Methods for recycling concrete construction and / or demolition waste.

Abstract

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

Description

[Technical Field]

[0001] The present invention relates to a method for recycling concrete waste from construction and / or demolition, comprising at least one microwave treatment step of concrete blocks, at least one mechanical treatment step, and optionally at least one carbonation step of concrete granules, wherein recycled concrete aggregate is obtained by the microwave treatment and mechanical treatment steps of the concrete blocks. [Background technology]

[0002] Concrete is one of the most widely consumed manufactured goods in the world. It mainly consists of cement, sand, and aggregates (coarse and fine gravel) mixed with water. In particular, France's annual aggregate consumption is 350 million metric tons, or 6 metric tons per person per year, or 17 kg per person per day. Projections indicate that the demand for aggregates, especially for the construction of new buildings, will continue to increase. Natural aggregates (NA) are generally obtained by mining alluvial sand, land sand, or sea sand and sedimentary gravel. Natural aggregates (NA) are not renewable resources, and although there are no technical limitations, their availability is decreasing due to social and environmental reasons. In particular, it has become increasingly difficult to open new quarries to meet the demand for natural aggregates (NA) because they would disturb nearby residents (noise, dust, increased traffic, etc.).

[0003] At the same time, the volume of material generated by the dismantling or demolition of buildings and their foundations is increasing, and this will continue for the next few years. In fact, buildings constructed during the 1950s reconstruction are gradually approaching the end of their lifespan, which means that a considerable volume of concrete will need to be recycled.

[0004] Furthermore, the calcination of natural limestone, a mineral resource required for cement production, accounts for nearly half of the CO2 emissions associated with the production of concrete, which is one of the most CO2-emitting materials produced by humans.

[0005] The recycling of concrete or stone building materials (e.g., construction and demolition waste) has been proposed as a method for manufacturing new concrete structures while avoiding landfills, reducing reliance on natural deposits, and conserving natural aggregate resources.

[0006] Construction and demolition concrete waste is generally recycled by crushing concrete blocks to form recycled concrete aggregate (RCA). Sorting can be performed to separate the RCA from the finer particles. However, the recycling methods currently available are not entirely satisfactory. Separation of NA from residual mortar is far from optimal. The RCA generally obtained is often composed of NA bound with a large amount of residual mortar from the original concrete. In particular, the presence of a high proportion of residual mortar in the NA, either adhering to the NA or in the form of aggregate at least equivalent in size to that of natural aggregate, hinders the formation of clean NA. With a high proportion of adhesive cement paste, such RCA is of second-rate quality compared to NA. They have higher water absorption rates and lower mechanical properties (lower impact resistance and / or higher abrasion resistance) than NA. Concrete produced from RCA mixed under normal conditions loses workability during transport in drums and thus may become unsuitable for use upon arrival at its destination. The current concrete standard NF EN 206 / CN mandates that reclaimed concrete (RCA) be used as the maximum possible substitute for natural concrete (NA) in the production of new concrete. This ratio varies depending on the type of RCA, particularly its components, and the exposure level of the structure being constructed. Because these RCAs are of lower quality, they are primarily used in low-value-added structures, especially as low-value-added backfill for road embankments, road coverings, or quarry backfills. However, the recycling capacity in the road construction sector is not unlimited, and this form of downcycling does not fully meet the standards of sustainable development.

[0007] In addition, crushing greatly breaks down the NA, contributing to a reduction in the size of the NA compared to the initial particle size distribution and an increase in fine particles due to the NA fragments. The resulting recycled fine particles have a composition that makes recovery and recycling even more difficult. Finally, because a high proportion of cement paste adheres to or binds with the RCA, the amount of fine particles generated is small compared to the amount of mortar found in concrete. Existing industrial facilities generally do not recover the fine fragments, and the fragments are considered industrial waste.

[0008] Several publications assume the direct use of fine concrete particles as a cement raw material for the production of clinker. For example, Non-Patent Document 1 describes incorporating recycled fine concrete particles (5-15%) into the cement raw material as a substitute for conventional siliceous materials. Various technical configurations have been used to separate the mortar fraction from the aggregate and to separate the resulting fine particles from the recycled sand. However, Non-Patent Document 1 points out that collecting large quantities of fine particles is difficult.

[0009] As a result, there remains a need for a recycling method that enables both obtaining large quantities of high-quality recycled concrete aggregate for recovery and recycled concrete aggregate that is as clean as possible (i.e., with as little residual mortar as possible) and / or has improved quality so that it can be used at a high rate to form new concrete structures. Therefore, there is a need for a method that enables the recycling of all renewable parts of concrete, namely both NA and the surrounding mortar. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] Schoon et al. "Cement and Concrete Composites" 58, 2015, 70-80 [Overview of the Initiative]

Problems to be Solved by the Invention

[0011] As a result, the object of the present invention is to overcome the disadvantages of the prior art and, in particular, to obtain a large amount of recycled fine particles and / or, in particular, good quality pozzolan and hydraulic activity, and to provide a method for recycling concrete waste from construction and / or demolition that enables the production of RCA with high cleanliness. This method is simple, industrially applicable, uses abundant raw materials, and is environmentally beneficial.

Means for Solving the Problems

[0012] The first main subject of the present invention is at least the following steps, namely, i) One or more microwave treatment steps of concrete blocks from construction and / or demolition having centimeter-scale sizes to form micro-crushed concrete blocks, ii) One or more mechanical treatment steps that enable the extraction of recycled concrete aggregate (RCA) containing natural aggregate without adherents and natural aggregate combined with adherent residual mortar, and recycled fine particles from the micro-crushed concrete blocks, iii) One or more steps of carbonating the recycled fine particles in the presence of carbon dioxide to form carbonated recycled fine particles, characterized by including A method that does not require a carbonation step for recycled concrete aggregate (RCA). A method for recycling concrete from construction and / or demolition.

[0013] The method of the present invention is simple and easy to execute, and as a result, carbonated recycled fine particles are obtained. The carbonated recycled fine particles contain a large amount of cement paste and / or amorphous silica that is particularly reactive in a cementitious medium, and has good quality, especially for pozzolan activity, especially after generation by carbonation step iii).

[0014] [[ID=I32]]<I Furthermore, this method has industrial applications and reduces environmental impact by enabling the recycling of unused construction or demolition concrete while utilizing abundant raw materials (concrete waste from construction or demolition) and ensuring the use or recovery of CO2. The method of the present invention is a complete concrete recycling method in that it recycles all of the original concrete, that is, both the fine-grained and the natural aggregate (NA).

[0015] The method is for recycling concrete from construction and / or demolition, particularly in the sectors of buildings and public works. In other words, the concrete may be concrete waste from the construction of buildings and / or pavement structures, scrap from concrete production, concrete from the demolition of buildings or pavement structures, or mixtures thereof.

[0016] definition In this invention, the term "cement" refers to a hydraulic binder, that is, a finely ground inorganic material (as defined in standard EN 197-1) that, when mixed with water, fixes or hardens through a hydraulic reaction and process, and forms a paste that maintains strength and stability even in water after hardening.

[0017] In this invention, the term "cement paste" (hereinafter also referred to as "CP") refers to a mixture of cement and water that hardens through a hydraulic reaction. The cement paste may optionally contain one or more additives. The amount of cement paste adhering to the RCA is a criterion for RCA cleanliness.

[0018] In this invention, the term "concrete" refers to a mixture of cement, aggregate (sand and gravel), and water. This is the initial material containing all the components that will be recovered (aggregate and cement paste).

[0019] In this invention, the term "natural aggregate (NA)" refers to gravel particles resulting from natural sand, alluvial sand, land sand, or sea sand and deposited gravel.

[0020] In this invention, the term "recycled concrete aggregate (RCA)" refers to sand and gravel particles that are generated from concrete and reused as a substitute for NA for the purpose of manufacturing concrete or for any other use.

[0021] In this invention, the term "residual mortar" refers to a mixture of cement paste and NA particles smaller than the mesh size of the RCA in question. The majority of the residual mortar is found adhering to the surface of the RCA under consideration. Therefore, the definition of residual mortar varies depending on the particle size fraction of the RCA under consideration. M However, RCA's particle size fraction G M -G m The higher mesh size is G m When the mesh size is smaller, the residual mortar combined with this particle size fraction of the RCA is cement paste and <G m It contains a mixture of NA of the specified size. In this invention, the term "residual mortar" is also referred to as "residual cement base material."

[0022] The term "fine-grained" refers to the smallest size G of the finest fraction of RCA produced by cement paste and concrete recycling methods. m In this invention, it is used to refer to a mixture with smaller size NA.

