STATE OF THE ART In practical operations there are a diverse number of methods for manufacturing moulding bodies made of lightweight concrete in the way described above. Most methods known in practical operations use chemical foaming agents in order to foam a liquid concrete mix and consequently to reduce its density.

These chemical aggregates are, even if they no longer diffuse out of the set moulding body, often detrimental to the health of the operating personnel at the building site, or to those who work on the production line. Furthermore, reproducing the achieved density of the lightweight concrete moulding body is seldom guaranteed due to the inexactness of the dosage. Finally, the lightweight concrete moulding body produced in a mould has an essentially uniform density over its cross section, which is indeed often intended, but which also means an unnecessarily high total weight when being used in brickwork or when manufacturing prefabricated house elements.

DE-A-1 029 278 shows a method for manufacturing moulable, hydraulically setting porous masses which essentially consist of mineral filling materials, water and of aggregates which can develop gases in the mix. After pouring the liquid mixture into the mould, the mould is abruptly subjected to shock waves, wherein these discontinuously deposited, essentially low-frequency vibrations or shaking motions cause a delay in the setting process as well as a reduction in the strength in the area of the cell walls formed around the pores by the gas. The known method does not enable a rapid manufacturing of a lightweight moulding body having a especially densified surface and at the same time a concrete mix quickly setting. It can only be applied by using a high energy consumption. Furthermore, an artificial resin is to be added to the concrete mix for a quicker setting, thus causing dosage problems and exposing the workers employed for the manufacturing to health injuries.

CH-A-220 704 shows a method for manufacturing porous material which drives a fibrous mixture in such a manner, when using gas emitting means, that the resulting moulding body can be used as a cork replacement.

DE-A-43 27 074 shows a method for manufacturing a mineral light insulating board, wherein a foam concrete is manufactured which is subsequently put into a mould, wherein water and carbon dioxide as an air pore former as well as air are added to the foam generating unit. To the foam produced in this way is added, into a stir unit, cement as well as further aggregates, where these are mixed together. The foamy concrete mix is subsequently put into the mould through an irradiator unit. The irradiator unit subjects the foam concrete to a high frequency electro-magnetic radiation with a frequency of 27 Mhz, thereby achieving an increase in temperature of the foam concrete and an increasing of the reaction speed or of the reaction speed of the single components of the foam concrete, respectively. Therethrough, a reduction in the setting time is achieved.

This heating up step before pouring into the mould has proved in practice to be hard to handle for several reasons. On the one hand, it is often not possible to fill up larger moulds so quickly that the mould can be cooled down uniformly such that a moulding body having homogenous structure could be created.

Consequently, undesired textures arise over the course of the moulding body which deviate from an ideal gradient, for example density gradient or tensile gradient. Furthermore, the pore growth, which is especially desired when adding a driving gas, is halted by the setting process started by heating up the mix. Since the foam concrete poured into the mould has already been warmed up, there is a danger of premature degassing when filling the mould so that the efficiency of the added gas can only be used incompletely. Finally, the heating up in the named frequency field can also induce disadvantageous effects, since individual metallic components of the mix are heated up considerably and form particles with the parts adherent to them, said particles sinking to the ground due to the increase in their own weight, thus causing an undesired distribution of density. This danger is an important drawback when manufacturing large moulding bodies, for example complete prefabricated building elements.

DE-journal"Spektrum der Wissenschaft" (Spectrum of science), April 1989, pages 60 to 66 describes sonochemical reactions which are caused by a gas being fed into a liquid recipe component and by acoustically irradiating the 2- phase mixture with the aid of an ultrasonic generator.

DISCLOSURE OF THE INVENTION It is the object of the invention to provide a method for manufacturing a moulding body made of lightweight concrete according to the preamble of claim 1 wherein a favourable density distribution of the moulding body is achieved.

This object is achieved according to the invention by the features of the characterizing clause of claim 1 in that the water mixed with gas is subjected to a sonochemical treatment step before and/or after being admixed to the concrete mechanical mixture such that before completely setting of the liquid concrete mix, said mix undergoes an increase in volume, whereby the density of the manufactured moulding body is reduced.

