AU748483B2 - Grid-type reinforcement for strengthening road structures, in particular made of bitumen - Google Patents

Abstract

The invention concerns a reinforcement (7) made basic to accelerate bitumen demulsification whereon it is set, and consisting of a fibreglass grid (22), a fine nonwoven (20) on its top surface and an incorporated heat-sealing product (21). Said reinforcement strongly prevents the bitumen from being thrust upwards under the weight of heavy-construction machines It also saves time and bitumen.

Description

"1 -1- GRID-TYPE REINFORCEMENT FOR STRENGTHENING ROAD STRUCTURES, IN PARTICULAR MADE OF BITUMEN The present invention concerns the technical sector of public works, more precisely that of the construction and maintenance of roads, highways, roadways, truck routes and the like.

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

It is known that roadways are paved with a layer of hydrocarbonic materials, often called "blacktop" or "asphalt concrete", since this product is derived from a petroleum residue (asphalt).

More precisely, in a general (but non-limiting) way, roadways are constituted by a base, generally a "blacktop," a layer of emulsion on top of the base serving as a binder course, a reinforcement like that of the above invention, and finally another layer of blacktop, from about 4 to about S cm thick, in one or more layers separated by a fine emulsion binder course.

It will be recalled that blacktop is a mixture of fine aggregates and bitumen.

15 For a long time it has appeared to be necessary to reinforce such pavements, particularly to prevent the formation of cracks or fissures due to the mechanical stresses exerted by traffic or to thermal stresses.

Various reinforcements have been incorporated into this bituminous surface course, such as for example textile reinforcements (FR A 2 592 411, FR A 2 635 542), fiberglass fabrics, grid structures or complex reinforcements combining a grid and a nonwoven fabric.

In particular, the products "ROADTEX" and "ROTAFLEX" (trademarks of the CHOMARAT company) are known. Structures of the ROADTEX type are constituted by an open grid of continuous glass filaments joined by a thermoplastic polymer. Structures of the ROTAFLEX type are constituted by a polyester nonwoven reinforced by a glass grid.

European patent EP 0 368 600 (Netlon Ltd.) describes a twolayer structure comprising: a mesh grid on top, particularly made of polypropylene, comprising a thick nodule and non-oriented at each junction of fibers, and a polyester fabric underneath the grid, hence intended to come into contact with the bituminous layer deposited on the roadway.

According to this document, an aqueous bitumen emulsion is deposited on the roadway, followed by the two-layer structure, then another layer of bitumen. It is indicated that the polypropylene of the grid is subjected to a heat treatment during production, in order to prevent shrinkage during the thermal shock caused by the temperature at which the blacktop is deposited.

An important characteristic of the Netlon patent is the fact that the laminate is characterized in that the fabric is combined with the plastic mesh only at the level of the thickest junctions of the mesh and not at the level of the fibers of the mesh.

Also known is European patent EP 0 318 707 (Bay Mills Ltd.), which describes a reinforcement for road pavements comprising: an open grid pre-impregnated with resin, with a mesh that remains open after the impregnation; an adhesive cbating applied to the lower surface of the impregnated grid, without filling in the mesh.

It is indicated that this adhesive coating can be activated by heat or pressure and forms a bond between the grid and the asphalt. However, this adhesive does not result in the bonding of the two asphalt layers on either side of the grid, which is appropriate for certain roadway applications.

US patent 3,581,631 (Enka Corp.) describes a reinforcement that consists in a film comprising fibers or filaments, forming meshes that are totally or partially filled in by an adhesive.

This adhesive is chosen from certain resins and certain polymers having a softening point above 50 0 C, and is poured hot over the film. The adhesive wets and "impregnates" the film, and is miscible with the bituminous layer.

Lastly, it is known to combine a ROADTEX product with a layer of heat-fusible product applied to one of its surfaces, which melts at a lower temperature than the bituminous layer.

The documents of the prior art sought to optimize the properties of road structures.

The first problem posed resides in the need to completely bond the various layers forming the structure to one another, the base (often a blacktop), the strengthening reinforcement, and generally an upper layer (often a blacktop applied hot over everything).

There is a second problem, which follows from the first one.

