Abstract:
In a method of making insulated concrete tilt-up panels, an insulating material such as polystyrene is formed into a desired shape corresponding to the panel shape. Attachment grooves are formed across the surface of the insulating material. Preferably, the attachment grooves have a substantially triangular cross-section. The insulating material is laid groove-side-up in a concrete form and wet concrete is poured into the form. The concrete fills the grooves, attaching the insulation to the concrete panel. When the concrete is cured, the panel may be stood up and set in place so that the insulating material forms the exterior surface of the panel. A finishing material may be applied to the exterior surface of the panel. A panel set for use in constructing low-income residential housing includes four concrete tilt-up panels. The insulating material and concrete forms may be prepared in the quantity desired for the entire construction project and transported to a casting area at the construction site. The panels may be rapidly cast and assembled, reducing the time and labor required to complete the project.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of co-pending provisional application No. 60/937,027 filed Jun. 25, 2007. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates to concrete wall construction. This invention relates particularly to a process for creating insulated concrete tilt-up wall panels and the resultant products. 
       BACKGROUND 
       [0003]    Building structures using tilt-up concrete wall panels are well known in the art. They can significantly reduce the initial cost of construction, increase the life of the structure and reduce maintenance cost. Tilt-up panels are made under controlled conditions and the exterior surface can be inexpensively finished with rollers to shape an attractive product. Such panels can be pre-cast, fabricated and stored in the factory and then transported to the building site, or made in-situ, forming the panels at the building site. Walls, and therefore buildings, can be assembled rapidly using the panels. 
         [0004]    In general, tilt-up concrete panels are made by attaching a concrete form having the dimensions of the desired panel to a casting surface, then filling the cavity of the concrete form with freshly mixed concrete and letting the concrete cure. Concrete forms are conventionally constructed on-site as needed for each building and made of wood or metal; these forms are removed after the panel is cured. Alternatively, the forms may be pre-made forms of foam, plastic or metal into which the concrete is poured; these forms become integral with the panel. Metal ties such as rebar span the forming panels to connect and maintain the positions of the opposed forming panels as the concrete is placed. Often the ties are formed into grids, webs, chairs, or a combination thereof. The ties are left in the concrete as it hardens, and thus reinforce the strength of the panels, as well as provide support for connecting the formed panels to each other when constructing a continuous wall. The edges of the tilt-up panels may be beveled to provide some tolerance when placing the panels together in the wall, and the joints created between the tilt-up panels are caulked. 
         [0005]    Concrete walls have large thermal mass, but are poor insulators. That is, once the heat or cold is absorbed by the concrete, it is conducted unfortunately rather well. It would therefore be advantageous to insulate a concrete tilt-up panel. Further, it would be more advantageous to insulate the tilt-up panel along its exterior surface, so that the thermal mass of the concrete is cooled or heated by the environment inside the structure rather than from the outside. A wall using such panels would reduce energy consumption of heating and air conditioning units by regulating the temperature of the interior space. 
         [0006]    Some known methods of insulating tilt-up panel walls use insulating materials commonly known in the construction industry, such as rigid pre-formed foam panels or spray foam that hardens. However, it is difficult to attach rigid foam panels to the relatively smooth finished exterior surface of a concrete tilt-up wall, and spray foam does not stick in place long enough to harden. A common solution is to insert a layer of insulation between two layers of concrete, either during formation of a single panel or once the panels are in place in the wall. This solution does not take full advantage of the thermal mass of the tilt-up wall, allowing part of the wall to heat or cool without insulation while providing a smaller thermal mass for regulation of the interior temperature. Further, the uneven heating and cooling of the wall may weaken its structural integrity. A tilt-up wall with a fully insulated thermal mass is needed. 
         [0007]    Therefore, it is an object of the invention to provide a process for creating insulated tilt-up concrete panels. It is a further object that the tilt-up concrete panels be individually insulated on the exterior surface. It is another object of the invention to provide a process for creating insulated tilt-up concrete panels which improves the efficiency of on-site panel construction. 
