IE46542B1 - Improvements in or relating to the manufacture of articlesmade from a water-hardenable mass and a reinforcing element - Google Patents

Description

This invention rebates to the manufacture of articles made from a water-hardening substance, for example a cement mortar or a gypsum-based material.

On safety grounds- and because of depletion of supplies 5 asbestos-cement sheets are likely to become less readily available and attempts have already been made to produce alternative sheets which have equally good or better properties and which, preferably, are no more costly to produce and can be handled and cut or otherwise formed at least as easily as asbestos-cement sheets.

In order to provide a complete, and satisfactory, replacement of asbestos-cement sheets it is necessary that the materials shall be readily available, non-toxic and should not give rise to difficulties in manufacture.

Furthermore, such articles must have adequate strength properties and be capable of handling and forming to the desired shape or size.

Attempts to meet these requirements have not so far proved fully successful despite a considerable amount of research Work. Prior proposals have had the specific disadvantages of excessive cost, inadequate strength in some respects including unfavourable ageing characteristics of the composites and/or difficulty in successfully carrying out their manufacture.

British Patent specification 1,130,612 discloses and claims as a reinforcement for Portland cement concrete mixtures, fibrillated polypropylene film cut up into short lengths. The reinfdrcement and portland cement are mixed in a conventional mixer and the resultant product, when cured, exhibits some increase in impact strength . How5 ever, this prior proposal provides no solution to the problem of replacing asbestos cement in thin sheet materi al since the short lengths of reinforcement (up to 7.5 mm) simply pull out and thus provide no additional tensile strength. There is no suggestion in this prior specification that the reinforcement should be incorporated in any way other than a random distribution as is to be expected from the use of a rotary mixer According to the present invention, there is provided a process for the manufacture of sheets or other art15 icles made from a water-hardenable substance comprising the incorporation of fibrillated organic film in the form of network means as layers in the water-hardenable substance. 6 5 4 2 Further according to the present invention, there is provided a sheet or other article comprising fibrillated organic film in the form of network means disposed in layers in a water-hardened substance.

Still further according to the present invention, there is provided a sheet or other article comprising a water-hardened substance with a reinforcement of network means of fibrillated organic film arranged as layers.

Yet further according to the present invention, there is provided an article comprising a water-hardened substance and network means of fibrillated organic film in the form of a plurality of expanded, nonwoven layers embedded within said substance, the fibrils of said film providing continuous mechanical bondings to reinforce the water-hardened substance so that under excess loading the article exhibits multiple cracks.

Yet further according to the present invention, there is provided an article comprising a water-hardened substance and network means of fibrillated organic film in the form of a plurality of layers embedded in the water-hardened substance, the effective volume of film in one direction of tensile stress, when loaded, amounting to more than 1|% of the overall volume of the article and the fibrils of said film providing continuous mechanical bonding to reinforce the water-hardened substance in said direction of tensile stress so that under excess loading the article exhibits multiple cracks.

By the use of a continuous organic fibrillated organic film incorpor25 ated as a network arranged as layers in a water-hardening mass, it becomes possible to manufacture articles which have properties which at least in some respects are substantially superior to those of for example asbestoscement, and which can be competitive in cost.

Preferably the network used in the process is based on fibrillated polyolefin film since this gives particularly good properties at a cost which is currently competitive with conventional asbestos fibres. By incorporating the most preferred reinforcing materials namely polypropylene, it becomes possible by incorporating a large number of layers I 1 per centimetre thickness of the product, to obtain a final product which has adequate strength properties for the production of cement-based sheets so that the process produces an end product which is not only competitive in price with asbestos-cement but has properties which enable its use in many situations where asbestos-cement cannot be used.

For certain purposes it may be desirable to provide go between two spaced layers of water-hardening mass and network, at least one inter-layer of a water-hardening substance or other material without any reinforcement. intended The term water-hardenable substance is to mean herein a dry or substantially dry mixture of one or more inorganic materials capable, when mixed with water, of setting to a solid, rigid mass. is The term water-hardening substance/intended to mean herein a dry or substantially dry mixture of one or more inorganic materials which when mixed with water sets to a solid, rigid mass. Portland cement and gypsum are examples of such a substance.

