IE56925B1

IE56925B1 - A mixture of fibres for the reinforcement of construction materials specifically for the reinforcement of hydraulic binding agents,a method of reinforcing construction materials and formed articles of said mixture

Info

Publication number: IE56925B1
Application number: IE494/85A
Authority: IE
Original assignee: Redco Sa
Priority date: 1984-03-01
Filing date: 1985-02-28
Publication date: 1992-01-29
Also published as: DE3562221D1; DK94585D0; GR850498B; DK94585A; EP0155520B1; TR23396A; NO850819L; MA20360A1; PT80039B; ES540845A0; ES8606813A1; JPS60204649A; EP0155520A1; PH23179A; CH660357A5; DK160484B; CA1234703A; IE850494L; PT80039A; DK160484C

Abstract

1. A mixture of polyacrilnitrile and polyvinylalcohol fibres as reinforcing fibres for materials setting after the molding thereof, specifically for hydraulically setting materials, characterized in that said mixture of fibres comprises 50-90% polyacrilnitrile fibres and 50-10% polyvinylalcohol fibres.

Description

The present invention relates to a fibre mixture for the production of fibre-reinforced materials, such as, for example, hydraulically setting materials, specifically of a cement material which contains polyacrylonitrile fibres and polyvinylalcohol fibres as reinforcing fibres. The invention further relates to the application of such fibre mixtures in the production of shaped members from materials setting after the molding thereof.

The polyacrylonitrile fibres will be designated hereinafter respectively as PAN-fibres, and the polyvinylalcohol fibres will be designated as PVA-fibres.

It is generally known that components, shaped in the most varied of ...... ........ 'ways,such as purlins, corrugated plates, tubes or garden articles can be produced from hydrous suspensions, consisting, for example, of asbestos and cement, by means of dewatering machines, e.g. Hatschek machines, or by means of injection methods. During the past few decades, such components have been able to secure a dominant position amongst construction materials. In the past few years, however, it became increasingly clear that the most important raw material for the production of these products, namely asbestos, will not be available for much longer for this application, for the most varied of reasons, such as availability, price trends, and also because of health aspects, Not only do the known, excellent properties of use of asbestos cement rest on the unique combination of properties of asbestos fibres, but also they form the basis of the Hatschek dewatering method, which is spread worldwide. - 3 For a years, all the ebove~K©ntion®d circumstances have set in motion an Intensive research activity, which had the task of finding replacement fibres, which can totally replace the asbestos in the existing production processes of the dewatering methods. However, it very quickly became apparent that no single type of fibre was able to be found, which combined within it all the positive properties of asbestos.

Principally, it is the following properties which distinguish asbestos at the sme time as an excellent process fibre and as a reinforcing fibre : high specific surface good dispensability - excellent chemical resistance high cement hold-back capacity good fleece formation capacity high tensile strength high modulus of elasticity - small elongation at rupture As a process aid, asbestos displays an excellent distribution capability in a hydrous cement suspension. During the dewatering step, due fo the good filtration capability and the good cenent affinity, asbestos is able to hold back the cement in the composite substance which is being produced. In the hydratised end product, the high tensile strength, combined with the high modulus of elasticity and the small elongation at rupture has a positive effect, which is able to give the asbestos ces&ent products the known high bending strength.

As neither natural nor synthetic fibres with the caisihination of properties of asbestos were able to be found, if arose from the research efforts in seeking for possible replacement products that fibre mixtures have to be used, corresponding to the two inain functions of asbestos, in order to be able to produce fibre cement with these new fibres on existing installations (see, for example, DE-PS-3 002 484 of Afiiiantus). The filtration properties of asbestos can be simulated through additions of celluloses and/or synthetic fibrides in the fibre - 4 mixtures. Reinforcing fibres are used for the reinforcing effect.

Such fibres may be organic or inorganic high modulus fibres, which are usually added in cut lengths of 4-12 wsa.

There is scarcely any synthesis fibre which would not have been tested as a cement reinforcing fibre as regards this purpose of application. Most fibres, however, have not been able to be successful for the most varied of reasons, such as insufficient chemical resistance, poor cement affinity, insufficient mechanical properties, or due to too high a price. From the entire range of fibres on offer, to date only two types of synthesis fibres have been able to be successful, which satisfy the requirements of a cement reinforcing fibre. One of the fibres was developed on the basis of polyacrylonitrile and has been brought onto the market for example by the firm Hoechst (Federal Republic of Germany) under the trademark Dolan 10 (see also CH-PS Patent Application No. 1919/81-8). The other fibre is composed on the basis of polyvinylalcohol and is obtainable, for example, under the mark Kuralon of the firm Kurarai, Japan (DE-PS-2 850 337). The most important properties of these fibres are grouped together in Table 1.

