FR2948711A1 - Reinforced concrete wall stripping method for building, involves applying electrical field using energy sources that are placed between reinforcements connected on anodes and formwork walls connected on cathodes, respectively - Google Patents

Abstract

The method involves applying an electrical field using electric energy sources (4a, 4b) e.g. current generators, after pouring the concrete between formwork walls (1a, 1b), where the formwork walls are made of stainless steel. The energy sources are provided with anodes (6a, 6b) and cathodes (5a, 5b), and are placed between metal reinforcements (2) connected on the anodes and the formwork walls connected on the cathodes, respectively. An independent claim is also included for an installation for stripping a reinforced concrete wall arranged between formwork walls.

Description

METHOD FOR DECREASING WALLS IN ARMED CONCRETE

The present invention relates to a method of dismantling a reinforced concrete wall disposed between formwork walls. Such a process will be implemented especially on construction sites during the manufacture of buildings, the realization of prefabricated walls, pre-walls and pre-slabs prefabrication plant. The invention also relates to an installation for implementing this method. Such an installation will for example be designed by manufacturers of electrical equipment and will find its application on the site where the concrete structures are built. Reinforced concrete is well known to those skilled in the art and used in most building constructions comprising concrete walls. Also, a reinforced concrete wall is formed on the one hand, concrete consisting of a mixture of gravel, sand, water and cement and, on the other hand, a reinforcement or a metal reinforcement. in particular steel which increases the mechanical strength of the concrete wall. During the manufacture of the wall, the metal frames are disposed between formwork walls constituting a mold and the concrete is poured between said formwork walls. Once the concrete has hardened, the formwork is removed by removing the formwork walls. Traditionally, release agents such as lubricants or formwork oils are used and deposited on the inner faces of the formwork walls to form a release layer separating said inner face and the concrete, which prevents the bonding of concrete on the internal face of the formwork walls and thus allows demolding or stripping without altering the external surfaces of the concrete wall. However, these mold release agents do not always guarantee stripping without tearing the concrete and may in some cases cause color defects. Indeed, the final appearance of the concrete wall depends essentially on the demolding agent used. In addition, the cost of such demoulding agents has an impact on the cost of manufacturing the building; their use also has an impact on the environment which can be detrimental.

The object of the present invention is to overcome the disadvantages that currently exist and proposes for this purpose a method of dismantling a reinforced concrete wall placed between formwork walls of the banches type. These reinforced concrete walls consist for example of load-bearing walls of buildings. However, it can be envisaged that these concrete walls constitute any type of reinforced concrete structures. In the remainder of the description, the term "concrete walls" will be used by default to define the reinforced concrete walls. The formwork walls are in particular of the type banches and made of electrically conductive materials so that the inner faces of said formwork walls intended to be in contact with the concrete are electrically conductive. These formwork walls can be made of a single electrical conductor block, steel, preferably stainless, or even aluminum or other conductive metals. However, it would be possible to provide a casing wall composed of a first thickness, for example, of wood or of composite materials, non-electrical conductors, and of a second thickness constituting the internal face of said shuttering wall intended to come into contact with concrete, made of electrically conductive materials, preferably steel or stainless steel. Remarkably, the method consists, after pouring concrete between the formwork walls, to apply an electric field by means of a source of electrical energy provided with an anode and a cathode between, on the one hand, reinforcement or metal reinforcement disposed in the poured concrete to form the reinforced concrete wall, this reinforcement or metal reinforcement being connected to the anode of the electric field and, on the other hand, the formwork walls, in particular their internal face, electrical conductor, these being connected to the cathode of the electric field. Such a method makes it possible to apply an electric field in the concrete between the metal reinforcement connected to the anode and the internal face of the shuttering wall connected to the cathode; the water contained in the concrete still fresh, that is to say uncured, will promote a displacement of the water contained in said concrete from the anode to the cathode, and thus allows to form a film of water on the inner face of the formwork wall, constituting a non-adhering separating layer between said inner face and the concrete which, once the hardened concrete, allows the demolding or stripping of said formwork walls without tearing concrete. The method thus makes it possible to form the concrete wall without the use of demoulding agents, which advantageously reduces the cost of building construction and avoids any environmental pollution. According to the method of the present invention, the electric field is applied between the metal reinforcement or reinforcement and the shuttering wall at the beginning of the setting of the concrete. The beginning of the setting of the concrete means a time interval from the start of setting of the concrete as such, that is to say the moment when the concrete begins to harden, and about two hours twenty five minutes before early start of the concrete. This has the advantage of being in a range of application of the electric field during which the conductivity is most conducive to obtain a suitable migration of water to the inner face of the formwork walls.

