GB2050854A

GB2050854A - Method for supplying additives to concrete or cement

Info

Publication number: GB2050854A
Application number: GB8015208A
Authority: GB
Original assignee: Heidelberger Zement AG
Current assignee: HeidelbergCement AG
Priority date: 1979-05-08
Filing date: 1980-05-08
Publication date: 1981-01-14
Also published as: CH646093A5; ATA243880A; AT390397B; DE2918451A1; NL8002527A; DE2918451C2; GB2050854B; BE883177A

Abstract

A method for dosing and uniformly mixing additives in concrete or cement, wherein the additive is drawn in by a water stream in accordance with the principle of a water jet pump, mixed with the water and introduced into the concrete or cement together with the water stream. <IMAGE>

Description

SPECIFICATION Method for supplying additives to concrete or cement The invention relates to a method for dosing and uniformly mixing additives in the form of liquids, solutions, emulsions or dispersions or gases, into concrete or cement.

Various methods and devices or installations are available for the dosing of additives. Frequently, an electrically driven pump, e.g. a gear pump, is used together with a time control system. The functions of conveying and dosing are in such a case performed by a single unit. For control of the dosing, flow clocks, monitor lamps, visual cylinders and similar devices are used. A dosing pump is sensitive because of its moving parts, and disturbances or even failure of the pump can occur due to clogging up.

Occasionally, technically better but more expensive and uneconomic installations are used, in which instead of the dosing time, the dosing quantity is used, determined by a weighing device or in an analog manner by means of a potentiometer with a float, or by way of measurement electrodes.

Furthermore, arrangements are available which convey the additive by compressed air and which are less liable to disturbance, because of the lower number of moving parts.

These known arrangements and methods operate satisfactorily with sufficiently large dose amounts.

However, in many cases it is necessary to accurately dose only small or very small amounts, and to provide uniform mixing in low concentration, in a conveying medium for example in make-up water for concrete, cement, or their dry constituents. The dosing and mixing of such small amounts as additives is a problem, for example where large amounts of concrete must be prepared in a very short time, such as in motorway or airport construction, and most of all in large engineering works or in the concrete transporting or prefabricated concrete industries. The mixing times in such plants, which mix a number of cubic meters of concrete per charge, frequently lie considerably below 60 seconds.

The additives used in such cases in small doses, such as for example air-pore materials or liquid, are expensive and for reasons of concrete technology, must be accurately dosed and well mixed in.

The known installations are in such cases not usable or only usable under some conditions. Dosing by hand is technically inadequate.

It is an object of the invention to provide a method by which additives can be reliably dosed, even in small quantities, and rapidly and uniformly mixed in a conveying medium, whereupon the additive, fineiy distributed in the conveying medium, can be introduced into the material to be provided with the additive, namely concrete or cement, directly after the mixing, or later.

The invention consists in a method for dosing and uniformly mixing additives in concrete or cement, wherein the additive is drawn in by a water stream in accordance with the principle of a water jet pump, mixed with the water and introduced into the concrete or cement together with the water stream.

The additive may be mixed with the water stream in a suction and mixing chamber and is preferably swirled. The additive can be used in the form of a concentrated solution or a solution with predetermined dosing. It can be introduced into the concrete or cement directly after mixing in the water stream, and together therewith. In a preferred embodiment of the method, the mixture of additive and water is sprayed before being introduced into the concrete or cement. The mixture is advantageously introduced during the mixing of the concrete or cement. The water used for the water jet can be used at the same time as make-up water in the production of concrete or cement.

In the method according to the invention, a principle similar to a water jet pump is used, the additive being fed and dosed and combined with the stream of water and intensively mixed and swirled, preferably in high dilution.

Since the mixture of the additive and water can be introduced into the concrete or cement charge to be provided with the additive, directly after the mixing procedure, the additive can be distributed therein with little loss or can be sprayed with a large effective contact surface.

