GB2441999A

GB2441999A - A concrete building block containing crushed glass

Info

Publication number: GB2441999A
Application number: GB0610156A
Authority: GB
Inventors: Gary Bell
Original assignee: Brand & Rae Ltd
Current assignee: Brand & Rae Ltd
Priority date: 2006-05-23
Filing date: 2006-05-23
Publication date: 2008-03-26
Also published as: GB0610156D0

Abstract

A concrete building block is prepared from a mixture comprising cement; water; coarse aggregate; and fine aggregate; wherein the fine aggregate comprises dust and crushed glass. The crushed glass may be present in an amount of up to 45% by weight, without the addition of furnace ash. The use of glass in an amount greater than 45% by weight requires the presence of furnace ash. The blocks exhibit improved compressive strength, reduced shrinkage and improved weather resistance. Also described is a method of preparing the afore described block comprising the steps of preparing a mixture of coarse aggregate, dust and crushed glass, adding cement to the mixture, adding water to the mixture, coating the mixture in a mould and curing the block. The water may be added to the mixture over a period of time. The blocks may be cured at ambient condition. Also disclosed is a building block prepared from a mixture comprising cement, water, coarse aggregate and crushed glass, the crushed glass being present in an amount of from 10-45% by weight.

Description

CONCRETE BUILDING BLOCK AND METHOD FOR PRODUCING THE

SAME

The present invention relates to concrete building blocks and to a method for producing the same.

Concrete has been known as a material for use in construction for many years. One form in which concrete is employed as a constructional material is by way of concrete blocks. Concrete blocks are typically cast, allowed to cure and subsequently shipped to the construction site for use. It is a feature of the components used to prepare concrete blocks that the mixture must have properties suitable to allow the blocks to be formed in a cast or mould and thereafter quickly removed, to allow the cast or mould to be reused. Once removed from the cast or mould, the mixture must allow the block to be free standing and not deform or slump'.

A typical mixture for forming concrete blocks in this way comprises a coarse aggregate, a fine aggregate, such as sand and/or dust, cement and water. An example of a typical mixture of components for forming concrete blocks is as follows: Coarse Aggregate 36.5 wt %; Dust 36.5wt%; Sand 13.5wt%; Cement 6.75 wt %; and Water 6.75wt%.

The present invention is concerned with improved concrete blocks, in particular concrete blocks that have been prepared from a mixture comprising glass. Glass has been proposed for inclusion in concrete materials, in particular concrete blocks.

Thus, GB 558,994 discloses moulded blocks, slabs, tiles or the like made of concrete or artificial stone. The slab, block or tile is formed from a mixture of cement and breeze or clinker, ground into small particles. The mixture may comprise granulated or powdered glass. The objective of this disclosure is to provide a concrete material that can be prepared to resemble natural building stone. The glass appears to be included to meet this objective.

GB 792,639 is concerned with concrete blocks and their production.

The blocks are prepared from a mixture of cement and a ground silica-containing flux. The flux may be any suitable high-silica content material.

Examples of suitable materials are indicated to be arenaceous quartz, fine slag, clay, ground pumice, slate and slate residue, glass powder or fireclay.

The flux is required to be very finely ground.

GB 1,418,056 discloses improvements in concrete building blocks.

The blocks are prepared from a mixture containing glass chips, having a specific particle size of from 1/2 inch to 50 mesh (U.S. sieve size), Portland cement, water and sand and/or gravel. Glass may be present in an amount of up to 60% by weight of the mixture, excluding water. The examples of concrete blocks disclosed in GB 1,418,056 are all prepared from a mixture comprising crushed glass, sand and gravel. GB 1,418,056 indicates that glass is a suitable material for inclusion in concrete blocks and that the glass may be sourced from glass stocks unusable for other purposes. Some increase in compressive strength of the concrete blocks incorporating glass is claimed in GB 1,418,056.

More recently, FR 2,682,413 discloses a lightweight concrete block containing cellular glass granulates and coal fly ash. The blocks are first cast in a mould and then held in a moist atmosphere for an extended period of time.

