LU88716A1 - Method for protecting steel armaments from reinforced concrete structures - Google Patents

Description

"Method for protecting steel reinforcements from reinforced concrete structures."

The present invention relates to a method for protecting steel reinforcements incorporated in a mass of concrete, in which a layer rich in zinc is applied to at least one surface of the mass of concrete to establish a potential difference between the zinc and the frames.

Such a process is known from PCT patent application No. WO-A-92 13116 for protecting reinforcements from a mass of concrete, immersed in salt water, more particularly reinforcements in the area between low tide and high of a marine environment. To protect the reinforcements, a current of electrons passes from zinc to the steel of the reinforcements. This migration is made possible by the fact that the concrete, which is a porous material and of low conductivity, is impregnated with salt water, which ensures the conductivity.

The disadvantage of the known method is that it only works in salt water environments. Salt water is indeed necessary to achieve the conductivity of concrete.

The invention therefore aims to remedy this drawback by ensuring conductivity of the concrete, without being limited to marine environments.

In order to achieve this in accordance with the invention, said method is characterized in that before the application of said zinc-rich layer, an electrolyte is introduced into the mass of concrete by application of an electric field in order to increase the conductivity of the concrete and, after introduction of the electrolyte, said electric field is removed.

By introducing said electrolyte into said mass of concrete, conductivity of the concrete is ensured, even in non-marine environments. Thus a current of electrons passes from zinc to the steel of the reinforcements and this galvanic current created protects the reinforcements from corrosion. The advantage of this protection is that an external energy source is not essential, which is indeed the case in cathodic protection methods.

What characterizes the invention is the fact that an electrically conductive connection is applied through the mass of concrete between said zinc-rich layer and said reinforcement, by applying through the mass of concrete bars or wires insulated with respect to the mass of concrete.

Other details and advantages of the invention will emerge from the following description of a method for acting against corrosion of reinforcements in a mass of concrete according to the invention.

This description is only given by way of example and does not limit the invention. The reference notations relate to the elements included in the accompanying drawings.

FIG. 1 shows schematically and in a longitudinal section a mass of concrete comprising reinforcements, which mass of concrete comprises on the surface the mass of fibers with the anode.

FIG. 2 is a similar view in which the fiber mass and the anode have disappeared from the surface of the concrete mass and replaced by a layer rich in zinc.

Figure 3 shows in a similar section how the electrical connection between the zinc-rich layer and a reinforcement is made.

Concrete is a composite material which consists of cement with possibly additives, aggregates, water and air. Above all these latter components considerably determine the service life of the concrete. An excess of water and air gives a porous structure into which harmful gases and liquids can easily penetrate, and can, in the presence of moisture, react with the elements of the cement matrix.

Reinforced concrete owes its excellent technical characteristics to the good cooperation between the reinforcing steel and the cement matrix. The alkaline elements of the cement matrix create in the pore water of the concrete a high alkalinity state, measured in pH value, so that on the reinforcing steel a layer of microscopic stable crystalline oxide is formed. This oxide layer, called passivation layer, protects the steel from corrosion; the steel is in a passivation state.

Two important phenomena can now attack this passivation layer and thus cause corrosion of the reinforcements. The corrosion process leads to an increase in the volume of the reinforcing steel, since the corrosion products take up a much larger volume than the corresponding steel / so that great pressure is built up in the concrete layer. The effect of accumulation in concrete is the tensile stresses which cause the layer of concrete to tear and decompose. Reinforcing steel is exposed to the aorta as the corrosion process is accelerated, the steel decreases in diameter further, and the stability of the concrete construction is jeopardized.

The most common concrete damage is due to corrosion of reinforcement.

The first phenomenon concerns the most natural reaction, that is to say the carbonation of concrete in which the alkaline elements of the cement matrix are neutralized by acid gases from the air such as carbon dioxide (Cû2) and sulfur dioxide (SO2). The effect is a drop in pore water pH below 9.5.

Carbonation is a continuously progressing process so that sooner or later the carbonation front reaches the reinforcements and the corrosion process can start on the reinforcements.

