GB2091572A

GB2091572A - Production of foamed concrete

Info

Publication number: GB2091572A
Application number: GB8201803A
Authority: GB
Original assignee: Thermal Structures Ltd
Current assignee: Thermal Structures Ltd
Priority date: 1981-01-23
Filing date: 1982-01-22
Publication date: 1982-08-04
Also published as: GB2091572B

Abstract

In a method of producing lightweight foamed concrete of pre- determined density, successive batches of pre-determined amounts of starting ingredients are supplied automatically to a mixer 6; each batch of ingredients consisting of at least cement, filler, water and aqueous foam from a foam generator. The concrete is discharged into hopper 12 having an exit 14 through which the outflow of concrete is regulated by the control of a pinch valve 16, 28 responsive to signals from an electrical controller so as to maintain the upper surface of the concrete in the hopper at the level of level detecting probe 26. Transducers 22 send signals to the controller corresponding to the weight of the volume of concrete in the hopper. The controller computes the density of the concrete and if it differs from a desired density value, regulates the amount of foam supplied in the next batch of starting ingredients so that the density of the concrete mixed therefrom becomes closer or substantially equal to the desired value. <IMAGE>

Description

SPECIFICATION Production of foamed concrete This invention concerns a method of producing foamed concrete and equipment therefor.

It is known to make articles of lightweight concrete by setting a wet lightweight concrete mix in a mould. At least one reason why the concrete is lightweight, in comparison with conventional concrete, is that the lightweight concrete contains a mass of gas bubbles, for example air bubbles.

One technique of producing lightweight concrete is to foam the wet concrete mix so that it contains bubbles which remain trapped in the set concrete.

The density of lightweight concrete is inversely proportional to the amount of gas forming the bubbles. But if there is too much gas in the concrete due, for example, to excessive foaming, the lightweight concrete when set may be too weak for its intended purpose.

Since the density of lightweight concrete is inversely proportional to the extent of gas bubble formation in a given volume of the concrete and thus inversely proportional to the strength of the concrete, the density of wet lightweight concrete is a measure of the strength that the set concrete will have.

According to a first aspect of the invention there is provided a method of producing foamed concrete comprising supplying successive batches of pre-determined amounts of starting ingredients to driven concrete mixing apparatus to produce wet flowable foamed concrete mix from said ingredients, each said batch of starting ingredients consisting of at least cement, water and foam from foam supply means supplying the foam to the mixing apparatus, making a measurement of the density of the wet flowable concrete mix produced from each batch, determining whether or not the measurement differs from a desired predetermined value, and if the measurement does differ then using control means to control the supply of foam from the foam supply means so as to automatically control the amount of foam in a succeeding batch so that the measurement of density of the wet flowable concrete mix produced from said succeeding batch approaches nearer to or substantially equals the desired value.

According to a second aspect of the invention there is provided equipment to produce foamed concrete comprising driven concrete mixing apparatus to give an output of wet flowable concrete by mixing together starting ingredients of at least cement, filler, water and foam, said starting ingredients, being suppliable to the mixing apparatus as a batch of pre-determined amounts of the ingredients from cement, filler, water and foam supply means under the control of control means, means to produce a signal which is a function of the density of the wet flowable concrete mix produced from said batch, said control means being arranged to utilize said signal to determine whether or not the density differs from a desired pre-determined value, the control means being also arranged such that if the density does differ then the supply of foam in a succeeding batch of starting ingredients is automatically regulated by the control means to vary the density of the concrete produced from that batch so that the density is nearer or substantially equal to said pre-determined value.

The concrete can be lightweight foam concrete formed by mixing starting ingredients which are, for example, portland cement, filler (for example, sand, stonedust or pulverised fuel ash), water and foam. The foam can be initially produced by a foam generator using a foaming agent which may be an aqueous foaming agent, for example a foaming agents used in fire-fighting, producing a stable foam.

The mixing is carried out in power driven concrete mixing apparatus to which successive batches of starting ingredients are added. Each batch consists of at least a pre-determined amount of cement, a pre-determined amount of water, and a pre-determined amount of foam.

Although each batch preferably also includes a pre-determined amount of filler.