Table 1 Textile mechanical properties of fibre types suitable for cement reinforcement : Fibre type Breaking strength cH/dtex Elongation at rupture % Modulus of elasticity cN/dtex Polyacrylonitrile PAN (e.g. Dolan 10) 6.0-8.5 10-16 min. 130 Polyvinylalcohol PVA (e.g. Kuralon) 10-15 5.5-15 min. 175 The comparison of the textile mechanical properties of the PVA- with the PAN-fibres shows that PVA-fibres have the better mechanical - 5 properties. If 6 cut fibres of these two types are distributed in a hydrous cement suspension and are processed into small fibre cement plates on a filter press, it is found at the measured strengths of the small plates that the better fibre properties are also able to give higher strengths to the end product (Table 2).

Table 2 Strength values of small fibre cement plates, produced on a filter press, from Portland cement and the high modulus fibres on the basis of , 10 PVA and PAM f Fibres %—wt Bending strength (according to ISO) ^/rnm2 Energy of fracture kJ/m2 Density g/ccm Mater absorption % PAM fibres 20 1.0 12.5 0.203 1.982 15.0 1.5 14.7 0.457 1.920 14.5 2.0 16.0 0.701 1.851 15.7 PVA 25 fibres 1.0 14.8 0,652 1.935 14.6 1.5 16.1 1.208 1.900 15.1 2.0 19.5 1.835 1.863 16.0 30 Textile mechanical proper ties of the fibres used Tensile Modulus of Elongation Titer 9 strength elasticity at rupture cM/dtex cM/dtex % dtex 1 35 PAU 7.5 150 11 3.0 PVA 12 240 6 2.0 The energy of fracture represents a very important property in terms of - 6 material technology. It provides evidence of the brittleness, or respectively the impact toughness of a product. In practice, this can have the effect that, for example, on laying purlins with variously high values for the energy of fracture, but with identical bending strengths, under the load by the roofer, in one instance, the plates suddenly fracture without prior warning (brittle fracture), and in the second instance, however, the load is taken up by a higher deflection.

The analysis of the results shows that the PVA-fibres with the better textile mechanical properties are not only able to give the small fibre cement plates a higher bending strength, but that also the energy of fracture is very much higher than in the case of the ΡΑϊΊ-fibres. The energy of fracture in these experiments is defined as the area under the stress-strain curve up to the point at which the maximum bending strength is reached, i.e. the plate is ruptured.

In the knowledge of the correlations between the fibre data and the resulting product properties of the fibre cement plates, it would be simple to produce fibre cement products upon which very high requirements are set as regards bending strength, impact toughness and energy of fracture, exclusively with the use of PVA-fibres. However, this solution is opposed by the high prices of PVA-fibres. Due to the high raw material costs, combined with a very costly thread production process, the costs for the production of PVA-fibres are.approximately 50 to 100% higher than for PAM-fibres. If one considers, in addition, that the present asbestos prices are only a fraction of the synthesis fibre prices, then it is obvious that the fibre price must be given crucial importance so that economic fibre cement products can be produced at all. It would therefore be desirable, to the highest degree, for the fibre cement industry to find a fibre with the properties of the described PVA-fibres, but which is economically acceptable, i.e. is not substantially more expensive than the ΡΑϋ-fibre.

According to the mixture rule which is valid for fibre-reinforced composite materials, it would be expected that in the case of fibre mixtures, the strengths resulting for the reinforced material, or respectively the energy of fracture, follow in a linear manner and proportional to the mixture ration (cf. Fibre-Reinforced Cement - 7 Composites, Technical Report 51.067, The Concrete Society, Terminal House, Grosvenor Gardens, London 1973, and H.Krenchel Fibre Reinforcement, Akademisk Foralg Copenhagen, 1964).

Surprisingly, it was now found that a very high proportion of PVA-fibres can be substituted by cheap PAN-fibres, without a loss of the positive properties being observed in the fibre cement product.

The mixture of PVA- and PAN-fibres according to the invention is characterized in that it contains as few as possible, but at least 10%, PVA-fibres.

The fibre mixtures according to the invention are to be explained in further detail according to the following practical test examples.

High modulus polyacrylonitrile fibres, which have a modulus of elasticity of a minimum 15.0 cH/dtex, an elongation at rupture of a maximum 16% and a tensile strength of af least 6 cH/dtex, are suitable as fibres for mixtures of PAN-fibres with PVA-fibres in accordance with the invention.

