TECHNICAL FIELD

5 The present invention belongs to the technical field relating to infrastructure construction and maintenance, in general with reference to the railway sector. More particularly, the present invention relates to works for the completion and maintenance of sections of the railway line, with particular reference to railway bridges. In practice, the0 invention intends to propose a new method for waterproofing the aforementioned sections, which is more effective, economical and quick to apply than those currently available and implemented.

For reasons of simplicity of presentation, although the method object of the invention can be applied to any railway section that5 requires an intervention designed to prevent the penetration of rainwater beyond the upper layer of the roadbed, the same invention will be described in detail below reference to waterproofing of railway bridges; in the latter, in fact, the invention finds its own application of choice. 0

BACKGROUND ART

The national network of railway lines, as on the other hand in many other European and non-European countries, is very developed and covers the territory extensively. The latter, in our country, has a5 particularly varied orography, which involved the construction of a large number of bridges and viaducts. Among the most common types of bridges are arched bridges (see Figure 1), with one or more spans, generally made of masonry or reinforced concrete, and deck bridges, made with a mixed structure of steel and concrete, or in reinforced0 concrete. In the illustrations, no deck bridges have been reported, but the considerations brought for arch bridges are also valid for deck bridges, unless otherwise specified. Although many of the bridges currently in use have been built and put into operation for many years now (many of them date back to before the last world war), they are still maintained in sufficient static conditions to guarantee the safety of the convoys passing through them, despite the intensity of rail traffic that currently affects them.

TECHNICAL PROBLEM

However, a problem that often afflicts arched and deck bridges concerns the general state of conservation, often characterized by severe conditions of degradation of the materials and structural elements that compose them. These problems of the state of conservation manifest themselves with breaking of bricks, corrosion of the reinforcements, washing away of mortars, disintegration of concrete etc. In most cases, the aforementioned degradation phenomena can be traced back to a single cause, namely the infiltration and stagnation of rainwater, due to the loss of efficiency of the waterproofing system and removal of rainwater.

In detail, as is well known to those skilled in the art, the ballast M is located above the bearing structure of any bridge 1, made up of gravel or crushed stone 2 of large size, collected between opposing retaining walls 3, 4. This structure can be clearly recognized in Figure 2, which refers to a known waterproofing technique which is now described. Between the gravel or the crushed stone 2 the sleepers 5 are placed on which the rails 6 are then fixed. A layer of waterproof material is placed between the ballast and the bearing structure of the bridge 7. The latter was once made by means of a casting of poured bitumen and sand, installed at the time of construction of bridge 1 or on the occasion of exceptional maintenance interventions. In the most recent interventions, the bitumen is applied by means of a spraying machine (not shown in the figure). A sheet of non-woven fabric is applied over the bitumen layer (also not shown). This allows to operate above the first layer of bitumen without obviously getting entangled in it. Then the spraying machine performs a second pass applying an additional layer of bitumen.

An alternative variant, not illustrated, provides for the use of prefabricated bituminous membranes, produced in rolls and placed side by side, with suitable overlapping heat-sealed on site.

In summary, up to the 1970s, interventions were carried out using poured bitumen and sand, to then move on to the use of fiber- reinforced bituminous membranes, prefabricated in rolls (currently still in use in the construction of new bridges). In recent years, from around 2010 onwards, bituminous membranes made on site (bitumen + TNT + bitumen) are also used, a very effective solution but feasible only on particularly large surfaces, due to the need to spread the very hot bitumen, by means of a tanker heated to 160 °-180 °.

For interventions on areas of a certain extent, however, the application of sheaths made on site has recently returned, with new generation bitumen reinforced with the inclusion of special fabrics.

The aforementioned bituminous materials do not offer adequate resistance to the stresses transmitted by the overlying crushed stone, which constitutes the ballast, therefore the bitumen sheath must be covered with a protective layer, sometimes made of concrete, possibly reinforced, and in other cases instead, more often, with a bituminous conglomerate.

Considering that the average life of a bridge can easily reach and exceed 80-100 years, it is clear that for this to happen it is necessary to proceed with the remaking of the waterproofing system of each bridge even several times during its operational life. However, this operation is not easy to carry out and is hindered, if not even prevented, by the only possible execution methods of the operation, which constitute a second limitation of traditional waterproofing systems. To carry out the waterproofing again, it is necessary to put the railway line out of service, for a sufficiently long period of time, i.e. from 3 to 4 days for the smaller bridges, but even longer, up to 15 days for the longer bridges. It is in fact necessary to disassemble the tracks, completely remove the gravel 2 of the ballast M, pour the bitumen 7 again, spread the protective layer in concrete or asphalt and reposition the ballast and the tracks.

