WO2000029679A1

WO2000029679A1 - Concrete slab with embedded tubes for circulation of a gas and a method for manufacturing the concrete slab

Info

Publication number: WO2000029679A1
Application number: PCT/SE1999/002051
Authority: WO
Inventors: Jonatan Paulsson
Original assignee: Jonatan Paulsson
Priority date: 1998-11-16
Filing date: 1999-11-11
Publication date: 2000-05-25
Also published as: ATE242827T1; SE9803903L; DK1131497T3; DE69908808D1; EP1131497B1; SE524158C2; SE9803903D0; EP1131497A1; AU1701100A; EP1131497B8

Abstract

A concrete slab (1) with internally cast ducts (2) for circulating gas, preferably air. The ducts are arranged in a predetermined spaced-apart relationship over the extent of the concrete slab and connected to at least one inlet (6) and one outlet (7) for the circulating gas. Furthermore, the ducts (2) communicate directly with the surrounding concrete (3) to allow migration of substances from the concrete (3) into the ducts (2) and removal of the same by means of the gas circulating in the ducts (2) as well as migration of substance in the gas circulating in the ducts (2) into the concrete (3). The invention also relates to methods for producing said concrete slab.

Description

Concrete Slab with Embedded Tubes for Circulation of a Gas and a Method for Manufacturing the Concrete Slab.

The present invention relates to a concrete slab with internally cast ducts for circulating gas, preferably air, said ducts being arranged in a predetermined spaced-apart relationship over the extent of the concrete slab and connected to at least one inlet and one outlet for the circulating gas, as well as to a method for producing said concrete slab.

In the building industry, it is currently very difficult to dry out a concrete floor sufficiently in a rea- sonable time and at a reasonable cost in order to obtain a floor design having low emissions, in particular after the application of carpets etc. Today a number of possibilities are available, but none of them seems to be able to solve the problems in a reliable and resource-saving manner.

Floors on the ground, for instance small houses on concrete slabs, may take up moisture from the underlying ground on a later occasion during the life of the floor. The source of the moisture can, for instance, be ground damp in the form of a high steam content of the ground or water contact with the floor due to insufficient draining or submersion.

Especially floors on the ground with floor heating have been found to be difficult to construct in a ois- ture-proof way. HUS AMA 98 does not, for instance, offer an approved solution to this technique, in spite of the fact that the consumer wants to have floor heating. The basic problem is that the ground under the slab is considerably heated in winter and if the floor heating is turned off in spring and summer, the slab may get a lower temperature than the ground, which may result in the slab getting a lower steam pressure than the ground. Therefore, moisture in the form of water vapour is transferred from the ground to the concrete slab which cannot dry out upwards .

Existing floor heating systems also require considerable installations in the form of permanent pipe systems (hot-water heating systems) or in the form of permanent electric cables. As a rule, the price is high and natural resources are required. In addition, the long-term performance of the systems is often questioned. US-A-4, 852, 319 discloses a drainage device for cavi- ties, i.e. a number of drainage devices to drain an embedded pipe structure to the outside of a concrete slab. The drainage devices also serve as support means for the pipe structure when casting the concrete slab. An integral system of ducts for drainage/ventilation/heating of a concrete slab by means of circulating gas is not known from this patent specification.

Swedish published patent application 431,356 relates to a method for ventilating draining layers under concrete slabs, thereby preventing migration of moisture from the ground into the concrete slabs. A number of drainage pipes are arranged in the drainage layer under the concrete slab and connected to an air-heating fan. A certain degree of drying-out of the concrete slab may thus also be achieved, but not as efficiently as if the drainage pipes were arranged inside the actual concrete slab. It is not possible to ventilate or heat the concrete slab by means of the underlying drainage pipes, nor is it justifiable from an economic point of view.

Swedish published patent application 500,465 dis- closes an intermediate floor structure which can be used for heating a housing space. Inside the intermediate floor structure, a pipe system is embedded, which comprises tight pipes for the circulation of a heating medium, said pipes being laid in a symmetric pattern from a heating assembly which is arranged centrally in the intermediate floor structure. The intermediate floor structure is dried by expelling the moisture in the con- crete by means of the heat in the pipe system through the upper surface of the intermediate floor structure.

