GB2525683A

GB2525683A - Improved concrete mix

Info

Publication number: GB2525683A
Application number: GB1407855.4A
Authority: GB
Inventors: Allan Barnes
Original assignee: NORTHERN CHIMNEY LINING SYSTEM
Current assignee: NORTHERN CHIMNEY LINING SYSTEM
Priority date: 2014-05-02
Filing date: 2014-05-02
Publication date: 2015-11-04
Also published as: GB201407855D0

Abstract

A method of lining a chimney 10 is described, comprising lining the chimney with a cementitous composition. The composition comprises, by weight, 50 - 80% of base cement, 8 - 28% by weight of high alumina cement (HAC), 12 - 24% by weight of expanded perlite and up to about 0.08% of ceramic fibres. The ceramic fibres may be elongate micro fibers with a length from 19-40mm. A chimney lining composition with this formulation is also detailed. The composition gives a preliminary setting time of about an hour. The lining may be applied to the chimney 10 by pumping the composition between the walls of the chimney and an inflatable former 11. Thus the inflatable former 11 can be removed much sooner than is the case when alternative compositions are used.

Description

Improved Concrete Mix

Field of Invention

The invention relates to an improved concrete mix for use in the lining of chimneys.

Background to the Invention:

A known process of lining chimneys is to position an inflatable rubber former centrally in a chimney, and then pump liquid cement into the chimney to fill the space between the former and the walls of the chimney. Once the cement has hardened, the former can be deflated and removed, leaving a smooth cylindrical flue within the chimney. A suitable concrete mix for use in such a process is shown in GB2246772A. However, this mix can become damaged when exposed to high temperature conditions and high temperature fluctuations. The internal chimney environment experiences temperatures in excess of 11OOC, when the outside ambient temperature is relatively stable and between -1St and 30t. Such high temperatures and high temperature differences cause severe thermal stress on the liner. Known concrete mixes have inferior tensile strength and become easily damaged when exposed to fluctuating temperatures due to high degrees of heating and subsequent cooling. Therefore, a concrete mix that is more durable and robust is required.

It is an aim of the present invention to improve the heat resistance of concrete used in the lining of chimneys. An improved concrete mix will improve the durability and longevity of the liner when exposed to extreme conditions. It is a further aim to provide a concrete mix for use in lining chimneys that maintains integrity when exposed to various temperature gradients.

The concrete mix must be tolerant to cyclical variations in temperature and extremes of temperature that are experienced in a chimney.

Summary of the Invention

According to the present invention, there is provided a method of lining a chimney and a chimney lining composition as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims and the description which follows.

A method of lining a chimney is provided. The method comprises lining the chimney with a composition comprising, by weight, 50 -80% of base cement, 8 -28% of high alumina cement, 12 -24% of expanded perlite and 0.08% or lower of ceramic fibres (i.e. up to 0.08% of ceramic fibres, by weight). Furthermore, the ceramic fibre component may be between about 0.04% and about 0.08%.

Preferred ranges are 60-76% of base cement, 10-20% of high alumina cement, 15- 19% of expanded perlite and up to 0.08% of ceramic fibres. Furthermore, the ceramic fibre component may be between about 0.04% and about 0.08%.

The ceramic fibres may be micro fibres. The fibres may have a length of about 40mm or lower. Preferably, the fibres have a length between about 19mm and about 40mm. The fibres provide improved flexibility. The mix may benefit from increased tensile strength. If the concentration of fibres is too high, the mixture is weakened. Therefore, there is an optimum range of fibre concentration. The fibres are very lightweight and are elongate.

The base cement may comprise ordinary portland cement or sulphur resistant cement.

Preferably the compositions are applied by mixing the ingredients with water in a volume ratio of from 2 to 3 parts of composition to I part water. A preferred ratio is 2% parts composition to I part water.

The composition may be applied to the chimney by pumping the composition between the walls of the chimney and an inflatable former Preferably the three components of the composition are thoroughly mixed in bulk under controlled conditions, and quantities of the mixture are then transported to the chimney site for mixture with water Preferably the components are pm-mixed to provide a basic supply of up to 1016 kg (one ton) by weight of composition, or multiples thereof.

The expanded perlite provides good heat resistance because of its insulation properties.

However, the high alumina cement brings about two important additional advantages. Firstly, the alumina content of the cement brings about additional heat insulation properties, because of its refractory nature.

