Expanded polystyrene formwork for cast in place concrete structures
A formwork for use in constructing concrete structures is made out of expanded polystyrene coated with an epoxy hard coat on the surfaces of the formwork against which concrete is applied or poured in the construction of concrete structures. A method of making the formwork involves constructing the expanded polystyrene to a desired shape and applying the epoxy to the surfaces of the polystyrene to be used to contact concrete and allowing the epoxy to cure. A method of constructing concrete structures involves using the formwork described.
This application is related to Provisional Application Ser. No. 60/493,114 filed Aug. 6, 2003, the disclosure of which is incorporated by reference herein in its entirety, and to which priority is explicitly claimed herein to the filing date thereof.
BACKGROUND OF THE INVENTION1. Field of the Invention
The invention, in general, relates to the field of building construction. More precisely, the invention relates to the construction of concrete structures using a new formwork. Specifically, the present invention relates to using a formwork composed of expanded polystyrene (EPS) coated with a two-part liquid epoxy hard coat for the construction of concrete structures.
2. Discussion of the Related Art
Historically, builders have used formworks in the construction of elevated concrete slabs and beams. For example, when forming an elevated slab, concrete is poured on top of a formwork deck and over horizontally projected rebar (structural steel). The formwork deck is held in place at the desired elevation by numerous methods. These include, but are not limited to, scaffolding and wooden posts. Concrete columns and walls have been poured previously in order to hold up the elevated deck and beams. Upon sufficient curing of the concrete, the formwork is removed from below to leave a free-standing elevated concrete deck and beam system.
Currently, elevated concrete beam and slab systems are constructed using formwork systems which are composed of plywood, steel, or fiberglass. Each of these methods is costly, and takes large amounts of work to install properly. Plywood formwork beam and slab systems are the easiest of the three. The finished surface left by plywood typically contains wood grain impressions retained in the concrete from the wooden surface of the plywood sheets. This can be remedied by employing the use of high grade plywood. However, this increases the cost tremendously. Steel pans are also used in the construction of beam and slab systems.
Steel pans are more expensive than using plywood decking. They are also much larger in weight, making the man hours required for construction of the beam and slab system even higher. The finished surface that is left by steel pans is better than that left by plywood decking. Fiberglass formwork for beam and slab systems is the most expensive means of constructing a concrete deck.
Fiberglass formwork is also much heavier than either plywood decking or steel pans, and is an even more labor-intensive construction practice. The finished surface of the concrete, using fiberglass for formwork, is typically much better than that of both steel pans and plywood.
The possibility of reusing plywood, steel, and fiberglass varies. Plywood can be reused several times, with the finished surface of the concrete decreasing in quality with each reuse. Plywood also demands the harvesting of valuable natural resources required for its production. It cannot be recycled at the conclusion of its usefulness and must be disposed of in landfills. Similarly, steel pans can be reused as formwork numerous times. Steel pans produce a finished surface on the concrete that also diminishes with use of the steel pans. Steel pans, however, can be melted down for reuse at the end of a job. Fiberglass forms can typically be used for multiple pours for the duration of a construction project with minimal decline in the finished surface of the concrete. However, at the conclusion of a construction project fiberglass formwork cannot be recycled and must be disposed of.
With the current implementation of plywood, steel, or fiberglass formwork, there is a limit to the shapes which are attainable in concrete construction. Irregular shapes, such as intricate curves, are not an option using current construction methods.
An alternative approach more recently available from a company known as Alkus ((http://alkus.de/gb/NN_index.html) Aug. 3, 2004) involves manufacturing formwork panels out of polypropylene reinforced with aluminum or glass fiber mat. A problem with such panels is that they are difficult to shape and suffer the same disadvantages and more than the aforementioned steel and fiberglass forms, and cannot be molded into intricate shapes.
