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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a non-provisional application claiming priority from provisional patent application Serial No. 60/344,094 filed on Dec. 20, 2001, the disclosure of which is hereby incorporated herein by reference. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    This invention relates to a method for casting hollow core concrete panels in which the hollow cores are made by the use of foam billets held in place during the pours by using a raft connector. Extruders are eliminated via the invention herein. This represents the only hollow core concrete panel which may include cast in openings.  
           [0004]    Previously, hollow core concrete panels have been formed by many methods, including single and multiple pass casting using moving beds and with stationary beds. The hollow cores are made by using slipform extruders that leave core material in place over which concrete is formed. Once cured, the panels are cut to length and lifted and tilted to remove the core material which may be reused.  
           [0005]    Some hollow core panels have been made with an insulating layer across the entire surface, as shown in U.S. Pat. No. 4,628,653, the disclosure of which is incorporated herein by reference. Basically, a hollow core panel is cast and interlocking sheets of insulation are laid down before a final pour of concrete. This uniform layer of insulation increases the R-value of the finished wall panels and floor plank.  
           [0006]    U.S. Pat. Nos. 4,041,669 and 4,141,946, the disclosures of which are incorporated herein by reference, describe a hollow-core concrete slab in which an inverted U-shaped foam piece is manually placed on a first layer of concrete that is ridged by a screed. The inverted U-shapes define a hollow void that remains after the second pour of concrete is made over the foam. Unfortunately, these early attempts proved to be unworkable and the problem of floatation of foam remained until this invention.  
           [0007]    The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    The invention provides all of the benefits of hollow core concrete panels with the advantages of insulating foam billets in the hollow core regions. This eliminates the need to use core material to form the hollow cores. In addition, extruders to extrude in the core material are no longer required. Since the extruders may be eliminated, it is also now possible with the invention to cast openings into the panels by placing forms to limit where the concrete flows. The use of core material necessitates additional handling difficulties, including lifting and tilting the panels to remove the core material, as best shown in U.S. Pat. No. 4,398,761, the disclosure of which is incorporated herein by reference. Even with the extra steps of forming lifting inserts, and having cranes to lift and tilt the panels, about a ton of core material is left in each panel, adding undesired weight and cost.  
           [0009]    The generally rectangular-shaped foam billets are held together with raft connectors into a “raft” of foam billets. The unique raft connectors allows the foam billets to be connected together after each billet is placed on the bed. Alternatively, an entire raft of billets may be placed on the bed after being pre-assembled. The finished panel and plank is only “hollow core” in that cores of foam are formed throughout the panels and planks which provides insulation, requires far less concrete and eliminates a great deal of weight per panel or plank. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    A detailed description of the invention is hereafter described with specific reference being made to the drawings in which:  
         [0011]    [0011]FIG. 1 is a perspective view of a typical apparatus for casting concrete panels;  
         [0012]    [0012]FIG. 2 is a cross-sectional view of a concrete panel of the invention;  
         [0013]    [0013]FIG. 3 is an end view of a raft connector of the invention;  
         [0014]    [0014]FIG. 4 is a top view of the raft connector of the invention of FIG. 3;  
         [0015]    [0015]FIG. 5 is a perspective view of the raft connector of the invention of FIGS. 3 and 4;  
         [0016]    [0016]FIG. 6 is a cross-sectional view of a casting bed with foam billets, connectors and a lower concrete layer cast;  
         [0017]    [0017]FIG. 7 is an alternative raft connector of the invention;  
         [0018]    [0018]FIG. 8 is a perspective view of a casting bed with foam billets in place in an alternative raft connector;  
         [0019]    [0019]FIG. 9 is a top view of a mesh lattice used with a u-shaped bracket as an alternative raft connector; and  
         [0020]    [0020]FIG. 10 is a front elevational view of the u-shaped bracket. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    With reference to the Figures, the inventive concrete slabs, panels or planks of the invention are formed with a standard concrete casting apparatus as shown in U.S. Pat. Nos. 3,217,375; 3,523,343; 4,004,874; 4,289,293 and 4,457,682, the disclosures of which are incorporated herein by reference. Basically, as shown in FIG. 1, such apparatus  10  include a casting bed  12  that is either stationary or is driven along rails. The casting bed  12  has a bottom pallet  14  and side walls  16 ,  18 . A concrete dispensing hopper  20  is shown in schematic form and can be of any of the current hoppers used to distribute concrete onto a moving bed. Alternatively, the hopper  20  may move relative to a stationary bed. Lower and upper prestressed cables,  22 ,  23 , respectively, are positioned along the length of the bed  12 .  
