FR2530528A1 - Process for manufacturing a lightweight panel made from cellular concrete. - Google Patents

Abstract

This process consists in filling a mould 1 with a slurry of cellular concrete, and then in removing from the mould the panel formed after the slurry has hardened, this panel then being baked. The process according to the invention is characterised in that it comprises a stage which consists in applying pressure to the upper face of the said slurry, whilst it is in the plastic state inside the mould 1, in order to form a compressed surface on the said concrete panel.

Description

METHOD FOR MANUFACTURING A LIGHTWEIGHT CONCRETE PANEL.

 The present invention relates to a method for manufacturing a lightweight panel of aerated concrete and more particularly to a method for defining the upper surface of a grout of aerated concrete disposed in a mold.

 Cellular concrete panels are commonly used to make the external walls of prefabricated buildings. The technique, most commonly used when it is desired to form a decorative or relief design on the exterior surface of a cellular concrete panel, consists in making this panel by molding a cellular grout composed of cements, concrete mixture , of water, etc ... in a mold having on its lower surface, in hollow, the reasons or drawings which must be carried out on the surface of the panel.

After hardening of the cell grout, the panel is removed from the mold and is introduced inside an autoclave where it is subjected to firing at high temperature and under pressure. This light panel thus obtained then receives a layer of finishing paint in order to obtain a finished product.

 When using a cement slurry which is post expanded, in the case of the aforementioned process, there is an excess thickness at the upper periphery of the mold, excess thickness which must be removed by scraping or similar treatment, which results in a considerable loss of raw material and, consequently, increases the production costs of such a panel. Furthermore, after curing treatment, the cellular concrete panels thus produced have rough surfaces which are unsuitable for receiving a layer of finishing paint.

 Finally, the cellular concrete panels produced to date are poorly waterproof and have low mechanical characteristics, in particular with regard to surface hardness, abrasion resistance, etc. As a result, the surfaces of these panels can crack and scuff easily and even be partially broken during handling.

 The present invention aims to overcome these drawbacks.

 A first object of the present invention resides in a process making it possible to obtain a light panel of cellular concrete having a smooth surface condition and capable of receiving without further treatment a coating of the finish.

 Another object of the present invention relates to a process making it possible to produce a lightweight concrete panel whose surface has a very good seal and excellent mechanical characteristics and which, as a result, is less likely to be chipped, cracked or broken.

 The present invention also relates to a method for forming a lightweight concrete panel which, during its manufacture, avoids the formation of extra thicknesses, during the expansion of the concrete grout, which makes manufacturing easier and more economical.

 Furthermore, the method according to the invention makes it possible to increase the productivity during the manufacture of such a cellular concrete panel.

 In general, the method according to the invention for the manufacture of a lightweight panel of aerated concrete consists in filling a mold with a grout of aerated concrete and then unmolding the panel formed after hardening of the grout, said panel then being subjected to a baking treatment and the method according to the invention being characterized in that it comprises a step which consists in pressing on the upper surface of said grout while it is in the plastic state in the mold in order to form a compressed surface on said concrete panel.

 Such a method makes it possible to produce lightweight concrete panels which can be used as construction materials, for example for making the external walls of prefabricated buildings.

The invention and the advantages which it brings will however be better understood thanks to the following description and to the exemplary embodiments given for information but not limitation and which are illustrated by the attached diagrams in which
- Figure 1 is a perspective view of an apparatus used for implementing the method according to the invention, this view schematically representing the filling phase of a mold with a cement grout;
- Figure 2 is a schematic perspective view of a mold used in accordance with the example of Figure 1 and in which a steel reinforcing element is arranged
- Figure 3 illustrates the phase during which the grout is compressed;
- Figure 4 illustrates the grout in the compressed state inside the mold
- Figure 5 illustrates a variant according to the invention in which the compression phase of the grout inside the mold is obtained by means of a roller having patterns at its periphery
- Figure 6 illustrates another variant according to which the mold illustrated in Figure 1 containing the cement slurry is moved under an assembly making it possible to distribute on the surface fine light aggregates or other similar products
- Figure 7 illustrates the phase according to which the cement grout on the surface of which fine light aggregates have been distributed is compressed by means of a roller having a smooth surface
- Figure 8-is a temperature / time curve for the autoclave cooking of a concrete panel
- Figures 9 to 11 are specific weight / distance curves of finished cellular concrete panels in cross section.

