GB2082640A

GB2082640A - Fibre-cement board

Info

Publication number: GB2082640A
Application number: GB8025769A
Authority: GB
Original assignee: Amfu Ltd
Current assignee: Amfu Ltd
Priority date: 1980-08-07
Filing date: 1980-08-07
Publication date: 1982-03-10

Abstract

Heat resistant non-asbestos compression- moulded board of density at least 1500 kg/m<3> having a matrix of cured hydraulic cement containing fibrous wollastonite in an amount forming 10-60% by weight, any content of organic fibre in the board forming less than 0.5% by weight thereof; the board having a crushing strength of at least 50 MPa, a shear strength of at least 15 MPa and a cross breaking strength of at least 15 MPa. The board is made by forming a slurry of at least 30% of the solids in water, dewatering under pressure, e.g. in a ram-operated moulding press, and curing.

Description

SPECIFICATION Heat resistant board This invention relates to heat-resistant board having a matrix of cured hydraulic cement reinforced with fibre and being of density of least 1500 kg/m3.

A well known form of such board, used for example in circumstances where a load has to be supported at elevated temperature, as in a pneumatic press with a heated platen, takes the form of cured Portland cement reinforced with asbestos fibres and is made by compression-moulding an aqueous fibre/cement slurry. This entails subjecting the slurry, of initial solids content at least 30% by weight, to a pressure of the order of 10 MPa while it is in a mould permeable to water under pressure. The slurry is thus dewatered to form a moulded product, usually of thickness in the range 3-100 mm, which is then removed from the mould and set aside for the cement to cure or treated to cure the cement quickly.

The present invention provides a non-asbestos alternative to the board just described, having crushing strength, shear strength and cross-breaking strength approaching those of the known asbestos product.

According to the invention, heat-resistant non-asbestos compression-moulded board of density at least 1500 kg/m3 having a matrix of cured hydraulic cement contains fibrous wollastonite in an amount forming from 10 to 60% by weight, any content of organic fibre (cellulose, for example) forming less than 0.5% by weight, the board having a crushing strength of at least 50 MPa, a shear strength of at least 15 MPa and a cross-breaking strength of at least 15 MPa. These strengths are measured according to British Standard 3497 (1967).

The weight proportions of the various ingredients are preferably as follows: Hydraulic cement 60-85% Wollastonite 15-30% The hydraulic cement may, for example, be ordinary Portland cement, fine-ground (and therefore rapid-hardening) Portland cement or high alumina cement.

The reinforcement of the cured cement matrix is provided essentially by the fibrous wollastonite, but the board may also contain a small proportion (not greater than about 0.5% by weight) of non-wollastonite fibrous material for special purposes. For example, vitreous fibre (mineral wool or alkali-resistant glass fibre) may be included, suitably at a level of about 0.25% by weight, to reduce brittleness in the board; and rayon fibres may be included, suitably at a level of about 0.01%, for the same purpose.

Fillers, such as bail clay, may be included, at a level no greater than about 15% by weight, in order to improve the rheological properties of the slurry from which the board is prepared by compression moulding.

According to another aspect of the invention, there is provided a method of making a board as set forth above, in which a slurry of water-settable hydraulic cement and wollastonite and containing at least 30% by weight of solids, is dewatered under a pressure of at least 10 MPa and the dewatered product is cured.

The invention is further illustrated by the following examples: Example 1 A board highly resistant to heat shock was made by the following procedure: 1. 24 kg (25% by dry weight) of fibrous wollastonite (fibre length predominantly 200-1000 m) and 72 kg (75% by dry weight) of ordinary Portland cement were put into a ribbon mixer and mixed dry for 3 minutes to form a homogeneous mixture.

2. 30 litres of town supply water were then added to this mixture and the whole was mixed for a further 3 minutes.

3. The resultant slurry was then transferred to an entirely conventional ram-operated moulding press, and pressure was then applied progressively to it over 2 minutes to a maximum of 20 MPa to force water from the slurry through the gauze of the press.

4. The resulting board (thickness 40 mm) was allowed to cure at ambient humidity for 21 days. Its properties were: Density 2260 kg/m3 Crushing strength 125.8 MPa Shear strength 36.1 MPa Cross breaking strength 17.3 MPa The board had a smooth flat matt surface with no surface defects. It retained its integrity when transferred suddenly from room temperature to a muffle furnance at 850"C.

Example 2 Following generally the procedure of Example 1, a board 12 mm thick was made from the following ingredients in the following proportions by weight: Ordinary Portland cement 78% Wollastonite 17% Ball clay (90% passing 5 um aperture sieve) 5% Water (g/kg dry weight) 500 The properties of the board were as follows: Density 2340 kg/m3 Crushing strength 117.7 MPa Cross breaking strength 15.8 MPa Shear strength > 15 MPa

Claims

1. Heat resistant non-asbestos compression-moulded board of density at least 1500 kg/m3 having a matrix of cured hydraulic cement containing fibrous wollastonite in an amount forming 10-60% by weight, any content of organic fibre in the board forming less than 0.5% by weight thereof; the board having a crushing strength of at least 50 MPa, a shear strength of at least 15 MPa and a cross breaking strength of at least 15 MPa.

2. Board according to claim 1, in which the weight proportions of the various ingredients are: Hydraulic cement 60-85% Wollastonite 15-30%

3. Board according to claim 1 or 2, which contains up to 0.5% of non-wollastonite fibrous material.

4. Board according to claim 3, in which said fibrous material is formed by vitreous fibres.

5. Board according to claim 4, in which said vitreous fibres are of mineral wool.

6. Board according to claim 4, in which the vitreous fibres are alkali-resistant glass fibres.

7. Board according to claim 3, in which said fibrous material is formed by rayon fibres.

8. Board according to any preceding claim, which contains ball clay in an amount up to 15% by weight of the board.

9. Board according to any preceding claim in which the hydraulic cement is Portland cement.

10. A method of making a board as set forth in any preceding claim, in which a slurry of water-settable hydraulic cement and fibrous wollastonite and containing at least 30% by weight of solids is dewatered under a pressure of at least 10 MPa and the dewatered product is cured.

11. Board obtained by the method of claim 10.

12. Board substantially as described with reference to Example 1.

13. Board substantially as described with reference to Example 2.