ES2560895B2 - PROCEDURE AND MANUFACTURING PLANT OF TEMPERED BITUMINOUS BLENDS WITH RECOVERED MATERIAL OF BITUMINOUS BLENDS - Google Patents

Abstract

Procedure and manufacturing plant for tempered bituminous mixtures with material recovered from bituminous mixtures (MRMB) with the possibility of recycling up to 100% of said material. The procedure comprises the following steps: a) Provide MRMB with a particle size between 0 and a maximum diameter; b) Treat said MRMB to obtain at least two fractions of MRMB (one thin and one thick); c) Subject predetermined amounts of said MRMB fractions to a process of mixing and heating by flow of hot gases so that the heating times of each fraction are adapted to their particle size and that the temperature of the mixture at the end of the step is between 90 ° C-120 ° C; d) Knead the mixture obtained in the previous step with a predetermined amount of bituminous emulsion supplied at a temperature between 60 ° C and 80 ° C. The final mixture after step d) will reach a temperature between 90-110 ° C. The invention also comprises a plant for executing said method.

Description

Procedure and manufacturing plant for tempered bituminous mixtures with material recovered from bituminous mixtures

FIELD OF THE INVENTION

This invention relates to a method of manufacturing tempered bituminous mixtures to form the upper layers of road surfaces and other road infrastructure using material recovered from damaged and / or aged layers of bituminous mixtures, with the possibility of using a rate of up to 100% recovered material. The invention also encompasses a manufacturing plant for executing said process.

BACKGROUND OF THE INVENTION

In general terms we can define a bituminous mixture as a combination of bitumen (also called asphalt) and stone mineral aggregates in predetermined proportions that determine its physical properties and, eventually, its performance for a given use.

The conservation of road heritage involves planned rehabilitation and conservation operations to maintain its adequate structural durability and functional response. In the most widespread type of pavement, that of bituminous pavements, one of the most common and frequent operations is the milling and removal of deteriorated and / or aged layers and their replacement (replacement) by new layers using newly manufactured bituminous mixtures .

The product generated by milling of deteriorated and / or aged bituminous mixtures is usually called "RAP", using the acronym of the Anglo-Saxon denomination of said material (Reclaymed Asphalt Pavement) or MRMB (Recovered Material of Bituminous Mixtures) which will be the term that we will use onwards.

The MRMB is made up of materials of high technical and economic value, so its reuse or recycling is desirable. Hot manufacturing processes of bituminous replacement mixtures are known that can use a certain percentage of MRMB (up to about 50%) but not 100% because the high temperatures reached during the hot manufacturing processes (approximately between 160 ° C -180 ° C) deteriorate ("burn") the bitumen present in the MRMB thus damaging its properties.

Methods of manufacturing cold bituminous mixtures with bituminous emulsion that allow 100% MRMB to be used are known. However, these mixtures have important drawbacks such as the need for a curing period (which is usually a minimum of one year) and the weakness of their mechanical performance in the first moments after putting them into work. For these reasons, when these procedures are used, it is essential to add an additional rolling layer on top of the layer in which MRMB is being used.

For its part, the use of MRMB is not contemplated in the known processes of manufacturing tempered bituminous mixtures such as that described in patent ES 2 368 980 A 1.

Consequently, there is currently a large surplus of MRMB that is treated as a waste with the economic and environmental disadvantages that this entails.

The present invention is oriented to the solution of that problem.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide manufacturing processes for bituminous mixtures with a high level of mechanical and functional performance that allow a MRMB recycle rate of up to 100%.

Another objective of the present invention is to provide manufacturing processes for bituminous mixtures that allow reducing their cost with respect to known procedures.

Another objective of the present invention is to provide manufacturing plants for the execution of the mentioned processes.