 The process according to the invention can be carried out using a cellular concrete slurry which can consist of a pre-expanded cement composition, a post-expanded cement composition or a mixture of the two. Such grouts can be prepared according to any conventional process making it possible to obtain cellular cement compositions for the production of light concrete panels.

 The pre-expanded cement slurry in the present invention can be prepared by mixing a foaming agent and a cement paste which has been previously prepared by mixing cement such as Portland cements, silica cement or the like and water.

In order to obtain a pre-expanded grout, various additives commonly used during the preparation of grout for the production of light concrete panels, can be added to the aforementioned product, such as for example lime, powder of silica, aggregates, hardening retardants, cement mixtures .... As lime, both quicklime and slaked lime can be used. The aggregates can, for example, be light aggregates such as sand, gravel or the like. As the fast curing material, alumina-containing materials such as alumina cements can be used. The hardening retarders can be inorganic retarders such as gypsum and organic retarders such as hydroxycarboxylic acid and its salt, sucrose, etc.. Cement additives may include, for example, dispersants ...

The foam used in the above-mentioned pre-expanded cement grout can be prepared by mixing water and a foaming agent, such as surfactants and a protein foaming agent. The surfactant may for example consist of alkylbenzene sulfonates. The protein foaming agent may consist, for example, of keratin protein.
The pre-expanded cement grout according to the invention can be prepared by mixing a foaming agent with the above-mentioned cement composition beforehand.

The foaming agent may include aluminum powder, hydrogen peroxide, etc. After the composition has been poured into a mold, the expansion of said composition is carried out.
Furthermore, according to the present invention, the pre-expansion agent described above can be previously mixed with the cement slurry which is then stirred so as to form a pre-expanded cement composition which is then poured inside a mold.

 Optionally, the cell grout used for the implementation of the invention can be prepared by combining at least two of the three processes above for the preparation of pre or post expanded cell grout.

Such a cement composition thus prepared is, as illustrated in FIG. 1, poured inside a mold (1) using a feed hopper (3), the mold having a shape of conventional type and which, in the illustrated embodiment, is rectangular. In order to produce a reinforced concrete panel, a steel frame (2), previously subjected to any conventional anti-rust treatment (degreasing, washing with water, etc.) is placed inside the mold (1) such that this is represented in FIG. 2 and this, before the cell grout is poured into the mold (1). The upper surface of the composition put into the mold is leveled by any conventional means, such as by means of a plate and may sometimes slightly exceed the upper edges of said mold fol). After the cement composition has been poured according to the invention, it is allowed to come to a plastic state so as to have value
Proctor less than about a relative pressure of b, 8 atmospheres (100 psig) and preferably between 0.136 and 0.68 atomospheres (2 to 10 psig) -so that when the mold (1) is tilted, said composition does not not flow out of the mold. The time required to obtain such a plastic state depends on the nature of the grout used. Beyond the above-mentioned upper limit, the grout in the plastic state is liable to be damaged or broken when subjected to the subsequent compression treatment which will be described below. For grouts which are post-expanded, after hardening of the molded composition, one can scrape off: part of the extra thickness which can occur so that the upper face of the molded panel is positioned above the upper edges of the mold (1) and this, of a height corresponding substantially to the reduction in height resulting from the compression which will be carried out subsequently and described in the following description. Furthermore, before the compression process of the upper surface of the cell grout , it can be subjected to a conventional hardening treatment. When the cell grout is hardened beyond the plastic state, it is subjected, in accordance with the invention, to a compression treatment according to which the upper surface of said grout is pressed by means of any suitable system so as to form a flat surface compressed on the concrete panel that should be produced. The device for ensuring this pressure, can be constituted, for example, by a roller (4) having a smooth peripheral surface as shown in FIG. 3. It could be constituted by any equivalent device such as for example a flat plate or similar. The roller (4) will be based on any material such as for example plastic, steel, copper .... The opposite ends of the rollers (4) are integral with pinions (5) which engage with a rack (6) fixedly mounted on the upper edge of each side (2) of the mold (1) A shaft (8) is fixed externally in the center of each of the gables (5).

