Impregnated cloth

Abstract

A knitted spacer fabric has a tightly knitted bottom layer, a more loosely knitted upper layer and linking fibres extending across the space between the lower and upper faces. Settable material, e.g. cement, is introduced into the space between the upper and lower faces and can be caused to set by the addition of a liquid, e.g. water. Until set, the fabric is flexible and can be shaped but after the material in space has set, the fabric is rigid and can be used as a structural element in a wide range of situations. The bottom layer has an extension that extends beyond the upper face and is connected to the upper face by elastic connecting fibres that draw the extension towards the other face, thereby at least partly closing the space at the edge of the cloth and preventing the settable material from spilling out. In addition, the packing of the settable material and maximum space between the faces are such that only a predetermined amount of liquid can be accommodated within the space and that amount is matched to the water required to set the cement.

Claims

1. A flexible cloth that can be set to become rigid or semi-rigid, the cloth comprising: a first face; a second face separated from the first face by a space; linking fibres extending between the first and second faces; and a powder material, including a reagent, located in the space between the first and second faces, which material is capable of setting to a rigid or semi-rigid solid on the addition of a liquid, wherein there is a void fraction between the first and second faces due to imperfect tessellation of the powder material, wherein the void fraction and length, stiffness and quantity of the linking fibres are configured to control the maximum amount of liquid allowed to enter the space between the two faces to provide a ratio between the liquid and the reagent in the space such that there is below the optimum amount of liquid, thereby providing unset reagent within the set material which enables the cloth to impart limited self-healing properties.

2. The cloth of claim 1, wherein the two faces of the cloth are constrained by the arrangement, shape and physical properties of the linking fibres.

3. The cloth of claim 1, wherein the linking fibres are the same material as the first face or the second face.

4. The cloth of claim 1, wherein the settable powder material comprises cement.

5. The cloth of claim 1, wherein the first face has pores that are large enough to admit the powder material into the space, which pores are at least partly sealed or have been reduced in size, thereby retaining the settable powder material within the space.

6. The cloth of claim 5, wherein the pores are at least partly sealed by a sealant.

7. The cloth of claim 1, wherein the first face is backed by a damp proof layer being impervious to liquids or gases.

8. The cloth of claim 1, wherein the second face includes pores that are sufficiently small as to retain the powdered settable material within the space but allow the passage of the liquid to cause the powder material to set.

9. The cloth of claim 1 in which, once the cloth has set to provide set fill material, the fibres in the cloth provide reinforcement to the set fill material whereby if the set fill material becomes cracked, the cloth fails progressively rather than catastrophically, by the fibres in the cloth taking up the load on the cloth.

10. The cloth of claim 1 in which, the fibres in the cloth, provide reinforcement to the material, when set, and prevent crack propagation.

11. The cloth of claim 1, wherein, at one or more edges of the cloth, the first and second faces are connected by an elastic yarn that is shorter than the linking fibres, thereby at least partly closing the space at the edge of the cloth.

12. The cloth of claim 11, wherein, at said one or more edges, the first and/or second face includes an edge portion that extends laterally beyond the rest of the face and that is connected to the rest of the fabric by the elastic yarns, the elastic yarn drawing the or each extending edge portion towards the other face, thereby at least partly closing the space at the edge of the cloth.

13. The cloth of claim 11, wherein the elastic yarns are incorporated into the edges of the cloth, as some or all of the linking fibres, during the manufacture of the cloth.

14. The cloth of claim 1, wherein the powder material is compacted and wherein an amount and a type of reagent in the compacted powder material, and the volume and compaction of the powder material are such that:
MVOV=x*LV where: MV=the maximum volume of the space within the cloth per unit area of the cloth; thus MV includes both the volume of empty space in the cloth before addition of the powder material, and an additional volume resulting from any expansion of the space due to the pressure exerted by the swelling of the powder material during the addition of the liquid or during the setting of material; OV=the volume of the space within the cloth that is occupied by the particles of the powder material, which volume does not include the volume occupied by voids within the powder material per unit area of the cloth; LV=the volume of liquid per unit area of the cloth that results in the 28 day compressive strength, of the compacted powder material when set; and x=a factor between 0.65 and 1.1.

