EP0069015B1 - Composite structure for roads and roll-on areas - Google Patents

Abstract

1. Composite structure for roadways and surfaced areas, based on bituminous mixtures comprising various superposed courses of materials bonded with a bituminous binder from a base course (6) in contact either with the foundation or with the roadway or area to be surfaced and a surfacing course (2), the said structure being characterised in that at least its base course (6) consists of a bituminous material capable of withstanding an alternating flexure fatigue test lasting for 10**6 cycles while being subjected to relative deformations greater than 1,5 10**-4 , and in that the thickness of the said base course is restricted to at least a part of the zone subjected to tensile stresses (5) under the effect of a single moment acting on the composite structure.

Description

The invention relates to the field of materials for the construction of roadways and rolling areas. More particularly, it relates to a composite structure for paving roads.

We know that the development of the road network and its maintenance constitute an essential imperative. The research undertaken to date has had the essential object of adapting the qualities of the surfaces, so as to make them capable of withstanding the various constraints of road traffic.

The products which are used in the upper part of known flexible structures are bituminous mixtures. The materials used for the base courses must be, as widely as possible, insensitive to rutting phenomena. As for the coatings, they must protect the body of the road effectively, and be adapted to the particular forces to which they are subjected, both from vehicles and from bad weather. Thus, the pavements of new pavements must resist tangential forces, shears, thermal shocks, wear by studs, and all the constraints from road traffic. Maintenance coatings must present the same resistances and present a notable capacity of elongation under repeated efforts.

So far, compositions have been developed that are well suited to each particular need. For example, bituminous concretes are made with aggregates selected for their hardness, the roughness of their texture, or their resistance to polishing. Very solid mixes, such as poured bituminous concretes, are appreciated for their impermeability and their resistance to crampons. Asphalt mixes based on elastomeric binders have an interesting set of qualities: high elongation capacity under repeated efforts, good resistance to wear even with a very rough texture. Due to the relative prices of materials for the various pavement layers, efforts have been made to define the thicknesses of wearing courses as small as possible, taking into account the technology and behavior of these materials, in order to limit the cost of the work. .

The materials used in the base course distribute the stresses on the foundation. Applied in great thickness, they must resist rutting by creep in their mass, and elongation under repeated efforts when placed on a flexible foundation. The solution to the problem of rutting by creep has been obtained relatively inexpensively by using hard bitumens, at reduced dosages. The increase in cost involved in the manufacture of materials having a large capacity for elongation under repeated stresses is, on the other hand, notable, so that elongation under repeated stresses is often the critical characteristic in the design of a structure made with classic materials.

The invention relates to a composite structure for pavements and road surfaces, based on bituminous mixtures, comprising various superimposed layers of materials linked by a bituminous binder from the lower part in contact with either the foundation or the pavement or surface to be coated. up to the top layer or wearing course. Such a structure is known from FR-A-2 327 363.

The object of the present invention is to reduce the costs of structures based on bituminous mixtures for roadways and rolling areas, in particular for all road works, such as recharging or reinforcement, while obtaining a service life at least equal to that which the materials known until now make it possible to obtain for the same cost.

The invention also relates to a structure making it possible to reduce the total thickness of the layers and consequently, the consumption of materials and energy, as well as the cost of construction or reinforcement of the pavements.

The structure according to the invention is characterized in that the lower part at least of the composite structure consists of a bituminous material capable of withstanding a fatigue test in alternating bending during 10 ⁶ cycles by being subjected to greater relative deformations at 1.5. 10 → and this part has a thickness limited to at least part of the zone subjected to tensile stresses under the effect of a single moment acting on the composite structure.

The invention is based on the observation, made by the plaintiff, following studies carried out on the distribution of horizontal stresses in materials, that said stresses are pulls in the lower part of the structure, if it rests on a granular foundation, and compressions in the upper part of this structure. In the composite structure proposed by the invention, are arranged, at each level, materials having characteristics adapted to the constraints existing at the level where they are applied.

The invention is illustrated with reference to the appended drawing which schematically represents the distribution of stresses in a composite structure formed from layers of bonded materials.

The covering 1 is located at the top. The structure comprises a seat 2, made integral with the covering 1 by a layer of adhesive 3. The seat 2 may comprise one or more layers. If it has several layers, these are linked together so as to form a unitary whole.

The diagram shows, in a conventional manner, the stress diagram of the structure in service. In zone 4 which extends beyond the covering 1 in the seat 2, the stresses (sign +) are compression stresses exerting a shortening effect on the material. In zone 5, the constraints tes are tensile stresses (-) exerting an elongation force on the material.