The free end of each shaft (8) is equipped with a handle (9) for causing the rotation of the roller. During the compression operation, the roller (4) is moved over the cellular composition placed in the mold (1) from one end (10) of the mold to the other end. This movement can be carried out by two people who act on the handles (9) mounted on the roller (4), ie guidance being obtained by means of the pinion (5) and the racks (6). In this way, the grout (16) contained in the mold is compressed, which lowers the upper surface by a predetermined height, this surface being perfectly flattened and becoming compact as shown in FIG. 4. compression, the possibilities of compre-ssion of the concrete composition inside the mold are generally of the order of 2 mm. The reduction in thickness is, in general, between 2 and 7 mm for a concrete composition having a thickness between 50 and 250 mm. Beyond the upper limit, the composition of aerated concrete in the plastic state is likely to be damaged - or broken. The compression ratio can be adjusted by modifying the level of the upper surface of the cellular composition relative to the contact surface of the roller (4).

 This operation being carried out, the compressed cellular grout is left to harden, then said molding is carried out by any appropriate means (not shown) in order to obtain a cellular concrete panel. This cellular concrete panel is then subjected to a conventional baking treatment, such as baking in a humid environment and / or baking in an autoclave carried out before or after the removal of the mold. The conditions of this curing treatment depend on the nature of the cellular concrete composition.

 When the concrete panel is dry, it can be subjected, if necessary, to a treatment making it possible to cover its external surface with a finishing layer.

The cell panel thus produced is then transported to the place where it is to be used or stored for later use. The compression treatment carried out in accordance with the invention can be carried out by means of other devices of a roller (4) having a flat peripheral surface. For example, one can use, as illustrated in FIG. 5, a roller <11) presenting on its periphery patterns (12) which allow -to obtain a decorative effect (13). in relief, on the surface of the aerated concrete panel.

 Optionally, before carrying out the compression operation with the rollers or other similar rollers, particles of fine, light powder or aggregates, or even fibers such as cellulose fibers, nylon, acrylic fibers, carbon and asbestos, or pigments such as titanium oxide can be spread on the exterior surface of the cell grout in the fluid or plastic state, while it is placed in the mold This addition of materials can be carried out to improve the mechanical strength of the panel or other properties. Having done this, the grout compression operation is carried out, for example by means of the roller (4), which allows the materials which have been distributed on the surface with said panel to be firmly adhered. As shown in Figure 6, the distribution of additional materials (14) on the surface of the panel can be obtained by moving the mold (17) below a conventional dispensing system (15) mounted fixed on a frame not shown.

The displacements of the mold (17) are obtained by providing at the base of the latter wheels (18). The distribution of materials being thus carried out, the compression operation is carried out in the manner shown in FIG. 7, for example using a roller (4), which also makes it possible to adhere this material to the upper surface of cell composition.

 It may also be envisaged, after having adhered the material spilled onto the surface of the cell composition as indicated above, to subject this surface to a second compression optionally using a device making it possible to form patterns, for example using a roller comprising patterns on its periphery as illustrated in Figure 5.

Example I
A grout A is produced by mixing portland cement, silica powder and water in a mortar barrel rotating at 100 revolutions per minute. The mixture is obtained using 50 kg of each of the above products. The mixing is carried out for five minutes.

 In addition, 0.5 kg of foaming agent based on decomposed keratin protein and 10 kg of water are mixed in a mixer with high shearing power.

