CA1231276A - Method for obtaining a friction bond between concrete and coated object surfaces - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention relates to a method for obtaining a frictional bond between concrete and an object coated with a thermosetting plastic using an epoxy cement mortar mixture. The mixture contains an epoxy resin diammonium salt emulsion compri-sing a liquid epoxy resin, a latent curing agent and an emulsi-fier. A diamine of formula I or II:

H2N - CH2 - R - NH2 (I) H2N - R - CH2 - R - NH2 (II) wherein R is a substituted alkylene or a cycloalkylene residue with 6 to 9 C atoms or an aralkylene residue with 7 to 9 C atoms, neutralized with an acid consisting of or containing oxalic acid used as the latent curing agent, and a C8- to C14- alcohol or an adduct thereof with up to 10 ethylene-oxide groups is used as the emulsifier. The method is particularly useful in applying con-crete casings to powder-painted oil or gas transportation pipelines for providing additional weight or additional protection.

Description

This is a divisional application of Serial Number 430,361 filed June 14, 1983.
The present invention relates to a method for obtaining a frictional bond between conerete and a surface of an objeet which is coated with a thermosetting plastic using a particular epoxy resin cement mortar mixture. The parent application relates to an epoxy resin emulsion which can be used as an ingredient of the epoxy resin cement mortar mixture; to a process for its pro-duction; to an epoxy resin mortar mixture containing such an epoxy resin emulsion; to an epoxy resin cement mortar mixture containing such an epoxy resin emulsion and useful generally in construction field; and to a method for improving the water-retaining ability of fresh concrete by coating the surface of fresh concrete with such an epoxy resin emulsion.
In recent times, gaseous and liquid bulk goods, such as gas and oil, are being transported to an ever increasing extent, through pipeline systems, at times over considerable distances.
The fact that pipelines are laid on the sea bed and in mountain-ous country, under widely varying climatic conditions, indicates that considerable demands are placed upon the protective coating applied to the pipe for resistance to weathering and corrosion.
If unprotected metal pipes were used, they may be dam-aged during laying and, as a result of corrosion, this damage results in the pipe rusting after a short time. In recent years, therefore, paints, especiallypowder~paints, have been developed which ensure outstanding surface protection (cf., for example, German Offenlegungsschrift No. 25 07 786). In many cases it is desirable, or even necessary, to apply concrete casing -to powder-painted pipes, for example when a pipe requires additional weight for laying underwater or needs additional protec-tion. Finally, it may be desirable to secure the pipe firmly to concrete to ensure satisfactory laying, however, there is poor adhesion of concrete to the powder-painted surface of the pipe.
Where powder-coated structural steels are used, a frictional bond between the concrete and the reinforcing steels is also needed, but in many cases such a bond cannot be obtained satisfactorily due to the special shaping of the steel parts.
Methods are already known for ensuring adhesion between concrete and synthetic-resin surfaces and these may be applicable, in principle, to the bond between concrete and powder-coated objects. For example, Japanese Published Unexamined Patent Appli-cation No.53-041 020 describes the use oE silane-base primers for improving the adhesion between concrete and a urethane-resin coating. However, this method has the disadvantage that the improvement in adhesion requires an additional operation.
It is possible to produce a bond between metal surfaces and concrete with vinyl-acetate resins containing cement-powder, but although this provides adhesion, corrosion protection is not assured.
It has now been found that a good direct bond is ob-tained between concrete and surface coated with a theromsetting plastic by using a particular epoxy resin cement mortar mixture.
Thus, in accordance with the present invention, there is provided a method for obtaining a frictional bond between

