GB2106886A

GB2106886A - Rapid hardening of concrete

Info

Publication number: GB2106886A
Application number: GB08129712A
Authority: GB
Inventors: Roman Malinowski
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-10-01
Filing date: 1981-10-01
Publication date: 1983-04-20
Also published as: GB2106886B

Abstract

In a method of and a device for the rapid hardening of concrete and similar casting materials by carbonation, the capillary system of the material in the curing facility is caused to be effectively dried out, prior to and/or during carbonation, by means of controlled conditions comprising a combination of air flow, heat generation and moisture absorption in a circulating, continuous procedure. A device for applying the curing process includes a hermetically closed unit which contains equipment for air circulation, heat generation as well as a control device for conditioning, connected to the closed unit, by which the equipment units may be run individually or jointly, depending on the composition, structure, geometry, etc. of the material to be cured. The device may also be connected to a vacuum source.

Description

SPECIFICATION Method of and device for rapid hardening of concrete This invention relates to a method and a device to accelerate the hardening of concrete or similar products. The invention is a development based on the method for rapid hardening of concrete by carbonation described in Patent Application No. PTC/SE78/00107.

In said patent application, a method is described for the casting of different types of concrete products, without the need of a curing chamber or an autoclave. In this method, the concrete, subsequent to mixing, is cast and subjected, externally and/or internally, to a vacuum treatment in order to dewater and compact the concrete. Thereafter, carbon dioxide gas is fed to the mass, whilst maintaining the negative pressure so that the gas-as a result of the negative pressure diffuses into the capillaries formed in the concrete mass to harden it quickly.

Other methods and equipment for the rapid hardening of concrete materials are described in U.S. Patents No. 4,117,060 and No.

3,492,385. In U.S. Patent No. 4,177,060, there is described a method for the rapid hardening of concrete dried out by a relatively dry mixture containing a co-polymer of vinyl and dibutyl acetate which is exposed to pressure in a mould, whereafter carbon dioxide gas is supplied to the mixture through the mould. The effect of the method is dependent on the partial de-watering which occurs by the addition of the polymer. No specific solution is shown for the de-humidification process.

The method and apparatus of U.S. Patent No. 4,177,059 are based on the same idea as those of U.S. Patent No. 4,177,060 but an open chamber is used as a curing facility to effect continuous production of concrete products or the like. The carbon dioxide gas is supplied to the chamber instead of to the mould in the method disclosed in U.S. Patent No. 4,177,060.

In connection with the process of the two U.S. Patents discussed above, it is pointed out that the height of the chamber in relation to the thickness of the material is directiy decisive for the curing result. Furthermore, it is emphasised that the polymers stated are essential for the rapid hardening according to the described method.

in U.S. Patent No. 3,492,385 a method is disclosed in which the curing of concrete elements is accelerated by moving the concrete elements in their moulds vertically through alternating cold and warm zones with a carbon dioxide-enriched atmosphere. In this method, no solution is provided for de-watering and de-humidification problems.

It is an object of the present invention to provide an improved mathod of and device for hardening concrete and the like materials.

According to one aspect of the invention, there is provided a method of rapidly hardening concrete or similar casting materials by carbonation, in which the capillary system of the material to be hardened is casued to be effectively dried out in a curing facility prior to and during carbonation by means of controlled conditions which comprise a combination of air flow, heat generation and moisture absorption in a circulating, continuous procedure.

According to another aspect there is provided a device for de-humidification of concrete or similar casting materials in a curing facility by conditioning, the device including a hermetically closed unit consisting of equipment for air circulation, heat generation and de-humidification of the material as well as a control device for such conditioning connected to said closed unit, whereby the equipment units may be run individually, in combination with each other or jointly, depending upon the composition, structure, geometry, etc. of the material to be cured.

In one embodiment according to the invention-in which the concrete is de-watered and compacted by means of a mat or board placed thereupon and subjected to negative pressure through a pipe-the carbon dioxide gas is supplied through said mat or board whilst utilizing the negative pressure in the mass.

In another embodiment according to the invention, the negative pressure is applied from one of more sides of the mould towards the interior of the element being cast, either by means of special inserts, by holes or cavities inside the element or via a porus material layer in the inner portion thereof. Then the carbon dioxide gas is supplied in a similar way.

In certain instances, these two main embodiments may be combined in different ways. Furthermore, the concrete may be subjected, simultaneously or subsequently, to another type of treatment, such as impregnation by a suitable solution.

The factors having the greatest importance for the speed of the carbonation process are the effects, on the drying-out process of the material prior and during carbonation, of the ambient conditions and of the pore structure of the material.

The drying out of the material is affected by its temperature, the air movement, the ambient temperature and the relative humidity of the air as well as the movement of any carbon dioxide which may be present. Correct adjustment of these factors makes possible an optimum carbonation process.

Desirable properties for the concrete of like material are a low water binding ratio, an adequate by adjusted binder (preferably cement) and a suitable porosity which should be weighed against the desired strength, etc. To obtain rapid carbonation, the carbon dioxide should also be easily absorbed by the material.

