WO2002022519A1

WO2002022519A1 - Cast concrete products having exposed glass aggregate and process for the manufacture of the same

Info

Publication number: WO2002022519A1
Application number: PCT/GB2001/004071
Authority: WO
Inventors: Garry Mcbride
Original assignee: Evans Concrete Products Limited
Priority date: 2000-09-15
Filing date: 2001-09-12
Publication date: 2002-03-21
Also published as: GB2375348A; GB0022788D0; GB0213845D0; AU2001287854A1; GB2375348B

Abstract

A method is disclosed for the production of a cast concrete product having a homogeneous composition. A cementitious mixture is formed of cement, water and aggregate consisting at least in part of fragmented glass, and a mould is provided in the shape of the product to be cast. The cementitious mixture is introduced into the mould and the mixture is allowed to cure so as to form the cast product. The cast product is removed from the mould and fragmented glass is exposed at at least part of the surface.

Description

CAST CONCRETE PRODUCTS HAVING EXPOSED GLASS AGGREGATE AND PROCESS FOR THE MANUFACTURE OF THE SAME

This invention relates to a process for the manufacture of concrete products and to novel concrete products produced by that process.

Concrete is a widely used material in the construction industry. It consists essentially of cement, water and fine and coarse "aggregates". The aggregate can be any of a variety of particulate materials such as sand, gravel etc. Whilst the primary function of the aggregate is to contribute to the bulk of the concrete, in the case of concrete products manufactured by a casting process, the aggregate may be visible or exposed at the surface of the product to a greater or lesser degree, and this may confer a decorative effect on the product. Whilst a range of aggregates can be used, and these give quite a wide range of decorative appearances, these differ principally only in the size of the aggregate particles and to a certain extent their colour. The range of appearances which can be achieved is more limited than might be desired.

The decorative appearance of cast concrete products may also be modified by the incorporation of pigments. However, the range of pigments that is available is limited and certain colours are particularly difficult to obtain. Blue is one example of a colour for which a suitable pigment for concrete is not economically available.

It is also known to manufacture cast concrete products having decorative surface finishes, including exposed aggregate. However, such methods commonly employ different mixtures of materials for the bulk and surface regions of the product and are thus of inhomogeneous composition.

There has now been devised a process for the manufacture of concrete products that overcomes or substantially mitigates the above-mentioned or other disadvantages associated with the prior art. According to the invention, there is provided a method for the production of a cast concrete product having a homogeneous composition, which method comprises a) forming a cementitious mixture of cement, water and aggregate consisting at least in part of fragmented glass; b) providing a mould in the shape of the product to be cast; c) introducing the cementitious mixture into the mould and allowing the mixture to cure so as to form the cast product; d) removing the cast product from the mould; and e) exposing fragmented glass at at least part of the surface of the cast product.

The method according to the invention is advantageous primarily in that it yields a cast concrete product having a novel and attractive decorative appearance. The glass fragments confer on the product a three-dimensional surface and an appearance quite different to known concrete products. As such, the product is of distinctive and attractive appearance and lends itself to applications in which the visual appearance of the product is significant.

The fragmented glass may be obtained from any convenient source. However, it is particularly preferred to use recycled scrap glass, eg bottle scrap. Such scrap glass is readily and inexpensively available, eg from bottle banks and other recycling centres. The reuse of such glass for conventional applications is often uneconomic. The use of such glass in the performance of the invention therefore consumes otherwise unusable glass, with corresponding environmental benefits. Furthermore, scrap glass is sorted by colour and is therefore available in a number of distinct and reasonably consistent colours. One such colour is blue, which is the very colour that is not normally attainable in concrete products.

Because the glass fragments are exposed at the surface of the finished cast concrete product, in applications in which the surface may be accessible to, for instance, members of the public it may be desirable or necessary for safety reasons for sharp edges of the glass fragments to be removed prior to use. This may be achieved by tumbling of the glass, eg in a rotating drum, to give the fragments a rounder form with fewer or no sharp edges or points.

By the product having a "homogeneous" composition is meant that the product is formed from a single cementitious mixture, rather than different mixtures for the surface regions and the bulk interior of the product.

