Technical Field

The present invention relates to a system and a method for separating components of concrete, in particular waste concrete, obtained by means of a dehydration on a structural level and a loss of cohesion between the components forming the concrete.

In particular, the system and the method have the purpose of obtaining, as endproducts, hydrated and dehydrated cement powder, as well as sand and gravel cleaned from the cement matrix entrapping them.

The present invention has been developed with specific reference to the field of the recycling of waste concrete deriving from building and demolition activities.

Background Art

At present, in the field of the working of minerals, the main operations are size reduction, size separation, qualitative separation and physio-chemical treatments (among which, for example, the reactions leading to the formation of concrete).

In particular, in the state of the art of the recycling of concrete, it is known to carry out a preliminary step of separating concrete from the various waste deriving from building and demolition activities. In this step, the concrete consisting of blocks with different sizing is cleaned from organic and inorganic substances and this operation can be carried out by means of a manual or mechanical sorting. After that, the concrete is subjected to a so-called primary crushing reducing it to a particle size lower than 10 cm.

During the primary crushing step, there is further provided to perform the operations of iron removal, by means of magnetic separators, in order to remove the iron rods present in reinforced concrete.

At the end of the steps of primary crushing and iron removal, a bulk product with different particle sizes lower than 10 cm, as mentioned, is obtained, the composition of which is an aggregation of sand and gravel mutually bound by a cement matrix consisting of: unreacted cement (dicalcium silicate, tricalcium silicate, tricalcium aluminate and tetracalcium iron aluminate), crystalline and semi-crystalline products deriving from the process of hydration of cement (calcium hydrated silicates, calcium hydrated aluminates, calcium and calcium hydroxide hydrated ferrites), open or closed pores containing a water solution rich in positive and negative ions (Na ⁺ , K ⁺ , Mg ⁺⁺ , Ca ⁺⁺ , OH", Cl", SO4"), the concentration of which can give rise to a colloidal gel which solidifies over time, and finally air pockets. For carrying out the operations of qualitative separation of heterogeneous mineral conglomerates, such as the concrete deriving from the aforementioned primary crushing, some properties of the material are exploited, among which: compression strength, size, density, thermal conductivity, electrical conductivity, permittivity, dielectric dissipation factor, etc.

In the aforesaid field of the qualitative separation of heterogeneous mineral conglomerates, the development of the following treatments has been observed:

- mechanical treatment;

- conduction thermal treatment,

- dielectric loss thermal treatment with electromagnetic waves (microwaves);

- treatment with high-voltage electric discharges.

The qualitative separation of concrete into its original components aims at obtaining cement powder, hydrated and dehydrated, as well as sand and gravel cleaned from the cement matrix entrapping them. Such qualitative separation is necessary in order to produce high-quality recycled aggregates consisting of sand and gravel cleaned from the cement matrix. The cement powder, hydrated and dehydrated, obtained from said separation is suitable both for producing fresh concrete as mineral addition, and for producing fresh cement as raw material, with the peculiarity of releasing a lower content of carbon dioxide than in the traditional production of cement with calcium carbonate.

For obtaining qualitative separation, it has been proposed to cook the concrete, crushed to a diameter of approximately 5 cm, in rotary furnaces, gas furnaces, or electric resistance furnaces, for example, as illustrated in document PL417372A1. However, the heat transmission by conduction obtained with such thermal treatment has the following disadvantages:

- the need to heat up the environment in which the material is present;

- the dispersion of heat into the outer environment;

- a slow and non-selective propagation of heat into the material, which propagation proceeds from the outside towards the inside;

- a non-uniform transmission of heat;

- the release of greenhouse gases into the atmosphere when gas burners are used.

All of this turns into a high energy consumption, air pollution, low productivity, installations that are expensive and unsuitable for on-site operations.

In order to overcome the problems related to the conduction thermal treatment, the thermal treatment by microwave dielectric loss has been proposed, in which microwaves are let freely propagate within an appropriate closed housing suitable for shielding them.

As is known, when a dielectric material is subjected to an alternating electric field or a pulsed electric field, a certain amount of energy is absorbed by the material, which becomes polarized, and is dissipated into heat. This energy transformation is referred to as dielectric loss.

The technique of thermal treatment by microwave dielectric loss is beneficial because it selectively heats up water, the hydroxy groups and iron oxides inside the crushed concrete; in addition, the heating obtained is of the volumetric type, because it penetrates the object without proceeding from the outside towards the inside.

However, notwithstanding the fact that encouraging results have been obtained with said technique at an experimental level, at an industrial level the need to carry out processes requiring high wattage (higher than 50 kW) makes the microwave-generating apparatus very expensive. Furthermore, it is of utmost importance to shield the propagation of microwaves to ensure protection to workers so that they are not exposed to strong electromagnetic fields, and this contributes to make this technology very expensive. In order to overcome these problems, a plurality of microwave sources is used (for example, fifty 1 kW sources instead of a single 50 kW source). This, however, makes it necessary to create more bulky and hardly scalable apparatuses, making it difficult to create apparatuses that can be easily transported for on-site processing operations. In addition, the high frequencies of microwaves (UHF and EHF) resent the so-called skin effect, i.e., the tendency of an alternating electric current to become distributed in a non-uniform manner within a conductor and to prefer the surface thereof. As a result, for cement agglomerates having a diameter larger than 2-5 cm, heat is mainly generated on the surface and propagates inwards by conduction.

