WO1992000927A1

WO1992000927A1 - Fire-resistant fibre cement products

Info

Publication number: WO1992000927A1
Application number: PCT/AU1991/000271
Authority: WO
Inventors: Anthony Michael Cooke; Brian Patrick Sloane; William Barrington Elliott Hodgson
Original assignee: James Hardie & Coy Pty. Limited
Priority date: 1990-07-10
Filing date: 1991-06-26
Publication date: 1992-01-23

Abstract

An autoclaved fibre cement product comprising, cellulose fibres, cementitious material, and 1 % to about 40 % of magnesite on a dry weight basis. In preferred embodiments the percentage of cellulose fibres is in the range from 7 % to 8.5 % and the magnesite in a preferred range of between 25 % to 40 %. Silica and portland cement may also be included.

Description

Fire-resistant fibre cement products

TECHNICAL FIELD

The present invention relates to fibre-reinforced cementitious products and in particular to fire resistant fibre cement products.

BACKGROUND ART

The invention has been developed primarily for production of fire-resistant autoclaved-fibre cement boards for both internal and external applications and will be described hereinafter with reference to this use. However, it will be appreciated that the invention is not limited to this particular field.

In order to achieve a given fire rating, it is necessary that the fibre cement boards comply with the relevant Industrial Standards applicable to the country in which they are to be used. Whilst the standards vary from country to country, the criteria by which the materials are evaluated are much the same. The main criteria can be summarised as:

(a) Combustibility (temperature rise/flaming criterion)

(b) Thermal Shrinkage

(c) Heat and Smoke Evolved The existing fibre/cement boards available in Australia do not, for example, meet the requirements of the local combustibility Standard (AS1530 part 1) on the basis that they fail the flaming criterion. By contrast, the same boards fail the temperature rise criterion of the equivalent Japanese Standard JIS1321.

In addition to meeting the requirements of the relevant, fire related Industrial Standards, the boards also need to have certain desired mechanical and insulating properties.

It is an object of the present invention to provide an improved fibre cement product which will avoid or at least ameliorate the disadvantages of the prior art and thereby provide a product of improved combustibility rating.

The invention proceeds from the discovery that the inclusion of Magnesite (Magnesium Carbonate) in a fibre/cement board, improves the combustibility rating characteristics of the material thereby rendering it more fire resistant, whilst at least retaining, and in some cases improving, the required mechanical and" structural characteristics of the product. DISCLOSURE OF INVENTION

According to the invention there is provided an autoclaved fibre cement product comprising, cellulose fibres, cementitious material, and 1% to about 40% of Magnesite.

In a preferred embodiment this product also includes silica.

Preferably the proportion of cellulose fibres is in the range from 7% to 8.5%.

Preferably also the proportion of magnesite is between 25% to 40%.

It has been found that fibre cement mixtures according to this invention, that is incorporating 1% to 40% magnesite, display improved fire resistance qualities.

All percentage inclusion levels herein described refer to the percentage on a dry weight basis prior to processing.

More particularly tests have shown that pressed and unpressed autoclaved fibre cement mixtures made according to the invention with 8.5% cellulose demonstrate the following advantages:

(I) The invented product has an improved combustibility rating when tested compared to normal mixes with less than 5% cellulose which performed better in these tests than normal mixes containing 7 to 8.5% cellulose.

(II) The product demonstrates reduced thermal shrinkage when tested and compared with normal mixes containing 7 or 8% cellulose.

(III) The product, when tested, is found to have an equal modulus of rupture, an equal modulus of elasticity - A - and an equal tensile strength to normal mixes containing 7 or 8% cellulose.

(IV) The invented product also demonstrates an equal tensile strain to failure to normal mixes containing 7 or 8% cellulose.

(V) The invented product has a 100% greater flexural strain to failure than normal mixes containing 7 or 8% cellulose.

(VI) The invented product, when tested, demonstrates only 75% precarbonation moisture movement of that of normal mixes containing 7 or 8% cellulose.

(VII) The invented product has a cracking resistance index up to 500% above normal mixes containing 7 or 8% cellulose.

(VIII) The invented product has improved fire insulation characteristics compared to normal mixes containing 7 or 8% cellulose.

(IX) The invented product demonstrates an improved general fire performance which may be expected to continue improving after ageing and natural carbonation.

The following examples served to illustrate, without limiting the invention.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a graph showing the variation in temperature with time during combustibility tests for specimens containing 8.5% cellulose and various percentages of magnesite.

Figure 2 is a graph showing the variation of maximum temperature and time to maximum temperature with percentage substitution of magnesite.

Figure 3 is a graph showing the actual and predicted variation of percentage shrinkage with percentage magnesite content for specimens having 8.5% and 5% cellulose content.

BEST MODE FOR CARRYING OUT THE INVENTION COMBUSTIBILITY INVESTIGATIONS

Magnesite was incorporated in various proportions into hand made specimens containing 8.5% cellulose and tested in accordance with JIS1321. The resulting time-temperature curves are shown in Figure 1.

The addition of magnesite was found not only to reduce the peak exotherm temperature but also to increase the time at which the exotherm occurs. This is exemplified by the following table and graph shown in Figure 2.

