CA1137689A - Seal coats for construction works - Google Patents

Abstract

ABSTRACT OF DISCLOSURE A seal coaat for use in a traffic surface is formed by reacting a first component comprising a liquid epoxy resin and a blocked polyisocyanate prepolymer with a second component comprising an aliphatic or cycloaliphatic polyamine, and allowing the mixture to cure. Advantageous results are achieved if the mixture, before curing, is allowed to impregnate a matrix, e.g. a non-woven synthetic material.

Description

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This invention relates to binder compositions o-f the type which can be used to form seal coats having water-, and particularly salt water-, oil-, and wear-resistant properties. One example of the use of SUC]l coats is in sealing concrete works or metallic structures, particularly of orthotropic slabs.
The problems inherent in providing such coats are familiar to those skilled in the art, and no satisfactory solution has yet been provided with respect to both the seal coats and their wearing properties.
Known solutions in the case of sealing steel and concrete may be classified into two classes, the ~irst ~eing to use adhesive seal coats, generally comprising heat-curable epoxy resins 3 and the second being to use non-adhesive, so-called "independent" seal coats, generally comprising asphalt or bituminous materials. Both types of seal coats are often provided with abituminous concrete upper layer which function as a wearing course. ~otll the above classes of seal coats llave their specific drawbac~s, for example in the creepin~ of the bituminous coating over the seal coat layer (particularly in the case of ~eal coats comprising an epoxy film adhering to the coate~
structure~; in the deformation of the seal coat layer under stress (when using independent asphalt layers which do not adhere to the structure); in the formation of blisters between the application of the seal coat and the application of the wearing course (this is frequently the ~, f ~ ~376~3~

case with asphalt seal coats); and in the cracking of the seal coat, particularly at low temperatures.
This last drawback is frequently common to both types of seal coats because they become highly rigid at 5 low temperatures and9 in the case of asphalt, b~cause the independence of the asphalt layer from the structure is more theoretical than actual, the frictional forces frequently exceed the tensile strength of the asphalt layer.
In this latter case, loss of the sealing capacity is all 10 the more seriousO ~or example, the water may flow under the seal coat and reach all the cracl~s in the structure.
In the case of the seal coats comprising a Eilm o~
epoxy resin, the difference in degree of expansion of the too highly rigid resin film and the wea~er concrete skin 15 can cause stripping and cracking of the latter.
Finally, bituD~ ous coatings are often uns~tis-factory. If compact, such coatings tend to distort under localised stress; if less compact, water may penetrate and concentrate at th~ interface o:E the seal coat and the wear-20 ing course, causing destruction of the latter.
British Patent Specification No. 1J41S~493 dis-closes a seal coat comprising a plastics layer coated on both faces with a glass-fibre reinforced layer and, extern-ally, a bituminous layer. }rench Patent Publication Mo.
25 2,321,013 discloses an elastic sheet reinforced on both faces with a non-woven material and adhered to the struct-ure to be coated with a bituminous or tar binder. Botll these types of seal coat suffer from two main disadvant-ages. The first lies in the difficulty of adhering 30 lengths of material, particularly over curved structures 'such as bridges. The second lies itl the difficulty of achieving adhesion along banking on the e~ges of st-luctures to be coated.
British Patent Specification Mo. 1,509,10S
35 discloses a seal coat intended for use as an "all-wea+her"
sports ground wear surface. The coat is obtained by mixing a binder with a resilient material, the binder ' ' "-' ~.1~7~C~

being prepared, just before use, ~rom (A) a prepolymer of a polyure~hane having a~ least two terminal isocyanate groups which are each blocked by a phenol an~ (B) a liquid polyamine.
A novel binder composition suitable for use ~s or as part of a seal coat has no~ been discovered. ~e composition comprises the reaction product of a first component comprising a liquid epoxy resin and a blocked polyisocyanate prepolymer, with a second co~ponent comprising an aliph~tic or cycloaliphatic polyamine. The components may be formulated separately, to be mixed at the time of use.
A seal coat of this invention may comprise a cured binder composition as defined or a matrix impregnated ,with such a composition.
Aeeording to one aspeet of the present invention, there is provided a two-eomponent formulation, the eomponents of whieh may be mixed to form a binder eomposition, the first eomponent eomprising a liquid epoxy resin and a bloeked polyisoeyanate prepolymer, and the seeond eomponent eomprising an aliphatie or eyeloaliphatie polyamine.
Aeeording to another aspeet of the invention, there is provided a method of forming a seal eoat on a strueture, whieh eomprises spreading a binding layer over the strueture;
applying a matrix over the binding layer; and spreading a mixture of a first eomponent eomprising a liquid epoxy resin and a bloeked polyisoeyanate prepolymer with a seeond eomponent eomprising an aliphatie or eyeloaliphatie polyamine over the matrix, and thereby impregnating the matrix, and allowing the mixture to eure.
On eonerete struetures, the adhesion of some eoatings ean be impaired by the moisture present and, in these eireumstanees, the binding layer advantageously eonsists of :: :

.

