WO2017032995A1

WO2017032995A1 - A composite structural element

Info

Publication number: WO2017032995A1
Application number: PCT/GB2016/052601
Authority: WO
Inventors: Michael PEMBERTON
Original assignee: Trafalgar Marine Technology Limited
Priority date: 2015-08-21
Filing date: 2016-08-22
Publication date: 2017-03-02
Also published as: GB2527959B; GB2527959A; GB201514941D0

Abstract

A composite structural element has first, second, third and fourth reinforcement layers. The second reinforcement layer is adjacent the first reinforcement layer and has first and second pluralities of parallel spaced apart bars, the second plurality of bars being substantially orthogonal to the first plurality of bars. The third reinforcement layer is adjacent the second reinforcement layer and has third and fourth pluralities of parallel spaced apart bars, the fourth plurality of bars being substantially orthogonal to the third plurality of bars. The third reinforcement layer is provided such that the first plurality of bars are substantially parallel to and interspaced between the third plurality of bars, and the second plurality of bars are substantially parallel to and interspaced between the fourth plurality of bars. Also, the fourth reinforcement layer is adjacent the third reinforcement layer. The structural element further has at least one elongate strand interlaced with the second and fourth pluralities of bars over a length of the composite structural element which holds together the second and third reinforcement layers. An encapsulating material at least partially encapsulates the reinforcement layers and the at least one elongate strand.

Description

A composite structural element

TECHNICAL FIELD

The invention relates to a composite structural element, particularly a laminated ferrocement composite structural element.

BACKGROUND

Ferrocement, sometimes referred to as thin-shelled concrete, is a composite material made from cement mortar or plaster which typically incorporates layers of closely spaced reinforcement of small diameter mesh, such as square mesh, expanded metal mesh or chicken wire. Unlike conventional reinforced concrete, ferrocement does not contain coarse aggregates, and contains only fine aggregates, e.g. sand. Ferrocement is used to build relatively thin structural elements which are lightweight and exhibit reduced maintenance costs compared to purely steel constructions.

SUMMARY OF THE INVENTION

According to the invention, there is provided a composite structural element comprising:

a first reinforcement layer;

a second reinforcement layer adjacent the first reinforcement layer, the second reinforcement layer having a first plurality of parallel spaced apart bars and a second plurality of parallel spaced apart bars, the second plurality of bars being substantially orthogonal to the first plurality of bars;

a third reinforcement layer adjacent the second reinforcement layer, the third reinforcement layer having a third plurality of parallel spaced apart bars and a fourth plurality of parallel spaced apart bars, the fourth plurality of bars being substantially orthogonal to the third plurality of bars, the third reinforcement layer provided such that the first plurality of bars are substantially parallel to and interspaced between the third plurality of bars, and the second plurality of bars are substantially parallel to and interspaced between the fourth plurality of bars;

a fourth reinforcement layer adjacent the third reinforcement layer;

at least one elongate strand interlaced with the second and fourth pluralities of bars over a length of the composite structural element, thereby holding together the second and third reinforcement layers; and an encapsulating material at least partially encapsulating the reinforcement layers and the at least one elongate strand. When compared to known reinforced concrete structural elements, embodiments of the invention may allow for a smaller overall depth for a given specification. Therefore, certain embodiments of the invention may provide structural solutions which require less material and/or contain less embodied energy than existing solutions.

Preferably, the at least one elongate strand is a substantially flat strip. Use of a flat strip may further assist in minimising the overall depth of the composite structural element. Also, minimising of the overall depth of the composite structural element may be achieved in certain embodiments where the second and third reinforcement layers are positioned relative to one another such that the first and third pluralities of bars lie in common plane. In certain embodiments, the structural element further comprises at least one stressing tendon passing through the structural element for inducing compressive stresses in the encapsulating material. The at least one stressing tendon may be bonded to the encapsulating material and embody a tensile stress thereby inducing the compressive stresses in the encapsulating material. The at least one stressing tendon may be provided in a sheath to prevent bonding of the at least one stressing tendon and the encapsulating material to permit post-stressing of the tendon to induce compressive stresses in the encapsulating material.

The encapsulating material includes a self-compacting mortar. Additionally or alternatively, the encapsulating material may include at least one admixture from the group of: water-reducing admixtures, retarding admixtures, accelerating admixtures and superplasticisers.

