WO1999039887A1

WO1999039887A1 - Reinforcing a settable material

Info

Publication number: WO1999039887A1
Application number: PCT/NZ1999/000014
Authority: WO
Inventors: Douglas Wyndham Fisher Lewthwaite
Original assignee: Farrell, Elizabeth-Anne, Aileen
Priority date: 1998-02-06
Filing date: 1999-02-05
Publication date: 1999-08-12
Also published as: AU2553699A

Abstract

A reinforcing structure is provided for substantial encasement in a settable material, such as concrete. The structure has a grid-like configuration with interstices into which the settable material is received and comprises interlockable male (12) and female elements (10) of elongate flat proportions. The elements are of lower density than the settable material and are preferably made of fibregrass-reinforced plastics materials. The grid may be of squared or radial configuration. It may advantageously be applied to the manufacture of manhole covers and columns.

Description

REINFORCING A SETTABLE MATERIAL

This invention relates to reinforcing structures for settable materials.

In the construction industry it is known to use steel reinforcement for concrete structures. Steel, however, has a relatively high value on the waste or scrap market, with the result that structures are often destroyed in an attempt to remove the steel reinforcement inside. In addition steel may suffer from corrosion and contributes to the sometimes excessive mass of structures.

European Patent Publication Number EP 0 307 584A discloses a T-shaped concrete fender pillar having prestressing components extending in its lengthwise direction, these components being of high tensile composite fibre members, typically glass fibres in a plastics matrix. These provide protection against impact forces directed normally to the lengthwise direction, such as from a ship docking against the pillar.

German Patent Publication DE 4440 787A1 discloses a prefabricated support that may comprise a grid which has a layer of fibrous reinforcing material on its underside for purposes of strengthening. An upper fabric layer may be applied to increase stiffness.

United States patent US 5,423,627 describes a vault lid made up of a rib assembly comprising channel shaped beams assembled flange to flange and structurally interlocked to assist in distributing concentrated loads on the lid surface.

1 - The present invention seeks to provide a relatively low density reinforcing means to withstand compressive loads in excess of those bearable by competing higher density prior art means.

SUMMARY OF INVENTION

According to a first aspect of the invention, reinforcing means for inclusion in a settable material comprises a grating of slat-like elongate elements made of a relatively low density material compared with the settable material, the elements having opposite edges connected by a major surface and being arranged so as to present, in use, an edge with respect to an expected applied load.

In a preferred form of the invention, the low density material is a plastics composition. In a further preferred form it comprises a reinforcing material for such plastics. The reinforcing material may be a fibreglass reinforced resin.

In a further preferred form of the invention, the grating comprises interconnectable male and female elements. The elements preferably have interlocking means. The interlocking means include engagement means for engaging the elements at a point of juncture in use.

According to a second aspect of the invention, reinforcing means for inclusion in a settable material comprises a prefabricated grating-like structure comprising elongate first and second element types, the first such type having at least one slot through which an element of the second type is receivable and engagement means enabling engagement between the second and first in use.

In a preferred form of the invention, the elements are of flat, bar-like proportions having opposite edges connected by a major surface. In use, the elements present with an edge to an expected applied load.

- 2 In a further preferred form of the invention, the engagement means comprises a formation on one element that in use co-operates with a part of the other element. Preferably, the formation is on the second element and comprises a notch. The notch may engage with an edge of the first element.

According to a third aspect of the invention, a manhole cover comprises a composite body shaped to cover a manhole opening, the body comprising a settable material and an internal reinforcing structure encased in such material, the reinforcing structure being of a relatively less dense material than the settable material.

In a preferred form of the invention, the structure comprises a grating.

In a further preferred form of the invention the grating comprises elongate first and second elements. The elements are preferably of bar-like proportions, Further preferably, they are flat. The first elements may include slots for receiving elements of the second type. Elements of the second type preferably include a formation for engagement with the slots of the first type.

In a preferred embodiment, the structure comprises an outer frame to which the grating is attachable.

The slat elements of the grating may be arranged radially within the frame with respect to a central point. Alternatively, the slat elements of the grating are arranged in a generally square configuration.

According to a further aspect of the invention, a method of reinforcing a structure comprising settable material includes the steps of providing a grating made of a relatively low density material compared with the settable material;. the grating comprising interconnected elongate strip-like elements having opposite edges connected by a major surface, configuring the grating according to the structure to be reinforced so that elements present an edge toward an expected applied load in use, filling interstices in the grating with

- 3 - the settable material and forming the settable material into a predetermined shape according to the structure desired.

The invention extends to a manhole cover comprising a body of settable material shaped to fit over the opening of a manhole and having an internal support structure comprising a grid-like structure as described above and being made of a relatively less dense material than the settable material.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a side view of interlockable individual elements in an embodiment of the invention.