The sonochemical treatment step according to the invention can either take place when mixing the water with the gas, or preferably after the water mixed within the gas has been admixed to the concrete mixture to form a liquid concrete mix. The exact physical sequences with the sonochemical treatment have not yet been fully clarified. A well reproducible success, however, can be noted with the manufacturing method according to the invention to the extent that the concrete mix which was subjected to the sonochemical treatment step shows a great expansion after being put into the mould, wherein the expansion of the liquid mix leads to a strong density reduction and to an increase in volume after being put into the mould. The sonochemical treatment step herein causes a type of self-maintaining chain reaction over a longer period of time in the liquid concrete mix, as far as the forming of gas bubbles is concerned, wherein it can be presumed that the enriching with energy in the selected frequency spectrum promotes a quick phase transition liquid <--> gaseous of the components of the water carying gas. Supported by the immense volume increase at the transition of a liquid molecule in a gaseous phase, an unexpected large expansion of porosity or of the porous quota in the moulding body made of lightweight concrete ensues, the density thereof decreasing accordingly. This expansion phase or foaming continues to last beyond the period of pouring into the mould. By continuously setting in the mould, starting from the peripehral areas and working to the core or the middle area of the mould, and due to the chain reaction type expansion of the concrete mix which maintains itself, a relatively dense wall and an extremely light core of low density is advantageously achieved. It is at the same time possible to condition the mould in such a targeted way that a desired setting speed is achieved. Through carrying out the sonochemical treatment step according to the invention, only a very slight alteration in the temperature of the concrete mix ensues, so that a premature starting of the setting process before pouring into the mould is prevented and the driving process of the liquid concrete mix triggered by the sonochemical treatment step is maintained up to a moment at which the concrete mix usually is filled into the mould. Therethrough, it is possible to achieve moulding bodies of slight density and desired density gradients without disadvantageously premature starting the setting process. The driving of the sonochemically treated concrete also positively overcomes the capillary pressure of narrow hollow cylinders and the like.

The sonochemical treatment step preferably ensues in a treatment chamber which is run through by the liquid to be treated (with a gas added to water or to liquid concrete mix). In order to do this, one or a number of ultra sonic oscillators are arranged in the treatment chamber which, for example, produce an ultra sound by means of piezoelectric or magnetostrictive materials. This is preferably accomplished by using frequencies from a frequency range laying between about 900 Khz and about 1500 Khz. The sonochemical treatment step usefully ensues in a continuous and uniform manner during the run through of the liquid ; the loading of the liquid with energy will occur in a way simple to control, and almost constant or at least very uniform. It is especially possible, by emitting uniform ultrasonic waves, to control the loading with ultrasonic energy by volume flow automatic control of a feed pump or the like. Different to adding chemical aggregates, which necessitate much time and energy to be planned in the uniform distribution in the liquid, a later very uniform distribution of the pore growth is triggered in the concrete mix due to the continuous sonochemical treatment step in the treatment chamber, thus ensuring an excellent reproducibility when manufacturing the moulding bodies.

It is advantageously possible to sonochemically subject the liquid concrete mix as it is injected or pourred into the mould, i. e. the sonochemical treatment chamber is housed or integrated in an injection device such as a concrete sprayer device or pistol. Such specially designed injection devices for the liquid concrete can additionally be provided or used in place of separate chambers for the sonochemical treatment step. A very favourable energy effect ensues through the sonochemical treatment step carried out directly before or during pouring the liquid mix into the mould.

It is advantageously possible to heat up the mould before pouring in the liquid concrete mix in order to speed up the setting in the edge areas or peripheral portions locally-similar to a quenching process-and to produce an increased density of the edge zone or peripheral portion compared to the rest of the moulding body. The quick setting suppresses pore forming due to foaming.