Lastly, many experiments have been performed to develop a treatment with high- voltage electric discharges. The purpose of this treatment is to concentrate high-voltage electric pulses between two electrodes in order to break the material by means of repeated electric discharges. In particular, the electric discharges propagate from a wedge-like discharge electrode to a ground electrode, passing through the material interposed therebetween.

Several technical terms are used in literature to indicate the various treatments using high-voltage electric pulses for generating electric discharges. Said treatments are distinguished from one another by slight variations in procedures or specific parameters, such as, for example, the duration of the electric pulse. Two macro-categories can anyway be distinguished, depending on whether the pulses are transmitted to the material through water or by direct contact between the electrodes and the material. In the category of transmission through water, the following processes are known: electrical pulse disaggregation (EPD), electrodynamic disintegration (EDD) and electrohydraulic disintegration (EHD). The process providing for direct contact between the electrodes and the material is instead called electrical disintegration (ED).

In general, it is known that when a heterogeneous material is subjected to a high electric field, the various components of the material become polarized according to their electrical properties, and the change in the orientation of the electric charges, which change is different for each type of components, generates an unbalance in the interface regions between such components.

In the case of the treatment with high-voltage electric discharges, an intense electric field is applied and the difference in charge in the interface regions between the various components of the heterogeneous material generates a local electric discharge. The generation of such electric discharge is accompanied by a thermal expansion causing a radial shock wave. This phenomenon takes place in a few hundreds nanoseconds, sufficient to cause a very rapid and selective separation of the components of the material.

The processes employing high-voltage electric discharges have great efficacy in qualitatively separating components of a heterogeneous material and are used with great benefit for the separation of precious minerals from the rocks in which they are contained.

The use of said processes employing high-voltage electric discharges has limitations related to their low productivity (reaching a maximum of 4t/h of processed concrete), which limitations make the use thereof non-advantageous at an industrial level. Further problems are also encountered both in those processes carried out in water, because they involve an increase in the costs related to the dehydration of hydrated cement powder, and in those processes where the electrodes have to be in contact with the material, because the need for a continuous contact between the electrodes and the crushed material, with different particle sizes, makes it extremely difficult to implement a continuous process.

In the field of the recycling of concrete, there is therefore a lack of an industrially scalable technology suitable for wheeled transportation for on-site operations and capable of obtaining the double result of separating sand and gravel from the cement component and selectively dehydrating said cement component by means of a continuous process.

The object of the present invention is to provide a system and a method for separating components of waste concrete that are not subject to the prior art limitations and drawbacks forth above, in order to produce high-quality recycled aggregates consisting of hydrated and dehydrated cement powder, as well as sand and gravel cleaned from the cement matrix.

This and other objects are obtained with the system and method as claimed in the appended claims.

The claims are an integral part of the technical teaching provided herein in relation to the invention.

Summary of Invention

The system and method for separating components of waste concrete according to the invention are essentially based on the passage of concrete (which has already undergone primary crushing) through a radio-frequency alternating electric field or a radio-frequency pulsed electric field, generated between two or more electrodes of capacitors powered by a high-voltage radio-frequency alternating electric field generator or by a high-voltage radiofrequency pulsed electric field generator, respectively. The use of fields with radio frequencies up to 100 MHz allows for better penetration into the concrete in comparison, for example, with microwaves, by virtue of the lower frequency of said fields.

Thanks to the aforesaid passage of concrete through a radio-frequency alternating electric field or a radio-frequency pulsed electric field, selective heating, by dielectric loss, of the air and moisture inclusions (water solutions with ions) present in the open and closed pores of the concrete and the crystallization water present in the hydrated components of the cement. This causes an increase in the internal pressure, which increase results in the formation of vent channels and explosions, with consequent loss of cohesion and separation. Besides causing a different thermal expansion of the different components of concrete, as explained above, the aforesaid electric fields further cause a change in the orientation of the charges at the interfaces of the components of concrete, thus creating unbalances and possible formation of discharges with consequent loss of cohesion. The combination of the above-mentioned phenomena thus determines the so-called dielectric breakdown of the various components of concrete.

The system for separating components of concrete comprises:

- at least one dielectric heating unit comprising a capacitor having two electrodes and powered by a respective high-voltage radio-frequency alternating electric field generator or by a respective high-voltage radio-frequency pulsed electric field generator, said capacitor being configured to generate a radio-frequency alternating electric field or a radio-frequency pulsed electric field, respectively, which are confined between said electrodes,

- concrete loading means and concrete conveying means, configured, respectively, to load crushed concrete into the system and convey it, along a direction of advancement, between the electrodes of the capacitor of said at least one dielectric heating unit so that said crushed concrete passes through said radio-frequency alternating electric field or said radiofrequency pulsed electric field.

The electrodes of the capacitor of the at least one heating unit have a size much larger than that of the crushed concrete which is passed between them.

Optionally, the capacitor is a plan capacitor with plate electrodes. Among the possible geometries of the capacitor, the geometry with parallel plate electrodes of the plan capacitor of the at least one heating unit is the only one that creates, advantageously, a uniform electric field between the electrodes.

In the case of a plan capacitor with plate electrodes, at least one plate electrode is preferably movable (servo-assisted by pistons), so that the distance between the plate electrodes can be changed and thus the electrical power that is transferred from the plan capacitor to the crushed concrete can be adjusted.

