FR2823233A1 - A carriageway resistant to freeze/unfreeze cycles for use on secondary roads has an underlayer comprising stone granules of differing maximum and minimum diameters chosen to give a void volume after compaction of 15-25% - Google Patents

Abstract

A carriageway resistant to freezing and melting comprising a first, lower, road covering layer comprising quarry stone granular material and sandnon-stone material. The ratio of stone to sand is such that after compaction the amount of void is 15 vol.% or more. The second layer is cold rolled, waterproof bitumen A carriageway resistant to freezing and melting comprising a first, lower, road covering layer comprising 95-99 wt.% of quarry stone granular material with smallest diameter 6-20 mm and greatest diameter 10-40mm and up to 15 wt.% sand, 1-5 wt.% of non-stone material with relative density below 1 and 3-6 wt.% of bitumen emulsion. The ratio of stone to sand is such that after compaction the amount of void is 15 vol.% or more. The second layer is cold rolled, waterproof bitumen. The volume of void in the first layer is preferably 15- 25%. The ratio of largest to smallest diameters of the stone granulate is above 1 and preferably above 2. The non-stone material is sawdust and wood chips, polyethylene or polypropylene film, chips or granules. The thickness of the lower layer after compacting is 10- 20 cm and its elastic modulus E below 2000 MPa. The thickness of the upper layer after compacting is 3-6 cm, its elastic modulus E is 4000-5000 MPa and it has granulometry 0/10. The bitumen emulsion is a cationic emulsion containing 60-70 wt.% bitumen and with pH 1-4. An intermediate dressing layer is present between the lower and upper layers and comprises gravel of suitable sizes to lodge in the surface voids of the lower layer. A means of lateral protection of the carriageway to restrict the circulation of water within it is also present. An Independent claim is included for a method of making a carriageway by mixing and compacting the ingredients of the lower layer above, optionally forming a dressing layer on the lower layer and then forming a layer of cold rolled bitumen and compacting.

Description

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 The present invention relates to a pavement resistant to the action of freeze / thaw and a method of manufacturing such a pavement.

 The action of freezing / thawing on roadways is an acute problem that can have particularly disastrous repercussions (formation of ruts, cracks in the rolling coating, etc.) for said roads, in particular, if the soil-support of the roadway, is a gelling ground.

So-called sol-gel-a soil having the property of absorbing large quantities of water and being able to give rise to the phenomenon of gelation. This phenomenon is reflected during periods of frost by the formation of ice lenses. Not only do these ice lenses feed on the existing free water in the soil, but by capillarity or condensation, the water in the subsoil rises to replace the absorbed water. It follows a phenomenon of suction of the water towards the frost front and the expansion of these lenses of ice, which induces a very important swelling of the ground. Important constraints appear on the roadway. During periods of thaw, this water is suddenly released in area. The deeper layers remain frozen, forming impermeable layers that force the water to remain in the upper layer of soil. The surface layer of the soil thus becomes a "quagmire" and can no longer ensure full lift of the roadway.

 It follows from these phenomena, a very great weakening of the roadway. In areas where the ground is sensitive to freezing, all heavy vehicle traffic should be stopped at the first sign of frost.

"Tidal barriers" must be applied to prevent access of local economic areas to heavy vehicles. Depending on the strength and duration of the freeze, this access ban may be relatively long (ie several months), thus causing significant inconvenience to the local economy. Even if the soil is not very frosty, particular weather conditions (snow and avalanches in the mountains, abundant rains accompanied by ice or frost in the lowlands) can lead to premature aging and therefore weakening of the roadways. Finally, these phenomena of gelation do not only concern the ground-support of the roadway but also the roadway itself if the materials constituting it are freezing.

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 Before constructing a road surface on a given ground, we must at present take into account the importance of the traffic that it will have to bear (in particular, in heavy goods vehicle traffic), local weather conditions (climate, risks of frost, ...), the tablecloth regime and finally make direct measurements, i. e. surveys to study the heterogeneity of the terrain and its resistance. All this information then conditions the use of methods to protect pavement from the effects of freezing.

 One method is to deposit for example layers of cement sand which serve as lift elements of the rolling coating. Although recognized as effective, this method requires large thicknesses of implementation and greater than 20 cm, which makes the layers vulnerable to shrinkage cracking and thermal cracking. Another method is to limit the influx of water to the frozen area by waterproofing the shoulders or draining the pavement. However, this method is difficult and expensive to implement and has, alone, a limited effect for frosty soils.