One object of the present invention is to provide a concrete slab which has internally cast ducts and which can be efficiently drained and ventilated in reasonable time and at a reasonable cost.

Another object of the invention is to provide a method for casting a concrete slab, which reduces the time of erection and makes it possible to apply flooring earlier than otherwise normal.

Yet another object is to provide a method for producing a concrete slab in a resource-saving manner.

An additional object of the invention is to provide a concrete slab with an internally cast circulation sys- tern, by means of which the indoor environment in a housing space may be controlled in a reliable manner.

According to the invention, these objects are achieved by means of a concrete slab according to the introductory part, said concrete slab being characterised in that the ducts communicate directly with and are completely embedded in the surrounding concrete to allow migration of substances from the concrete into the ducts and removal of the same by means of the gas circulating in the ducts as well as migration of substances in the gas circulating in the ducts into the concrete.

A method for producing the concrete slab as described above is characterised in that the duct-forming elements are arranged substantially over the extent of the mould and at a distance from the sides of the mould, so that, in the casting, the duct-forming elements will be completely embedded in the concrete, and that one or more connection devices are arranged in the mould on at least one of its mould walls before said casting, each connection device connecting at least two ducts to each other.

Further developments of the invention will appear from the features stated in the dependent claims. The method according to the invention makes it possible for floors in floor structures as well as slabs on the ground to dry out in a cheap and resource-saving manner without any appreciable interference in the building process. The technique also allows the use of very limited resources as well as the provision of an inexpensive floor heating system having a high degree of moisture resistance.

The basic idea is to provide ducts in the con- crete slab, the walls of the ducts being open to gas and liquid. The ducts can be drained and ventilated, individually or in interconnection, during optional periods of the life of the concrete structure. As a consequence, the concrete can emit gas and liquid "to the inside" and thereby emit gas and liquid during an optional period, also after tight layers have been applied on the top side and/or the bottom side. The technique also allows gas and liquid supplied to the concrete at a later stage to be ventilated and drained away from the interior of the con- crete. As a result, radon emanating from the ground may be prevented from penetrating into housing spaces. Moreover, the technique makes it possible to use "simple" types of concrete having a low cement content and no admixtures, which in turn results in lower costs and less consumption of resources and less indoor emission.

By means of the method according to the invention, a floor is provided (a slab on the ground or a floor structure) which can dry out from the inside during its entire life. The system of ducts may also be used as floor heat- ing during the time of erection (rapid drying-out) as well as when the building is in use. The system may be designed in a number of different ways and the ducts may be ventilated in different ways. The outer sides of the concrete slab can, for instance, be ventilated separately with a higher temperature to compensate for heat emission through the external wall or the cooling effect of window surfaces. A heating cable which is embedded in the con- crete or extends freely (in external ducts) may also be used to locally increase the heat effect. Also water hoses (pipes) may be arranged with a play in the system of ducts. The air is then circulated by means of a fan and the air is continuously dehumidified. By means of the system of ducts, heating cables or water hoses, if any, may also be exchanged or repaired when the building is in use without any appreciable interference in the activities in the building. The technique according to the invention may also advantageously be used together with the raising and lowering method according to Swedish patent No. 9701043-3. In this manner, a moisture-proof floor without any cracks and without reinforcement may be provided (with floor heating, if desired) and, as a result, the drying-out time of a small house on the ground may be further reduced.

The technique can easily be applied also in a floor structure (in most cases multi-storey buildings). The duct-forming elements are placed in the floor structures between the reinforcing rods and extracted (if use is not made of perforated pipes) before the adjoining parts of the building are completed. In this manner, carpets etc can be applied much earlier than what is currently the case. The technique may also be used for concrete walls, retaining walls and concrete walls which are cast against a rock where the damp after the erection (from the concrete) and moisture transferred to, for instance, the external walls can be removed by ventilation during the entire life of the building. The system of ducts functions as a barrier against the migration of moisture in all directions.