In certain embodiments, the first and/or the fourth reinforcement layer has an open area of no more than 85% of the total area thereof. In certain alternative embodiments, the first and/or the fourth reinforcement layer has an open area of between 60% and 80% of the total area thereof. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example only, with reference to the accompanying figures, in which: Figure 1 shows an isometric view of a composite structural element according to an embodiment of the invention;

Figure 2 shows an exploded isometric view of selected components of the composite structural element shown in figure 1 ;

Figure 3 shows an isometric view of selected components of the composite structural element shown in figures 1 and 2; and

Figure 4 shows a further isometric view of selected components of the composite structural element shown in figures 1 to 3.

DETAILED DESCRIPTION

Figure 1 shows a composite structural element 10 according an embodiment of the invention. The composite structural element 10 is a laminated ferrocement panel 10 which may be suitable for use in the construction of permanent concrete formwork. The panel 10 has first surface 11a, an opposing second surface 1 1b and a depth D, where the depth D is defined as the distance between the first and second surfaces 11a, 11 b. The panel 10 includes a first reinforcement layer 12, a second reinforcement layer 14, a third reinforcement layer 16 and a fourth reinforcement layer 18. The panel 10 further includes elongate strands 20 passing through the length of the panel 10 for holding together the second and third reinforcement layers 14, 16. An encapsulating material 22 at least partially encapsulates the reinforcement layers 12, 14, 16, 18 and the elongate strands 20, thereby fixing the relative positions of the reinforcement layers 12, 14, 16, 18 and the elongate strands 20 and providing a protective cover thereto. The fourth reinforcement layer 18 and the encapsulating material 22 are shown partially cut away in figure 1 to allow the viewer to see the other constituent parts of the panel 10. However, outlines of the fourth reinforcement layer 18 and cementitious material 22 are indicated in broken lines. As illustrated in the accompanying figures, the panel 10 may also include stressing tendons 24 passing through the length of the panel 10 for inducing compressive stresses in the encapsulating material 22, as described below in more detail.

Figure 2 shows the reinforcement layers 12, 14, 16, 18 separated for clarity. Each of the reinforcement layers 12, 14, 16, 18 is substantially planar, thus allowing the reinforcement layers 12, 14, 16, 18 to be stacked one atop the other. In certain embodiments, at least two or more of the reinforcement layers 12, 14, 16, 18 may be substantially parallel to one another. However, in certain embodiments, the reinforcement layers 12, 14, 16, 18 may not be parallel to one another, as the relative position of the individual reinforcement layers 12, 14, 16, 18 may depend upon the desired shape of the panel 10. In the illustrated embodiment, the first reinforcement layer 12 is adjacent to the second reinforcement layer 14, the second reinforcement layer being also adjacent to the third reinforcement layer 16, i.e. the second reinforcement layer 14 is between the first and third reinforcement layers 12, 16. Further, in the illustrated embodiment, the third reinforcement layer 16 is also adjacent to the fourth reinforcement layer 18, i.e. the third reinforcement layer 16 is between the second and fourth reinforcement layers 14, 18. Therefore, it will be understood that the second and third reinforcement layers 14, 16 are both positioned between the first and fourth reinforcement layers 12, 18.

The first and fourth reinforcement layers 12, 18 include multiple small openings 26. The openings 26 may be square openings, or openings of any other suitable shape, for example diamond shaped or circular openings. In certain embodiments, the size of the openings 26 may be less than 5mm across. In certain embodiments, the size of the opening 26 may be between 0.1 mm and 3mm. The first and fourth reinforcement layers 12, 18 may be formed from small aperture mesh, e.g. square mesh, expanded metal mesh or chicken wire. Punched or otherwise perforated sheet products may also be used to provide either of the first and fourth reinforcement layers 12, 18. The openings 26 provide an open area of the first and fourth reinforcement layers 12, 18 to permit penetration of the encapsulating material 22 therethrough. In certain embodiments, the open area of either of the first and fourth reinforcement layers 12, 18 may be up to 85% of the total area thereof. In certain embodiments, the open area of either of the first and fourth reinforcement layers 12, 18 may be between 60% and 80% of the total area thereof. The first and fourth reinforcement layers 12, 18 may minimise the occurrence of cracking and/or the propagation of cracks through the encapsulating material 22. In certain embodiments, additional reinforcement layers according to the first and/or fourth reinforcement layers 12, 18 may be provided adjacent to the first and/or fourth reinforcement layers 12, 18.