The term continuous in relation to a fibrillated organic film is intended primarily to describe a situation in which the individual elements forming a network extend over a major dimension of an article incorporating the network such as the breadth or the length or both the breadth and the length.

More generally the term means that the network cannot be mixed in a with the water-hardening substance / rotary mixer. This contrasts with reinforced materials based on a water-hardening substance in which the reinforcement is of loose short fibres which can he mixed to obtain homogeneity in a rotary mixer. Film which is capable of achieving satisfactory results will be of such a length that if subjected to rotary mixing, instead of producing a homogenous product, the film would form a tangled substance largely separated from the water-hardening substance. Also the film cannot be sprayed from a gun with water-hardening substance as with sprayed fibre'cements and concretes.

The invention is not based on the water-absorption of the incorporated organic film but does not exclude such materials. For example when applied to polypropylene the water absorption is effectively nil in a humid atmosphere.

After immersion in water for 24 hours the absorption was below found to be/0.10% under conditions laid down by the American Society for Testing and Materials - Report D 570-63.

The incorporation of the film may be assisted by a dispersing agent which deflocculates the. suspension of particles of the water-hardening material and assists the penetration through the mesh to interlock the components firmly together. Generally suah dispersing agents which are suitable for the purpose consist of sulphonated polymeric materials such as low molecular weight resin, sulphonated melamine formaldehyde or sulphonated napthalene formaldehyde resin.

A dispersing agent is not, however, essential, the 46843 strength of the material depending on the mechanical interlock and on the very large surface area of the network for a given volume which controls cracking in the water-hardening substance.

Preferably a multiplicity of impregnated layers of mesh 5 made from a network of continous fibrillated organic film are incorporated and are pressed, trowelled or vibrated together in layers each generally less than 5 mm thick and successive layers are added until the required overall thickness for the product is achieved:.

The network is preferably derived from polyolefin film which has been stretched to promote Orientation of the molecular structure which gives high tensile strength and also increases the modulus of elasticity. In the presently used industrial applications of polypropylene film the stretching process produces an elongation in the polypropylene film of five to twenty times the unstretched length.

Alternatively, the film can be produced by fibrillar crystallisation.

After the stretching or crystallisation process, the film is in a state of imminent fibrillation and can become fibrillated during further handling or by suitable mechanical treatment, for example, by pin rolling in a manner similar to that employed on polypropylene film used as the raw material of binder twine, The mesh produced can be described as a flat opened 46342 network of non-woven polypropylene film in which the elements are made from the film as opposed to monofilaments. The term flat should not, however, be interpreted to mean that the network is necessarily plane in the finished product although before incorporation it will normally be so flexible that it will conform to a plane surface when laid on one.

The mesh which forms the reinforcement can, alternatively, be a weave, known sometimes as leno weave, in which the warp is doubled so that at each intersection the weft passes over one warp of the doubled warp and beneath the other warp of the doubled warp. The two warps are then twisted before the next weft again passes in the same manner between the two warps. This has the advantage of forming a mesh which retains its shape when handled in industrial equipment and the use of the doubled weft assists- in mechanical bonding between the and the water-hardening substance^ networks. While the woven fibre network has advantages from the viewpoint of manufacture, it has the disadvantage of being more costly and probably requires a greater volume of material to achieve equivalent properties.

The warp and weft of the leno weave are, like the non-woven networks, formed from flat fibrillated, but not expanded, polypropylene.

The preferred reinforcement Hereinbefore referred to is, however, the expanded non-woven mesh produced by mechanical .25 fibrillation in a regular pattern, of a stretched film as illustrated in Fighre 1, One advantage oi this non-woven form network, in addition to its greatly reduced cost, is that it can he made from very thin films and thus it becomes possible to increase the specific surface area of the mateiial and to incorporate many more layers of reinforcement in a given thickness of finished sheet for a given volume of reinforcement I material. The thickness of the film may range from 1 to 1000 microns, but the preference is for thinner films in the 15 to 150.micron range. 'the selection of the thickness depends, however, on the volume of network to be incorporated and hence the properties desired in the final product. The use of fibrillated organic thin film enables a very good mechanical interlock to be attained between the mass and the network, which it is believed gives rise to the useful properties achieved. This results in the desirable features of a reduced crack spacing and reduced crack width under post-cracking conditions in the product. Among the polyolefins, polypropylene is preferred but polyamides have suitable properties and can be fibrillated to provide either woven or non-woven networks. is The wat^r-hardening substance/preferably conventional Portland cement with a filler such as very fine sand and/or pulverized fuel ash and the fineness is important since otherwise there will not he adequate penetration between the network and the mass with resulting voids and weakness. The fineness of the filler becomes particularly important when a very large number of layers of network are incorporated and the grain size will be selected to take into account the number of layers of the reinforcement network.