2~

concrete and a surface of an object which is coated with a thermosetting plastic, which method comprises:
applying to the surface an epoxy resin cement mortar mixture containing A. 10 to 30% by weigh-t of an epoxy resin diammonium salt emulsion comprising a liquid epoxy resin, a latent curing agent, an emulsifier and water, wherein:
(a) the emulsifier is a primary aliphatic alcohol of 8 to 14 carbon atoms or its adduct with up to 10 ethylene-oxide groups; and (b) the latent curing agent is a reaction pro-duct obtained by complete neutralization, with oxalic acid or an acid mixture containing at least 40~ by weight of oxalic acid, of a diamine or the formula I or II:
H2N - CH2 - R NH2 (I) H2N - R - CH2 - R - NH2 (II) wherein R is selected from the group consisting of a substituted alkylene, a cycloalkylene residue with 6 to 9 carbon atoms and an aralkylene residue with 7 to 9 carbon atoms, and Bo 70 to 80~ by weight of cement mortar.
Diamines which are compounds of the latent curing agent are of formula I or II:
H2N CH2 R NH2 (I) H2N - R - CH2 - R - NH2 (II) wherein R is a substituted alkylene or a cycloalkylene residue with 6 to 9 carbon atoms or an aralkylene residue with 7 to 9 ~Z~ 7~i carbon atoms. Particularly suitable are tolylene residues and alkylene and cyclohexylene residues substituted by one to three methyl groups. It is preferable to use 2,2,4-trimethylhexa-methylene-diamine (TMD), xylyl-diamines, or diamines containing one or two cyclohexane rings, for example 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophorone-diamine, IPD) or 4,4'-diamino-3,3'-dimethyldicyclohexylmethane.
For neutralizing the diamine, an acid which may be oxalic acid alone or a mixture of oxalic acid with one or more other acids is used. Up to 25% by weight of oxalic acids may be replaced by acetic acid. Oxalic acid may also be replaced by an aliphatic dicarboxylic acid with 3 to 6 carbon atoms or by one of the isomers of phthalic acid, but the acid mixture should contain at least 40% by weight of oxalic acid where an aliphatic dicarboxylic acid or one of the phthalic acid isomers is mixed with oxalic acid. Aliphatic dicarboxylic acids, for example malonic acid or adipic acid, unsaturated aliphatic di-carboxylic acids, for example fumaric acid, or aliphatic dicar-boxylic acids containing one or more hydroxyl groups, for example tartaric acid, can be used.
Primary aliphatic alcohols with 8 to 14 carbon atoms, and mixtures thereof, are used as the emulsifier. Also suitable are adducts of these alcohols with up to 10 ethylene-oxide groups. Lauryl alcohol is preferred. If necessary, the stability of the emulsion can be improved by the addition of lauric acid.
Additionof from 10 to 25% of the emulsifier, in relation to the amount of epoxy resin used, has been found -to be satisfactory.

.L~3~6 Liquid epoxy resins suitable Eor cold-curing are mainly reaction products of epichlorhydrin or glycidol and a 2,2-bis(4-hydroxyphenyl) alkane. The precise chemical structure of commercially obtainable epoxy resins, for example EUREPOX
by Schering, serlin or RUTAPOX VE 2913 by Bakelite GmbH, Duisburg, is unknown.
The first step of the production of the emulsions is the preparation of an aqueous solution of the diamine. The amount of diamine is governed by data from the epoxy resin manu-facturer, for example the epoxy value of the epoxy resin usedor the ratio of the mixture of the resin and the curing agent.
The most satisfactory amount of water for an emulsion depends mainly upon the type of diamine. In the case of diamines with a relatively small number of carbon atoms, for example 7, less water is needed than for diamines with a larger number of carbon atoms, for example 12. The optimal amount may be easily deter-mined empirically in comparative tests by varying the amount of water between 30 and 130% of the amount of epoxy resin used.
Enough acid is then added to -the aqueous solution of diamine for complete neutralization. If the reaction heat is considerable, it is desirable to cool the reaction mixture. The emulsifier is then stirred into the solution which is at room temperature. The epoxy resin is then slowly added to the mix-ture, which is again at room temperature, with rapid stirring.
Stirring is continued for 0.5 to 1.0 hours after all of the epoxy resin has been added. In this way, emulsions are obtained which are stable at room temperature for months. If phase separation ~P3~7~

occurs, the mixtures may be rapidly homogenized again by renewed stirring.
The epoxy resin cement mortars produced in accordance with the present invention contain from 10 to 30% by weight, in relation to the cement mortar, of the epoxy resin diammonium salt emulsion described above.
In this way, all pain-ted objects can be coated with concrete; for example, it is possible to use objects which have been treated with a liquid epoxy resin. It has been found de-sirable, however, to start with powder-painted objects. Powder-paints based upon epoxy resins cured with amines are particularly suitable for use-under conditions of permanent humidity (for example, large pipes laid in the sea, reinforcing steels for bridges or the like).
Alternatively, it is possible to treat the painted surface intially with the aforesaid epoxy resin/curing agent emulsion and, after this has dried, to apply a conventional cement mortar mixture.
The external shape and even the size of the objects are not critical for the method; they may include, for example, rod, wire strip, sheet and pipes. The material from which the objects are made is also of secondary importance, as long as the paint or powder-paint adheres firmly thereto. It is possible to use wood, synthetic material, ceramic, glass and metal, for example. The present method has special significance in the bonding of powder-painted pipes and powder-painted reinforcing steels to concrete.