[0023] In this invention, the term "accelerated carbonation" refers to a carbonation method that operates at a CO2 concentration 250 to 12,000 times higher than the CO2 concentration in the ground atmosphere (415 ppm), resulting in carbonation dynamics that take several minutes compared to several years for natural carbonation. In the case of fine granules, the NA contained in the fine granules does not carbonize, so only the cement paste is carbonated. In this invention, the term "carbonation" used alone is synonymous with "accelerated carbonation." Therefore, the terms "accelerated carbonation" or "carbonation" are the opposite of the term "natural carbonation."

[0024] In the RCA of the present invention, the terms "natural aggregate without deposits," "clean natural aggregate," and "clean RCA" are synonymous. The natural aggregate without deposits in the RCA of the present invention preferably contains less than 5% by weight of CP, more preferably up to 4% by weight of CP, and even more preferably up to 3% by weight of CP, with respect to the total weight of the natural aggregate without deposits.

[0025] In the RCA of the present invention, the terms "natural aggregate bonded with adhesive residual mortar," "unclean natural aggregate," and "unclean RCA" are synonymous. The natural aggregate bonded with adhesive residual mortar in the RCA of the present invention preferably contains 5% to 30% by weight of CP, more preferably 7% to 25% by weight of CP, and even more preferably 10% to 20% by weight of CP, with respect to the total weight of the natural aggregate bonded with adhesive residual mortar.

[0026] Step i) The centimeter-scale concrete blocks used in step i) from construction and / or demolition contain NA (sand and / or gravel) and CP. In these centimeter-scale concrete blocks from construction and / or demolition, the NA is bonded to the CP to form the centimeter-scale block.

[0027] Step i) enables the formation of a primary fracturing network within the concrete block, more specifically around the NA (tissue dissociation of NA), and the formation of a secondary fracturing network at the CP. This causes selective fracturing of the concrete, allowing for the separation of NA from the bulk of the initial concrete CP without significantly damaging the NA.

[0028] Simultaneously, the high-density secondary micro-fracture network extending across the CP allows for the dissociation and aggregation of most of the CP in the initial concrete in the fine-particle-size fraction, which is beneficial for the subsequent extraction step ii). Micro-fracture of the CP also promotes the carbonation step iii) of the regenerated fine particles.

[0029] Thus, the formation of the primary and secondary crushing networks described above facilitates the subsequent step ii) which selectively dissociates NA contained in the construction and / or demolition concrete, thereby promoting the separation of NA from the fine particles without degrading the NA.

[0030] In other words, the greater the number of micro-fragments per unit volume of CP, the cleaner the resulting RCA becomes (i.e., the higher the NA content and the lower the adhesive residual mortar content), the greater the amount of CP in the fine particles, and the more efficient the method, especially the subsequent steps ii) and iii).

[0031] Unlike crushers that randomly break up concrete (as shown in Figure 1), microwave treatment selectively weakens CP without significantly altering the structure of NA. Therefore, the integrity of NA is preserved, and the combination of steps i) and ii) results in at least 75% by weight of CP from centimeter-scale concrete blocks from construction and / or demolition being recycled into fine particles.

[0032] The microwave treatment in step i) can be performed with an incident power sufficient to induce fracture in the concrete block.

[0033] Preferably, the microwave processing in step i) is performed at an output in the range of 1 kW to 50 kW, preferably 5 kW to 40 kW, more preferably 5 kW to 10 kW.

[0034] These outputs are particularly suitable for processing 1 ton of concrete blocks per hour.

[0035] Preferably, the microwave treatment (exposure time) in step i) is performed for a period of time ranging from about 30 seconds to about 10 minutes, more preferably from about 1 minute to about 5 minutes.

[0036] In the present invention, the term “centimeter-scale size” relating to concrete blocks from construction and / or demolition preferentially means that concrete blocks from construction and / or demolition have a size of up to about 10 cm, more preferably up to 7 cm, and most preferably up to about 5 cm.

[0037] Preferably, the concrete blocks from construction and / or demolition have a size of at least about 1 cm, more preferably at least about 2 cm, and most preferably at least about 3 cm.

[0038] Step i) can be performed by passing concrete blocks through a microwave tunnel.

[0039] Microwave processing i) may be performed at frequencies in the range of about 915 MHz to about 2450 MHz, more preferably at frequencies of about 915 MHz or about 2450 MHz. These frequencies are average frequencies limited to 902–928 MHz and 2400–2500 MHz, respectively.

[0040] Microwave processing i) can be performed continuously or in pulsed mode (for example, with symmetrical square wave pulses lasting at least 1 second).

[0041] Depending on the size of the concrete piece being processed, either a traveling wave or a standing wave propagation mode may be used (a standing wave if the concrete piece is smaller than 5 cm, and a traveling wave if it is larger than 5 cm).

[0042] Microwave processing i) can be performed inside the reflective cavity using guided waves or an antenna.

[0043] As a result of microwave treatment i), the material is dried, and it is advantageous if the evaporated water can be recovered, especially for reuse in the subsequent steps ii) to iii).

[0044] At the end of step i), the concrete block can be said to be "micro-crushed" due to the fact that the cement paste contained in the concrete block is greatly micro-crushed. As a result, the concrete block obtained in step i) contains micro-crushed cement paste.

[0045] Step II) In step ii), the finely crushed concrete block obtained as a result of step i) undergoes one or more mechanical processing steps.

[0046] Step i) provides a mechanical stress that is favorable to the shear force in step ii), which propagates the fracturing and fragments the micro-fractured concrete blocks while limiting the fracturing of NA, and helps to dissociate the RCA, which on the one hand contains natural aggregate without adhering material and natural aggregate bound with adhesive residual mortar, and on the other hand, the regenerated fine particles.

[0047] Step ii) allows for the extraction of RCA (Rigidized Concrete Aggregate) containing, on the one hand, natural aggregate without adhering material and natural aggregate bound to adhesive residual mortar, and on the other hand, recycled fine particles from the finely crushed concrete block. At the end of Step ii), the RCA is separated from the recycled fine particles, and at least 75% by weight of the CP contained in the original concrete being recycled is found in the recycled fine particles.

[0048] At the end of step ii), a fraction F1 of RCA is obtained, which contains natural aggregate without adhering material and natural aggregate bound with adhesive residual mortar, and a fraction F2 of recycled fine-grained material.

[0049] RCA preferably has a particle size of about 1 mm or larger.

[0050] Natural aggregate free of adhering materials preferably has a particle size of about 1 mm or larger.

[0051] The natural aggregate bonded with the adhesive retaining mortar preferably has a particle size of about 1 mm or larger.

[0052] According to a preferred embodiment of the present invention, the natural aggregate free of adhering substances (natural aggregate bonded with adhesive residual mortar) is selected from gravel, sand having a particle size of about 1 mm or more, and mixtures thereof.

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

[0054] Sand is generally defined as having a particle size of 4 mm or less.

[0055] In the present invention, the particle sizes of RCA, gravel, and sand are determined by methods well known to those skilled in the art, particularly by sieving (laboratory method) or sorting (industrial method) according to standard NF EN 933-1.

[0056] The residual mortar adhering to the NA preferably contains NA with a particle size smaller than about 1 mm.

[0057] Regenerated granules (fraction F2) generally contain (or consist of) a mixture of CP and NA with a particle size of less than approximately 1 mm.

[0058] The regenerated fine particles (fraction F2) preferably have a particle size of less than 1 mm.

[0059] In fraction F2, NA and CP may be separated as dissociated particles (containing either NA or CP) or combined as mixed particles (containing a mixture of NA and CP).

[0060] Step ii-1) Step ii) preferably includes at least one step ii-1) grinding the finely crushed concrete block.

[0061] Step ii-1) grinding the finely crushed concrete block may be carried out using at least one impact grinder (e.g., a jaw grinder, a swivel grinder, a cone grinder, or an impact grinder) or a non-impact grinder (e.g., a roller mill such as a single-roller or double-roller mill or a high-pressure roller mill).

[0062] Preferably, step ii-1) grinding the micro-crushed concrete block is a non-impact grinding step. In this embodiment, step ii-1) grinding the micro-crushed concrete block preferably uses at least one non-impact grinder.

[0063] Non-impact grinders have the advantage of applying a continuous compressive shear action. This prevents excessive damage to NA and / or maintains the integrity of particle size and mechanical properties.

[0064] Non-impact grinders are preferably roller mills, such as single-roller or double-roller mills. Roller mills may have smooth or toothed rollers.

[0065] A pulverizer-type roller mill can produce a specific maximum particle size corresponding to that found in the original concrete being recycled, by appropriately adjusting the operating parameters, particularly the feed rate, the rotational speed of one or more rollers, the spacing between rollers, and / or the applied hydraulic pressure.