Preferably, the at least one movable plate electrode of the plan capacitor is placed between two containment sheets and said containment sheets are preferably joined, at their ends facing against the direction of advancement of the crushed concrete, by a joining element configured to prevent the crushed concrete from entering between said containment sheets and the plate electrode placed therebetween.

The containment sheets are preferably made of a matrix comprising a technical ceramic and of a dispersion of particles of a susceptor ceramic material, thus fulfilling the function of transforming the energy of the alternating electric field into high-temperature heat, which contributes to separating components of crushed waste concrete.

Optionally, the capacitor comprises ring electrodes.

Optionally, the capacitor comprises bar electrodes arranged along a circumference or along a plane (coplanar electrodes).

Optionally, the electrodes are integrated in the conveying means.

Optionally, the conveying means act as secondary crushing means for the concrete. According to the invention, the conveying means preferably comprise: - a conveyor belt, or

- a vibrating plane, or

- a substantially vertical conduit configured to allow concrete to flow therein from top to bottom by gravity, or

- a cylindrical conduit with a longitudinal axis inclined relative to a horizontal plane.

The system according to the invention further comprises, preferably, a demountable frame, on which said at least one dielectric heating unit and said concrete loading means and concrete conveying means are mounted. This advantageously allows easy transportation of the system, by means of wheeled vehicles, because the whole system is contained within the road profile, and thus provides the possibility of treating concrete directly on-site.

The method for separating components of concrete comprises the steps of

- providing a radio-frequency alternating electric field or a radio-frequency pulsed electric field, which are confined between electrodes of a capacitor of at least one dielectric heating unit,

- conveying a continuous flow of crushed concrete between said electrodes, within said radio-frequency alternating electric field or said radio-frequency pulsed electric field, respectively,

- causing, by means of said radio-frequency alternating electric field or said radio frequency- pulsed electric field which are created between said electrodes, the dielectric heating and dielectric breakdown of the crushed concrete present between said electrodes.

The method according to the invention further comprises, preferably, the step of

- performing, either after or simultaneously with said step of causing the dielectric heating and dielectric breakdown of the crushed concrete present between said electrodes, a secondary crushing of said concrete, in order to help separate the components of said concrete.

The method according to the invention further comprises, preferably, the step of

- performing, after said step of causing the dielectric heating and dielectric breakdown of the crushed concrete present between said electrodes and said possible secondary crushing step, a screening and sorting or sieving of said concrete, in order to obtain a complete separation of the components of said concrete.

The dielectric loss heating causes dehydration of the hydrated components and of the pores containing water and ions in solution that are present in the concrete and determines, together with the dielectric breakdown, the loss of cohesion between the components of concrete, thus facilitating the separation of such components during the subsequent secondary crushing of concrete.

By virtue of the loss of cohesion and subsequent crushing obtained with the method according to the invention, hydrated and dehydrated cement powder as well as sand and gravel cleaned from the cement matrix that entrapped them are obtained.

The aforesaid method according to the invention might therefore by synthetically referred to as “Dielectric Drying and Breakdown for Concrete Recycling” (DDBCR).

The method according to the invention further comprises, preferably, the step of changing the distance between the electrodes of the capacitor of the at least one dielectric heating unit, and thus adjusting the electric power transferred from the capacitor to the crushed concrete.

The method according to the invention further comprises, preferably, the step of filling crushed concrete into part of the space between the electrodes of the at least one dielectric heating unit and controlling how long said crushed concrete stays in said space.

Advantageously, with the system and method according to the invention, a high productivity is reached, in the order of 20t/h of processed concrete per each dielectric heating unit. Advantageously, thanks to the fact that the system is modular, as more heating units connected to one or more generators of the above-mentioned type can be added, it is possible to increase production.

Advantageously, in the system and method according to the invention, neither direct contact nor contact by water is required between the electrodes and the concrete.

In addition, advantageously, the system and method according to the invention do not envisage to generate freely propagating electromagnetic waves. Indeed, although the heating of the concrete is effected by changing the electric field inside the capacitive cavity of the capacitor at the frequencies characteristic of radio-frequencies, no actual radio waves are generated or absorbed.

Brief Description of Drawings

These and other features and advantages of the present invention will become more evident from the following description of preferred embodiments given by way of nonlimiting examples with reference to the annexed figures, in which parts indicated with identical or similar reference numerals indicate parts with identical or similar function and structure, and in which:

Fig.1 is a perspective view of the system according to an embodiment of the present invention;

Fig.2 is a side view of a portion of a system according to a further embodiment of the present invention;

Fig.3 is a perspective view of a portion of a system according to a further embodiment of the present invention;

Fig.4 is a top view of the portion of system of Fig. 3;

Fig.5 is a side view of a portion of a system according to a further embodiment of the present invention;

Fig.6a-6b are a sectional perspective view and a top view of a portion of a system according to a further embodiment of the present invention, respectively;

Fig.7a-7b are a sectional perspective view and a top view of a portion of a system according to a further embodiment of the present invention, respectively;

Fig.8a is a partially sectional side view of a portion of a system according to a further embodiment of the present invention;

Fig.8b is a front view of a component of the system shown in Fig. 8a.

Description of Embodiments

Referring to Fig. 1, this schematically shows a system 10 for separating components of concrete by means of dielectric loss heating (also referred to as dielectric heating) and dielectric breakdown of crushed waste concrete (not shown), according to an embodiment of the invention.