The composite may also contain additives in the form of short staple fibres which, among other effects, improve the surface finish of the product.

Such additives do not however form part of the fibrillated organic film network, and will normally be distributed above and below that network.

Preferably, in a sheet which is to replace a conventional, average thickness, asbestos-cement sheet, at least six or sevei layers of mesh will be employed comprising about 5-7% of the volume of the sheet but higher strengths can be attained by increasing the number of mesh layers and, indeed,whencontinuou! networks made from very thin film are used as a starting material the number of mesh layers can be increased to several hundred · and, within limits, the impact strength and area under the load deflection curve in flexure and the area under the stress/strain curve in tension can be improved well beyond that attainable with asbestos-cement. It is believed that the upper limit is of the order of 15% by volume of film to water-hardenable substance.

It will normally be desirable in sheets which are to be symmetrically corrugated in the manner of asbestos-cement sheets for most of the layers of the mesh to be orientated in the same direction with respect to the corrugations but for other uses it may be preferable to arrange the mesh layers with alternate orientations or even different orientations through the thickness of the sheet, not necessarily at right angles to one another.

Where the direction of application of a tensile load can be predicted for an article in use, it is, of course preferable to align most of the fibrillated elements in that direction.

During the manufacture of the sheets it is desirable that and after a certain number of layers of water-hardening substance,, reinforcement have been deposited, pressure should be applied to encourage and promote mechanical bonding between the substance and the fibrillated .elements, and in addition, surplus water may be removed by applying vacuum through a filter mat as in many, processes in concrete production.

Many articles can be formed other than simple sheets. Multiple layers of network can in fact be wrapped round formers to produce desired special shapes.

Reference will now be made to Examples of articles embodying the invention and these Examples will refer to the accompanying drawings, in which: Figure 1 is an exploded isometric view of a sheet embodying 46S43 the invention and showing several continuous fibrillated film networks of non-woven form; Figure 2 is a graph plotting load in kN against deflection in.mm, and showing as an inset the corresponding fibrillated test specimen containing networks of non-woven/film; p Figure 5 is a graph plotting stress in MN/m against —fi strain.x 10“ for a further test specimen shown as an inset containing non-woven polypropylene fibrillated film; Figure 4 is a graph plotting load in kN-'against deflection ' in mm. and showing as an. inset the form and dimensions of a corresponding further test specimen of the same material as in Figure 3; Figure 5 is a graph plotting stress in MN/m against c. strain x 10 at the initial cracking stage and showing as an inset the form and dimensions of a further test specimen containing woven polypropylene; stress in MN/m2 Figure 6 is a graph plotting/against strain x 10“ illustrating post-cracking ductility for the test specimen shown in Figure 5; ' Figure,7 is a graph plotting load in kN against deflection in mm. for a test specimen incorporating woven polypropylene fibrillated film.

'Example 1 A specimen to be loaded in flexure was manufactured by the process in accordance with the invention and contained 6% of the total volume of the specimen of continuous flat networks of expanded stretched fibrillated polypropylene film of thickness about 100 microns. The following proportions by weight were chosen for the water-hardening substance cement 1.0; total water 0.34; pulverized fuel ash 0.25; fine sand passing 600 micron sieve 0.19; and dispersing agent (sulphonated melamine formaldehyde resin) 0,03.

