Method for recycling concrete waste resulting from construction and / or demolition

Abstract

The present invention relates to a method for recycling concrete waste from construction and / or deconstruction, comprising at least one step of microwave processing of concrete blocks, at least one step of mechanical processing, and optionally at least one step of carbonation of the concrete fines and the recycled concrete aggregates obtained by the steps of microwave processing of concrete blocks and mechanical processing.

Description

[0001] Process for recycling construction and / or demolition concrete waste

[0002] The present invention relates to a method for recycling concrete waste from construction and / or deconstruction implementing at least one step of microwave treatment of concrete blocks, at least one step of mechanical treatment, and optionally at least one step of carbonation of concrete fines, and recycled concrete aggregates obtained according to the steps of microwave treatment of concrete blocks and mechanical treatment.

[0003] Concrete is one of the most consumed manufactured materials in the world. It mainly consists of aggregates (gravel, chippings), mixed with cement, sand, and water. In particular, the annual consumption of aggregates in France is 350 million tons, or 6 tons per capita per year and 17 kg per capita per day. Projections show that the demand for aggregates continues to increase, particularly for the construction of new buildings. Natural aggregates (NA) are generally obtained by exploiting deposits of sand and gravel of alluvial, terrestrial, or marine origin. Natural aggregates (NA) are not a renewable resource and, although technically unlimited, they are increasingly less accessible for societal and environmental reasons.In particular, it is becoming increasingly difficult to open new quarries to meet the demand for natural aggregates (NG), as these cause nuisances for nearby residents (noise, dust, increased traffic, etc.).

[0004] At the same time, the volume of materials used in the deconstruction or demolition of buildings and infrastructure is increasing and will become increasingly significant in the coming years. Indeed, buildings erected during the reconstruction in the 1950s are gradually reaching the end of their life, which means that the volumes of concrete to be recycled will become considerable.

[0005] Furthermore, the calcination of natural limestone mineral resources needed to manufacture cement is responsible for almost half of the CO2 emissions associated with the manufacture of concrete, one of the most CO2-emitting materials produced by man. The use of recycling concrete or masonry works (e.g. construction and demolition waste) has been proposed in order to avoid their burial in landfills, to reduce dependence on natural deposits, and to manufacture new concrete structures while preserving natural aggregate resources.

[0006] Recycling of construction and demolition concrete waste is generally carried out by crushing concrete blocks to form recycled concrete aggregates (RCA). Screening can also be carried out to separate the RCA from the fines. However, the recycling processes currently proposed are not entirely satisfactory. The separation of NG from residual mortar is far from being optimized. The RGA generally obtained is composed of NG mainly associated with a significant quantity of residual mortar from the original concrete. In particular, the residual mortar is found largely among the NG either adhering to it or in the form of aggregates of a size at least equivalent to that of natural aggregates, thus preventing the production of clean NG.Given the high rate of adherent cement paste, such GBRs have poor quality compared to GNs: they have higher water absorption and weaker mechanical properties (lower impact resistance and / or higher friability) than GNs. Concrete made from GBRs mixed under normal conditions sees its workability drop during transport in a mixer, and this can sometimes go so far as to make it unfit for use once it arrives at its destination. The current concrete standard NF EN 206 / CN also imposes a maximum proportion of GBRs to replace GNs when manufacturing new concrete, and this proportion varies according to the type of GBR and in particular their constituents, as well as according to the exposure class of the structures to be constructed.Due to the poor quality of these GBRs, they are currently mainly used in low added value works, particularly in road earthworks as low added value embankment, as road sub-bases, or quarry filling. However, recycling capacities in the road sector are not unlimited, and this form of recycling into lower value materials (well known by the Anglicism "downcycling") does not satisfactorily meet the criteria of sustainable development.

[0007] Furthermore, crushing can significantly fracture GN, contributing to a reduction in the size of the GN compared to their initial particle size distribution and an enrichment of the fines in GN fragments. Thus, the recycled fines obtained have a composition that makes them more difficult to recover and / or recycle. Finally, as a large part of the cement paste adheres to or is associated with GBR, the quantity of fines produced is low compared to the quantity of mortar present in the concrete. The industrial installations currently in place generally do not recover the fine fraction, which is considered waste.

[0008] Some publications consider the use of concrete fines directly in the cement raw mix, as a raw material for clinker production. For example, Schoon et al. [Cement and Concrete Composites, 58, 2015, 70-80] describe the incorporation of recycled concrete fines (5-15%) into a cement raw mix as a replacement for conventional siliceous materials. Different technical configurations have been used to separate the mortar fraction from the aggregates, and to separate the generated fines from the recycled sand. However, Schoon et al. indicate that it is difficult to collect a large quantity of fines.

[0009] Therefore, there is still a need for recycling processes that allow both to obtain a greater quantity of good quality recycled concrete fines, in order to make them recoverable and to obtain recycled concrete aggregates that are as clean as possible (i.e. with the least possible residual mortar) and / or have an improved quality, in order to be able to use them in greater proportion to form a new concrete structure. There is therefore a need for a process that allows the recycling of all the parts of the concrete that are recoverable, namely both the GN and the mortar that surrounds them.

[0010] The aim of the present invention is therefore to overcome the drawbacks of the prior art and in particular to provide a method for recycling concrete waste from construction and / or deconstruction which makes it possible both to access recycled fines in greater quantity and / or of better quality, in particular in terms of pozzolanic and / or hydraulic activity, and to produce GBRs with a high cleanliness rate, which is simple, industrializable, uses abundant raw materials, and which is beneficial from an environmental point of view.

[0011] The first subject of the invention is a method for recycling concrete from construction and / or demolition, characterized in that it comprises at least the following steps: i) one or more step(s) of microwave treatment of construction and / or demolition concrete blocks having a centimeter size, to form micro-fractured concrete blocks, ii) one or more step(s) of mechanical treatment making it possible to extract from said micro-fractured concrete blocks, recycled concrete aggregates (RCA) comprising bare natural aggregates and natural aggregates associated with an adherent residual mortar; and recycled fines, and iii) one or more step(s) of carbonation of the recycled fines, in the presence of carbon dioxide, to form carbonated recycled fines, said method being free of step(s) of carbonation of the recycled concrete aggregates (RCA).

[0012] The process of the invention is simple, easy to implement, and leads to recycled carbonated fines, the recycled carbonated fines comprising a large quantity of cement paste and / or having a better quality, in particular in terms of pozzolanic activity following the production by the carbonation step iii) of amorphous silica which is particularly reactive in a cement medium.

[0013] Furthermore, the process is industrializable, uses abundant raw materials (construction or demolition concrete waste) and reduces the environmental impact since it allows the recycling of unused construction concrete or demolition concrete, while guaranteeing the use or recovery of CO2. The process of the invention is a complete concrete recycling process in that it allows the recycling of all the initial concrete, i.e. the fines on one side, and the natural aggregates (NG) on the other side.

[0014] The process is a method of recycling concrete from construction and / or demolition, particularly in the building and public works sector. In other words, the concrete may be waste concrete from the construction of buildings and / or road structures, scrap from concrete production, concrete from the demolition of buildings or road structures, or a mixture thereof.

[0015] Definitions

[0016] The term "cement" designates in the invention a hydraulic binder, that is to say a finely ground mineral material which, mixed with water, forms a paste which sets and hardens as a result of hydration reactions and processes and which, after hardening, retains its strength and stability even under water (definition according to standard EN 197-1);

[0017] The term "cement paste" (hereinafter also referred to as "CMP") refers in the invention to a mixture of cement and water, which hardens due to the hydration reaction. The cement paste may optionally contain one or more additives. The amount of cement paste that adheres to the GBRs is a criterion for the cleanliness of the GBRs.

[0018] The term "concrete" in the invention refers to a mixture of cement, aggregates (sand and gravel) and water. This is the initial material which contains all the constituents (aggregates and cement paste) which we are seeking to recover.

[0019] The term "natural aggregates (NA)" refers in the invention to particles of sand and natural gravel produced by exploitation of deposits of sand and gravel of alluvial, terrestrial or marine origin.

[0020] The term "recycled concrete aggregates (RCA)" refers in the invention to sand and gravel particles produced from concrete and reused as a replacement for GN, to make concrete or for any other application.

[0021] The term "residual mortar" refers in the invention to a mixture of cement paste and GN of a size smaller than the particle size of the GBR considered. The residual mortar is mainly found adhering to the surface of the GBR considered. Thus, the definition of residual mortar varies according to the particle size fraction of the GBR considered. Let GM be the upper mesh and G m the lower mesh of a GM-Gm granulometric fraction of GBR, then the residual mortar associated with this granulometric fraction of GBR contains a mixture of cement paste and GN of size < G m . In the invention, the term "residual mortar" is also referred to as "residual cementitious matrix".

[0022] The term "fines" designates in the invention a mixture of cement paste and GN of a size smaller than the smallest size Gm of the finest fraction of GBR produced by the concrete recycling process.