Furthermore, an overpressure forms in the mould due to the expansion of the liquid concrete mix which is still liquid after being poured into the mould and which foams due to the sonochemical treatment. The overpressure, on the one hand, works towards a volume expansion, on the other hand, it compresses those mix parts which are located at the edge areas, thus forming an external skin or layer which is mainly pore-free. Consequently, the resulting lightweight moulding body is of slight density as well as of extreme fluid-tightness. The moulding body manufactured in this way according to the invention therefore distinguishes itself through a very slight porosity in a continuous edge area, whilst a high porosity in the core area causes a slight volume weight of the moulding body. Furthermore, it is possible to plan a steam hardening step subsequent to the setting step.

Typically, the density of a moulding body manufactured according to the invention fluctuates between 30-50 kg/m3 and 1200 kg/m3. The density of the moulding body in the outer edge zone preferably lies at least twice as high as the average total density of the moulding body. The density of the outer edge area is preferably three times higher than the density of the core area of the moulding body. A density gradient is usefully provided from the outer wall of the lightweight moulding body to its core area such that the density decreases from the outside to the inside. Theretrough, a lightweight concrete moulding body is advantageously created having a solid outer wall but being at the same time lighter due to its slight density in the core. This operation is also advantageously performed if in the moulding body, e. g. a wall, certain recesses, blanks or openings are planned for windows or doors. In such a case a densified edge zone likewise forms at the border surface with the recess, connecting the outer wall areas opposing each other. The corner portion, which will have to support the most stresses, densifies especially well. Mountings for windows or the like are held safely in these densified edge zones.

The method according to the invention is advantageously combined with further steps which are suitable for forming gas bubbles in the liquid concrete mix, for example adding foaming means or blowing in steam. In the liquid concrete mix resulting from these preferred additional treatment steps, too, the sonochemical treatment step according to the invention causes a favourable behaviour after pouring into the mould, wherein a specially favourable density gradient of the moulding body manufactured according to the invention is achieved. A relatively slight pressure is produced with the method according to the invention, through which the mould also and the encasing material are lightweight dimensionable. This also makes it advantageously possible to work with light vertical moulds. The pressure arising on the outer surfaces through the foaming of the liquid mix is, however, sufficient for the moulding body to become especially dense at its outer surfaces, through which a resistance to extension and a compression-proof strengthening layer is formed. Advantageously, this layer is water-proof after setting due to its high density.

According to a very preferred improvement of the invention, the aggregates which are added to the concrete mixture include fibre sections as glass fibres, rock fibres, aramide fibres, carbon fibres, graphite fibres, metal fibres or other fibres. It has to be noted that the integral parts of the liquid concrete mix are then stirred in such a way that the fibres are uniformly distributed within the liquid mass. The sonochemical treatment step does not induce any texture forming in the fibres, so that these show a mainly isotropic distribution in the moulding body after the concrete mix has set. An undesired preferred direction of field properties (anisotropy) of the moulding body manufactured according to the invention is thus avoided. Quite the contrary, the circumstance that the sonochemical treatment step does not negatively affect the orientation of the fibres allows the forming of an inbeded matrix from a diverse number of fibres which have a similar advantageous effect for the strength as often otherwise used reinforcements, but without their disadvantageous punctual weight strain. The resistance towards tensile or pressure loads is more or less improved in a way which is neutral to weight.

In order to achieve a very homogenous mixing up of the three or less phases (liquid, gaseous, solid), a disk-shaped mixing tool is preferably used to achieve a cavitation, especially a cavitation disk.

The moulding body manufactured according to the invention, e. g. a lightweight concrete block or plate body, preferably shows a slight density between 30-50 and 1200 kg/m3, having edge areas being almost pore-free and showing continuously decreasing local density from the edge areas to the central areas. Theretrough it is possible, according to the invention, to manufacture a lightweight concrete moulding body in a quick production method which usefully combines a densified and tensile strong and compression-proof outer pressure- proof layer in one piece with a porous and light core layer, so that such a moulding body is especially suitable for manufacturing wall elements for prefabricated houses or the like, where an almost flat surface with slight total weight is desired.

The lightweight concrete moulding body manufactured in this way is lightweight as well as heat and sound insulating, but still stable and fire-resisting.

