FR3090682A1 - Bituminous mix preparation process - Google Patents

Abstract

The invention relates to a process for the preparation of bituminous mixtures in granular form which are not bound by mixing, at room temperature, aggregates and solid particles of a bituminous binder, with a particle size of less than approximately 1 mm. The invention also relates to the preparation of bituminous mixes from said bituminous mixtures.

Description

Description

Title of the invention: Process for the preparation of bituminous mixes

Technical field of the invention

The present invention relates to the field of bituminous mixes, in particular those intended for road construction sites. The invention relates more particularly to a bituminous mixture in unbound granular form which allows a bituminous mix to be reconstituted in situ by heating and mixing.

State of the art

Conventional methods for manufacturing bituminous mixes consist in heating the constituents before or at the time of mixing by mixing. After leaving the mixer, the temperature of the mixture rapidly decreases irreversibly depending on the atmospheric conditions. The operations of storage, transport and use of the mixture must therefore be carried out within a short time imposed before the temperature of the mixture decreases below the workability threshold. In the context of roadworks, this limited total duration generates very strong logistical and organizational constraints throughout the downstream part of the production chain from storage to use. This limited total duration also induces great vulnerability in the production chain; a one-off incident on just one of its elements affects the whole. On the other hand, the added value of production controls remains limited to an observation because they are carried out after the irreversible stage of hot mixing. If an anomaly is detected during these checks, the scope for corrective action remains very limited. Finally, the energy input by heating at the kneading stage is high because the period during which the temperature of the mixture must be maintained above the workability threshold includes the stages of storage, transport and implementation .

Application ER-A-3,045,648 describes a solid bitumen material at room temperature capable of being obtained by a process comprising the following steps: a) preparing an emulsion of bitumen drops in an aqueous phase, said bitumen comprising less than 1.4% of solid particles by mass relative to the total mass of bitumen base, b) preparing a silica sol or a silica gel from a silicon oxide precursor at pH ranging from 4 to 8, c) bringing the bitumen emulsion of step a) into contact with the silica sol or the silica gel of step b), and d) subjecting the bitumen suspension resulting from the step c) to an atomization treatment. This bitumen material can be used as a road binder for the manufacture of bituminous mixes by heating aggregates at a temperature ranging from 100 to 180 ° C and mixing the aggregates thus heated with the solid bitumen material.

Application WO 2018/046837 describes a process for manufacturing a material usable as a road binder, solid at room temperature in the form of granules, comprising a core based on a first composition comprising at least one bitumen base and optionally a layer coating based on a second composition. This method is implemented using a device for granulation which comprises at least two coaxial drums and a horizontal tread, the method comprising the following steps: (i) heating the first composition to a temperature at which it is fluid, (ii) the introduction of the first composition in the fluid state into the inner drum of the granulation device, (iii) the distribution of the first composition to the outside, in the form of drops at the through orifices of the external rotary drum, (iv) depositing the drops on the tread, and (v) optionally coating the drops with the second composition.

Application FR-A-3,032,961 describes a process for the preparation of cold bituminous coatings comprising the steps of: (i) preparation of a bituminous binder in the form of a cationic bitumen emulsion, (ii) preparation an aggregate comprising at least a first fraction of aggregate coated with lime, and (iii) forming said cold bituminous coating formed from at least said aggregate interpenetrated in said binder.

An objective of the present invention is to provide a material which can be used as road material, such as a road bituminous mix, which can be manufactured, stored, transported and used independently. Another objective of the present invention is to provide a material which can be used as a road material, such as a road bituminous mix, which can be obtained with a reduced energy supply.

Description of the invention

According to a first aspect, the invention relates to a process for preparing a bituminous mixture in unbound granular form which comprises:

a) the preparation of solid particles of a bituminous binder, with a particle size of less than about 1 mm;

b) mixing, at room temperature, the solid particles of bituminous binder thus obtained with aggregates.

The term “bituminous binder” is understood to mean any bituminous composition consisting of one or more bitumen bases and possibly one or more chemical additives, said composition being intended for road application.

The term “bitumen base” is understood to mean bitumens of natural origin, those contained in deposits of natural bitumen, natural asphalt or the tar sands and the bitumens obtained from the refining of crude oil. The bitumen bases according to the invention are advantageously chosen from bitumen bases originating from the refining of crude oil. The bitumen bases can be obtained by conventional methods, in particular by direct distillation and / or vacuum distillation of petroleum.

In one embodiment, the bitumen base comprises one or more additives commonly used in the road sector, such as crosslinked polymers or not (EVA, SBS, etc.) or non-petroleum additives.

