EP1194389A1

EP1194389A1 - Encapsulated metal nodules for the formation of sacrificial anodes in mortar or reinforced concrete and method for the production of said nodules

Info

Publication number: EP1194389A1
Application number: EP00927332A
Authority: EP
Inventors: Richard Guerin; Jacques-Henri Loyer
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-05-12
Filing date: 2000-05-11
Publication date: 2002-04-10
Also published as: FR2793486A1; WO2000069788A1; AU4575700A; JP2003512518A; CA2373435A1; FR2793486B1

Abstract

The invention relates to mortar and reinforced concrete used in the building industry and civil engineering. The inventive nodules respectively comprise: a metal core containing one or several metals or metal alloys chosen from those which have an electrochemical potential which is lower than that of iron, and a protective envelope surrounding the core and made in such a way that when the nodules are used to produce and apply a mortar, concrete or the like, sufficient mechanical resistance is provided when mixing occurs with grains that make up mortar, concrete or the like and a temporary barrier against water is established at least until the mortar, concrete or the like has set. The invention can be used to repair reinforced concrete structures which have been damaged by corrosion.

Description

ENCAPSULATED METAL NODULES FOR FORMING

SACRIFICIAL ANODES IN MORTAR OR REINFORCED CONCRETE

AND METHOD FOR MANUFACTURING SUCH NODULES

TECHNICAL AREA :

The present invention relates to the technical field of protection against corrosion of metal reinforcements of reinforced concrete or similar structures. It is known that metallic reinforcements, in particular steel, undergo a passivation phenomenon when they are used in mortars or hydraulic concretes, taking into account the high alkalinity of these latter results of the dissolution of alkalis in cement. This passivation ensures in the most common uses a correct protection of concrete metal reinforcements. However, this mode of protection of reinforcements is ineffective in the case of structures immersed in sea water or liable to be in contact with Cl ^" ions which destroy the passivity of steel reinforcements.

This is particularly the case of engineering structures which are subject to salting during the winter period in order to fight against ice. In the presence of chlorine ions in high concentration the pH of the concrete decreases and the passivation disappears so that the metal reinforcements are then the seat of oxidation phenomena which cause disorders in the structure of the structure. Indeed, it appears on the surface of the reinforcements a profuse rust causing cracking and bursting of the concrete of the structures. Likewise, the oxidation of the reinforcements leads to a structural weakening of these which can be detrimental to the resistance to the forces of the structures concerned.

The presence of a high concentration of Cl ^' ion is not the only cause of the initially high pH drop, reflecting a more or less premature aging of the concrete. Indeed, this drop over time, is also the result of the action of atmospheric carbon dioxide which is fixed, in the presence of moisture, on the lime released at the end of hydration of the cement, as part of a reaction, called carbonation. This This reaction leads to the reinforcement of the reinforced concrete reinforcements which are then subject to corrosion and the formation of expansive rust.

PRIOR TECHNIQUE:

In order to combat these corrosion phenomena, it is known to use what is known as anodic protection of the reinforcements. This protection can either involve the connection of the armatures to a direct current source to circulate a protective current therein, or involve sacrificial anodes based on one or more metals having an electrochemical potential lower than that of iron.

The invention relates more particularly to the second method which ensures protection of the metal reinforcements by the use of sacrificial anodes.

In this particular field, application FR 2 689 921 proposes, for example, to incorporate particles based on zinc within a mortar or repair concrete intended to be applied locally to regions of the structure to be repaired. in which the metal reinforcements have undergone strong corrosion. Given the difference in electrochemical potential between iron and zinc, oxidation-reduction reactions develop within the repair mortar in contact with the oxidized reinforcements which contribute to reducing the rust formed on the reinforcements. In addition, a kind of battery is formed which polarizes the reinforcements so as to protect them.

Thus, the sacrificial anodes formed by the grains of zinc are oxidized in place of the metal reinforcements which are then protected.