Suitable polyvinylalcohol fibres are high modulus fibres with the following specifications : Modulus of elasticity of at least 75 cN/dtex, elongation at rupture of a maximum 15% and a tensile strength of at least 10 cH/dtex.

Both types of fibre can be used with uniform titers or as mixtures of fibres of different titers. However, fibres are preferably used in the range of from 0.5-5.0 dtex. The fibres can either be cut to exact, uniform lengths, or they may be ground or present in mixed form in various lengths. Preferably the PVA-fibres are used in lengths of from 4-15 mm and the PAK-ίibres in lengths of from 2 to 12 mm.

The following examples will show that it is particularly advantageous if the PVA-fibres which are used are approximately 1/3 longer than the admixed PAN-fibres. - 8 As possible production methods for components in which the fibre mixtures according to the invention are used, for example dewatering methods by means of round or longitudinal screening machines are suitable, but also mono-line installations, injection installations or filter presses.

Mixtures which are suitable for processing on the above-mentioned installations also contain, in a hydrous suspension, in addition to the fibre mixtures according to the invention, a setting material, such as, for example, cement and, if required, additional fibrous substances with filter properties and also various fillers or additives.

Hydraulic inorganic setting materials such as cement, gypsum, earth alkaline silicates or earth alkaline aluminates are suitable as setting materials. However, organic setting materials such as, for example, synthetic resins, can also be used. Quartz sand, blast furnace slag, fly ash, puzzolane, mica, rock dust, are suitable for example as fillers and additives. Cellulose fibres in the form of sulphate cellulose, mechanical wood pulp, thermomechanical pulp and/or synthetic fibrides on the basis of plastics, such as, for example, polyethylene, may be used as auxiliary fibres, which serve to hold back setting materials and fillers on the screens. The retention capacity may be additionally further improved through the use of flocculation agents, e.g. on the basis of polyacrylamides.

Products which can be produced with these mixtures on the dewatering installations are, for example, flat plates, corrugated plates, tubes or moulded articles such as, for example, garden articles.

The PVA-/PA6*l-fibre mixtures according to the invention will be explained more precisely below in a few examples of application. a) Production of the fibre cement plates for test purposes The tests were carried out on a round screen dewatering machine of the ί Hatschek type.

In a separate pulper, the fibre cement suspensions were prepared with a - 9 ί J w solid matter content of 80g/l, and were pumped from there continuously into the draining tank of a Hatschek machine.

Shortly before running into the draining tank, additionally 200 ppm of a flocculation agent of the polyacrylamide type were added to improve the cement retention. Plates of approximately 6mm were produced on the machine with 22 revolutions of the format roller, which plates were pressed between oiled sheets for 60 min in a stack press at a specific applied pressure of 250 bar to a thickness of 4.8 mm. Unpressed samples were also produced from all the variants, and were tested. The setting of the fibre cement plates took place over 25 days in a humidity chamber of 100% r.humidity at 20°C. After the plates had been additionally stored for 3 days under water, the tests were carried out in wet state.

The tests in which fibre cement plates were produced consisting only of the fibre mixture according to the invention and cement, i.e. without filter adjuvants, have been produced on a filter press. b) Mixtures used For production on filter press : Portland cement (2800 Blaine) 100 parts Fibre mixtures 2.0 parts For production in the Hatschek process : Portland cement (2800 Blaine) 100 parts Waste paper (45° SR) 3.5 parts Polyethylene fibride (“Pulpex E-A, Hercules USA) 2.0 parts Fibre mixtures 2.0 parts The following variants were used as fibre mixtures : PAN 2 1.7 1.3 1.0 0.7 0 parts PVA 0 0.3 0.7 1.0 1.3 2.0 parts The textile technical properties of the fibres used were -PAH Titer 1.5 dtex, tensile strength 7.2 cH/dtex, modulus of elasticity 140 ·) 35 - 10 cN/dtex, elongation at rupture 9% -PVA Titer 2 dtex, tensile strength 12.5 cH/dtex, modulus of elasticity 250 cN/dtex, elongation at rupture 6.5¾ PAH-fibres and PVA-fibres were used in various combinations in 4 and 6 mm cut lengths.