15. The cloth of claim 1, wherein the settable powder material comprises a cement based dry concrete mix including plasticisers and other additives.

16. The cloth of claim 5, wherein the pores are at least partly sealed by an adhesive, a heat curable material or a layer of material applied to the first face.

17. A method of making an impregnated flexible cloth as claimed in claim 1, the method comprising: providing a fabric having a first face, a second face separated from the first face by a space and linking fibres extending between the first and second faces; and loading the space within the fabric with a powder material, including a reagent, that is capable of setting to a rigid or semi-rigid solid on the addition of a liquid, wherein there is a void fraction between the first and second faces due to imperfection tessellation of the powder material, adding a liquid to the cloth, wherein the void fraction and length, stiffness and quantity of the linking fibres are configured to control the maximum amount of liquid allowed to enter the space between the two faces to provide a ratio between the liquid and the reagent in the space such that there is below the theoretical optimum amount of liquid, thereby providing unset reagent within the set material which enables the cloth to impart self-healing properties.

18. A method as claimed in claim 17, in which the powder material is added by placing the settable material on the first face and vibrating the fabric and/or brushing powder material into the fabric.

19. The method of claim 17, comprising loading the powdered material into the space through pores in the first face and reducing the size of the pores or closing the pores once the powdered material has been loaded, by partly or completely sealing the pores by applying a sealant to the first face or by bonding a further layer onto the first face.

20. The method as claimed in claim 17 further comprising: using the impregnated flexible cloth: to form a cover of a prefabricated shelter; to form a track-way for vehicles, pedestrians or animals; to form a shelter by applying the fabric to a framework; to make formwork for casting concrete; to form barriers, e.g. to line tunnels; to repair or reinforce structures, e.g. roofs; to form floors or damp proof structures; to reinforce earth structures, e.g. river banks and unstable slopes; to provide flood defences; to repair existing pipes, including buried water pipes or to construct new pipes; to fireproof elements of new or existing structures; to form a hard surface, reduce dust hazards and contain fuel spills for aircraft; to reinforce sandbag structures and protect them from damage from the elements such as wind and ultra violet degradation; to line ground works and prevent the leaching of chemical contaminants; to form a waterproof lining for the containment of water; to form permanent awnings or roof structures; to line drainage ditches; to provide an external weatherproof facing for buildings; to form an integral part of a durable gabion structures; to repair and/or reinforce gabion structures and protect them from damage from the elements such as wind and ultra violet degradation; to form artistic or decorative forms, or to form hulls and superstructure of floating vessels such as boats or pontoons.

21. A method of setting a cloth as claimed in claim 1 in which the powder material is a settable powder material and comprising adding a liquid to the cloth to cause the settable powder material to set.

22. A method as claimed in claim 21, in which when the liquid is added the cloth has a low liquid to settable-powder ratio that is below the optimum amount of liquid to set reagent in the powder material fully such that unreacted reagent can impart limited self-healing properties to the material as cracks can allow liquid to penetrate the set material and react with the unreacted powder reagent held within the set material.

23. A method of setting a cloth as claimed in claim 1 in which the powder material is settable powder material and comprising submerging the cloth in a liquid to cause the settable powder material to set.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) There will now be described, by way of example only, a fabric material in accordance with the present invention, by reference to the accompanying drawings in which:

(2) FIG. 1 is a diagrammatic illustration of a spacer fabric;

(3) FIG. 2 is a cross sectional view through the fabric;

(4) FIG. 3 is a diagrammatic illustration of spacer fabric according to one embodiment of the present invention; and

(5) FIG. 4 is a needle diagram for knitting the spacer fabric of FIG. 3.

DETAILED DESCRIPTION

(6) Referring to the accompanying drawings, FIG. 1 shows a schematic knitted spacer fabric having a tightly knitted bottom face layer 10, a more loosely knitted upper face layer 12 and linking fibres 14 extending across the space 16 between the lower and upper face layers 10, 12. The spacer fabric is made of knitted polyethylene and is commercially available from Scott & Fyfe as 5 mm spacer fabric.