Such a method makes it possible in certain situations to ensure repair, restoration and sufficient protection of the reinforcements and of the concrete which contains them.

However, it appeared that, in other situations, the difference in electrochemical potential between the steel of the reinforcements and the zinc was not sufficient to ensure effective protection of said reinforcements. It should then be considered to use metals or alloys having an electrochemical potential lower than that of Zinc such as for example Aluminum. However, aluminum reacts strongly in the very alkaline aqueous medium constituted by a mortar or a fresh concrete. This reaction then leads to a strong release of hydrogen causing disorders within the concrete or mortar which then sees its mechanical strength reduced.

It therefore appears the need to have means making it possible to use, as sacrificial anodes in mortars, concretes or the like, metals or metal alloys which are highly reactive in very alkaline aqueous medium without the risk of altering the mechanical qualities. mortar or concrete by gassing resulting from electrolysis reactions developing in relation to the metal anodes. Furthermore, it has appeared that, when the zinc particles are used in a mortar or hydraulic concrete, electrolysis reactions occur spontaneously between the zinc, the alkalis of the cement and the water. These reactions then lead to a partial consumption of the zinc before it has been able to react with the reinforcements to be repaired or protected. It therefore appears the need to have means making it possible to temporarily block the electrolysis reactions between the sacrificial anodes used and the constituents of the mortar and of the implementation concrete so as to authorize the use as sacrificial anodes in a mortar, concrete or the like of metals, alloys or compounds having a lower or even much lower electrochemical potential than that of iron or the steel constituting the reinforcements.

PRESENTATION OF THE INVENTION:

In order to achieve this objective, the invention relates to metal nodules intended to constitute sacrificial anodes in a mortar, reinforced concrete or the like, characterized in that each nodule comprises:

a metallic core containing one or more metals or metallic alloys chosen from those having an electrochemical potential lower than that of iron, - And a protective envelope, surrounding the core, made so, when using the nodules for the preparation and implementation of a mortar, concrete or the like, to:

On the one hand, have sufficient mechanical strength to withstand mixing with aggregates constituting the mortar, concrete, or the like,

• and, on the other hand, constitute a temporary water barrier, until at least a partial setting of the mortar, concrete or the like.

The nodules according to the invention have the advantage, when they are used in a mortar or a concrete during the preparation and use thereof, of not reacting immediately. Thus, the sacrificial anodes formed by the metal cores are not consumed prematurely and there is no untimely release of gas insofar as the cores are liable to react strongly with the very alkaline aqueous medium of the mortar or concrete. This advantageous characteristic of the nodules mainly results from the mechanical and physico-chemical qualities of the protective covering of the nuclei. Indeed, this casing has the required mechanical strength to withstand without breaking the constraints of shock and abrasion to which the nodules are subjected during the preparation, mixing or kneading of mortar, concrete or the like in ^~ router or mixer especially. This mechanical resistance associated with the water-repellent characteristic of the envelopes prevents any premature contact of the nuclei with the alkaline aqueous medium. In addition, the temporary nature of the water-repellent properties of the protective covering makes it possible to ensure a kind of retarding effect which allows redox reactions involving the nuclei to be established only after at least a partial setting. mortar or concrete. Thus, these reactions only develop when the concrete or mortar has been used and has sufficient strength to be able to withstand possible releases of gas, in particular hydrogen, without the risk of plastic deformation and / or structural disorder. such as micro-cracks for example. The implementation of the nodules according to the invention therefore makes it possible to obtain mortars, concretes or the like which at the same time have mechanical strength characteristics compatible with their use in engineering structures, by example, and chemical properties suitable for the protection and repair of metal reinforcements.

The nuclei of the nodules preferably consist of or mainly contain a metal chosen from aluminum, magnesium, zinc or alloys of these. According to an advantageous characteristic of the invention, the cores are made from cast aluminum waste which is a relatively inexpensive material. The invention thus offers a possibility of recycling for this waste which is difficult to reuse elsewhere.