The system 10 comprises a dielectric heating unit 20, which comprises a plan capacitor 21 powered by a high-voltage radio-frequency alternating electric field generator (not shown).

The plan capacitor 21 comprises two plate electrodes 21a, 21b, substantially parallel to each other and arranged at a mutual distance preferably between 3 cm and 50 cm.

The plan capacitor 21 is configured to generate - powered by said generator - a radio-frequency alternating electric field confined between the plate electrodes 21a, 21b and varying at the frequency of the generator powering said capacitor.

The high-voltage radio-frequency alternating electric field generator preferably has a power between 10 and 300 kW and a frequency between 1 MHz and 100 MHz.

The system 10 further comprises concrete loading means 60 and concrete conveying means 70, configured, respectively, to load crushed concrete into the system 10 and convey it between the plate electrodes 21a, 21b of the plan capacitor 21 of the dielectric heating unit 20 so that the crushed concrete passes through said radio-frequency alternating electric field confined between said plate electrodes 21a, 21b.

According to the present embodiment, the loading means 60 comprise a hopper 61 preferably having a bottom 62 consisting of a vibrating channel configured to dose the crushed concrete and transfer it to the conveying means 70.

The conveying means 70 of the present embodiment comprise a substantially horizontally arranged conveyor belt 71. Said conveyor belt 71 is advantageously integrated with the plan capacitor 21, whose plate electrodes 21a, 21b are arranged one above the other beneath the conveyor belt 71, substantially parallelly to said conveyor belt. The conveyor belt 71 is thus configured to make the crushed concrete, received from the loading means 60, advance along a direction of advancement F, by making it pass through the plate electrodes 21a, 21b of the plan capacitor 21 and therefore through the radio-frequency alternating electric field confined between said plate electrodes.

According to the present embodiment, a plate electrode 21a of the pair of plate electrodes 21a, 21b of the plan capacitor 21 is mounted so as to be movable in a vertical direction and is servo-assisted by a piston 25, so as to be able to vary its own height and thus change the distance that separates itself from the other plate electrode 21b. This is of advantage because it allows adjustment of the electric power that is transferred from the plan capacitor 21 to the crushed concrete present between the electrodes 21a, 21b thereof, said power being a function of said distance between the electrodes.

The system 21 further comprises a control unit 90, configured to control actuation of the high-voltage radio-frequency alternating electric field generator, the loading means 60, the conveying means 70 and the piston 25 associated with the plate electrode 21a of the plan capacitor 21.

The system 10 according to the present embodiment further comprises a frame 11, on which the dielectric heating unit 20, the crushed concrete loading means 60, the crushed concrete conveying means 70 and the control unit 90 are mounted. Advantageously, the frame 11 is demountable, thus allowing easy transportation of the whole system 10 by means of a truck.

Referring to Fig. 2, according to an alternative implementation of the present embodiment, the system may comprise more than one dielectric heating unit 20', 20", 20"', each comprising a plan capacitor 22, 23, 24 and a respective high-voltage radio-frequency alternating electric field generator. The various plan capacitors 22, 23, 24 are placed one after another along the path of the conveyor belt 71, whereby the crushed concrete passes sequentially through the plate electrodes 22a, 22b, 23a, 23b, 24a, 24b of each plan capacitor 22, 23, 24.

Referring to Figs. 3 and 4, a system for separating the waste concrete components according to a further embodiment of the invention comprises two dielectric heating units 30', 30", each comprising a plan capacitor 31, 32 powered by a respective high-voltage radio-frequency alternating electric field generator (not shown).

Each plan capacitor 31, 32 comprises two respective plate electrodes 31a, 31b and 32a, 32b, substantially parallel to each other and arranged at a mutual distance preferably between 3 cm and 50 cm.

Each plan capacitor 31, 32 is configured to generate - powered by the respective generator - a radio-frequency alternating electric field confined between the plate electrodes 3 la, 3 lb e 32a, 32b and varying at the frequency of the respective generator powering said capacitor.

Each high-voltage radio-frequency alternating electric field generator preferably has a power between 10 and 300 kW and a frequency between 1 MHz and 100 MHz.

The system according to the present embodiment comprises concrete loading means 60 and concrete conveying means 70, configured, respectively, to load crushed waste concrete into the system and convey it between the plate electrodes 31a, 31b e 32a, 32b of the plan capacitors 31, 32 of the dielectric heating units 30', 30" so that the crushed concrete passes through the radio-frequency alternating electric field confined between said plate electrodes 31a, 31b and 32a, 32b.

According to the present embodiment, the loading means 60 comprise a hopper 63 directly communicating with a substantially vertical conduit 75 of the conveying means 70. The conduit 75 is configured to allow concrete to flow therein from top to bottom, by gravity, i.e., along the direction of advancement F shown in Figure 3.

The conduit 75 is integrated with the plan capacitors 31, 32. Indeed, said plan capacitors 31, 32 are arranged within said conduit 75, with the plate electrodes 3 la, 3 lb and 32a, 32b arranged vertically, whereby the crushed waste concrete, passing through the conduit 75 from top to bottom, passes between the plate electrodes 31a, 31b and 32a, 32b of the plan capacitors 31, 32 and thus through the radio-frequency alternating electric field confined between said plate electrodes.