SUMMARY OF THE INVENTIONThe present invention is directed towards constructing a static mold or formwork structure. The mold may be used to form a building structure such as an elevated beam and slab system. A generally U-shape channel form is especially adapted to form a concrete beam for the system. The slab is an outwardly extending section of concrete that is constructed at the same time as the beam. The system will be composed of a plurality of beams. The system will typically contain horizontally extending rebar (structural steel reinforcement bars). The formwork is composed of a certain density of Expanded Polystyrene (EPS). The density will depend on the structural requirements for the safe construction of said concrete system. Ordinarily, it is anticipated that the formwork will be made of two pound density expanded polystyrene. The EPS will be cut to the desired shape, and placed into a restrained system in order to preclude movement occurring at the time of concrete placement. The EPS will then be coated with a two-part epoxy/polyurethane enamel in order to provide a finish currently unattainable with present Cast in Place (CIP) forming methods. When properly vibrated and placed, the polyurethane “hard-coat” will leave the bottom surface (ceiling) of the elevated deck with a finish that will appear to be smooth and polished. This finish is currently unattainable solely with current formwork approaches. Upon sufficient curing of the concrete, the EPS CIP forms will be removed for reuse, recycling, or disposal.
A primary object of the invention is to provide a cheaper means of cast in place concrete construction. Another objective of the invention is to provide the finished concrete surface with an appearance that will be smooth and polished. The EPS formwork will be much lighter than typical wood, steel, or fiberglass decks, thus facilitating a construction cycle that is much quicker in installation than is currently attainable in industry. Another benefit of using EPS formwork is that it is recyclable after construction use. EPS formwork will not contribute to refuse in landfills, and does not require the use of valuable natural resources—such as those required by steel and wood formwork. Another benefit of using EPS formwork is the shapes which are currently unattainable in concrete cast in place construction. The EPS formwork can be cut into intricate designs and then cast into the bottom, or “ceiling” of the concrete beam and slab system.
BRIEF DESCRIPTION OF THE DRAWINGSHaving briefly described the invention, the same will become better understood from the appended drawings, wherein:
In accordance with the invention as illustrated in
In implementing the invention, specific types of expanded polyurethane are used, for example, as described in Appendix A1- A6 entitled “Typical Physical Properties of Expanded Polystyrene for Use in the Formwork”, which follow and are part of the specification, are incorporated by reference herein, and are located before the claims.
Appendix A2 also compares the material used (polystyrene) for the invention favorably relative to the use of plywood, and also describes other properties of the polystyrene material applicable for use in the invention.
As will be appreciated by those of ordinary skill in the art, this information is readily available from numerous websites such as www.carpenter.com as of Aug. 3, 2004 and others.
In the case of the invention, the expanded polystyrene is shown having certain properties in the shaded area in Appendix A1 and identified as type II exhibiting a density (in pcf) of at least 1.35, and preferably about 1.35 to about 1.79 is most preferred for use in accordance with the invention. While a preferred expanded polystyrene has been identified herein, it will be readily apparent to those of ordinary skill in the art, that alternative types can be employed as may be appropriate to the particular or specific application, depending on structural need and what is being built.
More specifically, in arriving at desired formwork load bearing calculations, published ASTM methods were reviewed and used to arrive at the desired load bearing calculations. More specifically, these ASTM methods are described in the following ASTM international publications, the disclosures of which are specifically incorporated by reference herein. The publications are as follows:
With respect to the epoxy/polyurethane enamel employed in accordance with the invention, one such enamel is available from Demand Products, Inc. under the name Liquid Rock. A Technical Data Sheet and Material Safety Data Sheet provide details about the specific material and is available form Demand Products, Inc. of Alpharetta, Ga. More specifically, a link to that company's website on the Internet is available at http://www.demandproducts.com and http://www.demandhotwire.com as of Aug. 3, 2004.
The material is a 2-component unfilled epoxy with low viscosity and good flow qualities which can be applied over plastic foam surfaces where a hard, durable, and smooth coating is required. With respect to its specific properties, they are set forth in the following Tables:
*Pot Life 100 gram Mass
*These times will change depending on volume and temperature.