The nuclei of the nodules have, preferably but not exclusively, an average particle size of between 1 and 10 mm approximately while the nodules have a particle size preferably but not exclusively of between 2 and 11 mm approximately. This particle size can vary depending on the use that will be made of the nodules. Thus, this range of grain sizes can be used for incorporation into concrete. On the other hand, in the case of incorporation into a mortar it is preferable to use nodules having an average particle size of 2 to 6 mm approximately or having cores with an average particle size of 1 to 4 mm.

The protective covering of the nodules is made of any suitable material or material having mechanical resistance characteristics and physicochemical properties in accordance with the function of the nodules according to the invention.

Thus, the protective envelope can be made of a polymer or a resin sufficiently hard after polymerization to form around the core a waterproof shell capable of withstanding impact and abrasion resulting from mixing with the aggregates of the mortar or implementation concrete. Furthermore, this polymer or this resin will be liable to be altered by the alkaline character of the mortar or concrete so that after a certain time, corresponding at least to the partial setting time of the mortar or concrete, allow the establishment of the reactions of redox involving the nucleus.

According to another preferred characteristic of the invention, the protective envelope consists of a shell which is porous to water and which has suitable mechanical strength and which is impregnated or covered with a water-repellent product intended to be altered over time, by the alkaline nature of the medium for implementing the nodules, to constitute a temporary barrier to water.

The porous shell is preferably made from a calcium-based compound. The shell is for example based on limestone or even more preferably, based on cement.

The water-repellent product is chosen so as to be alterable by the alkalis of the mortar in order, after its degradation, to allow the passage of water and of the ions responsible for the redox reactions. Preferably but not strictly necessary, the water-repellent product is chosen from silicones, silanes, siloxanes, stearates, fatty acids, paraffin or mixtures thereof.

According to another characteristic of the invention, each nodule comprises one or more conductive strands associated with the core. These strands in direct contact with the nuclei of the nodules and surrounded jointly with the nuclei by the protective envelopes promote the circulation of electric currents within the mortar or concrete implementing the nodules according to the invention. The electrically conductive strands are made of any suitable material inert with respect to the galvanic couples formed by the cores and the reinforcements. The conductive strands are preferably made of carbon fibers.

The invention also relates to a method of manufacturing nodules intended to constitute sacrificial anodes in a mortar, reinforced concrete or the like, characterized in that it consists in coating, metal cores containing one or more metals or metal alloys chosen from those with an electrochemical potential lower than that of iron, of a protective envelope which, when using nodules for the preparation and the implementation of a mortar, concrete or the like:

* on the one hand, has sufficient mechanical strength to withstand kneading with aggregates constituting mortar, concrete, or the like,

* and, on the other hand, constitutes a temporary barrier to water, until the setting of the mortar, concrete or the like, at least.

Thus, the envelope can be produced by coating the cores with any material having the properties required in accordance with the function of the nodules. This coating can be carried out by any method adapted to the nature of the cores and of the material or materials constituting the protective envelope such as, for example and without limitation, by kneading, soaking, spraying, deposition in a fluidized bed. According to a preferred characteristic of the invention, the manufacturing process consists in producing the protective envelopes around the cores, in: • possibly screening the cores,

• agglomerate a powder around the cores to form porous shells around said cores, • crystallize the shells to give them a protective and abrasion resistant character,

• apply to the crystallized hulls a water-repellent product intended to be altered by the alkaline character of the environment in which the nodules are used. The powder used is for example a powder based on calcium or its compounds such as a powder based on limestone. Preferably, the powder used is a powder or based on cement.

In the case of using dry cement for making the shells, the quantity of cement used represents a mass of approximately ^" 50 to 70% of the mass of the nodules.