~:~376~3~
3a an aqueous epoxy resin emulsion which may be spread in an amount of 400 to 800 g/m . The epoxy resin impregnates the concrete and reinforces its surface, provides good ahesion, and constitutes an adhesive layer for the subsequently applied matrix. On metallic structures, however, an epoxy emulsion need not be used and the binding layer may consist of a binder composition of the invention, e~g. in an amount of 700 to 1500 g/m2.
The method of this invention can provide an adhesive seal coat which prevents the potential flow of water under the sealing surface, which is capable of trans-mitting stress to the coated structure and which, with the optional addition of coal tar pitch, at low temperatures [- 20C], can exhibit an elongation in excess of 50%

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(I~O)o At t}le same temperature the elongation for thc epoxy resins used hitherto is too small to be measured.
~ ,hen it is desired to obtained particular~y good sealing and rcinforcing properties, an already applied 5 coating layer may be covered with an additional matrix, followed by another binding layer, e.g. of the novel binder composition. The matrices are preferably applied mutually orthogonally.
If used, the matrix will usually be fibrous and 10 is preferably a non-woven material, suitably of synthetic fibres, e.g. polyester, polypropylene or polyamide.A non-woven matrix preferabl~r has a weight o-f S0 to 200 g/m2 and preferably exhibits an elongation at break in excess of 40~ in all directions. Tlle amount of the impregnant, i.e.
15 t]le binder composition, is preferably from 1.5 to ~.5 kg/m2.W}len an impregnated non-woven material is used in a seal coat ot the invention, it can reinforce the seal coat and substantially increase its tear strength and its fatigue strength, absorb t~e stresses arising ~ron 20 differellces in expansion between the resin and concre~e and prevent perforation of the rcsin film by the sand and aggregates lihich may be spread over the resin surface prior to its final polymerisation.
Prior to polymerisation of the binder composit-25 ion of the invention, wllen used as a seal coat or as an impregnant in a matrix-reinforced seal coat, aggregrates may be spread over the incompletely cured binder layer.
If no subsequent wearing course is to be provided, aggregates having a particle size of 2 to 10 mm may be 30 spread in an amount of 5 to 8 kg/m2. If a wearing course is to be used, aggregates having a particle size of 0.5 to 3 mm may be spread in an amount of 3 to 6 kg/m2 Inorganic aggregates, preferably a mixture of sand and crushed gravel, may be used.
The first component of the binder composition of the invention may consist of, for example, 15 -to 50~
by weight of a conventional liquid epoxy resin, e.g. of ~ . 1~37~i~39 the type commercially availahle under the trade name Epikote 82~ or DX 214 (Shell) or DER 7475 (Dow Chemical);
and 85 to 50% by weigllt of a polyisocyanate prepolymer comprising phenol-blocked isocyanate groups. The purpose of the phenol-blocking is to make the product insensitive to humidity, which is obviously of fundamental importance in the production of seal coats used in the open.
Examples of suitable polyisocyanates are pre-polymers of toluene diisocyanate or diphenylmethane diisocyanate and polyethers, pre-ferably straight-chain polyethers, having a molecular weight of 600 to 2500, based on polyoxypropylene, polyoxybutylene or copolymers of polyoxypropylene and polyoxybutylene with polyoxyethy-lenes. The proportions of polyether and of diisocyanates are preferably such that, after the reaction, the free NC0 group content is 1.5 to 6% by weight prior to bloc~ing with a phenol.
It is well known to those expert in the art that the variety of possible chains is practically infinite.
The desired s¢lection will be governed by workability considerations, particularly with respect to the viscosity of the product obtained after blocking. Viscosities between 3,000 and 20,000 cps at 20C are preferred because they permit ready processing under the described conditions.
Examples of suitable phenols are phenol itself, cresols and tert-butylphenol.
If desired, plasticisers such as dibutyl phthalate, butyl adipate, octyl adipate, petroleum-derived plasticisers such as Dutrex (Shell ) may be includecl in the first and/or the seco~d component o-f the binder composit-ion. The preferred amount of plasticiser is rom 5 to 20% by weight, based on the total weight of the binder.
The seconcl component of the novel binder composition comprises an aliphatic or cycloaliphatic polyamine such as trimethylhexamet~ylellediamine, N-(2-aminoethyl)piperazine, isophorone dian~line, bis(4-amino-cyclohexyl)methane or 3,3'-dimethyl-4,4'-diaminodicyclo-hexylmethane. Such amines have as their chief eature that, at ambient temperatures, not only do they react 3'76~3~