Since the system of ducts can be used as floor heating, the heat to the building can, to a large extent, be distributed by the floor heating system. The system of ducts is then used as a hot-air floor heating system, which is essentially provided without any cost as almost all material has been recovered. An air-treatment assembly is, however, needed to heat and dehumidify the air. It goes without saying that the same assembly can also be used to heat the supply air to the building, and conse- quently the total cost of the heating equipment of the building may be low. The (hot) exhaust air of the building can also be used to heat the concrete slab (the floor structure) if the air is dehumidified before being circulated in the concrete slab. The price of the technique is low since almost all material can be reused after only 24 hours (or a few hours), and therefore also the amount of tied capital is small. The work is easy to carry out and today the equipment can be bought over the counter, which in principle makes it possible to commercialise the system of ducts immediately.

The amount of concrete can also be reduced, which speeds up the drying-out and reduces the consumption of material. The dead load of the slab is also slightly re- duced, which has positive effects when constructing a foundation on a ground inclined to settle.

The system of ducts solves the moisture problems during the building process as well as at a later stage. Moreover, buildings which are erected with the system of ducts can require less resources (primarily a smaller amount of cement in the concrete) than buildings erected with conventional technique. The system of ducts also makes it unnecessary to use admixtures in the concrete. Many consumers do not want any admixtures in the concrete any longer.

Below, preferred embodiments of the invention will be described by way of example and with reference to the accompanying drawings, in which

Fig. 1 is a vertical section through the concrete slab according to the invention and shows the positioning of the ducts in the slab; Fig. 2 is a plan view of the concrete slab according to Fig. 1;

Fig. 3 schematically shows, in an end view perpendicular to the plane of the sheet of paper in Fig. 1, a duct-forming element to be extracted from the concrete slab;

Fig. 4 is a partial view, similar to the one in Fig. 1, illustrating means for the circulation of gas through the ducts in the concrete slab; Fig. 5 is the area which is encircled in Fig. 1 and shows on a larger scale and in its left-hand part a duct- forming element in the concrete slab and in its right- hand part the formed duct without the duct-forming element ; Fig. 6 shows, in the same way as in Fig. 5, a duct- forming element in the concrete slab and the formed duct, respectively, with an optional electric heating wire positioned in the latter;

Fig. 7 shows, in the same way as in Fig. 5, a duct- forming element in the concrete slab and the formed duct, respectively, with an optional heating element positioned in the latter; and

Fig. 8 is a view similar to the one in Fig. 2 illustrating an alternative embodiment of the concrete slab. With reference first to Figs 1 and 2, a concrete slab 1 according to the invention is illustrated, said concrete slab having internally cast ducts 2 for gas, preferably air, circulating or flowing in the same to dry the concrete 3 in the concrete slab and to remove gases from the same. The ducts 2 are completely embedded in the concrete slab 1 in a predetermined spaced-apart relationship over the extent of the concrete slab. Preferably, the ducts 1 are oriented in a plane half-way between the top side and the bottom side of the concrete slab, but they may, if required, be arranged in more than one plane, for instance, in a zigzag pattern. The ducts 2 communicate directly with the surrounding concrete 3 to allow migration of moisture from the concrete as well as exhaustion of gas which has penetrated into the ducts and removal of moisture and gas, respectively, by means of the gas circulating in the ducts. This orientation and design of the ducts 2 makes it possible to dehumidify the concrete slab 1 quickly and efficiently since the concrete is close to the nearest duct, even if a barrier layer in the form of a flooring is arranged on the humid concrete slab 1. As already mentioned, the concrete 3 in the concrete slab 1 communicates directly with the ducts 2. This is accomplished in two ways, either by the walls of the ducts 2 being defined by the surrounding concrete, as shown in Fig. 5 in the right-hand part, or by the walls of the ducts constituting or being defined by perforated pipes 4, as shown in Figs 6 and 7 in the right-hand part. To achieve the optimum effect, the ducts 2 are preferably arranged substantially in parallel in the concrete slab 1 at a suitable distance from each other, for in- stance, in the same order of magnitude as the thickness of the concrete slab. However, in the embodiment which is presented below in connection with Fig.7, the ducts 2 may be arranged in a number of different ways, for instance, in a wave-shaped pattern or in an irregular pattern. In Fig. 2, the ducts 2 are connected to each other in series by means of pipe bends 5 which are embedded in the concrete slab 1 adjacent to its opposite end faces, at its short sides in the embodiment according to Fig. 2. The pipe bends 5 are arranged in the above-mentioned ori- enting plane of the ducts and can be formed with non-perforated or perforated walls. The inlet of the circulation gas is schematically illustrated by reference numeral 6 and the outlet by reference numeral 7. In Fig. 2, the inlet and outlet 6 and 7, respectively, are arranged at one side of the concrete slab 1, but it goes without saying that they may be arranged in an optional position on the concrete slab, for instance, at the centre of the slab. They can also be oriented at an angle to the plane of the slab.

