METHOD FOR SEPARATING DIFFERENT CONSTITUENTS OF A CONCRETE FOR DECONSTRUCTION

Abstract

A method of separating different constituents of a fine fraction that is produced in a prior method for separating a concrete for deconstruction. The method allows the reuse of these different constituents in the production of a new cement and/or of a new concrete, the fine fraction including sand and at least 30% by mass of hydrated cement paste.

Claims

1-8. (canceled)

9. A method for separating different constituents of a fine fraction resulting from a previous method for separating a concrete for deconstruction allowing the reuse of these different constituents in the production of a new cement and/or of a new concrete, the fine fraction comprising sand and at least 30% by mass of hydrated cement paste, the fine fraction being hereinafter referred to as the feed material, the method implementing a facility including: an attrition system, and a separation system, and wherein the method comprises: the feed of the system with the feed material to grind it, the attrition of feed material, and the separation of the ground feed material in the attrition system is carried out by means of a cut-off mesh of the separation system comprised between 50 and 300 micrometres so as to obtain a sandy fraction comprising an amount of hydrated cement paste less than or equal to 25% and greater than or equal to 5% by mass, and a fraction of hydrated cement paste comprising an amount of hydrated cement paste greater than or equal to 40% and less than or equal to 95% by mass.

10. The method according to claim 9, wherein the feed material feeding the attrition system has dimensions of less than 6 millimetres.

11. The method according to claim 9, wherein the separation is carried out by means of a cut-off mesh of the separation system comprised between 80 and 200 micrometres.

12. The method according to claim 9, wherein the attrition is carried out by means of the attrition system including grinding bodies of the ball or cylpebs type.

13. The method according to claim 12, wherein the attrition is carried out by means of the attrition system which comprises a substantially cylindrical chamber of length L and of diameter d, and wherein the ratio L/d is comprised between 1 and 5.

14. The method according to claim 12, wherein the attrition is carried out by means of the attrition system whose balls or cylpebs have a diameter comprised between 5 and 20 millimetres.

15. The method according to claim 12, wherein the rotational speed of the attrition system is comprised between 60 and 85% of a critical speed corresponding to the speed at which the balls are centrifuged.

16. The method according to claim 9, wherein the speed of the gas injected into the attrition system is comprised between 0.5 and 3 m/s.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0043] Other features and advantages of the invention will appear when reading the following detailed description for the understanding of which reference will be made to the appended drawings wherein:

[0044] FIG. 1 is a schematic representation of a method according to the invention;

[0045] FIG. 2 is a schematic representation of a facility according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0046] FIG. 1 shows a method 1 for separating different constituents of a fine fraction resulting from a previous method for separating concrete for deconstruction. The method 1 uses a facility 2 illustrated in FIG. 2. In what follows, the fine fraction becomes the feed material.

[0047] The facility 2 includes an attrition system 3 and a separation system 4. The attrition system 3 is a ball or cylpebs grinder. Balls are substantially spherical grinding bodies. The cylpebs are substantially cylindrical grinding bodies sometimes frustoconical shaped or barrel shaped.

[0048] The grinder 3 is fed with the feed material through an inlet 5 during a feeding step E1. In the grinder 3, the feed material is ground during an attrition step E2. The feed material includes at least 30% by mass of hydrated cement paste. In general, the feed material includes 35 to 50% by mass of hydrated cement paste. The hydrated cement paste is the result of the chemical reaction between cement and water mixed in an initial concrete. The feed material has dimensions less than 6 millimetres.

[0049] In the grinder 3, the attrition phenomenon frees the grains of sand from a matrix of hydrated cement paste, and grinds this hydrated cement paste into a fine powder. During a step E3, a gas flow, generally air, is sent inside the grinder 3 through a gas inlet 14. This gas flow allows to drive the finest portion of the material towards the separation system 4. The other portion, namely the larger grains, is discharged through a discharge outlet 6 located at an end 7 of the grinder 3. In a variant, not shown in the drawings, all or a portion of the material exiting through the discharge outlet 6 can be transported by a handling means to the separation system 4 in order to remove the hydrated cement paste therefrom. More generally, the material can be transported by any handling means.