[0023] The term "accelerated carbonation" refers in the invention to a carbonation process that operates at a CO2 concentration 250 to 12,000 times higher than that of the Earth's atmosphere (415 ppm), which leads to carbonation kinetics on the scale of a few minutes compared to years for natural carbonation. In the fines, only the cement paste carbonates, the NG contained in the fines does not carbonate. In this invention, the term "carbonation" used alone is synonymous with "accelerated carbonation". The term "accelerated carbonation" or "carbonation" is therefore opposed to the term "natural carbonation".

[0024] In the GBRs of the invention, the terms "bare natural aggregates" and "clean natural aggregates" and "clean GBRs" are synonymous. The bare natural aggregates in the GBRs of the invention preferably comprise less than 5% by mass of PdC, particularly preferably at most 4% by mass of PdC, and more particularly preferably at most 3% by mass of PdC, relative to the total mass of the bare natural aggregates.

[0025] In the GBRs of the invention, the terms "natural aggregates associated with an adherent residual mortar" and "non-clean natural aggregates" and "non-clean GBRs" are synonymous. The natural aggregates associated with an adherent residual mortar in the GBRs of the invention preferably comprise from 5% to 30% by mass of PdC, particularly preferably from 7 to 25% by mass of PdC, and more particularly preferably from 10 to 20% by mass of PdC, relative to the total mass of the natural aggregates associated with an adherent residual mortar.

[0026] Step i)

[0027] The centimetric construction and / or demolition concrete blocks used in step i) comprise GN (sand and / or gravel) and PdC. Within the centimetric construction and / or demolition concrete blocks, the GN are combined with PdC to form said centimetric blocks.

[0028] Step i) allows the formation of a primary fracture network within the concrete blocks, and more particularly around the GN (textural release of the GN); then the formation of a secondary fracture network in the PdC. This leads to selective fracturing of the concrete, allowing the GN to be separated from the major part of the PdC of the initial concrete, without significant damage to the GN.

[0029] At the same time, the dense secondary network of microfractures innervating the PdC allows the release and concentration of the majority of the PdC from the initial concrete in a fine particle size fraction, which favors the following extraction step ii). The microfracturing of the PdC also favors step iii) of carbonation of the recycled fines. The formation of the primary and secondary fracture networks mentioned above thus makes it possible to favor the following step ii) of selective release of the GN contained in the construction and / or demolition concrete, and consequently to favor the separation of the GN on one side, and the fines on the other without however degrading the GN.

[0030] In other words, the greater the number of microfractures per unit volume in the PdC, the cleaner the GBRs obtained (i.e. high GN content and low adherent residual mortar content), the more the fines contain a large quantity of PdC, and the more efficient the process is, and in particular the following steps ii) and ill).

[0031] Unlike a crusher that randomly fractures the concrete (as explained below in Figure 1), microwave treatment selectively weakens the PdC, without significantly altering the structure of the GN. The integrity of the GN is therefore preserved, and at least 75% by mass of the PdC of centimetric construction and / or demolition concrete blocks can then be found in the recycled fines thanks to the combination of steps i) and ii).

[0032] The microwave treatment of step i) may be carried out at an incident power sufficient to induce fracturing of the concrete blocks.

[0033] Preferably, the microwave treatment of step i) is carried out at a power ranging from 1 kW to 50 kW, preferably ranging from 5 kW to 40 kW and particularly preferably from 5 kW to 10 kW.

[0034] These powers are particularly suitable for processing 1 t / h of concrete blocks.

[0035] Preferably, the microwave treatment of step i) (exposure time) is carried out for a duration ranging from approximately 30 s to 10 min, and particularly preferably from approximately 1 min to 5 min.

[0036] In the invention, the term "centimetric size" relating to construction and / or demolition concrete blocks preferably means that the construction and / or demolition concrete blocks have a size of at most approximately 10 cm, particularly preferably at most 7 cm, and more particularly preferably at most approximately 5 cm.

[0037] Preferably, the construction and / or demolition concrete blocks have a size of at least about 1 cm, particularly preferably at least about 2 cm, and more particularly preferably at least about 3 cm. Step i) can be carried out by passing the concrete blocks through a microwave tunnel.

[0038] The microwave treatment i) may be carried out at a frequency ranging from approximately 915 MHz to 2450 MHz, and particularly preferably at a frequency of approximately 915 MHz or 2450 MHz. These frequencies are medium frequencies with limits of 902-928 MHz and 2400-2500 MHz respectively.

[0039] Microwave treatment i) can be carried out in continuous mode or in pulses (for example with pulses in symmetrical slots of at least 1 second).

[0040] Propagation modes in progressive or standing waves can be used depending on the size of the pieces of concrete to be treated (pieces of concrete to be treated smaller than 5 cm: standing waves, pieces of concrete to be treated larger than 5 cm: progressive waves).

[0041] Microwave treatment i) can be carried out via guided waves or antennas inside reflective cavities.

[0042] Microwave treatment i) results in drying of the material, and the evaporated water can advantageously be recovered, in particular for reuse during the following steps ii) to ill).

[0043] At the end of step i), the concrete blocks are said to be “micro-fractured”, due to the fact that the cement paste contained in said concrete blocks is massively microfractured. Said concrete blocks obtained at the end of step i) therefore comprise a microfractured cement paste.

[0044] Step ii)

[0045] During step ii), said micro-fractured concrete blocks from step i) undergo one or more mechanical treatment steps.

[0046] Thanks to step i), a mechanical constraint which favors the shear forces during step ii) makes it possible to propagate the fractures, fragment the micro-fractured concrete blocks while limiting the fracture of the GN, and release on the one hand GBR comprising bare natural aggregates and natural aggregates associated with an adherent residual mortar, and on the other hand recycled fines.

[0047] Step ii) makes it possible to extract from said micro-fractured concrete blocks, GBR comprising bare natural aggregates and natural aggregates associated with an adherent residual mortar on the one hand; and recycled fines on the other hand. At the end of step ii), the GBR are separated from the recycled fines, and at least 75% by mass of the PdC contained in the initial concrete to be recycled is found in the recycled fines.

[0048] At the end of step ii), we then obtain a fraction Fi of GBR comprising bare natural aggregates and natural aggregates associated with an adherent residual mortar; and a fraction F2 of recycled fines.

[0049] GBRs preferably have a particle size greater than or equal to approximately 1 mm.

[0050] Bare natural aggregates preferably have a grain size greater than or equal to approximately 1 mm.

[0051] Natural aggregates combined with an adherent residual mortar preferably have a grain size greater than or equal to approximately 1 mm.

[0052] According to a preferred embodiment of the invention, the bare natural aggregates (respectively the natural aggregates associated with an adherent residual mortar) are chosen from gravel, sands with a grain size greater than or equal to approximately 1 mm, and one of their mixtures.

[0053] Gravel is generally defined as having a grain size greater than approximately 4 mm.

[0054] Sands are generally defined as having a grain size of approximately 4 mm or less.

[0055] In the present invention, the granulometry of the GBR, gravel, and sand is determined by methods well known to those skilled in the art, and in particular by sieving (for example according to standard NF EN 933-1) (laboratory method) or by screening (industrial method).

[0056] The residual mortar adhering to the GBR contains GN preferably with a grain size of less than approximately 1 mm.

[0057] Recycled fines (fraction F2) generally comprise (or consist of) a mixture of PdC and GN with a particle size of less than approximately 1 mm.

[0058] The recycled fines (fraction F2) preferably have a particle size of less than 1 mm. In fraction F2, GN and PdC can be separated into released particles (containing GN or PdC), or combined into mixed particles (containing a mixture of GN and PdC).

[0059] Step ii-1)

[0060] Step ii) preferably comprises at least one step ii-1) of crushing the micro-fractured concrete blocks.

[0061] Step ii-1) of crushing the micro-fractured concrete blocks can be carried out using at least one percussive crusher (e.g. a jaw crusher, a gyratory crusher, a cone crusher, or an impact crusher), or a non-percussive crusher (e.g. a roller mill such as a single or double roller mill or a high-pressure roller mill).

[0062] Preferably, step ii-1) of crushing the micro-fractured concrete blocks is a non-percussive crushing step. In this embodiment, step ii-1) of crushing the micro-fractured concrete blocks preferably uses at least one non-percussive crusher.

[0063] A non-percussive crusher has the advantage of implementing a continuous compressive shear action. It thus avoids excessive damage to the NG and / or preserves the integrity of their granulometric and mechanical properties.

[0064] The non-percussive crusher is preferably a roller mill such as a single or double roller mill. The roller mill can have smooth or notched rollers.

[0065] The roller mill type crusher makes it possible to produce a particular maximum particle size corresponding to that of the GN present in the initial concrete to be recycled, by suitable adjustment of its operating parameters, in particular the feed rate, the rotation speed of the roller(s), the spacing between the rollers and / or the hydraulic pressure applied.