[0066] The roller spacing is adapted to the maximum particle size of the NA of the initial concrete being recycled, minimizing fragmentation.

[0067] This method, in particular, Multiple grinding steps ii-1) after microwave processing step i), Multiple consecutive sequences of microwave processing step i) and grinding step ii-1), This may include multiple grinding steps ii-1) by performing the following.

[0068] When a plurality of grinding steps ii-1) are carried out after step i), a series of non-impact grinders such as a roller mill can be used, and by appropriate adjustment of the operating parameters of the continuous grinder, particularly the feed rate, roller rotation speed, roller spacing, and / or the applied hydraulic pressure, it is possible to continuously produce RCA with an increasingly finer maximum particle size.

[0069] To produce RCA with an increasingly smaller particle size and obtain the cleanest possible RCA (i.e., with a high NA content and a low content of residual adherent mortar) and to optimize the generation of recycled fine particles, the roller spacing can be continuously reduced.

[0070] When a plurality of consecutive sequences of steps i) and ii-1) are carried out, a single non-impact grinder such as a roller mill can be used after each step i), and by appropriate adjustment of its operating parameters, particularly the feed rate, the rotation speed of one or more rollers, the roller spacing, and / or the applied hydraulic pressure, it is possible to continuously produce RCA with an increasingly finer maximum particle size.

[0071] It is advantageous for the grinding step ii-1) to be carried out in a dry process. Since the preceding microwave treatment step i) contributes to the drying of the material, the dry process is particularly suitable.

[0072] By means of one or more grinding steps ii-1), RCA (natural aggregate with or without adherent residual mortar) is obtained, which, inter alia, has a particle size G M ≦ 45 mm or G M ≦ 25 mm or G M ≦ 11.2 mm or G M ≦ 4 mm), preferably with a particle size G (corresponding to the maximum particle size of the NA of the original concrete being recycled) of at most about 45 mm, or at most about 25 mm, or at most about 11.2 mm, or at most 8 mm, or at most 4 mm. M having.

[0073] Preferably, the RCA (natural aggregate with or without adhesive residual mortar) obtained after the grinding step has a minimum particle size G of at least about 1 mm. m It has.

[0074] Step ii-2) Step ii) further includes at least one sorting step ii-2) (also called sieving) following step ii-1). This step ii-2) allows the RCA and fine particles to be classified by particle size.

[0075] The sorting step ii-2) can be carried out in a dry or wet process, preferably in a wet process.

[0076] Sorting step ii-2) may be carried out using any type of vibrating, swirling, or rotating screen or sieve, preferably a rotating screen or swirling sieve. A rotating screen is also called a rotating sieve, rotating screen, trommel screen, or trommel sieve.

[0077] Sorting step ii-2) separates fraction F1 of RCA from fraction F2 of regenerated granules, and optionally allows for the separation of RCA within fraction F1 according to particle size. Classification of RCA by particle size within fraction F1 allows for the recovery of additional regenerated granules between each sorting step ii-2).

[0078] This method preferably includes multiple sorting steps ii-2), which maximizes the fraction of regenerated fine particles that are abundant in the cement paste.

[0079] One or more screens used in one or more sorting steps ii-2) include a mesh having an opening suitable for allowing such separation.

[0080] The screen (or series of screens) preferably has a mesh size suitable for the pulverizer (or series of pulverizers) used in step ii-1) or step ii-1).

[0081] According to a preferred embodiment of the present invention, step ii-2) is G m ≦G1≦G M Particle size G1, or G m ≤G 1’ <G1≦G M Particle size fraction G 1’ - Includes a first sorting step ii-2a) which allows for the isolation of RCAs having G1.

[0082] For example, the RCA separated in the first sorting step ii-2a) has a particle size G1 of at least about 4 mm.

[0083] For example, the RCA separated in the first sorting step ii-2a) has a particle size G1 of up to approximately 45 mm, or up to approximately 25 mm, or up to approximately 11.2 mm, or up to 8 mm, depending in particular on the intended use and / or the particle size of NA found in the original concrete to be recycled.

[0084] For example, the first sorting step ii-2a) may allow for the separation of RCA having a given particle size fraction, i.e., 4-8 mm, or 8-11.2 mm, or 11.2-25 mm, or 25-45 mm.

[0085] The particle size fraction limits are provided as guidelines only, and other limits may be used depending on the intended use and / or the particle size of NA found in the original concrete being recycled.

[0086] In the first selection step ii-a), RCA (fraction F) having particle size G1 1a ) is regenerated fine granules (fraction F 2a ) and also RCA (fraction F) which has an arbitrarily small particle size. 1b , fraction F 1c It is separated from (etc.).

[0087] The RCA having the particle size of G1 includes natural aggregate without deposits and natural aggregate combined with adhesive residual mortar.

[0088] Step ii-2) further includes a second screening step ii-2b) that enables isolation of RCA having a particle size fraction G-G2 where G ≤ G2 < G1, or G ≤ G < G2 ≤ G1 < G1 ≤ G. m ≤ G2 < G1, or G m ≤ G 2’ < G2 ≤ G1 < G1 ≤ G M such that the particle size fraction G 2’ -G2.

[0089] For example, the RCA separated in the second screening step ii-2b) has a particle size G2 of up to about 4 mm.

[0090] For example, when the first screening step ii-2a) enables isolation of RCA having a particle size fraction of 4-8 mm, the second screening step ii-2a) can enable isolation of RCA having a particle size fraction of 1-4 mm. When the first screening step ii-2a) enables isolation of RCA having a particle size fraction of 8-11.2 mm, the second screening step ii-2a) can enable isolation of RCA having a particle size fraction of 4-8 mm. When the first screening step ii-2a) enables isolation of RCA having a particle size fraction of 11.2-25 mm, the second screening step ii-2a) can enable isolation of RCA having a particle size fraction of 8-11.2 mm. When the first screening step ii-2a) enables isolation of RCA having a particle size fraction of 25 mm-45 mm, the second screening step ii-2a) can enable isolation of RCA having a particle size fraction of 11.2-25 mm.

[0091] ​​​​​​1b ) is regenerated fine granules (fraction F 2b ), and optionally, recycled concrete aggregate RCA (fraction F) with small particle size 1c It is separated from (etc.).

[0093] Recycled concrete aggregate with particle size G2 includes natural aggregate without adhering material and natural aggregate bound with adhesive residual mortar.

[0094] Thus, step ii) may include one or more sorting steps ii-2). In particular, one or more sorting steps [steps ii-2a), ii-2b), ii-2c), etc.] may be required to separate RCA from the recycled fine particles as much as possible. This may depend, in particular, on the particle size distribution of NA used in the original construction and / or demolition concrete to be recycled.

[0095] The method of the present invention, in particular step ii), may include a plurality of grinding steps ii-1) and a plurality of sorting steps ii-2).

[0096] In this embodiment, step ii) is Multiple sorting steps ii-2) followed by multiple grinding steps ii-1) or, Multiple consecutive sequences of grinding step ii-1) and sorting step ii-2), It may include.

[0097] Step ii) preferably includes a series of steps ii-1) and ii-2).

[0098] As a result of steps i) and ii), the present invention makes it possible to obtain RCA aggregate with high cleanliness and a large amount of fine particles, since most of the RCA is dissociated from the residual mortar (and consequently the cement paste CP contained in the mortar) adhering to the NA.

[0099] After step ii), if this method includes multiple sorting steps ii-2), different fine-grain fractions (F) from different sorting steps are obtained. 2a ,F 2b ,F 2c The method may further include steps that combine such as the above.

[0100] The reuse of these large quantities of fine particles from concrete construction and demolition waste, as mineral additives that reduce the demand for cement in concrete, and / or as components of raw materials used to produce cement, has the potential to reduce CO2 emissions and the demand for natural resources for concrete production.

[0101] At the end of step ii), particularly steps ii-1) and ii-2), the recycled fine particles are separated or recovered. Preferably, these contain at least 75% by mass of the CP contained in the original concrete being recycled, whereas in an optional grinding step following the prior art sorting step, the recycled fine particles will contain less than 25% by mass of the CP contained in the original concrete being recycled.

[0102] Preferably, the regenerated granules further contain NA having a particle size of less than 1 mm.

[0103] In the regenerated fine particles, NA with a particle size of less than 1 mm and cement paste can be debonded, bonded, or partially bonded, and can generally be partially bonded.

[0104] The recycled granules are in the form of particles with a very fine particle size (at least 45% by mass, preferably at least 50% by mass, of the total mass of the recovered recycled granules have a particle size of <0.25 mm) and are well usable for carbonization.

