GB2201104A

GB2201104A - Concrete units

Info

Publication number: GB2201104A
Application number: GB08802807A
Authority: GB
Inventors: Allan John Dowson
Original assignee: Marshalls Mono Ltd
Current assignee: Marshalls Mono Ltd
Priority date: 1987-02-07
Filing date: 1988-02-08
Publication date: 1988-08-24
Anticipated expiration: 2008-02-08
Also published as: GB2201104B; GB8802807D0; GB8702813D0

Abstract

In a continuous process, concrete paving flags 3 are transported by a continuous conveyor 2 through a first spray station 4, where a primer coat followed by a plurality of different colour paint coats are applied to the upper surface of the flags 3. At least one of the other coats is discontinuous, to provide a shaded effect. After passing through a first drying station 5, the flags 3 enter a second spray station 6, where a layer of clear polymer is applied, and this is subsequently cured in a second drying station 7. Thus, the concrete paving flags are provided with a decorative coating comprising the shaded paint coats, and the clear polymer layer imparts a shiny appearance to the paving flags 3. <IMAGE>

Description

CONCRETE UNITS This invention relates to concrete units, and is concerned particularly although not exclusively with the manufacture of precast concreta.)pavlng flags and blocks.

There are many known methods of producing concrete flags with flat, textured or profiled surfaces.

In addition to being produced in a conventional grey colour, concrete flags are now ten produced in various different colours, with the aid of suitable pigments.

However, they inevitably have a rather dull appearance.

The present invention is concerned with producing concrete units which have a relatively shiny appearance.

Preferred embodiments of the present invention aim to provide concrete paving flags to which there is applied a decorative coating which gives both an enhanced effect of a textured surface, together with an attractive shiny appearance.

According to one aspect of the present invention,.

there is provided a method of applying a decorative coating to a concrete paving flag, comprising the steps of: spray applying a coat of. rimer paint to the surface of the flag; spray applying a plurality of coats of different coloured paints to the surface of the flag, on top of the primer coat, at least one of said coats of different coloured paints being discontinuous, so as to create an effect of varying shades of colours; applying heat to the surface of the flag to cause at least partial drying of said coats of paint; spray applying a coat of a translucent polymer to the surface of the flag, on top of said coats of paint; and applying heat to the surface of the flag to cause at least partial drying of said coat of polymer, so as to impart a shiny appearance to the paving flag.

The surface of the paving flag may be textured.

The steps of applying heat may comprise passing the coated flags under infra-red heating means.

The method is preferably carried out as a continuous process, whereby a succession of said flags are conveyed successively through a first spray station where said coats of primer and different coloured paints are applied, a first drying station where the paints applied at the first spray station are at least partially dried, a second spray station where said coat of polymer is applied, and a second drying station where the polymer applied at the second spray station is at least partially dried.

/ Said coats of different coloured paints may be applied by robotic spray devices programmed to apply predetermined spray patterns to the surface of each successive flag.

The polymer may be an acrylic polymer or an epoxy polymer, or a co-polymer of one or more of these.

According to another aspect of the present invention, there.is provided a concrete unit having on at least one surface a translucent polymer layer which imparts a permanent "wet-look" appearance to the unit.

In a further aspect, the invention provides a method of manufacturing a concrete unit, including the step of forming on at least one surface of the unit a translucent polymer layer which imparts a permanent "wetlook" appearance to the unit.

The polymer may be, for example, an acrylic polymer or an epoxy polymer.

The polymer layer may be on one surface only of the unit. The layer may be applied to at least the upper surface of the unit.

The layer of polymer may be formed, at least partly, by incorporating polymer in a wet concrete mix and, during formation of the unit, causing the polymer to settle out as a liquid surface layer.

The polymer layer may be formed, at least partly, by applying the polymer as an external coat to the unit, after the unit has been formed. The unit may be dried, for example, by the application of a flame, prior to the application of the external polymer coat.

The layer of polymer may incorporate a grit, to afford an anti-slip finish.

A plurality of layers of differing polymers may be applied to the or each respective surface of the unit, to build up a decorative pattern.

For a better understanding of the invention and to show how the same may be carried into effect, some examples will now be given.

Example 1 Concrete flags are manufactured, following the known "wet cast" method, but with variations to produce concrete flags embodying the invention.

Firstly, a wet concrete mix is prepared, having an aggregate to cement ratio in the-range 4:1 to 6:1, and a water to cement ratio in the range 0.4 to 0.6.

Into this wet mix, there is introduced an additive of an acrylic polymer emulsion, having a proportion to the total mix in the range 1% to 6% w/v.