Figure 2 presents in (a) a top and in (b) a side view of a grating-like reinforcing structure in an alternative embodiment of the invention.

Figure 3 presents in (a) a sectional perspective view partially cut away along line A-A of figure 2 and in (b) a sectional side view along line A-A of figure 2

Figure 4 presents in (a) a top and in (b) a side view of a radial grid according to the invention.

Figure 5 presents in (a) a cross section of the grid of figure 4 cut away along line A-A and in (b) a perspective view, partially cut away along line A-A, of the grid in figure 4.

Figure 6 is a perspective view of a reinforcing structure according to the invention applied to an elongate construction.

DETAILED DESCRIPTION OF THE INVENTION

The reinforcing structure according to the first aspect of the invention is relatively of low density in comparison with the material it is intended to reinforce. It is shaped to provide load-bearing capabilities. A preferred

- 4 - configuration for the structure is a grating or grid having slat- or strip-like elements disposed edge-on toward the direction of an applied load when in use.

The grating or grid may be manufactured from a single body of material. As such, it may be an integral structure cut or punched from the parent body. Alternatively it may be manufactured by a process whereby a liquid or flowable material is caused to assume a predetermined shape and allowed to harden or set. Examples of such processes are moulding processes, such as pressure or injection moulding.

An alternative method of producing a reinforcing structure includes steps of providing individual elements for assembly into the desired configuration, such as the grating structure referred to above. The elements may be moulded using any of the processes above, or may be manufactured by means of an extrusion-type process such as pultrusion. Long strips for the elements are made in this way, whereafter the necessary slots are punched or cut out.

Elements according to the invention in this embodiment comprise two types - those of the first being interconnectable, preferably interlockable, with elements of the second in use. Although in its most basic form a grating-like reinforcing structure may comprise only one element of each type locked together, in order to form a grating-like structure of the simplest effective type, one element of one type needs to be interlocked with at least two elements of the other. Interlocking is preferably achieved by twisting or rotating an element of one type with respect to an element or elements of the other. Preferably the grating-like structure comprises at least two elements of each type, so that an interstice is defined between the elements when connected together. The settable material being reinforced should then desirable enter the interstice and harden around the structure.

To facilitate interconnection, elements of the first type have a series of openings spaced along their lengths. The openings are shaped and sized to receive an element of the second type. Spacing is preferably regular.

- 5 - Elements with these openings will be referred to below as female elements. Each element of the second type would typically in use fit through openings in two or more elements of the first type and, on being twisted axially, engage with the receiving element. The elements that are thus insertable, will be referred to below as male elements.

In a preferred embodiment, the openings have one lateral dimension greater than the other, giving them a slot-like appearance. For example, the slots may be generally oval in aspect, or may be of flattened hexagonal or even rectangular shape. The elements of the second type would thus be shaped complementally to have cross sectional dimensions allowing such elements to pass through the slots when oriented in one relative position, but, when twisted axially, will abut the sides of the slot at its narrower dimension. To enable engagement to take place, the elements include facilitating formations. These may be suitably-shaped indentations in one or both opposing edges of the second element type. Preferably such indentations are notch-like.

The notch-like indentations may be the same or of different lengths. They enable interlocking engagement of a mechanical rather than a mere frictional nature to take place on axial rotation of one element with respect to the other.

The elements are preferably slat-like and made of a relatively low density material compared with the density of the settable material in which they are included as reinforcement. However, a higher density material, such as a steel or other metal may be chosen in the second aspect of the invention. For reinforcement to be effective, the grating comprising the slats should possess load-distributing properties. The relatively low density material is preferably a substance that provides a rigid, light weight structure. Preferred materials are plastics. Hard setting polymers are desirable. Preferred are reinforced plastics materials. Fibreglass reinforced resin is particularly preferred.

The material may be provided in sheet form so that individual slats may be cut from it or punched out or pressed or otherwise formed according to methods well known in the art.

- 6 - An example of a pair of interiocking elements is shown in figure 1. Here a slat of the female type 10 is viewed side on with a male slat 12 partially inserted but not yet twisted into locked configuration. The slats are of sheet-laminated fibreglass. Female slat 10 has a series of hexagonal slot-like openings 14 spaced at regular intervals along its length. The openings are of a flattened hexagonal shape, with their wider dimensions 16 oriented with the length of the slat and their narrower dimension 18 lying transverse across the slat. The reader will appreciate that other orientations are possible within the scope of the invention.

