EP0034515B1 - Use of autodestructive mixtures of resins and oxydant charges in the temporary bonding of constructional elements - Google Patents

Abstract

1. Application to the production of temporary bonds of construction elements (11) by means of cold-curable resin (14) and of inorganic filler, characterized in that the bond is made by a hardened mixture, self-destructible by combustion and non-detonating, of the resin (14) and of an oxidizing inorganic filler, the quantity by weight of resin being included between 20 and 40 % of the total mixture, an ignition system (15, 16, 17) triggering off combustion.

Description

The present invention relates to the application to the realization of temporary connections of building elements, by means of cold-hardenable resin and mineral filler. The invention relates more particularly to the fields of building and public works.

A major problem in the field of construction is that of temporary connections, necessary to ensure the holding of a structure for a given time during which work is carried out on said structure or around it and which become useless once said work is finished. We can thus cite the example of tie rods which are used to hold a wall of a building or building while work is being carried out on the building or building, or while excavations are being carried out. proximity, and which become useless after the end of the work. We can also cite as an example the case, in the cantilever construction of a bridge deck, those temporarily placed between the piers or the central segments of each beam or that, in the field of underwater works , wedges intended to hold props where to temporarily compensate, during the construction phase, for the effects of pressure.

When the presence of said temporary connections is no longer necessary, there then arises the problem of their destruction which is generally complex and expensive because these connections are often made from resistant and hardly destructible materials, such as concrete or l 'steel. In some cases, all or part of these links can be left to exist, but there are some where, for operational reasons or for regulatory reasons, it is imperative to destroy the link.

This is the case, for example, with the anchors mentioned above. The anchors are made up of cables or metal bars fixed at one of their ends to the structure which must be maintained and retained in the ground by the other of their ends. In order to ensure good retention, the buried end is generally coated with a bulb of solid material such as concrete or a curable resin. At the end of the work, it was customary to shear the aerial part of the tie rods and leave the sealed part in the ground. However, it is not always possible or permissible to leave such elements and an increasing number of national legislations obliging users of tie rods to proceed to their complete withdrawal.

We then sought solutions that allow such a withdrawal. A first solution, proposed in FR-A-2 274 740, consists in not coating the buried end of the tie rods in a bulb, but in welding this end to a buried metal plate and in placing around the welds an aluminum-thermal composition whose ignition causes the tie rods to shear and allows their withdrawal. This solution is however not very satisfactory insofar as the welds are always weak points and do not make it possible to give a high mechanical strength to the tie rods; moreover, after shearing, the metal anchoring plate remains in the ground. A second solution, proposed in US-A-3,936,924, consists in coating the tie rods with a thermoplastic resin which is melted and possibly burned using an auxiliary heat source, at the end of the work, to release the tie rods and remove them. This resin is made combustible by adding a mineral filler such as black powder or thermite. This solution has several drawbacks: it requires a significant additional source of heat and is therefore relatively expensive, and if it does allow the ground rods to be removed, it leaves agglomerates of molten resin, which does not entirely answer the problem posed and furthermore makes any subsequent reuse of drilling impossible for the laying of a new tie rod, finally it does not ensure regular and non-explosive combustion.

The present invention aims to remedy these drawbacks and, for this purpose, it provides, for the application to the realization of temporary connections of building elements by means of cold-hardenable resin and mineral filler, that the connection is made. by a hardened mixture, self-destructing by combustion and not detonating, of the resin and of an oxidizing mineral filler, the quantity by weight of resin being between 20 and 40% of the total mixture, an ignition system triggering the combustion.

Thanks to the use of an oxidizing mineral filler, it is possible to use bonding mixtures ensuring regular and non-detonating combustion.

By placing an ignition device in contact with said temporary connection, constituted for example by an electric igniter and a pyrotechnic ignition composition, it is possible to cause, at the appropriate time, the complete combustion of the combustible connection which will be completely destroyed by very simple way.