Vacuum suction may also be connected to the device by the curing facility, whenever vacuum treatment is possible, for instance in the case of a closed mould or a closed chamber. Total de-humidification of the casting material can take place provided air circulation, heat supply and de-humidification occur in a closed system which includes the casting material.

Embodiments of the invention are described in further detail below, by way of example, and the accompanying drawing, which is a schematic block diagram, illustrates how the invention can be combined with different types of curing facilities.

In the preferred embodiments of the present invention, the factors affecting the curing process may be controlled so as to function jointly or individually or jointly in different combinations or may be moved time-wise in relation to each other and adjusted to the shape and structure of the element to be cured to achieve optimum curing conditions.

A suitable device which thus comprises the necessary conditioning equipment i.e. heat source, fan and de-humidifier (e.g. salt or condensation device), control device for conditioning and possibly vacuum equipment for the supply of carbon dioxide, can be connected to the following alternative curing facilities: a closed mould, a parcel of closed moulds, a closed chamber, an open tunnel or similar curing facilities.

In a closed mould, consisting of a single mould or a parcel of moulds, vertically or horizontally assembled, it is possible--when the moulds(s) has (have) been filled with the material to be cast-to first de-water the mass by vacuum suction and to feed carbon dioxide, simultaneously or immediately following the vacuum treatment, whilst maintaining a certain negative pressure in the mass. Afer the introduction of carbon dioxide, heat is applied with a fan so as to create closed air circulation, thus making possible de-humidification of the circulating air by means of salts or condensation. Alternatively, a certain amount of carbon dioxide may also be supplied during the heat treatment.

In the case of a closed mould, another alternative is to feed carbon dioxide in the aforementioned procedure, after de-watering has taken place by vacuum treatment, at the same time as the heat fan and de-humidification are activated.

In a curing system with a closed chamber, the moulded material, with or without mould, is generally introduced compacted and with a low water content. In a preferred mathod of embodying the invention, the introduced material is first dried out and de-humidified by means of a heating fan and de-humidification equipment, whereafter the material is vacuumtreated. Carbon dioxide is then supplied to the chamber at the prevailing negative pressure.

In the case of a continuous production process process in an open chamber or tunnel, the material moulded in the tunnel is supplied by means of a conveyor belt at specified speed.

In an embodiment adapted to such a process, a heating fan is first used for drying-out, the air flow from the heat fan being made to circulate in the opposite direction to the motion of the material.

In an open chamber (tunnel) process, no vacuum treatment can be applied. Partial dewatering can be achieved by additives which also accelerate the curing process. The curing time may be shortened further by agitating the surrounding air and/or the cast material which, depending on the air temperature, relative humidity and direction of motion, accelerates de-watering and also may cause the carbon dioxide gas to circulate in the curing facility.

Tests of the method and the device according to the invention have been carried out on concrete facing stones. The prerequisites for the tests and their results were as follows: 1. Cement 1, sand 2.7, water 0.3 Water-cement ratio 0.31 Initial temperature 20-23"C Vacuum: negative pressure 0.5 bar, 10 min.

CO2-gas: temperature 24-34"C, pressure 0.1 bar De-humidification: circulation of warm air 24-35"C Curing time: 42 min., density 2.1 Strength: mean value 30 MPa 2. Same as above with additive (polymers) Strength: 18.9 MPa 3. Prerequisites for the materials as under 1.

No vacuum C02-gas: pressure 0.1 bar Temperature: 23-32"C De-humidification: circulation of warm air 24-34"C Curing time: 34 min., density 2.1 Strength: mean value 24.3 MPa 4. Same as under 3 with additive (polymers) Strength: 18.1 MPa

Claims

1. A method of rapidly hardening concrete or similar casting materials by carbonation, in which the capillary system of the material to be hardened is caused to be effectively dried out in a curing facility prior to and during carbonation by means of controlled conditions which comprise a combination of air flow, heat generation and moisture absorption in a circulating, continuous procedure.

2. A method according to claim 1, in which the conditioning procedure is combined with a vacuum treatment applied before carbonation, these operations being carried out in a hermetically closed system.

3. A method according to claim 1 or claim 2, in which the carbon dioxide gas is introduced into the material's capillary system at a maintained negative pressure or at normal atmospheric pressure during simultaneous or subsequent controlled conditioning in a closed mould either from the external surface of the material and/or from the interior of the material.

4. A device for de-humidification of concrete or similar casting materials in a curing facility by controlling, the device including a hermetically closed unit consisting of equipment tor air circulation, heat generation and de-humidification of the material as well as a control device for such conditioning connected to said closed unit, whereby the equipment units may be run individually, in combination with each other or jointly, depending upon the composition, structure, geometry, etc. of the material to be cured.

5. A device according to claim 4, which is connected to the carbonation-curing facility and which acts continuously in a closed, preferably hermetically tight system.

6. A device according to claim 4 or claim 5, in which the conditioning equipment and the control device are supplemented by equipment for vacuum treatment.

7. A device according to claim 4, 5 or 6, in which the conditioning unit and the control device are connected to a CO2-gas container.

8. A method of rapidly hardening concrete substantially as hereinbefore described.

9. A device for use in the rapid hardening of concrete, substantially as hereinbefore de scribe.

1 0. Any novel feature or combination of features described herein.