The figure shows a structure according to the invention in which a part 6 (in hatching) of the lower layer, is made of a bituminous material with high elongation capacity under repeated forces. The thickness x of this layer 6 is entirely included in zone 5. We have also shown in y the level of the so-called neutral zone where stress inversion occurs.

According to the essential characteristic of the invention, at least the lower part of the composite structure consists of a bituminous material capable of withstanding a fatigue test in alternating bending during 10 ⁶ cycles while being subjected to relative deformations greater than 1 , 5 10- ⁴ and this part has a thickness limited to at least part of the area subjected to tensile stresses.

For the purposes of the present description, the term “material with high elongation capacity under repeated stresses” means a bituminous material capable of withstanding a fatigue test in alternating bending during one million (10 ⁶ ) cycles by being subjected to deformations. relative well above 1.5. 10- ^4, usually between 2 and 3. 10-4 10-4. The characteristics and the conditions for carrying out such a fatigue test are described in the document “LPC Research Report No. 58, September 1976 of the Central Laboratory of Bridges and Roads”, entitled “Influence of the formulation parameters on the behavior at the fatigue of a bituminous mix ”by S. Soliman.

As a document illustrating the prior art, there may be mentioned French patent 2327363 which describes a structure comprising a layer of gravel-bitumen consisting of an aggregate coated with 4 to 5.2% by weight of bitumen, more particularly between 4 and 4 , 4%. This patent also teaches a certain number of examples of structures comprising a base or foundation layer, consisting of a gravel-bitumen coated according to the preceding specifications.

The nature of the gravel-bitumen used in patent FR 2 327 363 does not allow it to meet the definition of a material with high elongation capacity under repeated stresses, as indicated above. The bitumen content at ESSO provides a richness module of the order of 2.5 to 3.2, whereas, according to the present invention, such a module is always greater than 3.5, and generally between 3, 8 and 4.5.

Thus, the layer of gravel-bitumen of patent FR 2 327 363 could not be suitable in the composite structure according to the present invention.

Other previous documents may be taken into account and are not relevant.

US Patent 4,113,401 relates to a method for repairing worn and cracked areas. It consists of hot applying an elastomeric material based on bitumen and rubber. It is possible to apply tar on the road to be repaired beforehand. It is therefore a coating, known in the art under the name of membrane, which plays the role of a very thin layer (1 to 2 cm) absorbing stresses due to its flexibility. Such a coating does not have any common characteristic with a structure comprising an asphalt, that is to say a mixture of pebbles and binder as will recognize a technician of road construction.

Swiss patent 483473 relates to a bituminous binder having a particular composition which allows it to have a high elongation capacity. This binder is intended for the production of a bituminous layer. This patent CH 483473 in no way teaches a composite structure, with a characteristic arrangement of superimposed layers and, in particular a lower layer responding to determined characteristics of thickness and nature.

French patent 2,021,922 relates to a structure intended for the construction of roads, which consists of three layers: a concrete base layer, an elastomeric membrane and a covering layer. This type of structure therefore comprises a hydraulic foundation, whereas, according to the present invention, the base layer is formed of a bituminous mix. For a road construction technician, the structures are therefore fundamentally different from a technical point of view. It will also be observed that the structure according to the invention does not have any elastomeric membrane, of the type provided by patent FR 2021922, that is to say a flexible film originating, for example, from copolymerization of dienes.

US Patent 2083900 teaches a composite structure of superimposed layers, which may consist of bituminous mixes. It is explicitly provided, in this prior patent, that the dosage and the hardness of the bituminous layers increase from bottom to top.

It is exactly the opposite in the present invention. This provides for limiting the thickness of the lower layer, by choosing the nature of the bituminous material, to make it capable of withstanding repeated efforts.

German patent application DE-OS 1816704 relates to a structure comprising a support layer made of a particulate material added with a hydraulic binder. We can add an organic binder based on hydrocarbons. This flexible structure has a high modulus of elasticity. This prior patent describes a hydraulic type seat, which is fundamentally different from the present invention. Furthermore, it does not relate to a multilayer composite structure of bonded materials.

German patent application DE-OS 1,594,805 describes a mixture of resin, bituminous binder and rubber, which may additionally contain mineral fillers, for example sand. It is therefore a kind of asphalt mix.

• (a) une couche inférieure à grande capacité d'allongement sous efforts répétés, et
• (b) une couche supérieure, cette dernière étant constituée d'un matériau classique.

This patent does not relate to a multilayer composite structure of bonded materials. In a simple form, the structure according to the invention consists of two layers:

• (a) a lower layer with high elongation capacity under repeated stresses, and
• (b) an upper layer, the latter being made of a conventional material.