In Fig. 8, the ducts 2 are connected in parallel by means of an inlet manifold 8 and an outlet manifold 9, which are embedded in the concrete slab 1 instead of the above-mentioned pipe bends. It is, of course, also possible to combine the two pipe laying systems, which is obvious to the one skilled in the art, and to connect the manifolds to the concrete slab on the outside after the ducts 2 have been cast.

With reference to Fig. 6, the right-hand part, it is shown that an electric heating wire 11 can be arranged in the ducts 2 to heat the gas circulating in the ducts. This heating or cooling of the gas can also be carried out by means of a non-perforated pipe 12 for circulating heating/cooling fluid, such as water or oil, as illustrated in Fig. 7, the right-hand part. The outer diameter of the inner pipes 12 should be considerably smaller than the diameter of the ducts 2 so as not to interfere too much with the flow of the gas circulating in the ducts. Fig. 4 schematically illustrates an example of a system for control and treatment of the gas circulating in the ducts 2. In order to detect the moisture in the concrete slab 1, a number of moisture sensing devices 13 are embedded in the concrete slab and electrically connected to a controlling and regulating device 14. This device is in turn connected to a fan device 15 in the recirculation pipe 16 for the circulating gas. The right- hand portion of the pipe 16 is not shown, but it will readily be understood that it is connected to the outlet at the opposite side of the concrete slab. The controlling and regulating device 14 is preferably also connected to an air-treatment assembly 17, in which the circulation gas can be heated/cooled, dehumidified and freed from the gas which has been removed from the concrete slab 1. The method for producing the concrete slab 1 according to the invention will now be described with reference in particular to Figs 3 and 5-7.

In the mould (not shown) of the concrete slab 1, a number of duct-forming elements 18 are arranged at the locations where the ducts 2 are supposed to be located in the completed concrete slab. Said duct-forming elements 18 are, for instance, bars, non-perforated pipes, pressurised hoses or the like, which keep aside the concrete in the subsequent casting. This results in concrete walls which define the ducts and which are permeable to liquid and gas. The duct-forming elements 18 are preferably supported in the mould by the reinforcement (not shown) arranged in the same or by means of supports which are arranged at a suitable distance from each other along said elements and which support are left in the concrete slab. Said pipe bends 5 are arranged at one side of the mould (the left one in Fig. 2) and releasably connected to the elements 18, which preferably have a surrounding release layer of form oil, plastic or the like. Thereafter, the concrete is cast in the mould.

As an alternative to said elements 18, use can be made of a body, which is substantially impermeable to the concrete mixture but permeable to gas, if it allows said circulation of gas. Said body is thus left in the concrete slab 1 and can consist of steel wool, fibres or the like, preferably packed more densely at the surface of the body than at its centre.

After about 4-8 hours, when the concrete has set enough to be firm, the duct-forming elements 18 are extracted from the mould and may be reused. See Fig. 5, in whose left-hand part the duct-forming element 18 is shown and in whose right-hand part the element 18 has been removed and the formed duct 2 is illustrated. Subsequently, pipe bends 5 are provided at the other side of the mould and aligned with the thus formed ducts 2, which mould side has been moved (to the right in Fig. 2) to make room for the pipe bends, and the thus-formed space 10 is also filled with concrete. Instead of the pipe bends 5, the manifolds 8 and 9 can be arranged in a corresponding manner. It goes without saying that it is also possible to let the ends of the duct-forming elements 18 project from the opposite mould sides and then connect the pipe bends 5 and the manifolds 8, 9, respectively, in the last- mentioned manner. Two elements 18 may then be used for each duct. In that case, the elements 18 must be able to resist the casting pressure of the concrete as well as the action of immersion vibrators or the like during casting without interruption of the continuity of the ducts formed in the concrete.

