GB2275647A

GB2275647A - Manufacture of pre-cast concrete building panels

Info

Publication number: GB2275647A
Application number: GB9402107A
Authority: GB
Inventors: Edward Bryan Small
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-02-05
Filing date: 1994-02-04
Publication date: 1994-09-07
Also published as: GB9302262D0; GB9402107D0

Abstract

Pre-cast concrete panels for use in the construction industry for walls and cladding for buildings are made by applying a skin of concrete to at least one reinforcing sheet in a mould and filling a mould cavity peripheral to said sheet with concrete either before or after the application of said skin wherein the concrete for forming both the skin and peripheral structure incorporate strands of polypropolene.

Description

Improvements Relating to the Manufacture of Pre-cast Concrete Panels This invention relates to the manufacture of Pre-Cast Concrete panels typically for use in the construction of lowcost buildings. The invention particularly although not exclusively, relates to a method of manufacturing pre-cast concrete building panels for use as wall cladding and construction of buildings.

There is a considerable range of pre-cast concrete building panels and slabs which are commercially available. It is known to provide a building slab or panel with cavities in order to reduce the overall weight of the panel and to improve the insulation of the panel. However this method has inherent problems in that the panels tend to lose rigidity and strength therefore care must be taken to ensure that the panel strength is not so impaired as to make the slab or panel unusable.

One solution which has already been patented by the applicant under patent no.1452833 i8 to reinforce the rear of a thin concrete skin with hardboard or the like sheet material and this solution has given improved results in the reduction of the thickness of concrete whilst maintaining the strength and rigidity of the panel. A further improvement to this method is disclosed in patent no.GB1502681 wherein the panels produced are of higher strength without the weight of said panels being increased.

The method as patented in patent no. GB1502681 involves soaking a sheet of hardboard or similar fibrous material in water and supporting said soaked reinforcing sheet in a mould. The upper surface of the reinforcing sheet is then covered with a skin of concrete in the plastic state whilst the reinforcing sheet is still wet. A cavity in the mould around the periphery of the sheet is filled with concrete in the plastic state so that the concrete of the skin and the cavity become integral and the reinforcing sheet edges are trapped within the concrete. Once dry and cured the concrete panel is removed from the mould and the panel is then available for use.

This method has been found to utilise the strength of the hardboard as an integral part of the panel to give the panel considerable strength such that no further reinforcing elements are required in the concrete skin. Typically said further reinforcing elements are in the form of wire reinforcements embedded in the concrete.

The use of the reinforcing panel in the soaked state which subsequently dries serves to tension the concrete panel and results in a 50% increase in the strength and load bearing properties of the panel over panels of similar thickness manufactured of concrete. These panels have been used extensively throughout the building industry.

During use it has been found that there is an inherent weakness in the area adjacent the change in concrete thickness around the reinforcing panel periphery. This inherent weakness has been found to occur in the form of cracks which, although not necessarily visually discernable to the human eye are sufficient to allow ingress of water and/or frost. These cracks have been found to increase with the age of the panel and therefore a fault which is not apparent at the time of construction has been found to become increasingly important with the increase in the age of the panels. In an attempt to reduce this problem the process of drying or curing the panels is carefully monitored and controlled in order to reduce the opportunity for cracking to take place.

The aim of the present invention is to provide a method of manufacturing precast concrete panels which are not prone to cracking in the area of the periphery of the reinforcing panel.

The present invention provides a method for manufacture of precast concrete panels, said method comprising the placing of at least one reinforcing sheet into a mould and covering said sheet with a skin of concrete in a plastic state; filling a cavity in the mould around the periphery of the reinforcing sheet with concrete before or after the concrete skin such that the concrete of the skin and in the cavity become integral wherein the concrete used to provide the skin and/or to fill the cavity includes a quantity of strands of polypropylene or a material with similar characteristics.

In one embodiment of the invention the reinforcing sheet to be used will be made of a fibrous material and will first be soaked in a liquid, typically water, prior to the sheet being placed and supported in the mould.