• La figure 1 représente un tirant d'ancrage dont la partie scellée est enrobée par une résine chargée selon l'invention.
• La figure 2 représente une variante d'exécution du dispositif représenté à la figure 1.
• La figure 3 représente des cales utilisées lors de la construction en encorbellement d'un tablier de pont par fléaux construits symétriquement de part et d'autre des piles.
• Les figures 4 et 5 représentent une cale pouvant être utilisée sous l'eau.
• La figure 6 représente des éléments préfabriqués dissociables, rendus provisoirement solidaires par une résine chargée selon l'invention.
• La figure 7 représente une pièce de renfort collée provisoirement à une poutre par une résine chargée selon l'invention.

The invention will be better understood with the aid of the description and examples which follow and which refer to the figures listed below.

• FIG. 1 represents an anchoring tie, the sealed part of which is coated with a charged resin according to the invention.
• FIG. 2 represents an alternative embodiment of the device shown in FIG. 1.
• Figure 3 shows wedges used during of the cantilever construction of a bridge deck by symmetrically constructed beams on either side of the piers.
• Figures 4 and 5 show a wedge that can be used underwater.
• FIG. 6 represents dissociable prefabricated elements, temporarily made integral by a charged resin according to the invention.
• FIG. 7 represents a reinforcement piece temporarily bonded to a beam with a charged resin according to the invention.

As already mentioned above, the temporary connections according to the invention are produced from mixtures consisting of a cold-hardening resin made combustible by the addition of an oxidizing mineral filler, the quantity by weight of resin being between 20 and 40% of the total mixture, said mixture being hardened and preferably having an ignition temperature equal to or greater than 500 ° C.

A temporary bond according to the invention is therefore essentially constituted by a cold-hardening resin and made combustible by the addition of an oxidizing mineral filler. The resin must be cold hardenable, usually in the presence of a catalyst, so that it can be easily poured and hardened on a site. The resin must have two essential qualities: it must, once hardened, have good mechanical strength and must not be corrosive with respect to the elements which it makes integral, in particular when the latter are metallic elements. One can say that as a general rule strongly acidic or basic resins, possibly due to the catalyst used, are to be avoided. The preferred resins according to the invention are polyurethane, polyester or polyepoxy resins. These resins are two-component resins which harden in the presence of a catalyst which is generally a tertiary amine or a metal salt of fatty acid for polyurethane resins, a peroxide associated with a metal salt or an amine for resins polyesters, an amine for polyepoxy resins.

Said resin is mixed in the liquid state with an oxidizing mineral filler which increases its mechanical strength after hardening and which makes the mixture combustible. For safety reasons, it is preferable that the hardened mixture of charged resin has an ignition temperature equal to or higher than 500 ° C so as not to risk accidental ignition. Furthermore, the charged resin must be perfectly combustible but must not, for safety reasons, present risks of detonation during combustion. Oxidizing charges such as potassium chlorate are therefore not recommended. The Applicant has found that oxidizing mineral fillers chosen from the group consisting of perchlorates and nitrates of an alkaline nature meet the criteria set out above. The term “perchlorates or nitrates of an alkaline character” means perchlorates or nitrates in which the cation is a true alkali or alkaline earth metal, or in which the cation is the ammonium group.

The preferred alkali perchlorates and nitrates are potassium perchlorate, ammonium perchlorate and potassium nitrate. The oxidizing mineral filler must advantageously have a particle size between 40 and 200 microns. The quantity by weight of resin must be between 20 and 40% of the weight of the mixture and preferably between 23 and 30%. The Applicant has observed that mixtures consisting of 25% resin and 75% oxidizing mineral filler give very good results.