The second phenomenon concerns the attack by chlorine or bromine ions which pierce the passivation layer and start the corrosion process. The level of chloride allowed is established in the European pre-standard CEN 206. This form of corrosion, which is the most dangerous type, most of the time causes a local and deep attack of the reinforcing steel (corrosion of wells ) as a result of which the rebar section decreases rapidly.

These harmful ions can come from an external source such as thaw salts, sea air and other maritime atmospheres but can also be mixed beforehand in concrete like calcium chloride as a setting time accelerator. or insufficiently washed marine sand and aggregates.

It is also possible that both phenomena are present in the same concrete construction.

Reinforcement corrosion can also be caused by other aggressive ions such as sulphides.

The method according to the invention and illustrated by the appended figures comprises in a first step the application along the external surface 1 of the mass of concrete 2 with a mass of porous fiber 3 in which an anode 4 is incorporated. By the anode is meant, for example, a steel network.

In the mass of porous fibers 3, an electrolyte is incorporated. This electrolyte consists, for example, of conductive ions belonging to the group of sodium, potassium or lithium ions.

To migrate the electrolyte in the direction of the armature 5, a direct current source 6 is applied, connecting the positive polarity of the source with the anode 4 via the conductor 7 and the negative polarity of the source with the armature 5, acting as a cathode, via the conductor 7 '.

After a period which depends on the local circumstances but which in many cases can be estimated at a week, it is checked whether the electrolyte occupies all the space in the mass of concrete which extends, by referring to FIG. 1, between the outer wall 1 and the frame 5. If necessary, this step is extended.

In a second step, the mass of porous fibers 3 is removed with the anode 4 and the current source, the surface of the concrete mass 2 is well cleaned and a layer 8 rich in zinc is applied along the external wall. concrete mass 2. As a zinc-rich layer, metallic zinc or an organic coating with a high zinc content can be used. This can be applied by spraying or applying by brush.

Under certain circumstances, the zinc-rich layer can be protected by an organic coating.

By the difference in electrochiraic potential between zinc and steel, a difference in natural potential of the order of 0.3 to 0.4 V is created. The protective current which flows from the zinc layer towards the steel of the reinforcement 5 guarantees a durable corrosion protection of the steel.

In practice, an electrical connection is applied at different locations, depending on the structure of the concrete mass, between the layer 8 rich in zinc and the reinforcements 5. This is done by applying a conductive connection between the layer 8 rich in zinc and the reinforcement 5. This can be done by applying through the mass of concrete conductive bars or wires 9, insulated from this mass of concrete, on which an electrical connection 10 - 10 'is connected which leads, by the through a connection box with the necessary measuring instruments 11, to layer 8 rich in zinc.

The invention is not limited to the embodiment described here by way of example and many modifications could be made to it as long as it falls within the scope of the claims which follow.

Claims (5)

1. Method for protecting steel reinforcements (5) incorporated in a mass of concrete (2), in which a layer (8) rich in zinc is applied to at least one surface of the mass of concrete to establish a potential difference between the zinc and the reinforcements, characterized in that before the application of said zinc-rich layer, an electrolyte is introduced into the mass of concrete (2) by application of an electric field in order to increase the conductivity of the concrete and, after introduction of the electrolyte, said electric field is removed. 2. Method according to claim 1, characterized in that said electrolyte is introduced into the concrete mass by applying to the surface of the concrete mass a layer comprising an anode (4) in a porous product (3) which contains electrolyte, and by applying a DC voltage between the armature (5) acting as a cathode and the anode (4) which is present in the porous mass (3). 3. Method according to claim 1 or 2, characterized in that one uses for the electrolyte conductive ions, belonging to the group of sodium, potassium or lithium ions. 4. Method according to claim 1, characterized in that one uses for said zinciferous layer (8) metallic zinc. 5. Method according to one of claims 1 to 4, characterized in that one applies through the mass of concrete an electrically conductive connection (9) between said layer (3) rich in zinc and said reinforcement (5), by applying through the mass of concrete bars or wires (9) insulated from the mass of concrete.