         [0022]    [0022]FIG. 2 shows a cross-sectional view of a completed concrete panel  26  of the invention. The panel includes spaced foam billets  30  between each of the prestressed cables  22 . When used herein, the term “foam billets” refers to billets of any material that become an integral member of the finished panel. Where billets is used herein, it refers to foam billets but also to any shape holding structure that may be placed in the bed to form a void for the hollow core panels to be formed. They could be formed from a corrugated cardboard product or any other material which would define the hollow core void as well. Although shown as generally rectangular in cross-section, the billets  30  may be shaped to require less concrete by being closer to each other while still avoiding the prestressed cables  22 .  
         [0023]    The raft connectors  36  of the invention tie into the foam billets  30  and the upper prestressed cable  23 . Additionally, they may tie into any lateral rebar that is placed on top of the foam billets secured together by the raft connectors  36 .  
         [0024]    The raft connectors  36  as shown in FIGS.  3 - 5  may be molded of plastic and may include for each billet  30 , a pair of spaced L-shaped brackets  40 ,  42  of plastic held together in the spaced relation by a cross-bar  36 . The L-shaped brackets  40 ,  42  function to hold adjacent end to end billets together. An opening  48  may be provided through a remote end as shown to allow attachment of the raft connector to a second billet that is end to end with the billet that the cross-bar  38  crosses. The billets  30  may have ends that are formed to interlock together as well. The cross-bar  36  may include downwardly projecting spikes  44  that cut into the foam billets  30  and hold the raft connectors  36  to the foam billets  30 . A prestressed cable connector  46  may also be formed in the raft connector to simply snap onto the prestressed cable. In addition, the raft connector may have half-clips  50  spaced along the top to which lateral rebar may be attached, if desired.  
         [0025]    The raft connectors  36  may be a single piece to cover the entire width of the bed or may be formed in sections that can be attached to form widths that cover the bed, to fit any bed width. FIG. 7 shows an alternative raft connector  60  which is a single piece the width of the casting bed  12  that includes spikes  62  to press into the billets  30 , prestressed cable connectors  64  to attach to the prestressed cable  23  and side guides  66  that fit on either side of each billet  30 . If lateral rebar is desired on top of the billets, the raft connector of FIG. 7 may have half-clips on its top as in the raft connector  36 .  
         [0026]    Alternatively, as shown in FIG. 8, the raft connectors  36  may be formed from a rebar  70  that has downwardly descending studs  72  welded or otherwise affixed thereto at spaced intervals such that a stud  72  is on each side of a foam billet  30  and the rebar crosses the top of the billet. The foam billets  30  may be bonded better to the top layer of concrete by piercing the foam billet with pins that pierce the foam and have projections above the foam layer that are buried in the upper layer of concrete. Wire ties may be added to the raft connectors to tie the raft connectors to the prestressed cable  23 .  
         [0027]    Another alternative raft connector is shown in FIGS. 9 and 10. Those figures show a u-shaped bracket  90  which is positioned underneath each foam billet  30 . A top mesh lattice  92  extending across the width of the bed  12  is placed above the billet and secured to the prestressed cable  23  with wire ties or the like. The u-shaped member  90  may be placed from above through the mesh lattice  92  until its end tabs  94 ,  96  contact crossbars  98  of the mesh lattice  92 . After so positioning, the foam billets  30  may be slid into the opening defined by the u-shaped brackets  90  and the mesh lattice  92 , securely holding the foam billets from movement in all but the longitudinal direction.  
         [0028]    In operation, as, shown in FIG. 6, a first layer of concrete  80  is cast with a very fluid mix called “self-compacting concrete” in the industry. This concrete does not require a screed step. The rafts of billets  30  are either then made by connecting billets to the raft connectors  36  on the bed  12  or partially assembled rafts are simply laid on top of the first layer and are attached to the prestressed cables  23 . Any lateral rebar is then attached to the raft connectors. Finally, the top layer of concrete  82  is cast which is a traditional concrete mix. Any insulating sheets are placed on top of the structural section.  
         [0029]    While this invention may be embodied in many different forms, there are shown in the drawings and described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.  
         [0030]    The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims.  
         [0031]    Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim 1 should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below.  
         [0032]    This completes the description of the preferred and alternate embodiments of the invention.

Summary:
A method for casting hollow core concrete panels includes the use of raft connectors to hold a plurality of spaced foam billets in place during the manufacture to create panel or plank with spaced foam-filled cores.