The oxidizing mineral filler is mixed, in a manner known per se, in a kneader, either with one of the liquid components of the resin, in which case the second liquid component generally containing the catalyst is then added, or directly with the liquid resin not containing the catalyst, which is only added immediately before use. The loaded liquid resin containing the curing catalyst is then applied to the elements which should be made integral. The hardening of the charged resin is then very rapid. One thus has a solid bond which can be easily destroyed by combustion. To do this, there is, or contact of the connection formed by the charged resin, an ignition device which generally consists of a pyrotechnic priming paste and an electric igniter. The electric igniter, which can be controlled remotely, ignites the priming paste, which itself ignites and burns the charged resin. After combustion of the resin, the elements made temporarily united, regain their individuality.

The temporary connections according to the invention find multiple applications in the field of construction.

Thus, in the case of anchor tie rods, with reference to FIG. 1, a tie rod 11 made up of several metallic cables sealed inside a corrugated plastic sheath 13 by means of a charged resin 14 according to the invention, and constituting the steel-sheath seal, crosses a retaining wall 12 to anchor in the ground by means of a bulb constituted by a cement grout 19 injected in place. The free part of the tie rod is protected, over its entire buried length, by a second smooth sheath 18. A priming paste 15 composed, for example, of 75% by weight of potassium nitrate, 15% of magnesium and 10% of a resin serving as a binder is placed on the external surface of the resin. An electric igniter 16, connected to a control station 17 and embedded in the priming paste, allows the latter to be ignited; this thus ignites the resin 14 which, on burning, will release the complete tie rod 11 is lying. It is then possible to remove the tie rod 11 1 over its entire length either permanently or to replace it in the event of damage.

It is indeed advantages of the invention, compared to the prior art solutions, to achieve total destruction of the seal allowing the easy replacement of a tie rod if necessary.

As shown in Figure 2, the resin 14 can also be used to seal the tie rod 11 directly in a material without passing through a cement slurry or a sheath 13 when said material is sufficiently homogeneous as in the case of rock for example.

Another interesting application of the invention, represented in FIG. 3, relates to the cantilever execution of a bridge deck by beams constructed symmetrically on either side of the piers. It is necessary in this case, if one wants to avoid shoring, to securely secure the central segment 21 of each beam on its pile 22, around the final bearings 23 of the deck on the piles, to stabilize the plagues as long as these are not interconnected. This fixing is advantageously carried out by interposition, between the segment 21 and the stack 22, of fuel wedges 24 produced from a charged resin according to the invention. When the construction of the bridge is finished, it is easy to get rid of the wedges that have become useless by causing them to burn.

Another interesting application of the invention is in the field of underwater work. A simple example is the temporary setting of a forestay which will have to be removed at the end of the realization of a metal or concrete structure, as shown in Figures 4 and 5. The forces transmitted to the forestay 41, during the construction of the structure, pass from the forestay to the support 42 by means of a wedge produced according to the invention.

The fuse block may have a circular or rectangular shape or any other shape suitable for the use. It consists of two support plates 431 and 432 between which is placed a ring of combustible resin 44 charged according to the invention and bonded to the two plates so as to create a combustion chamber 45. An ignition composition 46 is applied on the walls of this chamber and an igniter 47 allows the fuel crown to be ignited. A nozzle 48 allows the evacuation of combustion gases. The nozzle 48 can advantageously be equipped at the outlet with a non-return valve 481 preventing the penetration of water into the hold or be extended by a vent pipe. The flexible seals 49 seal the assembly.

When it is desired to remove the wedge, it suffices to cause, by means of the electric igniter 47, the ignition and the combustion of the combustible ring 44. The disappearance of this ring will release the stresses between the walls and the applied force and it will become easy to remove the jack 41.

FIG. 6 represents another possible application of the invention. Two prefabricated elements 51 and 52 are temporarily made integral by bonding with an intermediate layer 53 of combustible resin loaded according to the invention. After combustion of the intermediate layer the two elements regain their individuality.

FIG. 7 represents another possibility of applying the invention.