~;23~

It is known to coat objects with powdered coatings (cf., for example, Ullmanns Encyklopadie der technischen Chemie, 4th Edition, Vol.15, pages 347 et seq., 1977). The polymers in this reference which are applied to the metal surface in the form of powders, and form a protective coating after melting, may be a non-cross-linked or self-cross-linking single-component system.
Because of their satisfactory mechanical properties (adhesion to a metal base, resistance to abrasion, impact strength) and thier satisfactory protection against corrosion (especially in the case of salt-stressing), bonding mixtures of the present invention based upon liquid epoxy resins, for example bisphenol A, are suitable for such purposes - e.g. bridge-s-tructures subject to salt-dew stress, off-shore drilling platforms, large submarine pipes foroil and gas-transportation encased in concrete for the purpose of adding weight. The exact chemical structure of com-mercially available products such as EPIKOTE 1004 and EPIKOTE
828 (manufactured by Deutsche Shell AG., Hamburg) is not known.
As cross-linking components for epoxy resins, acid-reacting multifunctional resins, e.g. polyesters containing car-boxyl groups, modified acid-anhydrides, or basic hardeners, for example dicyandiamides, imidazolines or imidazoles may be used.
However, other powder-paint systems, for example those based upon OH-containing polyesters and aromatic or cycloaliphatic isocyanates, and those based upon acrylates containing glycidyl groups and polyesters containing carboxyl groups, are also used for coating.

~23~7~ , Flow-control resins and pigments and, if necessary, accelerators and fillers, are also added in known fashion to the aforesaid bonding~agent combinations.
For the purpose of coating painted objects, use may be made of conventional cement-mortar mixtures, for example a mixture of the following composition:

100 parts by weight of Portland cement PZ 35 F
60 parts by weight of water 60 parts by weight of electro-filler ash (EFA) 170 parts by weight of 0/1 mm sand 85 parts by weight of l/3 mm sand 170 parts hy weight of 2/3 mm sand.
An advantage of the present method is that a frictional connection can be accomplished between concrete and powder-painted objects, with no additional operation, for the purpose of applying an adhesive and, at the same time, good corrosion-protection is achieved. The present method may be used more particularly in the laying of pipes and has other applications in the construction sector.
The invention is further illustrated in the following examples.
Example 1.
Upon each of two plates 1.5 mm in thickness, with a surface measuring 150 x 95 mm and coated with a powder-paint based upon the epoxy resin EPIKOTE 1004 (by Deutsche Shell AG, Hamburg) and 2-phenylimidazoline, was arranged a pipe-section 20 mm in height and 70 mm in diameter in such a manner as to produce a cylindrical cavity. Cement-mortar mixtures of the following composition were poured into these cavities:

~3~

100 parts by welght of Portland Cement PZ 35 328 parts by weight of quartz sand 0-2 mm 72 parts by weight of quartz flour W4 20 parts by weight of emulsion A and B
50 parts by weight of water.
The emulsion had the following compositions:
Emulsion A.
100 g of a bishphenol A-based epoxy resin (epoxy value 0.56) 23.5 g of IPD
8.5 g of oxalic acid

3.8 g of acetic acid 6.2 g of phthalic acid 14.5 g of lauric acid 5.0 g of lauryl alcohol 87.5 g of water 247 g Emulsion B.
100 g of a bisphenol A-based epoxy resin (epoxy value 0.56) 23.5 g of IPD
20.0 g of oxalic acid 6.0 g of 2-ethylhexanol 60.0 g of water 209.5 g A hook (having a leg 80 mm in length) was then placed upon the centre of each cement mortar surface and was pressed into the mixture as far as the plate. After a curing period of 24 hours, the sections of pipe were removed. Weights were suspended from the hooks, the load being increased by 1 Newton (N) increments until the concrete element came loose from the plate.
Two similarly made test pieces were first water-cured for 7 days and then air~cured for 7 days at 23C, and were then loaded. The adhesion-values are given in Table 1.