In such a structure, the layer (a) can be a mix based on elastomeric binders. By this expression is meant products of the kind defined in the document LPC Research Report No. 62, December 1976, of the Central Laboratory of Bridges and Roads (Ministry of Equipment) entitled "Concrete coating of modified hydrocarbon binders by JP Grimaux et al.

The elastomeric binders consist of bitumens, polymers or copolymers, resins and dopes. A concrete example of elastomeric binders is the product "COLFLEX" 0 from the company COLAS which is a doped bitumen containing, as elastomers, linear styrene-butadiene-styrene copolymers.

In such a structure, the layer (b) can be made of a conventional material such as a mix based on conventional binders, for example of the semi-aggregated bituminous concrete type, studded bituminous concrete, discontinuous bituminous concrete. A particular material corresponding to such a definition is that known under the name "RUGASPHALT" ® from the company COLAS SA, which is a discontinuous rough mix, manufactured either with a bitumen as binder, or with an elastomeric bitumen of the "COLFLEX" ® type. (see above).

In general, these mixes contain aggregates having the characteristics close to those recommended, either in the document "Directive for the realization of surface layers of pavements in bituminous concrete of the Ministry of Equipment and Housing - Road Directorate and road traffic - Technical Studies Service of Roads and Motorways (SETRA) and Central Laboratory of Bridges and Roads (LCPC) "of September 1969, ie in the Directive of SETRA and LCPC of September 1972 for the realization of the foundations of pavements in serious bitumen and bitumen sand.

An exemplary structure, in accordance with the invention, comprises a lower layer 4 to 5 cm thick in a mix based on elastomeric binders such as "COLFLEX" ₀ and a layer 4 to 7 cm thick d '' a mix based on conventional binders, such as road bitumen with a penetration of 40/50, 60/70, or 80/100 depending on the region and traffic. The penetration values characterize the penetration at 25 ° C and are measured according to the AFNOR T66-004 standard of July 1963.

• a) une couche inférieure à grande capacité d'allongement sous efforts répétés.
• b) une couche de liaison.
• c) une couche de roulement.

As a variant, a structure according to the invention can comprise three superimposed layers:

• a) a lower layer with high elongation capacity under repeated stresses.
• b) a tie layer.
• c) a wearing course.

In such a three-layer structure, layer a) is of the same type as in the above-mentioned two-layer structure. Its thickness can be, for example, from 5 to 6 cm. The bonding layer b) also corresponds to the layer b) of the above-mentioned two-layer structure. It has, for example, a thickness of 4 to 6 cm. The wearing course c) consists of a special mix based on conventional binders or elastomeric binders, for example "COLFLEX" ®. Its thickness can be of the order of 3 to 4 cm.

The numerical indications mentioned above by way of examples for composite structures are to be compared with those of analogous conventional structures known from the prior art. The total thickness of conventional structures is greater for the same service capacity. An increase of 50% constitutes a reasonable order of magnitude.

The reduction in thickness corresponding to the transition from a conventional structure to a composite structure according to the invention varies from 30 to 40% depending on the case.

Another structural variant according to the invention comprises three layers, a lower layer constituted by a serious bitumen with high elongation capacity at break, an intermediate layer constituted by a conventional serious bitumen and an upper layer constituted by a coated base. conventional binder or elastomeric binder. The respective thicknesses of these layers, for example, may vary, for the lower layer between 8 and 10 cm, for the intermediate layer between 8 and 12 cm and for the upper layer between 3 and 6 cm. Particular materials meeting the needs of the invention are, for the lower layer, a very high performance bitumen gravel, for the intermediate layer a bitumen gravel of the kind described in the SETRA and LCPC directive of September 1972, for the realization of paving courses in gravel-bitumen and sand-bitumen.

Within the meaning of the present description, a serious bitumen with a high elongation capacity at break is a material capable of successfully undergoing the alternating bending fatigue test described above.

Another variant for a multilayer structure according to the invention comprises, like the previous one, a lower layer of gravel-bitumen with high elongation capacity at break, a first intermediate layer formed of conventional gravel, a second intermediate layer formed of '' a mix based on conventional binders and an upper top layer consisting of a mix based on elastomeric binders. The respective thicknesses of these layers can be of the order of 12 cm for the lower layer, 10 cm for the first intermediate layer, 4 to 5 cm for the second intermediate layer and 3 to 4 cm for the top mix. .

• - grave-bitume à forte capacité d'allongement à la rupture,
• - grave-bitume classique
• - matériau (b)
• - matériau (c).

Specific materials which can respectively constitute this four-layer structure are the following:

• - gravel-bitumen with high elongation capacity at break,
• - classic bitumen
• - material (b)
• - material (c).

The invention will be further illustrated without being in any way limited by the following examples.