The specimen was rectangular with dimensions 13.5 mm x 50 mm x 150 mm. Tests over a span of 135 mm were carried out and the results are illustrated in the graph of load in kN against deflection in mm. of Figure 2. The considerable post-cracking ductility was made possible by interlocking of the continuous network with the cement matrix and carrying load, without pulling out, after cracking of the matrix had occurred, The load was removed at a deflection of about 6 mm. and the deflection recovered to within 1½ mm. of the initial zero. No cracks were readily visible to the naked eye on the tensile face of the beam after the load was removed but inspection with a microscope revealed very fine cracks between 1. mm. and 3 mm. spacing. ι In Figure 2, at the point of load removal, the modulus of rupture calculated in the conventional manner on an elastic analysis was about 27 ®/m2 but the maximum load had not been reached. Other similar specimens have achieved modulii of rupture in excess of 30 MN/m2, In Figure 2, 1 kN = 14.8 MN/m2 modulus of rupture.

Example 2 Although it is preferable to have a volume of reinforcing elements in excess of 5%, it is also possible in accordance with the invention to achieve multiple-cracking in tension and in flexure and increase in bending strength with lower volumes of continuous, flat, non-woven, networks.

A tensile load specimen (Figure 3) was made employing the of water-hardening substance/Example 1 with 324 layers of a flat opened network of non-woven polypropylene fibrillated film. The thicknes: of eaoh film was at the lower end of the thickness range. The specimen was rectangular in section with dimensions 15 mm x 30 mm x 280 mm and there were therefore about 22 layers of film per mm thickness. The total film volume was 2.3% of the overall volume of the specimen. The effective film volume in the direction of tensile stress is difficult to determine with flat, opened, networks but was probably between 1,5% and 2% in this Example, The specimen was then tested and the results are shown in Figure 3.

A considerable post-cracking ductility was made possible as in Example 1.

Example 3 1 A flexure load specimen was made of the same material described in Example 2. The specimen was rectangular with dimensions 14,5 mm x 50.5 mm x 150.00 mm. Tests over a span of 135.0 mm were carried out and the results are illustrated in the graph of load in kN against deflection of Figure 4. The increase in load after cracking, was made possible by the post-cracking behaviour described in Example 1. In this test the modulus p of rupture is given by 1 kN = 12.7 kN/m , Examnl e 4 In this Example a corrugated sheet was manufactured and the 5 water-hardenablo substance hadycoinposition the same as that of Example 1.

Woven material (leno weave) was used as the reinforcement and was made of continuous orientated, fibrillated, polypropylene film with 3 mm. mesh and approximately two warps to one weft. Six layers of mesh were incorporated to give a thickness of 5» 5 mm. Pour layers were arranged with the warp parallel to the corrugations and two with the weft parallel to the corrugations.

The finished sheet 0.23m x 1.1m with a corrugation height of 20 mm. was tested in accordance with B.S. 690 Part 3, 1973, and sustained the required load of 334 Newtons. Cyclic loads were applied, initially up to 150N, then 35ON, 400N and finally at 800 Newtons. Three loading cycles were carried out at each load. At 150N one or two minor cracks were formed: at 35ON crack spacing was 10 to 40 mm; at 400N the crack spacing was reduced and at 800N there was substantial deflection and the crack spacing,was in the range of 3 to 6 mm.

Long term loading tests on a similar sheet were carried out with sustained, uniformly-distributed, loads of 0.75 kN/ 2 for 27 days and 1.5 kN/n]2 for a further 33 days. The residual creep deflection after removal of the load was less than 2 mm. in a span of 0.93m , . The uniformly-distributed load was increased to 2 kN/^2 at which point the load-deflection curve <6542 indicated, that significant cracking had occurred. Further sustained loading at 0.75 kN/m2 in the cracked state produced, a creep deflection of 0.25 mm. in 30 days. The uniformlydistributed loads are those specified in B.S. 5249 Part 14 1975 for asbestos-cement sheet.

Example 5 A tensile load specimen was made employing the mixture of Example 1 and 150 layers of woven polypropylene (Leno weave), the layers being subjected to pressure during build-up of the layers. 8% by volume of the specimen v/as taken up by the network.