One method of exposing the fragmented glass involves the use of a substance effective to retard curing of the cementitious mixture. Such a substance may be applied to the internal surface of the mould (or at least to that part of the mould surface corresponding to the part of the cast product at which it is desired for the fragmented glass to be exposed) prior to introduction of the cementitious mixture.

The substance effective to retard curing of the cementitious mixture may be any substance known to have such an effect. Examples of suitable retarding substances are commercially available and marketed for this purpose.

The retarding substance is coated on the surface of the mould corresponding to the surface of the finished cast product on which it is desired for the glass fragments to be exposed. The retarding substance may be applied by painting on or spraying the relevant mould surface.

After withdrawal of the cast product from the mould, the uncured cementitious mixture can be removed by any suitable means, eg by washing, preferably using a jet of water under pressure. After sufficient mixture has been removed to sufficiently expose the glass fragments at the surface of the product , the product may be allowed to stand for a further period of time in order that complete curing is effected.

Another method of exposing the fragmented glass involves etching of the concrete by the application of a suitable etching agent to the surface of the product after removal from the mould. Such agents include acids, a particularly preferred acid being hydrochloric acid.

Most preferably, the etching agent is painted onto the surface of the cast product, eg by brushing (rather than the product being dipped or immersed in a bath of etching agent). This permits greater control over the degree of etching that is achieved, and so enables the optimum surface effect to be attained.

The process according to the invention may be used for the manufacture of cast concrete products having an almost limitless variety of forms. Examples of products which may be produced are kerb stones, bollards and other products intended for installation in such a way that at least a part of their surface is visible and of decorative significance. Other such products include paving slabs, coping stones, tiles, cladding panels and building facades.

Where, as is particularly preferred, the glass fragments are blue, or contain substantial proportions of blue fragments, the concrete products may be particularly suitable for use in environments associated with water. Examples are swimming pools, marinas, fountains etc.

Equally attractive effects can however also be achieved using glass fragments of other colours, including other colours realisable using scrap glass, eg brown, green or clear glass, all of which are available as bottle scrap.

A wide range of sizes of glass fragments may be used in the invention. However, it is found that a particularly attractive effect may be achieved by the use of glass fragments having a size of the order of 10mm. Thus, it is preferred that the aggregate comprise glass fragments, a major proportion of which have maximum dimensions in the range 3 to 20mm, particularly 5 to 15mm. By "a major proportion" is meant at least 50% by weight of the glass fragments, more preferably at least 70% by weight. The glass fragments may be produced by crushing of the raw glass (eg bottles or broken bottles) in a suitable mechanical crushing machine. Obviously, the final size distribution of the glass will depend on the precise nature of the crushing machine, the time for which it is operated etc. By appropriate choice of operating conditions in general any desired particle size distribution may be achieved.

Although it is preferred to use at least a substantial proportion of glass fragments having the relatively large dimensions referred to above, ie sizes of the order of 10mm, it may be advantageous to mix such fragments with finer glass particles, which may be so fine as to be considered to be dust. Such dust may be the product of the tumbling process referred to above for the elimination of distinct sharp edges from the glass fragments.

The glass fragments may be irregularly shaped, and indeed a heterogeneity of the glass fragments, both in terms of size and shape may add to the attractiveness of the surface appearance of the finished cast product.

Although the benefits of the invention are described herein primarily in relation to the decorative effects that can be achieved, the incorporation of glass fragments into the cast product may also have other advantages. For instance, the glass may confer enhanced reflective properties on the product, which may be of benefit in certain applications. Also, the glass (being, like sand, a silica-based material) is chemically very compatible with the other components of the cementitious mixture.

According to a further aspect of the invention there is provided a cast concrete product formed from a cementitious mixture comprising cement, water and aggregate material consisting at least in part of glass fragments of which a major proportion have maximum dimensions in the range 3 to 20mm, glass fragments being exposed over at least a part of the external surface of the cast concrete product. By the glass fragments being "exposed" is meant that the glass fragments at the surface, whilst being embedded in the concrete matrix, stand proud of the surface of the product so that the surface has a three-dimensional relief profile.

