WO2005016618A1

WO2005016618A1 - A structural element

Info

Publication number: WO2005016618A1
Application number: PCT/AU2004/001102
Authority: WO
Inventors: Gerardus Maria Van Erp; Timothy John Heldt; Craig Leslie Cattell; Darren James Browne; Roy Marsh
Original assignee: The University Of Southern Queensland
Priority date: 2003-08-18
Filing date: 2004-08-18
Publication date: 2005-02-24

Abstract

A structural element comprising at least one timber member; and a polymer concrete cover member covering the timber member; wherein the polymer concrete cover member is bonded to the at least one timber member.

Description

TITLE "A STRUCTURAL ELEMENT" FIELD OF THE INVENTION This invention relates to a structural element. In particular, the structural element is primarily used as a substitute for timber decking boards and therefore will be described in this context. However, it should be appreciated that the structural element may be used for other purposes such as beams, posts, bench tops or the like elements. BACKGROUND OF THE INVENTION Developments in civil engineering and the building industry have created a continual demand for building materials with new and improved performance attributes. A popular recreational space used in many houses, especially in warmer climates, is a deck or patio. Most decks are produced using wooden decking boards that are fastened onto timber bearers. The decking boards are then painted or oiled to protect the timber decking boards from deterioration from the environment. In order to prevent the deterioration of decking boards, the decking boards must be re-oiled or re-painted. This re-oiling or re-painting is normally conducted annually. This task is labour intensive, time consuming, and expensive. As decking boards are located outside in the environment, the decking boards are usually made from hardwood. Hardwood is better equipped to cope with the riggers of the environment and less likely to rot in wet conditions and crack in dry conditions. However, hardwood is expensive and is not a renewable environmental resource. The hardwood that is used to make decking boards must also be straight. It must not contain wood imperfections such as knots, gum veins, checks and insect markings as these reduce the strength of the timber decking board and also are not aesthetically pleasing. This also adds to the cost of the hardwood as only hardwood of sufficient quality can be used. OBJECT OF THE INVENTION It is an object of the invention to overcome or alleviate one or more of the above disadvantages or provide the consumer with a useful or commercial choice. SUMMARY OF THE INVENTION In one form, although not necessarily the only or broadest form, the invention resides in a structural element comprising: at least one timber member; and a polymer concrete cover member covering the timber member; wherein the polymer concrete cover member is bonded to the at least one timber member. Preferably, the timber member is made from softwood such as pine. Preferably, corners of the timber member that are covered by the polymer concrete cover member are curved. The timber members may have a series of apertures located through the timber members. The apertures may be sized to allow polymer concrete to pass through the apertures. The polymer concrete cover member normally has: a first layer of: an amount of polymer resin; an amount of a light aggregate with a specific gravity less than that of the resin; and an amount of a heavy aggregate with a specific gravity larger than that of the resin and; a second layer of: an amount of polymer resin; and an amount of a light aggregate with a specific gravity less than that of the resin. The timber is normally bonded to the second layer of the polymer concrete cover member. The resin may be any suitable polyester, vinylester, epoxy or polyurethane resin or combination of resins dependent on the desired structural and corrosion resistant properties of the polymer concrete cover member. Preferably, the resin content is between 25-30% by volume. The light aggregate with a specific gravity less than that of the resin can be any type of light aggregate or combination of light aggregates dependent on the desired structural and corrosion resistant properties of the polymer concrete cover member. Usually, the light aggregates have a specific gravity of 0.5 to 0.9. Preferably, the light aggregate has a specific gravity that is close to the specific gravity of the resin. The light aggregates usually make up 20-25% by volume of the polymer concrete cover member. Preferably, the light aggregate are centre spheres. The centre spheres normally have a specific gravity of approximately 0.7 and are 20 - 300 microns in size. Alternately, hollow glass microspheres with a similar specific gravity and volume may be used. The heavy aggregate with a specific gravity larger than that of the resin can be any type of heavy aggregate or combination of heavy aggregates dependent on the desired structural and corrosion resistant properties of the polymer concrete cover member. The heavy aggregates usually make up 40-60% by volume of the polymer concrete cover member. Preferably, the heavy aggregate is basalt. Usually the basalt is crushed. The crushed basalt may have a particle size of 5 to 7 mm. Preferably, the basalt makes up between 40-50% by volume of the polymer concrete cover member. The basalt normally has a specific gravity of approximately 2.8. Alternately, sand that has a similar specific gravity as basalt may be used. Preferably, the sand makes up between 50-60% by volume of the polymer concrete cover member. Alternatively, the heavy aggregate may be made up of one or more of coloured stones, gravel, limestone, shells, glass or the like material. Preferably, the resin contains a thixotrope to keep the light aggregate in suspension. The amount of thixotrope is normally between 0.5% to 1 % of the resin weight. Preferably, the thixotrope is fumed silica such as found in Cabosil or Aerosil. The polymer concrete cover member of the present invention may also include fibrous reinforcement material to increase the structural properties of the polymer concrete cover member mix. The reinforcement material may be glass, aramid, carbon, timber, and/or thermo plastic fibres. In another form, the invention resides in a method of forming a structural element, the method including the steps of: choosing a timber member; choosing a polymer concrete; locating the polymer concrete cover member in a mould; placing at least one timber member within the mould so that the polymer concrete cover member contacts the timber member and bonds to the timber member; and removing the structural element from the mould. The method may also include the step of allowing the polymer concrete cover member to settle to form a first layer and a second layer of different consistency within the structural element. The timber member may be bonded to the second layer. The timber member may have a series of apertures located through the timber member. Thus, the timber member may allow resin and light aggregate to pass through the apertures. An additional mixture of resin and light aggregate may be located on top of the timber member. A top surface of the first layer may be polished to provide an aesthetically appealing top surface. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will be described with reference to the accompanying drawings in which: FIG. 1A is a perspective view of a timber decking board according to a first embodiment of the invention; FIG. 1 B is a perspective view of a timber decking board according to a second embodiment of the invention; FIG. 2A is a front view showing a first step in producing the decking board of FIG. 1A; FIG. 2B is a front view showing a second step in producing the decking board of FIG. 1 A; FIG. 2C is a front view showing a third step in producing the decking board of FIG. 1 A; FIG. 2D is a front view showing a fourth step in producing the decking board of FIG. 1 A; FIG. 3 is a perspective view of a bench top produced in accordance with a second embodiment of the invention; FIG. 4A is a front view showing the first step in producing the bench top of FIG. 3; FIG. 4B is a perspective view showing the first step in producing the bench top of FIG. 3; FIG. 5A is a front view showing the second step in producing the bench top of FIG. 3; FIG. 5B is a perspective view showing the second step in producing the bench top of FIG. 3; FIG. 6A is a front view showing the third step in producing the bench top of FIG. 3; FIG. 6B is a perspective view showing the third step in producing the bench top of FIG. 3; FIG. 7A is a front view showing the fourth step in producing the bench top of FIG. 3; FIG. 7B is a perspective view showing the fourth step in producing the bench top of FIG. 3; FIG. 8A is a front view showing the fifth step in producing the bench top of FIG. 3; FIG. 8B is a perspective view showing the fifth step in producing the bench top of FIG. 3. FIG. 9 is a perspective view of a post according to an embodiment of the invention; FIG. 10A is a front view showing a first step in producing the post of FIG. 9; FIG. 10B is a front view showing a second step in producing the post of FIG. 9; FIG. 10C is a front view showing a third step in producing the post of FIG. 9; FIG. 11A is a perspective view of a first embodiment of a decking board; FIG. 11 B is a perspective view of a second embodiment of a decking boarding; and FIG. 12 is a perspective view of the two decking boards of