       SUMMARY OF THE INVENTION 
       [0008]    This invention is a method of making insulated concrete tilt-up panels and the resultant products. An insulating material is formed into a desired shape. Preferably, the insulating material is pre-formed rigid polystyrene. A standard panel typically has a substantially rectangular insulating material, while custom panels may have irregular shapes, such as cutouts for a door or window. Multiple panels of a given shape may be pre-made for use in a construction project where the panel shapes are repeatedly used. 
         [0009]    One or more attachment grooves are formed across the surface of the insulating material. Preferably, the attachment grooves have a substantially triangular cross-section. One edge of the insulating material may be formed with a tongue and the opposing edge formed with a groove, or the edges may be interlocking, such that one panel may be easily and securely attached to another panel. 
         [0010]    One or more segments of insulating material are laid horizontally within a conventional concrete tilt-up panel form. If multiple segments are used in a single form, each seam between the segments may be sealed to prevent seeping of wet concrete. The attachment grooves face up to receive the concrete. The concrete is poured onto the insulating material until the form is filled. The concrete fills the triangular grooves, thus attaching the insulation to the concrete panel. When the concrete is cured, the panel may be stood up and set in place so that the insulating material forms the exterior surface of the panel. 
         [0011]    A combination of four panels, each having a different shape, is disclosed which may be used to build the exterior walls of multiple models of residential homes, such as those in a subdivision of low-income housing. The insulating material may be prepared in the quantity desired for the entire construction project and transported to a casting area at the construction site. The panels may be rapidly cast and assembled, reducing the time and labor required to complete the project. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of insulating material with the attachment grooves facing up. 
           [0013]      FIGS. 2   a - 2   f  are cross-section views of various shapes of the attachment grooves. 
           [0014]      FIG. 3  is a perspective view of an alternative embodiment of insulating material showing the attachment grooves in combination with attachment perforations. 
           [0015]      FIG. 4   a  is a cross-section view of an attachment perforation. 
           [0016]      FIG. 4   b  is a top view of an attachment perforation. 
           [0017]      FIGS. 5   a - d  are perspective views of various edge shapes which may be used on the insulating material or its segments. 
           [0018]      FIG. 6  is a perspective view of three segments of insulating material connected to each other and lying on a casting surface and within a concrete form. 
           [0019]      FIG. 7  is a perspective view of the segments of insulating material of  FIG. 6  connected to each other with glued seams. 
           [0020]      FIG. 8  is a perspective view of three segments of insulating material and spacing material within a concrete form. 
           [0021]      FIG. 9   a  is a partial end view of two segments of insulating material connected to each other with a glued seam. 
           [0022]      FIG. 9   b  is partial, isometric end view of an insulated tilt-up panel, in which the insulating material is resting atop the concrete. 
           [0023]      FIG. 10   a  is a perspective view of the casting surface, concrete form, and insulating material of  FIG. 6  with rebar added to the concrete form. 
           [0024]      FIG. 10   b  is a cross section view of an insulated tilt-up panel, illustrating the rebar chair supporting the rebar. 
           [0025]      FIGS. 11   a - f  are cross-section views of various methods of sealing a joint. 
           [0026]      FIG. 12  is a front view of a panel set for building low-income homes. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]      FIGS. 1-12  illustrate a concrete tilt-up wall panel  10  in accordance with the present invention. The exterior walls of a structure are formed by erecting and arranging a plurality of concrete tilt-up wall panels, referred to herein as panels  10 , and permanently connecting the panels  10  to each other. A panel  10  comprises concrete  11 , which may be any building concrete desired by the builder, and an insulating material  12 . 
         [0028]    Insulating Material 
         [0029]    The insulating material  12  is preferably a substantially rigid insulating foam which may be cut with a hot knife and will not be damaged when wet concrete is poured onto it as explained below. Further, the insulating material  12  preferably has an R-value, used in the art to measure resistance to heat flow, of four per inch or higher. Two examples of such material which are known in the art are molded expanded polystyrene (“MEPS”) and extruded expanded polystyrene (“EEPS”). In the present invention, EEPS is preferred due to its higher resistance to water vapor and heat flow. The insulating material  12  most preferably has an R-value of 4.5 per inch. Other polymer foams having a higher density and R-value, such as polyisocyanurate or polyurethane, may be used. 
