GB2240977A

GB2240977A - Composition and method for treating cementitious layers

Info

Publication number: GB2240977A
Application number: GB9102680A
Authority: GB
Inventors: Peter Frederick Gibbins
Original assignee: Flowcrete Systems Ltd
Current assignee: Flowcrete UK Ltd
Priority date: 1990-02-08
Filing date: 1991-02-08
Publication date: 1991-08-21
Anticipated expiration: 2011-02-08
Also published as: GB2240977B; GB9002886D0; GB9102680D0

Abstract

In order to upgrade weak or failing cement/sand screeds in situ a low viscosity, polymer based, curable composition is applied thereto. The composition is one that penetrates the cementitious material and binds and strengthens same on curing. Such composition may be based on an epoxy resin or a polyisocyanate prepolymer.

Description

Title: Compositions for and method of treatment of cementitious layers, such as screeds and floor toppings.

DESCRIPTION This invention concerns compositions for and method of treatment of cementitious layers, such as screeds and floor toppings.

Traditional cement sand screeds are widely used as a regulating layer over concrete base slabs to provide a flat smooth regulating layer and uniform support for soft floor finishes, for example, carpets, thermoplastic tiles, sheet vinyl and linoleum.

When properly laid cementitious screeds can achieve high strengths and be wholly satisfactory.

However, cementitious screeds have developed a poor reputation with many failures occurring due to crushing under service loading. Research by many eminent authorities, i.e. Building Research Establishment and Cement & Concrete Association, have identified poor mixing and batching and poor compaction as major causes of failure. The recently published revision of the British Standards on Cementitious Screeds, BS.8203 and BS.8204 includes for use of Forced Action Mixers and also includes for testing by means of the BRE (Building Research Establishment) test method, principally developed to assess screed qualities for point and crushing load resistance. All of these revised standards and test methods are intended to avoid screed failures, but unfortunately screed failures are still all too common.

Repairs and or screed removal and replacement can be extremely disruptive and costly. Furthermore, the delays of drying out time of repaired or replaced screed can cause major problems to clients (a 50mm cementitious screed can take upto two months to dry out to reach specified moisture content, as defined under BSI.8203:1987 and BSI.8204:1987 Part 1).

An object of this invention is to provide a means of enabling rapid upgrading of weak failing cement sand screeds in situ, to conform to BRE Test requirements as defined within current British Standards. and so avoid the need for costly disruptive repairs and/or replacement of screeds and delays in drying out periods.

According to this invention it is proposed that cementitious layers to be treated with a low viscosity polymer based composition that penetrates the cementitious material and binds and strengthens same on curing.

The preferred compositions for use in the invention are substantially, preferably totally, solvent free i.e. free of both volatile and non-volatile solvents and substantially, preferably totally, free of plasticisers. The presence of solvents or plasticisers in the compositions of -the invention could be harmful due to migration thereof to the surface leading to attack on plasticisers in flooring adhesives and/or floor coverings. Also, the absence of solvents and plasticisers provides improved performance relative to fire or health hazards.

Preferably the polymer(s) used in the compositions of the invention are substantially fully reactable to give maximum cross-linking of constituents on curing.

Furthermore, the presence of solvents and/or plasticisers in the compositions used in the invention could have the effect of retarding curing, which give rise to slower strength development and hence lower ultimate strength for the polymer. In addition, volatile solvents could become trapped in the polymer as it cures. That would reduce polymer strength, could give rise to health and fire hazards and slow migration of solvent ultimately causing damage to floor adhesive and/or coverings, inclusive of attack on plasticisers contained therein.

The polymer compositions suitable for use in the invention preferably also have one or more of the following properties: (1) good impregnation properties, i.e.

wettability and depth of penetration; (2) substantially odourless; (3) provide rapid strength development after impregnation into cementitious layers.

Preferably both traffic and floor covering replacement will be possible within 18 to 24 hours after impregnation.

To achieve (1) above low viscosity is a desirable property but preferably not to be achieved by addition of solvents and/or plasticisers.

The preferred compositions for use in the invention will comprise a curable polymer and a reactive diluent. One suitable type of curable polymer is an epoxy resin, such as based on Bisphenol A and/or Bisphenol A & F resin systems.