[0066] The spacing of the cylinders is adapted to the maximum granulometry of the GN of the initial concrete to be recycled, so as to minimize their fragmentation.

[0067] The process may comprise several grinding steps ii-1), in particular by carrying out:

[0068] - several grinding steps ii-1) after step i) of microwave treatment, or - several successive sequences of a step i) of microwave treatment and a grinding step ii-1).

[0069] When several grinding steps ii-1) are carried out after step i), a series of non-percussive crushers such as roller mills can be used, and can successively produce increasingly finer maximum GBR particle sizes, by suitable adjustment of the operating parameters of the successive crushers, in particular the feed rate, the rotation speed of the roller(s), the spacing of the rollers and / or the hydraulic pressure applied.

[0070] The cylinder spacing can be continuously decreased, so as to produce an increasingly narrower GBR granulometry and obtain the cleanest possible GBRs (i.e. high GN content and low adherent residual mortar content), and optimize the production of recycled fines.

[0071] When several successive sequences of steps i) and ii-1) are carried out, a single non-percussive crusher such as a roller mill can be used after each step i), and makes it possible to successively produce increasingly finer maximum GBR particle sizes, by suitable adjustment of its operating parameters, in particular the feed rate, the rotation speed of the roller(s), the spacing of the rollers and / or the hydraulic pressure applied.

[0072] The grinding step ii-1) is advantageously carried out using the dry method. The dry method is particularly suitable because the previous microwave treatment step i) contributes to the drying of the material.

[0073] By means of one or more grinding steps ii-1), GBR (natural aggregates with or without adherent residual mortar) are obtained which preferably have a GM granulometry (which corresponds to the maximum granulometry of the GN of the initial concrete to be recycled) of at most approximately 45 mm, or at most approximately 25 mm, or at most approximately 11.2 mm, or at most 8 mm, or at most 4 mm, in particular depending on the intended application and / or the granulometry of the GN present in the initial concrete to be recycled (i.e. GM < 45 mm, or GM < 25 mm, or GM < 11.2 mm or GM < 4 mm).

[0074] Preferably, the GBRs obtained at the end of the grinding stage (natural aggregates with or without residual adherent mortar) have a minimum particle size G m of at least about 1 mm. Step ii-2)

[0075] Step ii) may further comprise, in particular after step ii-1), at least one step ii-2) of screening (also called sieving). This step ii-2) allows granulometric sorting of the GBR and fines.

[0076] Screening step ii-2) can be carried out in a dry or wet process, and preferably in a wet process.

[0077] Screening step ii-2) may be carried out using any type of vibrating, gyratory or rotary screen or sieve, and preferably using a rotary screen or gyratory sieve. A rotary screen is also known as a rotary screener or rotary sieve or trommel screen or trommel screen.

[0078] The screening step ii-2) makes it possible to separate the fraction Fi of GBR from the fraction F2 of recycled fines; and possibly to separate said GBR according to their particle size within the fraction F1. Separating said GBR according to their particle size within the fraction F1 makes it possible to recover additional recycled fines during each of the screening steps ii-2).

[0079] The process preferably comprises several screening stages ii-2). This makes it possible to maximize the fraction of recyclable fines rich in cement paste.

[0080] The screen(s) used during screening step(s) ii-2) comprises (comprise) an opening mesh adapted to allow such separation(s).

[0081] The screen (series of screens) preferably has a mesh adapted to the crusher (series of crushers) used in step ii-1) or steps ii-1).

[0082] According to a preferred embodiment of the invention, step ii-2) comprises a first screening step ii-2a) making it possible to isolate GBRs having a particle size G1 such that G m G1 < GM, OR a particle size fraction G1 -G1 such that G m Gr < G1 GM.

[0083] For example, the GBRs separated during the first screening step ii-2a) have a particle size G1 of at least approximately 4 mm.

[0084] For example, the GBRs separated during the first screening step ii-2a) have a particle size G1 of at most approximately 45 mm, or at most approximately 25 mm, or at most approximately 11.2 mm, or at most 8 mm, in particular depending on the intended application and / or the particle size of the GNs present in the initial concrete to be recycled. For example, the first screening step ii-2a) can make it possible to separate GBRs having a given particle size fraction: 4-8 mm, or 8-11.2 mm or 11.2-25 mm or 25-45 mm.

[0085] The limits for the granulometric fractions are given for information purposes only and any other limit can be used depending on the intended application and / or the granulometry of the GN present in the initial concrete to be recycled.

[0086] During the first screening stage ii-2a), the GBRs of particle size Gi (Fraction Fia) are separated from the recycled fines (Fraction F2a), and possibly from GBRs of lower particle size (Fraction Fib, Fraction Fie, etc.).

[0087] GBRs of Gi granulometry include bare natural aggregates and natural aggregates associated with an adherent residual mortar.

[0088] Step ii-2) may further comprise a second screening step ii-2b) making it possible to isolate GBRs having a particle size G2 such that G m G2 < G1, or a particle size fraction G2-G2 such that G m G2' < G2 Gr < G1 < GM.

[0089] For example, the GBRs separated during the second screening step ii-2b) have a G2 particle size of at most approximately 4 mm.

[0090] For example, when the first screening step ii-2a) has made it possible to isolate GBRs having a particle size fraction of 4-8 mm, the second screening step ii-2a) can make it possible to isolate GBRs having a particle size fraction of 1-4 mm; when the first screening step ii-2a) has made it possible to isolate GBRs having a particle size fraction of 8-11.2 mm, the second screening step ii-2a) can make it possible to isolate GBRs having a particle size fraction of 4-8 mm; when the first screening step ii-2a) has made it possible to isolate GBRs having a particle size fraction of 11.2-25 mm, the second screening step ii-2a) can make it possible to isolate GBRs having a particle size fraction of 8-11.2 mm; when the first screening step ii-2a) has made it possible to isolate GBRs having a particle size fraction of 25-45 mm, the second screening step ii-2a) can make it possible to isolate GBRs having a particle size fraction of 11.2-25 mm.

[0091] Preferably, the GBRs separated during the second screening step ii-2b) have a particle size G2 of at least approximately 1 mm. During the second screening step ii-2b), the GBRs of particle size G2 (Fraction F) are separated from the recycled fines (fraction F2b), and possibly from recycled concrete aggregates GBR of lower particle size (Fraction Fie, etc.).

[0092] Recycled concrete aggregates of G2 granulometry include bare natural aggregates and natural aggregates associated with an adherent residual mortar.

[0093] Step ii) may thus comprise one or more screening steps ii-2). In particular, one or more screening steps [steps ii-2a), ii-2b), ii-2c) etc.] may be required to separate the GBR from the recycled fines as much as possible. This may depend in particular on the particle size dispersion of the GN used in the initial construction and / or demolition concrete to be recycled.

[0094] The process of the invention, and in particular step ii), may comprise several grinding steps ii-1) and several screening steps ii-2).

[0095] In this embodiment, step ii) may comprise:

[0096] - several grinding stages ii-1) followed by several screening stages ii-2), or

[0097] - several successive sequences, of a grinding step ii-1) and a screening step ii-2).

[0098] Step ii) preferably comprises several successive sequences, of a grinding step ii-1) and a screening step ii-2).

[0099] The process of the invention resulting from steps i) and ii) thus makes it possible on the one hand to obtain GBR aggregates having a high cleanliness rate and on the other hand to obtain a large quantity of fines since the vast majority of the GBR has been freed from the residual mortar (and consequently from the PdC cement paste that the mortar contains) adhering to the GN.

[0100] The method may further comprise, after step ii), when the method comprises several screening steps ii-2), a step during which the different fractions of fines from the different screening steps (F2a, F2b, F2c, etc.) are combined.

[0101] The reuse of this large quantity of construction and demolition concrete waste fines, as a mineral addition to reduce the demand for cement in concrete and / or as a constituent of the raw material used to produce cement, is a potential vector for reducing CO2 emissions and the demand for natural resources in concrete for its manufacture.

[0102] At the end of step ii), and in particular steps ii-1) and ii-2), the recycled fines are separated or recovered. They preferably comprise at least 75% by mass of the PdC contained in the initial concrete to be recycled, where a crushing step possibly followed by screening step(s) of the prior art leads to recycled fines which contain less than 25% by mass of the PdC contained in the initial concrete to be recycled.

[0103] Preferably, the recycled fines further comprise GN with a particle size of less than 1 mm.

[0104] In recycled fines, GN with a grain size of less than 1 mm and cement paste can be dissociated, associated, or partially associated, and generally partially associated.

[0105] The recycled fines are in the form of particles with a very fine particle size (at least 45% by mass, and preferably at least 50% by mass, relative to the total mass of the recovered recycled fines have a particle size < 0.25 mm) and are fully accessible for carbonation.