         [0030]    Some MEPS and EEPS insulating foam has a thin material, called facing, applied to its outer surfaces in order to protect the foam from damage during handling. Some types of facing may also form a vapor barrier and increase the insulating material&#39;s  12  resistance to heat flow. The facing may be a polymeric film, aluminum foil, kraft paper, or another thin protective layer. In the present invention, insulating foam having facing has been shown to perform better than foam without facing. Preferably, a facing is used that has increased vapor impermeability, such as a polymeric film. 
         [0031]    To make a panel  10 , the insulating material  12  is formed into a desired shape and thickness. As used in the present disclosure, “shape” refers to the two-dimensional outline of a component. For example, the insulating material  12  may have the shape of a rectangle and a thickness of two inches or more. See  FIG. 1 . The insulating material  12  may be formed as a single piece for each panel  10 , or it may be formed in segments  13  which are fit together in a panel  10 , as shown in  FIG. 6  and described below. 
         [0032]    One or more attachment grooves  14  are cut, such as by a hot knife, into the insulating material  12 . The attachment grooves are shaped so that when concrete hardens in them the concrete is prevented from being pulled out of the groove because the foam acts as a physical barrier to block it. In other words, the maximum width of the portion of the attachment groove  14  that extends into the insulating material  12  is wider than the opening of the attachment groove  14  on the surface of the insulating material  12 . In the preferred embodiment, at least part of the attachment groove  14  has a substantially triangular cross-section, as shown in  FIGS. 2   a - 2   e . These figures are not exhaustive, and various angles, base widths, sizes, and heights will suffice, depending on the material properties, cost, and manufacturing factors of the insulating materials, cutting tool, and concrete. The triangle shape may also have a neck attached, as shown in  FIG. 3   a . Alternatively, any groove shape that prevents hardened concrete from being pulled out of the groove will suffice, such as oval, spherical, elliptical, or trapezoidal shapes. Again, this list is not exhaustive, and various shapes, angles, widths, diameters, and heights will suffice, depending on factors such as the material properties, cost, and manufacturing factors of the insulating materials, cutting tool, and concrete. 
         [0033]    Preferably there are at least two attachment grooves  14  per segment  13  of insulation material  12 . The attachment grooves  14  may run parallel or perpendicular to the structure foundation, but preferably are perpendicular to it. In an alternative embodiment, attachment perforations  15  are made in the foam panel. See  FIGS. 3 and 4   a - b . These attachment perforations  15  may be used alone or in conjunction with the attachment grooves. In the alternative embodiment, the attachment perforation  15  is a substantially cylindrical groove formed in the insulation. The attachment perforations  15  may be formed by machines similar to lawn aerators, with pegs extending from a rolling cylinder. Preferably the attachment perforations do not extend entirely through the foam panel, but they may do so, depending on factors such as material properties, cost, and manufacturing factors of the insulating materials, cutting tool, and concrete. 
         [0034]    The edges  16  of the insulating material  12 , including the edges  16  of any individual segments  13 , are preferably squared off to provide a smooth contact surface when separate pieces of insulating material  12 , or separate segments  13 , are laid next to each other. See  FIG. 5   a . Alternatively, the edges  16  may be fashioned into joint structures such as a tongue and groove, mortise and tenon, or interlocking pattern. See  FIGS. 5   b - c.    
         [0035]    Casting 
         [0036]    Referring to  FIG. 6 , a panel  10  is formed on a casting surface  30 , preferably a substantially smooth concrete slab that is larger than the panel  10 , such as the pad of a foundation of a house, or a parking lot. The insulating material  12  is placed flat on the casting surface  30 , grooved side up, within a concrete form  31  which will determine the shape of the panel  10 . If the insulating material  12  is divided into segments  13 , the segments  13  are fit together within the concrete form  31 . The segments  13  are then attached together, and the seams  18  between them sealed, by a sealant  17 . See  FIG. 7 . The sealant  17  may be any type of adhesive compound or other substance that will adhere to the insulating material  12  and seal the seam  18 , such as adhesive-backed paper or plastic, duct tape, joint tape, caulk, joint compound, or expanding foam glue, and preferably has insulating properties similar to the insulating material  12 . In the preferred embodiment, the sealant  17  is a heat- and water-resistant expanding foam glue. Examples of such a glue are made by Hilti® and Touch ‘n’ Seal®. 