Comparison Example A.
For comparison purposes, a test piece was produced without any emulsion, but with the corresponding amount of water instead. Apart from this, the procedure was as in Example 1.
Table 1. Adhesion-values (loading in Newton until release) in the case of a powder-coating based upon an epoxy resin EPIKOTE
1004/2-phenylimidazoline:

Hardening TimeComparison Emulsion A Emulsion B
At 23 in Days Example A
.
1 29.4 98.1 98.1 14 22.6 105.0 144.2 Example 2 As in Example 1, a plate was coated with powder-paint based upon EPIKOTE 1004/polyester resin URALAC P 2228 (by Scado B.V., Swolle, Holland). Adhesion-values of a cement mor-tar mixture, containing emulsion B from Example 1, appear in Table 2 below.
Comparison Example B.
For comparison purposes, a test piece was produced withou-t any emulsion, but with the corresponding amount of water instead. Apart from this, the procedure was as in Example 2.
Table 2. Adhesion values (loading in Newton until release) in the case of powder-coating based upon Epoxy resin EPIKOTE 1004/
polyester resin URALAC 2228.
Example 2. Comparison Example B.
63.8 19.6 ~L~3~

Examples 3 to 5, Comparison Examples C to E.
.
Several painted plates were produced and were treated, as in Example 1, with cement mortar mixtures. Whereas in Examples 3 and 4, and comparison examples C and D, use was made of powder-paints, a cold-curing epoxy resin system was used in Example 5 and in comparison example E. The paint composition and adhesion-values appear in Table 3.
Table 3. Adhesion-values (loading in Newton until release) for different paint systems after 24 hours hardening at 23C.

Example Paint Composition Cement-Mortar Mixture with Water Emulsion A Emulsion B

3 Acrylic Resin VP 34.3 67.7 3949a) C " 19.6

4 Cross-Linking Agent 34.3 98.1 BF 1540 )/Polyester P 3356b) D Cross-Linking Agent 26.0 BF 1540 )/Polyester P 3356b) EPIKOTE 828 )/
Isophorondiamineb) 53.0 73.6 E " 34.3 .. ... _ . . ... . .. . . _ . .
a) manufactured by: Degussa AG, Frankfurt b) manufactured by: Chemische Werke His AG, Marl c) manufactured by: Deutsche Shell AG, Hamburg 3~ .h Example 6.
Epoxy resin emulsion B from Example 1 was painted onto a plate coated with a powder-paint based upon epoxy resin EPIKOTE 1004/2-phenylimidazoline. after a drying period of 24 hours, the test piece was coated with the cement mortar mix-ture from comparison example A, and the adhesion was determined by the measuring process described in Example 1 to give a value of 95.0 N.
Example 7.
For the purpose of testing the adhesion between struct-ural steel and cement-concrete, a smooth-walled steel element 18 mm in diameter and 80 mm in length, as normally used in concrete structures, was coated with a powder-paint based upon EPIKOTE
1004/2-phenylimidazoline and was pressed so far into the middle of a block (base area 100 x 100 mm, height 64 mm) made of cement concrete with emulsion B (see Example 1), as to project by 8 mm from both sides. After a hardening time of seven days, the steel element was forced out of the block. The force required for the purpose was 29,100 Newtons.
Comparison Example F.
I'he procedure was as in Example 7, but a concrete mixture according to Comparison Example A was used. In this case the force required to expel the steel element was 5,900 Newtons.
For the purpose of reference, a) production of emulsions is illustrated as follows:
(Amounts of oxalic acid always are of its dihydrate.) Reference Example l.
105 parts by weight of water and 28.2 parts by weight of isophorone-diamine (IPD) were placed in a flat-bottomed flask having a magnetic stirrer. 10.2 partsby weight of oxalic acid, 4.5 parts by weight of acetic acid, and 7.5 parts by weight of phthalic acid were added to this solution. After the reaction mixture had cooled to room temperature, 6.0 parts by weight of lauryl alcohol and 17.4 parts by weight of lauric acid, in por-tions, were stlrred into the mixture. Thereafter, 120 parts by weight of epoxy resin RUTAPO VE 2913 were slowly added to the mixture with rapid stirring (at about 1 000 r.p.m.). Stirring was continued, at the same r.p.m., for another hour. This produced a low-viscosity emulsion which showed no change after two months.
Reference Example 2.
A stable, low viscosity emulsion was produced, as des-cribed in Reference Example 1, from 90 parts by weight of water, 28.2 parts by weight of IPD, 19.8 parts by weight of oxalic acid, 3 parts by weight of tartaric acid, 12 parts by weight of lauryl alcohol, and 120 parts by weight of epoxy resin RUTAPO VE 2913.
The slight segregation arising after three months of storage was eliminated by stirring the mixture.
Reference Example 3.
A stable, low viscosity emulsion was produced, as des-cribed in Reference Example 1, from 15 parts by weight of water, 4.4 parts by weight of 2,2,4-trimethylhexamethylene-diamine (TMD), 3.5 parts by weight of oxalic acid, 2.0 parts by weight of lauryl ~z~

