EP0733757A1 - Method for protecting concrete-embedded reinforcing elements against oxidation effects - Google Patents

Abstract

The reinforcements (2) to be protected are assemblies of wires or rods in a duct, within the mass of concrete. To overcome imperfections from the concrete production, such as porosity or voids, a hole (4) is bored in the concrete up to the reinforcement. A corrosion inhibiting solution is then injected into the bore and a pulsating wave of high power applied. This ensures penetration of the solution. The reinforcement may be pre or post stressed and after injection of inhibiting solution, the voids may be filled by injection with cement. The solution may be introduced under pressure, using a pulsating pump (5). Alternatively, an ultrasonic high power emitter may be used, instead of a pulsating pump.

Description

The invention relates to a method of protection against the effects of oxidation on active reinforcements embedded in a mass of concrete, said reinforcements being able to be in the form of a set of wires or strands arranged in a sheath, and also to put at the same time highlight the imperfections of the injection grout (voids, porosities).

Although the invention applies to the protection of any type of reinforcement in a concrete mass, the invention will be described more particularly in the context of protection against the effects of the oxidation of reinforcements or the assembly of reinforcements such as these are found in civil engineering works built using so-called prestressing or post-stressing techniques.

By prestressed and / or post-stressed concrete is meant a technology enabling beams, slabs or any concrete element to be given sufficient own strength to enable them to fulfill the function assigned to them.

This inherent resistance is achieved by tensioning either wires, steel bars or strands, with very high resistance limits, generally called active reinforcements. The tensile force exerted to tension these reinforcements is transferred to the concrete which, by reaction, undergoes a compression effect. Normal efforts and moments of bending thus created balance the actions of the external loads, thus achieving the required resistance.

Active reinforcements are high-strength steels which are particularly sensitive to degradation by the effect of corrosion due to the action of oxygen. Protection against corrosion of these reinforcements is conventionally achieved by coating them with a mortar, or with a cement grout. In the latter case, the active reinforcements are enveloped by a continuous sheath, most often made of steel strips but also of PVC or, more recently, of high density polyethylene. This sheath constitutes the conduit which allows the injection of the protective cement grout. The protection of active prestressing reinforcement by adhesion is that conferred by structural concrete.

In principle, this protection against corrosion should be sufficient since it acts as a barrier to the penetration of oxygen from the air, it provides water tightness and, moreover, it gives the medium a pH basic preventing the development of corrosion.

Many factors, including injection imperfections or, quite simply, the inevitable physical phenomenon of the removal of mortars or cement grouts, are responsible for insufficient or imperfect protection. Even when protection is provided at a high percentage, the low percentage of imperfection is more than sufficient to cause oxygenation alterations in the active reinforcements.

These protection faults, even localized and protected from air renewal, sooner or later pose corrosion problems.

The fight against ice and snow being done more often by spreading, sometimes in very large quantities, of calcium chloride or sodium chloride, with contamination by chlorine can reach the active reinforcements, thanks to a defect of the coating medium. The physico-chemical conditions favorable to corrosion can easily become such that corrosions develop with, in the extreme case, failure of reinforcements.

The pathology described concerns road bridges as well as any type of pre-stressed or post-stressed construction.

Another source of corrosion of active steels is the loss of the highly basic character of the environment surrounding the steels (mortar, cement grout, concrete) due to the carbonation of this environment.

The object of the invention is therefore to propose a new and original process capable of remedying the effects of oxidation on active reinforcements, this term being taken in its broadest sense.

The invention therefore consists in penetrating in all cases, even with perfectly injected sets of cement, the corrosion inhibiting solution on all of the metallic elements present.

To achieve this objective in accordance with the invention, a channel is first drilled in the mass of concrete opening out facing the reinforcement which must be protected and in that a corrosion inhibiting solution is then injected into said channel. to which is applied a pulsating wave of high power intended to make it penetrate.

In one embodiment particular and when the active reinforcement is surrounded by a sheath as used in pre- or post-stressing, the aforementioned channel is drilled, through said sheath so that the corrosion inhibiting solution can come into contact with the reinforcement , or the set of wires or strands to be protected and that afterwards a cement grout is injected in order to fill the pores and voids of the sheath injection grout.

Still according to the invention, at least one second channel is drilled opening out facing the armature to be protected in order to control the path of the inhibiting solution along said armature respectively inside the aforementioned sheath.

A remarkable characteristic of the invention resides in the fact that the inhibiting solution is introduced under pressure by making use of a high frequency reciprocating pump capable of producing a pulsed effect on the inhibiting solution.

Other details and advantages of the invention will emerge from the description which will be given below. This description is given by way of example only and does not limit the invention. The reference notations refer to the attached figures.

Figure 1 is a schematic view of an installation illustrating the method according to the invention.

Figures 2 and 3 show on a larger scale a detail of the installation according to Figure 1, adapted to the protection of a sheathed frame.

The process illustrated by these figures is characterized by several steps which will be described below.

In the figures, the reference 1 designates a prestressed concrete beam. The reinforcements 2 to be protected against the effects of oxidation can be placed in a sheath which has not been explicitly reproduced in FIG. 1. In FIGS. 2 and 3 this sheath is visible and is designated by the reference 3, and a cement grout coats the reinforcements 2.

