WO2001049939A1

WO2001049939A1 - Hot-setting bitumen-coated material containing rubber

Info

Publication number: WO2001049939A1
Application number: PCT/FR2000/001069
Authority: WO
Inventors: Eric Godard
Original assignee: Colas
Priority date: 2000-01-07
Filing date: 2000-04-21
Publication date: 2001-07-12
Also published as: CA2396528A1; JP2003519306A; HUP0203927A2; PL365073A1; AU4302400A; AU749952B2; CZ20022334A3; EP1248884A1; SK9902002A3; FR2803608A1

Abstract

The inventive hot-setting bitumen-coated material is used for forming the top layer of a road and comprises a granular mixture with varying granulometry and a bonding agent in the form of a conventional bitumen or a modified bitumen. Said granular mixture contains chips, a sandy fraction and powdered rubber, said sandy fraction having a lower volume than the interstitial volume of the chips. According to the invention, the particles of powdered rubber are less than 1.5 mm in size and the percentage of rubber in the granular mixture is less than 1.5 %.

Description

BITUMINOUS HOT COATING COMPRISING RUBBER

The invention relates to a hot bituminous mix, intended to constitute a surface course of a road and comprising rubber. The invention also relates to a method of manufacturing such a bituminous mix and a method of producing a wearing course with such a mix.

For many years, it has been known to produce road surfaces with asphalt containing recycled rubber. An example is known from document EP-A-0.672.791. . The introduction of rubber into bitumens makes it possible to improve the properties of coated materials, to give greater flexibility to the coatings produced, to improve their resistance to fatigue at low temperatures, and to reduce noise and reflective phenomena. light sources. The use of recuperated rubber for this purpose also makes it possible to contribute to the disposal of used tires of various origins.

Thus, methods have been developed in which the rubber is mixed with the bitumen in the manner of an aggregate.

For the implementation of this type of process, it was first considered necessary to use granules having a particle size between 1 and 3 or 2 and 4 mm, that is to say rubber granules having a particle size comparable to that of gravel (see for example US-A-4,548,962).

A road surface was then produced which, at least in places, had a thickness of rubber of several millimeters between two aggregates or traditional gravel. Rubber having an extremely low modulus of elasticity, such a thickness of rubber between two traditional aggregates which are hard materials, leads to very significant deformations of the coating when it is subjected to a high local stress such as that produced by the passage of a truck and therefore a significant deformation of the coating which quickly leads to deterioration thereof. To remedy this problem, part of the sandy fraction which traditionally accompanies gravel has been replaced by rubber powder, the particles of which have an average diameter of between 0 and 1.5 mm. To the granular skeleton thus obtained, a bituminous binder was then added which could be a pure bitumen or a bitumen modified by additives, often polymers.

The latter technique is generally satisfactory. However, it is sought to further improve the resistance of the road, for example for applications in parking areas where maneuvers are frequent and very short turns. Furthermore, it has been found that rubber is sensitive to humidity, which sometimes gives rise to a certain number of drawbacks. The object of the invention is to provide a hot bituminous mix comprising rubber powder, which avoids the drawbacks mentioned above.

The bituminous mix must moreover make it possible to obtain a road surface having good surface water drainability and good sound properties.

The object of the invention is achieved by a hot bituminous mix intended to constitute a wearing course of a road and comprising for this purpose a granular mixture of discontinuous particle size and, as binder, a bitumen. The granular mixture comprises gravel, a sandy fraction and rubber powder, the sandy fraction and the rubber powder taken together having a volume less than the interstitial volume of the gravel.

According to the invention, the particle size of the rubber powder is less than 1.5 mm and the percentage of rubber in the granular mixture is less than 1.5% by mass.

To ensure good roughness, the total sand content (mineral + rubber) must not exceed the volume of the interstitial voids between the gravel, i.e. around 30 to 40% of the overall volume. Thus, the rubber powder is used in substitution for, and not in addition to the usual sandy fraction.