The reactive diluent is preferably an ether, such as a glycidyl ether. Preferred ethers will have relatively low viscosities preferably below 20 mPa.s, especially below 15 mPa.s, at 25 degrees C. Low vapour pressure is also an important property for the reactive diluent, vapour pressures at 20 degrees C preferably being below 2.0 mbar, especially below 1.0 mbar.

To initiate curing and hardening of the polymer, a curing agent may be included in the compositions of the invention. Suitable curing agents include polyamines, especially aliphatic polyamines, including modified polyamine adducts and modified polyamines.

Other optional ingredients of the composition for the invention include wetting agent, such as fluorinated alkyl esters, antifoaming agent, such as branched chain acrylics, and dye tracer.

The compositions of the invention may be applied to a cementitious layer, such as a screed or topping, in any suitable manner such as by spraying, rolling or brushing. The repair of floor screeds involves removal of floor coverings and old adhesive residues, plus any underlayment, i.e. 1.5mum self smoothing system used to level and finish cementitious screed. In order to provide effective controlled removal of aforementioned material it is important that such work is completed dust-free.

Methods have been developed utilising electric powered specialist Scarifying machines, i.e. Von Arx or Errutt scarifiers and similar, especially vacuum controlled to prevent and control dust. Areas to be treated will be subject to the use of high capacity air movement equipment to create a negative pressure area with a positive air flow. The air mover incorporates filtration equipment to remove any airborne dust particles. The clean filtered air is then to be discharged via tubing and/or ducting to external atmosphere. The use of such filtered air moving equipment is a secondary precaution in case dust was created for whatever reason.

A composition of the invention is then produced normally by mixing of components and then applying the mixture to the surface to be treated. The composition penetrates the surface to a sufficient depth and curing takes place to form reinforced substrate. The compositions of the invention are specially designed and formulated to penetrate the pore structure of weak screeds, so as to provide an insitu hardening and internal reinforcement of treated screed.

Typical cementitious screeds can have up to 30% or even greater volume of voids. With this invention it is not always necessary to fill pore structure totally in order to strengthen a weak screed adequately. The composition is sufficiently liquid to penetrate and wet out the voids, coating them internally and providing high adhesive strengths to bind fine and course aggregate particles together. The compositions, after penetration, then polymerises (crosslinks) to reinforce and toughen the screed with exceptionally high adhesive binding strengths to provide a dramatic improvement in BRE Test results, i.e. low indentation values, within very short time periods (with 12 to 24 hours of treatment). The resultant polymer reinforced cement sand screen also shows a dramatic increase in compressive, flexural and tensile strengths, plus much improved abrasion and point load resistance.

Another major advantage is the marked improvement of water resistance of treated cementitious screeds, i.e. treated screed shows a marked decrease in permeability.

The cured compositions of the invention preferably have tensile strength in the range of 2025N and flexural strength in the range of 30-35N. It is also preferable that shrinkage be less than 0.0%. In addition the curing reaction is preferably a low to medium exotherm reaction.

It is also possible to base the present invention on a polyurethane type system, for example using one or more polyisocyanate prepolymers, such as based on Polyisocyanate MDI based Prepolymer S blended with Polyisocyanate (based on Di-Phenyl Methane Di Isocyanate), that may be cured by reaction with atmospheric humidity and moisture within the cementitious layer being treated. Such polyurethane system may be solvent free, have low viscosity and may be used as a one or two component system.

The use of such systems can provide very long usable lives and the polyurethane on penetration into creeds and other substrates, commences curing and hardening due to moisture, i.e humidity within the substrate and atmosphere to produce a tough adhesive binding reinforcement of treated substrates.

Such polyurethane systems can be accelerated to improve hardening and strength development by addition of selected accelerator, particularly when moisture content within the substrate and/or atmosphere is low.

The polyurethane type system differs from epoxy based systems in that the hardening (curing) of the polyurethane system is initiated by reaction with moisture present in substrate and atmosphere, thus providing a long open usable life and longer penetration time with the polymer system, as compared to the two components epoxy system which has a limited usable life and limited time for penetration of a substrate when its two components are mixed, due to resultant increases in viscosity as polymerization commences.

