Patent Application
20080236069
Not Applicable.
This invention relates to precast concrete panels, and in particular to lightweight concrete panels.
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.
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.
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.
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.
A detailed description of the invention is hereafter described with specific reference being made to the drawings in which:
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
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.
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.
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.
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.
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.