 The objective of the present invention is therefore to provide a method for producing a pavement resistant to the action of freeze / thaw. This simple process in its design and implementation, fast and economical should allow, in addition to a technical advance, the realization of pavements resistant to the action of freeze / thaw preferentially for the secondary road network.

 To this end, the invention relates to a pavement resistant to the action of freeze / thaw comprising at least a first lower layer of road surface and at least a second upper layer of road surface.

 According to the invention, the first lower layer comprises: (a) 95 to 99% by weight of a granular material consisting of a d / D mixture of aggregates where d is the smallest diameter and D is the largest diameter aggregates, whether or not reconstituted, having a d between 6 and 20 mm and a D ranging between 10 and 40 mm, for example: 6 / 10-6 / 15-6 / 20-10 / 20- 10 / 30-

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 10 / 40-20 / 40, and optionally up to 15% by weight, based on the total weight of the aggregates, of at least one quarry sand; and (b) 1 to 5% by weight of at least one non-stony material having a density of less than 1, and (c) 3 to 6% by weight, based on the total weight of (a) and (b) d an emulsion of bitumen; (d) the weight proportions of the first aggregate, second aggregate and possibly quarry sand being such that, after compaction, the first lower layer has a void ratio of at least 15% by volume; and the second upper layer is a waterproof, cold bituminous concrete surfacing.

- le taux de vide de la première couche inférieure compactée est de 15 à 25% en volume, - le rapport D/d des granulats pierreux est supérieur à 1, de préférence supérieur à 2, - le matériau non pierreux est choisi parmi la sciure et les copeaux de bois, les films, copeaux et granulés de polyéthylène et les films, copeaux et granulés de polystyrène, - la première couche inférieure a une épaisseur usuelle, après compactage, de 10 à 20 cm, - la deuxième couche supérieure a une épaisseur, après compactage de 3 à 6 cm, - la première couche inférieure, après compactage, a un module élastique E inférieur à 2000 MPa, - la couche supérieure, après compactage, a un module élastique E d'environ 4000 à 5000 MPa,

- la couche de roulement a une granulométrie de l'ordre de 0/10, - l'émulsion de bitume est une émulsion cationique renfermant 60 à 70% en poids de bitume et ayant un pH allant de 1 à 4, - la chaussée comporte une couche intermédiaire de bouchardage entre la première couche inférieure et la seconde couche supérieure, In various particular embodiments of the freeze / thawable pavement, each having particular advantages and capable of many technically possible combinations:

the void rate of the first compacted lower layer is 15 to 25% by volume, the D / d ratio of the stone aggregates is greater than 1, preferably greater than 2; the non-stone material is chosen from sawdust; and wood chips, films, chips and pellets of polyethylene and films, chips and granules of polystyrene, - the first lower layer has a usual thickness, after compaction, of 10 to 20 cm, - the second upper layer has a thickness, after compacting from 3 to 6 cm, the first lower layer, after compacting, has an elastic modulus E less than 2000 MPa, the upper layer, after compaction, has an elastic modulus E of about 4000 to 5000 MPa,

the wearing course has a particle size of the order of 0/10, the bitumen emulsion is a cationic emulsion containing 60 to 70% by weight of bitumen and having a pH ranging from 1 to 4, the pavement comprises an intermediate bush-hammering layer between the first lower layer and the second upper layer,

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On appelle ici-bouchardage-l'opération qui consiste à obstruer er les vides de la zone superficielle de la première couche inférieure par du sable ou de petits gravillons de diamètre d'très inférieur au diamètre d des premiers granulats pierreux en vue d'obtenir une surface rugueuse présentant une bonne planéité.

In this case, the operation of blocking the voids of the upper surface zone of the first lower layer with sand or small gravel diameters of much less than the diameter of the first stony aggregates in order to obtain a rough surface with good flatness.

 the bush-hammer layer comprises chippings of appropriate size to lodge in at least a portion of the surface voids of the first lower layer, the pavement possibly comprises a lateral protection device of the pavement reducing the circulation of water in the pavement; .

 The invention also relates to a method of manufacturing a pavement resistant to the action of freeze / thaw.