[0106] Steps i) and ii) of the process of the invention are so efficient that the vast majority of the cement paste is found in the recycled fines in very fine granulometric form and well innervated with microfractures. This thus makes it possible to optimize the following step iii) of carbonation of the fines by promoting in particular the access and diffusion of carbon dioxide in the PdC which contains the reactive carbonatable phases, in particular portlandite, lime and hydrated calcium silicates (CSH).

[0107] Correspondingly, isolated or recovered recycled concrete aggregates GBR, more particularly GBR with a grain size greater than or equal to 1 mm, at the end of step ii), and in particular steps ii-1) and ii-2), have a structure as close as possible to that of the natural aggregates GN of the initial demolition and / or construction concrete.

[0108] They have such a cleanliness rate that they do not require carbonation step(s) in the presence of carbon dioxide and can be directly used in the production of new concrete. Consequently, the process according to the first subject of the invention does not include carbonation step(s) of the recycled concrete aggregates (RCA).

[0109] Indeed, steps i) and ii) make it possible to obtain very clean GBRs.

[0110] The process of the invention is selective in that it allows the different granulometric fractions of the GBR as well as the fines to be well separated.

[0111] In particular, the GBRs obtained from a given particle size fraction, greater than or equal to 1 mm, comprise at most 10% by mass of PdC, preferably at most 8% by mass of PdC, and even more preferably at most 5% by mass of PdC, relative to the total mass of the GBRs of said given particle size fraction.

[0112] At the end of step ii), and in particular steps ii-1) and ii-2), the recycled concrete aggregates GBR obtained from a given particle size fraction, greater than or equal to 1 mm, preferably comprise from 65 to 95% by mass of GN of said given particle size fraction, more preferably from 70 to 90% by mass of GN of said given particle size fraction, and even more preferably from 75 to 85% by mass of GN of said given particle size fraction, relative to the total mass of GBR of said given particle size fraction. This is also referred to as the recovery rate.

[0113] Preferably, the recycled concrete aggregates GBR obtained from a given particle size fraction, greater than or equal to 1 mm, comprise from 5 to 20% by mass of GN with a particle size smaller than said given particle size fraction, and more preferably from 7 to 15% by mass of GN with a particle size smaller than said given particle size fraction, relative to the total mass of GBR of said given particle size fraction.

[0114] In particular, the recycled concrete aggregates GBR obtained from a given granulometric fraction, greater than or equal to 1 mm, comprise from 5 to 35% by mass of residual mortar, preferably from 10 to 30% by mass, and even more preferably from 15 to 25% by mass of residual mortar, relative to the total mass of GBR of said given granulometric fraction.

[0115] The GBRs obtained at the end of step ii) can be used directly in the preparation of new concretes. They include such a low proportion of residual mortar that their water absorption and abrasion properties are 2 to 3 times better than those of GBRs obtained by the prior art processes.

[0116] The contents of the GBRs obtained from a given particle size fraction, greater than or equal to 1 mm, in PdC, GN of said given particle size fraction, GN of particle size less than said given particle size fraction, and residual mortar, as defined above, are obtained by selective dissolution of the PdC present in said GBRs with hydrochloric acid, weighing and measuring the various aforementioned constituents.

[0117] The method of the invention is efficient in that it makes it possible to obtain, for each given particle size fraction, greater than or equal to 1 mm, GBRs having a high cleanliness rate.

[0118] In the GBRs of the invention, the mortar (PdC + GN of granulometry lower than said given granulometric fraction) is distributed / adhers heterogeneously around the GN of said given granulometric fraction. This then leads in practice to obtaining majority clean GBRs (i.e. bare natural aggregates or clean natural aggregates) and minority non-clean GBRs (i.e. natural aggregates associated with an adhering mortar or non-clean aggregates).

[0119] In particular, at the end of step ii), and in particular steps ii-1) and ii-2), the recycled concrete aggregates GBR obtained from a given particle size fraction, greater than or equal to 1 mm, preferably comprise at least 50% by mass of natural aggregates clean from said given particle size fraction (i.e. bare natural aggregates or GBR clean from said given particle size fraction), more preferably from 55 to 85% by mass of natural aggregates clean from said given particle size fraction (i.e. bare natural aggregates or GBR clean from said given particle size fraction), and even more preferably from 60 to 75% by mass of natural aggregates clean from said given particle size fraction (i.e. bare natural aggregates or GBR clean from said given particle size fraction), relative to the total mass of GBR of said given particle size fraction.

[0120] Corollarily, at the end of step ii), and in particular steps ii-1) and ii-2), the recycled concrete aggregates GBR obtained from a given particle size fraction, greater than or equal to 1 mm, preferably comprise a content of less than 50% by mass of non-clean natural aggregates of said given particle size fraction (i.e. natural aggregates associated with adhering residual mortar or non-clean GBR of said given particle size fraction), more preferably from 15 to 45% by mass of non-clean natural aggregates of said given particle size fraction (i.e. natural aggregates associated with adhering residual mortar or non-clean GBR of said given particle size fraction), and even more preferably from 25 to 40% by mass of non-clean natural aggregates of said given particle size fraction (i.e.natural aggregates associated with adhering residual mortar or non-clean GBR of said given granulometric fraction), relative to the total mass of GBR of said given granulometric fraction.

[0121] The contents of the GBRs obtained from a given particle size fraction, greater than or equal to 1 mm, in clean GBRs and non-clean GBRs as defined above are obtained by optical and / or visual sorting to separate the clean GBRs and the non-clean GBRs, then verification of the proportion of PdC in the clean GBRs and the non-clean GBRs by selective dissolution of the PdC present in said clean and non-clean GBRs with hydrochloric acid, weighing and measuring.

[0122] The method of the invention may comprise several microwave treatment steps i), several grinding steps ii-1) and several screening steps ii-2), and preferably several successive sequences of a microwave treatment step, a grinding step ii-1) and a screening step ii-2).

[0123] Step a)

[0124] The method may further comprise at least one step a) of cleaning the GBRs. This thus makes it possible to reduce the proportion of residual mortar in the GBRs, to contribute to an even higher cleanliness rate of the GBRs and to increase the recovery rate of recycled fines.

[0125] Step a) is preferably carried out by abrasion, in particular using a rotary screen or a gyratory sieve.

[0126] Abrasion is a known mechanical process of surface cleaning.

[0127] Step a) is preferably carried out after the grinding step ii-1).

[0128] Step a) may be carried out at the same time as (i.e. concomitantly with) screening step ii-2), before or after screening step ii-2), and preferably at the same time as screening step ii-2). In the case where steps a) and ii-2) are concomitant, they may be carried out using a rotary screen or a gyratory sieve.

[0129] In the case where steps a) and ii-2) are not concomitant, the abrasion step a) can be implemented in a rotating drum, with or without lifters.

[0130] In the case where several screening steps are carried out (eg step ii-2a) and ii-2b)), the method may comprise several cleaning steps a), in particular concomitant with each of the screening steps, before or after or each of the screening steps.

[0131] In order to facilitate step a), and in particular to facilitate the abrasion of the residual mortar, GN can be added to the GBR before step a).

[0132] The added GNs may represent up to 99.5% by mass, preferably up to 95% by mass, and particularly preferably up to 50% by mass, relative to the total mass of the aggregates (GN + GBR) used in step a).

[0133] Step b)

[0134] The method may further comprise at least one step b) of washing the GBRs. This thus makes it possible to reduce the proportion of fines which could adhere to the surface of the GBRs.

[0135] Step b) is preferably carried out by washing with water, and particularly preferably by sprinkling or spraying with water.

[0136] Step b) may be carried out at the same time as (i.e. concomitantly with) step a) of cleaning or abrasion, and / or at the same time as step ii-2) of screening, and / or between step a) of cleaning or abrasion and step ii-2 of screening), and preferably at the same time as step ii-2 of screening and optionally at the same time as step a) of cleaning or abrasion.

[0137] This thus helps to promote the entrainment of recycled fines and their separation from the GBR.

[0138] In the case where several screening steps are carried out (e.g. step ii-2a) and ii-2b)), the method may comprise several washing steps b), in particular concomitant with each of the screening steps ii-2) and / or cleaning steps a), or between each of the cleaning steps a) and screening steps ii-2). According to a preferred embodiment of the invention, steps ii-2) and a) are carried out at the same time, in particular using a rotary screen or gyratory sieve, and particularly preferably in a wet process. The wet process is preferably carried out by sprinkling or spraying water (e.g. water spray, which can reuse the evaporated and then condensed water from step i). In other words, in this wet process embodiment, steps ii-2), a) and b) are carried out at the same time. This makes it possible to eliminate recycled fines which could adhere to the surface of the GBR and thus concentrate them in the final fraction of recycled fines.