In a first aspect, these and other objectives are achieved with a continuous process of manufacturing bituminous mixtures from Recovered Bituminous Mixture Malerial (MRMB) and a bituminous emulsion comprising the following steps:

a) Provide MRMB of a particle size smaller than a maximum diameter "D3" determined by the sieves of the mill to be used;

b) Treat said MRMB to obtain at least two MRMB fractions whose maximum sizes are not larger than D1 mm and D2 mm;

e) Subject predetermined amounts of said MRMB fractions to a process of mixing and heating by flow of hot gases so that the heating times of each fraction are adapted to their particle size, being shorter and with less intensity of exposure for a smaller fraction (because it has a greater amount of binder adhered to the aggregate, since it has a greater specific surface area than the larger aggregate, thus preventing the deterioration of the binder due to the exposure of hot gases) than for a larger one (which has a lower amount of binder and may be exposed to hot gases for longer without deteriorating the binder), and that the temperature of the mixture at the end of the step is between 90 ° C-120 ° C;

d) Knead the mixture obtained in the previous step with a predetermined amount of bituminous emulsion supplied at a temperature between approximately 60 ° C and 80 ° C. The final mixture after step d) will reach a temperature between 90110 ° C.

Advantageously, the granulometry of the first fraction is between Omm and 7mm (and more advantageously between Omm and 5mm) and the granulometry of the second fraction is between 4mm and 30mm (and more advantageously between 5mm and 25mm.

The procedure admits the incorporation of virgin aggregate into the mixture to improve its properties. Also, if desired, to make mild mixtures with an MRMB recovery rate of less than 100%.

In cases where 100% of the starting material is MRMB the amount of bitumen emulsion is between 2.5% -3% by weight of the total bituminous mixture, providing a bitumen percentage much lower than necessary when Recycled materials are not used.

In a second aspect, the aforementioned objectives are achieved with a plant for the manufacture of bituminous mixtures from Material Recovered from Bituminous Mixtures (MRMB) and a bituminous emulsion comprising:

a) a unit for pretreatment of material from old firms, either by milling or by demolition of a bituminous pavement, in which the material of more than a maximum diameter D3 is rejected. The fraction between approximately a diameter of 02 mm and 03 mm is fed to a crushing mill. The fraction smaller than 02 mm is taken directly to the exit screen together with the product of the crushing mill. This crushing mill separates, with the minimum possible fragmentation of the stone matrix, the fractions joined by the binder, that is, what it really does is "take off" them. This pretreatment unit can incorporate a magnetic separator that prevents the entry of spikes or metal remains present in the material to be fed. The product of this stage that is obtained in the output screen are two or more fractions of MRMB at room temperature.

b) a first hopper for a first MRMB fraction with a granulometry whose maximum size is not larger than 01 mm, a second hopper for a second MRMB fraction with a granulometry whose maximum size is not larger than 02 mm and an emulsion tank bituminous provided with metering devices of the material contained in them;

c) a drying drum with the burner delayed for heating and mixing of materials configured as a parallel flow drum, in which the material to be heated and the hot gases coming from its combustion chamber circulate in the same direction, and provided with two material inputs at a different distance from its combustion chamber;

d) a first transport device (for example a conveyor belt) arranged to transport predetermined quantities of the first MRMB fraction to the inlet of the drying drum furthest from its combustion chamber and a second transport device (for example a belt conveyor) arranged to transport predetermined quantities of the second fraction of MRMB to the inlet of the drying drum closest to the combustion chamber;

e) a kneader, to knead the mixture made in the drying drum with a predetermined amount of bituminous emulsion - coming from the bituminous emulsion tank that is arranged so that it receives by gravity the mixture made in the drying drum.

Advantageously, the drying drum comprises a controlled recirculation system of a part of the effluent fumes and is provided with a bag filter for the treatment of non-recirculated fumes.

Advantageously, the kneader comprises a system for measuring its energy consumption that allows estimating the humidity of the final bituminous mixture.

The plant may also comprise a device for raising the kneaded product to a waiting hopper, thus adapting the continuous flow of the installation to the discontinuous of the trucks. The lifting device can be, for example, a racket elevator. For long waiting times, instead of a hopper, a larger silo can be used, heated and heated at its base.

The plant can also comprise a third and fourth irid aggregate hoppers connected to the second transport device so that it can also transport predetermined quantities of virgin aggregate to the drying drum. The granulometry of the virgin aggregate will be the one necessary to obtain the final granulometry of the desired mixture with the percentages determined in the working formula obtained in the laboratory.

The third and fourth hoppers can also be used alternatively for a third and a fourth fraction of the MRMB if more than two fractions of recycled material are to be used in the manufacturing process.

Other features and advantages of the present invention will be apparent from the following detailed description of illustrative embodiments of its object in relation to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a functional diagram illustrating an embodiment of the manufacturing process of tempered bituminous mixtures object of the invention.

