GB1590384A

GB1590384A - Fire resistant cavity walls

Info

Publication number: GB1590384A
Application number: GB4304876A
Authority: GB
Original assignee: Steetley Minerals Ltd
Current assignee: Steetley Minerals Ltd
Priority date: 1977-10-13
Filing date: 1977-10-13
Publication date: 1981-06-03

Description

(54) FIRE RESISTANT CAVITY WALLS (71) We, STEETLEY MINERALS LIMITED (formerly STEETLEY (Mfg) LIMITED), a British Company, of Gateford Hill, Worksop, Nottinghamshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to fire resistant structures and more particularly to a process for improving the fire resistance of cavity walls and the product obtained by such a process.

By the term "cavity walls" is meant any structure comprising a pair of walls arranged substantially in parallel and having a cavity between them, at least one of the walls being made at least in part of a combustible material.

Such walls may form the exterior cladding of a building or internal partitions thereof.

It has been found that the fire resistance of these cavity walls can be improved by the in situ filling of the cavity with a foamed magnesia cement. It is thereby possible to upgrade the fire resistance of an existing building with a minimum of disturbance and expense.

Accordingly, the present invention provides a process for improving the fire resistance of a cavity wall (as hereinbefore defined) which process comprises filling or partly filling the cavity with a liquid foamed magnesia cement and allowing the cement to set to a solid foam, wherein the liquid foamed magnesia cement comprises magnesium oxide having a specific surface area of from 10 to 100 m2/ g.

The present invention includes a cavity wall (as hereinbefore defined) the cavity in which is at least partially filled with a solid foamed magnesia cement by such a process.

The combustible wall or walls forming the cavity may be framed or frameless. If framed, the frames may be covered with or enclose filling materials. If frameless, the wall may be composed of a self-supporting material either in the form of a sheet or as individual bricks or blocks bonded together.

The frame, where one is present, may be wood, metal, or plastics.

The filling or self-supporting material may be cementitious, wood, plastics, glass, or brick.

Magnesia cements are well known, and those of particular use in the cavity walls of the present invention are based on magnesium oxysulphate, magnesium oxyphosphate, magnesium oxychloride and mixtures of two or more of these materials. Preferably the magnesium cement is based on magnesium oxychloride or a mixture of this with the oxysulphate, the oxyphosphate or even the oxysulphite. The presence of the oxyphosphate is advantageous in that it decreases the corrosion of any iron which may be present in the cavity such as tie bars.

The foamed magnesia cement used in the present invention may be made by a process which comprises forming a mixture containing the appropriate magnesium salt or mixture of salts (e.g. the chloride sulphate or phosphate), magnesium oxide, water, optionally a mineral acid such as phosphoric acid or hydrochloric acid to modify the rate of setting, and a foaming agent and entraining air, and/or other gas in the mixture (e.g. by mechanical agitation or blowing in air). The foamed mixture is preferably punped into the cavity through one or more suitably engineered holes in the wall and there the foamed mixture is allowed to set or cure. The magnesium salt and water may be present in such quantities as to make a saturated solution of the magnesium salt in the water.

The proportion of magnesium oxide to magnesium chloride in a magnesium oxychloride cement for use in the invention is preferably from 35% to 65% magnesium oxide to 65% to 35% magnesium chloride, the percentage being by weight based on the weight of the two magnesium compounds.

In order to obtain the appropriate setting time the magnesium oxide is preferably one which has been calcined at a temperature in the range 14000F to 18000F. The particle size of the magnesium oxide is such as to have a specific surface area of 10-100 m2lg but it preferably has a surface area of 25 to 50 m2/g.

The foaming agent may be an acid compatible detergent present in amounts varying from 0.1% to 5% by weight based on the weight of the mixture. Suitable detergents for use as foaming agents include non-ionic surfactants such as polyoxyethylene, ethoxylated alkyl phenols, ethoxylated aliphatic alcochols, carboxylic amides, polyoxyethylene fatty acid amides and anionic surfactants such as aromatic sulphonates. A preferred detergent is a nonylphenol/ethylene oxide condensate containing 9 ethylene oxide units per unit of phenol.

