GB2327416A

GB2327416A - Cement construction block containing waste plastics

Info

Publication number: GB2327416A
Application number: GB9714998A
Authority: GB
Inventors: John Prigmore; Roman Pobiarzyn
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-07-17
Filing date: 1997-07-17
Publication date: 1999-01-27
Also published as: GB9714998D0

Abstract

A paving slab comprises contaminated recycled plastics waste having an average particle size of e.g. about 1 cm or less, and sand and cement. There may be about 50% recycled plastics material, the balance comprising a mixture of sand and cement. The mixture of sand and cement may comprise about three parts sand and one part cement. The recycled plastics material is e.g. UPVC, polyethylene, polypropylene, polystyrene (expanded or otherwise), ABS or mixtures of such plastics. Chips of the plastics material may give texture to a top face of the slab. Elastomer may be included in the slab to soften it and enhance the grip on its surface.

Description

CONSTRUCTION BLOCK COMPOSITION The present invention relates to construction blocks and more particularly to paving slabs employed in the paving of domestic garden patios and like areas and applications.

Recycling of plastics components is a substantial industry which is important both from an economic perspective and for environmental reasons. Large users of plastics materials such as, for example, UPVC window frame manufacturers, generate a substantial amount of waste in the form of off-cuts. Such waste can be recycled by shredding or pulverising the reclaimed waste and subsequently reusing the granulated or powdered plastic in the formation underground ducting, pipes or other extruded products.

However, the reuse of plastics is limited by the extent of any impurities which find their way into the waste material prior to its use. There are numerous opportunities for such impurities to introduce themselves and it is a persistent problem for the recycling industry to maintain the purity of their end product. Indeed, the result of the need to maintain high levels of product purity results in a considerable quantity of rejected end product which cannot be reused but, instead, has to be scrapped. Thus instead of having a residual value, this plastics can, and frequently does, have a negative value in the cost of disposing of such unusable waste.

Clearly, it is in the interests of the recycling industry to ensure the highest possible standards of purity, but at the same time the costs of achieving such standards, (for example, by extremely careful sorting of the scrap received to eject foreign bodies which will contaminate the final product), has to be balanced against the ultimate value of the end product. The balance that is most economic still leaves a significant quantity of pulverised or granulated plastics which are not saleable by virtue of the impurities which they contain.

Accordingly, it is an object of the present invention to identify an application for such impure recycled pulverised or granulated plastics materials so that the losses incurred through its disposal can be mitigated.

It is well known to construct paving slabs and like construction blocks from concrete having a constitution of three parts sand and one part cement. Such blocks are very satisfactory and serve a wide variety of needs and have various other compositions beyond three parts sand one part cement mentioned above. However, such paving blocks, at least, tend to be very heavy because of the density of the sand and cement, on the one hand, and also tend to be quite brittle unless reinforced. Moreover, sand is not a commodity which is without cost.

It is therefore a further object of the present invention to provide a paving slab which does not suffer from these disadvantages, or at least mitigates their effects.

In accordance with the present invention there is provided a paving slab comprising contaminated particulate recycled plastics waste, and sand and cement.

Preferably the recycled plastics have a particle size of between 8 to 10 mm or less. However, larger sizes may also find application. Preferably the paving slab comprises at least 30%, but not more than 85%, recycled plastics material, the balance comprising a mixture of sand and cement. Preferably the mixture of sand and cement comprises about three parts sand and one part cement.

It has been surprisingly discovered that the presence of small amounts, or even significant amounts, of contaminants in the plastics do not adversely affect the constitution of the paving slabs. At least, this has not been found to be the case where the contaminants are merely sufficient to render the plastics unsaleable for reuse in forming new plastics material components.

Moreover, it is found that paving slabs in accordance with the present invention are both lighter and, at least to some degree, stronger than conventional paving slabs.

It may be that the improved strength is due to a better bond between cement and certain plastics material, or be due to the enhanced ductility of the paving slab because of the plastics content thereof; and so that impacts which frequently shatter sand/cement-only paving slabs merely deflect paving slabs according to the present invention without causing them to shear. However, no particular theory is adhered to and the present invention should not be limited thereby. Another advantage realised by the present invention is the ability to cut the slabs with an ordinary saw, which makes working with them considerably easier. Indeed, because they are lighter than traditional concrete blocks, they are much easier to transport and more of them can be carried, either by an individual or on a lorry, per load.