The usable life of an epoxy system may be varied by means of the type and class of hardener component utilised. But the polyurethane type systems can offer an advantage over the epoxy systems in respect to ease of use as on site mixing is not required for one component system, usable life and open time may be longer and curing maybe initiated by moisture and humidity already present in the substrate being treated and atmosphere.

The polyurethane system may also be blended with for example, solvent-free polymers, including: a. Branched polyalcohol with ester and ether groups.

b. Hydroxyl bearing polyesters.

c. Polyols and polyethers.

d. Polyisocyanates, such as based on diphenyl methane diisocyanate.

The invention will now be further described with reference to the following Examples: EXAMPLE 1 A composition for use in strengthening a cementitious screed by penetration and curing was made from a two pack system as follows: Base Component Parts by Weight a. Liquid Epoxy Resin based on a blends of Bisphenol (A & F Resins) 70.00 b. Bi-functional diluent (1.4 Butanediol) Diglycidyl Ether) 30.00 c. Wetting agents - example Fluorinated Alkyl Ester 0.30 d. Antifoaming agent,example BYKAs00 0.20 Hardener Component e. Modified Aliphatic Polyamine 27.50 f. Tracer Dye (organic) Red or Blue 0.50 TOTAL 128.50 Liquid Epoxy Resin (solvent free) as (a) above may include types such as Bisphenol A type, and/or Bisphenol A & F blends.

EXAMPLE 2 This composition is an improvement over Example 1, and provides the following advantages:a. Faster defoaming, i.e. air release behaviour.

b. Improved wetting out behaviour of surfaces.

c. Lower vapour pressure.

d. Lower toxicity (more user friendly).

e. Inhalation risks reduced.

f. Much improved penetration qualities.

Base Component Parts by Weight a. Liquid Bisphenol A or AF Epoxy Resin 70 - 75 b. C13/C15 Alkyl Glycidyl Ether (long chain Aliphatic) Reactive Diluent. 30 - 25 c. Wetting agent, example Fluorinated Alkyl Ester 0.3 d. Antifoaming Agent example BYK A500 type 0.2 Hardener component e. Dye Tracer (organic) to colour of choice 0.5 f. Modified Aliphatic Polyamine curing agent 38 - 39 The hardener component in either Example may be varied to include other hardener types, for example, modified polyamine adducts, selected cycloaliphatic amines, amidoamines or modified polyamines.

Claims

1. A method of treating cementitious layers comprising the step of applying to said layer a low viscosity polymer based composition that penetrates the cementitious layer and binds and strengthens same on curying.

2. A method as claimed in claim 1, wherein the polymer based composition is substantially free of organic solvent.

3. A method as claimed in claim 1 or 2, wherein the polymer based composition is substantially free of plasticisers.

4. A method as claimed in claim 1, 2 or 3, wherein the polymer is substantially fully reactable.

5. A method as claimed in any one of claims 1 to 4, wherein the polymer composition comprises a curable polymer and a reactive diluent.

6. A method as claimed in claim 5, wherein the curably polymer is an epoxy resin.

7. A method as claimed in claims 6, wherein the epoxy resin is based on bisphenol A and/or bisphenol A + F resin systems.

8. A method as claimed in claims 5, 6 or 7, wherein the reactive diluent is an ether.

9. A method as claimed in claim 8, wherein the ether is a glycidyl ether.

10. A method as claimed in claim 8 or 9, wherein the ether has a viscosity below 20 mPa.s at 250C.

11. A method as claimed in claim 10, wherein the ether has a viscosity below 15 mPa.s at 250C.

12. A method as claimed in any one of claims 8 to 11, wherein the ether has a vapour pressure at 200C below 2.0 mbar.

13. A method as claimed in claim 12, wherein the ether has a vapour pressure at 200C below 1.0 mbar.

14. A method as claimed in any one of claims 1 to 13, wherein the polymer composition further comprises a curing agent.

15. A method as claimed in claim 14, wherein the curing agent is a polyamine.

16. A method as claimed in claim 15, wherein the curing agent is an aliphatic polyamine.

17. A method as claimed in any one of claims 1 to 16, wherein the polymer composition further comprises a wetting agent.

18. A method as claimed in claim 17, wherein the wetting agent is a fluorinated alkyl ester.

19. A method as claimed in any one of claims 1 to 18, wherein the polymer composition further comprises an anti-foaming agent.