         [0037]    In one embodiment, shown in  FIG. 6 , the shape of the insulating material  12  is the same as the shape of the concrete form  31 . This embodiment is useful when casting a complete wall as a single panel  10 . The joints between walls can then be capped as described below. In another embodiment, shown in  FIG. 8 , the shape of the insulating material  12  is smaller than the shape of the concrete form, leaving space between the insulating material  12  and the concrete form  31  on at least one side. This space may be filled by a spacing material  32  which is composed of or coated with a material that will not bond to wet concrete. Preferably, the spacing material  32  has the same thickness as the insulating material  12  and is sized to completely fill the empty space. The resulting panel  10  would have a solid concrete component  11  which extends past the insulating material  12  on any side on which the spacing material  32  was used during casting. As described below, and illustrated in  FIGS. 11   b - c , this allows two such panels  10  to be erected and attached to each other from outside the structure, and the joint between two such panels  10  to be covered by additional insulation when the panels  10  are erected. 
         [0038]    Once the insulating material  12  and any spacing material  32  is in place within the concrete form  31 , wet concrete  11  is poured into the concrete form  31  on top of the insulating material  12 . The wet concrete  11  fills the attachment grooves  14  and any attachment perforations  15 . See  FIG. 9 . Once the concrete form  31  contains the desired amount of concrete  11 , the surface tension of the concrete  11  against the insulating material  12  may cause the concrete  11  to adhere to the insulating material  12 . Further, some of the wet concrete may seep into the interstitial space within the insulating material  12 . If this adhesion is not desired, it may be prevented by using an insulating material  12  that has a facing as described above. Another effect of the weight of the wet concrete  11  is that it may press as much concrete  11  into the attachment groove  14  as possible, partially compressing the insulating material  12  into the sides of the groove and more firmly attaching the concrete  11  to the insulating material  12 . 
         [0039]    Referring to  FIG. 10   a , one or more reinforcement structures  33  may be added to the concrete form  31  to strengthen the panel  10 . The reinforcement structures  33  are positioned so they are at least partially encased by the concrete  11  when it is poured into the concrete form  31 , and may extend out of the concrete  11  so that they may be used to align the panel  10  or to attach other structures to the panel  10 . For example, the reinforcement structures  33  may be metal ties, such as rebar, which span the panel  10  and will connect and maintain the positions of additional panels  10  when the panels  10  are erected as described below. A reinforcement structure  33  may also be a conventional rebar chair for reinforcing the strength of the concrete panels, as shown in  FIG. 10   b . Other examples of reinforcement structures  33  are a weld post, which protrudes from the concrete  11  near an edge; a threaded anchor bolt sleeve, which is encased in the concrete  11  except for at its mouth, which is open for receiving an anchor bolt; and a roof hanger, which may be partially or fully encased within the concrete  11  and is positioned to receive a roof truss. Additional reinforcement structures  33  are contemplated, which may be fully encased within the concrete  11  or project outward from any surface of the panel  10 . Once the desired amount of concrete  11  is poured into the concrete form  31 , the interior surface  41  of the concrete  11  may be floated or otherwise finished as desired. It is referred to as the interior surface  41  because it will face into the structure when erected, so that wall studs, drywall, or other interior building material may be attached to it. 
         [0040]    When the concrete  11  cures, the panel  10  is finished. The interior surface  41  of the panel  10  is concrete  11  and the exterior surface  42 , which faces away from the structure, is insulating material  12 . 
         [0041]    Erecting 
         [0042]    Once cured, the panel  10  is tilted up, by means known in the art, and set in place in the structure. In one embodiment, the panel  10  is a complete wall which is moved into place and then fastened to other walls in the structure. In another embodiment, the panel  10  is part of a complete wall which comprises more than one panel  10 . In this embodiment, each panel  10  is set in place and fastened to adjacent panels  10 . 