This mixer is driven at a speed of 3000 revolutions per minute and makes it possible to obtain a mixture having a specific gravity of 0.046, 2008 of foaming agent thus obtained and 852 of the above-mentioned composition A 'are then mixed in a mortar barrel, the mixture being effected for five minutes, so as to form a cellular grout having a specific gravity of 0.53 which is then poured into a mold having 100 cm in width, 300 cm in length and 9 cm in depth as shown in FIG. figure 1. Inside this mold, is placed a steel frame, previously treated against rust. This steel frame is made of steel rods with a diameter of 5 mm, welded together so as to form a grid, the openings of which are 100 mm wide. The grout is then subjected to a wet hardening treatment at 50 "C for 5 hours. When the Proctor value of the cell grout thus treated reaches a relative pressure of 0.34 atmospheres (5 psig), the upper surface of the material is then subjected to compression while tralnant-; a decrease in height This compression is obtained by means of a roller of the type illustrated in FIG. 3, this roller having on its periphery a pattern imitating stone. The grout thus treated contained in the mold is then subjected to a second treatment of wet cooking for five hours at 50 "C and is then removed from the mold. The aerated concrete panel is then placed inside an autoclave in order to undergo a third cooking treatment 2 at a steam pressiode of 10 kg / cm ,, the temperature curve The time / time of this treatment being represented in FIG. 8. The panel thus treated is then stored for two weeks. at% room temperature in order to dry. The specific weight of such a cellular panel thus produced, in a direction going from the surface subjected to compression by the roller to the opposite surface of said panel is then determined, the results being grouped in the curve of FIG. 9.

It is clear from this curve that a compact, inclined layer B is continuously formed with the first surface. The finished product has a stone-like pattern on its external surface, said surface being smooth and capable of directly receiving a finishing layer. Such a product also has a very good seal and excellent mechanical strength, in particular as regards resistance to cracks.

Example 2
2 kg of sodium citrate are dissolved in 250 kg of water. This being done, under the same conditions as in Example 1, the said aqueous solution is mixed in a barrel with 250 kg of Portland cement, 250 kg of silica sand and 50 kg of alumina cement.

In the same way as in Example 1, the foam is obtained by mixing 25 kg of water and 2.5 kg of decomposed Keratin protein. The foam and the grout C thus obtained are then mixed in another mortar barrel, for five minutes, so as to form a cellular grout having a density of 0.805. This cell grout is poured inside a mold 100 cm wide, 500 cm long and 95 cm deep, as shown in Figure 1. The filling of the mold is carried out so that the upper surface of the concrete grout is positioned at approximately 7.5 mm above the upper edge of the mold, After having allowed to rest for twenty minutes at 30 "C the riboule thus filled, we distribute on the surface of the concrete grout, at a rate of 150 g / m2, silica powder having a grain ranging from 0.2 to 0.5 mm. This distribution is carried out as illustrated in FIG. 6. This being done, the assembly is left to stand for five minutes at 30 "C. . When the Proctor value of the cellular concrete grout reaches a relative pressure of 0.204 atmospheres (3 p'Ag), compression is exerted by means of a roller (4) of the type illustrated in FIG. 3 on the external surface . The compression ratio is such that the thickness of the molded material is reduced by 25 mm.

Then we do. a second compression, at a rate allowing a reduction in the thickness of 5 mm, by means of a roller having a pattern at its periphery.

Twenty minutes after these treatments, the solidified and demoulded aerated concrete panel is subjected to a curing treatment for 8 hours at 30 "C. The concrete panel thus treated is then subjected to autoclave curing in the same manner as in Example 1.

The specific weight of the cellular concrete panel thus produced, in a cross-sectional direction going from the surface subjected to compression by said roller to the opposite face of said panel, is then determined and the results are grouped in the curve of the figure. 10. The panel thus obtained represents an external surface having an excellent seal, a very good mechanical resistance and an excellent finish.