Thus, as may be appreciated not only does the invention involve a new and integrated structure for formwork to be used in concrete applications, there is also provided a method of making such formwork structures. The method generally involves cutting a shape in a structure made of expanded polystyrene into a desired shape for use in poured or applied concrete applications. An epoxy polyurethane enamel is then applied to the surface of the expanded polystyrene which is to bear against poured or applied concrete. The enamel is allowed to cure and the concrete is thereafter poured or applied to be in contact with the enamel. In a yet still further aspect, the invention involves constructing concrete structures using the formwork in accordance with the invention by assembling the formwork as previously described, thereafter pouring or applying the concrete and when the concrete has substantially or sufficiently cured, removing the formwork to result in a concrete surface which appears smooth and polished.
Having thus generally described the invention, the same will become better understood from the appended claims in which it is set forth in a non-limiting manner.
Appendix A1
typical physical properties of expanded polystyrene:
R-Control EPS Fabricators
1See ASTM C-578 Standard Specification for complete information
Alliance of Foam Packaging Recyclers:
Pacemaker Plastics Corp.
Pacemaker Expanded Polystyrene (EPS) Properties per ASTM C 578 and UL Tests
Appendix A2
Published Properties
Minimum Properties
Plywood Properties
Plywood Properties for 12″ Nominal Width
Appendix A3
Properties of a 12″ Wide Rectangluar Section
Appendix A4
Appendix A5
Appendix A5
Appendix A6
Appendix A6
Claims
1. A formwork for cast in place concrete structures, comprising:
- a formwork structure made of expanded polystyrene; and
- an enamel coating on at least one surface of said formwork to be in contact with poured or applied concrete which will make up at least a part of a concrete structure.
2. The formwork of claim 1, wherein said expanded polystyrene has a density of at least about 1.35 pcf.
3. The formwork of claim 2, wherein said expanded polystyrene has a density of at least about 1.35 pcf to about 1.79 pcf.
4. The formwork of claim 1, wherein the strength properties of said expanded polystyrene comprises: Compressive 10% Deformation Strength of at least about 15 psi; Flexural Strength of at least about 40 psi; Tensile Strength of at least about 18 psi; Shear Strength of at least about 26 psi; Shear Modulus of at least about 460 psi; and Modulus of Elasticity of at least about 320 psi.
5. The formwork of claim 1, wherein the strength properties of said expanded polystyrene comprises: Stress at 10% Compression of at least about 30 psi; Flexural Strength of at least about 58 psi; Tensile Strength of at least about 62 psi; and Shear Strength of at least about 70 psi.
6. The formwork of claim 1, wherein the enamel coating is polyurethane.
7. The formwork of claim 6, wherein the polyurethane coating is made from a two component unfilled epoxy mixed with a catalytic hardener, the resulting polystyrene having tensile strength properties of about 25,000 psi and comprehensive strength properties of about 40,000 psi.
8. A method of manufacturing a formwork for cast in place concrete structures, comprising:
- shaping a piece of expanded polystyrene into a predetermined formwork shape;
- applying an enamel coating on at least one surface of said formwork to be in contact with poured or applied concrete; and
- curing the enamel coating.
9. A method of manufacturing a concrete structure comprising:
- shaping a piece of expanded polystyrene into a predetermined formwork shape;
- applying an enamel coating on at least one surface of said formwork to be in contact with poured or applied concrete;
- curing the enamel coating;
- applying or pouring concrete into contact with the cured enamel coating to have the concrete assume a desired shape;
- allowing the concrete to cure; and
- removing the formwork after the concrete has cured sufficiently to result in at least a portion of a concrete structure.
Type: Application
Filed: Aug 5, 2004
Publication Date: Mar 31, 2005
Inventor: Joe Fulbright (Morrisville, NC)
Application Number: 10/912,579