For the tests on the filter press, mixtures consisting only of Portland 10 cement and the PVA/PAN-fibres, were produced in water. c) Examination of the fibre cement plates The examinations of the test plates took place by means of a Wolpert 15 testing machine with three point bearing on plates of 25X25 cm. The bearing distance was 167 mm and the testing speed was 26mm/min. The evaluation of the results was carried out by means of a connected computer. d) Results The results are collected together in Tables 3 to 7. - 11 Table 3 Test results of small fibre cement plates with variable PVA-PAN-1 ratios, produced on a Hatschek machine Fibre mixt ure Bending Energy of Density Water PAftl, PVA strength fracture absorj 6mm parts 6mm parts N/mm2 kJ/m2 g/ccm % Pressed plates 2.0 22.4 3.047 1.941 12.3 0,3 1.7 21.1 2.799 1.934 11.4 0.7 1.3 21.8 2.884 1.943 10.9 1.0 1.0 20.7 2.698 1.982 12.0 1.3 0.7 21.3 2.532 1.919 11.9 1.7 0.3 19.0 2.105 1.932 12.4 2.0 - 17.1 1.108 1.911 12.1 Unpressed plates 2.0 14.8 4.272 1.555 20.1 0.3 1.7 14,7 3.820 1.567 19.9 0.7 1.3 14.5 4.133 1.557 19.8 1.0 1.0 13.6 3.740 1.539 21.2 1.3 0.7 13.8 4.010 1.500 23.7 1.7 0.3 13.1 3.205 1.532 20.8 2.0 - 12.4 1.902 1.514 21.9 j Table 4 Test results of small fibre cement plates with variable PVA-PAN-fibre ratios, produced on a filter press Fibre mixture Bending Energy of Density Water strength fracture absorption PAW, PVA 6mm 6mm parts parts N/mm2 kJ/m2 g/ccm % 2.0 14.2 2.603 1.753 19.9 0.3 1.7 14.4 2.512 1.758 19.8 0.7 1.3 13.9 2.543 1.752 19.7 1.0 1.0 13.9 2.527 1.754 19.8 1.3 0.7 13.7 2.410 1.732 19.9 1.7 0.3 13.1 1.700 1.748 19.6 2.0 - 12.2 0.975 1.731 19.8 Table 5 Test results of small fibre cement plates with variable PVA-PAN-fibre ratios, produced on a Hatschek machine Fibre mixture Bending Energy of Density Water strength fracture absorption PAN, PVA 6mm 4mm parts parts N/mm2 kJ/m2 g/ccm % pressed plates - 2.0 24.2 3.075 1.935 12.6 0.3 1.7 23.1 2.418 1.942 11.6 0.7 1.3 20.4 1.990 1.919 12.0 1.0 1.0 19.2 2.001 1.920 11.6 1.3 0.7 18.9 1.820 1.923 11.2 1.7 0.3 17.5 1.221 1.917 11.8 2.0 - 17.1 1.108 1.911 12.0 - 13 Unpressed plates 0.3 2.0 1.7 15.0 14.7 4.519 4.095 1.550 1.541 22.6 22.4 5 0.7 1.3 14.2 3.465 1.528 21.9 1.0 1.0 13.4 2.968 1.536 20.4 1.3 0.7 13.1 2.436 1.532 20.4 1.7 0.3 12.7 2.150 1,521 21.3 2.0 - 12.4 2.100 1.514 21.9 10 Table 6 Test results of small fibre cement plates with variable PVA-PAN-fil ratios, produced on a filter press 15 Fibre mixture Bending Energy of Density Water strength fracture absorpt PAN, PVA 6fffin 4mm 20 parts parts N/mm2 kJ/m2 g/ccm % - 2.0 14.8 2.429 1.807 18.7 0.3 1.7 15.3 2.510 1.823 17.7 0.7 1.3 14.0 2.010 1.779 18.6 1.0 1.0 13.5 1.619 1.785 18.2 25 1.3 0.7 12.9 1.327 1.761 18.8 1.7 0.3 12.5 0.902 1.750 18.7 2.0 - 12.4 0.945 1.747 18.9 J - 14 Table 7 Small fibre cement plates produced according to the invention with variable PVA-PAM-fibre ratios, produced on a Hatschek machine.

Fibre mixture Bending strength Energy of fracture Density Water absorption PAN, 4mm parts PVA 6mm parts N/mm2 kJ/m2 g/ccm % pressed plates 2.0 22.6 3.331 1.938 12.2 0.3 1.7 22.8 3.115 1.933 12.1 0.7 1.3 22.1 3.101 1.941 11.0 1.0 1.0 22.0 2.987 1.931 11.5 1.3 0.7 21.3 2.605 1.929 12.3 1.7 0.3 18.2 1.980 1.937 12.0 2.0 - 15.3 0.972 1.941 11.1 Unpressed plates 2.0 15.1 4.657 1.548 22.3 0.3 1.7 15.2 4.450 1.551 22.0 0.7 1.3 14.8 4.522 1.550 21.9 1.0 1.0 14.8 4.186 1.542 22.6 1.3 0.7 14.1 3.475 1.553 21.9 1.7 0.3 12.9 2.497 1.561 20.7 2.0 - 11.7 1.303 1.568 19.9 Textile mechanical pi roperties of the fibres used in Table 7.