After agglomeration, in a kind of shell, of the powder around the nuclei, this shell is crystallized to give it sufficient mechanical strength. In the case of a powder based on limestone or cement, it is used as crystallizer an aqueous solution of silicate (s) applied to the hulls. The crystallizer preferably used is an aqueous solution of sodium silicate. Thus, to ensure the crystallization of the shells formed by agglomeration of cement powder around the cores, an aqueous solution of sodium silicate is used at a concentration of approximately 20% in an amount representing a mass of at most 10% of the mass of cement used to form the hulls. The hulls thus produced have a porous character, the invention therefore recommends applying a water-repellent product which covers and / or impregnates the cockles. This water-repellent product is chosen so as to be able to be altered by the alkaline nature of the mortar, concrete or the like using nodules. The water-repellent product makes it possible, first of all, to prevent any diffusion of water and ions through the shells of the nodules for a period corresponding at least to the period necessary for the mortar or concrete to take or acquire sufficient stiffness to no longer be sensitive to any gassing that could result from the oxidation of the nuclei. Then, the alteration of the water repellent product breaks the temporary barrier it formed and allows the development of redox reactions involving the nuclei. Furthermore, it should be noted that the nature of the porous shell advantageously contributes to the cohesion of the nodules with the mortar or the concrete in which they are used.

As mentioned above, the water-repellent product is chosen from silanes, silicones, siloxanes, stearates, fatty acids, paraffin, or mixtures thereof, with a preference for silanes. This water-repellent product is applied to the crystallized hulls in a proportion preferably but not exclusively representing 1 to 5% by mass of the total mass of the nodules.

The nodules thus produced and in accordance with the invention can be used in mortars, concretes or the like for the production of new works or for the repair of altered works.

In the case of use for the preparation of mortars or hydraulic concretes, the nodules represent, preferably but not necessarily, at most 10% by mass of the total mass of aggregates and cement.

Insofar as the nodules are used in mortars, concretes or the like which are not very alkaline in nature such as, for example, mortars or concretes involving an organic binder, it can be envisaged to correct the alkalinity by the addition of alkaline active elements such as for example sodium hydroxide.

The examples which follow will make it possible to better understand the invention in its various aspects relating to the nodules, to their manufacture and to their implementation. BEST WAY TO IMPLEMENT THE INVENTION:

EXAMPLES

EXAMPLE 1 MANUFACTURE OF NODULES CONFORMING TO THE INVENTION WITH CARBON FIBER CONDUCTING STRANDS

Aluminum foundry waste is used to make the cores. It is then proceeded as follows to manufacture from this waste nodules in accordance with the invention.

1) The metallic waste is stirred for approximately 5 minutes so as to undo any waste aggregates.

2) The sieves are screened to select cores with a particle size cut between 1 and 4 mm.

3) The selected nuclei are washed under running water for approximately 5 minutes with stirring.

4) The washed cores are drained and then dried with hot air.

5) 10 kg of cores thus prepared are mixed with 10 g of carbon fibers for dispersion in a concrete mixer or a kneader or other mixer.

6) Mix for approximately 15 to 20 minutes by gradually introducing 5 kg of cement of the CPA CEM I or CPJ CEM II type, until agglomeration of a cement shell around each core. If necessary, add 1 to 2 kg of cement to perfect the coating.

7) The mixing is continued for approximately 30 minutes by spraying an aqueous solution of sodium silicate up to a maximum of 10% of the weight of the cement added to ensure crystallization of the agglomerated cement shells. An exothermic reaction then develops and it may appear necessary to cool the mixing tank either by an external water jet or by a flow of fresh air inside. It should be noted that the exothermic nature of the reaction is advantageously used to ensure evaporation of the water from the silicate solution before the development of redox reactions at the nuclei.

8) The cores coated with their crystallized shell are then cooled by, for example, spreading the nodules on a flat and ventilated surface. It may take 2 to 4 hours for the nodules to cool completely.

9) After complete cooling, a water-repellent solution is applied by kneading to the crystallized shells of the nodules. This solution is, of course, applied in sufficient quantity, ie approximately 1 to 5% of the total weight, to ensure good recovery and / or good impregnation of the shells.