From the results above it can be seen that the substitution of silica by between 30 and 40% of magnesite is necessary to pass the JIS test for combustibility when used in a formulation containing 8 . 5% cellulose .

The mechanism by which the magnesite reduces the peak temperature is apparent in the time-temperature curves of the high percentage magnesite samples shown in Figure 1, where there is a pronounced dip in the curve around 700°C. This is due to the decomposition of magnesite which commences around 450°C. The dip in the time-temperature curve occurs at a higher apparent temperature due to the thermal lag arising from the location of the thermocouple. THERMAL SHRINKAGE

Investigation on the laboratory bench scale of the thermal shrinkage of mixes containing varying proportions of cellulose and Magnesite gave the results listed in the following table.

Analysis of the results indicated that the following relationship appears to apply the thermal shrinkage of Magnesite containing materials. Shr % = 4 + 0.39*%Cel - 0.09*%Mag The predicted and actual results are shown in Figure 3. MECHANICAL PROPERTIES

In light of the above discoveries an investigation was undertaken using a pilot scale Hatschek Machine and the following mixes were evaluated. F

* Selected from the group comprising mineral oxides, hydroxides and clays.

Each mix was evaluated for tensile and flexural mechanical properties, moisture movement and durability before and after carbonation. Tests were also carried out for combustibility and thermal shrinkage at 1000° before and after carbonation. Pilot fire tests were carried out using the material in single lamination of 5 mm thickness and double and treble laminations, at 10 and 15 mm thicknesses respectively.

Results of these tests were evaluated against the known average properties of standard fibre cement sheet without the addition of Magnesite. The following are typical results for uncarbonated sheets compared to standard formulation with 8 % Cellulose in the equilibrium condition. Property

Modulus of Rupture

Modulus of Elasticity

Strain to Failure

Interlaminar Bond

Tensile Strength

Tensile Strain to Failure

Moisture Movement Precarbonation

Cracking Resistance Index up to +500% up to +200%

In all properties except interlaminar bond the properties of the Magnesite substituted sheets containing either 7 or 8% Cellulose exceeded those of the unsubstituted sheets contain 8% cellulose. In general plain sheets containing only 7% cellulose have poorer mechanical properties than sheets containing 8% cellulose therefore the substitution of Silica by Magnesite represents a significant advantage.

Of particular significance is the increase in the Cracking Resistance Index. This is a measure of the propensity for the sheet to crack when subject to shrinkage while restrained. This property was improved by a factor of up to 6 over the plain board. THERMAL SHRINKAGE

The preliminary investigation predicted that the shrinkage of unpressed and uncarbonated Magnesite substituted sheets should lie between 3.5 and 4.3% depending on the mix. The following results were obtained.

Additionally it was found that the pressing the sheets reduced the shrinkage by an average of 0.4% while carbonating the sheets increased it marginally by about 0.06%. Pressing and carbonating the sheet reduced the shrinkage by about 0.2%. This shows that enhanced resistance against warping in a fire should be expected with compressed sheet compared to the unpressed sheets. Additionally there should not be any diminishment in performance with exposure to natural weathering. PILOT FIRE TESTS

The pilot fire tests showed some inconsistencies. The following results were obtained for insulation value of a single 5 mm layer of Magnesite substituted material.

Plain mix* 3.5

* Mix containing 7% Cellulose. It appears that the too great a substitution of Silica by Magnesite is not beneficial and that the best results may be obtained with less than the optimum amounts for shrinkage. It is speculated that the insulation value may be reduced because the evolution of CO, from the Magnesite during the fire test may transfer heat through the sheet by mass diffusion. This effect is compensated to some extent by the heat required to cause the decomposition of the Magnesite thus there will be a changeover percentage where the apparent conductivity to heat increases with increase in Magnesite content.

Therefore, from the results of the tests conducted to date, it appears that in order to improve the combustibility rating of the product whilst simultaneously achieving acceptable insulation values and general mechanical and structural characteristics, a product incorporating from around 25% to about 40% Magnesite is preferred.

Although the invention has been described with reference to only selected examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms including products not including silica and products containing lesser amounts of cellulose.

Claims

1. An autoclaved fibre cement product comprising, cellulose fibres, cementitious material, and 1% to about 40% of magnesite on a dry weight basis.

2. An autoclaved fibre cement product according to claim 1 wherein the proportion of cellulose fibres is in the range from 7% to 8.5% on a dry weight basis.

3. An autoclaved fibre cement product according to any one of the preceding claims wherein the proportion of magnesite is between 25% to 40% on a dry weight basis.

4. An autoclaved fibre cement product according to any one of the preceding claims including about 35% portland cement on a dry weight basis.

5. An autoclaved fibre cement product according to any one of the preceding claims including silica.

6. An autoclaved fibre cement product according to claim 5 wherein the proportion of silica is in the range of 12% to 25% on a dry weight basis.

7. An autoclaved fibre cement product according to any one of the preceding claims including about 4% filler material wherein the filler material is selected from the group comprising mineral oxides, hydroxides and clays.

8. An autoclaved fibre cement product substantially as herein described with reference to the examples.