GB2207365A

GB2207365A - A method and apparatus for producing an aerated cementitious composition

Info

Publication number: GB2207365A
Application number: GB08718114A
Authority: GB
Inventors: Peter Shelley Mills
Original assignee: Fosroc International Ltd
Current assignee: Fosroc International Ltd
Priority date: 1987-07-30
Filing date: 1987-07-30
Publication date: 1989-02-01
Anticipated expiration: 2007-07-30
Also published as: GB2207365B; GB8718114D0

Abstract

An aerated cementitious composition is produced by introducing water, cementitious powder and foam stabiliser through inlets (14 and 15) and a jet of compressed air through inlet (16) into the mixing chamber (11) of an auger mixer (10). The resultant aerated mixture is then pumped to the desired site through hose (18) using a positive displacement pump (17) operating on the progressive cavity pumping principle. <IMAGE>

Description

A METHOD AND APPARATUS FOR PRODUCING AN AERATED CEMENTITIOUS COMPOSITION This invention relates to a method and apparatus for producing aerated cementitious compositions for use, for example but not exclusively, in underground mines.

A method of and an apparatus for producing aerated cementitious compositions is disclosed in British Patent No. 2139517 which involves feeding cement, foaming agent and liquid to a mixing chamber open to the atmosphere, mixing the ingredients fed to the mixing chamber, and pumping the wetted mixture produced to a desired site. The capacity of pumping being greater than the feed rate of the ingredients into the mixing chamber such that, in operation, air is drawn into the mixing chamber and entrained in the wetted mixture. It is known to use such a technique for the filling of cavities up to a distance of about 200 m from the aerating pump.

The transport of cementitious materials underground is costly and complicated by the need for different materials to perform different duties. For example, the cementitious compositions described in British Patent No. 2139517 only find use for filling cavities with a light weight cementitious foam. Other cementitious compositions are used for forming monolithic blocks or packs which are positioned at the sides of underground roadways in the place of excavated coal or rock to help support the overlying strata. Other cementitious compositions are used to construct "stoppings" in the form of monolithic blocks or coatings on a support such as brattice cloth. Other cementitious compositions are used to grout fissures and voids in the strata surrounding a roadway or coalface.The present invention has for its object to provide a method and apparatus by which the aforementioned cementitious compositions may be aerated when it is wished to fill cavities with a weaker, lightweight composition, thereby avoiding the need to use a multiplicity of cementitious compositions. The cement used in the cementitious compositions may be any hydraulic cement e.g. a Portland type cement, a high alumina cement, anhydrite, Plaster of Paris, cements containing kleins compound, slag cement and blends thereof. In addition, the cementitious composition may further contain fly ash, calcium oxide or hydroxide, silica or calcium carbonate, and additives to confer desired properties, such as acceleration, thixotropy or retardation.

According to the present invention, there is provided a method of producing an aerated cementitious composition comprising introducing water, cementitious powder, foam stabiliser and a stream of compressed air into a mixer so as to produce an aerated cementitious composition; and pumping the composition under pressure to a site to be supplied with the aerated cementitious composition.

Also according to the present invention, there is provided apparatus for producing an aerated cementitious composition comprising a mixer including a mixing chamber having inlets for cementitious powder, foam stabiliser, water and compressed air; and a pump arranged to pump the aerated composition from the mixing chamber to a site at which a supply of aerated cementitious composition is required.

The provision of compressed air to the mixer means that it is not necessary for the capacity of the pump to be greater than the feed rate of the ingredients as it is not necessary to draw air into the mixing chamber to be entrained in the mixture, aeration being effected by the compressed air stream.

With such an arrangement, it is possible to vary the degree of aeration quite easily to achieve the desired degree of stabilisation of the foam by controlling the amount of air introduced into the composition. It will be appreciated that the smaller the quantity of air which is introduced, the higher will be the density of the foam thereby produced.

The foam stabilizer is chosen so as to be compatible with the cement with which it is used and may be any one or more of fatty acid salts, alkaryl sulphonates, alkyl sulphates and phenol ethoxylates.