The male slat 12 has spaced at intervals along its length pairs of indentations 20 along its opposite edges 22 and 24 respectively. When these are brought into alignment with the edges of the opening 14 in female slat 10 and male slat 12 is axially rotated anti-clockwise, for example, as shown by arrows 26, the indentations 20 engage with the narrower sides of the opening. The indentations are in the form of narrow notches having width substantially the same as the thickness of the female slat 10 and therefore fit snugly over these edges.

Apart from the indentations 20, the male slat has further cut-outs 28 giving it alternating portions of narrower and wider width. These cut-outs are provided to allow for greater penetration and encasement of the grating by the concrete or other settable material phase.

By providing a plurality of male and female elements, a grating can be constructed. Figures 2 and 3 illustrate such a grating formed of similar complemental and interlockable elements. Like parts found in figure 1 carry the same numbering. The grating formed of the elements is located in a terraced circular frame 30, to which it is connected. The frame has a double lip formation, the edge 32 being turned inwardly for protection against chipping of the settable material on handling of the final product. The ends of the central slats are preferably further reinforced, as shown at 34. Similar reinforcement is optionally provided at the central point intersection, as seen at 36.

This assembly, when formed of a relatively lightweight and low density rigid material such as fibreglass, is suitable for reinforcing a concrete manhole cover. To produce the manhole cover, the preformed grating is placed in a mould of the desired shape. Cement or other suitable settable substance is then poured into the mould so that the interstices in the grating are filled and the grating is substantially submerged, so that it will be at least partially encased when the settable material sets. The composition thus formed is permitted to set, whereafter it may be removed from the mould. It may, however, be advantageously left in the mould. In this configuration, the presence of the mould assists in resisting chipping of the settable material. Other applications in the construction and civil engineering fields are apparent.

To produce such a product, the reinforcing structure is prefabricated and then placed preferably in a suitably shaped mould, into which a settable material, such as concrete, is cast poured and allowed to set. The reinforcing structure is thus encased in the concrete so that the opposite edges of the slats forming the grating are aligned in the direction from which a load is expected to be applied in use. Because of the superior compressive strength of fibreglass, the flat slats when thus disposed provide a far stronger structure than would a steel structure of substantially the same construction and dimensions.

The grating may be allowed to protrude above the level of the settable material so a to provide an anti-slip surface.

An alternative embodiment of the grating in figures 2 and 3 is illustrated in figures 4 and 5. Here the slats 52 of a first type are radially disposed with respect to a central point 54 and contained within a circular frame 56. Slats of the second type, although not shown, may be concentrically arranged to interlock with the slats 52 through slots 62. Interstices 60 thus formed allow for penetration of settable material (not shown) between the slats. The slats

- 8 - 52 are commonly connected to a ring-like slat 58 located close to the central point 54.

The utility of the invention is not confined to reinforcement of manhole covers, but may be applied widely in the construction industry for load distribution and reinforcement. It may be applied to elongate structures such as pillars, columns, beams or walls. In a pillar requiring reinforcement against lateral distortion or bending, an elongated grating is provided and orientated with the edges of slats aligned in a plane coinciding with the direction of applied load against which protection is desired.

With reference to figure 6, a concrete column 40 is shown in schematic perspective view with the structure according to the invention providing internal reinforcement. Two female slats 10 are shown extending internally along the length of the column and connected by a plurality of transversely disposed interlocking male elements 12 shown in locked position. As such each such male element passes through an opening 14 in the female element, as described above with reference to figure 1. The inclusion of this internal structure provides reinforcement against lateral, rather than axial loads.

For elongate structures liable to bear both axial and lateral loads, a three- dimensional reinforcing grating is recommended. Such a grating comprises a series of two dimensional gratings as described with reference to figures 1 and 2 connected so as to be disposed in strata above, but spaced from, each other by two or more longitudinally orientated elements. These elements are positioned with their edges aligned to meet an expected lateral load side on, i.e. with the major plane of the element in alignment with the direction of the applied load.

Some of the advantages of the inventive products and method are that heavy metal structures may be replaced with lighter, stronger (weight for weight) and more corrosion resistant constructions. Where fibreglass replaces steel, a 5:1 improvement in strength per unit mass is achievable. In the case of manhole

- 9 - cover design, it has been found that a concrete cover, approximately 110mm to 140mm thick and manufactured with a fibreglass reinforcing grating according to the invention, may replace a conventionally manufactured and steel reinforced concrete cover 150mm thick without sacrificing efficacy.

In addition, the inventive reinforcing may be applied in the casting of the concrete manhole casing and other hollow cylindrical structures.

The strength of a manhole cover manufactured according to the invention was tested by means usually applied to steel reinforced covers. The results are discussed in the example that follows.