JP 2000-034,178 discloses a concrete block containing a sintered compact obtained by partially binding granular aggregates through porous crystallized glass. The use of such a compact is alleged to increase mechanical strength.

Perhaps most recently, US 2006/0000172 discloses a lightweight concrete composite block containing polystyrene, cement, water and glass.

The blocks may used to form retaining walls and border is gardens, due to their lightweight and ease of cutting.

With the increased interest in recycling materials, in particular glass, there is a significant quantity of crushed glass as a raw material. The present invention employs crushed glass, in particular recycled glass, in concrete blocks to provide an improved block, having improved properties. The present invention also reduces or removes the need to employ natural resources, in the form of natural aggregates, in the manufacture of concrete blocks for construction. Currently, legislation in many areas requires that any new construction includes a minimum percentage of recycled or recovered materials. For example, certain local authorities require the use of at least 20% recycled materials in any new construction. These minimum levels are set to increase in the short and medium term, increasing the burden on builders to meet the legal requirements for recycled constructional materials.

The present invention is significant in that, in addition to being of improved quality, the concrete blocks provided can contribute significantly to meeting the requirements for using recycled constructional materials.

According to the present invention there is provided, in a first aspect, a concrete building block prepared from a mixture comprising: cement; water; coarse aggregate; and fine aggregate; wherein the fine aggregate comprises: dust and crushed glass.

The concrete block according to the present invention exhibits improved properties compared with comparable blocks prepared using the known components, as discussed above. In particular, it has been found that the concrete blocks exhibit improved compressive strength. In addition, it has been found that concrete blocks according to the present invention exhibit less shrinkage during the manufacturing process, in turn allowing the manufacture of the blocks to be improved and a higher quality block obtained with a greater consistency.

The concrete block of the present invention is prepared from a mixture comprising cement. Suitable cements are well known in the art and commercially available. A particularly suitable cement is Portland cement.

The cement is present in an amount to provide the finished block with the required properties of strength. Preferably, cement is present in the mixture in an amount of from 5 to 10 % by weight of the mixture, more preferably in an amount of from 6 to 8 % by weight.

The water content of the mixture is determined according to principles known in the art. One important aspect of the water content is that the mixture should be easily introduced into the cast or moulds, but be of a sufficient viscosity such that the block does not deform when removed from the mould. This is referred to in the art as slumping'. In general, the mixture will remain in the mould for a short period of time, sufficient to compact the mixture in the mould to the required density. This is typically completed in a time of from 20 seconds to 1 minute. Thereafter, the mould is removed. The mixture should be such that the block does not slump upon removal from the mould.

Conventional aggregate from naturally occurring sources is absorbent and will absorb a portion of the water added to the mixture. This is a known effect and additional water is generally added to the mixture to compensate for the loss of water due to being bound up in the aggregate. However, glass, in particular recycled glass, is not water absorbent. Accordingly, the amount of water present in the mixture may need to be reduced compared with the quantity used with natural aggregates. The amount of water present may need to be decreased as the glass content of the mixture increases.

Suitable ranges of water content for the mixture may be determined for a given combination of components using techniques known in the art and by routine trial and error. The water content of the mixture is preferably in the range of from 5 to 10 % by weight of the mixture, more preferably from 6 to 8 % by weight of the mixture.

Coarse aggregate for use in the concrete block is well known and available commercially. The coarse aggregate is comprised of natural stones, such as quarried stones and gravel. Suitable particle size ranges for the coarse aggregate are known in the art. A preferred size range for the coarse aggregate particles is from 5 to 20 mm, more preferably from 6 to 15 mm.

The amount of coarse aggregate present in the mixture may also be determined using techniques known in the art. Preferably, the coarse aggregate is present in an amount of from 25 to 50 % by weight of the mixture, more preferably in an amount of from 30 to 40 % by weight of the mixture.

In addition to a coarse aggregate, the mixture used in the present invention comprises a finer material, herein referred to as a fine aggregate.