alcohol, and 20 parts by weight of epoxy resin RUTAPOX VE 2913.
Refexence Example 4.
A stable, medium viscosity emulsion was produced, as described in Reference Example 1, from 20 par-ts by weight of wa-ter, 6.6 parts by weight of 4,4'-diamino-3,3'-dimethyldicyclo-hexyl-methane, 3.8 parts by weight of oxalic acid, 2.0 parts by weight of lauryl alcohol, and 20 parts by weigh-t of epoxy resin RUTAPOX VE 2913.
eference Example 5.
A stable emulsion was produced, as described in Reference Example 1, from 10 parts by weight of water, 3.8 parts by weigh-t of xylylene-diamine (a mixture of isomers), 3.6 parts by weight of oxalic acid, 2.0 par-ts by weight of lauryl alcohol, 2.0 parts by weight of lauric acid, and 20 parts by weight of RUTAPOX VE
2913.
Reference Example 6.
A low viscosity emulsionwas produced, as described in Reference Example 1, from 40 parts by weight of water, 9.4 parts by weigh-t of IPD, 3.2 parts by weight of fumaric acid, 3.5 parts by weight of oxalic acid, 4.0 parts by weight of lauryl alcohol, 4.0 parts by weight of lauric acid, and 40 parts by weight of epoxy resin RUTAPOX VE 2913.
Reference Example 7.
A low viscosity emulsion was produced, as described in Reference Example 1, from 35 parts by weight of water, 9.4 parts by weight of IPD, 3.5 parts by weight of oxalic acid, 4.1 parts by weigh-t of adipic acid, 2.0 parts by weight of lauryl alcohol, ~3~7~"

2.0 parts by weight of lauric acid, and 40 parts by weight of epoxy resin RUTAPOX VE 2913.
Reference Example 8.
A low viscosity emulsion was produced, as described in Reference Example 1, from 35 parts by weight of water, 9.4 parts by weight of IPD, 3.5 parts by weight of oxalic acid, 2.9 parts by weight of malonic acid, 2.0 parts by weight of lauryl alcohol, 2.0 parts by weight of lauric acid, and 40 parts by weight of epoxy resin RUTAPOX VE 2913.
Reference Example 9.
A low viscosity emulsion was produced, as described in Reference Examp~el, from 35 parts by weight of water, 9.4 parts by weight of IPD, 1.5 parts by weight of acetic acid, 2.5 parts by weight of phthalic acid, 3.5 parts by weight of oxalic acid, 2.0 parts by weight of lauryltriglycol, 2.0 parts by weight of lauric acid, and 40 parts by weight of epoxy resin RUTAPOX VE
2913.
Reference Example 10.
-A low viscosity emulsion was produced, as described in Reference Example 1, from 15 parts by weight of water, 4.7 parts by weight of IPD, 0.5 parts by weight of tartaric acid, 3.3 parts by weight of oxalic acid, 2.0 parts by weight of lauryl alcohol, 0.5 parts by weight of a mixture of dodecyl- and tetradecyl alcohol (ALFOL 12/14) which had been reacted with 9 moles of e-thylene-oxide, and 20 parts by weight of epoxy resin RUTAPOX
VE 2913.

~23~7~

Reference Example 11.
A medium viscosity emulsion was produced, as described in Reference Example 1, from 12 parts by weight of water, 4.7 parts by weight of IPD, 0.5 parts by weight of tartaric acid, 3.3 parts by weight of oxalic acid, 2.0 parts by weight of lauryl triglycol, and 20 parts by weight of epoxy resin RUTAPOX
VE 2913.
Reference Example 12.
A stable emulsion was produced, as described in Reference Example 1, :Erom 10 parts by weight of water, 3.5 parts by weight of oxalic acid, 4.7 parts by weight of isophorone-diamine, 1.5 parts by weight of 2-ethylhexanol, and 20 parts by weight of epoxy resin RUTAPOX VE 2913.