Example:

Static compressive strength tests were conducted in respect of two manhole covers, each with a diameter of 572 mm and 140 mm in thickness and comprising concrete reinforced with a grid structure with square interstices as shown in figure 2. The grid was of fibreglass-reinforced plastics resin and the two covers were contained in a fibreglass dish-like mould. The two sample covers had a grid structure as illustrated in figures 2 and 3.

Testing was carried out on a compression testing rig capable of applying a force of up to 140kN at a rate of up to 36kN/min. Each sample for testing was set up on the rig as follows. The sample was placed on a resilient mat on the test bed. A plaster of paris cover was formed over the upper surface of the sample and finished to a plane surface. Upon this layer a hard wooden block was centrally placed.

Force was applied to the block increasing at a rate of up to 36kN/min so that it was transmitted through to the sample. When the force reached 135kN, it was maintained at this level for 30s while the sample cover was inspected for signs of stress damage.

- 10 Inspection of the underside of the cover samples at the prescribed load of 135kN revealed no cracking of the fibreglass mould. This was taken to be an indication that the concrete within was also intact. This conclusion was supported by the lack of apparent cracking at the upper surface.

The force was then increased further to the maximum available for the test rig. This maximum turned out to be 150kN (above the rated maximum of 140kN). Even at this level, there appeared to be no visible sign of damage to either sample.

Thus both manhole covers exceeded the South African industry standard requirements for a heavy duty class sample in withstanding a 135kN load for 30 seconds.

11

Claims

1. Reinforcing means for inclusion in a settable material comprises a grating of slat-like elongate elements made of a relatively low density material compared with the settable material, the elements having opposite edges connected by a major surface and being arranged so as to present, in use, an edge with respect to an expected applied load.

2. Reinforcing means according to claim 1 wherein the grating comprises interconnectable male and female elements.

3. Reinforcing means according to claim 2 wherein the male and female elements have complemental interlocking means.

4. Reinforcing means according to claim 3 wherein the interlocking means include engagement means for engaging respective male and female elements at a point of juncture in use.

5. Reinforcing means according to claim 4 wherein the engagement means comprises a formation on each male element that in use co-operates with a part of the female element with which it is engageable.

6. Reinforcing means according to claim 5 wherein the formation on the male element comprises a notch.

7. Reinforcing means according to claim 6 wherein the notch on the male element is engageable with an edge of the female element type.

8. Reinforcing means according to any one of the preceding claims wherein the grating comprises the slats arranged in a generally square pattern.

9. Reinforcing means according to any one of claims 1 to 7 wherein the grating comprises the male elements radially arranged with respect to a central point.

- 12 -

10. Reinforcing means according to claim 9 wherein the female elements are concentrically arranged with respect to the said central point.

11. Reinforcing means according to any one of the preceding claims in which the low density material is a plastics composition.

12. Reinforcing means according to claim 11 comprising a reinforcing material for such plastics.

13. Reinforcing means according to claim 10 wherein the reinforcing material is a fibreglass.

14. Reinforcing means for inclusion in a settable material, so as to provide reinforcement thereof when set, comprising a grating-like structure comprising interconnectable elongate first and second element types, the first such type having at least one slot through which an element of the second type is receivable and engagement means enabling engagement between the second and first in use.

15. Reinforcing means according to claim 14 wherein the elements are of flat, bar-like proportions having opposite edges connected by a major surface and are arranged in use to present an edge to an expected applied load.

16. Reinforcing means according to claim 15 wherein the engagement means comprises a formation on each first element type that in use co-operates with a part of the second element type.

17. Reinforcing means according to claim 16 wherein the formation on the second element type comprises a notch.

18. Reinforcing means according to claim 17 wherein the notch on the second element type is engageable with an edge of the first element type.

- 13 -

19. A manhole cover comprises a composite body shaped to cover a manhole opening, the body comprising a settable material and an internal reinforcing structure according to any one of claims 1 to 13 and being at least partially encaseable in such material, the reinforcing structure being of a relatively less dense material than the settable material.

20. A manhole cover according to claim 19 wherein the structure comprises an outer frame to which the grating is attachable.

21. A manhole cover according to claim 19 or 20 comprising a dish within which the structure is containable.

22. A method of reinforcing a structure comprising settable material includes the steps of providing a grating made of a relatively low density material compared with the settable material;, the grating comprising interconnectable elongate strip-like elements having opposite edges connected by a major surface, configuring the grating according to the structure to be reinforced so that elements present an edge toward an expected applied load in use, filling interstices in the grating with the settable material and forming the settable material into a predetermined shape according to the structure desired.

23. A method according to claim 22 wherein the grating has generally square interstices.

24. A method according to claim 23 wherein at least some of the elements are radially arranged with respect to a central point.

14