Bitumen emulsions are produced in the factory, and consist in aqueous liquid or semi-liquid emulsions that can be applied by the usual machines. These emulsions can demulsify in 5 minutes or in several hours, particularly depending the prevailing temperature at the application site. The quality of the bitumen is adapted to the season and the region inthe factory as much as possible, but it is impossible to produce a different batch for each site temperature. After the laying of a reinforcement, if the emulsion has not yet broken, or even after the emulsion has broken if the temperature of the site is too high (bitumen too soft), the road construction machines (which still have to deposit another layer of blacktop) cannot roll without having the bitumen stick to the wheels and without pulling up the reinforcement that has just been laid.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

According to a first aspect of the present invention there is provide a complex strengthening reinforcement of the type comprising a grid, for strengthening road structures, characterized in that it comprises: a grid a fine nonwoven laid over the grid a heat-sealing product being interposed between the nonwoven and the grid so as to cover its surface only partially.

15 Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of"including, but not limited to".

Furthermore, it would be economically advantageous to reduce the quantity 20 of bitumen used. With a grid product like ROADTEX, a conventional layer of emulsion (water and bitumen at approximately a 40-60% ratio by weight), at the rate of about 500g of emulsion/m 2 or about 300 g/m 2 of "residual bitumen." With a grid nonwoven product like ROTAFLEX 833, a nonwoven is used at a rate of 80 g/m 2 RA/ ,that case, it is necessary to go up to about 500 g/m 2 of residual bitumen, since the -4a nonwoven must be impregnated. One objective of the invention is to make it possible, despite a complex structure that includes a nonwoven, to reduce the amount of residual bitumen to values of 300 g/m 2 or even 200 g/m 2 to less than the usual amounts for binder courses. This reduction contributes to the reduction of the upwelling of bitumen.

Advantageously, at least in preferred forms, the present invention limits the upwelling of the bitumen through the mesh of reinforcements of the grid type.

According to one of its main aspects, the invention involves the combined use of a heat-sealing product.

According to one of its other aspects, the invention, using a basic treatment, accelerates the breaking or demulsification speed of the bitumen emulsion, which reduces the downtime of the work site and the upwelling of the bitumen (which is viscous) through the grid.

S

ooo *g •go« o ^°o *o o* o o o The invention applies to any road structure in the broad sense, which includes floors, tracks, airports, etc., comprising at least one hydrocarbonic binder, particularly so-called bituminous structures including, though not limited to, structures comprising at least one layer of blacktop or asphalt.

According to one particular embodiment, the invention concerns a complex reinforcement for road paving of the blacktop or asphalt type, which comprises: a grid a fine nonwoven laid over the grid a heat-sealing product being interposed between the nonwoven and the grid so as to cover its surface only partially.

The invention therefore proposes a three-layer structure wherein the nonwoven is only partially filled in by the heatsealing product in order to limit the upwelling of the bitumen.

t f The heat-sealing product fulfills a second function, that of a binder course for the final layer of bitumen (hot mix) that will subsequently be applied over everything, which makes it possible to sharply reduce the quantity of bitumen emulsion.

A preferred production process consists of preparing the fine nonwoven, and of "dusting" the heat-sealing product over the nonwoven. "Dusting" indicates the fact that, using any means of application known to one skilled in the art, the heat-sealing product is deposited so as to cover only part of the surface of the nonwoven. The dusting must also be as even as possible, though perfect uniformity is not necessary. "Part of the surface" indicates the fact'that approximately 30 to 70% of the surface of the nonwoven is covered. "Fine" nonwoven designates a nonwoven on the order of 20 to 80', preferably 20 to 50, preferably 20 to g/m 2 It is also possible to deposit the heat-sealing product in the form of an open film, in order to partially close the openings or pores of the nonwoven.

According to one particular and non-limiting embodiment, the heat-sealing product is an EVA (ethylene-vinyl acetate) copolymer.

The grid is then laid on the surface of the nonwoven that received the heat-sealing product.

For the application, the complex according to the invention is laid so that the grid forms the upper surface and the nonwoven forms the lower surface.

If using the option that consists of making at least one element of the complex reinforcement basic (see description below), this operation is inserted into the above process, or into the production of the element. For example, in impregnating the nonwoven with a basic agent, it is possible to perform the impregnation separately, or to perform the impregnation during the production of the complex before the deposit of the heatsealing product, or even at the time of the on-site application.