The invention also relates to the characteristics below considered in isolation or in all their technically possible combinations:

- The binder of the bonding layer can be a pure bitumen, also called conventional bitumen, or a modified bitumen and in particular a pure bitumen emulsion or a bitumen emulsion modified by polymers. Advantageously, but not necessarily, elastomeric emulsions will be used because of their chemical affinity with rubber.

- The grain size of the rubber is chosen to be close to that of as fine a sand as possible: 0/1 mm (90% of the particles have a size less than 1.0 mm, that is to say the rejection rate of the rubber particles in the 1 mm sieve must be less than 10% of the dry mass of the sample). This choice makes it possible to replace with rubber part of the sand constituting the granular skeleton of the bitumen, while ensuring that the desired characteristics of the asphalt are obtained. - The percentage of rubber in the granular mixture is between 0.5 and 1%.

- The granular mixture contains, in addition to the sandy fraction, gravel and rubber, a proportion of rock powder (preferably limestone) at least equal to 1.5% of the total mass of the aggregates.

This rock powder, also called wire 1, is characterized in that 90% of its mass passes through a sieve of 80 μm.

- The particle size composition of the granular mixture is determined using a calculation in terms of volume fractions of the granular mixture.

Indeed, taking into account the significant density difference between the different constituents i of the granular mixture that are gravel, the sandy fraction and the rubber, the particle size composition must be expressed in volume fractions rather than mass fractions if we want to have a good picture of the grain size distribution.

The proportion by volume V, - of each constituent i of the granular mixture is calculated by:

where Pj: proportion by mass of constituent i and pj: real density of constituent i. The granulometry of the granular mixture is then calculated according to the formula:

where B _j : percentage of passers by volume of the mixture with a sieve j. and Ai _] : percentage of by-passers by mass of component i through sieve j.

- The bitumen content L, that is to say the mass ratio between the bitumen and the total mass of the mix, is calculated from a richness module K, from a conventional specific surface Σ and of a coefficient α correcting the real density of the constituents i using the relation:

where K: value between 3.5 and 4.5

2.65 α: α =

P. Σ is defined by 100 Σ = 0.25 G + 2.3 S + 12 s + 1 35 f + 450 KU with the following weight proportions:

G of grains larger than 6.3 mm S of grains of 6.3 mm to 0.315 mm s of grains of 0.315 mm to 0.08 mm f of grains smaller than 0.08 mm KU of rubber particles

The proportion by weight KU takes account of the particular absorbency of rubber compared to a limestone fi lmer: While the absorbency of a limestone filler is 50 g (fine mass for 15 g of bitumen), it is 15 g for rubber. The rubber therefore absorbs 50/15 = 3.33 times more bitumen than filler.

- The wealth module preferably has a value between 3.8 and 4.2.

- The bitumen content is advantageously between 4 and 14% by weight.

Tables I and II show two calculation results, that is to say two reconstitutions of bituminous mix compositions according to the invention with gravel with a grain size of 0/1 0 and respectively 1% and 1.5% of rubber. .

Rubber is a porous material and moisture becomes deeply embedded in its structure as soon as its rate becomes high. The natural humidity of rubber in its production is low, that is to say generally less than 0.5%. This rate is acceptable for the manufacture of asphalt mix and it must not exceed 1% by mass.

The rubber generally wets during packaging, transport and above all storage operations. In particular when storing on asphalt production sites, it is compulsory to house the rubber bags. This results in an increase in its humidity in case of rain.

It has been found that loading rubber with a certain amount of bitumen, on the order of 1 to 15% of its mass, makes it possible to considerably limit the ability of the rubber to absorb water at depth. The presence of bitumen around the water-repellent rubber particles therefore the latter.

This improvement in the behavior of the rubber powder can be easily obtained by pretreatment of the rubber powder, that is to say by spraying bitumen on rubber powder at the end of the production chain. It suffices to pass the freshly produced rubber powder into a chamber where the bitumen is nebulized (micronized) at a temperature of the order of 150 ° C. The humidity is measured according to a method called "by drying in an oven" which is described in detail in standard NF P 94 050.