Reference is now being made to Fig. 6, in which an alternative method for producing the ducts 2 is shown. In this method, ducts are obtained which have walls, which on the one hand are formed of the surrounding concrete and, on the other, of pipe portions. In this case, the duct-forming elements 18 consist of perforated pipes 4 with through holes and/or slits 19 and are intended to be left in the concrete slab 1. However, in these elements elongated bodies 21, having a non-perforated outer surface, are releasably arranged and preferably, but not necessarily, they have a release layer on their outer surface, for instance, of the type mentioned above. Each body 21 is congruent with and abuts against the inner surface of the associated duct-forming element 18 and obstructs the holes and/or slits 19 in order to prevent the penetration of liquid concrete. In the same manner as in the first-mentioned method, the perforated elements 18 are connected to the pipe bends 5 and/or the manifolds 8, 9, however preferably by means of permanent joints, for instance, by welding or adhesion. After the concrete has set, the bodies 21 are extracted from the elements 18 and the concrete slab 1 is completed in a manner similar to that in the first-mentioned method, cf. the space 10. The duct-forming elements 18 do not in this case have to be self-supporting, if the body 21 can absorb the casting pressure until the concrete 3 has set. A geotextile is an example of a duct-forming element 18 that is not self- supporting . As an alternative, both the duct-forming element 18 and the body 21 can consist of perforated and/or slit pipes (not shown) , the walls of which are partly opened to liquid and gas, if the body 21 is displaced or turned in relation to the element 18. Reference is now being made to Fig. 7, which shows an additional alternative method for producing a concrete slab 1 according to the invention. If the perforations and/or slits 19 of the duct-forming elements 18 are relatively small, and a certain limited degree of penetration of concrete into the ducts is acceptable, it is possible in this method to use, as duct-forming elements, self- supporting perforated pipes 4 without using internal bodies 21 obstructing the holes 19. In that case, the pipes 4 must be able to resist the casting pressure of the concrete during casting without any interruption of the continuity of the ducts which are formed in the concrete. The pipes 4 can be connected to all the pipe bends 5 and/or manifolds 8, 9 before the concrete is cast. Immediately after the casting, a system of ducts is pro- vided, without the walls of the ducts preventing gas and liquid from penetrating into the ducts.

Moreover, it is possible, in the methods discussed above, to arrange one or more electric heating wires 11 (see Fig. 6, the right-hand part) or a pipe system 12 for heating/cooling fluid (see Fig. 7, the right-hand part) in the concrete slab 1. This is achieved by placing, in the methods associated with Figs 6 and 7, the wire/wires 11 or the pipes 12 inside the duct-forming elements 18 before casting, and in the method associated with Fig. 5 (and whenever applicable with Fig. 6) by arranging the same in a suitable manner in the formed ducts 2. By means of any of these three methods, a concrete structure is provided, which can remove gas and liquid (from both concrete and exterior sources) from the inside of the concrete slab during its entire life. The system of ducts may also be used for heating and cooling. The heating may take place during the time of erection (which results in a fast drying-out of damp after the erection) and when the building is completed, which provides a moisture-proof floor heating system. Heat and cold can be distributed by means of the gas (air mostly) which is circulated in the system of ducts by means of the fan device 15.

In the above description, the ducts 2 have been discussed in connection with gas circulation. The ducts in the concrete slab may also in connection with the embodiment according to Fig. 5, and when the ducts 2 are open to the opposite sides of the concrete slab 1, be used for pre-stressed reinforcement after casting and removal of the duct-forming elements 18. The reinforce- ment rods are inserted into the ducts 2 and anchored in conventional manner on the opposite side walls of the concrete slab. A particularly advantageous result is achieved if this is combined with the casting technique disclosed in above-mentioned Swedish patent No. 9701043-3. The invention is not limited to that described above and shown in the drawings and can be modified within the scope of the appended claims.