[0105] Steps i) and ii) of the present invention are highly efficient, as the majority of the cement paste is found in very fine particle size form in the regenerated fine particles, allowing for sufficient micro-fracture. The optimization of the next step iii), carbonation of the fine particles, is made possible by particularly promoting the utilization and diffusion of carbon dioxide in the carbonatable reaction phase, especially in the CP containing portlandite, lime, and hydrated calcium silicate (C-S-H).

[0106] As a natural consequence, RCA from which recycled concrete aggregate has been isolated or recovered, more specifically step ii), and in particular RCA with a particle size greater than or equal to 1 mm at the end of steps ii-1) and ii-2), will have a structure as close as possible to that of the natural aggregate NA of the initial demolition and / or construction concrete.

[0107] These materials possess a level of cleanliness that eliminates the need for a carbonation step in the presence of carbon dioxide, and can be used directly in the production of new concrete. Therefore, a method that fits the first objective of the present invention does not involve a carbonation step of recycled concrete aggregate (NCA).

[0108] In fact, steps i) and ii) make it possible to obtain a very clean NCA.

[0109] The method of the present invention is selective in that it allows for the separation of fine particles along with a variety of particle size fractions of NCA.

[0110] In particular, NCA obtained from a given particle size fraction greater than or equal to 1 mm contains 10% by mass or less of CP, preferably 8% by mass or less of CP, and more preferably 5% by mass or less of CP, with respect to the total mass of NCA from the given particle size fraction.

[0111] At the end of step ii), particularly steps ii-1) and ii-2), the recycled concrete aggregate RCA obtained with a given particle size fraction of 1 mm or larger preferentially contains 65% to 95% by weight of NA with the given particle size fraction, more preferably 70% to 90% by weight of NA with the given particle size fraction, and even more preferably 75% to 85% by weight of NA with the given particle size fraction, with respect to the total weight of RCA with the given particle size fraction. This is also referred to as the recovery rate.

[0112] Preferably, recycled concrete aggregate RCA obtained in a given particle size fraction of 1 mm or more contains 5% to 20% by weight of NA having a particle size smaller than the given particle size fraction, and more preferably 7% to 15% by weight of NA having a particle size smaller than the given particle size fraction, with respect to the total weight of RCA having the given particle size fraction.

[0113] In particular, recycled concrete aggregate (RCA) obtained with a given particle size fraction of 1 mm or larger contains 5% to 35% by weight of residual mortar, preferably 10% to 30% by weight, and more preferably 15% to 25% by weight, with respect to the total weight of the RCA with the given particle size fraction.

[0114] The RCA obtained at the end of step ii) can be used directly for the preparation of new concrete. Because these contain a low proportion of residual mortar, their water absorption and abrasion properties are 2 to 3 times better than those of RCA obtained by the methods of the background art.

[0115] The previously defined content of RCA, CP obtained in a given particle size fraction of 1 mm or larger, NA in a given particle size fraction, NA with a particle size smaller than the given particle size fraction, and residual mortar is determined by selectively dissolving the CP found in the RCA with hydrochloric acid, weighing it, and measuring the various components described above.

[0116] The method of the present invention is efficient in that it makes it possible to obtain RCA with high cleanliness for each of the given particle size fractions of 1 mm or larger.

[0117] In the RCA of the present invention, mortar (CP + NA having a particle size smaller than a given particle size fraction) is unevenly dispersed / adhered around NA having a given particle size fraction. In practice, this results in a large amount of clean RCA (i.e., natural aggregate without adhering material or clean natural aggregate) and a small amount of unclean RCA (i.e., natural aggregate bonded with adhesive mortar or unclean aggregate).

[0118] In particular, at the end of step ii), especially steps ii-1) and ii-2), the recycled concrete aggregate RCA obtained with a given particle size fraction of 1 mm or more shall, with respect to the total weight of the RCA having a given particle size fraction, preferentially consist of at least 50% by weight of clean natural aggregate (i.e., natural aggregate or clean RCA without deposits having a given particle size fraction), more preferentially 55% to 85% by weight of clean natural aggregate (i.e., natural aggregate or clean RCA without deposits having a given particle size fraction), and even more preferentially 60% to 75% by weight of clean natural aggregate (i.e., natural aggregate or clean RCA without deposits having a given particle size fraction).

[0119] As a natural consequence, at the end of step ii), particularly steps ii-1) and ii-2), the recycled concrete aggregate RCA obtained in a given size fraction of 1 mm or more preferably contains less than 50% by weight of unclean natural aggregate (i.e., natural aggregate bound with adhesive residual mortar or unclean RCA) with a given particle size fraction, more preferably 15% to 45% by weight of unclean natural aggregate (i.e., natural aggregate bound with adhesive residual mortar or unclean RCA) with a given particle size fraction, with respect to the total weight of RCA with a given particle size fraction.

[0120] As previously specified, the RCA content obtained in a given particle size fraction of 1 mm or larger in clean and unclean RCA is obtained by optical and / or visual classification to separate clean and unclean RCA, followed by selectively dissolving the CP found in clean and unclean RCA with hydrochloric acid, and then determining the ratio of CP in clean and unclean RCA by weighing and measuring.

[0121] The method of the present invention may include a plurality of microwave processing steps i), a plurality of grinding steps ii-1), and a plurality of sorting steps ii-2), and preferably a plurality of sequential sequences of microwave processing steps, grinding steps ii-1), and sorting steps ii-2).

[0122] Step a) This method may further include at least one step a) of cleaning the RCA. This reduces the proportion of residual mortar in the RCA, contributing to a higher degree of cleanliness for the RCA and increasing the recovery rate of recycled granules.

[0123] Step a) is preferably carried out by polishing, in particular by using a rotating screen or a swivel sieve.

[0124] Polishing is a well-known mechanical method for surface cleaning.

[0125] Step a) is performed preferentially after grinding step ii-1).

[0126] Step a) may be performed simultaneously with (i.e., in conjunction with) the sorting step ii-2), before or after the sorting step ii-2), and preferably simultaneously with the sorting step ii-2).

[0127] Steps a) and ii-2) may be performed using a rotating screen or a sieve, if performed in conjunction with them.

[0128] If steps a) and ii-2) are not performed in conjunction, the polishing step a) may be performed on a rotating drum with or without a lifter.

[0129] When multiple sorting steps (e.g., steps ii-2a) and ii-2b)) are performed, this method may include, in particular, multiple cleaning steps a) that are associated with each of the sorting steps or that precede or follow each of the sorting steps.

[0130] Prior to step a), NA may be added to the RCA to facilitate step a), and in particular to facilitate the polishing of residual mortar.

[0131] The added NA may amount to up to 99.5% by weight, preferably up to 95% by weight, and more preferably up to 50% by weight, with respect to the total weight of the aggregate (NA + RCA) used in step a).

[0132] Step b) The method may further include at least one step b) of cleaning the RCA, which reduces the proportion of fine particles that may adhere to the surface of the RCA.

[0133] Step b) is preferably carried out by washing with water, more preferably by sprinkling or spraying water.

[0134] Step b) may be performed simultaneously with (i.e., incidentally with) the cleaning or polishing step a), and / or simultaneously with the sorting step ii-2), and / or between the cleaning or polishing step a) and the sorting step ii-2), preferably simultaneously with the sorting step ii-2), and optionally simultaneously with the cleaning or polishing step a).

[0135] This also makes it possible to facilitate the entrainment of regenerated granules and their separation from the RCA.

[0136] When multiple sorting steps (e.g., steps ii-2a) and ii-2b)) are performed, this method may include multiple washing steps b) that are associated with each of the sorting step ii-2) and / or the cleaning step a), or between each of the cleaning step a) and the sorting step ii-2).

[0137] According to a preferred embodiment of the present invention, steps ii-2), a) and a) are performed simultaneously, particularly using a rotating screen or a sieve, and especially preferably in a wet process. The wet process is preferably carried out by sprinkling or spraying water (e.g., water spraying that reuses the water that condensed after evaporation in step i). In other words, in this wet process, steps ii-2), a) and b) are performed simultaneously. This concentrates the regenerated fine powder into the final fraction by eliminating any regenerated fine powder that may adhere to the surface of the RCA.

[0138] The recycled granules obtained at the end of step ii) can be used directly as a cement raw material, for example, for the production of calcium clinker, by adjusting the composition by adding other sources of materials used in the raw materials (e.g., to achieve a specific silicon or hydraulic ratio). By substituting for the fraction of natural limestone used in cement raw materials, the use of recycled granules in cement raw materials contributes to the preservation of natural limestone resources and reduces the carbon footprint of clinker by not releasing additional CO2 in the clinker step compared to the use (calcination) of natural limestone.