According to the method of the present invention, the temperature of the concrete is measured to determine the onset of setting of the concrete. Indeed, the mechanical properties of concrete evolve over time and change from a more or less fluid fresh state to a hardened state; this passage is the consequence of exothermic hydration reactions of the binder (cement and additional mineral); it is thus possible to determine for each of the existing concrete preparations on the market, the temperature at which the start of setting takes place. By measuring this temperature, it is therefore determined the onset of setting of the concrete and thus the time when it is appropriate to apply the electric field. According to the method of the present invention, an electric field is applied for a period of less than one hour so as to limit the amount of water migrated to the inner face of the formwork wall. According to the method of the present invention, the electric field is applied by means of a voltage less than 20 volts. According to one variant, this electric field can be applied by means of an electric intensity. In this case, the electrical current will be less than 500 mA. Preferably, an electrical voltage is applied, which has the advantage of increasing the amount of water migrating through the concrete to the inner face of the formwork wall.

Preferably, a voltage of the order of 1 volt is applied for a duration of the order of 10 minutes. This choice has the advantage of obtaining a remarkable surface condition both for the outer face of the concrete wall and for the inner face of the formwork wall during demolding. However, we can consider other pairs of voltage parameters and duration, or even intensity and duration, depending on the dimensions of the concrete walls to implement or even the choice of concrete. According to the method of the present invention, use is made of steel shuttering walls or at least having an internal face made of steel. Preferably, these formwork walls are made of stainless steel, which avoids corrosion problems on the formwork walls when they are not used or at the end of use. (Phrase suppressed) According to the method of the present invention, the anode of the electric field is connected to the reinforcement at a distance from the form wall greater than 15 mm. The present invention also relates to an installation for the demoulding of reinforced concrete walls disposed between formwork walls of the type banches, electrically conductive materials. The installation comprises at least one electrical energy source comprising an anode provided with connection means on the reinforcement or metal reinforcement of the reinforced concrete wall and a cathode provided with connection means on at least one wall of formwork. . It is of course possible to provide several sources of electrical energy including an anode and a cathode connected to the reinforcement and a formwork wall, as many electric power sources being necessary depending on the number of formwork walls used. According to one variant, the installation that is the subject of the invention can provide a single energy source comprising as many anodes and cathodes as there are shuttering walls used for the implementation of the concrete wall. According to the installation of the present invention, the source of electrical energy 30 for applying an electric field is a voltage source, in particular a voltage generator. According to an alternative embodiment, the source of electrical energy is a source of intensity, in particular a current generator. According to the installation of the present invention, it comprises an apparatus for measuring the temperature of the cast concrete to determine the onset of setting of the concrete in order to apply the electric field. Other features will appear during the course of reading the description which follows in support of figures among which: - Figure 1 shows schematically a fresh concrete poured between two walls of formwork, a stripping installation object of the present invention being illustrated; FIG. 2 illustrates a graph showing the variations of the electrical conductivity and of the heat flux as a function of time for a concrete used for carrying out the tests. FIG. 1 shows two shuttering walls 1a, 1b, between which metal reinforcement 2 or reinforcement is placed, fresh concrete 3, that is to say in the liquid state, poured between the two walls of formwork la, lb, the metal reinforcements being embedded in said concrete 3. This allows, once the hardened concrete, to obtain a reinforced concrete wall constituting for example a wall of a building. Of course, other formwork walls are also provided at the ends of the formwork walls 1a, 1b so as to close them and form a mold for containing the concrete in the liquid state. As illustrated in Figure 1, an installation for the formwork object of the present invention is connected to the metal frame 2 and the formwork walls la, lb. This installation comprises sources of electrical energy 4a, 4b whose cathodes 5a, 5b are connected to the formwork walls 1a, 1b made of electrically conductive materials, and whose anodes 6a, 6b are connected to the metal frames 2, also electrical conductors, which allows to form an electric field between the anodes 6a, 6b and the cathodes 5a, 5b, that is to say between the metal reinforcement 2 embedded in the concrete 3 and the inner face 7a, 7b shuttering walls 1a, 1b. The installation will include as many electrical sources for creating electric fields vis-à-vis the metal frame 2 and each of the formwork walls 1a, 1b. However, one can provide a single source of electrical energy comprising as many anodes and cathodes as existing formwork walls and necessary for the realization of the concrete wall.