The fine aggregate preferably comprises from 40 to 60% by weight of the mixture, more preferably from 45 to 55 % by weight of the mixture.

The fine aggregate comprises glass and may comprise a combination of materials, in particular dust and glass. The dust as herein referred to is a material having a particle size of 3 mm or less. Suitable dust material for inclusion in the mixture is well known and commercially available in the art. A most suitable dust material is one from a hard rock quarry source. The dust is preferably present in an amount of from 10 to 40% by weight of the mixture, more preferably in an amount of from 15 to 25% by weight of the mixture.

The fine aggregate may include sand as an additional component, 1 5 depending upon the amount of glass to be included. Thus, in one embodiment, the concrete block of the present invention is prepared from a mixture in which sand is present in an amount of from I to 10 % by weight of the mixture.

In an alternative embodiment, sand is absent from the mixture, the sand in a conventional mixture having been completely replaced by glass.

The key ingredient of the concrete block of the present invention is glass. The glass particles may be in the size range of up to 10 mm, more preferably up to 7.5 mm. The lower limit of particle size for the glass is as for the dust component, discussed above. Thus, the glass particles may range in size down to 3 mm or less. The glass component may comprise particles in the range of from ito 10 mm, more preferably from ito 7.5 mm. Glass with particles in the range of from 1 to 6 mm has been found particularly suitable.

Glass may be obtained from any suitable source and commercial particulate glass products are available. A particularly preferred glass component is recycled glass, in particular glass that has been obtained from the crushing of recycled bottles and the like. The properties of recycled glass have been found to be particularly well suited to providing the improved concrete blocks of the present invention.

The mixture may contain glass in any suitable amount. In one embodiment, the glass is present in an amount of from 5 to 45 % by weight of the mixture, more preferably in an amount of from 10 to 45% by weight of the mixture. It has been found that glass present in a concrete mixture undergoes degradation due to contact with cement. The degradation arises as a result of the reaction between the silica component of the glass and the alkali components in the cement. Such reactions are known in the art to occur between other siliceous materials and cement. To counter the alkali-silica reactions, it is known to include a component such as pulverized fuel ash (PFA), available as a residue from furnaces and the like after combustion of fuels (hereafter referred to as furnace ash in the present specification). It has been found that glass may be present in the mixture in an amount of up to 45% by weight, without any degradation occurring due to the alkali-silica reaction. Accordingly, with glass present in an amount of up to 45%, the concrete block may be prepared without the addition of furnace ash.

In an alternative embodiment, glass is present in an amount of greater than 45% by weight of the mixture, the mixture further comprising furnace ash.

The furnace ash is present in an amount sufficient to prevent the alkali-silica reaction occurring.

It has further been found that glass, in particular recycled glass is cementitious, when present in the mixture. Accordingly, the presence of glass may allow the amount of cement used to be reduced, compared with a mixture of conventional components. In this way, glass may act as a so-called cement saver'.

As noted hereinbefore, glass, in particular recycled glass, does not absorb water. This property renders the resulting concrete block less susceptible to damage by the action of weather, in particular frost.

Accordingly, the concrete blocks of the present invention are particularly well suited to exterior constructional applications, in particular in climates where sub-zero temperatures are encountered.

In a further aspect, the present invention provides a method of preparing a concrete block comprising the steps of: preparing a mixture of coarse aggregate, dust and crushed glass; adding cement to the mixture; adding water to the mixture; casting the mixture in a mould to form a block; and curing the block.

The mixing of the components is a conventional and well known step in the preparation of concrete blocks. In particular, the coarse and fine aggregates are first combined, after which cement is added to the resulting mixture. Finally, water is added to the required consistency and amount. In order to control the properties of the mixture, which may vary depending upon the composition, as described hereinbefore, the water is preferably added over a period of time or metered' into the mixture. This may be carried out either continuously or batchwise.

The mixture is introduced into a mould of the required shape and the contents of the mould compacted, to achieve the required density. Thereafter, the block is removed from the mould, at which point the mixture much be such that the block is free standing and free from slumping.