The conduit 75 of the conveying means 70 of the present embodiment has the advantage of having a longer service life than the conveyor belt of the preceding embodiment, which is usually more prone to wear caused by high temperatures and abrasion.

According to the present embodiment, the system further comprises one or more dosing units 80, arranged at a lower opening of the conduit 75, beneath the plan capacitors 31, 32. Such dosing units are, for example, rollers 81 with horizontal rotation axes parallel to the plate electrodes, and are configured to limit the exit of concrete from the lower opening of the conduit 75, thus allowing accumulation of the crushed waste concrete in the spaces between the plate electrodes 31a, 31b, 32a, 32b and allowing to control how long said crushed waste concrete stays within the radio-frequency alternating electric field confined between said plate electrodes.

It should be noted that, for the sake of clarity, in Fig. 3 the concrete 100 is shown only downstream of the dosing units 80.

According to the present embodiment, a plate electrode 31a, 32a of the pair of plate electrodes of each plan capacitor 31, 32 is mounted so as to be movable in a horizontal direction and is servo-assisted by a respective piston 35, 36 so as to be able to vary its own position in the horizontal direction and thus change the distance that separates itself from the other plate electrode 31b, 32b. This is of advantage because it allows adjustment of the electric power that is transferred from the plan capacitor 31, 32 to the crushed concrete present between the electrodes 31a, 31b, 32a, 32b thereof, said power being a function of said distance between the electrodes.

According to the present embodiment, the movably mounted plate electrode 31, 32a of each plan capacitor 31, 32 is placed between two respective containment sheets 41, 42 and 44, 45, said containment sheets preferably having a surface extension equal to the surface extension of the respective movable plate electrode 31a, 32 and being parallel to said plate electrode. The containment sheets 41, 42 and 44, 45, are joined, at their upper ends 41a, 42a, 43a, 44a, i.e., at their ends facing against the direction of advancement F of the crushed waste concrete, by corresponding joining elements 43, 46 configured to prevent the crushed concrete from entering between the containment sheets 41, 42 and the plate electrode 3 la placed therebetween, and between the containment sheets 44, 45 and the plate electrode 32a placed therebetween, respectively. The containment sheets 41, 42 and 44, 45 thus form, with the corresponding joining elements 43, 46, gaps in which the respective plate electrodes 31a, 32a can move without being hindered by the presence of the crushed waste concrete present between the plate electrodes.

According to the present embodiment, the containment sheets 41, 42, 44, 45 are made of a matrix comprising a technical ceramic such as, for example, aluminum oxide, and of a dispersion of particles of a susceptor ceramic material, such as, for example, silicon carbide, having the function of transforming the energy of the alternating electric field into high-temperature heat, which contributes to separating components of crushed waste concrete.

Therefore, the containment sheets 41, 42 and 44, 45 fulfil the double function of containing the concrete so that the plate electrodes 31a, 32a can be moved relative to the plate electrodes 3 lb, 32b, even when the concrete takes up all the space comprised between the hopper 63 and the dosing units 80, and constituting a high-temperature radiant member to further increase heating of the crushed waste concrete.

The system according to the present embodiment further comprises a control unit (not shown), configured to control the actuation of the high-voltage radio-frequency alternating electric field generator, of the pistons 35, 36 associated with the plate electrodes 31a, 32a, and of the dosing units 80.

In addition, also the system according to the present embodiment may comprise a frame (not shown), on which the dielectric heating units 30', 30", the crushed concrete loading means 60, the crushed concrete conveying means 70, the dosing units 80 and the control unit are mounted. Advantageously, said frame is demountable, thus allowing easy transportation of the whole system by means of a truck.

Referring to Fig. 5, a system for separating components of crushed waste concrete according to a further embodiment of the invention comprises three dielectric heating units 50', 50", 50'", each comprising a plan capacitor 51, 52, 53 powered by a high-voltage radiofrequency alternating electric field generator (not shown).

Each plan capacitor 51, 52, 53 comprises two respective plate electrodes 51a, 51b and 52a, 51b, 53a, 51b, substantially parallel to each other and arranged at a mutual distance preferably between 3 cm and 50 cm. Preferably, as shown in Figure 5, the lower plate electrode 51b is common to all the capacitors 51, 52, 53.

Each plan capacitor 51, 52, 53 is configured to generate - powered by said generator - a radio-frequency alternating electric field confined between the plate electrodes 5 la, 5 lb, 52a, 5 lb and 53a, 5 lb and varying at the frequency of the generator powering said capacitor.

The high-voltage radio-frequency alternating electric field generator preferably has a power between 10 and 300 kW and a frequency between 1 MHz and 100 MHz.

The system according to the present embodiment comprises concrete loading means (not shown) and concrete conveying means 70, configured, respectively, to load crushed waste concrete into the system and convey it between the plate electrodes 51a, 51b, 52a, 51b and 53a, 51b of the plan capacitors 51, 52, 53 of the dielectric heating units 50', 50", 50"' so that the crushed concrete passes through the radio-frequency alternating electric field confined between said plate electrodes.

According to the present embodiment, the loading means may comprise a hopper like the one shown in the embodiment of Fig. 1, which hopper doses the crushed concrete and transfers it to the conveying means 70.

The conveying means 70 of the present embodiment comprise a vibrating plane 72, arranged slightly inclined relative to the horizontal position, and configured to vibrate and thus make the crushed concrete present thereon to advance along a direction of advancement F, i.e., the direction towards which said vibrating plane 72 is slightly inclined.