Example 3
Example 2 is repeated with the only difference that 500 kg of Portland cement is used in place of silica sand. The grout thus obtained is then left to stand for 30 minutes at 30 ° C., Glass fibers having a length of 1 cm and a diameter of approximately 0.1 to 0.2 mm are then distributed over the upper surface of said grout. This being done, pressure is exerted on the upper surface by means of a rectangular-shaped plate. This compression is exerted for ten minutes and then a second pressure is exerted by means of another rectangular-shaped plate which has a stone-like pattern on its surface.

The assembly is then subjected to a baking treatment for ten hours at 52 "C. The concrete panel obtained is then removed from the mold and then stored at room temperature for two weeks. This produces a product which, like the previous products, has an aspect of excellent surface, good sealing and very good mechanical characteristics.

Example 4
The following components are mixed in a mortar barrel for ten minutes so as to form a concrete slurry having a specific gravity of 0.6:
- Portland cement: 40 kg
- silica weight: 60 kg
- water: 50 kg
- aluminum powder: 230 g
The concrete slurry thus prepared is then poured into a mold, as illustrated in Figure 1, this mold being 200 cm wide, 100 cm long, 10 cm deep. It is then subjected to a baking treatment for 4 hours at 30 "C. A part of the thickness of the expanded concrete grout is then partially removed by scraping off said upper surface, so that said surface is at a height 5 mm above. 9 upper edges of the mold. Then spread on the surface of the sand with a grain ranging from 0.5 to 2 mm and a specific weight of 0.3.

The assembly is then subjected to the action of a roller of the type illustrated in FIG. 3, so that a pressure is exerted making it possible to compress the grout by 5 mm when a relative pressure of 0.68 atmosphere (10 psig). The compressed cellular concrete grout contained in the mold is then introduced inside an autoclave where it undergoes a curing treatment under the same conditions as in Example 1.

This being done, the panel is removed from the mold. The cellular concrete panel obtained is of very good quality, waterproof exterior surface and has good mechanical characteristics. The specific weight of the panel thus produced in a cross-sectional direction going from the surface subjected to the action of the roller to the opposite surface is then determined and the results are grouped in the curve which is the subject of FIG. 11.

Comparative example
Example 1 is repeated with the only difference that the compression treatment of the cell grout is not carried out. The specific weight of the finished product, in a cross-sectional direction from one surface to the opposite surface, is substantially uniform and close to 0.5. The external surface of the finished panel which corresponds to the surface subjected to the action of the pressure of Example 1 is rough and is not likely to be directly covered with a finishing layer. In addition, such a panel is not very tight and has mechanical characteristics inferior to the panel according to the invention.

Claims (8)

 1 / A method of manufacturing a lightweight panel of cellular concrete-which consists of filling a mold (l) with a grout of cellular concrete and then unmolding the panel formed after hardening of the grout, said panel then being subjected to a treatment of cooking, characterized by the fact that it comprises a step which consists in pressing on the upper surface of said grout in order to form a compressed surface on said concrete panel.  2 / Processes according to the claim, characterized in that the compression step is carried out while the grout is in the plastic state and makes it possible to form a pattern on the surface of the panel.  3 / Method according to one of claims 1 or 2, characterized in that before performing the compression step, is distributed on the upper surface of the cell grout an additional material for improving the properties of said panel, the material thus distributed firmly adhering to said panel as a result of the subsequent compression step.  4 / A method according to claim 3, characterized in that the additional material distributed on the surface consists of fine, light aggregates, fibers and / or pigment.  5 / A method according to claim 3, characterized in that after compression, the material is subjected to a second compression step.  6 / A method according to claim 5, characterized in that the second compression step is performed using a device for forming a surface pattern.  7 / Method according to one of claims 1 or 2, characterized in that the compression step is carried out while the grout has a Proctor value lower than a relative pressure of 6.8 atmospheres (100 psig).  8 / A method according to claim 7, characterized in that the Proctor value is between Q, 136 and -0.68 atmospheres (2 to 10 psig).