The same Applicant, to obviate the drawbacks of the prior known art, briefly mentioned above, filed on 28/01/2014, the National patent application N° B02014A000034 entitled: " Method for waterproofing railway bridges and waterproofing material for carrying out this method', for which patent No. 1.421.994 was obtained. This patent discloses the use, instead of the aforementioned bituminous materials, of a single sheet of vulcanized rubber, previously made to measure, according to the size of the area to be waterproofed. The rubber sheet is possibly reinforced with a layer of fabric or canvas embedded in it.

The waterproofing, according to the method, is carried out first with the removal of the tracks and a limited layer of the gravel or crushed stone that forms the ballast, and then with the laying on the remaining part of gravel or crushed stone of one or more of said sheets of vulcanized rubber. The thickness of the rubber is such as to be sufficiently resistant to perforation by gravel or crushed stone, which is then placed on top of them, to complete the ballast. Finally, the previously removed tracks are rearranged.

The solution described above proved to be very effective and improved with respect to the pre-existing known technique, and is still used frequently and successfully. Vulcanized rubber has excellent properties as regards resistance to water and perforation of the crushed stone, while it can present some resistance limits if hit by aggressive chemical substances, such as solvents, hydraulic oils and the like, which could be released by the mechanical parts of the convoys or accidental spills.

Rubber also has a slow aging tendency which, in the long run, could damage it in the areas most exposed to air.

Another aspect that can sometimes limit the adoption of said vulcanized rubber sheets concerns their cost, which is significantly higher than that of traditional bituminous sheaths, and which can be penalizing at the time of the initial choice, even in the face of considerations on advantages of greater protection and longer duration over time. Lastly, it was found that the membrane's production methods do not allow the creation of other than flat rectangular slabs, while its reduced deformability in its own plane does not always allow it to be adapted to the 'three-dimensional' surface that must receive it (presence of plinths, recesses , overhangs, recesses, variations in bridge width, curvature of the layout, etc.)

OBJECTS OF THE INVENTION

The object of the present invention is therefore to propose a different method for waterproofing bridges, which is quick to implement and effective in its functionality, but which is above all capable of obviating the drawbacks of the methods and materials already known, as described above.

In essence, the proposed method must include:

- speed of implementation of the waterproofing system;

- cheapness of the materials used and of the production technology:

- adaptability of the system to the different types of bridges and to the different geometries.

Another object of the proposed method is to obtain a waterproofing that can offer adequate resistance not only to water, but also to corrosive or in any case aggressive liquids to which the vulcanized rubber of the known technique is unable to respond.

Finally, the object of the invention is to obtain a waterproofing which has adequate durability and excellent resistance to aging

SUMMARY OF THE INVENTION

These and other objects are fully achieved by means of a method for waterproofing bridges and similar structures intended for railway traffic, comprising an arched or deck structure, on which a ballast consisting of gravel or crushed stone is placed on which a or more tracks. The method involves the following steps:

- the detection of the surface and shape of the area of the bridge to be waterproofed;

- the reconstruction in an equipped establishment, using the data of the survey carried out, of a model area having characteristics of shape and size similar to that of said area of the bridge;

- the spray application, to cover the aforementioned model area, of one or more layers of polyurea with the addition of suitable reagents and additives designed to solidify it, incorporating a fabric (or sheet in non-woven material) with the function of support and reinforcement;

- the polymerization and solidification of the polyurea and the reinforcing material in a single mat of the desired thickness, such as to be sufficiently resistant to perforation by the gravel or crushed stone of said ballast;

- the removal of the tracks and a layer of gravel or crushed stone, for a predetermined depth;

- the laying of the mat on said possible remaining part of gravel or crushed stone of the roadbed;

- the repositioning of the layer of gravel or crushed stone on the polyurea mat, to rebuild the ballast;

- the re-installation of the tracks initially removed to restore the railway line.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristic features of the invention, even if not emerging from what has been said previously, will become evident from the following description of the steps of the proposed method, with reference to the accompanying drawing tables in which:

- Figs. 1 and 2 show an arch bridge and the conformation of the waterproofing system according to traditional methods of the prior art, seen from the side and in plan, respectively, with parts removed to better highlight the construction of the waterproofing system of the art Note;

- Figs. 3 and 4 show an arch bridge and the conformation of the waterproofing system according to the invention, with the bridge seen from the side and in cross section respectively;

- Fig. 5 represents the bridge of Figures 3 and 4 seen in plan with parts removed to better highlight the realization of the waterproofing system object of the present invention;

- Figures 6A to 6D illustrate details, with sectional views, of the bridge and of the waterproofing system according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

With reference to the aforementioned figures, 1 indicates, by way of example, an arch bridge (Fig. 3) for which maintenance is to be carried out with re-establishment of the waterproofing system using the method in question.