Figure 2 is a schematic plan view illustrating the main components of the manufacturing plant for tempered bituminous mixtures object of the invention.

Detailed description of the invention

The continuous manufacturing process of temperate bituminous mixtures with MRMB

We will describe in detail below the steps of the process of the invention following Figure 1.

a) The first step is to provide MRMB of a particle size of less than 03 mm, thus rejecting the MRMB of more than this diameter. Preferably, the particle size will be between Omm and a D3 value of less than 60mm.

b) In the second step the MRMB is treated to obtain at least two fractions f1 and f2 whose maximum sizes are not larger than 01 mm and 02 mm, which are arranged in preparations A1 and A2. Preferably, the value of D1 will be less than 7 mm and the value of 02 will be less than 30mm.

This treatment can be carried out by means of a first shredding operation of the MRMB between 02 and 03 in, for example, a tearing mill and a second screening operation of the shredded material and the rest of the MRMB (less than 02) to obtain said two fractions f1 and f2 of MRMB. It is important to note that the tearing mill separates the MRMB with the minimum fragmentation of the stone matrix, that is, what it really does is "detach" the aggregates joined by the bitumen.

The treatment of this step may also include the separation of metallic materials present in the MRMB by magnetic separators.

Preferably, the first fraction f1 has a particle size between O and 7mm (and more preferably between Omm and 5mm) and the second fraction f2 has a particle size between 4mm and 30mm (and more preferably between 5mm and 25mm).

At the end of the step, two (or more) MRMB fractions are obtained at room temperature, with two (or more) clearly differentiated granulometries and in which the humidity has been significantly reduced. In this way, the amount of bitumen present in each fraction of the MRMB can be calculated more accurately and with that information the working formula of the final bituminous mixture and the amount of bituminous emulsion to be added in the fourth step can be optimized.

c) In the third step, predetermined amounts of the fractions f1, f2 of MRMB (and in the case of other fractions) obtained in the previous step are subjected to a process of mixing and heating by flow of hot gases so that the times of heating are lower for the MRMB fractions of smaller size and that the temperature of the mixture is between 90 ° C-120 ° C at the end of this step c).

In one embodiment of the procedure, the execution of this step is carried out by first feeding hoppers T1, T2 destined for fractions f1, f2 of MRMB provided with dosing devices D1, D2 from the preparations A 1 and A2; supplying, in second term, predetermined amounts of said fractions f1, f2 to transport devices, for example feeder belts 81, 82 that take them to two differentiated inlets of a drying drum TS where said fractions are mixed and heated differently thus allowing a 100% recycling rate of MRMB for the reasons stated above.

Thus, in the process of the present invention the MRMB is heated directly but it is done so as not to affect the bitumen present therein.

The heating of the two fractions f1, f2 is carried out by contact with a flow of hot gases ac (avoiding contact with the flame that takes place in the counter-flow drying drums used in bituminous plants such as that described in the patent ES 2 368 980 A 1) And the heating time is different for the two fractions f1 and f2, by entering them at different points of the drying drum T8 to accommodate their different particle size and, therefore, the different amounts of binder ( bitumen) so as not to affect its properties.

The fraction f2, with the thickest MRMB, is introduced by the closest inlet to the hot gas source ae (at the beginning of the drying drum TS) as more time is needed to transmit the required amount of heat to the thickest fraction. The fraction f1, with the finest aggregate, is introduced through the furthest inlet of the source of hot gases ae which is located at an appropriate point of the drying drum TS so that the fraction f1 reaches the required temperature at the outlet of the drum TS drying that is between 90-120 ° C.

In addition to fractions f1 and f2 of MRMB, this step may include an additional fraction of virgin aggregate to improve the characteristics of the bituminous mixture. Where appropriate, this material would be supplied to the drying drum TS through the feeder band 82 used for fraction f2 of the MRMB. The granulometry of the virgin aggregate will be the one necessary to obtain the final granulometry of the desired mixture with the percentages determined in the working formula obtained in the laboratory. Alternatively, instead of using virgin aggregate, this step can include a third and fourth fraction f3 and f4 of the MRMB in case more than two fractions of recycled material are to be used in the manufacturing process. Preferably, the granulometries of the third and a fourth fraction f3 and f4 will be between 01 mm and 02 mm. Where appropriate, this material would be supplied to the drying drum TS also through the feeder belt B2 used for fraction f2 of the MRMB.

d) In the fourth step, the mixture obtained in the previous step is kneaded with a predetermined amount of bituminous emulsion supplied at a temperature between 60DC and BODC.