The specimen was then tested and the results attained are shown in Figures 5 and 6. In both Figures the stress in MN/m2 is plotted against strain χ 10_θ. In Figure 5i the Initial Modulus E = 21GM/m2. Figure 5 illustrates the initial cracking characteristics, while Figure 6 illustrates the total curve showing post-cracking ductility. The left-hand curve of Figure 6 is equivalent to Figure 5 to a different scale. Example 6 A flexure load specimen was made employing the mixture of Example l'and 100 layers of woven polypropylene were incorporated. The specimen was rectangular with dimensions 500 x 100 x 74.5 mm. The span during testing was 406 mm.

Tests were carried out and the results are illustrated in Figure 7 where the load in kN is plotted against deflection in mm. The modulus of rupture calculated in the conventional manner on an elastic analysis is expressed in this Figure as 10 kN £ 7.52 MN/ffl2.

As will be apparent the specimen was progressively loaded with higher and higher loads, a considerable increase in load carrying capacity being achieved after cracking had occurred.

Sheets made by the process in accordance with the invention are suitable for applications where asbestos-cement sheets have hitherto been used which are subjected to flexural loading and are liable to impact under certain conditions. It has been found that the sheets possess adequate toughness and a desirable pseudo-ductility, that latter · phenomenon being attributable to multiple fine cracking, without however the bending strength of the material being adversely affected.

An additional advantage is that nails may be driven directly through thin sheet without fracturing the sheet remote from the hole. The material is thus capable of high energy absorption during failure either under impact or under slowly increasing loads. In this respect therefore sheet material in accordance with the present invention presents an improvement over asbestos-cement which is liable to brittle fracture on impact, lhe ultimate strength of the sheet when subjected to direct tensile stresses is not likely to be increased in the same proportion as under flexural loading.

In the preferred construction with multiple layers of t networks the risk of weak spots owing to absence of reinforcement are substantially eliminated. With discontinuous fibres the risk of non-homogeneity i3 high.

The invention can be applied to corrugated, flat and asymmetric sheeting, .troughs, non-pressure pipes, and rain-water articles such as are used in the house building and construction industry. It is also possible that the material produced by ' the method in accordance with the invention can be used to produce garden furniture, sewer linings, ventilation shafts, crash barriers, box sections and cladding panels incorporating expanded polystyrene. Alternatively the material may incorporate polystyrene beads to produce a light-weight insulat ing material.

The invention may additionally be applied to reinforced concrete and other structural members as a permanent shutter not for structural strength but rather to produce a fine surface crack pattern. This would enable higher stresses to be applied to the reinforcement in the beam before a limiting crack width is reached when compared with normal reinforced concrete.

Sheets in accordance with the invention are not merely substitutes for asbestos-cement sheets but are additionally suitable for end uses in internal and external applications not previously served by asbestos-cement.

Claims (36)

1. A process for the manufacture of sheets or other articles made from a water-hardenable substance comprising the incorporation of fibrillated organic film in the form of network means as layers in the water hardenable substance.

2. A process for the manufacture of sheets or other articles comprising the incorporation in a water-hardening substance of network means of a fibrillated organic film arranged as layers.

3. A process according to claim 1 or claim 2 wherein the network means cover the whole of the area of the article.

4. A process according to claim 1, claim 2 or claim 3 wherein the network means is obtained by expanding the fibrillated organic film.

5. A process according to any one of the preceding claims, wherein the fibrillated organic film is a polyolefin film.

6. A process according to any one of the preceding claims wherein the organic fibrillated film is derived from poly olefin film which has been produced in such a way as to promote orientation of the molecular structure and the film, which is then in a state of imminent fibrillation, can be fibrillated by further mechanical treatment.

7. A process according to any one of the preceding claims, wherein the fibrillated organic film is a stretched organic film. _ 20 _

8. A process according to any one of the preceding claims, wherein the organic film is polypropylene.

9. A process according to any one of the preceding 5 claims, wherein the layers are subjected to vibration, pressure or suction or like mechanical action during the process so as to promote incorporation in the waterhardening or water-hardenable substance.

10. 10. A process according to any ope of the preceding claims, wherein a plurality of sheets of water-hardening or water-hardenable substance and layers of network means have at least one intermediate sheet of a waterhardening or water-hardenable substance between them.