with the epoxy resin, but also they displace the pher.ol to give what may bc designated a polyureide. This is a basic characteristic of the in~ention because, ~!hen the binder composition is spread as a l~atively thin film over large surfaces of several hundreds of squai^e metres,heating o-f the resin to cause polymerisation would be undesirable and expensive; it is therefore important that polymerisation should proceed at ambient tempera-tures.
The amount of the polyamine should be s~bstant~
ially stoichiometric with respect to the total amount of the epoxy resin and tlle polyisocyanate prepolymer of the first component. This amount, for the preferred relative weigllts of epoxy resin and polyisocyanate given above, is usually from about ~ to about 20~o by weight of the total weight of the epoxy resin plus polyisocyanate prepolymer.
Extenders may be added to the seconcL component in order to reduce cost wllile improving the ~ettability 20 of cancrete, steel and non-woven material surfaces.
Suitable ex~enders include, for example, coal tar pitch and colourless coumarone-, indene- and coumarone-indene-based resin pitch, e.g. commercially available materials such as Necires E~PL (Cindu Neville Chimie).
The preferred amount of any extender(s) in the second conmponellt is rom 10 to 100~ by weight of the total weight of binder~ i.e. of the two components.Coal tar pitch is generally the preferred extender, in vie~ oL its cost and wet-ting and water-proofing properties.
~ variety of inorganic fillers may be included in the second component. Example of such fillers are limestone and siliceous fillers capable o passing tllrough a lOO mesh screen. The amount of sucll fillers may be up to 40O by weight of the total weight of the binder composition, provided that the amount does not result in a viscosity increase up to a le-vel whicll would make the composition difficult to use. T!le inorganic ~illers may, if desired, be added on tlle work site, after mixing ~376139 the first and second components., It has been round that a resin formulation of the type described can not only exhibit the same utility and ~rorkability as conventional epoxy resins, e.g. excellent resistance to hu]nidity, polymerisation at room ~emperature, use in liquid form and excellent adhesion to concrete but also superior mechanical strength and superior elongation at break at low temperatures, while retaining good tensile strength at high tempera-tures. The formulations of the type described canprovide tensile strengths in excess of 20 ~ars at 25C, and elongations at break in excess of 50% at -10C.
Adhesion to concrete is limited only l~y the tensile strength of the concrete surface.
l~ The following two Exanmples illustrate the invention. The subsequent test is comparative. ~ll parts and percentages are by ~reigllt, unless otherwise specified.
_ ample l On the superstructure o-f a concrete bridge ~hich had been vigorously cleaned with a brush, 400 g/m~ of an aqueous epoxy resin emulsion obtained by admixture o~
300 g rater and 100 g of a 50:50 mixture o~ Eurcpox 716 and Euredur ~29 (trade names ~or a resin and curing agent sold by Scherin~ were applied.
When the resulting film began to clear, a non-woven polyester web having a weight of 120 g/m2 (sold as - Bidim by Rhone,Poulenc) was applied over the still sticky resin. A second resin was then immediately applied in an amount of 2 kg/m2.
The second resin comprisedtwo components, the irst component consisting of 100 parts Epikote D~ 21~
resin (Shell) and 100 parts of a prepolymer of toluene diisocyanate and polyoxypropylene-based polyether containing 3.5~ tert-butylphenol-blocked NCO groups, and the second component of 150 parts coal tar pitch (viscosity 30 EVT) ancl 26 parts ~-(2-aminoethyl)piperazille.
The binder obtained a~ter polymerisation had an elongation at break of 60~ at -10C and a tensile strength ~ . gL~7~82~