Figure 3 shows the first, second and third reinforcement layers 12, 14, 16 as they appear in figure 1 , with other components of the panel 10 omitted. The second reinforcement layer 14 includes a first plurality of parallel spaced apart bars 14a and a second plurality of parallel spaced apart bars 14b. The first plurality of bars 14a are substantially orthogonal to the second plurality of bars 14b. Similarly, the third reinforcement layer 16 includes a third plurality of parallel spaced apart bars 16a and a fourth plurality of parallel spaced apart bars 16b. The third plurality of bars 16a are substantially orthogonal to the fourth plurality of bars 16b. The second and/or third reinforcement layers 14, 16 may be provided as standard steel reinforcing mesh, sometimes referred to as "rebar". As is conventional with standard steel reinforcing mesh, the surface of any of the first, second, third and fourth pluralities of bars 14a, 14b, 16a, 16b may be contoured and/or textured to help form a bond between the bars 14a, 14b, 18a, 18b and the encapsulating material 22, In certain embodiments, the second and/or third reinforcement layers 14, 16 may be provided as A142 reinforcing mesh, having bar diameters of 6mm and a mesh size of 200mm x 200mm, i.e. the first and second pluralities of bars 14a, 14b, and the third and fourth pluralities of bars 16a, 16b have a bar spacing of 200mm, respectively. Of course, it will be understood that the exact specification of the second and third reinforcement layers 12, 14 will depend upon the design requirements of the panel 10. Specifically, the exact specification of the second and third reinforcement layers 14, 16 may depend upon the required ultimate and serviceability limit states of the panel 10. Any of the first, second, third and fourth reinforcement layers 12, 14, 16, 18 may be corrosion-resistant, for example the reinforcement layers 12, 14, 16, 18 may be hot dip galvanised or made from stainless steel.

As shown in the accompanying figures, the second and third reinforcement layers 14, 16 are positioned relative to one another such that the first plurality of bars 14a are substantially parallel to and interspaced between the third plurality of bars 16a, and the second plurality of bars 14b are substantially parallel to and interspaced between the fourth plurality of bars 16b. In certain embodiments, the second and third reinforcement layers 14, 16 are positioned relative to one another such that first and third plurality of bars 14a, 16a lie in a common plane, such that the second and third reinforcement layers 14, 16 are "nested" with one another. In such embodiments, the first plurality of bars 14a may contact the fourth plurality of bars 16b and third plurality of bars 16a may contact the second plurality of bars 14b. Nesting the second and third reinforcement layers 14, 16 enables the provision of a required amount of reinforcement using standard reinforcement products, for example A142 reinforcement mesh, while minimising the overall depth of the panel 10.

Figures 1 and 4 show the elongate strands 20 interlaced with the second and fourth pluralities of bars 14b, 16b over the length of the panel 10 to hold together the second and third reinforcement layers 14, 16. In the illustrated embodiment, each of the elongate strands 20 passes around a number of the second plurality of bars 14b on a side of the second reinforcement layer 14 which is closest the first reinforcement layer 12 and also passes around a number of the fourth plurality of bars 16b on a side of the second reinforcement layer 16 which is closest the fourth reinforcement layer 18. In certain embodiments, the elongate strands 20 may alternate between passing around one of the second plurality of bars and one of the fourth plurality of bars (this arrangement is that which is illustrated in the accompanying figures). In alternative embodiments, the elongate stands 20 may pass around more than one of the second plurality of bars 14b before passing around one or more of the fourth plurality of bars 16b and vice versa. A tensile force T1 (the direction of which is indicated in figure 4) may be applied to each of the elongate strands 20 during the manufacture of the panel 10, i.e. prior to forming the encapsulating material 22. The tensile force T1 may increase the resistance to separation of the second and third reinforcement layers 14, 16. The tensile force T1 applied to each of the elongate strands 20 may be between 10kN and 20kN. As illustrated in the accompanying figures, each of the elongate strands 20 may be a substantially flat strip. Use of flat strips may further assist in minimising the overall depth of the panel 10.