The blocks are then cured. This is preferably carried out at ambient conditions of temperature1 pressure and humidity. Typically, the blocks are left exposed to the ambient air for the required curing period. This is typically from 12 to 48 hours, more preferably about 24 to 36 hours.

Once cured, the blocks are ready for use.

As noted hereinbefore, it has been found that concrete blocks may comprise up to 45% by weight of glass, without degrading due to the alkali-silica reaction. Accordingly, in a further aspect, the present invention provides a concrete building block prepared from a mixture comprising: cement; water; coarse aggregate; and crushed glass, the crushed glass being present in an amount of from to 45 % by weight.

The components of the mixture are as hereinbefore described. It is of particular note that the concrete block of this aspect of the invention may be prepared without the use of furnace ash as a component.

A similar concrete block may be prepared with a glass content of greater than 45 % by weight of the mixture, provided the mixture further comprises furnace ash.

A further aspect of the present invention provides a concrete building block prepared from a mixture consisting of: cement; water; coarse aggregate; dust; and crushed glass.

The components of the mixture are as hereinbefore described.

Embodiments of the present invention will now be described by way of the following examples.

EXAMPLE 1

A concrete block was prepared from the following components: Coarse Aggregate 36.5 wt %; Dust 36.5wt%; Crushed glass 10.0 wt % Sand 3.5wt%; Cement 6.75 wt %; and Water 6.75wt%.

The block was prepared using the following procedure: The coarse aggregate, dust and crushed glass were dispensed into a conventional mixer and mixed until a uniform mixture was obtained. The cement was added, with further mixing. Finally, the water was added continuously by metering over a period of time, while controlling the properties of the mixture.

The resulting mixture was dispensed into a hopper, from where it was poured, under the action of vibration, into a block mould. The mixture was compacted in the mould. The mould was then removed and the block was cured at ambient conditions for from 24 to 36 hours.

The block exhibited no slumping when first removed from the mould.

The block cured with minimal shrinkage. A constructional block having excellent properties was produced.

EXAMPLE 2

A concrete block was prepared from the following components: Coarse Aggregate 36.5 wt %; Dust 20.Owt%; Crushed glass 30.0 wt % Cement 6.75 wt %; and Water 6.75wt%.

The block was prepared using the procedure described in Example 1.

No slumping was detected when the block was removed from the mould.

The block cured with minimal shrinkage. An excellent constructional block was produced.

COMPARATIVE EXAMPLE

For comparison purposes, a concrete block was prepared from the following components: Coarse Aggregate 36.5 wt %; Dust 36.5wt%; Sand 13.5wt%; Cement 6.75 wt %; and Water 6.75wt%.

The block was prepared using the procedure outlined in Example 1, with the sand taking the place of the crushed glass.

The block exhibited an increased shrinkage during curing, compared with the blocks prepared in both Examples 1 and 2. While the block exhibited good constructional properties, the block had a lower compressive strength, compared with the blocks prepared in both Examples 1 and 2.

Claims

1. A concrete building block prepared from a mixture comprising: cement; water; coarse aggregate; and fine aggregate; wherein the fine aggregate comprises: dust and crushed glass.

2. A concrete block according to claim 1, wherein the cement is Portland cement.

3. A concrete block according to either of claims 1 or 2, wherein the cement is present in an amount of from 5 to 10 % by weight of the mixture.

4. A concrete block according to claim 3, wherein the cement is present in an amount of from 6 to B % by weight of the mixture.

5. A concrete block according to any preceding claim, wherein the water is present in an amount of from 5 to 10 % by weight of the mixture.

6. A concrete block according to claim 5, wherein the water is present in an amount of from 6 to 8 % by weight of the mixture.

7. A concrete block according to any preceding claim, wherein the coarse aggregate is present in an amount of from 25 to 50 % by weight of the mixture.

8. A concrete block according to claim 7, wherein the coarse aggregate is present in an amount of from 30 to 40 % by weight of the mixture.