As bituminous binder capable of being used in the context of the present invention, mention may in particular be made of those sold by the company Total under the name Azalt®.

Initially, the bituminous binder is put in the form of fine solid particles, of particle size less than about 1 mm, preferably included in the range of about 200 pm to about 800 pm (these dimensions having been determined visually by light microscopy).

To do this, the bituminous binder is heated to a temperature allowing its flow, typically between about 100 ° C and about 140 ° C. The hot bituminous binder is then poured into plates or bars, the thickness of which can vary from a few mm to 1 or 2 cm. The bars or plates obtained are then cooled to a temperature such that the bituminous binder has a brittle fracture, typically a temperature ranging from approximately -5 ° C to approximately -40 ° C, advantageously from approximately -10 ° C to approximately

-30 ° C. The bituminous binder bars or plates which have become fragile are then ground, also at a temperature ranging from about -5 ° C. to about -40 ° C., so as to obtain the particle size distribution of solid bituminous binder particles desired, typically a smaller particle size about 1mm, preferably in the range of about 200 µm to about 800 µm.

The solid particles of bituminous binder having the desired particle size are maintained at the grinding temperature before being mixed, in a second step, with aggregates at room temperature. The mixing is carried out so as to obtain a coating of the bituminous binder particles with the fines of the granular fraction and to ensure a homogeneous dispersion of these bituminous binder particles in the mixture. The mixing can be carried out in a conventional manner in a kneader or a kneading drum, for a period of approximately 1 min to approximately 3 min.

In one embodiment, the mixture (solid particles of bituminous binder + aggregates) comprises approximately 2% by mass to approximately 10% by mass, preferably approximately 4% by mass to approximately 8% by mass, of solid particles bituminous binder.

In one embodiment, the aggregates comprise approximately 3% by mass to approximately 10% by mass, preferably approximately 3% by mass to approximately 8% by mass of fines.

In one embodiment, the aggregates belong to a granular class d / D expressed according to the standard EN 13043 with lower dimensions d and higher D sieves from 0/2 to 0/20 and / or sieves from 2 / 4 to 10/14, in particular a granular class chosen from classes 0/2, 0/4, 0/6, 0/8, 0/10, 0/14, 0/20, 2/4, 2/6, 4/6, 6/10, 10/14 and their mixtures.

The method described above makes it possible to dissociate the stages of manufacture, storage, transport and use of the bituminous mixes, so that the transport, storage and use times can be managed independently of each other. others. In the case of road construction sites, this separation makes it possible to reduce logistical and organizational constraints throughout the downstream part of the production chain from storage to use. This dissociation of the time constraint improves the resilience of the production chain to a specific incident affecting only one of its elements. On the other hand, this dissociation facilitates production controls and increases their added value because the majority of them can be performed, without time constraints, on the unbound material stored. If an anomaly is detected during these checks, a corrective action is therefore possible unlike the case of the conventional process for which the checks are carried out after the irreversible step of hot mixing of the aggregates and the binder. Finally, the energy input by heating is reduced because, hot mixing can be carried out on or as close as possible to the implementation site, the period during which the temperature of the mixture must be maintained above the threshold of workability after hot mixing is also reduced (no heating is required for storage and transport). The additional energy required to form the binder into particles is low since this binder represents only a small part of the mixture, typically less than 10% by mass. The process according to the invention also allows the packaging of bituminous mixtures in unbound granular form in transportable and storable bags, in particular in the form of "big bags".

The bituminous mixture in unbound granular form obtained by the process described above can be used to prepare bituminous mixes on conventional road works. The usual normalized characteristics of the bituminous mixes obtained (compactability, water sensitivity, rut resistance, stiffness modulus and fatigue resistance) are not significantly affected by the process described above.

In another aspect, the invention relates to a process for the preparation of bituminous mixes on the site of a construction site, in particular a road construction site, which consists in heating said bituminous mixture in unbound granular form and then in knead it.

This on-site implementation of bituminous mixes makes it possible to adapt to the lack of industrial infrastructure, especially in developing countries. Indeed, because of their flexibility of transport and storage, bituminous mixtures in unbound granular form can be produced far from their site of use and require only on the site of use heating equipment (micro- waves or other) and much less complex mixing than a conventional coating plant. On the other hand, the storage in bags of bituminous mixtures in unbound granular form makes it possible to adapt to construction sites with very low volumes such as occasional road repairs or landscaping for individuals. Finally, the storability of bituminous mixtures in unbound granular form allows demand to be adjusted to the price of bitumen by scheduling the production of bituminous mixtures in unbound granular form outside the usual period of construction of road works on which demand for bitumen is currently highly concentrated.