 According to the invention, the method comprises the steps of forming on a floor a lower layer of a material obtained by kneading: (a) 95 to 99% by weight of a granular material consisting of a d / D mixture of aggregates whose smallest diameter d ranges from 6 to 20 mm and the largest diameter D ranges from 10 to 40 mm, and optionally up to 15% by weight, relative to the total weight of the aggregates, of at least one sand careers ; and (b) 1 to 5% by weight of at least one non-stony material having a density of less than 1, and (c) 3 to 6% by weight, based on the total weight of (a) and (b) d an emulsion of bitumen; (d) the weight proportions of the first granulate, second granulate and possibly quarry sand being such that, after compaction, the first lower layer has a void fraction of at least 15% by volume and compact said layer; possibly forming on the lower layer a layer of bush-hammer elements and compacting said layer; and - forming on the compacted and possibly bush-hammered lower layer a cold bituminous concrete layer and compacting said layer to obtain a water-resistant wearing course.

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 The invention will be described in more detail with reference to the appended FIG. 1 which is a schematic representation of a roadway according to the invention.

 One of the requirements for making freeze / thaw resistant pavements is the shallow penetration of the frost into the natural soil. In other words, the penetration depth of the 0 C isotherm in the pavement bearing soil must be as low as possible. Ideally, the frost line should stabilize in the actual body of the roadway, which would then hardly suffer any damage if the roadway is made of non-freezing materials.

 Indeed, if the freezing front (isothermal 0 C) crosses the whole of the roadway and penetrates and then stabilizes in the ground-support, one can assist if the ground is freezing or has undergone abundant rains, with the formation of ice lenses. These can be associated with suction phenomena of the water present in the basement if the cold is sufficiently long. There is then swelling of the soil and the appearance of stresses on the pavement, weakening the latter.

 It is therefore sought to provide a pavement whose structural composition and the materials used provide thermal insulation of the ground-support of the roadway and therefore a depth of penetration of the gel front in the latter as low as possible.

 According to the invention as shown in Figure 1, the pavement 1 resistant to the action of freeze / thaw comprises at least a first lower layer 2 road surface and at least a second upper layer 3 road surface. The first lower layer 2 comprises 95 to 99% by weight of a granular material consisting of a d / D mixture of aggregates with the smallest diameter ranging from 6 to 20 mm, and the largest diameter D ranging from 10 to 40 mm, and optionally up to 15% by weight, based on the total weight of the aggregates, of at least one quarry sand. The aggregates are represented by a first granulate 4 of diameter d and a second granulate of diameter D. The ratio D / d of the first 4 and second 5 stone aggregates is chosen greater than 1, and in a preferred embodiment, this ratio is greater than 2. The first lower layer 2 also comprises 1 to 5% by weight of at least one non-stony material 6 having a density of less than 1. This material 6

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 is selected from sawdust and wood chips, films, shavings and pellets of polyethylene and films, chips and granules of polystyrene.

Wood chips or sawdust have advantageously underwent, according to a well-established method, an imputrescible treatment of heat-treating the pieces of wood by heating at temperatures between 400 and 800oC and then subjecting them to chemical treatment. to make said pieces inert. The first lower layer 2 comprises 3 to 6% by weight, relative to the total weight of (a) and (b) of a bitumen emulsion 7. In a preferred embodiment, this emulsion 7 is a cationic emulsion containing 60 at 70% by weight of bitumen and advantageously having a pH ranging from 1 to 4. The weight proportions of the first aggregate 4, second aggregate 5 and possibly quarry sand are such that, after compaction, the first lower layer 2 has a void ratio 8 of at least 15% by volume. Advantageously, this void ratio 8 is between 15 and 25% by volume. The thickness, after compaction, of the first lower layer 2 is 10 to 20 cm.

 The second upper layer 3 is a cold, waterproof, bituminous concrete surfacing. Its thickness after compacting is 3 to 6 cm and its elastic modulus E is of the order of 4000 to 5000 MPa. The modulus of elasticity of the second upper layer 3 is in a preferred embodiment of the order of twice the modulus of elasticity of the first lower layer 2 after compacting. The wearing course 3 has a particle size of the order of 0/10.

 The non-stony material 6 added has a thermal conductivity such that combined with a wearing course made of BBSG (bituminous-semi-grained concrete), for example, the thermal conductivity of the entire structure is advantageously less than 1.2 W / m. K to 23OC.