9. A concrete block according to any preceding claim, wherein the fine aggregate further comprises sand.

10. A concrete block according to claim 9, wherein sand is present in an amount of from 1 to 10 % by weight of the mixture.

11. A concrete block according to any of claims 1 to 8, wherein sand is absent from the mixture.

12. A concrete block according to any preceding claim, wherein the fine aggregate is from 40 to 60% by weight of the mixture.

13. A concrete block according to any preceding claim, wherein dust is present in an amount of from 10 to 40% by weight of the mixture.

14. A concrete block according to claim 13, wherein dust is present in an amount of from 15 to 25% by weight of the mixture.

15. A concrete block according to any preceding claim, wherein the glass is recycled glass.

16. A concrete block according to any preceding claim, wherein the glass is present in an amount of from 5 to 45 % by weight of the mixture.

17. A concrete block according to claim 16, wherein the glass is present in an amount of from 10 to 45% by weight of the mixture.

18. A concrete block according to either of claims 15 or 16, wherein the mixture does not comprise furnace ash.

19. A concrete block according to any of claims Ito 15, wherein glass is present in an amount of greater than 45% by weight of the mixture, the mixture further comprising furnace fly ash.

20. A method of preparing a concrete block comprising the steps of: preparing a mixture of coarse aggregate, dust and crushed glass; adding cement to the mixture; adding water to the mixture; casting the mixture in a mould to form a block; and curing the block.

21. The method according to claim 20, wherein the water is added to the mixture over a period of time, while mixing.

22. The method according to claim 21, wherein the water is added either continuously or batchwise.

23. The method according to any of claims 20 to 22, wherein blocks are cured at ambient conditions.

24. The method according to any of claims 20 to 23, wherein the blocks are cured for from 12 to 48 hours.

25. The method according to claim 24, wherein the blocks are cured from 24 to 36 hours.

26. A concrete building block prepared from a mixture comprising: cement; water; coarse aggregate; and crushed glass, the crushed glass being present in an amount of from to 45 % by weight.

27. A concrete block according to claim 26, wherein the cement is Portland cement.

28. A concrete block according to either of claims 26 or 27, wherein the cement is present in an amount of from 5 to 10 % by weight of the mixture.

29. A concrete block according to claim 28, wherein the cement is present in an amount of from 6 to 8 % by weight of the mixture.

30. A concrete block according to any of claims 26 to 29, wherein the water is present in an amount of from 5 to 10 % by weight of the mixture.

31. A concrete block according to claim 30, wherein the water is present in an amount of from 6 to 8 % by weight of the mixture.

32. A concrete block according to any of claims 26 to 31, wherein the coarse aggregate is present in an amount of from 25 to 50 % by weight of the mixture.

33. A concrete block according to claim 32, wherein the coarse aggregate is present in an amount of from 30 to 40 % by weight of the mixture.

34. A concrete block according to any of claims 26 to 33, wherein the fine aggregate further comprises sand.

35. A concrete block according to claim 34, wherein sand is present in an amount of from 1 to 10 % by weight of the mixture.

36. A concrete block according to any of claims 26 to 35, wherein sand is absent from the mixture.

37. A concrete block according to any of claims 26 to 36, wherein the glass is recycled glass.

38. A concrete block according to any of claims 26 to 37, wherein the mixture does not comprise furnace ash.

39. A concrete building block prepared from a mixture consisting of: cement; water; coarse aggregate; dust; and crushed glass.

40. A concrete block according to claim 39, wherein the glass is recycled glass.

41. A concrete block according to either of claims 39 or 40, wherein the glass is present in an amount of from 5 to 45 % by weight of the mixture.

42. A concrete block according to claim 41, wherein the glass is present in an amount of from 10 to 45% by weight of the mixture.

43. The use of recycled glass as an aggregate in a concrete block, the glass being present in an amount of up to 45 % by weight of the block.

44. A concrete block substantially as hereinbefore described.

45. A method of preparing a concrete block substantially as hereinbefore described.