The method according to the invention can be performed with an installation which is economic and not liable to disturbance. By means of a water jet which can be regulated by a water pressure connection, additive can be drawn from an additive container through a line and fed into a suction and mixing chamber, which is followed by a supplementary air supply and a spray nozzle. If the additive-water mixture is to be furthermore introduced into a substance, then this can be done by way of a pipe leading into a mixer.

In this manner a very small, easily dosable amount of additive can be finely distributed and introduced into a mix substance present in a mixer, where it can be rapidly and uniformly mixed in.

It is particularly advantageous if the conveying medium can be make-up water for concrete or cement, which in this manner, in the total amount or in part can be introduced through a branch line and intensively swirled with the additive fed by the action of the water jet pump system, and subsequently sprayed.

Water jet pumps have a low efficiency. However, the potential available is sufficient for the dosing of small amounts of additive, this being for example ensured by make-up water conveying the additive. Make-up water is available at all concrete mixing plants.

The effectiveness of the method according to the invention will be further explained with reference to several examples which relate to the mixing of additives in various kinds of concrete and structural cement.

Example 1 Road concrete: Consistency stiff (K1), Power mixer BHS 2m3 Concrete material B35 according to DIN 1045, with: 33% 0-2mm sand 26% 5-11 mm chippings 41% 1 1-22mm chippings Required LP (air pore material) content 4.0% LP material based on natural resins The following table shows: 1.0 Null Row: simple mixing of air-pore former in 10% dilution with water, with shortened mixing time, 1.1 Null Row: simple mixing ofairporeformerin 10% dilution with water, with normal mixing time, 1.2 Row: with the method of the invention, in 2.5% dilution with water, with shortened mixing time.

LP medium dose Wet mix time present LP (% by cement wt.) (seconds) (Vol, %) 1.0 0.08 50 3.2 1.1 0.08 75 4.1 1.2 0.06 50 4.2 Example 2 Compensation concrete Consistency soft (K3), Mobile mixer 5m3 Concrete material-compression resistance 3NImm2 after 28 days Grain: Exclusively sand 0-2mm Required LP content 40 to 45%, LP material synthetically based.

The following table shows: 2.0 Null Row: simple mixing ofthe LP material undiluted, with shortened mixing time, 2.1 Null Row: simple mixing Df the LP material undiluted, with normal mixing time, 2.2 Row: with the method according to the invention, in 2.5% dilution with water, with shortened mixing time.

LP medium dose Wet mix time present LP (% by cement wt.) (seconds) (Vol.

2.0 0.30 120 -26 2.1 0.30 360 43 2.2 0.14 120 A3 Example 3 Protective concrete, fibre reinforced Consistency flowable, Mobile mixer 5m3 Concrete material-compression resistance 6N/mm2 after 28 days bending resistance 5N/mm2 after 28 days Grain: Sand 0.2mm Fibre length 26mm Required LP content 20 to 25%, delay based on organic means, LP medium synthetically based.

For the concreting of large surfaces, for example flat roofs, it is necessary for the setting time of the concrete to be considerably delayed without the LP content being substantially reduced. Too great a change in the LP content would mean that the solid concrete characteristics such as gross density and strength have changed too greatly. Also, the dimensional tolerance of the structure would be questionable.

The following table shows: 3.1 Null Row: simple mixing of the LP medium, undiluted, 3.2 Row: with the method of the invention, in 2.5% dilution with water.

LP medium Wet present present LP loss dose mix LP LP within (% by cement time (Vol %) after 12 hours weight) 12 hours (Vol /O) (Vol %) 3.1 0.15 360 26 21 5 3.2 0.08 120 25 23 2 Example 4 Heavily delayed structural cement Consistency soft (K3), Mobile mixer 5m3 Cement strength 6.5N/mm2 after 28 days Grain: sand 0.2mm Required LP content, at least 20% after 36 hours.

Delay organically based, LP medium synthetic.

The following table shows: 4.1 Null Row: simple mixing of the LP medium, undiluted, 4.2 Row: with the method of the invention, in 2.5% dilution with water.