Said vibrating plane 72 is integrated with the plan capacitors 51, 52, 53. Indeed, according to the present embodiment, the vibrating plane 72, actuated by elastic actuators 73, coincides with the plate electrode 51b common to the three plan capacitors 51, 52, 53, whereby the advancement of the crushed waste concrete along the direction of advancement F causes said concrete to pass between the plate electrodes 51a, 51b, 52a, 51b and 53a, 51b of the plan capacitors 51, 52, 53 and thus through the radio-frequency alternating electric field confined between said plate electrodes.

According to further alternative implementations, not shown, the vibrating plane may be a separate element, arranged between the upper and lower electrodes of the capacitors.

The vibrating plane 72, usually made of metal, of the conveying means 70 of the present embodiment has the advantage of having a longer service life than the conveyor belt of the preceding embodiment, which is usually more prone to wear caused by high temperatures and abrasion.

According to the present embodiment, the plate electrodes 51a, 52a, 53a of the plan capacitors 51, 52, 53 are mounted so as to be movable in a vertical direction and are servoassisted by respective pistons 55, 56, 57 so that their distance from the plate electrode 51b can be varied. This is of advantage because it allows adjustment of the electric power that is transferred from the plan capacitors 51, 52, 53 to the crushed concrete present between the plate electrodes thereof, said power being a function of said distance between the electrodes.

The system according to the present embodiment further comprises a control unit (not shown), configured to control actuation of the high-voltage radio-frequency alternating electric field generator, of the pistons 55, 56, 57 associated with the plate electrodes 51a, 52a, 53a, and of the vibrating plane 72.

In addition, also the system according to the present embodiment may comprise a frame (not shown), on which the dielectric heating units 50', 50", 50"', the crushed concrete loading means 60, the crushed concrete conveying means 70 and the control unit 90 are mounted. Advantageously, said frame is demountable, thus allowing easy transportation of the whole system by means of a truck.

Referring to Figs. 6a, 6b and 7a, 7b, a system for separating components of crushed waste concrete according to two further embodiments of the invention comprises, respectively, for example, one (Figs. 6a, 6b) and four (Figs. 7a, 7b) dielectric heating unit(s) 120, 130', 130", 130'", 130"", each comprising a respective capacitor 121, 131, 132, 133, 134 powered by a by a high-voltage radio-frequency alternating electric field generator (not shown). It is possible to provide for alternative implementations having a different number of heating units with respect to the embodiments shown in Figs. 6a, 6b and 7a, 7b.

Each capacitor 121, 131, 132, 133, 134 comprises two ring electrodes 121a, 121b (in the embodiment of Figs. 6a, 6b), or two bar electrodes 131a, 131b, 132a, 132b, 133a, 133b, 134a, 134b (in the embodiment of Figs. 7a, 7b) arranged along a cylindrical surface. In both the aforementioned cases, the electrodes are substantially mutually parallel and arranged at a mutual distance preferably between 3 cm and 50 cm.

Each capacitor 121, 131, 132, 133, 134 is configured to generate - powered by said generator - a radio-frequency alternating electric field confined between the ring electrodes 121a, 121b and bar electrodes 131a, 131b, 132a, 132b, 133a, 133b, 134a, 134b, and varying at the frequency of the generator powering said capacitor.

The high-voltage radio-frequency alternating electric field generator preferably has a power between 10 and 300 kW and a frequency between 1 MHz and 100 MHz.

The system according to the two present embodiments comprises concrete loading means (not shown) and concrete conveying means 70, configured, respectively, to load crushed waste concrete into the system and convey itbetween the ring electrodes 121a, 121b and bar electrodes 131a, 131b, 132a, 132b, 133a, 133b, 134a, 134b of the capacitors 121, 131, 132, 133, 134 of the dielectric heating units 120, 130', 130", 130"', 130"", so that the crushed concrete passes through the radio-frequency alternating electric field confined between said electrodes.

According to the two present embodiments, the loading means may comprise a hopper like the one shown in the embodiment of Fig. 1, which hopper doses the crushed concrete and transfers it to the conveying means 70.

The conveying means 70 of the two present embodiments comprise a cylindrical conduit 76 (in the embodiment of Figs. 6a, 6b) and 77 (in the embodiment of Figs. 7a, 7b), rotating about its longitudinal axis L and arranged with its longitudinal axis L slightly inclined relative to the horizontal position, preferably by an angle between 5° and 45°, and configured to rotate about its longitudinal axis L, with the double function of making the crushed concrete present thereon to advance along a direction of advancement F (i.e., the direction towards which said cylindrical conduit 76 or 77 is slightly inclined) and to perform a secondary crushing thereof (autogenic crushing).

Said cylindrical conduit 76 or 77 is integrated with the ring capacitors 121 and the bar capacitors 131, 132, 133, 134, respectively. In addition, the cylindrical conduit 76 or 77 is preferably made of wear-resistant materials. In the case in which said materials are metal materials, the ring electrodes 121a, 121b and bar electrodes 131a, 131b, 132a, 132b, 133a, 133b, 134a, 134b are preferably insulated by means of insulating materials with high dielectric rigidity.