[0050] During a separation step E4, all or a portion of the ground feed material is separated in the separation system 4 so as to discharge the sandy fraction through a sand outlet 8 and to discharge the hydrated cement paste fraction with the gas flow through an exhaust 9.

[0051] The facility 2 comprises a filter 10 and a chimney 11. The gas flow carrying the hydrated cement paste fraction is filtered in the filter 10 then discharged through a chimney 11. The hydrated cement paste fraction is recovered through an outlet 12.

[0052] Advantageously, the sandy fraction contains an amount of hydrated cement paste less than or equal to 25% and greater than or equal to 5% by mass and the hydrated cement paste fraction contains an amount of hydrated cement paste greater than or equal to 40% and less than or equal to 95% by mass.

[0053] The recycling of the sandy fraction having such proportions of hydrated cement paste allows to reduce the use of natural resources for the production of concrete. Indeed, this sandy fraction can be used in large amounts as a substitute for natural sand.

[0054] Recycling the hydrated cement paste fraction having such proportions of sand allows to reduce the use of natural resources and in particular provides decarbonated lime, which reduces the use of limestone in the cement raw material and therefore the amount of CO.sub.2 emitted by the decarbonation of this limestone and the corresponding fuel consumption. Indeed, this hydrated cement paste fraction can be used in large amounts in the cement raw material.

[0055] The grinder 3 includes a substantially cylindrical chamber 13 with a substantially horizontal axis of rotation wherein the balls or cylpebs (not shown) are housed. The attrition is achieved by rotating the cylindrical chamber 13. The chamber 13 has a length L and a diameter d such that the ratio L/d is comprised between 1 and 5. Such a chamber 13 allows to obtain the necessary and sufficient residence time for the attrition of the material, without violently grinding the grains of sand.

[0056] The balls or cylpebs have a diameter comprised between 5 and 20 millimetres. The balls or cylpebs are made of steel. The size of the balls or cylpebs is adapted to provide the energy just necessary, that is to say neither too much nor too little energy, to the balls or cylpebs to grind the material without damaging the structure of the grains of sand, by limiting the intensity of the shocks between these balls or cylpebs and the feed material.

[0057] The speed of rotation of the chamber 13 is advantageously comprised between 60 and 85% of the critical speed. The critical speed is the minimum speed of centrifugation of the balls or cylpebs. This speed of rotation allows to provide the energy just necessary for the balls or cylpebs to grind the material without damaging the structure of the grains of sand.

[0058] The gas flow travels through the grinder 3 at a speed comprised between 0.5 and 3 metres per second. Such a gas speed allows to discharge from the grinder 3 the finest fraction of the material in order to prevent the grinder 3 from choking with the material and therefore to maintain the efficiency of the grinder.

[0059] The separation system 4 is a granulometric separator. Advantageously, the cut-off mesh of the granulometric separator 4 is comprised between 50 and 300 micrometres. This cut-off mesh allows to obtain a sandy fraction and a hydrated cement paste fraction containing respectively the proportions of hydrated cement paste and sand mentioned above.

[0060] Other cut-off meshes can be used.

[0061] For example, a cut-off mesh comprised between 50 and 120 micrometres allows to favour the quality of the hydrated cement paste fraction to the detriment of its amount and to the detriment of the quality of the sandy fraction.

[0062] A cut-off mesh comprised between 120 and 300 micrometres allows to favour the quality of the sandy fraction to the detriment of its amount and to the detriment of the quality of the hydrated cement paste fraction.

[0063] According to a preferred embodiment, this cut-off mesh is comprised between 80 and 200 micrometres in order to obtain the best compromise between the quality and the recycled amount of each fraction.