Examples of suitable acrylic polymer emulsions are the products sold by the company B.A.S.F. under the trade name ACRONAL (Registered Trade Mark) - e.g. ACRONAL S 600 or ACRONAL 1050. There are known already as concrete additives for various purposes, such as -increased physical strength, abrasion resistance and low water penetration. However, the known practice with such an additive is to incorporate it homogeneously in the wet mix.

The wet mix, together with the acrylic polymer additive, is placed into moulds, which are then vibrated to remove air and to consolidate the concrete. Usually, this would be carried out in such a way as to retain a thoroughly homogeneous mix. However, in contrast to this, the vibration of the moulds is carried out in such a controlled manner as to produce an upper surface layer of liquid, which is relatively zurich in the acrylic polymer emulsion. Operatives skill in the operation of mould vibration are generally aware of the manner in which the amplitude and frequency of vibration must be modified in order to achieve & homogeneous mix or, conversely, a liquid phase on the upper surface, and so further details of this are not given here.

After vibration, the concrete is allowed to set in the normal way. For example, the concrete mix may be left in the moulds for sixteen hours or more, until the concrete has hardened.

Thereafter, the flags are demoulded, and left to cure fully for an appropriate length of time - for example, about fourteen to twenty-eight days. During this final curing process, the flags may be stacked upon one another, but so spaced as to provide air gaps between the flags, to enable the water in the flags to evaporate.

When the flags have been sufficiently cured in this way, they are subject to a further external application of an acrylic polymer coating. This may be applied, for example, by handbrush or by spraying. The polymer coating may be what is known as a "single pack system" (that is, an air cured,^solvent or water-based material), or what is known aSa zapNtwo pack system" (namely a chemically cured system, using an iso-cyanate catalyst).

When the concrete flags first harden in their moulds, the surface layer of polymer remains as a translucent layer, which affords a degree of gloss to the flags. Thus, the flags have a "wet look" appearance, in which their surfaces have the enhanced shininess that is apparent when concrete is wetted.

This wet look effect is further enhanced by the subsequent external coating of polymer, which affords a higher degree of gloss.

Example 2 Concrete flags are manufactured using a wet face, dry back manufacturing method - for example that known as the "HERMATIC" principle.

In such a method, there is used special automatic machinery having sealed moulds, which prevent escape of fines and water.

A wet concrete mix is prepared, using a fine aggregate composition (e.g. of quartzite), with an aggregate to cement ratio in the range 3:1 to 5:1, and a water to cement ratio in the range 0.6 to 0.9.

The wet m-ix is placed in the moulds of the machinery to a thickness of at least 12mm, and vibrated as usual.

The moulds are then topped up with a relatively dry backing mix (for example, having an aggregate to cement ratio in the range 3:1 to 6:1, and a water to cement ratio in the range 0.3 to 0.35).

The two mixes are then consolidated in the moulds by the applicatio.. of pressure, during which water is driven from the wet layer to the dry layer.

The flags can then be immediately demoulded, and stood to cure fully - for example for fourteen to twentyeight days - generally as set forth in Example 1 above.

After sufficient curing, an external polymer coating is applied to the hardened flag, in a similar manner to that described in Example 1 above.

Optionally, a proportion (e.g. 1% to 6% w/v) of polymer emulsion may be incorporated in the wet concrete mix, prior to moulding. This method, however, does not lend itself to the formation of a liquid surface layer as in Example 1, but the addition of polymer emulsion in the wet mix can help to improve bonding of the subsequent external polymer coating.

Example 3 Concrete flags are manufactured in accordance with the "wet press" method, which uses special automatic machinery to produce hydraulically pressed flags.

A very wet concrete mix is prepared, having an aggregate to cement ratio in the range 4:1 to 8:1, and a water to cement ratio in the range 0.8 to 1.0.

The wet mix is dispensed into moulds, where it is dewatered under pressure.

The concrete flags which are thus formed are then demoulded immediately, following which they may optionally be sprayed with a polymer emulsion. - The flags are then stacked (with air gaps therebetween) and allowed to harden - for example for about 16 hours.

After this initial curing stage, the flags are left to continue curing, for example for a period of fourteen to eighteen days. Thereafter, they are brought into a controlled environment (for example, a ventilated and/or heated shed) for a period of time (e.g. seven days), to ensure that the surfaces of the flags are dry.

Each flag is then passed under a hot flame into a drying chamber, which dries the surface thoroughly and removes any latent dust. The surface temperature of the flags may be thus raised to a temperature of the order of 500C.

The flags are then allowed to cool slightly (e.g.

to around 250C), and then passed under a spray (for example a spray bar or moving jet), which spray applies a polymer coating. The polymer coating is allowed to cure (either naturally, which may take around two hours, or in a controlled drying environment), following which the flags are then restacked.

The external polymer coating provides a translucent surface layer which, as in the preceding Examples, imparts a permanent "wet look" appearance to the surface of the flags.