[0139] Step III) The method further includes one or more carbonation steps iii) of the regenerated granules [corresponding to fraction F2 recovered at the end of steps ii), ii-1), ii-2), ii-2a), or ii-2b] in the presence of carbon dioxide.

[0140] Carbonation targets the reaction phase, i.e., the CP found in the regenerated granules. At the end of step iii), carbonated regenerated granules containing a mixture of <1 mm NA and carbonated CP are obtained.

[0141] Carbonation of recycled granules allows for the storage of carbon dioxide and the acquisition of carbonated granules that potentially possess pozzolanic and / or hydraulic activity. These can then be used as mineral additives in concrete as substitutes for cement (e.g., CEM I or CEM II), or as cement components for the production of blended cements. For example, by substituting Portland cement in the mix design of structural concrete (buildings) or non-structural concrete (light concrete blocks, blocks, slabs, coping stones, technical mortar), the use of carbonated granules as mineral additives reduces the carbon footprint of concrete. This reduction is due to the low proportion of Portland cement in the concrete and the amount of carbon that is captured by the carbonated granules and acts as a carbon sink.

[0142] In other words, the carbonated recycled granules obtained by the previously described method can be used as a means of CO2 storage and / or as a substitute for all or part of cement. The use of these carbonated granules as a reactive mineral additive in concrete mixes reduces the carbon footprint of the concrete in proportion to the amount of cement that is replaced by the carbonated granules.

[0143] When used as a mineral additive, the regenerated fine particles derived from step ii) are preferably ground prior to the carbonation step iii) to obtain a particle size of, for example, less than about 80 μm, preferably between about 5 μm and about 20 μm.

[0144] Step iii) is preferably carried out in the presence of a CO2-containing gas which, with respect to the total number of moles of gas, preferably contains at least 1 mol% CO2, more preferably at least 10 mol% CO2, and most preferably at least 15 mol% CO2.

[0145] Carbon dioxide is obtained from CO2-containing steam, for example from a metanizer or a CO2-rich biogas stream generated by a biomass power plant, or from steam produced by industrial emission facilities such as a cement plant or thermal power plant, or it is prepared from a CO2 source. The CO2 source may or may not be stored in advance.

[0146] The CO2-containing vapor preferably contains at least 10% by volume of CO2 with respect to the total volume of gas present in the vapor.

[0147] The CO2-containing vapor may also contain other elements, particularly molecular nitrogen (N2), molecular oxygen (O2), and optionally, water.

[0148] A biogas stream may contain approximately 70% to 90% by volume of CO2 relative to the total volume of biogas.

[0149] In step iii), the regenerated fine powder may be introduced into a rotating drum or some other reactor, and these may come into contact with a gas containing carbon dioxide.

[0150] Step iii) can be performed at a CO2 partial pressure in the range of about 0.1 bar to about 100 bar, preferably about 0.1 bar to about 5 bar (i.e., 240 to 12,000 times the CO2 partial pressure in the atmosphere—0.415 millibars).

[0151] Step iii) can be carried out at a temperature in the range of about 18°C ​​to about 100°C, preferably about 20°C to about 80°C.

[0152] Step iii) can be performed at a relative humidity ranging from 0% to about 100%, preferably from about 10% to about 90%.

[0153] The accelerated carbonation of the fine particles produces carbonated regenerated fine particles that can store up to approximately 15% by weight of CO2, or approximately 150 kg of CO2 per metric ton of fine particles.

[0154] Step i 0 ) The method may further include step i0), prior to step i), crushing construction and / or demolition concrete to form concrete blocks from construction and / or demolition having a size on the centimeter scale as performed in step i).

[0155] The grinding step i0) can be carried out using a grinder such as a jaw grinder, cone grinder, swivel grinder, impact grinder, hammer grinder, or centrifugal rotor grinder.

[0156] According to a preferred embodiment of the present invention, step i) is performed immediately after step i0) (there are no intermediate steps).

[0157] According to a preferred embodiment of the present invention, this method does not include any step requiring a liquid phase between step i0) and step i).

[0158] The method of the present invention makes it possible to obtain from a concrete block from construction and / or demolition a distribution between aggregate and fine particles that is close to the initial distribution of the original concrete, namely, about 70% to 90% by weight of RCA (uncarbonated fraction F1) and 10% to 30% by weight of fine particles (carbonated fraction F2) with respect to the total weight of the concrete block from construction and / or demolition.

[0159] In particular, the combination of microwaves, mechanical treatment, and carbonation of fine particles in the presence of carbon dioxide enables the complete recycling of concrete waste from construction and / or demolition.

[0160] The second subject of this invention is the following steps, namely, i) One or more microwave treatment steps of concrete blocks from construction and / or demolition having centimeter-scale size for forming micro-crushed concrete blocks, ii) One or more mechanical processing steps that enable the extraction of recycled concrete aggregate (RCA) containing natural aggregate without adhering material and natural aggregate bound with adhesive residual mortar, and recycled fine particles from a finely crushed concrete block, It is characterized by including, This method does not require a carbonation step between the recycled concrete aggregate RCA obtained in step ii) and the recycled fine-grained aggregate. This is a method for recycling concrete from construction and / or demolition.

[0161] The method according to the second subject of the present invention, obtained as a result of steps i) and ii), allows for the acquisition of highly clean RCA aggregate and a large amount of fine particles, since most of the RCA is dissociated from the residual mortar (and consequently the cement paste contained in the mortar) adhering to the NA.

[0162] Since steps i) and ii) of the method according to the second subject of the present invention are very effective, very little cement paste adheres to the NA in the RCA. Similarly, since steps i) and ii) of the method according to the second subject of the present invention are very efficient, the majority of the cement paste consists of recycled fine particles of very fine particle size.

[0163] Step ii) preferably includes at least one step ii-1) grinding the finely crushed concrete block. The method may include multiple grinding steps ii-1).

[0164] Step ii) may further include at least one selection step ii-2) particularly after step ii-1). Step ii) may include one or more selection steps ii-2).

[0165] The method of the present invention, in particular step ii), may include a plurality of grinding steps ii-1) and a plurality of sorting steps ii-2).

[0166] This method may further include at least one step a) of cleaning the RCA.

[0167] The method may further include at least one step b) cleaning the RCA.

[0168] The method may further include step i0) prior to step i), which involves crushing construction and / or demolition concrete to form concrete blocks from construction and / or demolition having a size on the centimeter scale, as performed in step i).

[0169] Steps i), ii), ii-1), ii-2), a), b), and i0) are defined in the first subject of the present invention.

[0170] Therefore, this method allows the resulting RCA to be isolated directly in step ii). In other words, this corresponds to the method for manufacturing RCA.

[0171] The recycled fine powder obtained at the end of step ii) of the method according to the second subject can be used as is as a cement raw material, for example, for the production of calcium clinker, by adjusting its composition by adding other sources of materials used in the raw material (e.g., to achieve a specific silicon or hydraulic ratio). By substituting the fraction of natural limestone used in the cement raw material, the use of recycled fine powder in the cement raw material contributes to the preservation of natural limestone resources and reduces the carbon footprint of clinker by not releasing additional CO2 in the clinker step compared to the use (calcination) of natural limestone.

[0172] The RCA obtained at the end of step ii) of the method according to the second subject can be used as is for the preparation of new concrete.

[0173] The third subject of the present invention is recycled concrete aggregate (RCA) obtained by a method according to the second subject of the present invention or by a method according to the third subject of the present invention, characterized in that RCA having a given particle size fraction of 1 mm or more contains, with respect to the total weight of RCA having a given particle size fraction, at least 50% by weight of clean natural aggregate having a given particle size fraction (i.e., natural aggregate or clean RCA without deposits having a given particle size fraction), more preferably 55% to 85% by weight of clean natural aggregate having a given particle size fraction (i.e., natural aggregate or clean RCA without deposits having a given particle size fraction), and even more preferably 60% to 75% by weight of clean natural aggregate having a given particle size fraction (i.e., natural aggregate or clean RCA without deposits having a given particle size fraction).

[0174] As a natural consequence, recycled concrete aggregate (RCA) of 1 mm or larger preferably contains less than 50% by weight of unclean natural aggregate (i.e., natural aggregate or unclean RCA bound with adhesive residual mortar with a given particle size fraction) with respect to the total weight of RCA with a given particle size fraction, more preferably 15% to 45% by weight of unclean natural aggregate (i.e., natural aggregate or unclean RCA bound with adhesive residual mortar with a given particle size fraction) with respect to the total weight of RCA with a given particle size fraction, and even more preferably 25% to 40% by weight of unclean natural aggregate (i.e., natural aggregate or unclean RCA bound with adhesive residual mortar with a given particle size fraction) with respect to the total weight of RCA with a given particle size fraction.

