GB2237755A

GB2237755A - Cementitious mixes, constituents and products

Info

Publication number: GB2237755A
Application number: GB8925381A
Authority: GB
Inventors: Cyril Oury Duke
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-11-09
Filing date: 1989-11-09
Publication date: 1991-05-15
Anticipated expiration: 2009-11-09
Also published as: GB2237755B; GB8925381D0

Abstract

Plastics beads or granules, for use as or used as a constituent of a cementitious mix, have a "buoyancy-modifying surface coating applied prior to inclusion in the cementitious mix. The coating is applied as a mix of PVA (polyvinyl acetate) with sand and/or cement. An oxide may be incorporated in the PVA mix for colouration of the coating.

Description

"CEMENTITIOUS MIXES, CONSTITUENTS THEREFOR AND PRODUCTS MADE THEREFROM" The invention relates to cementitious mixes, constituents for such mixes and products rade therefrom. A cementitious mix in accordance with the invention may be used in the manufacture of a product by any of the usual processes, such as casting or pressing in a mould, or extrusion for example.

Concrete products, such as concrete slabs and blocks, are typically extremely heavy in the standard sizes in which they are normally cast. Thus they are difficult and expensive to handle and transport, and various proposals have been made for the manufacture of lightweight concrete products mainly by the addition of lightweight constituents to the cement/aggregate cementitious mix. One such proposal is that lightweight non-absorbent plastics beads or granules should be used as a constituent of the cementitious mix.

Whilst the use of such plastics beads or granules theoretically provides an excellent product with desirable properties such as light weight and thermal insulation, in practice it has been found extremely difficult to achieve a mix with satisfactory distribution of the beads or granules as, due to their buoyancy, they tend to float and thus congregate at an upper level in the mix. The object of the invention is to provide a solution to the problem of achieving satisfactory distribution of the beads or granules.

To this end plastics beads or granules, for use as a constituent of a cementitious mix, are aiven a coating of a heavier material prior to inclusion in the cementftious mix. Thus the pre-coatec beads or granules are of reduced buoyancy such that the tendency to float in the mix is markedly reduced and satisfactory distribution throughout the cementitious mix can be achieved. The plastics beads or granules are preferably of expanded polystyrene, and they can cheaply be produced from otherwise scrap polystyrene packaging material. The buoyancy-modifying surface coating of the beads or granules is preferably applied as a mix of PVA (polyvinyl acetate) with sand and/or cement and a suitable water dilution.

Various oxides, for example, may be added if colouration of the coating is required.

Preferably the PVA mi is applied as a "dry" coating such that when mixed up with the beads or granules the latter are individually coated such that they do not tend to bond one to another but remain as a mutually separate granular mass. The coating can be such that whilst the coated beads or granules are extremely light and retain their other desirable properties, such as high thermal insulation, they are just sufficiently heavy to overcome the problem of surface flotation when used as a constituent of a cementitious mix. Thus a satisfactory lightweight concrete product, such as a building block, slab or wall panel, for example, can be manufactured from the resultant cementitious mix by casting, pressing or extrusion.Preferably the cementitious mix is subjected to vibration during the product manufacture to assist in compaction and maintenance of the distribution of the coated beads or granules throughout the mix.

The invention includes within its scope not only the pre-coated beads or granules per se but also a cementitious mix of which the coated beads or granules provide a constituent, and also the resultant products manufactured from such a cementitious mix. The cementitious mix of the invention may suitably be used in the manufacture of cast concrete products by the method which is disclosed in our co-pending Patent Application No 88 22287.2. Thus, a mould may be partially filled with the cementitious mix - comprising cement, aggregate and a substantial proportion by volume of the coated plastics beads or granules - and then vibrated to assist in distribution of the beads or granules and to provide a good face where contacting the mould surface, and thereafter a coating may be applied to the reverse face of the moulding whilst still in the mould.This coating may be applied in accordance with Patent No 2 166 664, for example, or may be a further layer of a cement/aggregate mix but without the plastics beads or granules, and the mould may again be vibrated to provide a good free face for the moulding. Or such free face may be achieved by a pressing operation which also compacts the applied layer.

Concrete products in accordance with the invention, such as slabs, blocks etc, can be manufactured which have a weight of only about 50% of a conventional concrete product. Whilst being of comparable strength they are easy to handle and transport, and they have good thermal insulation properties. They have also been found to have excellent fire resistant properties, having less tendency to disintegrate when subjected to intense heat.