As an alternative to the preceding steps, following demoulding, the flags may be stacked (with airgaps) and allowed to harden and cure for a relatively short period - e.g. two to four days. Thereafter, the surface to be coated may be dried (e.g. by a hot air stream), depending on the condition of the flags. A first polymer layer may then be applied (e.g. by spray), and then cured relatively quickly (e.g. within about three minutes) by the application of heat. One or more further layers may then be applied, either immediately, or at a later, convenient time. Typically, such flags may still require additional time (e.g. fourteen to twenty-eight days) to cure fully.

In all of the above Examples, a decorative pattern may be built up on the surface of the flags, during the application of an external polymer coating.

For example, prior to applying a final coat of clear polymer, there may firstly be applied to the surface of the flags one or more polymer coatings incorporating pigments, to give coloured effects. Such coatings may be applied with varying thicknesses, to provide a "shadow" effect on the surface of the flags.

Where a plurality of layers of polymer are applied, it is desirable to allow each layer to cure, prior to the application of the next. Each polymer-layer may be allowed to cure naturally. Alternatively, curing of each polymer layer may be assisted by the application of external heat, and/or by forced air circulation (heated or otherwise).

An enhanced decorative effect may also be obtained by producing the flags themselves with an inherent mottled effect before applying any external coatings - for example, by using two or more differently coloured concretes in the initial wet mix.

Although the above Examples mention the use of acrylic polymer layers, it is possible to use polyurethane or epoxy materials instead. For example, one suitable material is an epoxide.resin protective coating, sold under the name EPISEAL by the company Nufins Limited.

Although in each case the concrete flags are provided with a permanent "wet look" appearance, this may have either a very high gloss finish or a relatively matt finish, as desired. If it is desired to provide an antislip finish, then a suitable grit such as fine silica sand (e.g. 75 micron) or aluminium oxide may be added to the polymer.

A method of applying a decorative coating to a concrete paving flag will now be described, by way of example, with reference to the accompanying diagrammatic drawing, in which: Figure 1 is a schematic representation of apparatus for carrying out a continuous process; and Figure 2 is a sectional view of a concrete paving flag produced by the apparatus of Figure 1.

The illustrated apparatus 1 comprises a continuous conveyor 2, which operates continuously to convey a succession of concrete paving flags 3 through a first spray station 4, a first drying station 5, a second spray station 6 and a second drying station 7. By way of example, the conveyor 2 may travel at a regular speed of 6 metres per minute, and the paving flags 3 may have a dimension of about 1 metre square.

The paving flags 3 are continuously loaded onto the conveyor 2. Preferably, the flags have a textured or sculptured upper surface. The paving flags 3 may also be pigmented with one or more colours - at least in the region of their upper surface.

The paving flags 3 are conveyed into the first spray station 4, where there is firstly spray applied to their upper surface a coat of prime paint, which seals the upper surface of the flags 3.

Immediately thereafter, still ' within the spray station 1, the upper surface of the flags 3 is coated by two or more coats of different coloured paints, on top of the primer coat, at least one of the different coloured coats of paint being discontinuous, so as to create on the upper surface of the flags 3 an effect of varying shades of colours. Preferably, the different coloured paints are spray applied to the upper surfaces of the paving flags 3 by means of robotic spraying devices, which are programmed to apply predetermined spray patterns to the upper surfaces of the flags 3. It is to be noted that such robotic spray devices need not apply exactly the same pattern to each successive flag.

Indeed, the robotic devices may be programmed in such a way as to apply different spray patterns to successive flags, and an element of random spraying may be introduced into the control of the robotic devices.

The primer paint and the subsequent paints of different colours may be water based.acrylic paints.

When the flags 3 have emetteX from the first spray station, they are warm dried by low-frequency infra-red heating elements, contained within the first drying station 5. By the time that the flags 3 emerge from the first drying station5, the primer and successive paint coats are at least--partially dry.

Preferably, they are fully dried within a period of up to thirty seconds.

Upon entering the second spray station 6, the paving flags 3 are coated with a translucent polymer, which is spray applied to the upper surface of the flags 3, on top of the dried coats of paint.

The second drying station 7 is similar to the first, and warm dries the flags by the effect of lowfrequency infra-red heating elements, which are disposed above the path of- the flags 3 on the conveyor 2. The translucent polymer layer is preferably fully cured in up to thirty seconds, as each flag 3 passes through the second drying station 7.

A suitable composition for the translucent polymer is ACRONAL S 600, which is referred to above.

This product is an aqueous dispersion of an acrylate/styrene co-polymer, and contains substances with fungicidal, bactericidal and algicidal effects. An alternative composition is ACRONAL 1050, which is an approximately 50% aqueous dispersion of a co-polymer based on acrylic ester and styrene.