This makes it possible to create an electric field through the concrete causing an electro-osmosis type reaction that will allow the water to move from the metal frame 2 to the inner faces 7a, 7b of the formwork walls 1a, 1b. The shuttering walls 1a, 1b are made of an electrically conductive material selected for example from steel, stainless steel or other electrical conductors. The source of electrical energy for applying an electric field between the armature 2 and the shuttering wall la, lab is chosen from voltage sources of the voltage generator type or electricity sources of the current generator type. .

The method according to the present invention can be implemented for any type of concrete existing on the market and can be obtained from concrete manufacturers or directly on site. The tests were carried out with a concrete having the following properties: Concrete With ash Fly fly ash (%) 30 30 Composition [Kg / m3] [Kg / m3] Cement 280 321 Fly ash 45 0 Sand 0/4 863 863 Crushed gravel 4 / 12.5 291 291 Gravillon crasséll.2 / 22.4 641 641 Water 185 193 Adjuvant 1.75 0 Water / binder 0.57 0.6 G / S 1.08 1.0820 Comparable tests were carried out in addition with pasta volumes of 28% and 32% of the same manufacturing, its tests to achieve similar results. Measurements of maturometry were carried out on the concrete used for its tests. Its maturometry tests consist in measuring the heat released over time by the concrete during exothermic hydration reactions of the binder (cement and mineral addition) resulting from the change of state of the concrete from a more or less fluid state to a hardened state. At the same time, his maturometry tests consist of measuring the evolution of the electrical conductivity of concrete over time. The tests carried out on the concrete, object of its tests, made it possible to reach the curve illustrated in figure 2. On the graph illustrated in figure 2, one notes a maximum value of the conductivity which is reached after a few hours after mixing of concrete ingredients, especially water and cement, ie about three hours, for which a concrete temperature value corresponds, close to the maximum temperature shown on the graph

It is therefore appropriate to apply the electric field between the metal reinforcement 2 and the shuttering walls 1a, 1b in this period where the electrical conductivity is maximum, that is to say at the time of start of setting concrete, or preferably before the start of setting concrete. Preferably, for the concrete used to carry out the tests, the electric field will be applied in a period of about two hours twenty five minutes before the beginning of setting of the concrete corresponding to the maximum value of electrical conductivity and the very beginning even taking concrete. This period will be more or less variable depending on the type of concrete used and its dosage. Moreover, knowing the temperature in the concrete corresponding to this maximum value of electrical conductivity, it is also possible to measure this temperature by means of a temperature probe 8 disposed in the concrete, as illustrated in FIG. once the measured temperature, corresponding to the beginning of setting of the concrete, it is appropriate to apply the electric field between the metal frame 2 and the form wall la, lb.

As stated above, the source of electrical power can be a source of voltage or a source of power. Various tests were carried out using a voltage source with voltages lower than 20 volts and with shuttering walls made of steel and stainless steel. Comparable tests have been carried out with a power source of the current generator type, with currents of less than 500 mA. These tests made it possible to quantify the amount of water migrated to the inside of the shuttering wall and to achieve the following results: Comparison of the results with applied voltage and applied intensity. Intensity (mA) 50 139 250 500 Formwork wall M (g) E (mm) M (g) E (mm) M (g) E (mm) M (g) E (mm) Steel 5.13 0.26 5.31 0.26 8.81 0.44 7.44 0.37 Stainless steel 5.24 0.26 5.51 0.27 8.11 0.40 8.42 0.42 Voltage (V) 2.5 5 8 15 Formwork wall M (g) E (mm) M (g) E (mm) M (g) E (mm) M (g) E (mm) Steel 5.1 0.25 7.31 0.36 9.54 0.47 5.6 0.28 Stainless steel 6.54 0.33 7.81 0.39 9.03 0.45 5.95 0.30 Where M is the transport water body and E is the thickness of the water film created between the shuttering wall and the concrete.

These tests show that the amount of water recovered with the stainless steel formwork walls is greater than that recovered with the steel mold, as the amount of water transported under the effect of the tension is higher. important than that transported under the effect of intensity (except in cases 15V - 500mA). For this purpose, stainless steel form walls are preferably chosen and an electric field is preferably applied by means of a voltage source.