Since the sonochemical treatment step according to the invention lengthens the driving process of the liquid concrete mix in the manner of a chain reaction, the manufacturing method according to the invention is also very suitable for the manufacturing of a moulding body having large or bulky dimensions where manufacturing thereof by filling the mould by pouring the mix takes a minimum of time, for example more than one minute or even more than three minutes or more.

The manufacturing method is also suitable for manufacturing moulding bodies where the liquid concrete mix is successively put or poured into the mould, especially also discontinuously, since the chain reaction like process causes the materials poured in in discontinuing stages to stick to one another, wherein no undesired layer borders negatively influence on the features of the moulding body manufactured according to the invention.

The method according to the invention especially enables a moulding body to be manufactured, the mould thereof having already been provided as a counter form to a prefabricated house, i. e. including a room with several times the volume that the concrete fills out and the height thereof being of 2.50 m per floor within a house constructed in a standard way. When manufacturing a prefabricated house according to the method according to the invention, the mould is up to 10 m high or higher, the wall thickness of the mould amounts to between 8 and 35 cm and the edge length of the mould likewise comes to several metres in length and breadth. The method according to the invention thus enables a prefabricated house without the intermediate floors to be manufactured from one single seamless lightweight concrete moulding body according to the invention. This seamless manufacturing according to the invention enables the lightweight concrete moulding body formed as a house to be preferably transported hanging in the air, due to its monolithic like seamless unit and its favourable density distribution, therefore showing an optimized strength weight ratio that had not yet been achievable in the past.

The lightweight concrete moulding body according to the invention can also be a planking layer of a support element if the support element is placed in the mould before the end of the setting step. Preferably, a lightweight honeycomb-like body is used as a support element, e. g. made of polypropylene which is completely surrounded by planking material manufactured according to the invention.

Further useful improvements of the invention will become appearant from the dependent claims and from the following description.

The invention will now be explained in more detail by means of an embodiment of the invention with reference to the attached drawings.

SHORT DESCRIPTION OF THE DRAWINGS Fig. 1 shows a schematic diagram for the manufacturing method according to the invention.

Fig. 2 shows different embodiments of moulding bodies according to the invention manufactured by the method according to the invention.

Fig. 3 shows further embodiments of moulding bodies according to the invention manufactured by the method according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION Fig. 1 schematically explains the manufacturing process for manufacturing a lightweight concrete moulding body. Therein, water 2 is loaded with and mixed together with a gas 1, preferably CO2, in a chamber 3. Chamber 3 preferably is embodied as a sono-probe wherein supersonic power converters 5 are arranged which subject the water-gas mix to supersonic waves such that a dispersed mix is fed into a mixer 6. Furthermore, a cavitation disk 4 is advantageously arranged in chamber 3 which provides, as a mixing unit, a particularly favourable distribution of the gas in a liquid.

In the mixer 6 cement 7 and further aggregates 8,9 are added to the water treated with CO2. Along with the aggregates, reinforcing materials, especially fibre sections made of glass, carbon or other suitable materials, can be added which are likewise uniformly distributed in the mixer 6. In order to achieve a favourably uniform distribution of the components of the mix, a cavitation means 13 is preferably provided again, in the above embodiment a cavitation disk.

Furthermore, it is possible to add a material 11 in exactly measured amount and temperature to the mix, for example a perlite or slate material which was heated and expanded in a swelling oven 12, and to mix it in, whereby the mix settles at a predetermined temperature. The upper layer of the said material will preferably have been hydrothermally converted before.

It is also possible to use foam glass, slate or other mineral or other granulated material pre-heated in another way instead of the hot perlite. It is likewise possible that the concrete is manufactured with pre-heated water in order to adjust the predetermined temperature.

