WO2015118258A1 - Method for improving the sealing of a reservoir with a concrete wall, and fluid reservoir obtained by this method - Google Patents

Abstract

To improve the sealing of a reservoir (1) comprising a concrete wall (10), a layer (2) of flexible sealing material is applied on the external surface of the concrete wall. A confinement structure (3) is assembled around the sealing layer, to prevent said layer from separating from the wall. The confinement structure is passive and comprises a layer substantially more rigid than the sealing layer.

Description

 Process for improving the watertightness of a tank with a concrete wall, and fluid reservoir obtained by this method

 The invention relates to improved sealing of a tank having a concrete wall.

 Concrete tanks, usually prestressed, subjected to pressure rises may have leaks. These defects can have several origins such as cracking of the concrete, its porosity, or the creep of the compressed concrete.

 To remedy this, traditional techniques consist in applying a waterproof coating to an outer surface of the concrete wall of the tank.

 When the coatings usually used adhere well to the wall of the tank, they do not yield just because of the pressure of the fluid in the tank.

 However, in the presence of a lack of adherence of the coating, the ruin can occur due to a phenomenon of blistering of the coating due to the pressure of the fluid in the tank.

Such a lack of adhesion can have several origins. For example, it may be related to a faulty installation of the coating, a lack of concrete cohesion or cracking of the wall of the tank.

 The lack of adhesion of the coating is thus located relative to the concrete wall of the tank and the action of the fluid pressure in the tank promotes the appearance of a blister at such a defect.

 In an incipient blister filled with fluid under pressure, rather high forces are exerted on the coating at the periphery of the blister. These forces may spread the loss of adhesion of the coating and cause the blister to grow.

The higher the blister increases, the greater the angle of inclination of the coating peeled off from the outer surface of the concrete wall increases and the detachment of the coating at the periphery of the blister is easy. The phenomenon of blistering is therefore a divergent phenomenon which ultimately leads to the rupture of the waterproof coating by bursting of the blister.

 To combat this phenomenon of blistering, a method described in FR 2 950 094 A1 comprises the application of a sealing layer of flexible material on an outer surface of the concrete wall, and the positioning, around the sealing layer, a containment structure comprising another layer of concrete and prestressing cables. The other layer of concrete is used to distribute the forces around the tank. It is pressed against the sealing layer by the prestressing cables. As a result, the sealing layer is more resistant to the pressure exerted by the pressurized fluid in the reservoir. This active confinement structure makes it possible to block growth of nascent blisters with robustness.

 Nevertheless, this solution can be relatively expensive and difficult to implement and can not be deployed on all the structures concerned.

 There is therefore a need for an alternative solution, simpler and less expensive.

 For this purpose, there is provided a method for improving the tightness of a tank having a concrete wall, which comprises applying a sealing layer of flexible material to an outer surface of the concrete wall, and placing a containment structure around the sealing layer to prevent the seal layer from peeling off the concrete wall. According to the invention, the confinement structure is passive and comprises a substantially more rigid layer than the sealing layer.

 The implementation of the confinement structure proposed here is much simpler than that described in FR 2 950 094 A1. Therefore, the deployment of this solution is economically advantageous on structures with moderate leaks.

In one embodiment, the rigid layer of the structure of confinement is made from the same flexible material as the sealing layer, but to which reinforcing elements are added. The reinforcing elements may comprise at least one fiber fabric integrated with the rigid layer of the confinement structure and / or short fibers embedded in the rigid layer.

 When the sealing layer is applied to the outer surface of the concrete wall by projection of a substance forming the flexible material after crosslinking, the establishment of the confinement structure may include the projection of the same substance at the same time. time as short fibers. After crosslinking the substance to which the fibers are embedded, a layer is obtained which is stiffer than the sealing layer which forms the passive confinement structure.

 According to a second aspect, the invention relates to a fluid reservoir obtained by the above method. This tank comprises: a concrete wall; a sealing layer of flexible material applied to an outer surface of the concrete wall; and a confinement structure surrounding the sealing layer to prevent the seal layer from peeling off the concrete wall. The containment structure is passive and has a substantially stiffer layer than the sealing layer.