The invention is illustrated by the following examples, given for information only.

Examples.

Example 1: preparation of bituminous mixes

AZALT® 35/50 bitumen was heated to 100 ° C, the hot bitumen having then been poured into bars. After cooling to -18 ° C, the bars were ground in a "blender" type grinder so as to obtain solid particles of approximately 200 μm to approximately 800 μm. These solid particles were then mixed in a mixer with aggregates and fines at room temperature for 2 min, in the proportions indicated in Table 1.

[Tables 1]

Components Proportion (% by mass) Aggregates 6/10 mm 40.68 Aggregates 2/6 mm 17.03 Aggregates 0/2 mm 32.64 Fine 4.26 Bitumen 35/50 5.39

Example 2: properties of coated materials

The storage conditions, at ambient temperature, of the bituminous mixtures of Example 1 were simulated by applying, using a piston, a vertical constraint to a sample of bituminous mixtures confined in a cylindrical mold with a diameter of 80 mm. A force of 5kN was applied to the sample at a temperature of around 20 ° C. For comparison, at the base of a material storage over a height of 3m, the equivalent force would be of the order of 0.5kN. After application of the load for 5 hours, no change in the sample, once removed from the mold, is observed.

In accordance with the recommendations of standard NF EN 13108-1, the stiffness modulus and the fatigue resistance of the bituminous mixes of example 1 were determined. 2.1 Rigidity modulus

Two-point bending modulus tests at 15 ° C and 10Hz on trapezoidal test pieces were carried out in accordance with standard NF EN 12697-26 annex A on test pieces of bituminous mixes cut after heating and compacting of the material. The results obtained are presented in Table 2 and are compared with those obtained with bituminous mixes of the same composition prepared according to the conventional method, namely hot mixing of the aggregates and the bituminous binder (reference formula).

[Tables2]

Ex.l reference difference (%) IE * I at 15 ° C and 10Hz (MPa) 12959 12020 +8

As can be seen, the bituminous mixes of the invention are slightly more rigid than "conventional" mixes, but this is not significant.

2.2 Fatigue resistance

A fatigue test on trapezoidal test pieces was carried out in accordance with standard NF EN 12697-26 appendix A on test pieces of bituminous mixes but on a single level of deformation equal to that for which the reference mixes have a service life 10 ⁶ cycles. The average lifespan obtained on 4 specimens is 1,366,621 cycles. The fatigue resistance of the bituminous mixes of the invention is therefore higher (+ 36%) than that of the reference mixes despite a higher vacuum content (5.2% for 3.6%).

Claims (1)

Claims [Claim 1] Process for the preparation of a bituminous mixture in unbound granular form which comprises: a) the preparation of solid particles of a bituminous binder, with a particle size of less than about 1 mm; b) mixing, at room temperature, the solid particles of bituminous binder thus obtained with aggregates. [Claim 2] Method according to claim 1, in which step a) comprises: al) heating the bituminous binder to a temperature allowing its flow; a2) pouring the hot bituminous binder into plates or bars; a3) cooling the bars or plates obtained, to a temperature ranging from about -5 ° C to about -40 ° C; a4) grinding, in the same temperature range as in step a3), bars or plates cooled until the particle size distribution of solid bituminous binder is obtained. [Claim 3] The method of claim 1 or claim 2, wherein the particle size of the solid bituminous binder particles prepared in step a) is in the range of from about 200 µm to about 800 µm. [Claim 4] The method of any of claims 1 to 3, wherein the mixture of solid bituminous binder particles and aggregates comprises from about 2% by mass to about 10% by mass of said solid bituminous binder particles. [Claim 5] The method of claim 4, wherein the mixture of solid bituminous binder particles and aggregates comprises from about 4% by mass to about 8% by mass of said solid bituminous binder particles. [Claim 6] The method according to any of claims 1 to 5, wherein the aggregates comprise from about 3% by mass to about 10% by mass of fines. [Claim 7] The method of claim 6, wherein the aggregates comprise from about 3% by mass to about 8% by mass of fines. [Claim 8] Process for the preparation of bituminous mixes, in particular on a road construction site, which consists in heating and then kneading the bituminous mixture in unbound granular form obtained according to the process of any one of Claims 1 to 7. [Claim 9] Process for the preparation of bituminous mixes according to claim 8, in which the heating of the bituminous mixture is carried out by microwaves.