The encapsulating material 22 forms a block in which at least the reinforcement layers 12, 14, 16, 18 and the elongate strands 20 are embedded. In certain embodiments, the encapsulating material 22 may form a block in which other constituent parts of the panel 10, such as the stressing tendons 24, are also embedded. The encapsulating material 22 defines the first and second surfaces 11a, 11b of the panel 10 and may provide cover to any component embedded therein, where cover is the minimum distance between a surface of an embedded component of the panel 10 and the either of the first and second surfaces 11a, 11 b. Sufficient cover may be required to prevent corrosion of the reinforcement layers 12, 14, 16, 18, particularly if the panel 10 is to be used in an aggressive (i.e. highly corrosive) environment, e.g. a marine environment. The minimum level of cover may be between 10mm and 80mm, with larger cover depths required to protect the reinforcement layers against corrosion in aggressive environments. However, in certain embodiments the first and/or fourth reinforcement layers 12, 18 may only be partially encapsulated by the encapsulating material 22, i.e. no cover is provided to the first and/or fourth reinforcing layer 12, 14. In such embodiments, the first and/or fourth reinforcing layers 12, 14 are partially exposed, i.e. proud of the respective surfaces 11a, 11b, and may help to bond the panel 10 to other structural elements.

The encapsulating material 22 may include a cementitious material, for example cement, lime or mortar. To form the encapsulating material 22, the cementitious material may be mixed with a liquid, such as water, to form a liquid-cementitious material mix, to which a suitable aggregate, for example sand, may be added. In certain embodiments, aggregate may be added to the liquid-cementitious material mix up to a particle size of 5mm. In certain embodiments, a self-compacting mortar may be used to increase the workability of the liquid-cementitious material mix. Further, the encapsulating material 22 may include one or more admixtures to advantageously effect its material properties, for example a corrosion resistant inhibitor may be added to the liquid-cementitious material mix, for example calcium nitrate. Fibres may also be added to the liquid-cementitious material mix, for example steel fibres or polymer fibres, to increase the structural integrity of the encapsulating material 22 and/or minimise cracking. When manufacturing the panel 10, the liquid-cementitious material mix is placed through the layers of reinforcement 12, 14, 16, 18, thus forming the encapsulating material 22 as the liquid- cementitious material mix cures and hardens. The liquid-cementitious material mix may be forced through the layers of reinforcement 12, 14, 16, 18 by manual placement of the liquid-cementitious material mix by hand. Alternatively, the liquid-cementitious material mix may be shot though the layers of reinforcement 12, 14, 16, 18 using a spray-gun device. The panel 10 may be horizontally cast. Specifically, the reinforcement layers 12, 14, 16, 18 and the elongate strands 20 may be horizontally arranged in a mould before the liquid-cementitious material mix is placed to form the encapsulating material 24.

As mentioned above, the panel 10 may also include stressing tendons 24. Inclusion of the stressing tendons 24 in the panel 10 improves the load-bearing strength thereof by allowing for the induction of a permanent compressive stress in the panel 10. When working loads are placed upon the panel 10, the stressing tendons 24 resist stresses which would otherwise be resisted by the encapsulating material 22. The induced compressive stresses in the encapsulating material 22 are reduced and undesirable tensile stresses in the encapsulating material 22 may be avoided.

Figure 2 most clearly shows the positon of the stressing tendons 24 relative to the reinforcement layers 12, 14, 16, 18. Specifically, in the illustrated embodiment, the stressing tendons 24 are shown passing through the panel 10 between the second and third reinforcement layers 14, 16 at the mid-depth of the panel 10. However, in certain embodiments, the stressing tendons 24 may be otherwise positioned within the panel 10, for example in embodiments with a different number of layers of reinforcement. Compressive stresses may be induced in the panel 10 by pre-tensioning or post- tensioning of the stressing tendons 24. To pre-tension the stressing tendons 24, a tensile force T2 (the direction of which is indicated in figure 4) is applied to the stressing tendons 24 when constructing the panel 10, i.e. prior to placing the liquid-cementitious material mix through the layers of reinforcement 12, 14, 16, 18, thereby introducing a tensile stress into the stressing tendons 24. The encapsulating material 22 forms around the stressing tendons 24 and, once cured, the encapsulating material 22 bonds to the stressing tendons 24. The bond formed permits the transfer of stresses between the encapsulating material 22 and the stressing tendons 24. The tensile force T2 is removed from the stressing tendons 24 to cause the transfer of tensile stress in the stressing tendons 24 into encapsulating material 22, thereby inducing the compressive stresses in the encapsulating material 22. To post-tension the stressing tendons 24 the tensile force T2 may be applied to each of the stressing tendons 24 after the placing of the liquid-cementitious material mix, but before the liquid-cementitious material mix has cured to form the encapsulating material 22. Alternatively, each of the stressing tendons 24 may be provided in a respective one of a plurality of respective sheaths (not shown). The sheaths prevent the bonding between the stressing tendons 24 and the encapsulating material 22, i.e. the stressing tendons 24 are free to move relative to the encapsulating material 22 after the liquid- cementitious material mix has cured. When the stressing tendons 24 are provided in such sheaths, the tensile force T2 is applied after the encapsulating material 22 has been formed and is transferred into the cementitious material 22 by the stressing tendons 24 acting against respective anchors (also not shown) provided in the perimeter of the panel 10.