The rubber powder thus treated is then used conventionally. It is then necessary to take into account in the following that part of the bitumen has already been incorporated into the rubber powder and to correct the amount of bitumen in the asphalt formula by the corresponding amount.

The behavior of the mix on the roadway in the presence of water must be checked. A methodology for verifying the mechanical strength of the mixture in the presence of water is established. This methodology consists of carrying out two specific tests: a) The classic Duriez test but requiring a value of immersion-compression greater than 0.85 and preferably greater than 0.90 while a value greater than 0.75 or 0 , 80 is usually considered sufficient for conventional mixes. b) The CANTABRO wear test (Spanish standard N LT 352/86, method established in Spain for drainage mixes) modified in that the number of revolutions of the "Los Angeles" drum is increased from 300 to 500, and what the test temperature is set at 18 ° C. Under these conditions, the percentage of loss of the test pieces of the asphalt tested must be less than 10% of the initial mass of the asphalt.

The asphalt is spread in a thin surface layer of a road, the thickness of the layer being between 1, 5 and 4 cm, preferably between 2.0 and 3.0 cm for a granularity 0/6 and between 2.5 and 3.5 cm for a granularity 0/10.

The invention also relates to a method for manufacturing a hot bituminous mix intended to constitute a wearing course of a road and comprising a granular mixture of discontinuous particle size and, as a binder, a conventional bitumen or a modified bitumen, the granular mixture comprising gravel, a sandy fraction and rubber powder, the method comprising the steps of bringing the gravel and the sandy fraction to the temperature of coating and kneading them with the binder in order to produce the bituminous mix.

According to the invention, the rubber powder is added in a percentage of less than 1.5% by volume of the granular mixture, the particles of the rubber powder having a size of less than 1.5 mm.

Since rubber fears very high temperatures, in particular the presence of a flame, it is introduced at a point in the production line where the aggregates are already at the desired coating temperature. In addition, whatever the method of manufacturing bituminous mix, it is important to take into account - for the introduction of rubber - the small size of the particles and their light weight which results therefrom. These two characteristics make it a material liable to be carried away by the strong draft of the drying. To compensate for this drawback, the rubber is generally introduced just before the end of the drying area for the gravel and the sandy fraction.

The invention also relates to the following characteristics, considered in isolation or in all their technically possible combinations:

• In the event that the mix is manufactured by a batch production center, the recycled rubber is introduced into the mixer in hot-melt bags or continuously at the foot of the hot elevator. • If the mix is manufactured by a discontinuous manufacturing center with a dosing hopper allowing granulate to be added to the foot of the hot elevator, it can be used.

• If the mix is manufactured by a continuous manufacturing center with a separate mixer, the recycled rubber is introduced at the mixer or at the foot of the hot elevator at the end of drying.

• If the mix is manufactured by a continuous mixing plant with mixing integrated into the drying drum, it is necessary to have a dosing hopper allowing the rubber to be incorporated at the end of the drying of the mineral aggregates by recycling ring. If this is not possible, injection by screw or pneumatic transport is then used. To be sure that the moisture content of the rubber powder does not exceed 1% by mass, we proceed according to two alternatives. According to the first, the humidity of the rubber powder is measured before introducing it into the mixer - and thus into the mixture of gravel and sandy fraction - and correcting the humidity if necessary. According to the second alternative, micronized rubber described above is used.

The invention also relates to a method for producing a surface course of a road with a bituminous mix as defined above. According to the invention, this production method comprises. stages of spreading a bonding layer on the road intended to receive the wearing course, spreading a layer of said bituminous mix and compacting this layer of bituminous mix. In a preferred embodiment of the invention, the compacting of the spread bituminous mix is carried out with a compactor other than a pneumatic compactor. Likewise, care is taken to avoid sticking of the mix to the compactor balls. Other characteristics and advantages of the invention will emerge from the description of two exemplary embodiments of the mix of the invention, and of an example of implementation of the process for manufacturing a bituminous mix according to the invention. .