Operation of the mixing apparatus and the supply of starting ingredients is under control of pre-programmed electrical control means comprising, for example, a micro-computer. The control means can be pre-programmed with a plurality of recipes for different concretes, and means can be provided enabling selection of a particular recipe so that starting ingredients in amounts corresponding to the selected recipe form a said batch supplied to the mixing apparatus. The control means can also be preprogrammed with a value of concrete density it is desired concrete mixed from a given recipe should have.

Cement and filler can each be stored in respective hoppers from which pre-determined amounts of cement and filler can be delivered automatically as required under the control of the control means. For example each hopper can have an outlet opening in its base through which the cement or filler falls when electrically powered obturating means is opened automatically in response to a signal from the control means. The falling cement or filler is received by weighing means providing an electrical signal which is a function of the weight of cement or filler it has received. On the pre-determined amount being received the electrical signal from the weighing means to the control means causes the latter to signal the obturating means which closes in response thus stopping further delivery of the cement or filler.The pre-determined weighed amounts of cement and filler can then be supplied automatically to the mixing apparatus by driven delivery means operated in response to signals from the control means. The weighing means can comprise a container receiving both the cement and filler and the delivery means can comprise a ribbon blender which mixes the cement and filler dry as it converys them in the concrete mixing apparatus which is continuously operating under control of the control means. To complete the preferred batch of starting ingredients supplied to the mixing apparatus pre-determined amounts of water and foam are supplied thereto at predetermined times. The water is stored in a reservoir tank from which water can be delivered by a pump to the mixing apparatus.The pump operates automatically in response to signals from the control means to pump a pre-determined volume of water into the mixing apparatus. The foaming agent is also stored in a reservoir from which under control of signals for the control means it is automatically supplied to foam supply means also operated automatically under control of signals from the control means to vigorously mix the agent with water to generate foam and deliver a pre-determined amount of the foam to the concrete mixing apparatus. The foam can be supplied to the concrete mixing apparatus at a substantially constant volume per unit time.

Accordingly the duration of foam supply determines the amount of foam supplied to the mixer. The supply of foam to the concrete mixing apparatus can be after the supply to the latter of the water The concrete mixing apparatus can comprise an approximately horizontal and substantially cylindrical driven drum mixer of known type into which the batch of starting ingredients is supplied at an adjacent one end and the wet flowable concrete mix output emerges from the other end of the drum. The concrete output from the mixing apparatus can be substantially continuous, provided batches of the starting ingredients are supplied in succession at appropriate times to maintain continuity of the concrete output. The time at which commencement of the supply of each batch occurs is controlled automatically by the control means in a manner to be subsequently described.

At least part of the wet flowable concrete mix is continuously introduced from the mixing apparatus into a receptacle or containing means through an upper opening therein.

The introduced concrete moves through the containing means and leaves through an exit opening in a lower part of the containing means.

The upper surface of the concrete in the containing means can be maintained substantially at a pre-determined level by varying the supply of concrete to or the outflow of concrete from the containing means in response to signals observed from detecting means detecting when the concrete level rises above or falls below the predetermined level. For example the exit from the containing means may be provided with obturating or valve means to regulate the rate of concrete outflow.

The containing means acts on weight detecting means providing a weight of concrete signal which can be an electrical signal. The weight of concrete signal is a function of substantially the whole weight of concrete in the containing means, this signal being a function of the concrete density since the volume of the moving concrete weighed remains substantially constant.

The weight of concrete signal is observed by the control means and if the signal indicates the weight of the concrete deviates or deviates too much, from a pre-determined value consistent with the concrete having the desired density for the particular recipe being mixed, the control means operates sending a signal to vary the amount of foam delivered to the mixing apparatus in a succeeding batch of starting ingredients with a view to bringing the density of the concrete output to or nearer to a desired density value.

If desired, the control means can be arranged to compute the density using the weight measurement signal(s). Preferably the weight measurement is made or sampled at pre-determined intervals and an average weight value or density computed for a given time period.

This average value is compared with the predetermined desired value. By using an average value, the chance of varying the foam input excessively (and thus changing the concrete density too much) is reduced.

The invention will now be described, by way of example, with reference to the accompanying drawing in which: Fig. 1 is a diagrammatic rear view partly in section of a fragment of an embodiment of equipment formed according to the second aspect of the invention for carrying out the method according to the first aspect, and Fig. 2 is a fragmentary side view, along arrow II in Fig. 1, showing a reception hopper or containing means in vertical section.