The quantity of foam stabilizer can be adjusted using an appropriate metering device to adjust the weight ratio of cementitious powder to foam stabilizer in the mixer. However, it may be preferred in some cases two provide a pre-mix of cementitious powder and powdery foam stabilizer in the desired weight ratio.

In the present invention, the pump is preferably of the positive displacement type and is most preferably a pump which operates on the progressive cavity pumping principle, e.g. where a helical rotor rotates within a resilient double helix stator having twice the pitch of the former, and where there is an interference fit between the rotor and the stator to form a continuous seal behind the cavity which progresses along the stator.

Preferably, the compressed air is introduced into the mixing chamber in such a way that mixing and aeration of the composition is assisted.

Embodiments of the present invention will now be described with reference to the accompanying drawing, in which: Fig. 1 is a schematic diagram of an apparatus according to the present invention, The apparatus shown in Fig. 1 comprises a continuous mixer 10 including a mixing chamber 11 enclosing a screw-type auger 12 driven by a motor 13. The components of the composition are metered into the mixing chamber 11 through respective inlets. In the present case, water is delivered through a water inlet 14 and a mixture of cement powder and foam stabiliser is delivered through a combined inlet 15, typically in the form of a hopper which, in this case, enters the mixing chamber 11 downstream of the auger 12 from the water inlet 14. The water, foam stabiliser and cement powder are mixed by the auger 12 and compressed air is introduced into the mixture from an air delivery jet 16.The jet 16 delivers compressed air into the mixture so as to effect aeration and assist mixing.

The aerated mixture is fed from the mixing chamber 11 into a positive displacement pump 17 which is connected to a length of small diameter (e.g. 1 inch) hose 18 leading to a site at which aerated cementitious material is to be supplied.

In the drawing, a continuous auger-type mixer is shown but a batch paddle mixer or a continuous paddle mixer could also be used.

While the cement and foam stabiliser are pre-mixed in the present case, these components could be introduced separately into the mixing chamber. It is also envisaged that the foam stabiliser and water could be pre-mixed and introduced together and the cement powder delivered in the pressurised air stream.

The jet of compressed air is generally introduced into the mixing chamber after initial mixing has taken place and in such a way that the mixture becomes aerated and completely mixed.

Claims

CLAIMS:

1. A method of producing an aerated cementitious composition comprising introducing water, cementitious powder, foam stabiliser and a stream of compressed air into a mixer so as to produce an aerated cementitious composition; and pumping the composition under pressure to a site to be supplied with the aerated cementitious composition.

2. A method as claimed in claim 1, wherein the stream of compressed air is introduced into the mixer after initial mixing of the cementitious powder, foam stabiliser and water has taken place.

3. A method as claimed in claim 1 or 2, wherein the pump is of the positive displacement type.

4. A method as claimed in claim 3, wherein the pump operates on the progressive cavity pumping principle.

5. A method as claimed in claim 1, substantially as hereinbefore described with reference to the accompanying drawing.

6. An aerated cementitious composition when produced by the method as claimed in any preceding claim.

7. Apparatus for producing an aerated cementitious composition comprising a mixer including a mixing chamber having inlets for cementitious powder, foam stabiliser, water and compressed air; and a pump arranged to pump the aerated composition from the mixing chamber to a site at which a supply of aerated cementitious composition is required.

8. Apparatus as claimed in claim 7, wherein the compressed air inlet is disposed between the pump and the inlets for the cementitious powder, foam stabiliser and water so that, in use, a jet of compressed air is introduced into the mixing chamber after initial mixing of the cementitious powder, foam stabiliser and water has taken place.

9. Apparatus as claimed in claim 7 or 8, wherein the pump is of the positive displacement type.

10. Apparatus as claimed in claim 9, wherein the pump operates on the progressive cavity pumping principle.

11. Apparatus as claimed in claim 7, substantially as hereinbefore described with reference to the accompanying drawing.