[0175] In particular, RCAs with a given particle size fraction of 1 mm or more contain up to 10 wt% CP, preferably up to 8 wt% CP, and even more preferably up to 5 wt% CP, with respect to the total weight of RCAs with a given particle size fraction.

[0176] Recycled concrete aggregate (RCA) having a given particle size fraction of 1 mm or larger preferentially contains 65% to 95% by weight of NA with the given particle size fraction, more preferably 70% to 90% by weight of NA with the given particle size fraction, and even more preferably 75% to 85% by weight of NA with the given particle size fraction, relative to the total weight of RCA with the given particle size fraction.

[0177] Preferably, recycled concrete aggregate (RCA) having a given size fraction of 1 mm or more contains 5% to 20% by weight of NA having a particle size smaller than the given particle size fraction, and more preferably 7% to 15% by weight of NA having a particle size smaller than the given particle size fraction, with respect to the total weight of the RCA having the given size fraction.

[0178] In particular, recycled concrete aggregate (RCA) having a given particle size fraction of 1 mm or larger contains 5% to 35% by weight of residual mortar, preferably 10% to 30% by weight, and more preferably 15% to 25% by weight of residual mortar, relative to the total weight of the RCA having a given particle size fraction. [Brief explanation of the drawing]

[0179] The attached drawings illustrate the present invention.

[0180] [Figure 1] Figure 1a) shows concrete crushing by a method of the background technology, and Figure 1b) shows concrete crushing by the method of the present invention for comparison. [Figure 2] Figure 2 shows a schematic diagram of the various steps of the method of the present invention. [Figure 3] Figure 3 shows the measured values ​​of RCA cleanliness through the change in residual CP (wt%) according to the size of the RCA, and the measured values ​​of RCA water absorption rate (%) according to the size of the RCA, according to the method of the present invention and, for comparison, according to the reference method. [Figure 4a] Figure 4a) shows a speciation analysis of the constituent elements of the initial concrete and RCA at the end of the reference method for comparison. [Figure 4b] Figure 4b) shows a speciation analysis of the components of the initial concrete and RCA at the end of the reference method of the present invention. [Figure 5] Figure 5 shows the performance of the present invention's method regarding the reference method and the theoretical limit. [Figure 6] Figure 6 shows the performance of the present invention's method regarding the reference method and the theoretical limit. [Modes for carrying out the invention]

[0181] Further features and advantages of the present invention will become apparent from the description of non-limiting examples of the methods according to the present invention.

[0182] [example] Example 1: Description of the method according to the present invention and the background art method not based on the present invention. Figure 1 includes an illustration of concrete crushing by the prior art method (a) of FIG. 1) and concrete crushing using the method of the present invention (b) of FIG. 1).

[0183] In a) of FIG. 1, the crushing is random and non-selective between NA and mortar. Thus, RCA with a low NA content (<60 wt% NA with respect to the total weight of RCA) and a high CP content (>10 wt% CP with respect to the total weight of RCA) and a high potential for intra-granular crushing of the original NA is produced. As a natural result, the recycled fine particles generated by crushing are few, and even if they aggregate, they are less than 25% of the CP of the initially recycled concrete.

[0184] In b) of FIG. 1, the crushing is selective between NA and mortar. This is advantageous for both the agglomeration of NA in RCA with a low content of adherent mortar and unchanged particle size and mechanical properties of NA, and the recovery in the fine fraction of CP contained in the initially recycled concrete. The micro-crushing of CP aggregates most of the CP from the initially recycled concrete in the fine particles and promotes the carbonation of CP in the fine particles.

[0185] Figure 2 shows step i) of microwave treatment in a microwave tunnel for concrete blocks from construction and / or demolition to form micro-crushed concrete blocks. And these are milled in a roller mill in step ii-1) to form a mixture of RCA with different particle sizes and recycled fine particles. The milling ii-1) makes it possible to obtain, for example, a particle size of 8 mm or less. Then, a first sorting or sieving step ii-2a) is performed using a rotary screen to extract a mixture of recycled fine particles and RCA having a particle size fraction G 1’ -G1 (for example, a particle size fraction of 4 mm to 8 mm) and RCA having a particle size <G1 (a particle size of less than 4 mm).

[0186] The recycled fine grains and the RCA having a particle size of <G1> are, on the one hand, the RCA having a particle size fraction G 2’ -G2 (for example, a particle size fraction from 1 mm to 4 mm) and, on the other hand, undergo a further sorting or sieving step ii-2b) using a rotary screen to extract the recycled fine grains (particle size less than 1 mm). The recycled fine grains recovered in step ii-2b) are carbonated in a carbonation reactor by step iii).

[0187] Optionally, the concrete blocks having a size on the centimeter scale (for example, ≤ 30 mm) and used in step i) are preferably obtained from the grinding of construction and / or demolition concrete using a jaw crusher (step i0).

[0188] In steps ii-2a) and ii-2b), steps of grinding a) and washing b) (water spraying) are preferably carried out in each of steps ii-2a) and ii-2b).

[0189] Example 2: Recycling of concrete from construction and / or demolition using the method according to the present invention 2.1 Formation and Characteristics of Concrete Samples The concrete was formulated from cement and crushed siliceous natural aggregates (NA) having a particle size less than 8 mm and a water / cement ratio of 0.6.

[0190] 2.1.1 The cement used is Lafarge CEM I from the Le Teil factory. The strength class is 52.5R, i.e., rapid hardening. This meets the European requirements of standard EN 197-1.

[0191] The physical and mechanical characteristics of the cement used are as follows. Blaine specific surface area = 4160 cm 2 / g Density = 3.15 g / cm 3

[0192] 2.1.2. The natural aggregate (NA) used is a mixture of sand (S) and gravel (G) from the crushed siliceous Parvado quarry (Saint-Christophe-du-Ligneron). The characteristics of these aggregates are as follows: Density=2640kg / m 3 Water absorption coefficient = 0.7% Chloride <0.001% Water-soluble sulfate <0.01% Active alkali content = 0.0022%

[0193] Table 1 below shows the particle size distribution of NA used in concrete mix design, more specifically, the weight percentages (mass fractions) of five different particle size fractions for the total weight of natural aggregate NA used in concrete mix design: 4 / 8 mm, 2 / 4 mm, 1 / 2 mm, 0.25 / 1 mm, and 0 / 0.25 mm.

[0194] [Table 1]

[0195] These mass fractions are interpreted as the average values ​​of the actual NA composition of the concrete used below. The last column of Table 1 defines the 0 / 1mm NA particle size fraction mentioned below. This fraction is a combination of 0.25 / 1mm and 0 / 0.25mm NA.

[0196] 2.1.3 Concrete mix design The ratios of binder (cement and superplasticizer), water, and NA used to produce concrete are shown in Table 2 below.

[0197] [Table 2]

[0198] Multiple concrete samples are prepared by mixing the components in a mortar mixer at low speed (62 rpm) for 60 seconds, high speed (125 rpm) for 40 seconds, a 90-second pause, and then high speed (125 rpm) for 60 seconds, and then pouring the mixture into a gray polypropylene cylindrical mold with a diameter of 25 mm and a height of 30 mm. The mold is then vibrated on a vibrating table for 2 x 10 seconds. In this way, multiple concrete cylinders with controlled composition and shape, and a maximum size of approximately 30 mm, are formed.

[0199] Then, to allow the concrete to harden, these cylindrical containers are stored under cellophane for 28 days in a room adjusted to 19°C.

[0200] After curing in a warm room for 28 days, the cylindrical concrete samples are oven-dried at 80°C for 48 hours. This time was determined after testing batches of aggregate, which were weighed at regular intervals until a certain mass (△m < 0.1%) was reached. This drying method ensures the reproducibility of the resulting concrete samples by imparting a controlled moisture content comparable to that of naturally degraded concrete.

[0201] The composition of concrete in the samples is measured by dissolving CP in 19 wt% hydrochloric acid after hardening and storage. The values ​​in Table 3 below show the range of compositional values ​​measured in multiple 30 mm concrete samples, each sample dissolved individually. This allows for evaluation of compositional variations in the concrete samples used.

