IE56580B1 - Production of pressed concrete product - Google Patents

Abstract

A process for producing a surface-patterned pressed concrete product involves placing on a perforate mould plate having a relief-pattern on the surface thereof, a sheet of fine mesh gauze co-extensive with the mould plate surface, pouring a concrete mix into said mould and pressing to extract water therefrom.

Description

This invention relates to a method of producing a concrete product, namely a load-bearing concrete paving slab, or kerb stone, with a relief pattern in a surface thereof.

Concrete paving slabs are manufactured by two distinct alternative processes. The simpler of the two is a simple casting process where a concrete mix is poured into a mould and allowed to harden. In the other process, concrete is poured into a mould and pressed in an hydraulic press to a pressure of around 2000 psi, to compact the concrete and squeeze out the water. The latter process produces high density slabs for heavy duty use: the former produces a relatively light weight product aimed mainly at the domestic market for use in paving areas which are not subject to heavy loading.

The simple casting process is quite versatile in the surface patterning which can be produced simply by forming patterns on the face plate of the mould· The nature of the pressing process makes it rather less adaptable to the production of relief patterned slabs. In this process there is a top and bottom perforate plate between which the concrete is pressed. These plates are of thick steel plate with apertures of about 1/8 inch over more or less their whole surface to permit drainage of water during pressing. > To prevent loss of cement from the concrete with the water, a sheet of rough filter paper is placed between each plate and the concrete. An attempt to avoid use of this paper is disclosed in GB 917 349 where a metal gauze is used in conjunction with a fabric as a filter. The product which is produced by this process has on its surface a multiplicity of surface protrusions left by the impression of the perforations of the plate. Any attempt to produce surface patterns on the slab is largely inhibited by the need for both plates to be perforate for removal of the water.

GB 936 958 describes manufacture of kerbstones by exerting high pressures on a mould box including a flat surface moulding die over which is placed a layer of metal gauze covered by a layer of strong paper. The metal gauze and paper allow the water pressed from the concrete in the mould cavity to pass therefrom but the paper prevents the concrete from passing through into the gauze.

Apart from use of such pressing methods concrete products can also be made by moulding assisted by the application of vacuum and/or vibration. GB 735 451 discloses such a method for making a concrete body by which method excess water is extracted from the fresh concrete by suction through adjacent means comprising a surface impervious to air and an opposed surface pervious to air and water between which is positioned a wire mesh defining a vacuum chamber. The pervious surface contacts the concrete under vibration which is maintained until the concrete is self-supporting and vacuum alone is used to finish the product.

An object of this invention is to provide a process for producing a surface-patterned pressed concrete product.

According to the present invention there is provided a non-vibrational process for producing a pressed concrete product having a relief pattern in a surface thereof comprising providing in a pressing machine a bottom perforate mould plate having a relief-pattern in the surface thereof, placing on said plate a sheet of fine mesh gauze co-extensive with said mould plate surface, pouring a concrete mix into said mould and pressing to extract water from the concrete and cause a relief pattern to be formed in the surface of the concrete in contact with said bottom plate by virtue of the increase in external pressure above atmospheric applied to the concrete during pressing.

It will be appreciated that in this process only one of the mould plates need be as defined, the other face can be of traditional configuration. In normal practice the bottom v - · ,·· plate of the mould of an otherwise conventional slab pressing machine would be replaced as defined by this invention.

Preferably the said gauze is of metal wire, for example the type of gauze used in Fourdinier belts used in a papermaking process. Typically the mesh size will be between 35 mesh and 40 mesh. Plastic gauzes may also be used. A sheet of rough filter paper may be placed between the gauze and the concrete to suppress the surface impression made by the Ιθ mesh of the gauze.

The process of this invention has been found particularly adaptable for the production of slabs having the surface appearance of riven stone. In making the mould plates a section of natural riven stone is dressed by a stonemason to produce the uniformity of thickness around the edges where the slab will abut adjacent slabs. A cast-iron or steel plate is then produced from the master pattern stone by conventional metal casting technology.

The following is a description of a pressing process of this invention by way of example.

The concrete mix used in this example had the following make-ups3 parts winstone, 2 parts sand, 1 part cement plus artificial colouring to produce a natural appearance.

In a conventional slab-pressing machine, the bottom plate was replaced by a plate having a relief pattern resembling that of riven stone, having been produced in the manner described hereinabove.

The size of the mould can be varied but in this example was 3 feet x 2 feet and of sufficient depth to produce a final product two inches thick.

A sheet of metal wire gauze was placed in the mould atop the relief-patterned plate followed by a sheet of filter paper.

A load of 55 kg of the aforesaid concrete mix was loaded into the mould.

The top plate of the press mould was of conventional type and a sheet of paper was placed atop the concrete mix in the usual way.

This mix was then subjected to a pressure of 2000 psi and water was extracted from above and below in the normal manner.

The final product had the appearance of a substantially smooth finish, save for almost indiscernible surface markings produced by the mesh and, of course, the relief pattern, riven stone slab.

Although, for simplicity of description, the invention has been described above in relation to a concrete slab which has one relief-patterned face, it is possible to manufacture kerbstones or edging stones where more than one surface of the product carries the relief-patterning.

For example, for a kerbstone, the mould may comprise a bottom plate as described above and an upstanding edge plate engaged therewith in a simple L-shaped keyway. The nature of the top and other side plates is irrelevant. The assembly is lowered into a mould box, concrete mix poured in, and the product pressed as normal. As the pressed product is ejected from the mould box by raising the bottom plate, the side plate falls away (or can be knocked away) once it is clear of the top edge of the mould box.

Claims (4)

1. I- A non-vibrational process for producing a pressed concrete product having a relief pattern in a surface thereof comprising providing in a pressing machine a bottom perforate mould plate having a relief-pattern in the surface thereof, placing on said plate a sheet of fine mesh gauze co-extensive with said mould plate surface, pouring a concrete mix into said mould and pressing to extract water from the concrete and cause a relief pattern to be formed in the surface of the concrete in contact with said bottom plate by virtue of the increase in external pressure above atmospheric applied to the concrete during pressing.
2. 2. A process according to claim 1 wherein an additional mould plate having a relief pattern in the surface thereof is provided for causing a relief pattern to be formed in another surface of the concrete, this additional mould plate being generally perpendicular to, and releasably connected to, the bottom perforate mould plate thus to provide a surface pattern in a pair of adjacent surfaces of the product.
3. 3. · A process for producing a pressed concrete product according to claim 1 and substantially as hereinbefore described.
4. 4. Λ pressed concrete product whenever produced by a process according to any one of claims 1 to '1.