The description of the implementation of the manufacturing process is made with reference to the single Figure showing a drum-dryer-mixer and elements necessary for the rubber supply.

As is already apparent from Tables I and II introduced above, the bituminous mix of the invention essentially comprises gravel of different sizes, including a sandy fraction, rubber powder and bitumen. Tables III and IV show two other examples of compositions. The first example is a bituminous mix comprising 1% of rubber, subsequently designated coated A, while the second example is a bituminous mix comprising 2% of rubber, subsequently designated coated B.

Asphalt A firstly comprises a granular mixture consisting of 95.5% of mineral aggregates, 78.5% of which are 6/10 in size while 17% are 0/2 in size, as well as 1% of a rubber with grain size 0/1. This mixture is completed by a filler (3.5%).

To this aggregate-rubber mixture, a modified bitumen is added. It represents 6.6% of the mass of dry aggregates.

Bituminous mix B differs from mix A in the percentages of the various components. Thus, the aggregate-rubber mixture comprises 83% of mineral aggregate with a grain size of 6/10 and 12% of mineral aggregate with a grain size of 0/2. The percentage of rubber with a grain size of 0/1 is 2% and that of the filler is 3%. The proportion of bitumen is 6.6%.

Asphalt A and B are produced at a temperature of 165 ° C and 150 ° C respectively.

To illustrate the particle size discontinuity of the mixture of aggregates used to form bituminous mixes according to the invention, Table IV presents a particle size distribution according to standard P 18-560 of mineral aggregates 6/10 and 0/2. In addition, Table IV contains the numerical values of the coefficients defined above, namely the specific surface Σ, the richness modulus K, the theoretical density of the aggregates and the real density V-, of the aggregates. The advantages of the bituminous mix of the invention emerge from the conventional tests carried out.

The results of the tests are contained in Table IV. These results show the compaction ability as well as the compressive strength and the water and air resistance of the mixes A and B.

Particular tests such as the CANTABRO test which makes it possible to evaluate the weight loss of the test piece to wear, and a creep / relaxation test were carried out on the asphalt mix. In fact, the CANTABRO test consists to mold cylindrical test pieces of about 1300 g, then to use them at a chosen temperature of 18 ° C in a rotating drum of Los Angeles type. The weight loss of each test piece is then measured after wear. The lower the loss, the more resistant the asphalt is considered to be. The results presented in Table IV demonstrate better resistance of the bituminous mix of the invention to this test than of bituminous mixes used before the invention.

In addition, noise measurements were made on different test sections corresponding to city roads and intercity links.

The principle adopted is to compare two coatings between them. For example, the old pavement and the new pavement according to the invention are compared, or even different pavements on the same route. The measurements were made according to the so-called "near field" method which consists in measuring the rolling noise of a light vehicle thanks to an on-board microphone positioned near a wheel, far from engine and exhaust noise. . Rolling noise (noise generated, less noise absorbed) is thus measured by eliminating other noise sources located much further away. Such a method therefore makes it possible to characterize a coating, even on an urban site, independently of its environment. This test has been put on. developed by the Regional Laboratory of Eastern Paris which carried out the measurements, the results of which are presented below.

In cities, the reference speed is 50 km / h. Three sections were the subject of measurements. The results are:

The gains are clearly higher than 4 dBA, which corresponds to a reduction in noise of more than 70%.

On a section of a departmental road, the applied surface layer is a conventional 0/10 bituminous concrete. However, the crossing of a hamlet was treated with a mix according to the invention.

Measurements are made at 90 km / h on this type of test road.

The mix of the invention allows to gain more than 4 dBA compared to an old coating and 3 dBA compared to a new 0/10 bituminous concrete.

The production of the bituminous mix in accordance with the invention can be carried out in batch type plants or alternatively, in continuous type plants using a drum-dryer-mixer shown, by way of example, in the single Figure.