 Other characteristics and advantages of the invention will emerge from the description which is given hereinafter, by way of indication and in no way limiting, with reference to the appended drawings, in which:

 FIG. 1 represents a sectional view of a wall of the tank whose sealing is improved according to the invention,

 FIG. 2 illustrates in a sectional view how the growth of a blister is at least limited thanks to the invention,

 - Figure 3 shows a sectional view of a first mode of forming a ruin by traction and / or bending of a sealing layer on which no containment structure is put in place,

FIG. 4 is a sectional view of a second method of forming a ruin by peeling, with respect to the concrete wall, a sealing layer on which no containment structure is placed, and

 - Figure 5 shows a sectional view of a third mode of forming a shearing ruin of the concrete wall coated with a sealing layer on which no containment structure is implemented.

 The inventors have found that the ruin of the waterproof coating placed outside a concrete tank can occur in several ways, depending on the characteristics of the concrete and the sealing layer forming the waterproof coating.

 Figure 3 shows that the portion of the sealing layer 2 which is peeled due to a lack of adhesion is put in traction by the pressure of the fluid. It undergoes a force perpendicular to the wall 10 of the tank, illustrated by the arrows shown in Figure 3. The adhesion of the sealing layer 2 to the wall 10 may be sufficient to prevent the separation of the sealing layer 2 spreads around the blister. The ruin can be reached when the traction of the part of the separation layer 2 reaches a threshold beyond which the blister explodes.

 The part of the sealing layer 2 which is peeled off due to the lack of adhesion also works in flexion around the periphery of the blister (dotted circles in FIG. 3). If the adhesion of the sealing layer 2 to the wall 10 is sufficient to avoid detachment of the sealing layer 2 at the periphery of the blister, the ruin may occur when bending moments sufficient to cause the cracking of the sealing layer 2 are achieved.

The ruin may result from a combination of the two phenomena above. The sealing layer 2 undergoes both traction and bending in proportions depending on its characteristics. A tensile contribution greater than a flexural contribution is indicative of a certain flexibility of the sealing layer 2, while a contribution in bending greater than the tensile contribution reveals a certain rigidity of the sealing 2. When the sealing layer 2 has a good tensile and / or flexural strength, it is the adhesion of this layer to the wall 10 which can become the limiting factor. A peel of the sealing layer 2 can then be observed at the interface between the sealing layer and the wall 10, because of the components of the pressure force exerted by the fluid which are tangential to the outer surface of the wall 10 (horizontal arrows in FIG. 4). By propagating by this phenomenon of peeling, the blister can achieve other adhesion defects and / or an edge of the sealing layer 2, and lose the sealing property.

 Another scenario that can lead to ruin is illustrated in Figure 5.

The sealing layer 2 is here supposed to have sufficient adhesion to the wall 10 and / or a good acceptable tensile and flexural strength. In this case, it is the cohesive force of the concrete that can become the limiting factor. The forces transferred by the sealing layer 2 to the wall 10 may exceed the shear breaking strength of the concrete and cause the sealing layer 2 to fail.

 The modification of the only characteristics of the layer 2, and more particularly of its flexibility or rigidity, may therefore be insufficient to ensure the durability of the seal.

 It should be noted here that the flexibility and stiffness of any layer can be expressed in terms of a stiffness usually expressed in Newton per meter.

 A satisfactory solution is achieved by a fluid reservoir according to the invention comprising a passive confinement structure 3 (FIGS. 1-2).

 The confinement structure is passive in that its mechanical role is limited to reaction forces to stresses coming from the concrete wall.

It can thus prevent blistering from starting, observation being made that the appearance of a blister is the prerequisite for all the modes of ruin discussed above with reference to FIGS. In particular, the passive containment structure 3 does not exert a radial force on the sealing layer and the concrete wall, otherwise by reaction to a possible radial outward force exerted by the sealing layer 2 due to the pressure of the fluid contained in the reservoir. The structure 3 is free of prestressing elements, such as those described in FR 2 950 094, which complicate significantly the implementation of the confinement structure.

 The flexibility of the sealing layer 2, relative to the rigidity of the confinement structure 3, gives rise to an advantageous behavior.

