GB2347413A

GB2347413A - Lightweight concrete

Info

Publication number: GB2347413A
Application number: GB9904701A
Authority: GB
Inventors: Dermot Lynch; Barrie Pimm-Smith
Original assignee: POLYBETON Ltd
Current assignee: POLYBETON Ltd
Priority date: 1999-03-03
Filing date: 1999-03-03
Publication date: 2000-09-06
Also published as: GB9904701D0

Abstract

A concrete mixture comprises cement, fine aggregate, expanded lightweight aggregate, and a sufficient amount of fibres to substantially constrain the expanded lightweight aggregate to an even distribution throughout the mixture. Ideally, the mixture is composed of 3.5 - 13% cement, 8 - 46% fine aggregate, and 45 - 87% expanded lightweight aggregate. Further, it may contains 0.03 - 0.2%w fibres. The lightweight aggregate may be provided by expanded polystyrene beads. Also shown is a method of producing set concrete by producing a concrete mixture as described, transporting to a site at or near the location where the concrete is to be used, and causing the concrete to set at that location. Alternatively, the cement, Fine aggregate, expanded lightweight aggregate and Fibres, e.g. polypropylene Fibres may be mixed at the site. The polystyrene may be expanded on site.

Description

Lightweight Concrete The present invention relates to lightweight concrete, in particular to concrete containing lightweight aggregates.

A known way of constructing buildings is by making prefabricated sections of concrete, taking them to the location at which the housing is required, and erecting the housing from the prefabricated sections.

The concrete is formed by adding water to a concrete mixture, stirring the mixture, and allowing to set and harden. Such a concrete mixture comprises cement, fine aggregate (such as sand), and coarse aggregate (such as pebbles). Such a concrete is relatively heavy, making transportation of the concrete expensive. This type of concrete is also brittle and is often reinforced by materials such as steel, which adds to the weight and expense.

A concrete with a lower weight may be obtained by replacing the coarse aggregate with a lighter material such as expanded polystyrene (EPS) beads. EPS beads are however difficult to mix with cement and sand, as, being much less dense, they are prone to float to the surface of the mixture when the mixture is agitated.

The object of the present invention is to provide a concrete which is both light in weight, and has an improved tensile strength.

According to the present invention there is provided a concrete mixture comprising cement, fine aggregate, expanded lightweight aggregate and fibres.

Preferably the cement, fine aggregate, and expanded lightweight aggregate mixture is composed of 3.5-13% cement, 8-46% fine aggregate, and 45-87% expanded lightweight aggregate.

Preferably, the expanded lightweight aggregate is expanded polystyrene.

Preferably the concrete contains 0.03-0.2% w fibres. Preferably the fibres are polypropylene.

According to another aspect of the invention, there is provided a method of producing set concrete including producing such a concrete mixture, transporting to a site at or near the location where the concrete is to be used, and causing the concrete to set at that location.

According to another aspect of the invention, there is provided a method of producing set concrete including transporting cement, fine aggregate, expanded lightweight aggregate, and fibres, to a site at or near the location where the concrete is required, mixing the cement, fine aggregate, expanded lightweight aggregate, and fibres to produce a concrete mixture, and causing the concrete to set at that location.

According to another aspect of the invention, there is provided a method of producing set concrete including transporting cement, fine aggregate, non-expanded polystyrene and fibres to a site at or near the location where the concrete is to be used, expanding the polystyrene so as to produce expanded polystyrene beads, mixing the cement, fine aggregate, expanded polystyrene beads, and fibres to produce a concrete mixture, and causing the concrete to set at that location.

When the component ingredients of the concrete are mixed, the fibres lie randomly throughout the volume of the concrete, creating an even matrix. This matrix traps the EPS beads and largely prevents them from moving independently through the concrete mixture, to float to the surface for example. The EPS beads remain constrained in this manner whilst water is added and mixed, and whilst the concrete sets. The fibres also contribute to the tensile strength of the concrete. The fibres should be of a sufficient length to form a matrix in which to trap the EPS beads, so their length will depend upon the bead size, but a typical length would be between 15 to 20 mm.

Such a concrete mixture may then be easily mixed at any location with tools such as conventional cement mixers. Since this mixture is so easy to mix, it may be transported in its component parts and made up near or on site. In particular, the polystyrene may be transported in a dense state to nearer the location and expanded as required, reducing the volume of materials that has to be transported. The ease of mixing of the concrete means that it is not necessary to mix and cast the concrete in a dedicated factory and have the bulky prefabricated sections transported to their destination which would make the cost prohibitive.

A lightweight concrete embodying the invention will now be described, by way of example, with reference to the drawing, which shows the location where the concrete is mixed with water and set; The concrete comprises sand, fine aggregates, expanded polystyrene beads, and polypropylene fibres. The precise proportions of the ingredients will depend upon the particular application for which the concrete is intended.

A typical mixture for a light and reasonably strong concrete is composed of approximately 7% cement, 27% sand, 66% EPS beads and 0.1 % w fibre.

For a stronger but heavier concrete, the mixture may be altered so as to be composed of approximately 16% cement, 33% sand, 50% EPS beads and 0.1% w fibre.