[0202] [Table 3]

[0203] 2.2 Implementation of the Method of the Present Invention 2.2.1 Microwave fracturing step i) The microwave bench used is a single-mode cavity waveguide manufactured by SAIREM, with the following characteristics: Frequency = 2450 ± 25 MHz Output = 2000 ± <0.1% watts Maximum operating power = 1700 watts Waveguide = WR340 (rectangular cross-section of 86 x 43 mm) Ripple wave <0.3%RMS Magnetron cooling system: Water

[0204] This microwave bench can process one 30 mm concrete sample at a time at a given power output for a given duration. The cylindrical concrete sample is placed in a quartz tube that acts as a sample holder, and the tube is placed in the chimney of the microwave bench. Each sample is processed for 4 minutes at an incident microwave output of 1.5 kW. The temperature reached at the concrete surface ranges from 450°C to over 600°C (the limit measurable by the infrared thermometer used).

[0205] 2.2.2 Mechanical processing step ii) 2.2.2.1 Non-impact fracture (step i-1) Non-impact grinding following microwave treatment is performed using a manual hydraulic press (Specac Atlas 15T). Concrete samples are compressed individually. The hydraulic press stroke stops at 8 mm from the surface on which the RCA is placed, corresponding to the maximum NA size of the concrete sample.

[0206] 2.2.2.2 Selection (Step II-2) Then, the ground sample is sorted by a dry process using standard 8mm, 4mm, 2mm, 1mm, and 0.25mm square mesh sieves to produce particle size fractions of 4 / 8mm, 2 / 4mm, 1 / 2mm, 0.25mm, and 0 / 0.25mm.

[0207] 2.2.2.3 Polishing (Step a) The 1 / 4 mm and 4 / 8 mm fractions of recycled concrete aggregate (RCA) produced by crushing and subsequent sorting are separately polished for a short period of 2 minutes in a cylindrical metal jar with an inner diameter of 10 cm and rotating at a speed of 100 rpm. The polishing packing consists of 336 g of 20 mm alumina beads and 200 ml of water. The product is then re-sorted at 8 mm and 4 mm to separate the 8 mm and 4 mm RCA from the fine particles after polishing.

[0208] At the end of steps ii-1), ii-2), and a), multiple fine-grained fractions are collected and gathered.

[0209] 2.2.3 Carbonation of fine granules (Step III) The resulting fine particles were ground to 80 μm using an automatic mortar and pestle, with an average size of d 50 The particle size is approximately 10 μm. This fineness is appropriate for the use of carbonated granules as a mineral additive. The step of carbonizing the ground granules is carried out in a suspension in a stirred reactor with an effective volume of 300 ml. The suspension used consists of 15 g of recycled concrete granules and 150 ml of distilled water. Mixing is ensured by a mobile agitator rotating at 800 rpm. The carbonization reactor operates at a controlled temperature of 60 °C and a CO2 partial pressure of 5 bar. The carbonation test lasts for 20 hours, during which the CO2 consumption by the granules is continuously measured. The final carbonation rate of the carbonated granules is determined by thermogravimetric analysis (TGA) or total carbon analysis (CHNS analysis).

[0210] Comparative Example 3: Regeneration of concrete from construction and / or demolition using a method other than the present invention The present invention was compared with a non-impact pulverization method, which represents the most efficient and state-of-the-art technology for producing recycled concrete aggregate. This comparison method, hereinafter referred to as the "reference method," was performed using the same concrete sample as described in Section 2.1. The reference method consists of mechanical treatment via non-impact pulverization and sorting steps under the same conditions as described in Section 2.2.

[0211] The step of carbonating the granules is carried out as described in section 2.2.3 of Example 2.

[0212] Example 4: Performance of the method of the present invention 4.1 Performance Evaluation Criteria The performance criteria used to define the characteristics of the method's performance are quality-related and utilize the properties of recycled concrete aggregate (RCA) and recycled concrete fine-grained aggregate.

[0213] About Recycled Concrete Aggregates (RCA) Quality • CP content (by weight) in a given RCA particle size fraction • Content of clean RCA (i.e., RCA with <5% by weight CP content) in a given RCA particle size fraction • Content (by weight) of natural aggregate (NA) with the same particle size fraction as RCA

[0214] 〇Usage characteristics • Water absorption rate of RCA by the WA24 method. This test measures the moisture content of RCA after drying according to standard NF EN 1097-5. This is expressed as a weight percentage. • Water resistance of the RCA as measured by the Micro Deval (MDE) test. This test measures resistance to abrasion caused by friction between the RCA and the abrasive load of the steel balls, according to standard NF EN 1097-1. The test results are expressed as a percentage, representing the weight percentage of particles <1.6 mm generated during the test.

[0215] About recycled concrete with fine particles (<1mm) Quality • Mortar content (by weight) in the fine particles (<1 mm) produced by this method • Content (by weight) of CP that aggregates in the fine particles (<1 mm) produced by this method • Carbonation rate of fine particles (weight %) of captured CO2

[0216] 4.2 Cleanliness of recycled concrete aggregate Attached Figure 3 shows the measurement of RCA cleanliness for variations in residual CP content (weight %) (left side) according to RCA size for the method of the present invention (solid circle) and the reference method (hollow circle). This content is measured by dissolving RCA with particle size fractions of 4 / 8 mm, 2 / 4 mm, 1 / 2 mm, 0.250 / 1 mm, and 0 / 0.25 mm in a 19 wt% hydrochloric acid solution.

[0217] The absence of overlap in the 95% confidence intervals for the mass fraction of residual CP down to an RCA particle size of 0.5 mm demonstrates that the method of the present invention produces RCA that is significantly cleaner than RCA produced by the reference method down to an RCA size of 0.5 mm.

[0218] Attached Figure 3 shows the measurement of the water absorption rate (as a percentage) of RCA (on the right) according to the size of RCA, for both the method of the present invention (long-chain curve) and the reference method (short-chain curve). This content is measured by dissolving RCA with particle size fractions of 4 / 8 mm, 2 / 4 mm, 1 / 2 mm, 0.25 / 1 mm, and 0 / 0.25 mm in a 19 wt% hydrochloric acid solution.

[0219] 4.3 Product Specification in the Method of the Present Invention Detailed analysis of product quality in the method (and reference method) of the present invention involves measuring the speciation of the initial components of the concrete (NA and CP, see part 2.1 of Example 2) before and after the method (and reference method) of the present invention (part 2.2 of Example 2 and Example 3). Speciation is used to refer to the traceability of the initial components of the product of the method (and reference method) of the present invention.

[0220] For clarification, the products used to clarify the performance characteristics of the concrete recycling method are 4 / 8RCA, 2 / 4RCA, 1 / 2RCA, and fine particles (particles <1 mm). The relevant components in the speciation measurement are natural aggregates 4 / 8NA, 2 / 4NA, and 1 / 2NA, fine particles represented as 0.25 / 1NA and 0 / 0.25NA, and CP.

[0221] Figures 4a and 4b illustrate this specification in detail, showing the reference method and the method of the present invention, respectively. X i and X' i This represents the initial composition of the concrete sample before performing the method. This composition is the same for both the reference method and the method of the present invention. Columns A and A' show the mass distribution of the products (4 / 8 RCA, 2 / 4 RCA, 1 / 2 RCA, fine particles) after performing the reference method and the method of the present invention, respectively. For the reference method (Example 3), the products are separated after grinding, and for the method of the present invention (Example 2, part 2.2), the products are separated after steps ii) and a), and their mass fractions are obtained by weighing. Columns B and B' show the speciation (in mass percentage form) of each product, in other words, each fraction of columns A and A', where B1 (or B'1) corresponds to the 4 / 8 RCA speciation of A1 (or A'1), B2 (or B'2) corresponds to the 2 / 4 RCA speciation of A2 (or A'2), and so on. Speciation measurement requires the selective dissolution of CP of each product in 23 wt% hydrochloric acid, followed by sorting (and optionally polishing), weighing, and drying of the particle size fraction of NA observed after dissolution. The direct measurement of the mass of CP observed in the product can be obtained from the mass loss after dissolution. Columns C and C' show the amount of CP in the selected fraction, along with the observed amounts of clean NA (or unadhered or clean RCA) and NA (or unclean or unclean RCA) bound with adhesive residual mortar. C1 (or C'1) corresponds to observations and measurements for the 4 / 8 NA fraction of B1 (or B'1), C2 (or C'2) for the 2 / 4 NA fraction of B2 (or B'2), and C3 (or C'3) for the 1 / 2 NA fraction of B3 (or B'3). X r and X' r This represents the composition recalculated for the concrete sample after performing the reference method and the method according to the present invention, respectively. This is determined based on the values ​​in columns B and B', and thus the specification of the initial components of the concrete in the product is obtained.