         [0043]    A joint  50  is formed at each intersection of panels  10 . The procedure of fastening panels  10  together at each joint  50  may depend on how each panel  10  is cast. If a panel  10  is cast without a spacing material  32 , the concrete  11  will be flush with the insulating material  12  at each edge of the panel  10 , as shown in  FIG. 11   a . In this case, one or more fasteners  51  are attached to adjacent panels  10  on the interior surface  41  of each panel  10 , over the joint  50 . A fastener  51  may be any fastener capable of attaching tilt-up panels to each other and securing them in place. Preferably, the fastener  51  is one or more welds, wherein weld posts  53  are inserted into the concrete  11  while it is curing, and welding plates are attached to the weld posts  53  of adjacent panels  10 . The seam  18  between the insulating material  12  of adjacent panels  10  may be sealed by the sealant  17 , applied from the exterior of the structure. 
         [0044]    As shown in  FIG. 11   b , when a panel  10  is cast using a spacing material  32  on the panel  10  edges that are perpendicular to the structure foundation, the joint  50  between two such panels will have spans of concrete  11  on either side which are not covered by insulating material  12 . One or more fasteners  51  may be attached on the structure&#39;s exterior side, and an insulating insert  52 , preferably composed of the same material as the insulating material  12 , may be placed over the space to seal the joint  50 , cover the uncovered concrete  11 , and maintain continuity between the exterior surfaces  42  of the panels  10 . The insulating insert  52  may be adhered to the concrete  11  using an adhesive, or it may be held in place by insulating filler  17  or another sealant applied to the seams  18  between the insulating material  12  of each panel  10  and the insulating insert  52 . As shown in  FIGS. 11   c - e , the same procedure and materials may be used for capping corners formed by the intersection of two panels  10  and sealing the joint  50  created at the intersection, as well as for covering connections to the roofing and foundation of the structure. Due to increased exposure to water, the fasteners  51  used on the exterior of the structure should be stainless steel to avoid oxidation and weakening of the welds. 
         [0045]    Once the panels  10  are secured in place, the exterior surface  42  of each panel  10  may be coated in a finishing material. The finishing material (not shown) may be any material which is used to create the desired appearance of the structure from the outside, and which will not degrade the insulating material  12 . Examples include house paint, stucco, shotcrete or other pneumatic concrete, and Gunite®. If an insulating material  12  having a facing was used, it may be necessary to remove the facing on the exterior surface  42  in order to apply the finishing material. 
         [0046]    Example Panel Set—Low Income Housing 
         [0047]    Referring to  FIG. 12 , a panel set of four panels  10   a - d  includes all of the tilt-up wall panel shapes needed to build the exterior walls of every home in a subdivision of low-income housing. The panels  10   a - d  are shown with triangular attachment grooves  14 , but without any reinforcement structures  33  so the shape of each panel  10   a - d  is clearly shown. For efficiency, the door and window heights and widths in each home are predetermined and uniform so that no panel shapes need to be customized for individual homes. The panel shapes are: a standard panel  10   a , which is preferably rectangular and is used for wall sections that do not require a door or window; a jamb panel  10   b , used where a door or window should be placed and having the same dimensions as the standard panel  10   a , but having a substantially rectangular cutout at the top of one side to receive the lintel, making the jamb panel  10   b  substantially L-shaped; a lintel panel  10   c , which is preferably rectangular and forms the top of a door jamb or window frame, fitting into the cutout in the jamb panel  10   b  for support; and a sill panel  10   d , which is preferably rectangular and forms the bottom of a window frame. 
         [0048]    By limiting the panels  10   a - d  to four shapes, the panels may be quickly mass-produced. Only four shapes of insulating material  12  and four concrete forms  31  are needed. The insulating material  12 , concrete forms  31 , concrete  11 , and other required building materials may be transported to and stored at the subdivision construction site. Labor is greatly reduced during production of the panels  10   a - d  because no customizing is necessary. Further, wall assembly workers will be able to follow a uniform assembly process for each home. As a result, effectively insulated homes may be produced at a lower overall cost in time, labor and materials. 
         [0049]    While there has been illustrated and described what is at present considered to be the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.