FIG. 11A joined together. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 A shows a perspective view of a structural member in the form of a decking board 10. The decking board 10 comprises a polymer concrete cover member 20 and a timber member 30. The polymer concrete cover member 20 is formed with a polymer concrete approximately 28% by volume of resin including a fumed silica that is 0.8% of the weight of the resin, 22% by volume of light aggregate and 50% by volume of heavy aggregate. The light aggregate is in the form of centre spheres having a specific gravity of approximately 0.7. The heavy aggregate is formed from crushed basalt having a specific gravity of approximately 2.8 and a particle size of 5-7 mm. The light aggregate has a specific gravity that is slightly less than that of the resin, whilst the heavy aggregate has a specific gravity that is larger than that of the resin. A thixotrope is added to the resin so that the light aggregate will stay in suspension within the resin and hence will be substantially uniformly distributed throughout the polymer concrete. Consequently, the resin together with the lighter aggregate in suspension becomes a flowable filled resin system in its own right. The amount of the lighter aggregate suspended in the resin can be varied as required. The timber member is made from a pine. However, it should be appreciated that various other soft woods may be used. Corners of the timber member 30 which are located within the polymer concrete cover member 20 are curved. This is to distribute stresses that may be transferred to the polymer concrete cover member during swelling or shrinkage of the timber member. FIGS. 2A to 2D show the process used to produce the decking board 10 shown in FIG. 1A. The first step in the process is to produce formwork of a desired shape to form a mould 50. In this example, the timber decking 10 is produced in an upside down manner. Polymer concrete used to form the polymer concrete cover member 20 is mixed and poured into the mould as shown in FIG. 2A and allowed to sit. The heavy aggregate settles to the bottom of the mould as shown in FIG. 2B. The amount of aggregate is chosen such that once the aggregate has settled a first layer 60 will stop approximately 20 mm below the surface of the polymer concrete. The first layer contains resin, thixotrope, light aggregate and heavy aggregate. Consequently there is a 20 mm second layer 61 of resin, thixotrope and light aggregate on top of the first layer 60 of the polymer concrete that is aggregate rich. Because there is no heavy aggregate in the upper layer 61 , the resin content in this layer is 56% by volume and the light aggregate in suspension in this layer is 44% by volume. The timber member 30 is then located in the mould in the second layer. The resin and light aggregate of the second layer 61 surrounds the timber member as shown in FIG. 2C. This resin and light aggregate of the second layer provide excellent adhesion for the timber members. Additional heavy aggregate is then added to the sides of the mould as shown in FIG. 2C. The heavier aggregate settles on the sides of the mould 50 and increases the level of the polymer concrete to the top of the mould. The polymer concrete is then allowed to cure to form the polymer concrete cover member and the timber decking is removed from the mould 10. An additional step of allowing resin and light aggregate to flow over the timber member can be performed to produce the decking board of FIG. 1 B. FIG. 3 shows a bench top 100 formed using a polymer concrete cover member 120 and a timber member 130. The polymer concrete cover member 120 uses the same polymer concrete used to produce the decking boards of FIG. 1A and FIG. 1 B. The timber member 130 is a marine ply sheet having a series of apertures 131 that extend through the marine ply sheet. The apertures 131 are formed by drilling holes through the marine ply sheet. FIGS. 4A to 8A and FIGS. 4B to 8B show the process used to produce the bench top 100 shown in FIG. 3. The first step in the process is to produce mould 150 of a desired shape of the bench top 100. In this example, the bench top 100 is produced in an upside down manner. The polymer concrete cover is mixed and poured into the mould 150 and allowed to sit as shown in FIGS. 4A and 4B. The heavy aggregate settles in the bottom of the mould 150. The amount of aggregate is chosen such that once the aggregate has settled a first layer 160 will stop approximately 10 mm below the surface of the polymer concrete. Consequently, there is a 10 mm second layer 161 of resin and light aggregate on top of the first layer 160 of the polymer concrete that is aggregate rich. Because there is no heavy aggregate in the second layer 161 , the resin content in this layer is 56% by volume and the light aggregate in suspension in this layer is 44% by volume. FIGS. 5A and 5B shows the timber member 130 placed on top of the second layer 161 containing only light aggregate and resin. Pressure is applied to the timber member 130 until the timber member 130 contacts the first layer of resin, light aggregate and heavy aggregate. Subsequently, the light aggregate and resin located in the second layer 161 passes through the apertures located within the timber member. An additional mixture of resin and light aggregate, the resin content being 56% by volume and the light aggregate content being 44% by volume, may be poured on top of the timber member 130. This is necessary if the timber member 130 is not fully covered by the light aggregate and resin in the second layer 131. The timber member 130 is shown covered by the light aggregate and resin in FIGS. 6A and 6B. A top of the mould is then placed on the second layer that covers the timber member as shown in FIGS. 7A and 7B. A side of the top mould is open and additional polymer concrete is placed into the side of the top of the mould to complete the forming process of the bench top 100. The bench top 100 is allowed to cure and then removed from the mould. The bench top100 is then polished to complete the bench top. FIG. 9 shows a perspective view of a post 200. The post 200 is formed from polymer concrete cover member 220 and a timber member 230. The polymer concrete cover member 220 uses the same polymer concrete used to produce the decking boards of FIG. 1A and

