GB2274602A - Foamed concrete mixer - Google Patents

Abstract

Foamed concrete, grout or mortar is produced by using an upwardly sloping elongate mixer drum (1) with inlets (8, 10) for raw materials and aqueous foam and an outlet (14) for mixed foamed concrete, the inclined drum at its base (2) at least lying at a clearance with a conical upwardly inclined rotary mixer/conveyor screw blade (12) of decreasing diameter in an upward direction. The drum can be mounted on a transverse axis (13) for tilting to empty the contents after mixing. Preferably a foam-creating mesh (27 Fig. 4, not shown), is provided at the foam inlet (10) to the mixer. The drum may swivel about a vertical axis. <IMAGE>

Description

IMPROVEMENTS IN THE INCORPORATION OF AIR INTO FLOWABLE WATER-CONTAINING CEMENTITIOUS MIXTURES This invention relates to the intentional incorporation of air into a flowable but hardenable mixture of water and cementitious material, and to the hardened and set cementitious product containing part or all of such incorporated air.

In particular the invention relates to a method and equipment for production of such a mixture constituting a foamed grout, foamed mortar, or foamed concrete, and to the material produced after the mixture has hardened and set.

The invention has general applicability, i. e. to the production of a grouting material (based upon water, cement powder and optionally a fine aggregate e.g. sand.

but always fluid and pumpable) or of a mortar material (based upon water, sand and cement and stiffer in consistency, e.g for use in bricklaying) or of a concrete material (based upon water, aggregate material, and cement and often containing a high proportion of aggregate of a larger size, e.g. 20 mm+). For convenience, except where specific discussion is needed of the other products the invention will be predominantly described in relation to the production of concrete a material known in the trade as "Foamed Concrete" which is usually a fluid pumpable wet mixture containing sand or a fine aggregate and has many of the characteristics of a foamed grout.

Concrete is made by mixing together a cement, water, and an aggregate material and occasionally other minor additives. The aggregate can be coarse or fine, can have a range of particle sizes or be screened to a standard size, and can if desired be a synthetic material. Synthetic aggregates are typically based upon fly ash (a waste product of coal from power stations) or clay materials. These materials can be pelletised and/or fired in some instances to give an aggregate of much lower bulk density than natural aggregates such as flint, chert, and similar gravels. Concrete is made and used by mixing the materials together and thereafter emplacing the material while wet into a desired mold or bulk and allowing the material to harden and then set.

When concrete is made up in the conventional fashion there is inevitably some small percentage of air mixed in with the other components. Indeed, it is commonplace when concrete is mixed and then poured to use penetrating vibrating rods in the wet material so as to ensure that this air is brought to the surface and that the concrete is as strong and homogeneous as possible.

There is however a need in special circumstances for concrete containing incorporated air at a level greater than can be incorporated by simple mixing. Such materials are necessary, for example, as special low strength concretes which in situ can match the strength of a surrounding environment. A primary example in that of intentionally low-strength concrete used for the back-filling of excavations in roads, where it is necessary that the material be eventually capable of re-excavation by traditional methods. There is also a requirement for concretes with a level of air incorporation which is such that they are light weight and can be used as cladding material without unduly loading the main structure.

A standard way of producing such air-incorporated, or foam, concrete is to blend together two materials, one material being a conventional wet concrete mix and the other material a preformed foam in liquid form.

Such a process is conventionally carried out using two supply units. One supply unit is a conventional concrete mixer, or a truck-mounted ready-mixed concrete supply. The other unit is a foam-producing unit and typically employs an air compressor and suitable metering equipment to supply a foam-producing material into an air stream produced by the compressors so that a liquid foam is produced. Some such foam-producing materials are foamable liquids, typically water-based and are used with suitable surface active agents as producers of a stable foam. Others are in powder form, for the same purpose. The wet concrete and the foam are then mixed together, prior proposals describing both techniques for such mixing in the concrete mixer itself or in a separate mixing chamber.

There are however problems with the above techniques. For example, the foam is not always stable for long enough periods. Also the foam and the concrete are typically of very different bulk densities. Even if lightweight aggregates are used, the bulk density of the concrete compared with that of the foam is very much higher. Because the bulk densities differ it is difficult to mix the two materials into a homogeneous mixture.

The present invention sets out to overcome the problem of incorporation of air into a hardenable flowable mixture of water and cementitious material, such as a grout, mortar or concrete, in a manner which avoids the complication of having to create the foam in advance of mixing.

In one aspect the invention provides a mixer for concrete or the like including as a rotary mixing element an inclined rotary screw conveyor of diameter decreasing from the lower to the highe end.