The foaming agent may be a chemical frothing agent, that is a substance which reacts with other compounds or upon heating to evolve gas. An example is limestone which can react with an acid to liberate carbon dioxide.

Sulphur dioxide may be bubbled through the mixture while it is being foamed and this is absorbed as magnesium sulphite which has a good degree of high temperature stability.

The foamed magnesia cement may contain solid materials such as fillers and/or fibrous materials. Examples of fillers are sand, expanded aggregates such as expanded perlite and expanded vermiculite, pulverised fuel ash, etc. Examples of fibrous materials are microfibrous materials such as sepiolite and macrofibrous materials such as mineral wool, glass fibre and asbestos. The amount of solid material may vary from 1% to 50% by weight of the cement.

The density of the foamed magnesia cement when set is desirably in the range 0.05 to 1.0 g/cm3 more desirably 0.2 to 1.0 g/cm3 .

The following Example is given to illustrate the present invention.

Example: A mixture was prepared as follows: 10 parts of magnesium oxide (surface area 3040 m2 /g) was mixed with 16 parts of magnesium chloride solution (density 1.27 g/cm3) and 0.1 parts of a surfactant (a nonylphenol/ethylene oxide condensate).

The mixture was foamed, using a mechanical mixer, such that about 2 volumes of air were included for every volume of unfoamed mixture.

The foamed mixture was poured into a cavity wall constructed from 3" x 2" timber and, faced with plasterboard but having a gap between the timber and plasterboard. The foamed mixture was pumped through a hole at the top of one wall of the cavity wall. The mixture was sufficiently fluid to flow into all apertures in the construction, and to fill the gap between the timber and plasterboard.

After completion of filling, the assembly was allowed to set and age.

One surface of the wall was then heated, such that after 30 minutes its temperature was in excess of 800"C, and after 100 minutes was in excess of 1000"C. At these temperatures, softwood has a controlled burning rate such that the 3 inch sections used in the construction would be expected to be totally combusted after approximately 2 hours. However, it was observed in this test, that the period from the onset of combustion to discontinuation of test, a period of over four hours, did not provide enough time for total destruction of the wood in the construction. Thus the casting of the foam against the wood surprisingly provided a means of reducing the combustion rate of the timber.

WHAT WE CLAIM IS: 1. A process for improving the fire resistance of a cavity wall (as hereinbefore defined) which process comprises filling or partly filling the cavity with a liquid foamed magnesia cement and allowing the cement to set to a solid foam, wherein the liquid foamed magnesia cement comrpises magnesium oxide having a specific surface area of from 10 to 100m /g.

2. A process as claimed in claim 1 wherein the magnesia cement is magnesium oxysulphate, magnesium oxychloride or a mixture of two or more of these materials.

3. A process as claimed in claim 2 wherein the magnesia cement is based on magnesium oxychloride optionally in admixture with magnesium oxysulphate, oxyphosphate or oxysulphite.

4. A process as claimed in any preceding claim wherein the magnesia cement contains from 1 to 50% by weight of fillers or fibrous materials or a mixture thereof.

5. A process as claimed in any preceding claim wherein the density of the set foamed cement is from 0.05 to 1.0 g/cm3.

6. A process as claimed in claim 5 wherein the density of the set foamed cement is from 0.2 to 1.0 g/cm3.

7. A process as claimed in any preceding claim wherein the liquid foamed magnesia cement is formed by a process comprising forming a mixture containing one or more magnesium salts containing desired anions, magnesium oxide, water, optionally a mineral acid, and a foaming agent and foaming the mixture.

8. A process as claimed in claim 7 wherein the mixture to be foamed contains from 35 to 65% of magnesium chloride and from 65 to 35% of magnesium oxide by weight based on the weight of these two magensium compounds.