More importantly however, we have discovered that the addition of the small quantity of high alumina cement means that a preliminary selling takes place after about one hour which is sufficiently effective to enable the inflatable former to be removed. With present mixtures, it may not be possible to remove the former for up to 12 hours.

The invention includes a chimney lining composition comprising, by weight, 50-80% of base cement, 8 -28% of high alumina cement, 12-24% of expanded perlite and 0.08% or lower of ceramic fibres (i.e. up to 0.08% of ceramic fibres, by weight). Furthermore, the ceramic fibre component may be between about 0.04% and about 0.08%.

The ceramic fibres may be micro fibres. The fibres may have a length of about 40mm or lower. Preferably, the fibres have a length between about 19mm and about 40mm. The 2 0 fibres provide improved flexibility. The mix may benefit from increased tensile strength. If the concentration of fibres is too high, the mixture is weakened. Therefore, there is an optimum range of fibre concentration. The fibres are very lightweight and are elongate.

The invention also includes chimneys when lined using the method or composition of the invention.

Brief Descrirtion of the Drawings For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which Figure lisa diagrammatic elevational view of the chimney being lined according to the invention; and Figure 2 is a plan view of the chimney after it has been lined.

Detailed Description of the Invention

Figure 1 shows a chimney 10 which requires a lining. This may be because the brickwork or mortar has deteriorated, with the result that flue gases are escaping through the walls of the chimney.

The chimney is first cleaned and then an inflated rubber former 11 is positioned centrally in the chimney. A bottom seal is provided at 12.

A particulate chimney sealing composition is then mixed with water to provide a slurry 13 which is fed into the hopper 14 of a pump 15.

The slurry is provided by mixing the composition with water in a ratio by volume of 2% parts of mixture to 1 part of water.

The mixture is provided in a ready mixed manner, from bulk supply which is prepared away from the chimney site, for example under factory controlled conditions.

The mixture comprises 60 -76% by weight of ordinary portland cement or other sulphur resistant cement, 10 -20% by weight of high alumina cement and 15 -19% by weight of expanded perlite and about 0.04 to about 0.08% of ceramic fibres. Alternatively, the composition of ceramic fibres may be around 0.06% with a minimum of 0.04% and a maximum of 0.08%.

The expanded perlite has the following particle size distribution.

PARTICLE SIZE DISTRIBUTION! COARSER THAN % mesh 67 0.15mm mesh 38 0.3 mm mesh 8 0.6 mm mesh 1 0.84mm 16 mesh -1.2mm The ceramic fibres are very lightweight and elongate micro fibres and have a length of about 19mm to about 40mm. The fibres provide the mix with improved flexibility and increased tensile strength. However, if the concentration of fibres is too high! the mixture may become weakened. Therefore! there is an optimum range of fibre concentration.

The slurry is pumped by the pump 15 along a feed pipe 16 and into the space between the chimney 10 and the former 11. The slun'y gradually fills up this annular space, and once the chimney has been filled to the top! pumping is ceased, the composition is allowed to harden, and the former 11 is then removed.

If desired, the pumping can be carried out in various stages, for example three stages, each stage being allowed to harden before the next stage continues.

However, it has been found that the addition of the small quantity of high alumina cement brings about an initial set within about 1 hour, as compared to 12 hours with normal materials. It may therefore be possible to carry out the pumping in a single operation. As soon as the composition reaches the bottom of the chimney, it begins to set, and this provides support for the composition which is added above, so reducing outward pressure on the base of the chimney.

The invention obviously makes it possible to line chimneys more quickly than with normal methods.

As already mentioned, the quicker selling material places less stress on the structure of the chimney.

The composition according to the invention requires less water, so here again less weight is placed on the chimney structure during lining, and there is also a reduction in the possibility of pockets or gaps occurring within the flue lining.

Not only does the blend of high alumina cement with ordinary cement bring about a quick initial set, but it also brings about higher heat resistance because of the refractory nature of alumina.

During the selling of cement, a certain amount of the water becomes chemically bonded with the cement composition. Eventually all the water is removed, any remaining free water being evaporated when the flue reaches a temperature of 10000, and the chemically bonded water eventually being driven off at higher temperatures often for example 650°C.

Wth a composition according to the invention, more of the water is initially held within the composition by chemical bonding. Thus the amount of free water is reduced, and this reduces the possibility of damp patches occurring on the walls of the chimney.