(7) Settable material, e.g. cement optionally together with fillers and other additives, is introduced into the fabric through pores 20 in the open-knit upper face layer 12. The pores 20 arise through the knitting process during manufacture of the spacer fabric. The cement can be placed on the spacer fabric and will fall through pores 20 into space 16. The penetration through the pores 20 can be assisted by placing the spacer fabric on a vibrating bed and by brushing the fill into the pores, e.g. using a rotating brush. Vibration also has the advantage of settling the cement within the space 16 to minimise voids or air pockets that are formed.

(8) The bottom face 10 has a relatively tight knitted structure and the pores in the bottom face are smaller than in the upper face layer such that the pores are sufficiently small to prevent substantial amounts of the cement from falling out.

(9) After the material has been introduced into the space 16, the upper face layer 12 is sealed by the application of a thin coat of PVC paste which is then cured by heating the surface.

(10) Water can penetrate into the fabric through the pores in the bottom face 10; hydration of the cement is aided by the linking fibres 14, which can wick water into the interior of the fabric.

(11) The cloth including the fabric and the settable fill material within the space 16 is flexible and can be formed to shape prior to the introduction of liquid to set the material within the space.

(12) The long fibres 18, together with the shorter fibres in the fabric, provide reinforcement to the material, when set and prevent crack propagation.

(13) FIG. 3 shows a spacer fabric that can be used for making the cloth of the present invention; except as set out below, it is identical to the fabric of FIGS. 1 and 2, and the same reference numbers as are used in connection with FIGS. 1 and 2 have been used in FIG. 3 to shown the same features. However, in the fabric of FIG. 3, the edge of the lower face layer 10 is extended beyond the edge of the upper face layer 12 by an extension 24 formed in exactly the same way as the rest of the lower face layer 10 except that linking fibres 26 connecting the extension to the upper face 12 is made of an elastic material which is stretched during knitting. When the tension is no longer applied to the elastic linking fibres 26, e.g. by removing the fabric from the knitting machine, the extension 24 is drawn up around the edge of the fabric by the linking fibres 26 and so closes off the edge of the fabric. When a settable fill is added through the pores 20 in the upper layer 12, it cannot spill out of the sides of the fabric.

(14) FIG. 4 shows the pattern of needles used for knitting the edge of the spacer fabric shown in FIG. 3 where the normal yarns used to form the bulk of the spacer fabric, e.g. polypropylene, are shown by the letter N while the elastic used to form the linking fibres 26 are shown by the letter E.

Example 1

(15) A high alumina cement is loaded into the fabric shown in FIG. 3 using the vibration and brushing techniques described above to form a filled cloth. Water is used to set the cement. The theoretical optimum water:cement ratio in this case is 0.4 by weight. The cloth has a porous face 10 of sufficiently closed construction to prevent the dry cement powder and also the cement powder once soaked in water from passing through it in significant quantities, the other face 12 has an impermeable PVC coated face to close off the pores 20. The two faces are linked by monofilament polyethylene linking fibres. The high alumina cement is compacted to give a total dry density of 1.35 g/cm.sup.3 and an average thickness of 7.3 mm between the outer surfaces of the two faces.

(16) The linking fibres are spaced, slightly bowed and of sufficient stiffness such that after immersion in water the swelling of the cement powder between the two faces is constrained to a 14% internal volume increase. When this increased volume is entirely filled with water as a result of immersion this represents a 10% increase in the weight of the material. In addition to the increase in volume, the water also displaces air from the void fraction and dissolves a proportion of the cement which results in a further 22% increase in weight.

(17) Continued immersion does not result in any further increase in weight. Therefore, the cloth construction limits the water to cement ratio to 0.32 being slightly below the 0.4 optimum to provide the maximum 28 day compressive strength. In other words, the factor x in the above formula is 0.32/0.4=0.8.