In the two present embodiments, the advancement of crushed waste concrete along the direction of advancement F makes said concrete pass through the capacitors 121 and 131, 132, 133, 134 and therefore through the radio-frequency alternating electric field confined between the electrodes of said capacitors.

The cylindrical conduit 76 or 77, usually made of metal, of the conveying means 70 of the two present embodiments has the advantage of having a longer service life than the conveyor belt of the preceding embodiment, which is usually more prone to wear caused by high temperatures and abrasion.

According to the two present embodiments, the ring electrodes 121a, 121b and bar electrodes 131a, 131b, 132a, 132b, 133a, 133b, 134a, 134b are fixedly mounted in a direction perpendicular and parallel to the longitudinal axis L of the cylindrical conduit and therefore to the direction of advancement F of the crushed waste concrete, respectively.

According to the two present embodiments, the crushed waste concrete rolls and is dragged upwards and made fall by the rotational movement of the cylindrical conduit; for this reason, the concrete undergoes dielectric heating and dielectric breakdown by means of the electric field and simultaneous mechanical crushing of autogenic type (secondary crushing).

The system according to the two present embodiments further comprises a control unit (not shown), configured to control actuation of the high-voltage radio-frequency alternating electric field generator.

In addition, also the system according to the two present embodiments may comprise a frame (not shown), on which the dielectric heating units 120, 130', 130", 130"', 130"", the crushed concrete loading means (not shown), the crushed concrete conveying means 70 and the control unit (not shown) are mounted. Advantageously, said frame is demountable, thus allowing easy transportation of the whole system 10 by means of a truck.

Referring to Figs. 8a e 8b, a system for separating components of crushed waste concrete according to a further embodiment of the invention comprises, for example, two dielectric heating units 140', 140", each comprising a capacitor 141, 142 powered by a high- voltage radio-frequency alternating electric field generator (not shown). It is possible to provide for alternative implementations having a different number of heating units with respect to the embodiments shown in Figs. 8a, 8b.

Each capacitor 141, 142 comprises two respective plate electrodes 141a, 141b, 142a, 142b substantially parallel to each other, coplanar and arranged at a mutual distance preferably between 3 cm and 50 cm.

Each capacitor 141, 142 is configured to generate - powered by said generator - a radio-frequency alternating electric field confined between the plate electrodes 141a, 141b, 142a, 142b and varying at the frequency of the generator powering said capacitor.

The high-voltage radio-frequency alternating electric field generator preferably has a power between 10 and 300 kW and a frequency between 1 MHz and 100 MHz.

The system according to the present embodiment comprises concrete loading means (not shown) and concrete conveying means 70, configured, respectively, to load crushed waste concrete into the system and convey it between the plate electrodes 141a, 141b, 142a, 142b of the plan capacitors 141, 142 of the dielectric heating units 140', 140" so that the crushed concrete passes through the radio-frequency alternating electric field confined between said plate electrodes 141a, 141b, 142a, 142b.

According to the present embodiment, the loading means may comprise a hopper like the one shown in the embodiment of Fig. 1, which hopper doses the crushed concrete and transfers it to the conveying means 70.

The conveying means 70 of the present embodiment comprise a substantially vertical conduit 78. The conduit 78 is configured to allow concrete to flow therein from top to bottom, by gravity, i.e., along the direction of advancement F of the crushed waste concrete shown in Figure 8a.

The conduit 78 is integrated with the capacitors 141, 142. Said capacitors 141, 142 are placed within said conduit 78, with the plate electrodes 141a, 141b, 142a, 142b arranged on a single wall 78a of the conduit 78, in an arrangement perpendicular to the direction of advancement F (as shown in Figs. 8a, 8b). It is possible to provide for alternative implementations (not shown) in which the plate electrodes 141a, 141b, 142a, 142b are arranged in an orientation parallel to the direction of advancement F of concrete.

The plate electrodes 141a, 141b, 142a, 142b are preferably electrically insulated by means of a wear-resistant material with high dielectric rigidity, whereby the crushed waste concrete, passing through the conduit 78 from top to bottom, passes between the plate electrodes 141a, 141b, 142a, 142b of the capacitors 141, 142 and thus through the radiofrequency alternating electric field confined between said plate electrodes.

According to the present embodiment, the wall 78b of the conduit 78 is moved by a mechanical system 85 typical of jaw crushers, in order to compress the crushed waste concrete against the fixed wall 78a, integrated with the electrodes 141a, 141b, 142a, 142b, with the double purpose of performing the dielectric heating and the dielectric breakdown by means of the electric field and simultaneously performing a mechanical crushing (secondary crushing).

The conduit 78 of the conveying means 70 of the present embodiment has the advantage of having a longer service life than the conveyor belt of the preceding embodiment, which is usually more prone to wear caused by high temperatures and abrasion.

The system according to the present embodiment further comprises a control unit (not shown), configured to control actuation of the high-voltage radio-frequency alternating electric field generator.

In addition, also the system according to the present embodiment may comprise a frame (not shown), on which the dielectric heating units 140', 140", the crushed concrete loading means (not shown), the crushed concrete conveying means 70, the dosing units (not shown) and the control unit are mounted. Advantageously, said frame is demountable, thus allowing easy transport of the whole system by means of a truck.

According to further embodiments, all the systems described above comprise, instead of the high-voltage radio-frequency alternating electric field generators, high- voltage radio-frequency pulsed electric field generators, which preferably have a power between 10 and 300 kW and generate pulses with frequencies between 1 Hz e 100 MHz.