9. A process as claimed in claim 7 or claim 8 wherein the magnesium oxide has been calcined at a temperature of from 14000F to 18000F.

10. A process as claimed in any one of claims 7 to 9 wherein the magnesium oxide has a specific surface area of from 25 to 50 m2/g.

11. A process as claimed in any one of claims 7 to 10 wherein the mixture to be foamed contains from 0.1 to 5% by weight of an acid compatible detergent.

12. A process as claimed in any one of claims 7 to 11 wherein the mixture is foamed by mechanical agitation.

13. A process as claimed in any one of claims 7 to 11 wherein the mixture is foamed

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. weight of the mixture. Suitable detergents for use as foaming agents include non-ionic surfactants such as polyoxyethylene, ethoxylated alkyl phenols, ethoxylated aliphatic alcochols, carboxylic amides, polyoxyethylene fatty acid amides and anionic surfactants such as aromatic sulphonates. A preferred detergent is a nonylphenol/ethylene oxide condensate containing 9 ethylene oxide units per unit of phenol. The foaming agent may be a chemical frothing agent, that is a substance which reacts with other compounds or upon heating to evolve gas. An example is limestone which can react with an acid to liberate carbon dioxide. Sulphur dioxide may be bubbled through the mixture while it is being foamed and this is absorbed as magnesium sulphite which has a good degree of high temperature stability. The foamed magnesia cement may contain solid materials such as fillers and/or fibrous materials. Examples of fillers are sand, expanded aggregates such as expanded perlite and expanded vermiculite, pulverised fuel ash, etc. Examples of fibrous materials are microfibrous materials such as sepiolite and macrofibrous materials such as mineral wool, glass fibre and asbestos. The amount of solid material may vary from 1% to 50% by weight of the cement. The density of the foamed magnesia cement when set is desirably in the range 0.05 to 1.0 g/cm3 more desirably 0.2 to 1.0 g/cm3 . The following Example is given to illustrate the present invention. Example: A mixture was prepared as follows: 10 parts of magnesium oxide (surface area 3040 m2 /g) was mixed with 16 parts of magnesium chloride solution (density 1.27 g/cm3) and 0.1 parts of a surfactant (a nonylphenol/ethylene oxide condensate). The mixture was foamed, using a mechanical mixer, such that about 2 volumes of air were included for every volume of unfoamed mixture. The foamed mixture was poured into a cavity wall constructed from 3" x 2" timber and, faced with plasterboard but having a gap between the timber and plasterboard. The foamed mixture was pumped through a hole at the top of one wall of the cavity wall. The mixture was sufficiently fluid to flow into all apertures in the construction, and to fill the gap between the timber and plasterboard. After completion of filling, the assembly was allowed to set and age. One surface of the wall was then heated, such that after 30 minutes its temperature was in excess of 800"C, and after 100 minutes was in excess of 1000"C. At these temperatures, softwood has a controlled burning rate such that the 3 inch sections used in the construction would be expected to be totally combusted after approximately 2 hours. However, it was observed in this test, that the period from the onset of combustion to discontinuation of test, a period of over four hours, did not provide enough time for total destruction of the wood in the construction. Thus the casting of the foam against the wood surprisingly provided a means of reducing the combustion rate of the timber. WHAT WE CLAIM IS:

1. A process for improving the fire resistance of a cavity wall (as hereinbefore defined) which process comprises filling or partly filling the cavity with a liquid foamed magnesia cement and allowing the cement to set to a solid foam, wherein the liquid foamed magnesia cement comrpises magnesium oxide having a specific surface area of from 10 to 100m /g.

by evolution of gas by reaction of a chemical frothing agent.

14. A process of improving the fire resistance of cavity walls (as hereinbefore defined) substantially as hereinbefore described in the Example.

15. A wall when produced by a process as claimed in any of claims 1 to 14.

16. A wall substantially as hereinbefore described in the Example.