[0222] Since the fine-grained fraction is defined as all particles smaller than 1 mm (0.25 / 1RCA + 0 / 0.25RCA), the specification analysis of the components shows that the method of the present invention agglomerates 31% of the concrete mass of this fine-grained fraction (column A' in Figure 4b), i.e., 16% of A'4 + 15% of A'5, compared to only 12% of the reference method (column A in Figure 4a), i.e., 8% of A4 + 4% of A5. Therefore, the method of the present invention makes it possible to agglomerate nearly three times more fine particles than the reference method, and these fine particles can be recycled as cement raw materials if not carbonated, or as mineral additives if carbonated.

[0223] The mass fractions of 4 / 8, 2 / 4, and 1 / 2 RCA in the method of the present invention are very close to the mass fractions of 4 / 8, 2 / 4, and 1 / 2 NA in the initial concrete, which can be explained by the mass fraction of NA recovered in the RCA, which is more than 75%, or even as much as 80%. In other words, the RCA produced by the method of the present invention contains less than 20% by weight of residual mortar, i.e., the CP mass fraction is between 5% and 8% by weight (see B'1, B'2, and B'3 in Figure 4b).

[0224] In comparison, the reference method RCA has an NA recovery rate of 40% to 60% by weight, and therefore the mass fraction of residual mortar in RCA is 60% to 40% by weight, meaning the CP mass fraction is 11% to 21% (see B1, B2, and B3 in Figure 4a).

[0225] Composition X of the concrete sample r and X' r Recalculation reveals that the method of the present invention maintains the size integrity of the initial NA better than the reference method. In fact, composition X' after recalculation of the reference method r The 4 / 8NA content is significantly lower than that obtained by the method of the present invention, which effectively leads to a large increase in the 2 / 4NA content by the reference method. This is due to the micro-fragmentation of CP induced by the microwave step, thus avoiding excessive NA fragmentation in the subsequent grinding step.

[0226] The degree of dissociation (or cleanliness) of NA in RCA was measured by visual classification, accompanied by verification of the CP content (columns C and C') of the separated fractions. This measurement demonstrates the selectivity of the present invention's method for NA recovery, which is conferred by the micro-fracture of concrete induced by the microwave treatment step. This selectivity results in a non-uniform distribution of residual CP, with residual CP agglomerating in small fractions of NA, while the majority of the RCA has a particularly low CP content. Here, this is referred to as clean (or unadhered) NA. The very high proportion of clean NA in RCA is a feature unique to the present invention's method. Dissociation measurements by visual classification were performed on RCA fractions of 4 / 8 mm (B1 and B'1), 2 / 4 mm (B2 and B'2), and 1 / 2 mm (B3 and B'3). In the right side of Figure 4b, labeled column C', it can be seen that over 60-70% of the RCA produced by the method of the present invention is clean (i.e., the RCA contains 1.6% to 3.2% CP), and the remaining 30-40% aggregates CP with a CP content of 3.9% to 10.7%. As shown by column C in Figure 4a, the degree of RCA dissociation (or degree of cleanliness) of the reference method ranges from 16% to 42%. In summary, for the three RCA particle size classes analyzed, the degree of NA dissociation (or degree of cleanliness) is twice as high with the method of the present invention compared with the reference method.

[0227] The performance of the present invention's method was compared to that of the reference method and to theoretical limits. For example, the theoretical limit for the cleanliness of an RCA with respect to residual CP content is 0%, while the maximum percentage for a 4 / 8 mm NA in a 4 / 8 mm RCA is 100%. All percentages are expressed as weight percent.

[0228] Figure 5 shows the performance of the present invention with respect to the reference method and the theoretical limit.

[0229] 4.4 Characterization of Carbonation At most, the aqueous carbonation method can achieve approximately 80% of the theoretical carbonation limit of the solid calculated based on its chemical composition.

[0230] The theoretical carbonation limit of the fine particles is directly related to the amount of calcium (Ca) they contain. Per unit mass of the fine particles, this theoretical limit is similar for the fine particles of the method of the present invention and the reference method, because it is shown by measurement that they have the same chemical composition. This theoretical limit is between 170 kg and 200 kg of CO2 per metric ton of the fine particles. Conversely, since the method of the present invention enables the production of more than 2.6 times as many fine particles as the reference method, the method of the present invention can store up to 2.6 times more CO2 per metric ton of recycled concrete than the reference method. Keeping in mind that the maximum value possible for concrete carbonation is estimated on the same basis as 70 kg of CO2 per metric ton of recycled concrete, this represents a CO2 storage capacity possible with the method of the present invention of 60 kg of CO2 per metric ton of recycled concrete, compared to 20 kg of CO2 per metric ton of recycled concrete for the reference method. Thus, for the fine particles, with respect to 1 metric ton of recycled concrete, the method of the present invention enables the storage of up to 3 times more CO2 than the reference method (Table 4 below).

[0231]

Table 4

[0232] The final carbonation rate of the carbonated fine particles is obtained by measuring the total carbon (CHNS analysis).

[0233] Table 5 below lists the results for the fine particles obtained by the reference method and by the method of the present invention.

[0234]

Table 5

[0235] Experimental measurements confirm that the carbonation ability of the fines is similar for the method of the present invention and the reference method, which results from the similar chemical composition. However, the results show that the fines produced by the method of the present invention are substantially advantageous, with a +1.3 increase in carbonation being seen with respect to the fines produced by the reference method. This result, along with the observation during the carbonation test of the fines that the fines produced by the method according to the present invention carbonize with better kinetic properties than the reference method, is probably the result of the micro-crushing of the CP induced by the microwave treatment step, which promotes the transfer of carbon dioxide (CO2) to the carbonizable element (calcium) found in the CP.

[0236] Figure 6 shows the performance of the method of the present invention with respect to the reference method and theoretically with respect to the limit.

[0237] Over all measured performance criteria, the method of the present invention is on average 2.3 times more efficient than the reference method.

Claims

1. At least the following steps, namely, i) One or more microwave treatment steps of concrete blocks from construction and / or demolition having a size on the order of centimeters in order to form micro-crushed concrete blocks, ii) One or more mechanical processing steps that enable the extraction of recycled concrete aggregate (RCA) containing natural aggregate without adhering material and natural aggregate bonded with adhesive residual mortar, and recycled fine particles from the finely crushed concrete block, iii) One or more steps of carbonating the regenerated granules in the presence of carbon dioxide so as to form carbonated regenerated granules, Characterized by including, This method does not require a carbonation step for recycled concrete aggregate (RCA). A method for recycling concrete from construction and / or demolition.

2. The method according to claim 1, characterized in that the concrete blocks from construction and / or demolition have a maximum size of 10 cm.

3. The method according to claim 1 or 2, characterized in that the microwave processing step of step i) is performed over a period of time ranging from 30 seconds to 10 minutes.

4. The method according to any one of claims 1 to 3, characterized in that the microwave processing i) is performed at a frequency in the range of 915 MHz to 2450 MHz.

5. The method according to any one of claims 1 to 4, characterized in that the RCA has a particle size of 1 mm or more.

6. The method according to any one of claims 1 to 5, characterized in that the regenerated fine particles have a particle size of less than 1 mm.

7. The method according to any one of claims 1 to 6, characterized in that step ii) includes at least one step iii-1) grinding a finely crushed concrete block.

8. The method according to claim 7, characterized in that step ii-1) grinding the finely crushed concrete block is a non-impact grinding step.

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

10. The method according to claim 9, characterized in that the sorting step ii-2) is performed using a rotating screen or a swirling sieve.

11. The method according to any one of claims 1 to 10, further comprising at least one step a) of cleaning the recycled concrete aggregate.

12. The method according to any one of claims 1 to 11, further comprising at least one step b) of washing the recycled concrete aggregate.

13. At least 10 volume percent of CO with respect to the total volume of the gas ２ The method according to any one of claims 1 to 12, characterized in that step iii) is performed in the presence of a gas containing .

14. The following steps, namely, i) One or more microwave treatment steps of concrete blocks from construction and / or demolition having a size on the order of centimeters in order to form micro-crushed concrete blocks, ii) One or more mechanical processing steps that enable the extraction of recycled concrete aggregate (RCA) containing natural aggregate free of adhering material and natural aggregate bound with adhesive residual mortar, and recycled fine particles from the finely crushed concrete block, Characterized by including, This method does not require a carbonation step between the recycled concrete aggregate RCA obtained in step ii) and the recycled fine particles. A method for recycling concrete from construction and / or demolition.

15. Recycled concrete aggregate (RCA) obtained by any one of claims 1 to 13 or by the method specified in claim 14, characterized in that RCA having a given particle size fraction of 1 mm or more contains at least 50% by weight of natural aggregate without adhering material having the given particle size fraction with respect to the total weight of the RCA having the given particle size fraction.

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