20. A method as claimed in claim 19, wherein the anti-foaming agent is a branched chain acrylic compound.

21. A method as claimed in any one of claims 1 to 4, wherein the polymer composition comprises one or more polyisocyanate prepolymers.

22. A method as claimed in claim 21, wherein the polymer composition comprises polyisocyanate MDI based prepolymer S blended with polyisocyanate based on diphenyl methane diisocyanate.

23. A method as claimed in claim 21 or 22, wherein the polymer composition contains an accelerator.

24. A method as claimed in claim 21, 22 or 23, wherein the polymer composition is blended with solvent free polymers selected from branched polyalcohols with ester and ether groups, hydroxyl bearing polyesters, polyols, polyethers and polyisocyanates.

25. A method as claimed in any one of claims 1 to 20, wherein the polymer composition is applied by spraying, rolling or brushing.

26. A method as claimed in any one of claims 1 to 21, comprising the step of removing existing floor coverings adhesive residues and any underlayment if present prior to application of the polymer composition.

27. A method as claimed in any one of claims 1 to 22 including the step of creating for an area to be treated a negative pressure with a positive air flow.

28. A method as claimed in claim 27, wherein said air flow is filtered.

29. A method as claimed in claim 1 and substantially as hereinbefore described with reference to any one of the foregoing Examples.

30. A composition for use in treating cementitious layers comprising a low viscosity polymer that penetrates the cementitious layer and binds and strengthens same on curying.

31. A composition as claimed in claim 30, which is substantially free of organic solvent.

32. A composition as claimed in claim 31 or 32, which is substantially free of plasticisers.

33. A composition as claimed in claim 30, 31 or 32, wherein the polymer is substantially fully reactable.

34. A composition as claimed in any one of claims 30 to 33 comprising a curable polymer and a reactive diluent.

35. A composition as claimed in claim 34, wherein the curable polymer is an epoxy resin.

36. A composition as claimed in claim 35, wherein the epoxy resin is based on bisphenol A and/or bisphenol A + F resin systems.

37. A composition as claimed in claim 34, 35 or 36, wherein the reactive diluent is an ether.

38. A composition as claimed in claim 37, wherein the ether is a glycidyl ether.

39. A composition as claimed in claim 37 or 38, wherein the ether has a viscosity below 20 mPa.s at 250C.

40. A composition as claimed in claim 39, wherein the ether has a viscosity below l5mPa.s at 250C.

41. A composition as claimed in any one of claims 37 to 40, wherein the ether has a vapour pressure at 200C below 2.Ombar.

42. A composition as claimed in claim 41, wherein the ether has a vapour pressure at 200C below l.Ombar.

43. A composition as claimed in any one of claims 30 to 42, further comprising a curing agent.

44. A composition as claimed in claim 43, wherein the curing agent is a polyamine.

45. A composition as claimed in claim 44, wherein the curying agent is an aliphatic polyamine.

46. A composition as claimed in any one of claims 30 to 45, further comprising a wetting agent.

47. A composition as claimed in claim 46, wherein the wetting agent is a fluorinated alkyl ester.

48. A composition as claimed in any one of claims 30 to 47, further comprising an anti-foaming agent.

49. A composition as claimed in claim 48, wherein the anti-foaming agent is a branched chain acrylic compound.

50. A composition as claimed in any one of claims 30 to 34, comprising one or more polyisocyanate prepolymers.

51. A composition as claimed in claim 50, comprising polyisocyanate MDI based prepolymer S blended with polyisocyanate based on diphenyl methane diisocyanate.

52. A composition as claimed in claim 50 or 51, containing an accelerator.

53. A composition as claimed in claim 50, 51 or 52, wherein the polymer composition is blended with solvent free polymers selected from branched polyalcehols with ester and ether groups, hydroxyl bearing polyesters, polyols, polyethers and polyisocyanates.

54. A composition for use in treating cememtitious layers substantially as hereinbefore described with reference to any one of the foregoing Examples.

55. A cementitious layer treated by a method according to any one of Claims 1 to 29.

56. A cementitious layer treated with a composition as claimed in any one of claims 30 to 54.