A driven concrete mixer, is shown at 2 to give a continuous output of wet concrete mix along a chute 4 emerging through an outlet opening 8 from an inclined rotating mixing drum 6 containing mixing blades.

A tube 10 containing a ribbon blender (not shown) feed cement and filler to the drum 6, supplies of water and foam being indicated by arrows W and F respectively.

Concrete discharged by the chute 4 is received to one side in a reception hopper 1 2 having an exit 14 connected to a resilient compressible tube 1 6 leading to a supply hopper 1 8 of a concrete delivery pump.

Hopper 12 is on legs 20 on weight detecting transducers 22, for example load cells, on firm supports 24 which are stationary relatively to hopper 12.

A concrete level detector or probe 26 is disposed in an upper part of hopper 12.

Press rolls 28 are disposed on either side of tube 1 6. At least one roller is movable relatively to the other under power, for example by an indexing electric motor, to squeeze the tube by varying amounts by which exit 1 4 is obturated.

On start up, the control means (not shown) signals the indexing motor to close the exit 1 4 and initiates the supply of the first batch of ingredients to drum 6 wherefrom, after an interval, mixed lightweight foam concrete is discharged via chute 4 to the hopper 12. Concrete discharge is now continuous, the control means acting to ensure successive batches of ingredients are supplied to maintain continuity of concrete output. For this the control means may include timer means to ensure, for a given output rate, that the batches are added at appropriate intervals, and/or inside the drum a level detector or probe 30 is provided sending an electrical signal to the control means to initiate supply of the next batch of starting ingredients when the level of the mix in the drum falls below the level which ensures output continuity.

The level of concrete in the hopper 12 rises until it reaches probe 26 which sends an electrical signal to the control means. This signals the indexing motor to widen the space between rolls 1 8 thus opening exit 14 whereby concrete leaves hopper 12 for hopper 18 and the feed pump.

Preferably the feed pump has a greater output than the maximum rate of supply to the hopper 1 8. The control means operates to open or close the exit 14 by varying degress depending on the signals from probe 26 to ensure the upper level of the concrete moving through the hopper 12 remains substantially at the level of the probe. The volume of concrete in hopper 12 thus remains substantially constant. The transducers 22 send to the control means electrical signals corresponding to the weight of the concrete in the hopper 1 2.

These are a function of the concrete density which if it deviates from the pre-determined value results in the control means varying the amount of foam supplied in the next batch of starting ingedients.

A level indicator or probe 32 may be mounted in hopper 18. If the concrete rises to the level of probe 32 due to the concrete feed pump stopping or slowing, the probe 32 signals the control means to stop operations of the mixing apparatus.

The hopper 1 2 may have a pressure transducer 34 sending to the control means pressure signals corresponding to the weight of the column X of concrete pre-determined volume within the moving mass. The signals from transducer 34 are also used to determine the density of the concrete.

For the equipment in Figs. 1 and 2 the control means may periodically sample the weight signals for computing an average density.

The chute 4 may be movable, relatively to the drum 6, into and out of a concrete delivery position. The movement may be manual or under power by motor means automatically operated,at the beginning and end of mixing for example, in response to signals from the control means at the beginning and end of mixing.

Claims

1. A method of producing foamed concrete comprising supplying successive batches of predetermined amounts of starting ingredients to driven concrete mixing apparatus to produce wet flowable foamed concrete mix from said ingredients each said batch of starting ingredients consisting of at least cement, water and foam from foam supply means supplying the foam to the mixing apparatus, making a measurement of the density of the wet flowable concrete mix produced from each batch, determining whether or not the measurement differs from a desired predetermined value, and if the measurement does differ then using control means to control the supply of foam from the foam supply means so as to automatically control the amount of foam in a succeeding batch so that the measurement of density of the wet flowable concrete mix produced from said succeeding batch approaches nearer to or substantially equals the desired value.

2. A method as claimed in claim 1, in which in each batch of starting ingredients there is also a pre-determined amount of aggregate or filler material.

3. A method as claimed in claim 1 or claim 2, in which from one batch to another, of the starting ingredients, only the amount of foam is varied.

4. A method as claimed in any one preceding claim, in which the control means controls the amount of each starting ingredient in each batch.

5. A method as claimed in any one preceding claim, in which the time at which the supply of a said batch of starting ingredients commences is controlled by said control means.