All the percentages of the ingredients given herein are quoted with respect to volume, except for the amount of fibre, as the fibre's volume will depend upon the degree of compaction, so it is more convenient to express the proportion of fibre as a percentage of the weight of the concrete mixture.

The use of the term'concrete mixture'here refers to the mixture of the dry ingredients making up the concrete.

For a satisfactory concrete, it has been found that a mixture cement, fine aggregate, and expanded polystyrene beads mixture should be composed of 3.5-13% cement, 8-46% fine aggregate, and 45-87% expanded polystyrene beads. The proportions of fibre may also be varied between 0.03-0.2% w, in order to vary the qualities, such as the strength of the concrete.

The size of the expanded polystyrene beads will depend, like conventional coarse aggregate, upon the intended use and situation of the concrete. Although the size then may be varied considerably, a typical bead diameter could be 1 cm.

Referring to the drawing, the mixing of the concrete with water is relatively easy to carry out, and may be achieved using readily available tools such as a conventional cement mixer. The dry mixture 10 is transported to a location at or near the intended position of the housing to be built with the concrete. The dry mixture is then mixed with water 16 using a cement mixer 12 and poured into various moulds 14. When the concrete has set sufficiently, it may be removed from the moulds 14 and left until it has cured completely. The moulds 14 form the concrete into the necessary component parts of a building, such as wall modules, roof beams, door frames and the like.

The mixing of the component parts of the concrete is also relatively straightforward, and again may be done using a conventional cement mixer.

The cement, sand, fibre and expanded polystyrene beads may be brought to a location on or near the intended housing site and mixed together at this location. After the components have been mixed together, the resulting concrete mixture is now ready to be mixed with water as described above.

Since the components may be so easily mixed together on site, they may brought from different sources. This is especially important in the case of the EPS beads, which may very conveniently be manufactured from unexpanded polystyrene in a nearby factory, mixing station, or even on site.

Conventionally, cement factories often supply a very wide area, resulting in a long distance between the cement factory and the site at which the materials are needed. By means of the present invention however, the unexpanded polystyrene may be transported separately to be expanded and mixed with the cement at mixing stations which are more local to where the concrete is required rather than mixing the EPS beads together with the other ingredients in the cement factory. This represents a great saving in the volume of material which has to be transported.

The polypropylene fibres could similarly be produced by a factory near to the site where the concrete is to be mixed from a dense form of polypropylene, and spun and cut into fibres at that factory. The fibres added to the concrete could also be composed partly or solely or steel of glass fibres which could be procured locally.

The ability to transport the dry concrete mixture or the component parts to the building site also means there is greater choice of what sections to cast when the concrete reaches its destination.

The concrete may also be used directly on site, for example poured directly into place to form the foundation trenches and floors. The concrete may also be cast into building components in a factory environment and then transported to the building site in a conventional fashion. The concrete could also be transported in a wet state, having been mixed in water and placed, for example, in a conventional lorry-mounted cement mixer.

The expanded lightweight aggregate could also consist of materials other than polystyrene, such as expanded clay beads, or vermiculite. A wide variety of materials could be used as the fibrous material of the concrete instead of polypropylene, such as other polymers, or organic material.

Although the embodiment herein described is directed towards domestic housing, the lightweight concrete can equally be used in applications for which conventional concrete is presently used, such as all manner of buildings, and the construction of bridges, roads, and the like.

Claims

CLAIMS 1. A concrete mixture comprising cement, fine aggregate, expanded lightweight aggregate, and a sufficient amount of fibres to substantially constrain the expanded lightweight aggregate to an even distribution throughout the mixture.
2. A concrete mixture according to claim 1 wherein the cement, fine aggregate, and expanded lightweight aggregate mixture is composed of 3.513% cement, 8-46% fine aggregate, and 45-87% expanded lightweight aggregate.
3. A concrete mixture according to either previous claim wherein the concrete contains 0.03-0.2% w fibres.
4. A concrete mixture according to any previous claim wherein the expanded lightweight aggregate comprises expanded polystyrene beads.
5. A concrete mixture according to any previous claim wherein the fibres are polypropylene.
6. A set concrete produced by a concrete mixture according to any previous claim.
7. A method of producing set concrete including producing a concrete mixture according to any of claims 1 to 5, transporting to a site at or near the location where the concrete is to be used, and causing the concrete to set at that location.
8. A method of producing set concrete including transporting cement, fine aggregate, expanded lightweight aggregate, and fibres, to a site at or near the location where the concrete is required, mixing the cement, fine aggregate, expanded lightweight aggregate, and fibres to produce a concrete mixture according to any of claims 1 to 5, and causing the concrete to set at that location.
9. A method of producing set concrete including transporting cement, fine aggregate, non-expanded polystyrene and fibres to a site at or near the location where the concrete is to be used, expanding the polystyrene so as to produce expanded polystyrene beads, mixing the cement, fine aggregate, expanded polystyrene beads, and fibres to produce a concrete mixture according to claims 4 or 5, and causing the concrete to set at that location.
10. A concrete mixture substantially as herein described and illustrated.
11. A set concrete substantially as herein described and illustrated.
12. A method of producing a set concrete substantially as herein described and illustrated.
13. Any novel and inventive feature or combination of features specifically disclosed herein within the meaning of Article 4H of the International Convention (Paris Convention).