Abstract:
A lightweight cast concrete panel including concrete having a wet weight of between about 132 to about 140 pounds per cubic foot, and air content of between about 7 to about 11 percent.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to precast concrete panels, and in particular to lightweight concrete panels. 
         [0003]    Concrete panels, as used herein, refers to elongated panels of cast concrete, with or without prestressing cables. The concrete panels may be solid concrete or a combination of lower and upper concrete layers surrounding an insulating layer. In all cases, due to the weight of concrete, concrete wall panels tend to be quite heavy. 
         [0004]    Additional weight increases the product cost due to added shipping charges. Attempts to decrease the weight of the concrete panels have focused on decreasing the volume of concrete within a given panel. This has involved creating a series of empty cores within the panel to newer techniques of using insulating foam blocks to both decrease weight and increase the insulating R-value of the concrete plank. 
         [0005]    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 
       [0006]    The invention provides concrete panels with a markedly decreased weight by dramatically increasing the air entrainment without decreasing the performance characteristics of the concrete panels beyond engineering specification guidelines. The inventors have found that concrete panels may be produced having excellent strength while decreasing weight by entraining air in the concrete between about 7 to about 11 percent. This results in wet concrete weights of between about 132 to about 140 pounds per cubic foot compared to conventional concrete for concrete panels of about 147 pounds per cubic foot. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    A detailed description of the invention is hereafter described with specific reference being made to the drawings in which: 
           [0008]      FIG. 1  is a cross-sectional view of a typical modem concrete plank formed of several layers, with prestressed cables and insulation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    It has been found that concrete panels may be manufactured with acceptable strength and handling characteristics while decreasing the weight of the panels. Decreased weight results in lower shipping costs as well as lower manufacturing cost due to a reduction in concrete used. A typical modem cast concrete panel  10  is shown in  FIG. 1 . It may include a lower layer of concrete  12 , an intermediate insulation layer  14  and an upper top concrete layer  16 . To reduce weight and provide other advantages, one or more foam billets  30  may be within the panel as shown. These billets are shown and described in U.S. Pat. No. 6,955,014, the disclosure of which is incorporated herein by reference. Note also that such panels often have reinforcing metal such as prestressing cables  22 . 
         [0010]    The following tables show data on testing done with a variety of concrete mixes in which air content was varied. In Table A, “Normal” refers to the usual mix of concrete in which entrained air content is about 4.5%, the unit weight while wet in pounds per cubic foot was 147.0, the slump was 9.00 inches and the compressive strength after a heat of “sure cure” was 4500 psi, at 7 days was 5950 psi and at 28 days was 7000 psi. 
         [0011]    The inventors have found that increasing air content to 9%±2% results in a reduction in wet weight to 136±4. Surprisingly, this decrease in wet weight and increased air entrainment resulted in excellent concrete panels that have the required compressive strengths after cure and are workable as shown by the slump characteristics. The concrete with the increased air content specified may be used in structural concrete panels in any or all of the layers, as desired, to gain the decrease of weight. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE A 
               
               
                   
                   
               
               
                   
                 Normal 
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Unit Weight - wet 
                 147.0 
                 142.2 
                 142.2 
                 133.8 
                 133.8 
                 132.2 
                 139.2 
                 142.4 
               
               
                 (lbs/ft3) Observed 
               
               
                 Air Content (%) 
                 4.5% 
                 6.5% 
                 7.5% 
                 12.0% 
                 10.5% 
                 12.5% 
                 9.0% 
                 7.0% 
               
               
                 Slump (in) 
                 9.00 
                 8.25 
                 5.50 
                 8.50 
                 5.75 
                 8.00 
                 3 
                 9.5 
               
               
                 fc-sure cure (psi) 
                 4500 
                 5768 
                 5889 
                 3832 
                 4524 
                 3007 
                 7157 
                 6772 
               
               
                 (8–10 hrs) 
               
               
                 fc-7-day (psi) 
                 5950 
                 9115 
                 9436 
                 6889 
                 8525 
                 7373 
                 9470 
                 8932 
               
               
                 fc-28-day (psi) 
                 7000 
                 10624 
                 10977 
                 7650 
                 11923 
                 10735 
                 12115 
                 11750 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE B 
               
               
                   
               
               
                   
                 H 
                 I 
                 J 
                 K 
                 L 
                 M 
                 N 
                 O 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Unit Weight - wet 
                 143.2 
                 137.2 
                 130.8 
                 132.6 
                 135.2 
                 138.0 
                 136.8 
                 134.4 
               