As already mentioned, the considerations brought for an arch bridge will also apply to deck bridges, unless otherwise specified.

On the arched or deck structure of the bridge 1 there is a ballast M made up of gravel or crushed stone 2 on which the tracks 6 of the stretch of railway line that connects the two ends of the bridge 1 extend. With the method object of the present invention, a waterproofing of the bridge 1 is carried out, in particular by intervening on the ballast M, according to the operating steps described below.

Using suitable tools, both traditional (localized excavations) and modern (laser scanners or drones equipped with cameras), the surface and shape of the part of the aforementioned bridge 1 to be waterproofed is measured. With the data acquired from the survey, a model area with characteristics of shape and size similar to that of said part of bridge 1 is reconstructed in an equipped factory.

The next phase involves the spray application of one or more layers of polyurea, in order to cover the aforementioned model area with a layer of desired thickness, which is then left to polymerize and compact until a single mat 10 is obtained. The operation of applying the polyurea is preceded, alternated or followed, by the deposition in the whole area to be covered, of a layer of reinforcing fabric, or non-woven sheet, intended to improve the mechanical characteristics of the mat 10 without compromising its flexibility and impermeability.

Advantageously, according to a variant of the method easily achievable with current technologies, a three-dimensional measurement of said surface and shape of the part of the bridge to be waterproofed is carried out, in order to also have the elevation profile of the same. With the data acquired from the survey, a model area with characteristics of shape and size similar to that of said part of bridge 1 is reconstructed in an equipped factory.

If the acquired data are of the three-dimensional type, said model zone is made in such a way as to faithfully reproduce also the three- dimensional profile of the part of the bridge 1 to be waterproofed.

The three-dimensional profile can be obtained, for example, by making suitable shapes of material sufficiently rigid to maintain the shape once it is placed in its position on the model area.

In the presence of a three-dimensional model area, a polyurea mat 10 will obviously be obtained, also profiled in three dimensions, able to perfectly follow the elevation profile of the corresponding part of the bridge 1 to be waterproofed.

The polyurea, obtained according to known technologies, is a coating elastomer obtained by polyaddition of an aliphatic or aromatic diisocyanate with a diamine. The polymerization reaction is similar to that which leads to the formation of polyurethanes, so the polyurea is essentially an amine terminated polyurethane.

The polyurea is advantageously added with suitable reagents and additives designed to make it solidify in a short time, which is allowed to pass to allow the formation of a single mat 10, whose thickness depends on the number of spray passes applied.

The realization in the factory, rather than on the construction site, allows both the optimization of the production process and an optimal management of the safety of the operators (given the toxicity of some reagents), without being affected by the meteorological conditions of the construction site, where the membrane arrives ready for the installation.

The thickness of the mat 10, thanks also to the reinforcement layer (s) in fabric or (or non-woven sheet), is in any case such as to be, once installed, sufficiently resistant to perforation by the gravel or crushed stone 2 of called M. The aforementioned intervention for removing the tracks 6 can be advantageously carried out in an automated mode, with known machines already in use for alignment work.

First, the tracks 6 are sectioned, by cutting with an oxy-acetylene flame, according to lengths of 18-20 meters, for each span C of bridge 1 (Figures 3 and 5). Then the tracks 6 are moved to the side, in an area which is not affected by the restoration operation; the displacement operation is carried out by means of a machine called loader.

Again with the loader, which it raises, and by means of a mechanical shovel, which moves and moves away, the required thickness of said layer of crushed stone 2 is removed to the extent required by the method in question.

The thickness of crushed stone 2 removed, as an indication and not for limitation purposes, is between 50 and 80 centimeters. Once the site has been prepared as described above, the polyurea mat 10 is transported up to deck 1 from the aforementioned equipped factory, duly arranged in a configuration with minimum bulk, for example rolled up.

The next step involves laying the polyurea mat 10 on the part of the ballast M that was left, making it coincide with the predetermined part of the aforementioned bridge 1 to be waterproofed.

Subsequently, the layer S of the gravel or crushed stone 2 previously removed on the polyurea mat 10 is repositioned, so as to reconstruct the pre-existing ballast M.

The last phase consists in the reinstallation of the tracks 6 initially removed for the restoration of the previously interrupted railway line.