In a first phase, a channel 4 is drilled in the mass of concrete up to the immediate vicinity of the reinforcements 2 and when a sheath is present. This drilling is also done through this sheath.

In the channel 4 thus drilled is injected a corrosion inhibiting solution to which a high power pulsating field is applied.

This can be done by making use of a high power ultrasonic transmitter such as an alternative pulse pump.

An ultrasonic transmitter which is particularly suitable for the application of the method according to the invention is known under the name of "sonotrode" built and marketed by the company S C P BISCORNET.

A high frequency alternating pulsating pump suitable for the application of the method according to the invention is shown schematically in the various figures by the reference 5. Such a pump is developed so that a sealed enclosure is formed allowing to put in alternative compression the corrosion inhibiting solution. The device known under the name of "sonotrode" makes it possible to put the inhibiting solution in overpressure and in depression and this at a sufficiently high frequency so that a pulsating effect of the liquid is obtained. This pulsating effect of the liquid promotes its penetration into the interstices and microcracks present in the concrete near the reinforcements to be protected. The ultrasonic transmitter has an injection tube 6 equipped externally with means which make it possible to achieve absolute sealing with respect to the channel 4 through which the liquid is injected. In FIG. 2, the compression chamber is given the reference 7. The inhibiting solution enters the ultrasonic emitter through line 8, while the coolant of the compression enclosure reaches the emitter through line 9. The cooling solution of the compression chamber leaves the ultrasonic emitter through line 10 and the corrosion inhibiting liquid through line 11 to the overflow tank 12. The circulation of a coolant is necessary in order to avoid overheating and possible degradation of the corrosion inhibiting liquid.

Ultrasound created by the high power ultrasonic transmitter which is used in the context of the method according to the invention has an additional effect. Indeed, the ultrasonic waves generated by the ultrasonic transmitter are powerful enough to create a cavitation effect in the liquid. This cavitation effect makes it possible to clear the entrances leading to the interstices and microcracks present in the concrete. In addition, the ultrasonic acoustic waves cause vibration inside these interstices and these microcracks and by the same allow the opening and closing of these at the frequency of the acoustic wave. This phenomenon promotes the advancement of the liquid in these interstices and microcracks.

In the context of the method according to the invention, as shown in FIG. 1, it is noted that outside the channels 4 intended for the injection of the corrosion inhibiting liquid, a series of secondary channels 4 ′ has also been provided. These channels also pass through the sheath inside which the reinforcements are arranged.

The channels 4 ′ make it possible to control the path of the inhibiting solution along the reinforcements 2, respectively inside the sheath 3.

Thanks to this arrangement, it is possible to continuously monitor the proper functioning of the process by observing the path of the inhibiting solution inside the concrete.

The method therefore makes it possible to evaluate the porosity of the mass 13 of the existing injection mortar. If it can be concluded that the said grout is either non-existent or very porous, it is possible, after injection of the inhibiting solution, to inject via the conduits (4), and this by conventional means or by the process which has just be described, a cement-based micro-mortar.

The invention is obviously not limited to the embodiment described above and many modifications could be made to it provided that these fall within the scope of the appended claims.

Claims (8)

Method for protecting against the effects of oxidation on active reinforcements embedded in a mass of concrete, said reinforcements being able to be in the form of a set of wires or strands arranged in a sheath, and also to highlight at the same time the imperfections of the injection grout (voids, porosities), characterized in that, firstly, a channel opens into the concrete mass facing the reinforcement which must be protected and that is injected then in said channel a corrosion inhibiting solution to which is applied a pulsating wave of high power intended to make it penetrate. Method according to claim 1, characterized in that, when the active reinforcement is surrounded by a sheath as used in pre- or post-stressing, the above-mentioned channel is drilled, through said sheath so that the solution inhibiting corrosion can come into contact with the reinforcement, or the set of wires or strands to be protected and that afterwards a cement grout is injected in order to fill the pores and voids in the grout with sheath injections highlighted according to claim 1. Method according to one of claims 1 and 2, characterized in that at least one second channel opens out facing the reinforcement to be protected in order to control the path of the inhibiting solution along said reinforcement respectively inside of the aforementioned sheath. Process according to any one of Claims 1 to 3, characterized in that a series of channels intended for the injection of the above-mentioned inhibiting solution are drilled along the armature to be protected and provision is always made along the frame to be protected, control channels for the injection of the injected inhibitor solution. Method according to any one of claims 1 - 4, characterized in that the inhibiting solution is introduced under pressure by making use of an alternating pulsating pump of sufficiently high frequency capable of producing a pulsed effect on the inhibiting solution. Method according to one of claims 1 to 5, characterized in that one introduces into each of the aforementioned channels intended for the injection of the inhibiting solution a tube intimately secured either to the wall of the channel, or to the aforementioned sheath. Method according to one of claims 5 and 6, characterized in that the aforementioned pulsating pump is connected to the aforementioned tube. Method according to one of claims 5 to 8, characterized in that a high power ultrasonic transmitter is used as an alternative pulsating pump.

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