Typically the polypropylene strands will be randomly mixed with the concrete and in sufficient quantity such that they act to bind together the concrete and provide increased cohesion between the concrete skin and the concrete filled mould cavity area thereby eliminating the risk of cracking during curing of the panel.

In another aspect of the invention there is provided a concrete substance for use in the manufacture of precast concrete panels wherein, in addition to the conventional constituents the concrete comprises strands of polypropylene or other similar material mixed into the concrete.

The concrete substance can be used in the manufacture of the pre-cast panels with or without the use of reinforcing boards.

In one embodiment of the polypropylene strands will be of a length in the region of 10-15 mm and a thickness of 15-20,Am.

A specific embodiment of the invention will now be described with reference to the accompanying drawings wherein; Figure 1 illustrates a precast concrete panel of the invention; and Figure 2 illustrates a cross sectional view of the panel of the invention.

Referring firstly to Figure 1 there is shown a concrete panel which typically embodies the advantages of the invention wherein the concrete panel 2 comprises a central portion 4 and a peripheral section 6.

Figure 2 illustrates in greater detail the relationship between the central portion 4 and the peripheral portion 6 of the panel 2. The central portion comprises a reinforcing board 8 which has been soaked in water and then placed in position in a panel forming mould (not shown). Applied to the board 8 is a skin of concrete 10 in a plastic state which, once cured serves to form the outer surface of the panel. The peripheral section 6 is formed at the same time from concrete and as can be seen is of a greater depth than the central dished 7 portion. This section of concrete also serves to trap and secure the edges 12 of the reinforcing board, and to be of such size as to adequately provide cover to the peripheral reinforcing rods 13 if provided.

The area which is particularly affected by cracking of the concrete during curing is indicated by the numeral 14 and is the area where the depth of concrete alters between the central portion 4 and peripheral section 6. This cracking can subsequently allow ingress of water and/or frost when the panels are used in buildings and has therefore been identified as a significant fault in the design of such panels. By incorporating strands of polypropylene into the concrete mixture it is found that a significant reduction in the amount of cracking is achieved. The strands serve to add strength to the bonding between the concrete and therefore prevent the concrete from cracking at the critical area 14.

An example of a typical concrete mixture of the invention would be to add 600 grammes of polypropylene strands per cubic metre of mixed wet concrete. The quantity added will depend on the consistency of concrete used and similarly the dimensions of the strands added can be varied according to the specific consistency of the concrete. However, a typical strand size would have a length of 20 mm and a thickness of 18 wm. A preferred form of polypropylene would be that represented by the compound C3H6.

Claims

1. A method for the manufacture of pre-cast panels comprising placing of at least one reinforcing sheet into a mould, covering said sheet with a skin of concrete in a plastic state; filling a cavity in the mould substantially around the periphery of the reinforcing sheet with concrete before or after the concrete skin such that the concrete of the skin and in the cavity become integral wherein the concrete used to provide each of, or both of the skin and filling the cavity includes a quantity of strands of polypropylene or a material with similar characteristics.

2. A method for the manufacture of pre-cast concrete panels as in Claim 1 wherein the reinforcing sheet is made from a fibrous material and is soaked in a liquid prior to the sheet being placed in the mould.

3. A concrete for use in the manufacture of pre-cast concrete panels wherein the concrete includes a quantity of strands of polypropylene or other material with similar characteristics therein.

4. A concrete as in Claim 3 wherein the polypropylene strands are randomly mixed into the concrete.

5. A concrete as in Claim 3 wherein the amount of polypropylene added to every cubic metre is in the region of 500 - 800 grammes.

6. A concrete as in Claim 5 wherein the amount of polypropylene added to every cubic metre is 600 grammes.

7. A concrete as in Claim 3 wherein the concrete is used in the manufacture of pre-cast concrete panels in conjunction with at least one reinforcing sheet.

8. A concrete for use as in Claim 3 wherein the concrete includes strands of polypropylene of a length in the region of 10-15 mm and thickness of 15-20 m.

9.A method as hereinbefore described with reference to the accompanying drawings.

10. A concrete as hereinbefore described with reference to the accompanying drawings.