[0139] The recycled fines obtained at the end of step ii) can be used directly in the cement raw mix, for example for the manufacture of calcium clinker, subject to compositional adjustments (e.g. to achieve specific silicic or hydraulic moduli) by adding other sources of materials used in the raw mix. By replacing a fraction of the natural limestone used in the cement raw mix, the use of recycled fines in the cement raw mix contributes to the preservation of natural limestone resources, and reduces the carbon footprint of the clinker by not emitting additional CO2 during the clinkerization step, compared to the use (calcination) of natural limestone.

[0140] Step iii)

[0141] The process further comprises one or more steps iii) of carbonation in the presence of carbon dioxide of the recycled fines [corresponding to the fraction F2 recovered at the end of step ii), ii-1), ii-2), ii-2a), or ii-2b)].

[0142] Carbonation concerns the reactive phases, i.e. the PdC present in the recycled fines. At the end of step iii), we therefore obtain carbonated recycled fines comprising a mixture of GN < 1 mm and carbonated PdC.

[0143] Carbonation of recycled fines allows, on the one hand, the storage of carbon dioxide, and on the other hand, to obtain carbonated fines potentially exhibiting pozzolanic and / or hydraulic activity. They can then be used as a mineral addition in concrete to replace a cement (for example CEM I or CEM II), or as a constituent of a cement in order to manufacture composite cements. By replacing, for example, Portland cement used in the formulation of structural concrete (constructions) or non-structural concrete (concrete blocks, blocks, slabs, coping stones, technical mortars), the use of carbonated fines as a mineral addition reduces the carbon footprint of concrete. This reduction comes from the reduction in the proportion of Portland cement in the concrete, and the quantity of carbon trapped in the carbonated fines which then act as a carbon sink.

[0144] In other words, the recycled carbonate fines obtained according to the process of the invention can be used as a means of storing CO2 and / or as a replacement for all or part of a cement. This use of carbonate fines as a reactive mineral addition in the formulation of concrete is a vector for reducing the carbon footprint of concrete in proportion to the rate of replacement of cement by carbonate fines.

[0145] When the recycled fines from step ii) are used as a mineral addition, they are preferably ground before the carbonation step iii), for example until particles with a particle size of less than approximately 80 pm are obtained, preferably ranging from approximately 5 to 20 pm.

[0146] Step iii) is preferably carried out in the presence of a gas containing CO2, preferably comprising at least 5% by volume of CO2, and particularly preferably at least 10% by volume of CO2, relative to the total volume of gas.

[0147] Carbon dioxide can come from CO2-containing flue gases, for example from a CO2-rich biogas stream generated by a methanizer or a biomass power plant, or from flue gas produced by an industrial emitter such as a cement plant or a power plant; or it can be prepared from a CO2 source. The CO2 source may or may not be previously stored.

[0148] Flues containing CO2 preferably contain at least 10% by volume of CO2, relative to the total volume of gas present in the flues.

[0149] Fumes containing CO2 may also contain other elements, in particular nitrogen N2, oxygen O2, and possibly water.

[0150] The biogas stream may contain approximately 70% to 90% CO2 by volume, relative to the total volume of biogas. In step iii), the recycled fines may be introduced into a rotating drum or other reactor where they may be brought into contact with the carbon dioxide-containing gas.

[0151] Step iii) may be carried out at a partial pressure of CO2 ranging from about 0.1 to 100 bar, and preferably from about 0.1 to 5 bar (i.e. 240 to 12000 times the partial pressure of CO2 in the atmosphere - 0.415 millibar).

[0152] Step iii) may be carried out at a temperature ranging from about 18°C ​​to about 100°C, and preferably from about 20 to about 80°C.

[0153] Step iii) may be carried out with a relative humidity ranging from about 0% to about 100%, and preferably from about 10% to about 90%.

[0154] Thanks to the accelerated carbonation of fines, we obtain recycled carbonated fines which can store up to approximately 15% by mass of CO2, or approximately up to 150 kg of CO2 per tonne of fines.

[0155] Step io)

[0156] The method may further comprise, before step i), a step io) of crushing construction and / or demolition concrete to form construction and / or demolition concrete blocks having a centimeter size such as that implemented in step i).

[0157] Step io) of crushing can be carried out using a crusher such as a jaw crusher, a cone crusher, a gyratory crusher, an impact crusher, an impact crusher, a hammer crusher or a centrifugal rotor crusher.

[0158] According to a preferred embodiment of the invention, step i) is carried out directly after step io) (no intermediate step(s)).

[0159] According to a preferred embodiment of the invention, the method does not comprise any step(s) implementing a liquid phase between steps io) and i).

[0160] The method of the invention makes it possible to obtain from construction and / or demolition concrete blocks a distribution between aggregates and fines close to the initial distribution of the original concrete, i.e. approximately 70 to 90% by mass of GBR (non-carbonated fraction F1), and 10 to 30% by mass of fines (carbonated fraction F2), relative to the total mass of construction and / or demolition concrete blocks. In particular, the combined use of microwaves, mechanical treatment, and carbonation of fines in the presence of carbon dioxide allows the complete recycling of concrete waste from construction and / or deconstruction.

[0161] The second subject of the invention is a method for recycling concrete from construction and / or demolition, characterized in that it comprises the following steps: i) one or more step(s) of microwave treatment of construction and / or demolition concrete blocks having a centimeter size, to form micro-fractured concrete blocks, and ii) one or more step(s) of mechanical treatment making it possible to extract from said micro-fractured concrete blocks, recycled concrete aggregates (RCA) comprising bare natural aggregates and natural aggregates associated with an adherent residual mortar; and recycled fines, said method being free of step(s) of carbonation of the recycled concrete aggregates (RCA) and recycled fines obtained in step ii).

[0162] The process in accordance with the second subject of the invention resulting from steps i) and ii) thus makes it possible on the one hand to obtain GBR aggregates having a high cleanliness rate and on the other hand to obtain a large quantity of fines since the vast majority of the GBR has been freed from the residual mortar (and consequently from the cement paste that the mortar contains) adhering to the GN.

[0163] Steps i) and ii) of the process according to the second subject of the invention are so efficient that a very small quantity of cement paste adhering to the GN remains in the GBR. In the same way, steps i) and ii) of the process according to the second subject of the invention are so efficient that the vast majority of the cement paste is found in the recycled fines in very fine particle size form.

[0164] Step ii) preferably comprises at least one step ii-1) of grinding the micro-fractured concrete blocks. The method may comprise several grinding steps ii-1).

[0165] Step ii) may further comprise, in particular after step ii-1), at least one screening step ii-2). Step ii) may comprise one or more screening steps ii-2). The method of the invention, and in particular step ii), may comprise several grinding steps ii-1) and several screening steps ii-2).

[0166] The method may further comprise at least one step a) of cleaning the GBRs.

[0167] The method may further comprise at least one step b) of washing the GBRs.

[0168] The method may further comprise, before step i), a step io) of crushing construction and / or demolition concrete to form construction and / or demolition concrete blocks having a centimeter size such as that implemented in step i).

[0169] Steps i), ii), ii-1), ii-2), a), b), and io) are as defined in the first subject of the invention.

[0170] The said process therefore makes it possible to isolate the GBRs directly obtained in step ii). In other words, it corresponds to a GBR manufacturing process.

[0171] The recycled fines obtained at the end of step ii) of the process in accordance with the second subject can be used directly in the cement raw mix, for example for the manufacture of calcium clinker, subject to compositional adjustments (e.g. to achieve specific silicic or hydraulic moduli) by adding other sources of materials used in the raw mix. By replacing a fraction of the natural limestone used in the cement raw mix, the use of recycled fines in the cement raw mix contributes to the preservation of natural limestone resources, and reduces the carbon footprint of the clinker by not emitting additional CO2 during the clinkerization step, compared to the use (calcination) of natural limestone.

[0172] The GBRs obtained at the end of step ii) of the process in accordance with the second object can be used directly in the preparation of new concrete.

[0173] The third subject of the invention is recycled concrete aggregates GBR obtained according to a process in accordance with the first subject of the invention or obtained according to a process in accordance with the second subject of the invention, characterized in that the GBR of a given particle size fraction, greater than or equal to 1 mm, comprise at least 50% by mass of natural aggregates specific to said given particle size fraction (i.e. bare natural aggregates or GBR specific to said given particle size fraction), more preferably from 55 to 85% by mass of natural aggregates specific to said given particle size fraction (i.e. bare natural aggregates or GBR specific to said given particle size fraction), and even more preferably from 60 to 75% by mass of natural aggregates specific to said given particle size fraction (i.e. bare natural aggregates or GBR specific to said given particle size fraction), relative to the total mass of the GBR of said given particle size fraction.

[0174] Corollarily, the recycled concrete aggregates GBR, greater than or equal to 1 mm, preferably comprise a content of less than 50% by mass of non-clean natural aggregates of said given particle size fraction (i.e. natural aggregates associated with adhering residual mortar or non-clean GBR of said given particle size fraction), more preferably from 15 to 45% by mass of non-clean natural aggregates of said given particle size fraction (i.e. natural aggregates associated with adhering residual mortar or non-clean GBR of said given particle size fraction), and even more preferably from 25 to 40% by mass of non-clean natural aggregates of said given particle size fraction (i.e. natural aggregates associated with adhering residual mortar or non-clean GBR of said given particle size fraction), relative to the total mass of GBR of said given particle size fraction.