 The roadway 1 comprises an intermediate layer 9 of bush-hammering between the first lower layer 2 and the second upper layer 3. This layer 9 comprises chippings of appropriate dimensions to obstruct the surface voids 8 of the first lower layer 2 and thus obtain a rough surface showing a good flatness after

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 compaction. The intermediate layer 9 called preimpermeabilization reduces the thickness of the wearing course 3 while ensuring tightness and flexibility to the structure.

 The roadway 1 also comprises a device 10 for side protection of the roadway 1 reducing the circulation of water in the roadway 1.

This device 10 is optional and essentially aims to prevent the lateral infiltration of water in the pavement 1 while allowing the water possibly present in said pavement 1 to be evacuated. This device 10 may be, for example, consists of flow ditches, the roadway and its shoulders being raised relative to them.

The invention also relates to a method of manufacturing a pavement 1 resistant to the action of freeze / thaw. According to the invention, a bottom layer 2 is formed on a floor 11 of a material obtained by kneading (a) 95 to 99% by weight of a granular material consisting of a d / D mixture of aggregates, the most small diameter d ranges from 6 to 20 mm and the largest diameter D ranges from 10 to 40 mm, and optionally up to
15% by weight, based on the total weight of the aggregates, of at least one quarry sand; and (b) 1 to 5% by weight of at least one non-stony material 6 of density less than 1, and (c) 3 to 6% by weight, based on the total weight of (a) and (b) an emulsion of bitumen 7.

 The weight proportions of the first granulate, the second granulate and possibly the quarry sand are such that, after compaction, the first lower layer 2 has a void ratio of at least 15% by volume. Advantageously, this void ratio 8 is between 15 and 25% by volume. This first lower layer 2 is then compacted. A layer of bush-hammer elements 9 obtained by obstruction of the surface voids 8 of the lower layer 2 with sand or small gravel of a diameter of very at the diameter of the first stony aggregates 4. The said layer 9 is compacted and on the compacted lower layer 2 and possibly bush-hammered 9 a layer is formed.

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 Cold bituminous concrete 3. This layer is also compacted to provide a water-resistant wearing course.

The method of the invention has been implemented, an example of which is presented here, this example showing the quality of the improvement of the thermal insulation obtained: Example 1
A freeze design study of a pavement 1, according to the invention, was carried out on the following structure: - 4 cm thick layer of 3 cm in BBSG (bituminous-semi-grouted concrete) - A seat 2 with a thickness of 15 (or 20) cm with the following materials: Severe bitumen, Severe emulsion, Sand cement and additions whose characteristics are comparable to those of cement sand.

 The meteorological conditions selected for this study are the following: - Simulation duration: 30 days - Freezing temperature: -10oC - Gel duration: 15 days.

The results obtained by this simulation are as follows:

<Tb>
<tb> Thickness <SEP> of <SEP> materials <SEP> of <SEP> basis <SEP> 15 <SEP> cm <SEP> 20 <SEP> cm
<tb> Penetration <SEP> of the <SEP> front <SEP> of <SEP> gel
<tb> Severe <SEP> bitumen <SEP> 43 <SEP> cm <SEP> 27 <SEP> cm
<tb> Serious <SEP> emulsion <SEP> 35 <SEP> cm <SEP> 3 <SEP> cm
<tb> Sand <SEP> cement <SEP> 37 <SEP> cm <SEP> 2 <SEP> cm
<tb> Adds <SEP> 4cm <SEP> 2cm
<Tb>

It is therefore observed that for a thickness of 15 cm thick bitumen, the isotherm 0 C penetrates 43 cm into the ground 11-support of the roadway 1.

This depth is only 27 cm when the seat in Grave bitumen is 20 cm thick. Note the good thermal insulation obtained for a seat 2 Sand cement 20 cm thick. However, such a thickness makes the seat 2 vulnerable to shrinkage cracks and thermal cracking. When the thickness of the seat 2 Sand cement

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 It is only 15 cm, again a great depth (37 cm) of penetration of the frost line into the natural soil 11 is obtained. The best behavior for a seat 2 with a thickness of 15 cm is obtained for the seat according to the invention, i. e. involving a mixture of stony and non-stony materials, a non-stony material of density less than 1 selected from sawdust and wood chips, polyethylene films, chips and granules and polystyrene films, chips and granules and said seat having, after compacting, a void ratio 8 of at least 15% by volume.