The present invention is not limited by the chemical composition of the plastics being recycled and successful paving blocks can be constructed from UPVC, polyethylene, polypropylene, polystyrene (expanded or otherwise), ABS or mixtures of such plastics. There may, of course, be various safety considerations in the application of some plastics materials, particularly those which are inflammable. Indeed, it is anticipated that the present invention will be restricted in its application to paving slabs for outdoor use, given that many plastics, on heating, give off harmful fumes.

There does not appear to be any impediment to there being mixtures of different plastics in the present invention, nor indeed the inclusion of the various impurities which may find their way into the plastics. Such impurities may comprise metal, glass or wood particles, which frequently find their way into the raw waste material supplies to a recycling plant. Indeed, contaminants find their way into already pulverised/shredded plastics after that process has been completed, for example, dirt and dust which can get admixed when a spillage occurs.

The size of the plastics particles mentioned above are the sizes of a sieve through which the particles would pass. Most plastics are in some form of sheet form once shredded so that they have major dimensions in one plane and a minor dimension outside of that plane. Larger particles are likely to give increased strength to the finished paving slab.

By broad selection of the plastics particles to be employed in the present invention, various decorative effects can be obtained in the finished block. Indeed, it is found that a paving block can be constructed having two faces, a bottom face being substantially devoid of any evidence of the plastic content of the block, and a top face having a considerably mottled appearance with many chips of plastics components lying flat on the surface and giving texture to the surface. It is this surface that can give different appearances to the block depending on the plastics employed.

Indeed, some contaminants such as rubber or other elastomers can be deliberately included, so that a softer surface feel to the paving block, and enhanced grip on the surface of the paving slab by objects, persons or animals passing over the slab, can be achieved.

Moreover there is nothing to prevent surface finishing of the blocks with appropriate proprietary finishes, or even polishing of the surface. Moreover, coloured cement can be employed.

The invention is further described hereinafter, by way of example, with reference to the following description of a specific embodiment of the invention.

Example I A paving slab of about 400 square millimetre area and thickness of about 25 mm was cast from the following composition: 50% by volume recycled UPVC material shredded to have a particle size of about 8 mm or less 50% by volume of a mixture of 3 parts sand and 1 part Rugby cement.

Sufficient water was added to cause curing of the cement and provide a castable constitution. On drying and curing of the slab, the result was a strong and relatively light block having a bottom which had a smooth, uninterrupted surface with no plastics material showing, and a top surface which had a mottled appearance with many shards of the plastics particles in its surface giving a pleasing, marbled appearance.

When the slab was dropped onto a floor from a height of about a metre, the slab did not break, whereas a comparable proprietary block of similar size and comprising sand and cement only was significantly heavier and broke when dropped onto the same floor from the same height.

Claims

1. A paving slab comprising contaminated particulate recycled plastics waste, and sand and cement.

2. A paving slab as claimed in claim 1, in which the recycled plastics has a particle size of 10 mm or less, preferably less than 8 mm.

3. A paving slab as claimed in claim 1 or 2, in which the paving slab comprises at least 30% recycled plastics material, the balance comprising a mixture of sand and cement.

4. A paving slab as claimed in claim 1, 2 or 3, in which the mixture of sand and cement comprises about three parts sand and one part cement.

5. A paving slab as claimed in any preceding claim, in which the recycled plastics material is UPVC, polyethylene, polypropylene, polystyrene (expanded or otherwise), ABS or mixtures of such plastics.

6. A paving slab as claimed in any preceding claim, in which the slab has a bottom face being substantially devoid of any evidence of the plastic content of the block.

7. A paving slab as claimed in any preceding claim, in which the slab has a top face having a considerably mottled appearance with chips of plastics components lying flat on the surface and giving texture to the surface.

8. A paving slab as claimed in any preceding claim, in which contaminants are deliberately included in the slab and comprise rubber or other elastomers so as to provide a softer surface feel to the paving slab, and enhanced grip on the surface of the paving slab by objects, persons or animals passing over the slab.

9. A paving slab as claimed in any preceding claim, in which surface finishing of the slab is effected with an appropriate proprietary finish.

10. A paving slab as claimed in any preceding claim, in which at least one surface of the slab is polished.