In a plant equipped with a drum-dryer-mixer, the bituminous mix of the invention is obtained in the steps of dosing the aggregates, adding a filler, drying these materials, dosing a bitumen and adding this bitumen to the aggregates, dosing and adding rubber powder, mixing all the materials and dedusting the bituminous mix obtained. In the drum-dryer-mixer 1, the mixture of gravel and fine fines is dried and then mixed with bitumen from a binder storage tank and rubber from a hopper 2. The rubber and the bitumen are advantageously added to the mixture by means of two lances 3, 4 whose outlet nozzles are arranged upstream of a recycling ring 5, and kneaded with all of the bituminous mix compounds.

TABLE I

TABLE II

TABLE III

Comparison between two mixtures of the invention with 1 and 2% KU

KU = rubber crumb r / R = Duriez reduction coefficient

K = richness modulus calculated according to the method of the invention

TABLE IV

(*) DURIEZ-LCPC simple compression test according to NF P98-251-1 (**) CANTABRO test according to Spanish standard NLT 352/86 TABLE IV (continued)

Claims

1. Bituminous hot mix intended to constitute a road wearing course, comprising a granular mixture of discontinuous particle size and, as binder, a bitumen, the granular mixture comprising as constituents i, gravel, a sandy fraction and powder of rubber, the sandy fraction and the rubber powder taken together having a volume less than the interstitial volume of the gravel, characterized in that the particle size of the rubber powder is less than 1.5 mm and in that the percentage of rubber in the granular mixture is less than 1.5% by mass.

2. A mix according to claim 1, characterized in that the particle size of the rubber powder is less than

1 mm for 90% of the particles.

3. A mix according to claim 1, characterized in that the percentage of rubber in the granular mixture is between 0.5 and 1%.

4. A coating according to any one of claims 1 to 3, characterized in that the particle size composition of the granular mixture is determined according to the formula

where B _j : percentage of passers by volume of the mixture with a sieve j

A, _] : percentage of by-passers by mass of component i through sieve j

Vi: proportion by volume of constituent i

5. Asphalt mix according to any one of claims 1 to 4, characterized in that the bitumen content L of the total mass of the mix is determined according to the formula

L = K α ^» V∑ in which the quantity K represents a richness modulus having a value between 3.5 and 4.5, α is a coefficient correcting the density V; real of the constituents i and Σ represents a conventional specific surface of the constituents i, this specific surface Σ being obtained by the definition 1 00 Σ = 0.25 G + 2.3 S + 12 s + 135 f + 450 KU with the weight proportions following:

G of grains larger than 6.3 mm

S des. grains from 6.3 mm to 0.315 mm s from grains from 0.315 mm to 0.08 mm f from grains less than 0.08 mm

KU of rubber particles

6. Asphalt mix according to claim 5, characterized in that the richness module K has a value between 3.8 and 4.2.

7. Method for manufacturing a hot bituminous mix intended to constitute a road wearing course and comprising a granular mixture of discontinuous particle size and, as binder, a bitumen, the granular mixture comprising gravel, a sandy fraction and rubber powder, the method comprising the steps of bringing the gravel and the sandy fraction to the coating temperature and kneading them with the binder in order to produce the bituminous mix, characterized in that the rubber powder is added in a percentage of less than 1.5% by volume of the granular mixture, the particles of the rubber powder having a size of less than 1.5 mm.

8. Method according to claim 7, characterized in that the rubber powder is pretreated by micronization of bitumen and in that the amount of bitumen added during kneading is corrected so as to take into account the bitumen content of the powder of micronized rubber.

9. Method according to claim 7 or 8, characterized in that, before the rubber powder is added to the mixture of gravel and the sandy fraction, its moisture content is measured and then, if necessary, corrected so as not to exceed 1% by mass.

1 0. Process for producing a road surface layer with a bituminous mix according to any one of claims 1 to 6 or obtained by implementing a manufacturing process according to any one of the claims 7 to 9, comprising the steps of spreading a bonding layer on the road intended to receive the wearing course, spreading a layer of said bituminous mix and compacting this layer of bituminous mix.