As illustrated in Figure 2, each concrete paving flag 3 is thus provided with a composite layer comprising a base coat 8 of primer, two or more colour coats 9 of paint and a clear coat 10 of polymer.

The shaded effect provided by the discontinuous colour coats 9 creates an impression of depth on the surface of the paving flag 3, and this is enhanced by the shiny surface provided by the clear polymer layer 10, which is preferably of a high gloss. The effect of depth on the upper surface of the paving flag 3 may be enhanced by having the upper surface physically textured, during the manufacture of the concrete flag 3. The colour effect imparted by the colour layers 9 may be enhanced by utilising two or more coloured pigments in the composition of the concrete paving flag 3 itself - at least in the region of its upper surface.

In all of the foregoing examples, there may be provided concrete flags which have a particularly attractive appearance, in that they are provided permanently with the enhanced colour contrast that is apparent when ordinary dull concrete becomes wetted. The above described methods illustrate ways in which such an appearance may readily be provided in a layer which may be very hard wearing and abrasion resistant, using materials which are already available, although traditionally used for different purposes.

The contents of all papers and documents filed concurrently with this specification are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, o-f the steps of any method or process so disclosed.

Claims

CLAIMS:

1. A method of applying a decorative coating to a concrete paving flag, comprising the steps of: spray applying a coat of primer paint to the surface of the flag; spray applying a plurality of coats of different coloured paints to the surface of the flag, on top of the primer coat, at least one of said coats of different coloured paints being discontinuous, so as to create an effect of varying shades of colours; applying heat to the surface of the flag to cause at least partial drying of said coats of paint; - spray applying a coat of a translucent polymer to the surface of the flag, on top of said coats of paint; and applying heat to the surface of the flag to cause at least partial drying of said coat of polymer, so as to impart a shiny appearance to the paving flag.

2. A method according to Claim 1, wherein the surface of said paving flag is textured.

3. A method according to Claim 1 or 2, wherein said steps of applying heat comprise passing the coated flags under infra-red heating means.

4. A method according to Claim 1, 2 or 3, carried out as a continuous prpcess, whereby a succession of said flags are conveyed successively through a first spray station where said coats of primer and different coloured paints are applied, a first drying station where the paints applied at the first spray station are at least partially dried, a second spray station where said coat of polymer is applied, and a second drying station where the polymer applied at the second spray station is at least partially dried.

5. A method according to Claim 4, wherein said coats of different coloured paints are applied by robotic spray devices programmed to apply predetermined spray patterns to the surface of each successive flag.

6. A method according to any of Claims 1 to 5, wherein said polymer is an acrylic polymer.

7. A method according to any of Claims 1 to 5, wherein said polymer is an epoxy polymer.

8. A method of applying a decorative coating to a concrete paving flag, the method being substantially as hereinbefore described with reference to the accompanying drawings.

9. A concrete unit having bion-at least one surface a translucent polymer layer which imparts a permanent "wetlook" appearance to the unit.

10. A concrete unit accord two claim 9, wherein said polymer is an acrylic polymer;

11. A concrete unit according to Claim 9, wherein said polymer is an epoxy polymer.

12. A concrete unit according to any of Claims 9, 10 and 11, wherein said layer is on one surface only of the unit.

13. A concrete unit according to any of Claims 9 to 12, wherein said one surface is an upper surface of the unit.

14. A method of manufacturing a concrete unit, including the step of forming on at least one surface of the unit a translucent polymer layer which imparts a permanent "wet-look" appearance to the unit.

15. A method according to Claim 14, wherein said polymer is an acrylic polymer.

16. A method according to Claim 14, wherein said polymer is an epoxy polymer.

17. A method according to any of Claims 14, 15 and 16, wherein said layer is on one surface only of the unit.

18. A method according to any of Claims 14 to 17, wherein said one surface is an upper surface of the unit.

19. A method according to any of Claims 14, to 18, wherein said layer is formed, at least partly, by incorporating the polymer in a wet concrete mix and, during formation of the unit, causing the polymer to settle out as a liquid surface layer.

20. A method according to any of Claims 14 to 19, wherein said layer is formed, at least partly, by applying the polymer as an external coat to the unit after the unit has been formed.

21. A method according to Claim 20, including the step of drying the unit, prior to the application of said external coat.

22. A method according to Claim 21, wherein said unit is dried by the application of a flame.

23. A method according to any of Claims 14 to 22, wherein said layer incorporates a grit, to afford an anti-slip finish.

24. A method according to any of Claims 14 to 23, wherein a plurality of layers of differing polymers are applied to the or each said surface, to build up a decorative pattern.

25. A method of manufacturing a concrete unit, substantially as described with reference to any of Examples 1 to 3 herein.