LP medium Wet Present Present LP loss dose mix LP LP within (% by cement time (Vol %) after 36 36 hours weight) seconds hours (Vol %) (Vol %) 4.1 0.17 360 28 17 11 4.2 0.09 120 29 23 6 The examples 1 to 4 relate to the mixing in of air pore formers. The considerably increased stability of the air pores according to the method of the invention is surprising. The use of concretes and cements with very high air pore content - up to 70% - which are economic and very workable, is made considerably more secure by the method of the invention.

The following example illustrates the method of the invention, using a liquifier.

Example 5 Concrete for the machine production of concrete plaster blocks: Consistency soildamp-stiff (K1), drum mixer 1 m3 Concrete material: compression resistance 63N/mm2 after 28 days Grain 0-16mm Additive plasticising concrete liquifier (CL) The following table shows: 5.1 Null Row: simple mixing of the CL in 10% dilution with water, 5.2 Row: with the method of the invention in 2.5% dilution with water.

CL dose Wet Compression Gross density dose mix resistance after 28 days time after28days 5.1 0.25% 120s 69.0N/mm2 2.27kg/l 5.2 0.15% 80s 71.2N/mm2 2.29kg/l Even with the admixing of liquifier is the effectiveness of the method of the invention clearly shown, by which a uniform distribution and an activation of the additive reagents in the concrete, and an increased stability is obtained. A further important technical advance of the method of the invention is the surprising rapid uniform mixing in of the additive. The method is furthermore especially economic owing to the extensive utilisation, that is to say sparing use, of the additive.

The method of the invention can of course also be used for the dosed mixing of an additive into a liquid, the additive-liquid mixture being stored and only used when required.

In the drawing, an example of a device for performing the method of the invention is diagrammatically illustrated.

The device is connected to a pressure water connection 10, and the dosing and mixing arrangement D is disposed at the central part of the device. The arrangement comprises a branch line 6 which is immersed in an intermediate or additive container 13, from which a water stream coming from the pressure water connection 10 draws a dosed amount of the additive, through the branch line 6. The additive passes into a suction and mixing chamber 5 where it mixes with the water, and is sprayed from a spray nozzle 3 through a fine sieve 2 into a pipe 1 arranged at the outlet side of the device. This pipe 1 leads from the dosing arrangement D into a collecting container or mixer (not shown) in which the water provided with the additive collects, or is mixed into a material, for example concrete.In the wall of the pipe a plurality of air inlets 4 are provided which promote better swirling and enlargement of the surface of the additive-water mixture.

At the end of the dosing arrangement D remote from the delivery end, a water meter 7 and a magnetic valve 8 are arranged. Between the pressure water connection 10 and the magnetic valve 8, a manually operable valve 9 is interposed, bywhich the quantity of waterflowing can be further regulated.

The magnetic valve 8 is electrically controlled by way of a relay 11 connected to an electric supply 12, the relay having a time selection member. Thus, depending on the setting of the time selection, a given amount of water can be conducted through the dosing arrangement.

A plurality of such arrangements can be connected one after the other, in order to introduce not just one, but a plurality of additives.

Claims

CLAIMS:

1. A method for dosing and uniformly mixing additives in concrete or cement, wherein the additive is drawn in by a water stream in accordance with the principle of a water jet pump, mixed with the water and introduced into the concrete or cement together with the water stream.

2. A method according to claim 1, wherein the additive is mixed and swirled with the water stream in a suction and mixing chamber.

3. A method according to claim 1 or 2, wherein the additive is used in the form of a concentrated solution or in the form of a solution with predetermined dosing.

4. A method as claimed in claim 1,2 or 3, wherein the additive is introduced into the concrete or cement directly after the mixing in the water stream and together therewith.

5. A method as claimed in claim 4, wherein the mixture of additive and water is sprayed before introduction into the concrete or cement.

6. A method as claimed in claim 4 or 5, wherein the concrete or cement to be supplied with the additive is mixed during the introduction of the mixture of additive and water.

7. A method as claimed in any one of claims 1 to 6, wherein the water stream serving as conveying medium is used at the same time as make up water for the concrete or cement.