11. A process according to claim 10, wherein each sheet of water-hardening or water-hardenable substance and layer of network means is 5 mm or less in thickness. 20

12. A process according to any one of the preceding claims except when appendent to claim 4 wherein the network means is obtained by weaving lengths of fibrillated organic film. 25

13. A process according to claim 12, wherein woven lengths have double warps and single wefts and at each intersection the weft passes over one warp and beneath the other warp. 30

14. A process according to claim 12 or claim 13 wherein the film is flat in the woven condition except at the intersections.

15. A process according to any one of the preceding 35 claims, wherein the water-hardening or water-hardenable substance incorporates cement, sand and/or pulverized fuel ash. - 21

16. A process according to any one of claims 1 to 15, wherein the water hardening or water-hardenable subst ance is gypsum. 5

17. A process according to any one of the preceding claims wherein the percentage by volume of organic film in the water-hardening or water-hardenable substance is at least 2%. 10

18. A sheet or other article comprising fibrillated organic film in the form of network means disposed in layers in a water-hardened substance. —-................ (Page 22 . follows)—-y 15 / - 22 4-65 4 2

19. A sheet or other article comprising a water-hardened substance with a reinforcement of network means of fibrillated organic film arranged as layers.

20. An article comprising a water-hardened substance and network 5 means of fibrillated organic film in the form of a plurality of expanded, non-woven layers embedded within said substance, the fibrils of said film providing continuous mechanical bonding to reinforce the waterhardened substance so that under excess loading the article exhibits multiple cracks. 10

21. An article comprising a water-hardened substance and network means of fibrillated organic film in the form of a plurality of layers embedded in the water-hardened substance, the effective volume of film in one direction of tensile stress, when loaded, amounting to more than 1)% of the overall volume of the article and the fibrils of said film 15 providing continuous mechanical bonding to reinforce the water-hardened substance in said direction of tensile stress so that under excess loading the article exhibits multiple cracks.

22. An article according to any one of claims 18 to 21, wherein the fibrillated organic film is derived from a polyolefin film which 20 has been produced in such a way as to orientate the molecules and has been fibrillated.

23. An article according to any one of claims 18, 19 or 21, wherein the network means is derived from fibrillated expanded organic film. - 23

24. An article according to any one of claims 18 to 23, wherein the network means is derived from a polypropylene film.

25. An article according to any one of claims 18, 19 or 21 to 24 except when appendent to Claim 20, wherein the network means is in the form of woven lengths of fibrillated organic film.

26. An article according to claim 25, wherein the network means is in the form of a weave with a doubled warp and a single weft so arranged that at each intersection the weft passes over one warp and beneath the other warp then the warps are twisted after insertion of the weft whereby to lock the weft in position.

27. An article according to any one of claims 18 to 26, wherein the network means is in the form of one or more layers of fibrillated and expanded organic film with an interlayer of water-hardened substance or other material without any reinforcement.

28. An article according to any one of claims 18 to 26, wherein the network means is in the form of a plurality of layers of a woven network of fibrillated organic film and there is at least one inter-layer of a water-hardened substance or other material without any reinforcement.

29. An article according to any one of claims 18 to 28, wberein the water-hardened substance comprises a mixture of sand and/or pulverized fuel ash and Portland cement.

30. An article according to any one of claims 18 to 28, wherein the water-hardened substance is gypsum. . 24. 4654%

31. An article according to any one of claims 18 to 29, wherein there are at least six layers of organic film. 5

32. An article according to any one of claims 18 to 31, wherein the percentage by volume of organic film in the water-hardened mass .... (Page 25 follows) V is at least 2%.

33. A sheet comprising a network of continuous, flat, fibrillated polypropylene film in the form of a plurality of layers embedded in a water-hardened mass of cement and sand, the volume of 5 polypropylene film amounting to over 2$ by volume of the overall volume,

34. A sheet according to claim 33, wherein the film amounts to at least 5% of the overall volume.

35. A process for the manufacture of sheets or other articles 10 comprising a water-hardenable mass and an organic fibre reinforcement substantially as hereinbefore described with reference to the Examples.

36. A sheet or other article substantially as hereinbefore described with reference to the Examples.