In another aspect the invention provides equipment for providing a batch supply of a flowable water-containing cemititious mixture, which comprises an elongate mixing drum with one end located higher than the other; an inlet opening for gravity feed of dry materials of the mixture at the top of the lower end of the drum; a discharge opening preferably selectively openable and closeable, at the base of the upper end of the drum; an inlet for continuous supply of an aqueous foam material at or near the top of the lower end of the drum; and an upwardly inclined rotary screw conveyor journalled within, and lying at a clearance with the base of the inclined drum, extending along the drum from beneath the inlet or inlets to generally above the discharge opening; and having a diameter decreasing upwardly so as to exhibit a generally conical nature or operating envelope.

Preferably the drum is conical in a manner corresponding to the conveyor shape at least in those parts which surround the conveyor.

A particularly preferred shape of drum has an upwardly convergent conical base generally surrounding an axially lower part of the screw mixer/conveyor, and convergent side walls attached to the convergent base.

The drum may conveniently possess a transversely extending horizontal tilt mounting so that the smaller end, normally higher, can be lowered to discharge mixed material through the discharge opening.

The invention further extends to an installation for producing batch supplies of a flowable water-containing cementitious mixture, comprising equipment as defined above communicating with a foam-producing nozzle arrangement itself in liquid communication with a metering device connected to both a pump for water and a supply reservoir for a foaming agent.

The foam-producing nozzle arrangement may itself comprise a housing apertured at its base; a liquid inlet nozzle at an upstream part of the housing to supply a sprayed mixture of water and foaming agent; and a transverse foam-creating mesh located to obstruct the sprayed mixture, and thus create a foam, located above the base aperture of the housing.

In a yet further aspect the invention consists in a method of providing a flowable water-containing cementitious mixture with incorporated air, in which the dry materials of the mixture and water are fed together with an aqueous foam continuously into the lower end of an elongate upwardly inclined mixing drum having an upwardly inclined screw mixer/conveyer of diameter decreasing from the lower to the higher end rotating therein, at a clearance with the drum internal surface, and in which thereafter the wet mixture is discharged by tilting the drum to become downwardly inclined, and causina or allowing the air-containing wet mixture to leave a discharge orifice in the base of the drum.

The invention will be further described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic longitudinal section through the mixing drum of an embodiment equipment for producing foam concrete, Figure 2 is an end view of the drum of Figure 1, taken in the direction of arrow A, Figure 3 is a flow diagram showing the steps in the provision of a foam component for incorporation into the drum of Figure 1, and Figure 4 is a diagrammatic section through a foaming nozzle for use in the procedure shown in the flow diagram of Figure 3.

Figure 1 shows in diagrammatic form a longitudinal section through a shaped mixing drum 1 for concrete. As shown in the drawings, the drum 1 generally decreases in cross-sectional area from left to right. More specifically, the base surface of the drum 2 is part conical, sloping upwardly from left to right in the drawing, and the flat sides 3, 4 of the drum converge from the lower end 5 to the upper end 6.

The top 7 of the drum is open, at least over its rearward part, to provide an inlet at 8 for the materials forming the concrete. These materials can be added dry, or can be added with part of their final water content present.

The back plate 9 of the drum may be suitably apertured at 10 so that a supply of continuously produced foam can be incorporated at this point, essentially to encounter the materials being loaded, so that foam and materials fall together by gravity into the drum. As an alternative, the foam could be added at the top of the drum, i. e. through part of the same opening 8 as the other materials.

Along the axis of the conical base surface 2 of the drum 1 there extends a rotary shaft 11, and fixed to this shaft there is a mixing screw blade 12 of diameter diminishing from left to right in the drawing. The mixing screw 12 is so dimensioned and positioned that, as it rotates, the maximum envelope of space defined runs at a clearance with the conical surface 2 of the drum 1.

The drum is mounted, at its larger end 5, for swivelling movement about a horizontal transverse axis 13. If desired, the mounting may be such that the drum is also capable of swivelling about a vertical axis, so as to alter the position of placement of mixed material.

Towards the higher, right hand, side 6 of the drum as shown in figure 1 there is a discharge opening 14 in the base conical surface. This is selectively openable when required to act as a discharge.