FIG. 1 B. The timber member 230 used to produce the post 200 is a square plank made of pine. The corners of the square plank have been routed to produce curved corners 231. FIGS. 10A to 10C show the process used to manufacture the post 200. A mould 240 is produced that has a wooden base 241 and a metal sheath 242 as shown in FIG. 10A. The metal sheath 242 is adhered to the base 241 and has two arms 243 that extend upwardly from the base 241. The two arms 243 are flexible and are able to move with respect to each other. Once the mould has been produced, polymer concrete used to produce the polymer concrete cover member 220 is poured into the metal sheath 242. The arms 243 are drawn away from each other and the timber member 230 inserted within the metal sheath 242 as shown in FIG. 10B. Once the timber member is located within the metal sheath 242, the arms 243 are drawn toward each other to produce the final shape of the post 200. Additional polymer concrete and/or heavy aggregate is added to fill the metal sheath 242. The polymer concrete cover member is allowed to set to complete the post 200. FIG. 11 A shows a beam 300 having a tongue 301 , and groove 302. The beam 300 includes a polymer concrete cover member 320 and a timber member 330. The polymer concrete cover member 320 is of the same formulation as described above. The timber member 330 is made from marine ply and has been shaped to have a tongue 301 and groove 302. The corners used to produce the tongue 301 and groove 302 have been cut to form rounded corners. The beam 300 is formed using the same method as that disclosed for the decking board 10. The tongue 301 and groove 302 allow adjacent beams to be joined as shown in FIG. 12. FIG. 11 B shows a beam 400 in which the timber member is of a slight varied shape. The structural members of the decking board, bench top, post and beam combines a special polymer concrete cover member with a timber member that provides the structural members with the necessary structural capacity. The structural members can be connected to other elements or support structures using traditional fastening systems such as screws and nails via the timber members. The structural members can be made with different stones such as gravel, limestone, glass, shells or the like to provide different finishes. Further, structural members have good temperature behaviour, there is little limitation to colours as different pigments are able to be added to the resin, are easy to clean, are wear resistant, are significantly lighter than stone tiles or stone bench tops, its strength can be tailored to requirement by including extra timber members or increasing the thickness of the polymer concrete cover member, are inexpensive to manufacture and virtually any shape may be formed quickly and easy by changing the shape of the mould. Further, the timber member used in the structural members need not be formed from hardwood. The quality of the timber used for the timber member may be of a lesser quality. For example, the timber member need not be perfectly straight and may have knots located throughout the timber member. The polymer concrete cover member provides the strength necessary to cater for any inherent faults of the timber member. It should be appreciated that various other changes and modifications may be made to the embodiment described without departing from the spirit or scope of the invention.