[0175] In particular, the GBRs of a given particle size fraction, greater than or equal to 1 mm, comprise at most 10% by mass of PdC, preferably at most 8% by mass of PdC, and even more preferably at most 5% by mass of PdC, relative to the total mass of the GBRs of said given particle size fraction.

[0176] The recycled concrete aggregates GBR of a given particle size fraction, greater than or equal to 1 mm, preferably comprise from 65 to 95% by mass of GN of said given particle size fraction, more preferably from 70 to 90% by mass of GN of said given particle size fraction, and even more preferably from 75 to 85% by mass of GN of said given particle size fraction, relative to the total mass of GBR of said given particle size fraction.

[0177] Preferably, the recycled concrete aggregates GBR of a given particle size fraction, greater than or equal to 1 mm, comprise from 5 to 20% by mass of GN of particle size less than said given particle size fraction, and more preferably from 7 to 15% by mass of GN of particle size less than said given particle size fraction, relative to the total mass of GBR of said given particle size fraction.

[0178] In particular, the recycled concrete aggregates GBR of a given particle size fraction, greater than or equal to 1 mm, comprise from 5 to 35% by mass of residual mortar, preferably from 10 to 30% by mass, and even more preferably from 15 to 25% by mass of residual mortar, relative to the total mass of GBR of said given particle size fraction.

[0179] Brief description of the drawings

[0180] The accompanying drawings illustrate the invention:

[0181] Figure 1 represents the fracturing of concrete according to a method of the prior art, and comparatively according to the method of the invention.

[0182] Figure 2 represents a schematic diagram of the different stages of the method of the invention.

[0183] Figure 3 represents the measurement of the cleanliness of the GBRs through the variation of the residual PdC rate (% by mass) as a function of the size of the GBRs; and the measurement of the water absorption of the GBRs (in %) as a function of the size of the GBRs, according to the method of the invention, and comparatively according to a reference method.

[0184] Figure 4 represents the speciation analysis of the constituents of the initial concrete and the GBRs at the end of the process of the invention, and comparatively of a process of a reference process.

[0185] Figure 5 shows the performance of the method of the invention compared to a reference method, and compared to the theoretical limit.

[0186] Figure 6 shows the performance of the method of the invention compared to a reference method, and compared to the theoretical limit.

[0187] Other characteristics and advantages of the present invention will appear in light of the description of non-limiting examples of the method according to the invention.

[0188] Examples

[0189] Example 1: representations of the method according to the invention and of a prior art method not according to the invention T1

[0190] Figure 1 includes a representation of the fracturing of concrete according to a method of the prior art (figure 1a)) and a representation of the fracturing of concrete according to the method of the invention (figure 1b)).

[0191] In Figure 1 a), fracturing is random and non-selective between GN and mortar. It produces GBRs with a low GN content (< 60% by mass of GN relative to the total mass of GBRs) and a high PdC content (> 10% by mass of PdC relative to the total mass of GBRs), with a high potential for transgranular fracturing of the original GNs. As a corollary, it produces few recycled fines in which no more than 25% of the PdC of the initial concrete to be recycled is concentrated.

[0192] In Figure 1 b), fracturing is selective between GN and mortar. It promotes both the concentration of GN in GBRs with a low rate of adherent mortar without altering the granulometric and mechanical properties of the GN, and the recovery of the PdC contained in the initial concrete to be recycled in a fraction of fines. Microfracturing of the PdC allows the concentration of the majority of the PdC of the initial concrete to be recycled in the fines, and promotes the carbonation of the PdC of the fines.

[0193] Figure 2 shows step i) of microwave treatment within a microwave tunnel of construction and / or demolition concrete blocks to form micro-fractured concrete blocks. These are then crushed according to step ii-1) in a roller mill to form a mixture of GBR of different particle sizes; and recycled fines. Crushing ii-1) makes it possible to obtain a particle size for example less than or equal to 8 mm. A first screening or sieving step ii-2a) is then carried out using a rotary screen to extract GBR having a particle size fraction G1 -G1 on the one hand (e.g. particle size fraction of 4 to 8 mm); and a mixture of recycled fines and GBR having a particle size < Gi on the other hand (particle size less than 4 mm).

[0194] The recycled fines and the GBRs with a particle size < Gi undergo a new screening or sieving step ii-2b) using a rotary screen to extract GBRs having a particle size fraction G2-G2 on the one hand (e.g. particle size fraction of 1 to 4 mm); and recycled fines on the other hand (particle size less than 1 mm). The recycled fines recovered during step ii-2b) are carbonated in a carbonation reactor according to a step iii). Optionally, the concrete blocks used in step i) and having a centimeter size (e.g. < 30 mm) can be obtained from the crushing of construction and / or demolition concrete, preferably using a jaw crusher [step io)].

[0195] In steps ii-2a) and ii-2b), abrasion steps a) and washing steps b) (spraying with water) are preferably carried out concomitantly with each of steps ii-2a) and ii-2b).

[0196] Example 2: recycling of concrete from construction and / or demolition using a process in accordance with the invention

[0197] 2.1 Production of concrete samples and characteristics

[0198] A concrete was formulated from cement and crushed siliceous natural aggregates (NAA) with a grain size of less than 8 mm, with a water / cement ratio of 0.6.

[0199] 2.1 .1 The cement used is a CEM I type cement from Lafarge, from the Teil plant. Its strength class is 52.5R, i.e. rapid setting. It meets the European requirements of standard EN 197-1.

[0200] The physical and mechanical characteristics of the cement used are as follows:

[0201] - Blaine specific surface area = 4160 cm 2 / g, and

[0202] - Density = 3.15 g / cm 3 .

[0203] 2.1 .2 The natural aggregates used (GN) are a mixture of sand (S) and gravel (G) from the Palvadeau sandpit (St Christophe du Ligneron) of the crushed siliceous type. The characteristics of these aggregates are as follows:

[0204] - Density = 2640 kg / m 3 ,

[0205] - Absorption coefficient = 0.7%,

[0206] - Chlorides < 0.001%,

[0207] - Water-soluble sulfates <0.01%, and

[0208] - Active alkali content = 0.0022%.

[0209] Table 1 below represents the particle size distribution of the GN used to formulate the concrete, and more specifically the % by weight (mass fractions) of 5 different particle size fractions, namely 4 / 8 mm, 2 / 4 mm, 1 / 2 mm, 0.25 / 1 mm and 0 / 0.25 mm, relative to the total weight of the natural GN aggregates used to formulate the concrete.

[0210] TABLE 1

[0211] These mass fractions are interpreted as the average values ​​of the actual GN composition of the concrete used below. The last line of this Table 1 defines the GN 0 / 1 mm particle size fraction to which reference will be made below. This fraction aggregates the 0.25 / 1 mm and 0 / 0.25 mm GN fractions.

[0212] 2.1 .3 Concrete formulation

[0213] The proportions of binder (cement and superplasticizer), water and GN used to produce the concrete are indicated in Table 2 below:

[0214] TABLE 2

[0215] Several concrete samples are prepared by mixing the constituents in a mortar mixer for 60 seconds at low speed (62 rpm), 40 seconds at high speed (125 rpm), 90 seconds of pause then 60 seconds at high speed (125 rpm) to form a mixture; then pouring the mixture into cylindrical molds made of gray polypropylene with a diameter of 25 mm and a height of 30 mm. The molds are vibrated 2x10 seconds on a vibrating table. This leads to the formation of several concrete cylinders of controlled composition and shape, approximately 30 mm in size in their largest dimension.

[0216] These concrete cylinders are then stored under cellophane in a room at 19°C for 28 days for the concrete to cure.

[0217] After curing for 28 days in a temperate room, the cylindrical concrete samples are dried in an oven at 80°C for 48 hours. This duration was determined following a test on a batch of aggregates weighed at regular intervals until a constant mass (Am<0.1%) is reached. This drying ensures reproducibility of the concrete samples produced, by giving them a controlled humidity level comparable to that of naturally aged concrete.

[0218] The composition of the concrete in the samples, after curing and storage, is measured by dissolving the PdC in 19% hydrochloric acid by mass. The values ​​shown in Table 3 below give the range of composition values ​​measured on several 30 mm samples of concrete, each sample being dissolved individually. This makes it possible to judge the variability in composition of the concrete samples used.

[0219] TABLE 3

[0220] 2.2 Implementation of the method of the invention

[0221] 2.2.1 Step i) of microwave fracturing

[0222] The microwave bench used is a single-mode cavity waveguide manufactured by SAIREM with the following characteristics: - frequency = 2450 ± 25 MHz,

[0223] - Output power = 2000 ± <0.1% W,

[0224] - Maximum usage power = 1700 W,

[0225] - Waveguide = WR340 (rectangular section 86x43mm),

[0226] - Wave ripple < 0.3% RMS, and

[0227] - Magnetron cooling system: water.