The mixture f1 + f2 obtained in the previous stage is discharged into an AM bitumen mixer or kneader where it is kneaded together with a preset amount of bituminous emulsion eb that is received at 60-BO ° C from a T3 tank equipped with a dosing device 03. In the present process when 100% MRMB is used as the starting material, the amount of bituminous emulsion eb is comprised between 2.5-3% by weight.

The bituminous mixture mb obtained after the fourth step can be supplied directly to a means of transport to take it to its destination or stored, by means of some lifting device in a hopper or waiting silo, which may be heated and heated.

The manufacturing plant for temperate bituminous mixtures with MRMB

We will describe in detail below an embodiment of the bituminous mixture manufacturing plant according to the invention using two MRMB fractions and, where appropriate, virgin aggregates following Figure 2.

Its fundamental components are the following:

Pretreatment unit (not shown in the figure) In a pretreatment unit of the material coming from the milling or demolition of a bituminous pavement (coming from old firm) the material of more than D3 mm is rejected. The fraction between approximately 02 mm and D3 mm is fed to a shredding mill, while the fraction smaller than 02 mm is taken directly to the outlet screen together with the product of the tearing mill. This tearing mill separates the MRM8 with minimal fragmentation of the stone matrix, that is, what it really does is "peel off" the fractions bound by the binder. This pretreatment unit can incorporate a magnetic separator that prevents the entry of spikes or metal remains present in the material to be fed. The product of this stage that is obtained in the exit screen are two or more fractions of MRM8 at room temperature. The values of 03 and 02 will depend on the size of the installation and the final material to be obtained, being usual values for 03: 60 mm and for 02: 30 mm.

Hoppers 1, 2, 3, 4 They are hoppers, with level and weight control contained in each of them and independent weighing feeders for the dosing of their content. Hoppers 1 and 2 are intended for the storage of, respectively, the fine fraction and the thick fraction of the MRMB that are produced in a pre-treatment unit of the MRMB. Hoppers 3 and 4 are intended to store virgin aggregates of different grain sizes that can also be used as starting materials for the manufacture of bituminous mixtures (either to improve the mixture with 100% MRMB or for mixtures with rates less than 100% of recycled material). Alternatively, the third and fourth hoppers can also be used for a third and a fourth fraction of the MRMB if more than two fractions of recycled material are to be used in the manufacturing process.

Drying drum 5 In a preferred embodiment it is a parallel flow drum (equi-current), driven by electric motors and fuel oil burner (although any other fuel such as gas can be used). Its combustion chamber 6 is arranged in a delayed position and has two entrances or rings in different positions. The closest to the combustion chamber 6 is intended for the thickest fraction / s of the MRMB and, where appropriate, for the virgin aggregates and the furthest for the finest fraction of the MRMB. The latter must be located at a point of the drying drum 510 furthest possible from the burner (to damage the bitumen as little as possible) but at a point that allows said fraction to reach the required temperature at the outlet of the drying drum that is between 90 ° C-120 ° C.

Its configuration with delayed flame and its great length allow to increase the residence time of the MRMB fractions to achieve the necessary heat transfer while avoiding direct contact of the MRMB with the flame. Being a parallel flow drum dampens the extreme temperature contacts to the materials fed to it. Materials and hot air circulate in the same direction unlike what happens in the drying drums of many bituminous plants and, in particular, the one described in ES 2 368 980 A1.

It is provided with frequency inverters that allow the rotation speed to be modified.

It is connected to a bag filter 13 with exhaust fan, to reduce harmful emissions and at the same time favor the combustion of the flame.

As it is a parallel flow drum - less thermally efficient than a counter-flow drum - it includes a recirculation system for effluent fumes. That is, a certain percentage of the exhaust fumes of the drying drum 5 are not sent to the bag filter 13 but are recirculated into the drying drum 5 by means of a system of recirculation ducts and solenoid valves.

The combustion gases can be mixed at the beginning of their cycle: they can be wrapped with a part of recirculated gases and another of fresh air by means of a tangential fan that creates the turbulence necessary for homogeneous heating (the amount of fresh air

can be modulated). With this partial gas recirculation system, the efficiency of the drum in equi-current or in parallel is improved.