When the upper layer of hot mix (at about 1600C) is deposited, the grid/nonwoven assembly traps a layer of air that will act as a thermal screen against the cold temperature of the lower base, and will therefore optimize the melting of the EVA by the heat supplied by the deposit of the upper layer of blacktop.

The nonwoven is preferably a fine hydrophobic nonwoven of the polyester or pblypropylene type, or a glass nonwoven, particularly at about 20-50 g/m, or even up to 80 g/m 2 It is especially possible to use a chemically bonded polypropylene at g/m 2 By way of comparison, the nonwovens of the prior art are used at about 120 g/m 2 This nonwoven must be broken down mechanically by being punctured by the granulates contained in the blacktop, as a result of gravity and of the compaction (see Fig. 3).

The fine nonwoven breaks down in the case of an open grid; in case of a closed grid, the nonwoven is thicker and breaks down less, or not at all. An "open grid" designates a grid with a large mesh relative to the granulates contained in the upper layer of blacktop.

The grid is preferably a glass filament grid: more than 70% open in a blacktop reinforcement.

closed in a reinforcement of the emulsion-based bituminous membrane.

The mesh of the products is preferably 5 x 5 mm; 10 x 10 mm; x 30 mm; 40 x 26 mm; 50 x 50 mm. A 40 x 26-mm mesh is preferred.

The invention also concerns a process and a reinforcement that makes it possible to break the bitumen emulsion more rapidly.

According to another aspect of the invention, one or more of the elements constituting the complex are brought to a basic pH, the grid and/or the nonwoven and/or the heat-sealing product is/are brought to a basic pH.

To do this, a basic agent can be incorporated into the mass of the grid, or into the mass of the heat-sealing product, or into the mass of the nonwoven.

Preferably, the structure according to the invention, or the grid/nonwoven assembly, or even more preferably, the nonwoven laid on the grid, is impregnated with a basic agent.

The basic agent is any agent or mixture of agents capable of giving the structure enough of a basic quality to significantly accelerate the "breaking" of the emulsion, like sodium carbonate for example. The emulsion can then be "broken" instantaneously, or nearly instantaneously. This additional step makes it possible to save a lot of time at the work site during installation, particularly by not making crews wait unnecessarily.

Any basic agent or any mixture of basic agents capable of, or adapted for, meeting the emulsion breaking requirement can be used. Such products are within the expertise of one skilled in the art.

On contact with the bituminous layer deposited on the base, the basic agent acts on the emulsion and, in a simple, efficient, and practical way, causes the demulsification or breaking of this emulsion. Without intending to be limited by any one theory, the Applicant considers the basic agent to deactivate the acid sites of the surface-active agents used to maintain the stability of the emulsion.

The invention will be more clearly understood by reading the following description, and by referring to the attached drawings, in which: Fig. 1 schematically represents a sectional view of a representative road structure.

Fig. 2 schematically represents a sectional view of a road structure comprising the reinforcement according to the invention. This figure is intended to represent the order in which the various elements are put in position. The final structure obtained is represented in Fig. 3.

Fig. 3 schematically represents a cross-section of the final structure obtained when the elements of the invention are disposed according to Fig. 2.

In the figures, the references have the same meanings, which are as follows: 1 soil 2 base course formed of flattened, compacted aggregates 3 lower bitumen emulsion, with a high content of residual bitumen (approx. 1 kg/m2) 4 "bituminous base course" (blacktop with larger size grading) surface course 6 bitumen emulsion (0.5 mm) (binder course) 7 reinforcement, which can be either a nonwoven that reinforces the bituminous membrane, a grid, or a grid/nonwoven complex, or the like 8 layer of blacktop (6 to 15 cm in one or more layers separated by a fine binder course) nonwoven 21 heat-sealing product 22 grid (with open mesh 23 aggregates of the blacktop Fig. 1 describes a conventional road structure when a reinforcement is incorporated. Deposited on the soil 1 and on a layer of flattened aggregates 2 is a fine binder course (emulsion) 3, followed by a layer of blacktop 4 that forms the "bituminous base course." This layer will receive the surface course 5, which in its simplest form is a fine layer of emulsion 6 on which the reinforcement 7 is placed, after which the final layer of blacktop 8 is deposited.