Example 1

In this example, a flexible pavement subjected to heavy and intense traffic has been reinforced, similar to the traffic class To of the Catalog of typical structures for new pavements of S.E.T.R.A. and the L.C.P.C. of 1977, namely a roadway subjected to traffic with a number of heavy goods vehicles per day on the busiest track, during the year of entry into service, between 750 and 2000.

The reinforcement structure according to the invention comprises a lower layer 4 cm thick of a discontinuous bituminous concrete "RUGASPHALT" _@ based on elastomeric binder "COLFLEX" ₀ and an upper layer 7 cm thick with a bituminous concrete based on road bitumen 60/70.

Example 2

In this example, we have reinforced a semi-rigid roadway seriously degraded by heavy and intense traffic, similar to the traffic class To of the Catalog of typical structures for new roadways of S.E.T.R.A. and the L.C.P.C. from 1977.

The reinforcement structure according to the invention comprises a lower layer of thickness 3.5 cm of a discontinuous bituminous concrete “RUGASPHALT” 8 based on elastomer binder “COLFLEX” ® and an upper layer of thickness 4.5 cm of bituminous concrete.

Example 3

In this example, we proceeded to the reconstruction of a busy urban road. This new pavement structure, designed to withstand, for 15 years, traffic comparable to the traffic class To of the Catalog of typical structures for new pavements of S.E.T.R.A. and the L.C.P.C. from 1977, rests on a platform floor of low lift.

The structure according to the invention comprises a lower layer 12 cm thick with a gravel-bitumen with high elongation capacity under repeated stresses, an intermediate layer constituted by a conventional gravel-bitumen 12 cm thick and a 4 cm thick top layer of bituminous concrete.

These three examples of composite structures, according to the invention, are to be compared with the thicknesses of the conventional structures initially planned in the three cases: 14 cm of bituminous concrete in the first example, 14 cm of bituminous concrete in the second example, 42 cm of gravel-bitumen with 8 cm of bituminous concrete in the third example.

Claims (9)

1. Composite structure for roadways and surfaced areas, based on bituminous mixtures comprising various superposed courses of materials bonded with a bituminous binder from a base course (6) in contact either with the foundation or with the roadway or area to be surfaced and a surfacing course (2), the said structure being characterised in that at least its base course (6) consists of a bituminous material capable of withstanding an alternating flexure fatigue test lasting for 10⁶ cycles while being subjected to relative deformations greater than 1.5 10-⁴, and in that the thickness of the said base course is restricted to at least a part of the zone subjected to tensile stresses (5) under the effect of a single moment acting on the composite structure.

2. Structure according to Claim 1, characterised in that it comprises essentially two courses :

a) a base course consisting of a bituminous material capable of withstanding an alternating flexure fatigue test lasting for 10⁶ cycles while being subjected to relative deformations greater than 1.5 1₀-⁴,

b) a surfacing course, the latter consisting of a conventional material.

3. Structure according to Claim 1, characterised in that it comprises essentially three superposed courses :

a) a base course consisting of a bituminous material capable of withstanding an alternating flexure fatigue test lasting for 10⁶ cycles while being subjected to relative deformations greater than 1.5 1₀-⁴,

b) a binder course,

c) a top surfacing course.

4. Structure according to either of Claims 2 or 3, characterised in that the course a) is a coated material based on elastomeric binders.

5. Structure according to any one of Claims 2 to 4, characterised in that the course b) is a coated material based on conventional binders.

6. Structure according to any one of Claims 3 to 5, characterised in that the surfacing course c) is a special coated material based on conventional binders or on elastomeric binders.

7. Structure according to Claim 1, characterised in that it comprises essentially three courses, a base course consisting of a gravel-sand-bitumen mixture capable of withstanding an alternating flexure fatigue test lasting for 10⁶ cycles while being subjected to relative deformations greater than 1.5 10-⁴, an intermediate course consisting of a conventional gravel-sand-bitumen mixture and a top surfacing course consisting of a coated material based on conventional binders or elastomeric binders.

8. Structure according to Claim 1, characterised in that it comprises essentially a base course of gravel-sand-bitumen mixture capable of withstanding an alternating flexure fatigue test lasting for 10⁶ cycles while being subjected to relative deformations greater than 1.5 10-⁴, a first intermediate course made of conventional gravel-sand-bitumen mixture, a second intermediate course made of a coated material based on conventional binders and a final course consisting of a coated material based on elastomeric binders.

9. Structure according to any one of Claims 1 to 8, characterised in that the constituent material of the base part of the structure is a coated material based on elastomeric binders or a gravel-sand-bitumen mixture capable of withstanding an alternating flexure fatigue test lasting for 10⁶ cycles while being subjected to relative deformations greater than 1.5 10-⁴.

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