In use, the raw materials of concrete (cement powder, aggregate, and potentially other mixtures for plasticising or internally reinforcing the concrete) either as dry materials, or materials which have been moistened with at least part of the eventually required mixing water, are added through the opening 8 at the rearward end. Simultaneously with this addition, a body of foam is incorporated at 10, near opening 8, as shown in the drawings. As described in more detail below, this foam is continuously produced and the amount added is metered so that its water content is known as a proportion, or all, of the total water content. The mixture and the foam are mixed together by the action of the tapering screw 12 within the converging drum.The action is not a simple conveying process, since the converging nature of the screw against the converging base gives a complex motion to the product. However, there is a general flow path up the drum 1 which transfers the material up the slope in a generally central zone, and permits return flow to pass backwards at the edge regions. Overall the action is of a gentle nature and blends foam into the body of the material to give an even and fine bubble structure.

When the required degree of mixing has been achieved, the vessel is tipped about its horizontal axis 13 so that the base of the drum, previously upwardly sloping, now slopes downwardly. The screw is kept in motion and thus assists in the ejection of materials through the selectively opened discharge opening 14.

The extent of tilt can be varied depending upon the exact position of the required discharge opening, and if desired a swivelling motion about a simple vertical axis can also be incorporated in the drum mounting so as to give further facility for discharge exactly where needed.

The provision of foam as such, continuously into the inlet end of the mixer, may be distinguished from prior proposals in this field, which involve the incorporation of a preformed foam in discrete volumes, or involve mixing processes of high energy input to create a foam within an otherwise unfoamed total mixture.

The foam as added in the present invention is metered since it constitutes a measured proportion or all of the mixing water used. A way of achieving this is shown in Figure 3, in which a water reservoir 20 is placed in communication over a suitable pump 21 with a metering device 22 into which the requisite amount of foaming agent is introduced from 22a. The mixture of water and foaming agent is passed through a foaming nozzle 23 and the continuous supply of foam thereby produced is fed into the mixing vessel at 10.

Figure 4 shows diagrammatically a type of foaming nozzle 23 which may be used. It consists essentially of a split housing having a rearward portion 24 and a forward portion 25, so shaped so as also to define a lower opening 26. Between the two parts 25, 26 of the housing is clamped a suitably apertured mesh 27. The rearward portion of the housing is placed in communication with the metering device 22, and possesses a nozzle 28 with a divergent nozzle opening at 29, such as to spray a mixture of water and foaming agent at the mesh 27, where its movement is interrupted and a fine continuous supply of foam is produced.

Claims (8)

CLAIMS:

1. A mixer for concrete or the like including as a rotary mixing element an inclined rotary screw conveyor of diameter decreasing from the lower to the higher end.

2. Equipment for providing a batch supply of a flowable water-containing cemititious mixture, which comprises an elongate mixing drum with one end located higher than the other; an inlet opening for gravity feed of dry materials of the mixture at the top of the lower end of the drum; a discharge opening preferably selectively openable and closeable, at the base of the upper end of the drum; an inlet for continuous supply of an aqueous foam material at or near the top of the lower end of the drum; and an upwardly inclined rotary screw conveyor journalled within, and lying at a clearance with the base of the inclined drum, extending along the drum from beneath the inlet or inlets to generally above the discharge opening; and having a diameter decreasing upwardly so as to exhibit a generally conical nature or operating envelope.

3. Equipment as claimed in claim 2 in which the drum is conical in a manner corresponding to the conveyor shape at least in those parts which surround the conveyor.

4. Equipment as claimed in claim 2 in which the drum has an upwardly convergent conical base generally surrounding an axially lower part of the screw mixer/conveyor, and convergent side walls attached to the convergent base.

5. Equipment as claimed in claim 2, 3 or 4 in which the drum possesses a transversely extending horizontal tilt mounting so that the narrower end, normally higher, can be lowered to discharge mixed material through the discharge opening.

6. An installation for producing batch supplies of a flowable water-containing cementitious mixture, comprising equipment as claimed in any one preceding claim communicating with a foam-producing nozzle arrangement itself in liquid communication with a metering device connected to both a pump for water and a supply reservoir for a foaming agent.

7. An installation as claimed in claim 6 in which the foam-producing nozzle itself comprises a housing apertured at its base; a liquid inlet nozzle at an upstream part of the housing to supply a sprayed mixture of water and foaming agent; and a transverse foam-creating mesh located to obstruct the sprayed mixture, and thus create a foam, located above the base aperture of the housing.

8. A method of providing a flowable water-containing cementitious mixture with incorporated air, in which the dry materials of the mixture and water are fed together with an aqueous foam continuously into the lower end of an elongate upwardly inclined mixing drum having an upwardly inclined screw mixer/conveyer of diameter decreasing from the lower to the higher end rotating therein, at a clearance with the drum internal surface, and in which thereafter the wet mixture is discharged by tilting the drum to become downwardly inclined, and causing or allowing the air-containing wet mixture to leave a discharge orifice in the base of the drum.