A concrete beam 61, having a weakening, is temporarily reinforced by a metal plate 62 bonded by means of a layer of combustible mixture 63 according to the invention.

When temporary consolidation is no longer necessary, for example because the overload of the powder has been removed, it suffices to cause the burning of the layer 63 to remove the plate 62.

A number of possible industrial applications of the invention have been indicated above; those skilled in the art can, depending on the problems with which they are confronted, find others without departing from the scope of the present invention, the scope of protection being determined by the content of the claims.

The following examples illustrate certain specific embodiments of the invention.

Example 1

This example concerns anchor rods. Two types of test were carried out on tie rods coated with charged resin according to the invention.

1. Measurement of tensile strength

A 12 mm diameter metal cable is trapped in a plastic sheath filled with resin loaded with 75% by weight of potassium perchlorate.

A second test piece is produced using an unfilled resin. A polyester resin was used on the one hand and a polyepoxy resin on the other hand.

The cable is pulled using a cylinder in 50 bar steps with a stop time of one minute between each level. It was considered that the adhesion break is reached when the pressure drop is recorded. The following results were obtained.

2. Combustion tests

The tests were carried out on 12 strands sealed on one meter by resin loaded inside a metal sheath of 65 mm in diameter. The ignition was carried out using a wick and a priming paste.

The combustion times of the charged resin were timed. With an epoxy resin loaded with 75% by weight of potassium perchlorate, 22 minutes of regular combustion were observed; with a polyester resin loaded with 73% by weight of potassium perchlorate, 33 minutes of regular combustion were observed. In both cases the combustion was complete and was carried out throughout the duration at a uniform speed.

Example 2

The purpose of this example is to verify the possibility of burning a charged resin according to the invention in a confined atmosphere. To do this, we used solid cylindrical blocks with a diameter of 34 mm and a height of 28 mm consisting of a polyester resin loaded with 75% by weight of potassium perchlorate. The blocks were placed in a metal combustion chamber having roughly the outside dimensions of the block and closed by a metal nozzle. The ignition was carried out using a wick and a priming paste.

The following combustion times were observed depending on the diameter of the nozzle:

In all cases the combustion of the block was complete.

Claims (10)

1. Application to the production of temporary bonds of construction elements (11) by means of cold-curable resin (14) and of inorganic filler, characterized in that the bond is made by a hardened mixture, self-destructible by combustion and non-detonating, of the resin (14) and of an oxidising inorganic filler, the quantity by weight of resin being included between 20 and 40% of the total mixture, an ignition system (15, 16, 17) triggering off combustion.

2. Application according to Claim 1, characterized in that said mixture constituted by a resin rendered combustible by the addition of an oxidizing inorganic filler presents a temperature of inflammation equal to or greater than 500°C.

3. Application according to either one of Claims 1 or 2, characterized in that said cold-curable resin is selected from the group constituted by polyester resins, polyepoxy resins, and polyurethane resins.

4. Application according to any one of Claims 1 to 3, characterized in that said oxidizing inorganic filler is selected from the group constituted by perchlorates and nitrates of which the cation is a true alkali or alkaline-earth metal, or of which the cation is the ammonium group.

5. Application according to Claim 4, characterized in that said inorganic filler is selected from the group constituted by potassium perchlorate, ammonium perchlorate and potassium nitrate.

6. Application according to either one of Claims 4 or 5, characterized in that said oxidizing inorganic filler has a granulometry of between 40 and 200 pm.

7. Application according to Claim 6, characterized in that the quantity by weight of resin in the mixture is included between 23 and 30%.

8. Application according to any one of Claims 1 to 7, characterized in that said temporary bond is used for sealing tie-rods (11).

9. Application according to any one of Claims 1 to 7, characterized in that said temporary bond is used for making destructible shims (431,432).

10. Application according to any one of Claims 1 to 7, characterized in that said temporary bond is used for making provisional adhesive bonds between different construction elements (51, 52).

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