 It is also noted that beyond a certain thickness (20 cm), one does not gain more in terms of frost protection.

 This method can advantageously be used for the manufacture of pavements 1 resistant to the action of freeze / thaw for secondary roads.

Claims (14)

 1. pavement (1) resistant to the action of freeze / thaw comprising at least a first layer (2) of lower road surface and at least a second layer (3) upper road surface, characterized in that: - the lower first layer (2) comprises: (a) 95 to 99% by weight of a granular material consisting of a d / D mixture of stone aggregates (4,5) having the smallest diameter d ranging from 6 to 20 mm and whose largest diameter D is from 10 to 40 mm, and optionally up to 15% by weight, based on the total weight of aggregates (4,5), of at least one quarry sand; and (b) 1 to 5% by weight of at least one non-stony material (6) having a density of less than 1, and (c) 3 to 6% by weight, based on the total weight of (a) and (c) b) a bitumen emulsion (7); (d) the weight proportions of the aggregates (4,5) and possibly quarry sand being such that, after compaction, the lower first layer (2) has a void fraction (8) of at least 15% by volume ; and the upper second layer (3) is a waterproof, cold bituminous concrete surfacing.  2. Pavement according to claim 1, characterized in that the void ratio (8) of the first compacted lower layer is 15 to 25% by volume.  3. Pavement according to claim 1 or 2, characterized in that the D / d ratio of stony aggregates (4,5) is greater than 1, preferably greater than 2.  4. Pavement according to any one of claims 1 to 3, characterized in that the non-stony material (6) is selected from sawdust and wood chips, films, shavings and pellets of polyethylene and films, chips and polystyrene granules.  5. Pavement according to any one of the preceding claims, characterized in that the lower first layer (2) has a thickness, after compaction, of 10 to 20 cm. <Desc / Clms Page number 11>  6. Pavement according to any one of the preceding claims, characterized in that the second layer (3) has a greater thickness, after compaction, 3 to 6 cm.  7. Pavement according to any one of the preceding claims, characterized in that the first layer (2) lower, after compaction, has an elastic modulus E less than 2000 MPa.  8. Pavement according to any one of the preceding claims, characterized in that the layer (3) upper, after compaction, has an elastic modulus E of about 4000 to 5000 MPa.  9. Pavement according to any one of the preceding claims, characterized in that the wearing course has a particle size of the order of 0/10.  10. Pavement according to any one of the preceding claims, characterized in that the bitumen emulsion (7) is a cationic emulsion containing 60 to 70% by weight of bitumen and having a pH ranging from 1 to 4.  11. Pavement according to any one of the preceding claims, characterized in that it comprises an intermediate bush-hammering layer (9) between the lower first layer (2) and the second upper layer (3).  12. Pavement according to claim 11, characterized in that the bush-hammer layer (9) comprises appropriately sized chippings for lodging in at least a portion of the surface voids (8) of the lower first layer (2).  13. Roadway according to any one of the preceding claims, characterized in that it comprises a lateral protection device (10) of the roadway (1) reducing the circulation of water in the roadway (1).  14. A method of manufacturing a pavement resistant to the action of freezing / thawing, characterized in that it comprises the steps - forming on a floor (11) a lower layer (2) of a material obtained by mixing of (a) 95 to 99% by weight of a granular material consisting of a d / D mixture of stone aggregates (4,5) having the smallest diameter d ranging from 6 to 20 mm and the most <Desc / Clms Page number 12>  large diameter D ranges from 10 to 40 mm, and optionally up to 15% by weight, relative to the total weight of aggregates (4,5), at least one quarry sand; and (b) 1 to 5% by weight of at least one non-stony material (6) having a density of less than 1, and (c) 3 to 6% by weight, based on the total weight of (a) and (c) b) a bitumen emulsion (7); (d) the weight proportions of the aggregates (4,5) and possibly quarry sand being such that, after compaction, the lower first layer (2) has a void fraction (8) of at least 15% by volume and compacting said layer; - May form on the lower layer (2) a layer of bush-hammer elements (9) and compact said layer; and - forming on the bottom layer (2) compacted and possibly bush-hammered a cold bituminous concrete layer (3) and compacting said layer to obtain a wearing course, waterproof.