GB2032570A - Method for the repair of damaged surfaces - Google Patents

Abstract

The method comprises forming an adherent layer of a plastics foam, especially a rigid polyurethane foam, on a damaged surface using shuttering. In particular, the flexible shuttering 15 covering an internally damaged sewer pipe 11 is moulded to accommodate tiles 19 for facing a rigid polyurethane foam layer produced when a cartridge 25 containing separated foam-forming ingredients is broken inside the shuttered cavity 17. Reinforcement 21 may be incorporated in the foam. <IMAGE>

Description

SPECIFICATION Method for the repair of damaged surfaces This invention relates to the repair of damaged surfaces and especially to the repair of damaged sewer pipes.

In its broadest aspect, the present invention provides a method for repairing a damaged surface which comprises arranging shuttering at a distance from the damaged surface, introducing a plastics foam-forming mixture into the space formed between the shuttering and damaged surface, and allowing the mixture to foam and cure.

The shuttering may be any device which supports the formation of a layer of plastics foam in contact with the damaged surface. It may be made of wood or metal, such as aluminium or steel, or of a plastics material, such as a glassreinforced polyester or a polyurethane elastomer.

The shuttering may be arranged and held at a distance from the damaged surface by any convenient means and need only be held in place for as long as it takes the foamed mixture to adhere to the surface and become self-supporting.

The shuttering may be designed to enable facing materials or reinforcements to be applied to the foam layer. For example, shuttering made from a flexible moulded polyurethane elastomer may be provided with retaining members on its internal face for holding ceramic tiles in contact with the foaming mixture.

The distance at which the shuttering is arranged from the damaged surface will be determined by the thickness of the layer of foam required and the nature of any facing materials and reinforcements used.

The plastics foam used in the invention may be any such foam described in the art but is preferably a rigid foam. As suitable plastics foams we would mention unsaturated polyester foams and isocyanate-based foams. These latter foams include polyurethane, polyurea and polyisocyanurate foams and mixtures of these foams. Mixtures of one or more of these foams with other resins are also contemplated in the present invention. An example of these last mentioned mixtures is a mixture of a urethane foam and an unsaturated polyester resin.

Foam-forming mixtures suitable for the production of isocyanate-based foams are weliknown and have been fully described in the prior art. Such mixtures contain an organic polyisocyanate, a blowing agent and optionally other conventional ingredients such as organic polyols, catalysts and surface active agents. To produce a conventional polyurethane foam an organic polyol is usually present in an amount substantially equivalent to the isocyanate.To produce a polyisocyanate foam, the isocyanate is present in an excess amount relative to the polyol and, in fact, the polyol may be completely omitted.

Isocyanurate formation is effected by including an isocyanate polymerisation catalyst. Polyurea foams are formed when a polyisocyanate reacts with water. Carbon dioxide is liberated and acts as a blowing agent. Water may be introduced into a polyurethane mixture to act as blowing agent either alone or together with another conventional blowing agent. The resulting foam will contain both urethane and urea linkages.

Any polyisocyanate described in the art may be used, but in applications where toxic vapours may be a nuisance, for instance, in sewer pipe repairs, it is preferred to use a polymeric diphenylmethane diisocyanate composition (polymeric MDI). These compositions are obtained by the phosgenation of mixtures of amines obtained by the reaction of formaldehyde with aniline in the presence of hydrochloric acid and consist of diphenylmethane 4,4'-diisocyanate in admixture with isomers thereof and with methylene-iinked polyphenyl polyisocyanates containing more than two isocyanate groups.

Polyols suitable for use in the invention are those polyols widely used in formulating rigid polyurethane foams. As examples we mention oxypropylated and oxyethylated hydroxyl and amino compounds such as tolylene diamine, diamino diphenylmethane, glycerol, triethanolamine, sorbitol, sucrose, pentaerythritol, ethylene diamine, diethylene triamine, trimethylolpropane, urea and diethylene glycol.

Other examples are polyesters made from adipic acid or phthalic acid and diethylene glycol, proplyene glycol or glycerol.

Any of the conventional blowing agents, including water, may be used and will normally be present in sufficient quantity to expand the foamforming mixture from 2 to 10 times, and preferably from 3 to 5 times, its original volume.

Other ingredients which may be added to the foam-forming mixture including fillers, for example silicates, borates, especially borax, vermiculite, petite and glass fibres: fire retardants, for example, tris-2-chloroethylphosphate and tris-2chloropropylphosphate: plasticisers, for example, butyl benzyl phthalate, "CELLOSOLVE" (RTM); chlorinated hydrocarbons such as "CEROCLOR" (RTM); surfactants; catalysts, for example, dibutyl tin dilaurate; and fungicides and biocides.

Desirably the foam-forming mixture will have a low viscosity and long cream time so that it will flow into the space between the damaged surface and shuttering and penetrate cracks and other damaged areas of the surface to be repaired.

In addition it will have short cure time to allow the shuttering to be quickly removed and good adhesion to the damaged surface as well as to any reinforcements and facing materials used. Ideally the cured foam will be tough and non-brittle to provided a robust repair.

Polyurethane and polyisocyanurate foams made by a frothing process may be used to advantage in the present invention. This type of process is one in which foaming is due, at least in part, to the vaporisation of a blowing agent, such as dichlorodifluoromethane, by reducing the pressure on the foam-forming mixture. Foams made in this way are fully described in, for example, British Patents Nos. 1 328953 and 1364071. Frothing processes have the advantage that they generate less pressure enabling cheaper, lighter and more flexible shuttering to be used.