PAM, 4mm titer 3.0 dtex, tensile strength 7.2 cM/dtex, modulus of elasticity 1.52 cN/dtex, elongation at rupture 9.8% PVA, 6mm titer 2.0 dtex, tensile strength 12.5 cN/dtex, modulus of elasticity 250 ciii/dtex, elongation at rupture 6.5% - 15 10 δ I

Claims

1. A mixture of polyacrylonitrile and polyvinylalcohol fibres as reinforcing fibres for materials setting after the molding thereof, specifically for hydraulically setting materials, wherein said mixture of fibres comprises 50-90 1 ¾ polyacrylonitrile fibres and 50-10% polyvinylalcohol fibres.

2. The mixture according to claim 1, wherein the PAN-fibres have a modulus of elasticity of at least 130 cN/dtex, a maximal elongation af rupture of 16% and a strength of at least 6 cN/dtex.

3. The mixture according to claim 1, wherein the PVA-fibres have a modulus of elasticity of af least 175 cN/dtex, a maximal elongation af rupture of 15% and a strength of at least lOcN/dtex.

4. The mixture according to claims 1 to 3, wherein the used PVA- and PAN-fibres comprise titers in the range of 0.5-10 dtex.

5. The mixture according to one or more of claims 1 to 3, wherein the length of the PAN-fibres is in the range of 2 to 12 mm.

6. The mixture according to one or more of claims 1 to 3, wherein the length of the PVA-fibres is in the range of 4 to 15 iran.

7. The mixture according to one or more of claims 1 to 6, wherein the preferred ratio of the cut length of the PVA- and PAN-fibres, respectively, amounts to 4:3 to 3:2.

8. The mixture according to one or more of claims 1 to 7, wherein the reinforcing fibre mixture further contains an additive as a process aid

9. The mixture according to claim 8, wherein the additive comprises cellulose fibres.

10. The mixture according to claims 8 wherein the additive comprises synthetic pulp. 1 35 - 16

11. The mixture according to claim 8, wherein the additive comprises cellulose fibres and synthetic pulp.

12. The mixture according to claim 8 wherein it further comprises a filler.

13. The mixture according to claim 12, wherein the filler comprises quartz sand. V

14. The mixture according to claim 8 wherein the filler comprises amorphous silicic acid.

15. The mixture according to claim 8 wherein the filler comprises blast furnace slag.

16. The mixture according to claim 8 wherein the filler comprises fly ashes.

17. The mixture according to claim 8 wherein the filler comprises puzzolane.

18. The mixture according to claim 8 wherein the filler comprises 1imestone.

19. The mixture according to claim 8 wherein the filler comprises mica.

20. - Use of the mixture according to any of claim 1 to 19 for reinforcing hydraulically setting materials.

21. Use according to claim 20 wherein the hydraulically setting material comprises reinforcing cement.

22. Use according to claim 20 wherein the hydraulically setting material comprises reinforcing gypsum. ί

23. Use according to claim 20 wherein the hydraulically setting material comprises reinforcing earth alkaline-silicates. - 17

24. Use according to claim 20 wherein the hydraulically setting material comprises reinforcing earth alkaline-aluminates.

25. The use according to any of claims 20 to 24 for the production of 5 the fibre reinforced shaped articles whereby a diluted, hydrous suspension is produced from said hydraulically setting materials, which hydrous suspension is produced and moulded into the desired shape and set thereafter. 10

26. The use according to claim 25 wherein the fibre reinforced shaped articles comprise plates.

27. The use according to claim 25 wherein the fibre reinforced shaped articles comprise corrugated plates.

28. The use according to claim 25 wherein the fibre reinforced shaped articles comprise tubes.

29. Shaped articles whenever produced by utilization of a mixture of 20 reinforcing fibres according to any of claims 1 to 19.

30. Shaped articles according to claim 29, wherein they contain 1 to 5% preferably 1.5 to 2.5% of the reinforcing fibre mixture. 25

31. A mixture of polyacrylonitrile and polyvinylalcohol fibres substantially as hereinbefore described by way of Example.

32. Use of the mixture according to any of claims 1 to 19 or claim 31 substantially as hereinbefore described by way of Example.

33. Shaped articles substantially as hereinbefore described by way of Example.