Of course, the implementation of the method of the invention with other materials for the conductive formwork walls and other sources of electrical energy remains possible. Various tests have been carried out by means of a voltage source by varying the voltage, for values less than 20 volts, and the duration of application of the electric field, for values of less than one hour, between the reinforcement 2 and the shuttering wall 1a, 1b; these tests led to the following results: Concrete wall Formwork walls Classification Aspect of microbullage Dusting Dusting Clogging Points grip 5 Volts ù 50 Insignificant Medium Bad Very Very Average 7 minutes Important 3.7 Volts ù 50 Insignificant Bad Bad Very Very Average 8 minutes important important 3.5 Volts ù 30 Bad Average Bad Important Important Low 4 minutes 3.5 Volts ù 20 Bad Bad Bad Important Important Medium 6 minutes 3.5 Volts ù 10 Bad Medium Bad Important Important Medium 5 minutes 3.5 Volts ù 5 Bad Fair Medium Medium Fair Light 3 minutes 2.5 Volts ù 10 Poor Good Medium Fair Medium Fair 3 minutes 1 Volts ù 10 Very good Very good Very good Very light Very light 2 minutes 1 Volts ù 5 Very good Very good Very good Very light Very light 2 minutes Agent of Very good Very good Very good Very light Without Without 1 stripping The results of these tests have found easy removal, with a good appearance of the internal faces of the formwork walls and a good quality of the faces of the concrete wall, obtained for a voltage of the order of one volt, applied for a period of l 10 minutes or 5 minutes. We will therefore choose these preferred values to apply the electric field. Of course, other values of voltage and duration during which this voltage is applied may be chosen according to the dimensions of the formwork walls 1a, 1b, the connection position of the anodes on the reinforcement 2 and the choice of concrete. These voltage values will however remain less than 20 volts, just as the duration of application of the electric field will remain less than one hour. Preferably, the anodes are positioned at a distance greater than 25 mm from the internal face 7a, 7b of the shuttering wall. This distance may vary substantially depending on the parameters chosen for the application of the electric field. For example, tests have been carried out with a distance of about 50 mm.

The electrical energy source or sources 4a, 4b of the installation that is the subject of the invention comprise connection means 9a, 9b, 10a, 10b of the cathodes and anodes on the formwork walls laq, lb and on the reinforcement or These connecting means 9a, 9b, 10a, 10b may, for example, consist of simple connection clamps or even of a fastening system by bolting or clamping collar or the like.

Claims (13)

REVENDICATIONS1. A process for demoulding a reinforced concrete wall disposed between shuttering walls of an electrically conductive material, said method consisting, after pouring the concrete between the shuttering walls, of applying an electric field by means of a source of energy comprising at least one anode and at least one cathode between, on the one hand, the reinforcement (2) in poured concrete, connected to the anode and, on the other hand, the formwork walls (1a, 1b) connected to the cathode. 2. Method according to claim 1, wherein the electric field is applied at the beginning of setting of the concrete. 3. Method according to claim 2, wherein the temperature of the concrete is measured to determine the onset of setting said concrete. 4. Method according to one of claims 1 to 3, wherein the electric field is applied for a period of less than one hour. 5. Method according to one of claims 1 to 4, wherein a voltage is applied less than twenty volts. 6. Method according to claims 4 and 5, wherein a voltage of the order of one volt is applied for a duration of the order of ten minutes. 7. Method according to one of claims 1 to 6, wherein the anode is connected to the reinforcement (2) at a distance from the shuttering wall (la, lb) greater than 25 mm. 8, Method according to one of claims 1 to 7, wherein using formwork walls (la, lb) made of steel. 9. The method of claim 8, wherein using form walls (la, lb) of stainless steel. 10.Installation for the demoulding of a reinforced concrete wall disposed between formwork walls (la, lb) of the type banches, of electrically conductive material, said installation comprising at least one source of electrical energy (4a, 4b) comprising an anode (6a, 6b) provided with connection means (9a, 9b, 10a, 10b) on the reinforced concrete reinforcement and a cathode (5a, 5b) provided with connection means on at least one form wall (ia, ib) ). 11.Installation according to claim 10, wherein the source of electrical energy (4a, 4b) is a voltage source. 12.Installation according to claim 10, wherein the electric power source (4a, 4b) is a current generator 13. Installation according to one of claims 10 or 12, which comprises an apparatus (8) for measuring the temperature of the concrete.