On top of the grid, one or more superposed layers of blacktop 8 are applied, depending on the type of road structure.

The topmost layer of blacktop is called the surface course. The layers of blacktop are then bound to one another by a fine binder course of the layer type 6. The invention also applies to such variants.

Fig. 2 represents the order of disposition of the elements according to the invention. The binding emulsion 6 is deposited on the bituminous base course 4. This emulsion, in accordance with an important advantage of the invention, preferably contains only 200 300 g of residual bitumen per m Z 2 The complex 7 according to the invention, for example produced as described above, is then laid. This complex consists of the grid 22 and the fine nonwoven 20 that carries the heat-sealing product 21 on its lower surface. Next, the layer of blacktop 8 (or the first layer if there are several of them), which contains aggregates 23, is deposited. The temperature allows the water to escape from the emulsion 6. This ig even easier if the emulsion is rapidly broken by a basic agent, for example incorporated into the nonwoven as described above. The heat of the layer 8 also brings the heatsealing product 21 to its melting point. If this point is relatively high, for example like that of EVA, which can have a melting point of around 80 0 C, the layer of air trapped between the bituminous base and the nonwoven will prevent the heat sealing material and the lower surface of the blacktop from being cooled by the "cold" layer 6).

Fig. 3 represents the final state of the road structure after the sequence shown in Fig. 2. It shows that the aggregates 23 of the blacktop 8 have penetrated between the fibers of the grid 22, through the fine nonwoven 20, tearing it if necessary, and possibly coming into contact with the binder course 6, which has been softened by the heat and is therefore at least partially integrated into the assembly. It is not practically possible to represent the heat-sealing product 21, which has melted and has been integrated into theassembly, substantially at the level of the nonwoven. The assembly forms a structure wherein all the layers are completely integrated.

The invention also concerns a process for reinforcing road structures characterized in that a reinforcement as described above is deposited on the layer of bitumen emulsion covering the bituminous base course, followed by a layer of blacktop, and also, in one particular variant of embodiment, to the process for reinforcing road structures described above characterized in that one or more upper layers of blacktop are also deposited, each layer being bound by an intermediate layer of bitumen emulsion.

According to a preferred embodiment, the invention also concerns the process for reinforcing road structures that consists of unrolling the prefabricated complex reinforcement according to the invention onto the layer of emulsion covering the bituminous basd course.

It is also possible to unroll the various elements of the complex reinforcement separately on site. In particular, it is possible to unroll the grid, followed by the nonwoven carrying the heat-sealing product "dusted" or deposited in an open film onto its lower surface. The nonwoven can be pre-impregnated with a basic agent or can include a basic agent in its mass. The basic agent can also be incorporated into the heat-sealing product deposited on the nonwoven. Finally, a basic agent can be deposited onto the grid or onto the nonwoven as it is unrolled.

The invention also concerns a process for reinforcing road structures characterized in that at least one layer of blacktop is deposited on the reinforcement, or characterized in that several layers of blacktop are deposited on the reinforcement, each layer being separated by a binder course of bitumen emulsion.

The invention also concerns a process for reinforcing road structures characterized in that an emulsion with 200 300 g/m 2 of residual bitumen is used as the lower binder course of bitumen emulsion.

Generally, the invention also concerns a process for reinforcing road structures according to which one uses a nonwoven (possibly alone at certain work sites), or any type of complex grid-type reinforcement, possibly including a nonwoven or a similar structure, characterized in that said nonwoven, or one or more of the elements constituting the grid-type complex, is brought to a basic pH capable of accelerating the breaking or demulsification of the lower bitumen emulsion. Within this general process, it is possible to fully or partially implement all of the applicable variants of the invention, by adapting them to the nonwoven or the type of complex reinforcement used.

One skilled in the art would know how to modify or adapt the 13 Invention based on the normal criteria of the profession.