6. A method as claimed in any preceding claim, in which when a batch of starting ingredients is supplied the time of commencement of the supply of each of the ingredients is controlled by said control means.

7. A method as claimed in any one preceding claim, in which a said measurement of the density is obtained by making a weight measurement of a pre-determined volume of aforesaid flowable concrete mix.

8. A method as claimed in any one of claims 1 to 6, in which making a said measurement of the density of aforesaid wet flowable concrete mix comprises introducing the concrete into containing means having an exit towards which the introduced mass of concrete moves, maintaining an upper surface of the moving mass substantially at a pre-determined level and making a measurement of the weight of a pre-determined volume of the concrete whilst concrete occupying said volume moves in the containing means.

9. A method as claimed in claim 8, in which the concrete is substantially continuously introduced into the containing means and leaves continuously through said exit, and the rate at which the concrete leaves is varied to maintain said upper surface at substantially said pre-determined value.

10. A method as claimed in any one of claims 7 to 9, in which said weight measurement is sampled periodically and an average weight or density value of the concrete mix is computed from a number of said samples of the weight measurement.

11. A method as claimed in any one of claims 1 to 6, in which a moving mass of the concrete mix there is a measurement of the density of the concrete mix is obtained by making a measurement of the pressure exerted by a predetermined head of a continuously moving mass of concrete.

12. Equipment to produce foamed concrete comprising driven concrete mixing apparatus to give an output of wet flowable concrete by mixing together starting ingredients of at least cement, filler, water and foam, said starting ingredients being suppliable to the mixing apparatus as a batch of pre-determined amounts of the ingredients from cement, filler, water and foam supply means under the control of control means to produce a signal which is a function of the density of the wet flowable concrete mix produced from said batch, said control means being arranged to utilize said signal to determine whether or not the density differs from a desired pre-determined value, the control means being also arranged such that if the density does differ then the supply of foam in a succeeding batch of starting ingredients is automatically regulated by the control means to vary the density of the concrete produced from that batch so that the density is nearer or substantially equal to said predetermined value.

12. Equipment to produce foamed concrete comprising driven concrete mixing apparatus to give an output of wet flowable concrete by mixing together starting ingredients of at least cement, filler, water and foam, said starting ingredients being suppliable to the mixing apparatus as a batch of pre-determined amounts of the ingredients from cement, filler, water and foam supply means under the control if control means to produce a signal which is a function of the density of the wet flowable concrete mix produced from said batch, said control means being arranged to said signal to determine whether or not the density differs from a desired predetermined value, the control means being also arranged such that if the density does differ then the supply of foam in a succeeding batch of starting ingredients is automatically regulated by the control means to vary the density of the concrete produced from that batch so that the density is nearer or substantially equal to said predetermined value.

13. Equipment as claimed in claim 12, in which containing means is provided to receive at least part of a continuous concrete mix output from the mixing apparatus, said containing means is provided with means by which an outflow of concrete for the containing means can be controlled to maintain the upper surface of the concrete at substantially a pre-determined level in the containing means, means to supply to said control means a signal which a function of the weight of concrete in the containing means.

14. A method of producing foamed concrete as claimed in claim 1 and substantially as hereinbefore described.

15. Equipment to produce foamed concrete as claimed in claim 12 and substantially as hereinbefore described.

New claims or amendments to claims filed on 26th April 1982.

Superseded claims 1, 11, 12.

New or amended claims

1. A method of producing foamed concrete comprising supplying successive batches of predetermined amounts of starting ingredients to driven concrete mixing apparatus to produce wet flowable foamed concrete mix from said ingredients, each said batch of starting ingredients consisting of at least cement, water and foam from foam supply means supplying the foam to the mixing apparatus, making a measurement of the density of the wet flowable concrete mix produced from each batch, determining whether or not the measurement differs from a desired predetermined value, and if the measurement does differ then using control means to control the supply of foam from the foam supply means so as to automatically control the amount of foam in a succeeding batch so that the measurement of density of the wet flowable concrete mix produced from said succeeding batch approaches nearer to or substantially equals the desired value.

11. A method as claimed in any one of claims 1 to 6, in which a moving mass of the concrete mix a measurement of the density of the concrete mix is obtained by making a measurement of the pressure exerted by a pre-determined head of a continuously moving mass of concrete.