Providing the stressing tendons 24 between the second and third layers of reinforcement 14, 16 minimises the risk of any of the stressing tendons 24 breaking out of the panel 10 while under tension and causing personal injury. In the event any of the stressing tendons 24 should fail, the second and third reinforcement layers 14, 16 may contain the failed stressing tendon 24 within the panel 10. The tensile force T2 applied to each of the stressing tendons may be between 10kN and 20kN.

Certain embodiments of the invention may provide a less expensive alternative to purely steel structural elements, while delivering the structural performance of similarly sized steel structural elements. Further, when compared to known reinforced concrete structural elements, embodiments of the invention may allow for a smaller overall depth for a given specification, i.e. for a desired maximum design load. In certain embodiments, the overall depth of the structural element does not exceed 100mm. In certain embodiments, the overall depth of the structural element does not exceed 50mm. In certain embodiments, the overall depth of the structural element does not exceed 300mm. Therefore, certain embodiments of the invention may provide structural solutions which require less material and/or contain less embodied energy than existing solutions. Certain embodiments of the invention may also reduce whole life costs of a structure, as composite structural elements according to the invention may require less maintenance during their life, when compared to known structural elements. In certain embodiments, the composite structural element 10 may be suitable for use in constructing floor slabs, walls, beams, columns, foundations, frames, piles, bridge piers and/or caissons. As mentioned above, the composite structural element 10 may also be suitable for use in the construction of permanent concrete formwork, sometimes referred to as shuttering. For use as permanent formwork, at least one composite structural element 10 is provided adjacent at least one other composite structural element 10 such that a void is defined there between, the two composite structural elements may be connected by steel reinforcement. Concrete may then be placed between the two composite structural elements 10 to form, for example, a shear wall or retaining wall.

In certain embodiments, the composite structural element 10 may include multiple further reinforcement layers in accordance with either the first, second, third or fourth reinforcement layers 12, 14, 16, 18, depending upon the required specification, i.e. the required maximum design load.

All of the features disclosed in this specification (including any accompanying claims and drawings) may be combined in any combination, except combinations where at least some of such features are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings). The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims.

Claims

1. A composite structural element comprising:

a first reinforcement layer;

a fourth reinforcement layer adjacent the third reinforcement layer;

at least one elongate strand interlaced with the second and fourth pluralities of bars over a length of the composite structural element, thereby holding together the second and third reinforcement layers; and

an encapsulating material at least partially encapsulating the reinforcement layers and the at least one elongate strand.

2. A composite structural element according to claim 1 , wherein the at least one elongate strand is a substantially flat strip.

3. A composite structural element according to claim 1 or 2, wherein the second and third reinforcement layers are positioned relative to one another such that the first and third pluralities of bars lie in common plane.

4. A composite structural element according to any preceding claim, wherein the structural element further comprises at least one stressing tendon passing through the structural element for inducing compressive stresses in the encapsulating material.

5. A composite structural element according to claim 4, wherein the at least one stressing tendon is bonded to the encapsulating material and embodies a tensile stress thereby inducing the compressive stresses in the encapsulating material.

6. A composite structural element according to claim 4, wherein the at least one stressing tendon is provided in a sheath to prevent bonding of the at least one stressing tendon and the encapsulating material to permit post-stressing of the tendon to induce compressive stresses in the encapsulating material.

7. A composite structural element according to any preceding claim, wherein the encapsulating material includes a self-compacting mortar.

8. A composite structural element according to any preceding claim, wherein the encapsulating material includes at least one admixture from the group of: water-reducing admixtures, retarding admixtures, accelerating admixtures and superplasticisers.

9. A composite structural element according to any preceding claim, wherein the overall depth of the structural element does not exceed 100mm.

10. A composite structural element according to any preceding claim, wherein the overall depth of the structural element does not exceed 50mm.

11. A composite structural element according to any preceding claim, wherein the overall depth of the structural element does not exceed 30mm.

12. A composite structural element according to any preceding claim, wherein the first and/or the fourth reinforcement layer has an open area of no more than 85% of the total area thereof.

13. A composite structural element according to any preceding claim, wherein the first and/or the fourth reinforcement layer has an open area of between 60% and 80% of the total area thereof.