In one specific procedure for producing the coated beads or granules of the invention, a 1:3 mix of cement and soft sand plus diluted PVA, the dilution being such as to produce a very dry mix, is put inte a paddle mixer or cement mixer for example. To it there is added expanded polystyrene beads or granules which are to be coated, and the whole mixed up until the beads or granules are evenly coated with the dry mix. The dryness of the mix is such that whereas it will coat and stick to the beads or granules, it will not cause the beads or granules to adhere one to another. Thus the individually coated beads or granules readily separate out from the granular mixed mass, prior to use as a constituent of a cementitious mix to be used in the manufacture of lightweight concrete products in accordance with the invention.If a coloured coating of the beads or granules is desired, to suit the final product, an appropriate colour pigment or oxide can be added to the PVA mix.

The advantages of a lightweight product with good thermal insulation properties have already been mentioned.

Products in accordance with the invention also have price and environmental advantages. A cheaper product is achieved particularly if otherwise scrap packaging material is used as a source of the uncoated plastics granules, and it is environmentally friendly to "lock up" in this way the otherwise waste hydrocarbons rather than incinerating them which is the usual method of disposal. A satisfactory product results if the coated beads or granules are used in the ratio of 40%:60% by bulk with a standard mix of cement and sand and/or ballast. Using a dry mix with vibration, whether production involves casting, pressing or extrusion, ensures a resultant concrete product with good strength characteristics and even distribution of the coated beads or granules.

Claims

CLAIMS:

1. Plastics beads or granules, for use as or used as a constituent of a cementitious mix, wherein the beads or granules are given a "buoyancy-modifying" surface coating of a heavier material prior to inciusion in the cementitious mix.

2. Plastics beads or granules according to claim 1, wherein the beads or granules are of expanded polystyrene.

3. Plastics beads or granules according to claim 2, wherein the beads or granules are produced from scrap polystyrene packaging material.

4. Plastics beads or granules according to any one of the preceding claims, wherein the surface coating of the beads or granules is applied as a mix of PVA (polyvinyl acetate) with sand and/or cement and a suitable water dilution.

5. Plastics beads or granules according to claim 4, wherein a colourant, such as an oxide, is added to the PVA mix for colouration of the coating is required.

6. Plastics beads or granules according to claim 4 or 5, wherein the PVA mix is applied as a "dry" coating such that when mixed up with the beads or granules the latter are individually coated so that they do not tend to bond one to another but remain as a mutually separated granular mass.

7. Plastics beads or granules according to claim 6, wherein said coating is applied as a 1:3 mix of cement and soft sand plus diluted PVA.

8. Plastics beads or granules according to any one of the preceding claims, wherein the coating is such that whilst the coated beads or granules are extremely light they are just sufficiently heavy to overcome the problem of surface flotation when used as a constituent of a cementitious mix.

9. A lightweight concrete product which is manufactured by casting, pressing or extrusion from a cementitious mix incorporating coated beads or granules according to any one of the preceding claims.

10. A concrete product according to claim 9, wherein the product is a building block, slab or wall panel.

11. Manufacture of a concrete product according to claim 8 or 9, wherein the cementitious mix is subjected to vibration during the manufacture to assist in compaction and maintenance of the distribution of the coated beads or granules throughout the mix.

12. A cementitious mix wherein coated beads or granules in accordance with any one of claims 1 to 9 provide a constituent of the cementitious mix.

13. A cementitious mix according to claim 12, wherein the coated beads or granules are used in the ratio of 408:608 by bulk with a standard mix of cement and sand and/or ballast.

14. A concrete product manufactured from a cementitious mix in accordance with claim 12 or 13.

15. Coated plastics beads or granules, a cementitious mix incorporting such beads or granules, or a concrete product manufactured from such a cementitious mix, substantially as hereinbefore particularly described.

Amendments to the claims have been filed as follows 1. Plastics beads or granules, for use as or used as a constituent of a cementitious rnix, whereon the beads or granules are given a "buoy ncy-mocifying" surface coating applied as a riy of PVA (polyvinyl acetate) with sand and/or cement prior to inclusion in the cementitious mix.

z. Plastics beads or granules accordirc to claim 1, wherein the PVA mix includes water as a diluent.

3. Plastics beads cr granules according te claim 1 or claim 2, wherein a colourant, such as an oxide, is added to the PVA mix for colouration of the coating.

4. Plastics beads or granules according to any one of the preceding claims, wherein the beads or granules are of expanded polystyrene.

5. Plastics beads or granules accordina to any one of the preceding claims, wherein the beads or granules are produced from scrap polystyrene packaging material.

6. Plastics beads or granules according to any one of the preceding claims, wherein the PVA mix is applied as a "dry" coating such that when mixed up with the beads or granules the latter are individually coated so that they do not tend to bond one to another but remain as a mutually separated granular mass.