Claims (19)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for obtaining a frictional bond between con-crete and a surface of an object which is coated with a thermo-setting plastic which method comprises:
treating the surface with an epoxy resin cement mortar mixture containing A. 10 to 30% by weight of an epoxy resin diammonium salt emulsion comprising a liquid epoxy resin, a latent curing agent, an emulsifier and water, wherein:
(a) the emulsifier is a primary aliphatic alcohol of 8 to 14 carbon atoms or its adduct with up to 10 ethylene-oxide groups; and (b) the latent curing agent is a reaction product obtained by complete neutralization, with oxalic acid or an acid mixture containing at least 40% by weight of oxalic acid, of a diamine of the formula I or II:
H2N - CH2 - R NH2 (I) H2N - R - CH2 - R - NH2 (II) wherein R is selected from the group consisting of a substituted alkylene, a cycloalkylene residue with 6 to 9 carbon atoms and an aralkylene residue with 7 to 9 carbon atoms, and B. 70 to 90% by weight of cement mortar.

2. A method according to claim 1, wherein the object is a powder-painted object.

3. A method according to claim 2, wherein the powder-paint has an epoxy resin/amine base.

4. A method according to claim 1 or 2, wherein the object is a metal or plastic tube.

5. A method according to claim 2, wherein reinforcing steel members are used as the objects.

6. A method according to claim 1, 2 or 3, wherein the emulsifier also contains lauric acid.

7. A method according to claim 1, 2 or 3, wherein an acid mixture containing oxalic acid and up to 25% by weight of acetic acid is used for the neutralization of the diamine.

8. A method according to claim 1, 2 or 3, wherein an acid mixture containing oxalic acid and up to 60% of an acid selected from the group consisting of a dicarboxylic acid with 3 to 6 carbon atoms which may be substituted with one or more hydroxyl groups and an isomer of phthalic acid is used for the neutral-ization of the diamine.

9. A method according to claim 1, 2 or 3, wherein the emulsion contains 10 to 25% by weight of the emulsifier based on the amount of the epoxy resin.

10. A method according to claim 1, 2 or 3, wherein the di-amine of the formula (I) or (II) is 2,2,4-trimethylhexamethyl-enediamine, a xylyldiamine, 3-aminomethyl-3,5,5-trimethylcyclo-hexylamine, 4,4'-diamino-3,3'-dimethyldicyclohexylmethane or a mixture thereof.

11. A method according to claim 1, 2 or 3, wherein the liquid epoxy resin is a reaction product of epichlorhydrin or glycidol with a 2,2-bis(4-hydroxyphenyl)alkane.

12. A method according to claim 1, 2 or 3, wherein the acid is oxalic acid alone or an acid mixture containing oxalic acid and up to 25% by weight of acetic acid or an acid mixture containing oxalic acid and up to 60% by weight of an acid selected from the group consisting of a dicarboxylic acid with 3 to 6 carbon atoms which may be substituted with one or more hydroxyl groups and an isomer of phthalic acid; the emulsion contains 10 to 25% by weight of the emulsifier based on the amount of the epoxy resin; the diamine of the formula (I) or (II) is 2,2,4-trimethylhexamethylenediamine, a xylyldiamine, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, 4,4'-diamino-3,3'-dimethyldicyclohexylmethane or a mixture thereof; and the liquid epoxy resin is a reaction product of epichlorhydrin or glycidol with a 2,2-bis(4-hydroxyphenyl)alkane.

13. A method according to claim 1, wherein the object is a powder-painted pipe for the transportation of oil or gas; and the concrete is to be applied as a casing of the pipe for pro-viding additional weight for laying underwater or additional protection.

14. A method according to claim 13, wherein the diamine has formula I.

15. A method according to claim 13, wherein the diamine is 3-aminomethyl-3,5,5-trimethylcyclohexylamine (namely isophorone-diamine, IPD).

16. A method according to claim 13, 14 or 15 wherein the epoxy resin is based on bisphenol A.

17. A method according to claim 1, wherein alternatively the coated surface of an object is treated with an epoxy resin diammonium salt emulsion (A), the emulsion on the thus-treated surface is dried, and then cement mortar is applied to the thus-treated surface.

18. A method according to claim 17 wherein the object is a powder-painted pipe for the transportation of oil or gas; and the concrete is to be applied as a casing of the pipe for providing additional weight for laying underwater or additional protection.

19. A method according to claim 13, wherein the diamine is 3-aminomethyl-3,5,5-trimethylcyclohexylamine (namely isophorone-diamine, IPD).