Claims

1. A concrete slab (1) with internally cast ducts (2) for circulating gas, preferably air, said ducts being arranged in a predetermined spaced-apart relationship over the extent of the concrete slab and connected to at least one inlet (6) and one outlet (7) for the circulating gas, c h a r a c t e r i s e d in that the ducts (2) communicate directly with and are completely embedded in the surrounding concrete (3) to allow migration of substances from the concrete (3) into the ducts (2) and removal of the same by means of the gas circulating in the ducts (2) as well as migration of substances in the gas circulating in the ducts (2) into the concrete (3).

2. A concrete slab as claimed in claim 1, c h a r a c t e r i s e d in that the ducts (2) are defined by the surrounding concrete (3) .

3. A concrete slab as claimed in claim 1, c h a r - a c t e r i s e d in that the ducts (2) are defined by perforated pipes (4) .

4. A concrete slab as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the ducts (2) are arranged substantially in parallel in the concrete slab (1) and connected to each other in series by means of pipe bends (5) which are embedded in the concrete slab.

5. A concrete slab as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that the ducts (2) are arranged substantially in parallel in the concrete slab (1) and connected with one of their ends to an air inlet manifold (8) and with the other end to an air outlet manifold (9) .

6. A concrete slab as claimed in any one of the pre- ceding claims, c h a r a c t e r i s e d in that an electric heating wire (11) is arranged in at least some of the ducts (2) .

7. A concrete slab as claimed in any one of claims 1-5, c h a r a c t e r i s e d in that a non-perforated pipe (12) is arranged in at least some of the ducts (2) to let a heating/cooling fluid flow therethrough.

8. A concrete slab as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that one or more moisture sensing devices (13) is/are embedded in the concrete slab (1) and connected to a fan device (15), which communicates with said outlet (7) and/or inlet for circulation of the gas through the ducts (2), and to an air-treatment assembly (17).

9. A method for producing a concrete slab (1) with internally cast ducts (2) for circulating gas, said ducts being arranged in a predetermined spaced-apart relation- ship over the concrete slab and connected to at least one inlet (6) and one outlet (7) for circulating gas, comprising the steps of arranging a number of duct-forming elements (18) in a mould in a predetermined spaced-apart relationship and casting concrete in the mould, c h a r a c t e r i s e d in that the duct-forming elements (18) are arranged substantially over the extent of the mould and at a distance from the sides of the mould, so that, in casting, the duct-forming elements (18) will be completely embedded in the concrete (3) , and that one or more connection devices (5; 8, 9) are arranged in the mould on at least one of its mould walls before said casting, each connection device (5; 8, 9) connecting at least two ducts (2) to each other.

10. A method as claimed in claim 9, c h a r a c - t e r i s e d in that the duct-forming elements (18) are elongated bodies with a non-perforated outer surface, which extend from said connection device (5; 8, 9) to the opposite mould wall, said bodies having a surrouding release layer of form oil, plastic or the like and being extracted from the concrete slab (1) after the setting of the concrete.

11. A method as claimed in claim 9, c h a r a c t e r i s e d in that the duct-forming elements (18) are tubular bodies which have perforations (19) and are intended to be fixed in the concrete (3) . 12. A method as claimed in claim 11, c h a r a c t e r i s e d in that elongated bodies (21) with a non- perforated outer surface, before said casting, are arranged in the duct-forming elements (18), each elongated body (21) being congruent with and abutting against the inner surface of the associated duct-forming element

(18), and that the elongated bodies (21), after the setting of the concrete (3), are extracted from the duct- forming elements (18).

13. A method as claimed in any one of claims 9-11, c h a r a c t e r i s e d in that heating/cooling means (11, 12) are arranged in the duct-forming elements (18) before said casting.

AMENDED CLAIMS

[received by the International Bureau on 22 March 2000 (22.03.00); original claims 1-13 replaced by new claims (3 pages)]

1. A concrete slab (1) with internally cast ducts (2) for circulating gas, preferably air, said ducts being arranged in a predetermined spaced-apart relationship over the extent of the concrete slab and connected to at least one inlet (6) and one outlet (7) for the circulating gas, c ha r a c t e r i s e d in that the ducts (2) communicate directly with and are completely embedded in the surrounding concrete (3) to allow migration of substances from the concrete (3) into the ducts (2) and removal of the same by means of the gas circulating in the ducts (2) as well as migration of substances in the gas circulating in the ducts (2) into the concrete (3) .