10) Finally, the nodules are dried either by spreading for 24 hours on a flat and ventilated area, or by kneading under a flow of dry air.

The nodules thus produced are then in accordance with the invention and ready to be used in the manufacture of a mortar, a concrete or the like.

It should be noted that the joint coating, by the protective envelope, of the carbon fibers forming conductive strands with the cores ensures intimate and electrically effective contact between the carbon fibers and the sacrificial anodes formed by the cores. During the implementation of the nodules, this electrical contact is then favored by the development of aluminate crystals in the vicinity of the nucleus. EXAMPLE 2 - MANUFACTURE OF NODULES ACCORDING TO THE INVENTION WITHOUT STRANDS

CONDUCTORS

The procedure is substantially the same as for Example 1, except that step 5 of mixing the cores with carbon fibers is omitted.

EXAMPLE 3 - USE OF NODULES IN A MORTAR

It is possible to use nodules according to the invention for preparing a mortar having a workability of approximately 30 minutes.

The composition of such a mortar could be:

• Cement type CPA CEM I or CPJ CEM II 300 kg

• Limestone, siliceous or silico-limestone sand from 0 to 4mm 900 kg

• Nodules according to example 1 or 2 of particle size

• from 2 to 6 mm 100 kg • for a total of aggregates of 1300 kg

• Mixing water about 150 liters depending on the required consistency

Such a mortar can then be used for repair operations or corrosion prevention operations as a coating in particular.

EXAMPLE 4 - USE OF NODULES IN CONCRETE

It is possible to use nodules according to the invention for preparing a concrete having a workability of approximately 30 minutes.

The composition of such concrete could be:

• Cement type CPA CEM I or CPJ CEM II 350 kg

• Limestone, siliceous or lime-sand from 0 to 25 mm 1,650 kg

• Nodules according to the invention from 2 to 6 mm 200 kg • for a total of aggregates of 2200 kg

• Mixing water about 175 liters depending on the required consistency When using nodules as manufactured according to Example 1 and used in the context of a mortar according to Example 2 or a concrete according to Example 3, the spontaneous electrolysis reaction at the level of the nuclei will start after approximately 2 hours of contact with the mixing water. The release of hydrogen, which then occurs, will be of no consequence due to the stiffness of the mortar or concrete, a partial setting of which will have occurred.

Furthermore, the appearance of a potential difference between the paste thus prepared and applied to a work to be repaired and the steel frame of this work can be checked by means of a device for measuring potentials with wet electrodes of the "Canine" type. A potential difference between 300 and 1500 mV approximately can be observed.

In the above examples, the nodules are used directly for the preparation of mortars or concretes intended to be implemented immediately or at least quickly.

However, the nodules according to the invention can also be added to commercially available dry or wet mortars or concrete ready for use. We will then choose to introduce the nodules just before using the material. Of course, it will be checked beforehand that the duration of handling, of the mortar or ready-mixed concrete supplied, is compatible with the reaction time of the nodules.

Claims

CLAIMS:

1 - Metallic nodules intended to constitute sacrificial anodes in a mortar, reinforced concrete or the like, characterized in that each nodule comprises: - a metallic core containing one or more metals or metallic alloys chosen from those having an electrochemical potential lower than that iron, - and a protective envelope, surrounding the core, made so, when using nodules for the preparation and implementation of a mortar, concrete or the like, to:

* on the one hand, have sufficient mechanical strength to withstand kneading with aggregates constituting mortar, concrete, or the like,

* and, on the other hand, constitute a temporary barrier to water, until at least a partial setting of the mortar, concrete or the like,.

2 - Metallic nodules according to claim 1, characterized in that each nodule comprises one or more conductive strand (s) associated with the core.