Hereinbefore, the sonochemical treatment was already carried out after the gas 1 had been mixed to the water 2. But it is also possible to provide the sonochemical treatment after admixing the water with the gas to the mechanical concrete mixture for generating the liquid concrete mix (the mix is then sonochemically treated), wherein the sonochemical treatment is then also advantageously followed by a cavitation step which is effected in the present embodiment by the cavitation disk 13. The design of a chamber for the sonochemical treatment of the liquid concrete mix would approximately correspond to the design of aforementioned chamber 3. It has to be noted that the sonochemical treatment step especially triggers off interactions gas <-> liquid through special energy treatment which can last for a period of a few seconds up to some minutes, depending upon the emitted energy and the irradiated volume, so that a special advantage underlying the treatment step according to the invention is its continuing activity in the mould after pouring in the liquid concrete mix.

It is especially possible in the case of multi-branched moulds and moulding bodies, respectively, to achieve a favourable reaction in that the sonochemical treatment step occurs at different places, such that a very uniform energy load is achieved with reference to a normal, e. g. the moment of pouring into the mould. Therefore, it is also possible that the mould is provided as treatment chamber, wherein the sonochemical treatment step ensues before the setting.

Subsequent to the mixing in the mixer 6, the liquid lightweight concrete mix is pumped via a concrete pump 14 and via a tube 16 into the mould 18. The concrete pump 14 usefully contains a spiral blade 15 as a pump member which advantageously creates a pumping conveyance in such a way that the mix does not sediment in individual layers. The tube 16 is usefully held, over a heat source 17, at a predetermined temperature, whereby the heat loss of the swelling oven 12 (which was used to manufacture the perlite) is advantageously reused in an energy-saving way.

It is possible to introduce reinforcement sections or tissues 19 and/or honeycomb cores 20 into the mould 18, which also will mostly comprise sheathings, before pouring in the lightweight concrete mix, wherein the honeycomb cores 20 advantageously show an in cross section console-like front surfaces 21 for a better anchoring of the concrete. It is possible to preheat the mould to a predetermined temperature, whereby a defined setting speed is selectable. Furthermore, introducing the said sections or tissues enables embossed optical structures to be created as well as colour variations. The structures can also be disposed punctually or in special areas.

It has to be understood that the devices and apparatus mentioned hereinabove can be combined to one or several devices and can be operated according to the cycle of a production line or in touch with the setting of the concrete. It is also possible, for example, to use the same chamber for the sonochemical treatment of water mixed with gas, and of liquid concrete mix, whereby the water sent through the chamber cleans the chamber. The control and automatic control of the individual processes of the manufacturing method according to the invention can be monitored and controlled by a control unit 22 which clocks the individual method steps and co-ordinates them in terms of a continuous process. The fact that the sonochemical treatment step keeps itself alive over a longer period of time is beneficial for optimizing the cycle times, because, contrary to numerous known methods, driving the liquid concrete mix is no longer a time-critical factor with the method according to the invention.

By use of pre-heated material for the sonochemical treatment step and for the mechanical cavitation step, it is possible to considerably accelerate the setting step, without at the same time reducing the expansion of and consequently the density of the resulting moulding body. Adjusting the temperature of mould, concrete mix, water and further components involved in the manufacturing method to predetermined values ensures an excellent reproducibility in the quality of the resulting moulding body.

It is possible to treat the above-mentioned perlite or slate material before the swelling process in such a way that the upper layer is hydrothermally converted. Furthermore, the building material can be changed in a targeted way by adding gypsum or other ceramic materials, sand, pebbles or chippings, plastic granulates, other setting agents, setting accelerators and organic and inorganic aggregates in different ratios and combinations for admixing in alternate variations with different properties, also concerning heat and sound insulation, setting speed and capability, as well as adhesive properties. It has to be noted that also adding chemical additives for forming foam can positively influence the driving operation of the liquid concrete mix in terms of an acceleration so that an even quicker setting induces an even stronger acceleration of the manufacturing method on the whole. It is likewise possible, through additional treatments in a spectrum other than the ultrasonic frequency spectrum, to achieve further influences, especially in view of the temperature by irradiating with microwaves, wherein these effects superpose with the result of the sonochemical treatment step. On the whole, the whole manufacturing method will take place in an automatic way to a large extent, and the dosing of the material as well as the temperature equalisation and the dimensioning of the throughput times of the individual components before and during the manufacturing method will be electronically controlled, in order to achieve an optimum and reproducible result when manufacturing the lightweight concrete moulding body according to the invention, especially in view of its density.