The pre-mixing of the composition in bulk, under controlled conditions, has two major advantages.

Firstly, very thorough mixing is ensured, which reduces the risk that there will be local anomalies when water is added. Local anomalies can for example bring about quick local setting in the slurry, which may make it impossible to pump the sluny.

Secondly, the very thorough mixing brings about an extremely smooth slurry which has enhanced flowability. This means that small holes in the chimney are sealed almost immediately by material which sets quickly, and this reduces the chance of the composition seeping out of the chimney.

The composition can be pre-mixed to suit the conditions under which it will be used.

Although the chimney eventually reaches a high temperature, once the flue is put into use, basic setting occurs under ambient temperature conditions. During cold weather, the setting time for a given composition will increase. Therefore, the high alumina cement content is increased in inverse proportion to the ambient temperature.

It is not essential to use a single former and provide a single flue. Where a chimney is to be used to provide more than one flue, for example coming from different appliances, two or more fomiers can be used to provide two or more flues within a single chimney. Figure 2 shows an arrangement in which three flues 17, 18 and 19 have been provided within the chimney 10.

This is simply achieved by appropriately spacing three different formers. It will be seen that the flues can have different diameters.

The industrial application of the invention is readily appreciated from the description herein. In particular, the method and composition are used and made in industry, especially in the energy sector.

Although preferred embodiment(s) of the present invention have been shown and 2 0 described, it will be appreciated by those skilled in the art that changes may be made without departing from the scope of the invention as defined in the claims.

Claims

Claims 1. A method of lining a chimney comprising lining the chimney with a composition comprising, by weight, 50 -80% of base cement, 8 -28% of high alumina cement, 12 -24% of expanded perlite and up to 0.08% of ceramic fibres.
2. A method as claimed in Claim 1 in which the composition comprises, by weight, 60 -76% of base cement, 10 -20% of high alumina cement, 15 -19% of expanded penile and up to 0.08% of ceramic fibres.
3. A method as claimed in Claim 1 or Claim 2, in which the base cement comprises portland cement.
4. A method as claimed in Claim I or Claim 2, in which the cement comprises sulphur resistant cement.
5. A method as claimed in any one of the preceding claims, in which the ceramic fibres have a length of about 40mm or lower
6. A method as claimed in any one of the preceding claims, in which the ceramic fibres have a length of about 19mm to about 40mm.
7. A method as claimed in any one of the preceding claims, in which the composition is applied by mixing the ingredients with water in a volume ratio of from 2 to 3 parts of composition to 1 part water.
8. A method as claimed in Claim 7, in which the volume ratio is 2% parts composition to 1 part water.
9. A method claimed in any one of the preceding claims, in which the composition is applied to the chimney by pumping the composition between the walls of the chimney and aninflatable former.
10. A method as claimed in any one of the preceding claims, in which the components of the composition are thoroughly mixed in bulk under controlled conditions, and quantities of the mixture are then transported to the chimney site for mixture with water.
11. A method as claimed in Claim 10, in which the components are pre-mixed to provide a basic supply of up to 1016 kg (one ton) by weight of composition, or multiples thereof
12. A method of lining chimneys substantially as hereinbefore described, with reference to the accompanying drawings.
13. A chimney lining composition comprising, by weight, 50 -80% of base cement, 8 - 28% of high alumina cement, 12-24% of expanded perlite and up to 0.08% of ceramic fibres.
14. A chimney lining composition as claimed in Claim 11, comprising, by weight, 60 - 76% of base cement, 10-20% of high alumina cement, 15-19% of expanded perlite and up to 0.08% of ceramic fibres.
15. A chimney lining composition as claim in Claim 13 or Claim 14, in which the base cement comprises portland cement.
16. A chimney lining composition as claimed in Claim 13 or Claim 14, in which the base cement comprises sulphur resistant cement.
17. A chimney lining composition as claimed in any of Claims 13 to 16, in which the ceramic fibres have a length of about 40mm or lower.
18. A chimney lining composition as claimed in any of Claims 13 to 16, in which the ceramic fibres have a length of about 19mm to about 40mm.
19. A chimney lining composition substantially as hereinbefore described.
20. A chimney when lined by the method of any one of Claims Ito 12, and/or using the composition claimed in any one of Claims l3to 19.