The combination of the delayed burner (and therefore the absence of direct contact with the flame) and an adequate control of the temperature through the partial recirculation of the fumes, makes the treatment of the bitumen present in the MRMB very careful, not damaging it and enabling its reuse.

The burner of the drying drum 5 is fed with fuel oil (although any other fuel such as gas can be used) by means of a pump from a tank at approximately 40 ° C and this is filtered through passage filters.

-

Transport devices 7, 8 from hoppers 1, 2; 3, 4 to the drying drum 5. The quantities required at all times of the thin and thick fractions of MRMB are delivered, respectively, to transport devices 7, 8 (in the example shown in Figure 2 are conveyor belts) as well as , where appropriate, the virgin aggregates to the transport device 8 by means of dosing devices (band feeders with integrated frequency inverter and scale) integrated in the hoppers 1, 2, 3, 4 And said transport devices lead them to the drum of drying 5. The transport device 8 is connected to the inlet of the drying drum 5 closest to the combustion chamber 6 and the transport device 7 is connected to the farthest inlet.

Bitumen emulsion tank 10. It is a heated and heated tank with sufficient capacity to store the bitumen emulsion for the process. It is connected to a pump driven with a frequency inverter and governed by a control system (PID) that is based on the readings of a flowmeter to supply the bitumen emulsion to the mixer 9.

-

Kneader 9. The kneader 9 receives the flow of output material from the drying drum 5 and the bituminous emulsion of the tank 10 at a temperature between 60-80 ° C. The kneader 9 is arranged under the drying drum 5 so that it can receive by gravity the mixture of the MRMB fractions (and, where appropriate, of virgin aggregates) reaching the final mixture at a temperature between 90-1100C. It is therefore a different arrangement to that of temperate bituminous mix plants as described in ES 2 368 980 A 1.

5 The mixer 9 includes an energy consumption measurement system to estimate, using appropriate correlation tables, the humidity of the final mixture. This parameter is essential, therefore, to ensure adequate compaction at work, it is necessary that the humidity of the mixture ranges between 0.5 and 11%.

10 The installation foresees the possibility of adding water to the mixer to achieve the desired humidity in the final mixture.

-

Device 11, 12 for evacuation of the bituminous mixture. The bituminous mixture leaving the mixer 9 is carried to a waiting hopper 12 15 by means of a lifting device such as, for example, a booster

eleven.

Although the present invention has been described in connection with various embodiments, it can be seen from the description that various combinations of elements, variations or improvements can be made therein and that are within the scope of the invention defined in the appended claims.

Claims (20)

1. Continuous process of manufacturing tempered bituminous mixtures from recovered material from bituminous mixtures (MRMB) and a bituminous emulsion, characterized in that it comprises the following steps: a) Provide MRMB of a particle size between O and D3 mm; b) Treat said MRMB to obtain at least two fractions of MRMB whose maximum sizes are not larger than 01 mm and D2 mm; e) Subject predetermined amounts of said MRMB fractions to a process of mixing and heating by flow of hot gases so that the heating times and the intensity of exposure of each fraction are adapted to its particle size, being shorter for a fraction smaller than for a larger one, and that the temperature of the mixture at the end of the step is between 90 'C-120' C; d) Knead the mixture obtained in the previous step with a predetermined amount of bituminous emulsion supplied at a temperature between approximately 60De and BODe, reaching the final mixture after step d) a temperature between 90110 'C.

2.

Continuous process of manufacturing tempered bituminous mixtures according to claim 1, characterized in that the rate of recovered material is 100%

3.

Continuous process of manufacturing bituminous mixtures according to any one of the preceding claims, characterized in that in step b) a first fraction of MRMB of a particle size between Omm and D1mm is obtained, and a second fraction of MRMB of a particle size between D1mm and D2mm.

4. Continuous process for manufacturing tempered bituminous mixtures according to any one of the preceding claims, characterized in that in step b) the maximum size of the first fraction D1 is less than 7mm, preferably less than Smm

5.

Continuous process of manufacturing tempered bituminous mixtures according to any one of the preceding claims, characterized in that in step b) the maximum size of the second fraction 02 is less than 30mm, preferably less than 25mm.

6.