The capacitors 21, 22, 23, 24, 31, 32, 51, 52, 53, 121, 131, 132, 133, 134, 141, 142 of the various systems illustrated above, when powered by high-voltage radio-frequency pulsed electric field generators, generate a radio-frequency pulsed electric field, confined between the electrodes of such capacitors and varying at the frequency of the generator powering said capacitors. It should be noted that, in such cases, electric discharges propagating from one electrode to the other are not usually generated, unlike what happens in the wedge-like electrodes of prior art. Electric discharges may be generated only at the interfaces between the components of concrete, thus causing a thermal expansion and a resulting shock wave that causes separation between said components.

According to further alternative implementations, not shown, also the plate electrodes 21a of the embodiment of Fig. 1, the plate electrodes 22a, 23a, 24a of the embodiment of Fig. 2 and the plate electrodes 51a, 52a, 53a of the embodiment of Fig. 5 may be enclosed between containment sheets like those described with reference to the embodiment of Figure 3 and 4.

In addition, according to further alternative implementations, all the systems described above may further comprise cooling members for cooling the high-voltage radiofrequency alternating electric field generators or the high-voltage radio-frequency pulsed electric field generators, protective means for preventing escape of the concrete processed in the systems, and systems for collecting the water vapor lost by the concrete during dehydration thereof caused by the dielectric heating. This last operation is useful to prevent generation and propagation of electric discharges between the electrodes.

The system for separating components of concrete according to the different embodiments and alternative implementations shown above preferably further comprises, downstream of the dielectric heating units, means (not shown) for carrying out a further mechanical crushing of concrete, referred to as secondary crushing, suitable for crushing concrete to a size preferably smaller to 5 cm. Such secondary crushing means are of a known type. The system for separating components of concrete according to the different embodiments and alternative implementations shown above preferably further comprises, downstream of the dielectric heating units and possible secondary crushing means, means (not shown) for performing a screening and sorting of concrete, configured to obtain a complete separation of the components of said concrete (sand, gravel and cement powder). Said screening and sorting means are of a known type.

In the embodiments illustrated in Figs. 6a, 6b, 7a, 7b, e 8a, 8b, the conveying means also act as secondary crushing means.

A preferred embodiment of the method for separating components of crushed waste concrete is described below.

The method essentially comprises the steps of:

- providing a radio-frequency alternating electric field or a radio-frequency pulsed electric field, which are confined between the electrodes 21a, b (or 22a, b 23a, b, 24a, b, or 31a,b, 32a, b, or 51a, 51b, 52a, 53a, or 121a, b, or 131a,b, 132a, b, 133a, b, 134a, b, or 141a, b, 142a, b) of the capacitor 21 (or 22, 23, 24, or 31, 32, or 51, 52, 53, or 121, or 131, 132, 133, 134, or 141, 142) of the dielectric heating unit 20 (or 20', 20", 20"', or 30', 30", or 50', 50", 50'", or 120, or 130', 130", 130'", 130"", or 140', 140"),

- conveying a continuous flow of concrete (previously crushed to a size preferably smaller than 10 cm during the so-called primary crushing), between said electrodes, within said radio-frequency alternating electric field or said radio-frequency pulsed electric field, respectively,

- causing, by means of said radio-frequency alternating electric field or said radio-frequency pulsed electric field which are created between said electrodes, the dielectric heating and dielectric breakdown of the crushed concrete present between said electrodes.

The method preferably further comprises the step of:

- performing, either after or simultaneously with said step of causing the dielectric heating and dielectric breakdown of the crushed concrete present between said electrodes, a secondary crushing of said concrete, in order to help separate the components of said concrete.

The above-mentioned secondary crushing, by crushing the concrete to a size preferably smaller than 5 cm, contributes to the separation of the components of concrete. Indeed, the dielectric heating and dielectric breakdown alone would not be able to perfectly separate the components; therefore, use is made of the secondary crushing to separate said components, which, because of the dehydration of the cement matrix, are no longer cohesive.

The method preferably further comprises the step of changing the distance between the plate electrodes 21a, b (or 22a, b 23a, b, 24a, b, or 31a,b, 32a, b, or 51a, 51b, 52a, 53a) of the plan capacitor 21(or 22, 23, 24, or 31, 32, or 51, 52, 53) of the dielectric heating unit 20 (or 20', 20", 20"', or 30', 30"; 50', 50", 50'"), and thus adjusting the electrical power that is transferred from the plan capacitor to the crushed concrete present between the plate electrodes.

The method preferably further comprises the step of filling crushed concrete into part of the space between the electrodes 21a, b (or 22a, b 23a, b, 24a, b, or 31a,b, 32a, b, or 51a, 51b, 52a, 53a, or 121a, b, or 131a, b, 132a, b, 133a, b, 134a, b, or 141a, b, 142a, b) of the capacitor 21 (or 22, 23, 24 , or 31, 32 , or 51, 52, 53 , or 121 , or 131, 132, 133, 134 , or 141, 142) of the dielectric heating unit 20 (or 20', 20", 20'", or 30', 30", or 50', 50", 50'", or 120; 130', 130", 130'", 130"", or 140', 140") and controlling how long said crushed concrete stays in said space.

The method preferably further comprises the step of:

- performing a screening and sorting or sieving of said concrete, in order to obtain a complete separation of the components of said concrete.