[0228] This microwave bench can treat a 30 mm concrete sample at a time, at a given power and for a given time. A cylindrical concrete sample is placed in a quartz tube serving as a sample holder, the tube being placed in the chimney of the microwave bench. Each sample is treated for 4 minutes at an incident microwave power of 1.5 kW. The temperatures reached on the surface of the concrete range from 450°C to more than 600°C (limit measurable by the infrared thermometer used).

[0229] 2.2.2 Step ii) of mechanical treatment

[0230] 2.2.2.1 Non-percussive crushing (step i-1)j

[0231] The non-percussive crushing following the microwave treatment is carried out using a manual hydraulic press (Specac Atlas 15T). The concrete samples are compressed individually. The stroke of the hydraulic press stops 8 mm from the surface on which the GBRs are placed, which corresponds to the maximum size of the GN of the concrete samples.

[0232] The crushed sample is then screened dry on standard square mesh sieves of 8 mm, 4 mm, 2 mm, 1 mm and 0.25 mm to produce the particle size fractions 4 / 8 mm, 2 / 4 mm, 1 / 2 mm, 0.250 / 1 mm and 0 / 0.25 mm.

[0233] 2.2.2.3 Abrasion (step a).)

[0234] The fractions of recycled concrete aggregates (RCA) 1 / 4 mm and 4 / 8 mm produced by crushing and screening are abraded for a short time of 2 minutes separately in a cylindrical metal jar with an internal diameter of 10 cm, rotating at a speed of 100 rpm. The abrasive load consists of 336 g of alumina balls of 20 mm diameter and 200 ml of water. The products are then rescreened to 8 mm and 4 mm in order to separate the 8 mm and 4 mm RCAs respectively from the abrasion fines.

[0235] At the end of steps ii-1), ii-2) and a), several fractions of fines are recovered and collected.

[0236] 2.2.3 Carbonation of fines (step iii))

[0237] The fines obtained are ground to 80 pm with an automatic mortar-pestle, with an average size dso = approximately 10 pm, this fineness being justified for the use of carbonated fines as mineral addition. The carbonation step of the ground fines is carried out in suspension in a stirred reactor with a useful volume of 300 ml. The suspension used consists of a mixture of 15 g of recycled concrete fines and 150 ml of distilled water. The mixing is ensured by a stirring rotor rotating at 800 rpm. The carbonation reactor operates under a CO2 partial pressure of 5 bar at a controlled temperature of 60°C. A carbonation test lasts 20 hours, during which the consumption of CO2 by the fines is continuously measured. The final carbonation rate of the carbonated fines is obtained by thermogravimetric analysis (TGA) or by measuring total carbon (CHNS analysis).

[0238] Comparative example 3: recycling of concrete from construction and / or demolition using a process not in accordance with the invention

[0239] The method of the invention was compared with a non-percussive crushing process, which represents the most efficient current technology for producing recycled concrete aggregates. This comparative process, hereinafter referred to as the 'reference process', was implemented with the same concrete samples as those described in point 2.1. The implementation of the reference process consists of mechanical treatment via non-percussive crushing and screening steps under the same conditions as those described in point 2.2.

[0240] A fines carbonation step is carried out as described in Example 2, Part 2.2.3.

[0241] Example 4: performance of the method of the invention

[0242] 4.1 Performance evaluation criteria The performance criteria used to characterize the performance of the process relate to the quality and usage properties of recycled concrete aggregates (RCA) and recycled concrete fines.

[0243] For recycled concrete aggregates (RCA):

[0244] • Quality :

[0245] ❖ Rate (mass %) of PdC in a given particle size fraction of GBR,

[0246] ❖ Clean GBR rates (i.e. GBR with a PdC rate < 5% by mass) in a given GBR particle size fraction, and

[0247] ❖ Rate (mass %) of natural aggregates (NG) of the same granulometric fraction as the GBR.

[0248] • Usage properties:

[0249] ❖ Water absorption of GBRs using the WA24 method. This test measures the water content of GBRs after drying according to standard NF EN 1097-5. It is expressed as a mass percentage.

[0250] ❖ Wear resistance of GBRs measured by the Micro Deval (MDE) test. This test measures the resistance to frictional wear between GBRs and an abrasive load of steel balls according to standard NF EN 1097-1. The test result is expressed in % and represents the mass percentage of particles with a size < 1.6 mm produced during the test.

[0251] For recycled concrete fines (< 1 mm):

[0252] • Quality :

[0253] ❖ Rate (mass %) of mortar that the process concentrates in the fines (< 1 mm) produced

[0254] ❖ Rate (mass %) of PdC that the process concentrates in the fines (< 1 mm) produced

[0255] ❖ Rate (% by mass of CO2 captured) of carbonation of fines.

[0256] 4.2 Cleanliness of recycled concrete aggregates

[0257] The attached figure 3 shows the measurement of GBR cleanliness through the variation of the residual PdC rate (% by mass) (on the left) as a function of the size of the GBR for the process of the invention (solid circles) and for the reference process (empty circles). This rate is measured by dissolving the GBR of particle size fractions 4 / 8 mm, 2 / 4 mm, 1 / 2 mm, 0.250 / 1 mm and 0 / 0.25 mm by a 19% by mass hydrochloric acid solution.

[0258] The absence of overlap of the 95% confidence intervals of the residual PdC mass rate up to a GBR particle size of 0.5 mm demonstrates that the process of the invention makes it possible to produce GBRs that are significantly cleaner than the GBRs produced by the reference process up to GBRs of size 0.5 mm.

[0259] The attached Figure 3 also shows the measurement of the water absorption of the GBRs (in %) (on the right) as a function of the size of the GBRs for the process of the invention (long dotted curves) and for the reference process (short dotted curves). This rate is measured by dissolving the GBRs of particle size fractions 4 / 8 mm, 2 / 4 mm, 1 / 2 mm, 0.250 / 1 mm and 0 / 0.25 mm by a 19% by mass hydrochloric acid solution.

[0260] 4.3 Speciation of products during the process of the invention

[0261] The detailed analysis of the quality of the products during the process of the invention (vs. reference process) consists of measuring the speciation of the initial constituents of the concrete (GN and PdC, see example 2, part 2.1) before and after the process of the invention (vs. reference process) (example 2, part 2.2 and example 3). Speciation means the traceability of the initial constituents in the products of the process of the invention (vs. reference process).

[0262] As a reminder, the products used to characterize the performance of concrete recycling processes are GBR 4 / 8, GBR 2 / 4, GBR 1 / 2 and fines (particles < 1 mm). The constituents of interest in the speciation measurement are natural aggregates GN 4 / 8, GN 2 / 4, GN 1 / 2, and fines represented by GN 0.25 / 1, GN 0 / 0.25 and PdC.

[0263] Figures 4a) and 4b) show this speciation in detail for the reference process and the process of the invention respectively. In these figures:

[0264] Xi and X'i represent the initial composition of the concrete samples, before implementation of the processes. This composition is the same for the reference process and for the process of the invention. - Columns A and A' give the mass distribution of the products (GBR 4 / 8, GBR 2 / 4, GBR 1 / 2 and the fines) after implementation of the reference process and the process according to the invention respectively. The products are separated by screening after crushing for the reference process (example 3), and after steps ii) and a) for the process of the invention (example 2, part 2.2); and their mass fractions are obtained by weighing.

[0265] - Columns B and B' give the speciation (in the form of mass percentage) of each of the products, in other words, of each of the fractions of columns A and A': B1 (respectively B'1) corresponds to the speciation of GBR 4 / 8 of A1 (respectively A'1), B2 (respectively B'2) corresponds to the speciation of GBR 2 / 4 of A2 (respectively A'2) etc.... The speciation measurement consists of the selective dissolution of the PdC in each of the products in hydrochloric acid at 23% mass, followed by screening (and possibly abrasion), weighing and drying of the granulometric fractions of GN present after dissolution. The loss of mass after dissolution gives a direct measurement of the mass of PdC present in the products.

[0266] - Columns C and C' give the observed quantity of clean GN (or bare or clean GBR) and GN associated with an adherent residual mortar (or not clean or not clean GBR), as well as the quantity of PdC in the selected fraction: C1 (respectively C'1) corresponds to the observations and measurements for the GN 4 / 8 fraction of B1 (respectively B'1), C2 (respectively C'2) for the GN 2 / 4 fraction of B2 (respectively B'2) and C3 (respectively C'3) for the GN 1 / 2 fraction of B3 (respectively B'3).

[0267] - Xr and X'r represent the recalculated composition of the concrete samples, after implementation of the reference method and the method according to the invention respectively. It is established on the basis of the values ​​of columns B and B' which give the speciation of the initial constituents of the concrete in the products.

