the vertical side  13  of the concrete form. Typically a construction worker holds the baseplate  12  or projection  10  to position the baseplate on the form, visually estimating the distance between the top of the form and the top of the baseplate at the de sired spacing (usually at least 0.5 inches). A hammer stapler can drive a fastener  16  into the baseplate to tack the baseplate to the concrete form, and the projection can be held until two or three more fasteners are placed to hold the projection to the form. Sufficient fasteners  16  are used to not only hold the projection perpendicular to the vertical side  13  of the concrete form  12 , but to hold the periphery of the baseplate  14  against the vertical side  13  to block concrete from flowing between the form and the baseplate. Although, a little concrete and even fine aggregate, such as sand, may pass between the baseplate and the form, it typically is not enough to block access to the opening  24  in the baseplate into which the slip dowel  30  is inserted. 
     A series of projections  10  are fastened to the concrete form, with the projections spaced a distance apart corresponding to the rebar gridwork spacing, typically about 18 inches. The construction workers can visually align the projections  10  to align with a projecting end of a rebar, or they can place the projections  10  to be located between the projecting ends of two adjacent rebar. In some cases, rebar ends are placed vertically above each other and the projection  10  is located to extend between the two projecting ends to provide a stronger interlock joint between adjacent slabs. The sequence of the above steps may vary, depending on equipment and worker availability and depending on the design of the concrete slab to be poured. 
     The first concrete  26  is then poured, the slab has its exterior (top) surface leveled and then finished as desired. After the first concrete  26  has hardened sufficiently, the at least one concrete form  12 , and more typically the plurality of concrete forms  12  are removed by pulling them laterally away from the edges of the concrete, leaving the baseplates  12  and projections  10  embedded in the first concrete with the ends of the fasteners exposed. Advantageously, each fastener  16  has a fastener head abutting the baseplate  14  and restraining the fastener from being pulled through the baseplate  14 , and each fastener has no barbed ends or laterally extending protrusions that retain the fastener in the concrete form  12  (e.g., screw threads), so the forms are easily stripped from the hardened first concrete so as to leave the fastener heads and baseplates  14  embedded in the first concrete  26 . As the stripped concrete forms  12  have no fasteners or large holes in them as required by prior art cold joint methods, the concrete forms may be reused as concrete forms or used for other purposes. The ends of the fasteners  16  extending from the edge of the first concrete  26  may optionally be bent against the first concrete by manual tools or by stepping on them with a person&#39;s booted foot, but the fasteners are advantageously weak enough and short enough that they do not penetrate with boots of construction workers if accidently kicked. The exposed edges of the first concrete form one side of a cold joint. In some cases an expansion strip may be placed along an exposed edge of the first concrete with the adjoining second concrete poured against the expansion strip. 
     One or more edges of the first concrete  26 , when hardened, may comprise a concrete form having a height the same as that of the first concrete&#39;s top surface. A construction worker then inserts the slip dowel  30  through the openings  22 ,  24  of the tubular projection  10  and baseplate  14 , into the inside of each of the respective tubular projections  10 . The above described steps are then repeated to form a second concrete  32  adjoining one or more sides of the first concrete  26 , with the wet, second concrete poured against the hardened side of the first concrete (with or without the expansion strip interposed between adjoining concrete slabs). 
     Optionally, the concrete form  12  may be pre-marked with a line extending along the length of its vertical side  13  to indicate the spacing and location of the top of the baseplate. A line along the top and bottom of the vertical side  13  allows the concrete form  12  to be placed with either edge by the ground and still provide the desired spacing guidance. A painted center strip along the length of the concrete form  12  could alternatively create lines indicating the area within which the baseplate could be placed. The projections  10  can be fastened to the concrete form  12  before or after the forms are placed against the ground to define the periphery of the poured concrete slab. 
     The detailed description set forth above in connection with the drawings is intended as a description of some, but not all, of contemplated embodiments of the disclosure, and is not intended to represent the only form in which the present disclosure may be constructed or utilized. The description sets forth the functions and the sequence of steps for developing and operating the disclosure in connection with the illustrated embodiments. 
     It is to be understood, however, that the same or equivalent functions and sequences may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the disclosure. It is further understood that the use of relational terms such as first and second, top and bottom, and the like are used solely to distinguish one entity from another entity without necessarily requiring or implying any actual such relationship or order between such entities. 
     The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present disclosure only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present disclosure. In this regard, no attempt is made to show structural details of the present disclosure in more detail than is necessary for the fundamental understanding of the present disclosure, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present disclosure may be embodied in practice.