3 - Nodules according to claim 1, characterized in that the conductive strands consist of carbon fibers. 4 - Nodules according to one of claims 1 to 3, characterized in that the protective envelope consists of a shell porous to water which has a suitable mechanical resistance and which is impregnated or covered with a water-repellent product intended to be altered over time by the alkaline nature of the medium for implementing the nodules to constitute a temporary barrier to water. 5 - Nodules according to claim 4, characterized in that the porous shell contains a calcium-based compound.

6 - Nodules according to claim 4, characterized in that the porous shell is based on cement.

7 - Nodules according to claim 4, characterized in that the porous shell is based on limestone. 8 - Nodules according to one of claims 4 to 7, characterized in that the water-repellent product is chosen from silicones, siloxanes, stearates, fatty acids, paraffin or, preferably, silanes, or mixtures of these.

9 - Nodules according to one of claims 1 to 8, characterized in that the core consists of a metal chosen from aluminum, magnesium, zinc or alloys thereof.

10 - Nodules according to one of claims 1 to 8, characterized in that the core is made from cast aluminum waste.

11 - Nodules according to one of claims 1 to 10, characterized in that the cores have an average particle size of 1 to 10 mm.

12 - Nodules according to one of claims 1 to 10, characterized in that they have an average particle size of 2 to 11 mm.

13 - Mortar characterized in that it comprises metallic nodules according to one of claims 1 to 12. 14 - Mortar according to claim 13, characterized in that it comprises at most 10% by weight of nodules.

15 - Mortar according to claim 13 or 14, characterized in that the nodules have an average particle size of 2 to 6 mm approximately.

16 - Concrete characterized in that it comprises metallic nodules according to one of claims 1 to 12.

17 - Concrete according to claim 16, characterized in that it comprises at most 10% by weight of metal nodules.

18 - Concrete according to claim 16 or 17, characterized in that the nodules have an average particle size of 2 to 11 mm approximately. 19 - Method for manufacturing metal nodules intended to constitute sacrificial anodes in a mortar, reinforced concrete or the like, characterized in that it consists in coating metal cores containing one or more metals or metal alloys chosen from those having a potential electrochemical lower than that of iron, of a protective envelope which, when using nodules for the preparation and the implementation of a mortar, concrete or the like: * on the one hand, has sufficient mechanical strength to withstand kneading with aggregates constituting mortar, concrete, or the like,

* and, on the other hand, constitutes a temporary barrier to water, until at least a partial setting of the mortar, concrete or the like,.

20 - A method of manufacturing metal nodules according to claim 19, characterized in that, to produce the protective envelope, it consists in particular in:

• possibly sift the cores, • agglomerate a powder around the cores to form porous shells around said cores,

• crystallize the shells to give them a protective and abrasion-resistant character,

• apply to the crystallized hulls a water-repellent product intended to be altered by the alkaline character of the environment in which the nodules are used.

21 - Process according to claim 20, characterized in that it consists in using a powder based on calcium or its compounds to produce the shells. 22 - Process according to claim 20, characterized in that it consists in using a cement-based powder to produce the shells.

23 - Method according to claim 22, characterized in that it implement a cement load representing 50 to 70% of the weight of the nodules.

24 - Process according to claim 20, characterized in that it consists in using a powder based on limestone to produce the shells.

25 - Method according to one of claims 21 to 24, characterized in that it consists in using as crystallizing an aqueous solution of silicate (s) and preferably sodium silicate.

26 - Process according to claim 22, characterized in that it consists in using as an crystallizer an aqueous solution of silicates and preferably sodium silicate, representing by weight at most about 10% of the weight of cement used.

27 - Method according to one of claims 20 to 26, characterized in that it consists in applying as a water-repellent product a product chosen from silicones, siloxanes, stearates, fatty acids, paraffin or, preferably , silanes, or mixtures thereof.

28 - Process according to claim 27, characterized in that it consists in using a mass of water-repellent product representing 1 to 5% approximately of the total mass of cores coated with their crystallized shell. 29- Method according to one of claims 19 to 28, characterized in that it consists in associating the metal cores with conductive strands before proceeding to the joint coating of the cores and strands.