Claims (5)

14- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. Complex strengthening reinforcement of the type comprising a grid, for strengthening road structures, wherein it comprises: a grid; a fine nonwoven laid over the grid; a heat-sealing product being interposed between the nonwoven and the grid so as to cover its surface only partially. 2. Reinforcement according to claim 1, wherein the nonwoven is only partially filled in by the heat-sealing product. 3. Grid-type reinforcement for strengthening road structures according to claim 1 or 2, wherein one or more of the grid and/or the nonwoven and/or the heat-sealing ":•product constituting the complex are brought to a basic pH. ooo• 4. Grid-type reinforcement for strengthening road structures according to claim go* 3, wherein the grid and/or the nonwoven and/or the heat-sealing product is/are •o•V S 15 brought to a basic pH. 5. Grid-type reinforcement for strengthening road structures according to claim 3 or 4, wherein a basic agent is incorporated into the mass of the grid, or into the 0.00.mass of the heat-sealing product, or into the mass of the nonwoven. 6. Grid-type reinforcement for strengthening road structures according to any of claims 3 through 5, wherein the structure according to the invention, or the grid/nonwoven assembly, or the nonwoven laid on the grid, is impregnated with a basic agent. 7. Grid-type reinforcement for strengthening road structures according to any of claims 3 through 6, wherein the basic agent is chosen from any agent of mixture capable of giving the complex structure enough of a basic quality to significantly accelerate the "breaking" of the emulsion, like sodium carbonate for example. 8. Grid-type reinforcement for strengthening road structures according to according to any of claims 1 through 7, wherein at least one of the components of the complex, and particularly the grid/nonwoven assembly, or the nonwoven laid on the grid, or the grid, or the heat-sealing product, is impregnated with a basic agent. 9. Grid-type reinforcement for strengthening road structures according any of claims 1 through 8, wherein the nonwoven is laid on the upper surface of the grid and in that the heat-sealing product is interposed between the grid and the nonwoven by "dusting," or in an open film, in order to partially close the mesh of the nonwoven. Grid-type reinforcement for strengthening road structures according to according to any of claims 1 through 9, wherein the heat-sealing product is an EVA(ethylene-vinyl acetate) copolymer. 11. Grid-type reinforcement for strengthening road structures according to according to any of claims 1 through 10, wherein the nonwoven is a fine nonwoven of the polyester or polypropylene type, or a glass nonwoven, at about 20 80 g/m 2 preferably 20 50 and particularly 20 30 g/m 2 and especially a chemically bonded *polypropylene at 25 g/m 2 12. Grid-type reinforcement for strengthening road structures according to any of claims 1 through 11, wherein the grid is a glass filament grid with a mesh of 5 x mm; 10 x 10 mm; 30 x 30 mm; 40 x 26 mm; 50 x 50 mm; preferably 40 x 26 mm. 13. Process for reinforcing road structures according to which a complex grid- type reinforcement is used, wherein a reinforcement according to any of claims 1 through 12 is laid on the layer of bitumen emulsion covering the asphalt concrete. -16- 14. Process for reinforcing road structures according to claim 13, wherein at least one layer of blacktop is deposited on the reinforcement. Process for reinforcing road structures according to claim 13 or 14, wherein several layers of blacktop are deposited on the reinforcement, each layer being separated by a binder course of bitumen emulsion.

16. Process for reinforcing road structures according to any of claims 13 through wherein an emulsion with 200 300 g/m 2 of residual bitumen is used as the lower binder course of bitumen emulsion.

17. Process for reinforcing road structures according to any of claims 13 through 16, wherein it consists of unrolling the prefabricated complex reinforcement according to any of claims 1 through 12 onto the layer of emulsion covering the asphalt concrete.

18. Process for reinforcing road structures according to any of claims 13 through 16, wherein it consists of unrolling the various elements of the prefabricated complex go reinforcement according to any of claims 1 through 12 onto the layer of emulsion covering the asphalt concrete separately on site.

19. Process for reinforcing road structures according to claim 18, wherein the grid is unrolled, followed by the nonwoven carrying the heat-sealing product .ooo "dusted" or deposited in an open film onto its lower surface, the nonwoven being pre-impregnated or not with a basic agent, or being capable of comprising a basic agent in its mass, or the basic agent being incorporated into the heat-sealing product deposited on the nonwoven, or the basic agent being deposited onto the grid or onto 7 he nonwoven as it is unrolled. 17- A complex strengthening reinforcement substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings. DATED this 2 nd day of April, 2002 6D SOLUTIONS Attorney: JOHN D. FORSTER Fellow Institute of Patent and Trade Mark Attorneys of Australia of BALDWIN SHELSTON WATERS •go *o• *ooo* oo