of 40 Bars at 20C.
4 kg/m2 of 0. 5/3 mm sand were sprayed over the coating prior to complete polymerisation of the resin.
Exa~ple 2 Over the concrete bed o-f a nuclear power plant adapted to accomodate the tank of a reactor, previously scrape~ with a percussion device, 600 g/m2 of an epoxy resin emulsion comprising 100 g DET 331 resin (Dow Chemical) and lOO g Casamide 350 ~Akzo) and 400 g water were applied.
When the film cleared, a non-woven material of the same type as in Example 1 was applied and, immediate-ly thereafter, 2. 5 kg/m~ of a second resin ; before completion of the polymerisation, the process was repeated by cross-wise application of lengths of thc non-woven material and new applications of 2.5 kg/m2 oE the second resin, to give a coating having ~ood properties.
The second resin comprised two components, the first component consisting of 30 parts DER 7475 epoxy resin (Dow) and 70 parts liquid prepolymer having a molecular weight of about 2000, obtained by reaction of toluene diisocyanate with polypropylene glycol containing 3% phenol blocked isocyanate groups, and the second component of 15 parts bis(4-aminocyclohexyl)methane, 45 parts EVT 30tar and 5 parts dibutyl phthalate.
50 parts dry siliceous -filler were added to the mixture of the two componènts bcfore spreading the resulting mixture. In this Example, it was unnecessary 3~ to spray sand over the surface of the resin.
The mixture of the two components had a tensile strength of 40 Bars at 20C and an elongation at break of more t~lan 200~o at -10C and of more than lOO~o at -20C.
Comparative Example A conventional epoxy resin fornlu]ation was made up from 50 parts DX 214 resill (Shell ) J 40 parts 30EVT pitch and 10 parts N-(2-aminoetllyl)piperazine.
This resin ha~l a tensile strength of more than 25 Bars ~L~L3~6~39 at 20~C ~ howe~-e~r~ the elong~itlon at break was less than S~ at 0C and not measurable at -10C.
/~ sealing coat of this invention on a concrete block was tested by suitable apparatus to an ultimate 5 tensile strength test which produced a crac~ in the concrete. No break-down of the seal coat for a 1.~ mm - crack was observed and opening and closing the crack 1000 times ailed to cause break-down of the seal coat, at a temperature of 0C. When the same test was conducted with 10 the comparative Example, break-down occurred -for a 0.~ mm crack and, at 0C, five opening and closing cycles of an 0.4 mm crack were sufficient to break the filni.
Throughout the preceding description, bracketted names indicate the source of trade~narued 15 materials.

It will be understood that, for use in the present invention, the polyamine must comprise labile hydrogen atoms which can displace the phenol blocking group. Usually, therefore, it comprises two primary or secondary amine groups and the nature of the components of the formulation is such that the displacement can occur at O to 100, e.g. 5 to 50 and usually 8 to 40, C. For ease of use, the components of the formulation of the present invention are liquid.
The a~ount of any filler comprised in the second component may be up to a maximum of 60~o by weight of of the binder composition.
While particular embodiments of this invention are described above, it will be understood that the invention may be varied and modified without departing from its broade.r aspects, as defined in the following claims.

Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A two-component formulation, the components of which may be mixed to form a binder composition, the first component comprising a liquid epoxy resin and a blocked polyisocyanate prepolymer, and the second component comprising an aliphatic or cycloaliphatic polyamine.

2. A formulation according to claim 1 in which the first component consists essentially of from 15 to 50°%
by weight epoxy resin and from 85 to 50% by weight blocked isocyanate prepolymer, the said prepolymer comprising from 1.5 to 6% by weight thereof, before blocking, of isocyanate groups.

3. A formulation according to claim 1 in which the polyamine is present in a substantially stoichiometric amount with respect to the liquid epoxy resin and blocked polyisocyanate prepolymer.

4. A seal coat which has been formed by mixing the two components of a formulation according to claim 1, and allowing the mixture to cure.

5. A seal coat according to claim 4 comprising a matrix impregnated with the cured composition.

6. A method for forming a seal coat on a structure, which comprises spreading a binding layer over the structure; applying a matrix over the binding layer;
and spreading a mixture of a first component comprising a liquid epoxy resin and a blocked polyisocyanate pre-polymer with a second component comprising an aliphatic or cycloaliphatic polyamine over the matrix, and thereby impregnating the matrix, and allowing the mixture to cure.

7. A method according to claim 6 for forming a seal coat on a concrete structure, in which the binding layer comprises an aqueous epoxy resin emulsion which is spread in an amount of from 400 to 800 g/m2.

8. A method according to claim 6 in which the binding layer comprises a mixture of a first component comprising a liquid epoxy resin and a blocked polyisocyanate prepolymer with a second component comprising an aliphatic or cycloaliphatic polyamine.

9. A method according to claim 6 in which the matrix is a non-woven material.

10. A method according to claim 9 in which the non-woven material is of synthetic fibres.

11. A method according to claim 12 in which the non-woven synthetic fibrous material has a weight of from 80 to 200 gm and an elongation at break in excess of 40% in all directions.

12. A method according to claim 6 in which an inorganic aggregate is spread over the coat prior to its final cure.

13. A traffic surface including a seal coat prepared by a method according to claim 6.