A multitude of geometries of lightweight concrete moulding bodies can be realized by the manufacturing method according to the invention, e. g. blocks, plates, columns, supports, roofs, ceilings, walls, figures and other objects, from hollow as well as from solid material in different sizes and thicknesses. The lightweight concrete moulding bodies according to the invention show a pronounced bubble structure in their cental portion.

With regard to figures 2 and 3, lightweight concrete moulding bodies according to the invention manufactured by the method according to the invention will now be described.

Figure 2 shows wall constructions 23 with honeycomb core reinforcements which can be manufactured in diverse forms 24 to 27 and shapes.

A reduction in the weight is achieved herein once again in that a hollow body is manufactured by the method according to the invention instead of a solid body, wherein merely the peripheral portions, surrounding e. g. a honeycomb body 27, are planked with a concrete layer manufactured according to the invention, so that the lightweight concrete moulding body according to the invention is embodied essentially as thin wall coating the honeycomb 27. The honeycomb body 27 enables this concrete layer to be modelled thinly in that it provides a firm connection with the concrete layer. The resulting lightweight concrete moulding body, which surrounds the honeycomb core in its hollow space, provides almost the strength of a solid body, while simultaneously being of an extremely low weight.

Referring to Fig. 3, further embodiments of the lightweight concrete moulding body according to the invention manufactured with the method according to the invention are represented. Such a lightweight concrete moulding body 28 is, for example, formed as a complete house, whilst the lightweight concrete moulding body 29 is industrially manufactured as a large space cell and the lightweight concrete moulding body 30 is industrially manufactured as a complete roof or solar roof. These large parts can be transported with conventional transport means, especially with the represented gooseneck transport vehicle 32, with a ship 33 or with an airship or helicopter 34 due to their slight density and consequently relatively slight weight in spite of their large dimensions. It has to be noted that it has become possible, due to the method according to the invention, to manufacture extremely large size lightweight concrete moulding bodies like the house 28 or the space cell 29, wherein the volume surrounding the lightweight concrete moulding body is a multiple volume of the volume that the lightweight concrete moulding body itself fills. This ratio, which can easily range over 5 or even over 10, is further increased in that the walls of the lightweight concrete moulding body 28 form a type of sandwich construction with the honey comb techniques represented in Fig. 2 such that the actual concrete volume input ratio in relation to the confined volume even further decreases (by approx. 60%). In a corresponding proportion, e. g. by 50% to 80%, the weight of the lightweight concrete moulding body according to the invention manufactured according to the invention drops so that it is possible to transport even very large volumes with known apparatus to transport in the air, on water or over land. In this way it is possible to achieve approx. 100 to 150 m2 floor area below 20,000 kg.

Therethrough, it is advantageously possible to economically manufacture and transport lightweight concrete moulding bodies according to the invention with one floor or several floors as transportable prefabricated houses, transportable space cells, for prefabricated garages, energy centres, energy and water storers, sewage works, complete buildings with sizes of up to 200 m2 floor or useful areas and the like. Provided the above mentioned lightweight concrete moulding bodies show a division, this can be planned in any chosen way.

The invention has been explained hereinbefore in detail by embodiments, wherein the selected details, especially concerning the manufacturing process, are not to be seen as a limitation. In this way, for example, any type of concrete pump, cavitation means, ultrasonic means, gas, aggregates, cement can be used in the manufacturing method according to the invention.

Furthermore, any chosen shape of a lightweight concrete moulding body according to the invention can be manufactured with the method according to the invention, and the building shapes mentioned above are not to be understood as a limitation but only as preferred examples. As far a skilled person directly recognises listed or non-listed measures other than the listed measures with the same effect from the alternatives described above, these are likewise to be seen as belonging to the invention. This especially applies for the selected dosages and for the values for the material, time and power input, which the person skilled in the art ascertains through tests carried out for the desired purpose.