2. A concrete slab as claimed in claim 1, c ha r a c t e r i s e d in that the ducts (2) are defined by the surrounding concrete (3) .

3. A concrete slab as claimed in claim 1, c ha r - a c t e r i s e d in that the ducts (2) are defined by perforated pipes (4) .

5. A concrete slab as claimed in any one of claims 1-3, c ha r a c t e r i s e d in that the ducts (2) are arranged substantially in parallel in the concrete slab (1) and connected with one of their ends to an air inlet manifold (8) and with the other end to an air outlet manifold (9) .

6. A concrete slab as claimed in any one of the pre- ceding claims, c ha r a c t e r i s e d in that an electric heating wire (11) is arranged in at least some of the ducts (2) .

7. A concrete slab as claimed in any one of claims 1-5, c h a r a c t e r i s e d in that a non-perforated pipe (12) is arranged in at least some of the ducts (2) to let a heating/cooling fluid flow therethrough. 8. A concrete slab as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that one or more moisture sensing devices (13) is/are embedded in the concrete slab (1) and connected to a fan device (15) , which communicates with said outlet (7) and/or inlet for circulation of the gas through the ducts (2) , and to an air-treatment assembly (17) .

9. A method for producing a concrete slab (1) with internally cast ducts (2) for circulating gas, said ducts being arranged in a predetermined spaced-apart relation- ship over the concrete slab and connected to at least one inlet (6) and one outlet (7) for circulating gas, comprising the steps of arranging a number of duct -forming elements (18) in a mould in a predetermined spaced-apart relationship and casting concrete in the mould, wherein the duct-forming elements (18) are arranged substantially over the extent of the mould and at a distance from the sides of the mould, so that, in casting, the duct-forming elements (18) will be completely embedded in the concrete (3) , and wherein one or more connection devices (5; 8, 9) are arranged in the mould on at least one of its mould walls before said casting, each connection device (5; 8, 9) connecting at least two ducts (2) to each other, c h a r a c t e r i s e d in that the duct -forming elements (18) are elongated bodies with a non-perforated outer surface, which extend from said connection device (5; 8, 9) to the opposite mould wall, said bodies having a surrouding release layer of form oil, plastic or the like and that said bodies are extracted from the concrete slab (1) after the setting of the concrete. 10. A method as claimed in claim 9, c h a r a c t e r i s e d in that heating/cooling means (11, 12) are arranged in the duct-forming elements (18) before said casting.

11. A method for producing a concrete slab (1) with internally cast ducts (2) for circulating gas, said ducts being arranged in a predetermined spaced-apart relationship over the concrete slab and connected to at least one inlet (6) and one outlet (7) for circulating gas, comprising the steps of arranging a number of duct -forming elements (18) in a mould in a predetermined spaced-apart relationship and casting concrete in the mould, wherein the duct-forming elements (18) are arranged substantially over the extent of the mould and at a distance from the sides of the mould, so that, in casting, the duct-forming elements (18) will be completely embedded in the concrete (3) , and wherein one or more connection devices (5; 8, 9) are arranged in the mould on at least one of its mould walls before said casting, each connection device (5; 8, 9) connecting at least two ducts (2) to each other, c h a r a c t e r i s e d in that the duct-forming elements (18) are tubular bodies which have perforations (19) and are intended to be fixed in the concrete (3) .

12. A method as claimed in claim 11, c h a r a c t e r i s e d in that elongated bodies (21) with a non- perforated outer surface, before said casting, are ar- ranged in the duct-forming elements (18) , each elongated body (21) being congruent with and abutting against the inner surface of the associated duct -forming element (18) , and that the elongated bodies (21) , after the setting of the concrete (3) , are extracted from the duct- forming elements (18) .

13. A method as claimed in claim 11, c h a r a c t e r i s e d in that heating/cooling means (11, 12) are arranged in the duct -forming elements (18) before said casting.