A first variant of the method provides that in the aforementioned reconstruction phase of said model zone, the latter is made with a perimeter edge exceeding the data of the dimensional measurement of the part of the bridge 1 to be waterproofed, so that the resulting polyurea mat 10 has larger dimensions, useful for adaptations on site to be carried out in the subsequent phase of laying it on the gravel or crushed stone 2 of the ballast M.

In addition or as an alternative to the aforesaid procedure, a second variant of the method provides that in the aforementioned phase of reconstruction of said model zone, the latter is made so that any additional areas of said part of the bridge 1 to be waterproofed are included, thus that the resulting polyurea mat 10 comprises said additional areas, either in a single body or in detached parts.

In another variant of the method it is envisaged that in the step of spraying the polyurea, for the realization of said polyurea mat 10, further shaped sheets of rigid or semi-rigid reinforcing material, for example of glass fiber or of other composite material, intended to be stably joined to the polyurea mat 10 itself, in a suitable lower and/or intermediate and/or higher position with respect to its thickness, in areas where this can be particularly stressed.

A further variant of the method provides that in the step of spraying the polyurea, for the realization of the mat 10, further layers of reinforcing fabric or non-woven sheet are applied, of such dimensions as to affect the entire surface of said model zone and also they are intended to be stably joined to the polyurea mat 10 itself, in a suitable position with respect to its thickness.

Another variant of the method provides that in the spraying phase of the polyurea, for the realization of said mat 10, different thicknesses are locally realized, suitable to increase the mechanical resistance of the polyurea mat (10) itself, in predetermined areas

With the above described method steps it is possible to carry out the maintenance intervention with the restoration of the waterproofing system in a few hours, for those bridges for which the traditional system required a few days. Since the crushed stone 2 usually has rather irregular shapes, the provision of using polyurea for the construction of the mat 10 proves to be advantageous as this material is particularly suitable for adapting to the shapes on which the mat 10 is laid, or to those of crushed stone 2 which will be repositioned above it.

Once the mat 10 has been installed and the waterproof "carpet" is obtained, the edges 24 of the same must be fixed to the retaining walls 3, 4 of the ballast 2 (Figures 4 and 6B).

To avoid lateral water infiltration, the carpet must extend beyond the limits defined for the ballast by the retaining walls 3, 4 and vertically or obliquely along the surface of the walls themselves. The edges 24 of the carpet are fixed to the walls 3, 4 by mechanical means, for example steel flashings (not shown) with through screws driven into the wall of the low walls.

The seal between the edges 24 and the walls 3 is usually sufficient to prevent the passage of water, if metal flashings are provided, placed over the edge of the waterproof carpet. In addition to the junction of the waterproof carpet with the retaining walls 3, 4 of the ballast, it is necessary to provide the necessary slopes and terminal flaps (Figure 6A) so that the water collects in points from which it can then be easily drained, in order to avoid the useless filling of the "tub" formed by the carpet.

As illustrated in Figures 6C and 6D, at the collection points the water is captured and drained by means of unions 27 tightly joined to the sheets and ducts 28 which originate from the rubber sheets 10 and flow to the outside of the ballast M and of the bridge 1.

In the optimal embodiment, the discharge ducts terminate in a water removal system (not illustrated) in a manner that will be known and evident to those skilled in the art. In deck bridges it may be sufficient to take advantage of the slope that is foreseen for the bridge under construction.

In the case of arched bridges, on the other hand, it is appropriate to provide for the removal of the crushed stone 2 of the ballast in such a way as to create a sloping configuration of the surface of the polyurea mat 10.

In both cases, a slight slope can be provided towards one or both ends of the bridge 1 , so as to collect the water in a corner area R of the waterproof mat, in which the unions 27 and the ducts for water collection are subsequently placed. From the above description the advantages that can be achieved with the proposed method emerge clearly, in particular due to the fact that polyurea has been used for the realization of the mat, which in addition to the qualities of resistance to water and the perforation of the crushed stone, comparable to that of vulcanized rubber, has excellent properties as regards resistance to aggressive chemicals, resistance to aging, the possibility of creating any three-dimensional surfaces, without particular size limits in width and length.

The interesting characteristic features mentioned above can also be obtained at a lower cost than the previous systems, including the one that provides vulcanized rubber sheets, and this economic advantage derives in part from the cost of the material and in part from the originality of the method, where it is planned to realize in a place apart from the bridge, the polyurea mat, using a model area that reproduces the surface to be waterproofed previously measured. It is understood that the above has been written by way of non limiting example, therefore any variants of the method in question are understood to be included in the scope of protection granted to the invention, as claimed below.