Reinforcing materials may be introduced in the foam layer and will conveniently be in mat or roll form and permeable to the foam-forming mixture.

Usefully the mats can expand as the mixture foams so that the reinforcement fills uniformly the damaged areas and space between the shuttering and damaged surface. Suitable mats are continuous filament glass fibre mats and high loft swirl glass fibre mats of the kind used in air filters and for insulation. Incompressible mats may also be used if the foam-forming mixture can flow through them and preferably expand their structure.

Meshed materials, such as wire mesh and integral mesh thermoplastic nets like "NETLON" (RTM) may also be used.

The foam-forming mixture may be introduced into the space between the shuttering and damaged surface by injection using conventional polyurethane dispensing equipment. Alternatively the foam-forming mixture may be prepared within the shuttered space by techniques such as those described in OLS 2123271 and British Patent No.

1476978. The favoured technique is that described in the aforementioned British patent whereby a cartridge containing separated foamforming ingredients is broken at an appropriate moment and the contents mixed so that a foam is formed in situ.

In carrying out the method of the invention the damaged surface will preferably be prepared first by, for example, cleaning with water and brushing to remove loose material. If cartridges carrying the foam-forming ingredients are to be used holes of about 50 mm diameter will be drilled in the damaged surface to accommodate these. Any reinforcing material to be used will be fixed over the damaged surface and the shuttering then arranged at the desired distance from the damaged surface. Conveniently, the cartridges, if used, can be inserted through holes in the shuttering into the holes drilled in the damaged surface. The cartridges are then broken, the ingredients mixed and the holes in the shuttering plugged. Normally, the shuttering will be removed after the mixed ingredients have foamed and the foam so formed has cured.It may, however, be removed as soon as the foam has sufficiently adhered to the damaged surface and has become self-supporting.

The present invention is of particular value for repairing large diameter (6 to 12 ft) sewer pipes which may have cracked or eroded. Replacement of damaged sewer pipes is an expensive and time consuming operation and the present invention provides a relatively cheap and quick alternative.

Other applications for this invention include the repair of tunnels, mine shafts and ventilation shafts.

By way of example only, the invention is further described with reference to the accompanying drawings in which: Figure 1 is a cross section through a damaged sewer pipe under repair; and Figure 2 is a detail from Figure 1.

In the drawings, a 12 ft diameter sewer pipe 11 has a damaged inner surface 13. Flexible shuttering 15, supported by means not shown, extends along part of the length of the pipe 11 and is arranged at a distance x from the surface 13 and covers half the inner circumference of the pipe.

The shuttering 15 and surface 11 define therebetween an enclosed space 17. The shuttering is made from a polyurethane cast elastomer and is moulded on its convex surface 18 to accommodate facing tiles 19. A reticulated reinforcing material 21 is placed between the shuttering and damaged surface (see Figure 2).

Drilled holes 23, only one of which is shown, house cartridges 25 which contain separated polyurethane foam-forming ingredients (a polyisocyanate and a polyol blend). A hole 27, in register with the drilled hole 23, passes through the shuttering and between adjacent tiles.

In operation, the cartridge 25 is broken with a rod (not shown) which is passed through the hole 27 and the contents are quickly mixed using the end of the rod. The rod is then withdrawn and the hole 27 plugged. The other cartridges are broken in similar fashion and the associated holes in the shuttering plugged. The mixed ingredients foam in situ and fill the space between the shuttering and inner sewer pipe surface and the damaged areas.

When the foam has cured the shuttering is removed.

The rest of the inner surface of the sewer pipe is repaired in a similar manner. To complete the repair, the new tiled facing layer is grouted.

A suitable foam-forming mixture for use in the process of the invention is prepared by mixing together 180 parts by weight of polymeric MDI and a polyol blend obtained by mixing together the following ingredients: parts by weight a blend of oxypropylated toylenediamine of hydroxyl value 480 mg kOH/g and oxypropylated triethanolamine of hydroxyl value 525 mg kOH/g 3.5; oxypropylated glycerol of hydroxyl value 540 mg kOH/g 21.5; trichloroproyl phosphate 18.0; oxyethylated/oxypropylated ethylene 4.0; glycol of hydroxyl value 53 "Silicone L 5340" (obtainable from Union Carbide). 1.0; a catalyst which is a blend of ethylene glycol (20 pbw), potassium acetate (20 pbw) and water (1.5 pbw) 1.2; acetylacetone 0.1; trichlorofluoromethane 25.

The foam-forming mixture may conveniently introduced into a space formed between shuttering and a damaged pipe surface by injection. It has the following reactivity characteristics: cream time 70 seconds; string (gel) time 185 seconds; tack-free time 203 seconds; end of rise time 225 seconds; and density of foam 44.5 k#jm3 under free-rise conditions.

Claims (5)

1. A method for repairing a damaged surface which comprises arranging shuttering at a distance from the damaged surface, introducing a plastics foam-forming mixture into the space formed between the shuttering and damaged surface, and allowing the mixture to foam and cure.

2. A method as claimed in claim 1 in which the shuttering is made from a flexible moulded polyurethane elastomer and is provided with retaining members for holding ceramic tiles in contact with the foam-forming mixture.

3. A method as claimed in claim 1 or claim 2 in which the foam-forming mixture forms a rigid foam.

4. A method as claimed in claim 3 in which the rigid foam is a mixture of a urethane foam and an unsaturated polyester resin.

5. A method as claimed in claim 1 substantially as herein described with reference to the accompanying drawings.