               
                 (lbs/ft3) Observed 
               
               
                 Air Content (%) 
                 7.5% 
                 10.0% 
                 14.0% 
                 12.5% 
                 11.4% 
                 9.8% 
                 8.2% 
                 11.4% 
               
               
                 Slump (in) 
                 9 
                 9.5 
                 spread 
                 8.0 
                 8.5 
                 8.0 
                 spread 
                 9.25 
               
               
                 fc-sure cure (psi) 
                 6215 
                 1981 
                 1937 
                 1806 
                 4487 
                 6708 
                 3764 
                 5658 
               
               
                 (8–10 hrs) 
               
               
                 fc-7-day (psi) 
                 9705 
                 7315 
                 5033 
                 6498 
                 7465 
                 10348 
                 5924 
                 8684 
               
               
                 fc-28-day (psi) 
                 12758 
                 9770 
                 6124 
                 8275 
                 9377 
                 12363 
                 7569 
                 11297 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE C 
               
               
                   
                   
               
               
                   
                 P 
                 Q 
                 R 
                 S 
                 T 
                 U 
                 V 
                 W 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Unit Weight - wet 
                 134.0 
                 135.8 
                 132.8 
                 138.6 
                 135.8 
                 134.4 
                 136.2 
                 136.6 
               
               
                 (lbs/ft3) Observed 
               
               
                 Air Content (%) 
                 11.5% 
                 10.0% 
                 11.8% 
                 9.4% 
                 10.6% 
                 11.0% 
                 9.8% 
                 10.0% 
               
               
                 Slump (in) 
                 8.5 
                 8.5 
                 9.5 
                 8.5 
                 8.0 
                 9.0 
                 8.75 
                 8.0 
               
               
                 fc-sure cure (psi) 
                 5631 
                 5694 
                 4455 
                 6625 
                 5853 
                 4893 
                 5688 
                 5462 
               
               
                 (8–10 hrs) 
               
               
                 fc-7-day (psi) 
                 9253 
                 9486 
                 6498 
                 9684 
                 9068 
                 7657 
                 9200 
                 8601 
               
               
                 fc-28-day (psi) 
                 11211 
                 11106 
                 8289 
                 12350 
                 11704 
                 10300 
                 10686 
                 10189 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE D 
               
               
                   
                   
               
               
                   
                 X 
                 Y 
                 Z 
                 AA 
                 AB 
                 AC 
                 AD 
                 AE 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Unit Weight - wet 
                 137.4 
                 138.2 
                 139.8 
                 137.4 
                 131.4 
                 130.8 
                 136.4 
                 136.6 
               
               
                 (lbs/ft3) Observed 
               
               
                 Air Content (%) 
                 9.5% 
                 10.0% 
                 8.5% 
                 10.0% 
                 12.5% 
                 12.8% 
                 10.2% 
                 9.5% 
               
               
                 Slump (in) 
                 8.5 
                 9 
                 7.5 
                 8 
                 7.75 
                 18.0 
                 8.0 
                 8.0 
               
               
                 fc-sure cure (psi) 
                 6308 
                 5662 
                 4947 
                 4000 
                 5375 
                 5383 
                 4753 
                 4898 
               
               
                 (8–10 hrs) 
               
               
                 fc-7-day (psi) 
                 10403 
                 10998 
                 10019 
                 9759 
                 8271 
                 8873 
                 8084 
                 9004 
               
               
                 fc-28-day (psi) 
                 11215 
                 11242 
                 10064 
                 9824 
                 9890 
                 8561 
                 9984 
                 11418 
               
               
                   
               
             
          
         
       
     
         [0012]    Cast concrete panels made according to the invention may save over 10 pounds per cubic foot in shipping cost since the concrete may typically be 136 pounds per cubic foot versus conventional concrete in concrete panels of about 147 pounds per cubic foot. The additional entrained air decreases the concrete weight. Under the parameters of the invention, this results in concrete having acceptable performance characteristics both in handling and in the final concrete panels. This invention works for both fixed bed and moving bed casting operations. As used herein, concrete panels refers to concrete cast at a plant using a rolling bed or fixed bed method. On-site pours of concrete do not involve shipping concerns and do not realize the benefits of saved weight. 
         [0013]    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. 
         [0014]    This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.