Claims

CLAIMS:

1. A structural element comprising: at least one timber member; and a polymer concrete cover member covering the timber member; wherein the polymer concrete cover member is bonded to the at least one timber member.

2. The structural element of claim 1 wherein the timber member is made from soft wood.

3. The structural element of claim 1 wherein the corners of the timber member that are covered by the polymer concrete cover member are curved.

4. The structural element of claim 1 wherein the timber member has a series of apertures located through the timber member.

5. The structural element of claim 1 wherein the polymer concrete cover member normally has: a first layer of: an amount of polymer resin; an amount of a light aggregate with a specific gravity less than that of the resin; and an amount of a heavy aggregate with a specific gravity larger than that of the resin and; a second layer of: an amount of polymer resin; and an amount of a light aggregate with a specific gravity less than that of the resin.

6. The structural element of claim 5 wherein the timber is bonded to the second layer of the polymer concrete cover member.

7. The structural element of claim 5 wherein the resin is made from any suitable polyester, vinylester, epoxy or polyurethane resin or combination of resins.

8. The structural element of claim 5 wherein the resin content is between 25-30% by volume. 9. The structural element of claim 5 wherein the light aggregate has a specific gravity of 0.5 to 0.

9.

10. The structural element of claim 5 wherein the light aggregates makes up 20-25% by volume of the polymer concrete cover member.

11. The structural element of claim 5 wherein the light aggregate is centre spheres.

12. The structural element of claim 5 wherein the heavy aggregate makes up 40-60% by volume of the polymer concrete cover member.

13. The structural element of claim 5 wherein the heavy aggregate is basalt having a particle size 5 to 7 mm.

14. The structural element of claim 13 wherein the basalt makes up between 40-50% by volume of the polymer concrete cover member.

15. The structural element of claim 13 wherein the basalt normally has a specific gravity of approximately 2.8.

16. The structural element of claim 5 wherein the resin contains a thixotrope to keep the light aggregate in suspension.

17. The structural element of claim 16 wherein the amount of thixotrope is between 0.5% to 1 % of the resin weight.

18. The structural element of claim 17 wherein the thixotrope is fumed silica.

19. A method of forming a structural element, the method including the steps of: choosing a timber member; choosing a polymer concrete; locating the polymer concrete in a mould; placing at least one timber member within the mould so that the polymer concrete contacts the timber member and bonds to the timber member; and removing the structural element from the mould.

20. The method of claim 19 including the step of allowing the polymer concrete to settle to form a first layer and a second layer of different consistency within the structural element and placing the timber member within the polymer concrete so that it bonds to the second layer.

21. The method of claim 19 further including the step of allowing resin and light aggregate located within the polymer concrete to pass through the apertures.

22. The method of claim 19 further including the step of allowing resin and light aggregate located within the polymer concrete to surround the timber member.

23. The method of claim 19 further including the step of polishing a top surface of the structural member.