 The deformations caused by a possible lack of localized adhesion are then limited mainly to the sealing layer 2 (FIG. 2), the relative rigidity of the confinement structure 3 preventing the growth of a blister. The tensile break and / or bending cracking limit of the sealing layer 2 will generally not be reached.

 By allowing a significant deformation of the sealing layer

2 under the action of tensile forces and / or bending, the flexibility of the sealing layer 2 further allows to limit the concentration of stress at the periphery of the possible blister. The phenomenon of peeling of the sealing layer 2 and the concrete shearing phenomenon of the concrete wall 10 are to a large extent avoided. This prevents a blister propagates until other adhesion defects and / or an edge of the sealing layer 2 are reached.

 The flexibility of the sealing layer 2 can further support the deformations of the concrete wall 10 and bridge any crack openings, still without increasing the surface of the separation zone.

 In each case, the propagation and / or growth of the blister is blocked by the confinement structure 3 which is substantially rigid.

As shown in Figure 1, the passive containment structure 3 consists essentially of a substantially rigid layer. It is however possible to provide several layers, provided that the whole remains passive.

 An interesting possibility is to make the rigid layer of the passive containment structure 3 from the same flexible material as the sealing layer 2, by adding reinforcing elements 30. For example, the reinforcing elements 30 may comprise fiber fabric integrated with said layer. They may also consist of short fibers embedded in said layer. Therefore, the rigidity of the layer of the confinement structure 3 depends on its content of reinforcing elements 30.

 The content of reinforcing elements 30 can be finely controlled. In one embodiment, the confinement structure 3 is placed around the sealing layer 2 by spraying the same substance as that used for the layer 2 and crosslinking this substance. The concentration of short fibers incorporated in the substance stream is adjustable to obtain the desired value of rigidity.

 The sealing performance of the tank 1 according to the invention is therefore related to the fact that the sealing layer 2 and the confinement structure 3 form a multilayer coating with variable rigidity.

 In this sense, the present invention is not limited to a two-layer coating, nor to a strictly increasing variation of the stiffness of the coating as one moves away from the wall of the tank 1. The man However, in the art, it will be understood that there is a definite interest in the sealing layer being relatively flexible, at least with respect to one of the layers of the passive confinement structure.

 The deployment of the newly proposed solution will be economically advantageous on the many so-called medium leakage structures, where the forces exerted on the sealing layer by the pressurized fluid contained in the reservoir are small enough not to justify the deployment of a solution. Active heavier and more expensive as described in FR 2 950 094.

Claims

A method for improving the sealing of a tank (1) having a concrete wall (10), the method comprising:  - applying a sealing layer (2) of flexible material on an outer surface of the concrete wall (10); and  - placing a containment structure (3) around the sealing layer (2), to prevent the sealing layer (2) from being detached from the concrete wall (10), characterized in that the confinement structure (3) is passive and has a substantially stiffer layer than the sealing layer (2). The method of claim 1, wherein said substantially stiffer layer of the containment structure (3) comprises the flexible material of the sealing layer (2) to which reinforcement elements (30) are added. 3. Method according to claim 2, wherein the reinforcing elements (30) comprise at least one fiber fabric integrated in the layer of the confinement structure (3). A method according to any one of the preceding claims, wherein the application of the sealing layer (2) to the outer surface of the concrete wall (10) comprises projecting a substance forming the flexible material after crosslinking, and the establishment of the confinement structure (3) around the sealing layer (2) comprises the projection of the same substance simultaneously with short fibers integrated in the jet. 5. Reservoir (1) of fluid comprising:  - a concrete wall (10); - a sealing layer (2) of flexible material applied to an outer surface of the concrete wall (10); and - a containment structure (3) surrounding the sealing layer (2), to prevent the sealing layer (2) from being detached from the concrete wall (10), characterized in that the confinement structure (3) is passive and has a substantially stiffer layer than the sealing layer (2). 6. Reservoir (1) fluid according to claim 5, wherein the layer of the containment structure (3) comprises the flexible material of the sealing layer (2) which are added reinforcement elements (30). The fluid reservoir of claim 6, wherein the reinforcing members (30) comprise at least one fiber fabric integrated with the layer of the containment structure (3). The fluid reservoir of claim 6, wherein the reinforcing members (30) comprise short fibers embedded in the layer of the containment structure (3).