[0268] The fraction of fines being defined as all particles smaller than 1 mm (GBR 0.25 / 1 + GBR 0 / 0.25), the speciation analysis of the constituents shows that the process of the invention concentrates 31% of the mass of the concrete in this fraction of fines (column A' of figure 4b): 16% of A'4 + 15% of A'5), compared to only 12% for the reference process (column A of figure 4a): 8% A4 + 4% A5). The process of the invention therefore makes it possible to concentrate almost 3 times more fines than the reference process, fines which can be used as cement raw material if they are not carbonated, or as mineral addition if they are.

[0269] The mass rate of GBR 4 / 8, 2 / 4 and 1 / 2 of the process of the invention is very close to the mass rate of GN 4 / 8, 2 / 4, 1 / 2 of the initial concrete, which is explained by a mass rate of recovery of GN of more than 75%, or even 80%, in the GBR. In other words, the GBR produced by the process of the invention contain less than 20% by mass of residual mortar, i.e. still a mass rate of PdC between 5% and 8% (see B'1, B'2 and B'3 of figure 4b).

[0270] By comparison, the GBRs of the reference process have a mass recovery rate of GN between 40 and 60%, therefore a mass residual mortar rate of 60 to 40%, in the GBRs, or still a PdC rate between 11% and 21% (see B1, B2 and B3 of figure 4a).

[0271] The recalculation of the Xr and X'r compositions of the concrete samples indicates that the method of the invention preserves the size integrity of the initial GN better than the reference method. Indeed, a GN 4 / 8 rate in the recalculated composition X'r of the reference method is observed to be significantly lower than that obtained for the method of the invention, which de facto induces a greater increase in the GN 2 / 4 rate with the reference method. This is explained by the microfracturing of the PdC induced by the microwave step which avoids excessive fragmentation of the GN during the following crushing step.

[0272] A measurement of the degree of release (or degree of cleanliness) of GN in the GBR was carried out by visual sorting, with verification of the PdC rate of the separated fractions (columns C and C'). This measurement demonstrates the selectivity of the process of the invention with respect to the recovery of GN, this selectivity being provided by the microfracturing of the concrete induced by the microwave treatment step. This selectivity is reflected in the heterogeneity of distribution of the residual PdC, the latter being concentrated on a small fraction of the GN, while the majority of the GBR has a particularly low PdC rate. The latter are here referred to as clean (or bare) GN. The very high proportion of clean GN in the GBR is a specificity of the process of the invention. The release measurement by visual sorting was carried out on the GBR fractions 4 / 8 mm (B1 and B'1), 2 / 4 mm (B2 and B'2) and 1 / 2 mm (B3 and B'3).On the right side of Figure 4b, illustrated by column C', we notice that more than 60-70% of the GBR produced by the process of the invention are clean (these are GBRs which contain between 1.6% and 3.2% of PdC), the remaining 30-40% concentrating the PdC with a PdC content between 3.9% and 10.7%. Illustrated by column C in Figure 4a, the degree of release (or degree of cleanliness) of the GBRs of the reference process ranges from 16% to 42% only. In summary, for the 3 particle size classes of GBR analyzed, the degree of release (or degree of cleanliness) of the GN is 2 times higher for the process of the invention than for the reference process.

[0273] The performance of the inventive process was compared with the reference process and the theoretical limit. For example, the theoretical limit of cleanliness of a GBR in terms of residual PdC rate is 0%, while the maximum % of GN 4 / 8mm in 4 / 8mm GBRs is 100%. All percentages are given in % by mass.

[0274] Figure 5 shows the performance of the method of the invention compared to the reference method, and compared to the theoretical limit.

[0275] 4.4 Characterization of carbonation

[0276] In the best case, aqueous carbonation processes allow approximately 80% of the theoretical carbonation limit of solids to be reached, which can be calculated on the basis of their chemical composition.

[0277] The theoretical limit of carbonation of fines is directly linked to the quantity of calcium (Ca) they contain. Per unit mass of fines, this theoretical limit is similar for the fines of the process of the invention and the reference process, insofar as measurements demonstrate that they have the same chemical composition. This theoretical limit is between 170 and 200 kg of CO2 / tonne of fines. On the other hand, the process of the invention makes it possible to produce 2.6 times more fines than the reference process, so that the process of the invention can store at most 2.6 times more CO2 per tonne of recycled concrete than the reference process. This represents a CO2 storage potential of the process of the invention of 60 kg of CO2 / tonne of recycled concrete compared to 20 kg of CO2 / tonne of recycled concrete for the reference process, knowing that the maximum carbonation potential of concrete is estimated on the same bases at 70 kg of CO2 / tonne of recycled concrete.Thus, in fines, relative to a tonne of recycled concrete, the process of the invention makes it possible to store a maximum of 3 times more CO2 than the reference process (table 4 below).

[0278] The final carbonation rate of the carbonated fines is obtained by measuring the total carbon (CHNS analysis).

[0279] Table 5 below lists the results for the fines obtained according to the reference method and according to the method of the invention.

[0280] TABLE 5

[0281] The experimental measurement confirms that the carbonation potential of the fines is close for the process of the invention and the reference process, which results from their close chemical compositions. The results are however significantly to the advantage of the fines produced by the process of the invention, with a carbonation gain of +1.3 compared to the fines produced by the reference process. This result, to which is added the observation during the carbonation tests of the fines that the fines of the process according to the invention carbonate with better kinetics than those of the reference process, probably results from the microfracturing of the PdC induced by the microwave treatment step, which facilitates the transfer of carbon dioxide (CO2) to the carbonatable elements (Calcium) present in the PdC.

[0282] Figure 6 shows the performance of the method of the invention compared to the reference method, and compared to the theoretical limit. Across all the performance criteria measured, the method of the invention is on average 2.3 times more efficient than the reference method.

Claims

Claims 1. A method for recycling concrete from construction and / or demolition, characterized in that it comprises at least the following steps: i) one or more step(s) of microwave treatment of construction and / or demolition concrete blocks having a centimeter size, to form micro-fractured concrete blocks, ii) one or more step(s) of mechanical treatment making it possible to extract from said micro-fractured concrete blocks, recycled concrete aggregates (RCA) comprising bare natural aggregates and natural aggregates associated with an adherent residual mortar; and recycled fines, and iii) one or more step(s) of carbonation of the recycled fines, in the presence of carbon dioxide, to form carbonated recycled fines, said method being free of step(s) of carbonation of the recycled concrete aggregates (RCA).

2. Method according to claim 1, characterized in that the construction and / or demolition concrete blocks have a size of at most 10 cm.

3. Method according to any one of the preceding claims, characterized in that the microwave treatment of step i) is carried out for a duration ranging from 30 s to 10 min.

4. Method according to any one of the preceding claims, characterized in that the microwave treatment i) is carried out at a frequency ranging from 915 MHz to 2450 MHz.

5. Method according to any one of the preceding claims, characterized in that the GBRs have a particle size greater than or equal to 1 mm.

6. Method according to any one of the preceding claims, characterized in that the recycled fines have a particle size of less than 1 mm.

7. Method according to any one of the preceding claims, characterized in that step ii) comprises at least one step ii-1) of crushing the micro-fractured concrete blocks.

8. Method according to claim 7, characterized in that step ii-1) of grinding the micro-fractured concrete blocks is a non-percussive grinding step.

9. Method according to claim 7 or 8, characterized in that step ii) further comprises at least one screening step ii-2).

10. Method according to claim 9, characterized in that step ii-2) of screening is carried out using a rotary screen or a gyratory sieve.

11. Method according to any one of the preceding claims, characterized in that it further comprises at least one step a) of cleaning the recycled concrete aggregates.

12. Method according to any one of the preceding claims, characterized in that it further comprises at least one step b) of washing the recycled concrete aggregates.

13. Method according to any one of the preceding claims, characterized in that step iii) is carried out in the presence of a gas comprising at least 10% by volume of CO2, relative to the total volume of gas.

14. A method for recycling concrete from construction and / or demolition, characterized in that it comprises the following steps: i) one or more step(s) of microwave treatment of construction and / or demolition concrete blocks having a centimeter size, to form micro-fractured concrete blocks, and ii) one or more step(s) of mechanical treatment making it possible to extract from said micro-fractured concrete blocks, recycled concrete aggregates (RCA) comprising bare natural aggregates and natural aggregates associated with an adherent residual mortar; and recycled fines, said method being free of step(s) of carbonation of the recycled concrete aggregates (RCA) and recycled fines obtained in step ii).

15. Recycled concrete aggregates (RCA) obtained according to a process as defined in any one of claims 1 to 13 or according to a process as defined in claim 14, characterized in that the RCA of a given particle size fraction, greater than or equal to 1 mm, comprise at least 50% by mass of bare natural aggregates of said given granulometric fraction, relative to the total mass of GBRs of said given granulometric fraction.

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