The aggregate may consist entirely of the glass fragments. Alternatively, the glass fragments may be mixed with other aggregate materials. Such materials may be sand, gravel or other conventional aggregate materials.

Apart from the use of glass fragments as the aggregate, or as a component of the aggregate, the composition of the cementitious mixture may be generally conventional.

The cement used in the invention, and sand and other aggregate components (if any) other than glass may be similar or identical to those conventionally used in the manufacture of cast concrete products.

The invention will now be described in greater detail, by way of illustration only, with reference to the following Example.

Manufacture of a tile

Components : 1.5 parts 10mm Spanish Dolomite

0.5 parts 10mm recycled glass fragments 2.0 parts 0.3mm Spanish Dolomite fines 1.0 parts White Castle Cement

The above materials are blended, and water is added to the mix in a 0.5 water/cement ratio. The mixing process is continued until the mix is sufficiently constant.

The appropriate volume of concrete is introduced into a mould of appropriate form and dimensions, which is pre-coated with a mould release oil. As the mix is placed within the mould, vibration takes place to ensure compaction and air displacement. The concrete is finally trowelled off to its required level and stood until set.

Once the concrete tile has set to a satisfactory strength, it is stripped from the mould.

One major face of the cast tile is finally washed off with 28% hydrochloric acid in water. This process etches the concrete and exposes the glass fragments and other aggregate to the depth of choice.

Claims

1. A method for the production of a cast concrete product having a homogeneous composition, which method comprises a) forming a cementitious mixture of cement, water and aggregate consisting at least in part of fragmented glass; b) providing a mould in the shape of the product to be cast; c) introducing the cementitious mixture into the mould and allowing the mixture to cure so as to form the cast product; d) removing the cast product from the mould; and e) exposing fragmented glass at at least part of the surface of the cast product.

2. A method as claimed in Claim 1 , wherein the fragmented glass is obtained from recycled scrap glass.

3. A method as claimed in any preceding claim, wherein the fragmented glass is tumbled in a rotating drum prior to formulation of the cementitious mixture.

4. A method as claimed in any preceding claim, wherein the fragmented glass is exposed using a substance effective to retard curing of the cementitious mixture.

5. A method as claimed in Claim 4, wherein the retarding substance is applied to at least part of the internal surface of the mould prior to introduction of the cementitious mixture.

6. A method as claimed in Claim 5, wherein the retarding substance is applied by painting on or spraying the relevant mould surface.

7. A method as claimed in any one of Claims 4 to 6, wherein the uncured cementitious mixture is removed using a jet of water under pressure.

8. A method as claimed in any one of Claims 1 to 3, wherein the fragmented glass is exposed by the application of an etching agent to the surface of the product after removal from the mould.

9. A method as claimed in Claim 8, wherein the etching agent is an acid.

10. A method as claimed in Claim 9, wherein the etching agent is hydrochloric acid.

11. A method as claimed in any one of Claims 8 to 10, wherein the etching agent is painted onto the surface of the cast product.

12. A method as claimed in any preceding claim, wherein a major proportion of the fragmented glass has maximum dimensions in the range 3 to 20mm.

13. A method as claimed in any preceding claim, wherein a major proportion of the fragmented glass has maximum dimensions in the range 5 to 15mm.

14. A method as claimed in any preceding claim, wherein the fragmented glass is produced by crushing raw glass in a mechanical crushing machine.

15. A method as claimed in any preceding claim, wherein the fragmented glass is irregularly shaped.

16. A cast concrete product formed from a cementitious mixture comprising cement, water and aggregate material consisting at least in part of glass fragments of which a major proportion have maximum dimensions in the range 3 to 20mm, glass fragments being exposed over at least a part of the external surface of the cast concrete product.

17. A cast concrete product as claimed in Claim 16, wherein the aggregate consists entirely of the glass fragments.

18. A cast concrete product as claimed in Claim 16, wherein the glass fragments are mixed with sand, gravel or other conventional aggregate materials.

19. A cast concrete product as claimed in any one of Claims 16 to 18, wherein a major proportion of the glass fragments have maximum dimensions in the range 5 to 15mm.

20. A cast concrete product as claimed in any one of Claims 16 to 19, wherein the glass fragments are irregularly shaped.