Continuous process of manufacturing tempered bituminous mixtures according to any one of the preceding claims, characterized in that, when 100% MRMB is used as the starting material, the amount of bituminous emulsion is comprised between 2.5% -3% by weight of the total bituminous mixture.

7.

Continuous process of manufacturing tempered bituminous mixtures according to any one of the preceding claims, characterized in that the input material to step e) also comprises a predetermined amount of virgin aggregate.

8. Continuous process of manufacturing tempered bituminous mixtures according to any one of the preceding claims, characterized in that the input material to step e) also comprises a third and a fourth fraction of the MRMB in case more than two fractions of recycled material are to be used in the manufacturing process.

9.

Continuous process of manufacturing tempered bituminous mixtures according to any one of the preceding claims, characterized in that step c) provides for the recirculation of a part of the effluent fumes and filtration for the treatment of non-recirculated fumes.

10.

Continuous process of manufacturing tempered bituminous mixtures according to any one of the preceding claims, characterized in that step d) provides for the measurement of its energy consumption and the addition of water.

eleven . Plant for the production of tempered bituminous mixtures from recovered material from bituminous mixtures (MRMB) and a bituminous emulsion characterized in that it comprises: a) a unit for pretreatment of material from old firms in which the material of more than 03 mm is rejected and the fraction between approximately 02 mm and 03 mm is fed to a shredding mill, while the smaller fraction of 02 mm is taken directly to an exit screen together with the product of the crushing mill, the product obtained in the exit screen being two fractions of MRMB at room temperature b) a first hopper (1) for a first MRMB fraction with a grain size whose maximum size is not larger than 01 mm, a second hopper (2) for a second MRMB fraction with a grain size whose maximum size is not larger than 02 mm and a bitumen emulsion tank (10) provided with metering devices of the material contained therein; c) a drying drum (5) with a delayed burner for heating and mixing materials configured as a parallel flow drum, in which the material to be heated and the hot air from its combustion chamber (6) circulate in the same address, and equipped with two material inputs at a different distance from its combustion chamber (6); d) a first transport device (7) arranged to transport predetermined quantities of the first MRMB fraction to the inlet of the drying drum (5) furthest from its combustion chamber (6) and a second transport device (8) arranged to transport predetermined amounts of the second fraction of MRMB to the inlet of the drying drum (5) closest to the combustion chamber (6); e) a kneader (9), to knead the mixture made in the drying drum (5) with a predetermined amount of bituminous emulsion from the bituminous emulsion tank (10), which is arranged so that it receives by gravity the mixture made in the drying drum (5).

12.

Plant for manufacturing tempered bituminous mixtures according to claim 11, characterized in that the transport devices (7) and (8) are conveyor belts.

13.

Plant for the production of tempered bituminous mixtures according to claim 11, characterized in that the drying drum (5) comprises a recirculation system of a part of the effluent fumes and a filter (13) for the treatment of non-recirculated fumes.

14.

Plant for manufacturing tempered bituminous mixtures according to claim 13, characterized in that the filter (13) for the treatment of non-recirculated fumes is a bag filter.

fifteen.

Plant for the manufacture of tempered bituminous mixtures according to any of claims 11-14, characterized in that the mixer (9) comprises a system for measuring its energy consumption that allows estimating the humidity of the final bituminous mixture.

16.

Plant for manufacturing tempered bituminous mixtures according to any of claims 11-15, characterized in that the necessary means for adding water to the mixer (9) have been provided to achieve the desired humidity in the final bituminous mixture.

17.

Plant for manufacturing tempered bituminous mixtures according to claim 11, characterized in that it includes two devices 11, 12 for lifting and storing the final bituminous mixture.

18.

Plant for manufacturing tempered bituminous mixtures according to any of claims 11 ~ 17, characterized in that it also comprises a third and a fourth hopper (3, 4) connected with the second transport device (8) so that it can also transport predetermined quantities from the material stored in the third and fourth hoppers (3, 4) to the drying drum (5).

19.

Plant for manufacturing tempered bituminous mixtures according to claim 18, characterized in that the third and fourth hoppers (3, 4) are intended to store virgin aggregate.

twenty.

Plant for the manufacture of tempered bituminous mixtures according to claim 18, characterized in that the third and fourth hoppers (3, 4) are intended to store a third and a fourth fraction f3 and f4 of the MRMB in case they want to be used in the Manufacturing procedure more than two fractions of recycled material.