Method for Recycling Concrete Construction and / or Demolition Waste

Abstract

The present invention relates to a method for recycling concrete from construction and / or demolition, the method comprising at least one step of subjecting concrete blocks to microwave treatment, at least one mechanical treatment step, and at least one step of carbonating recycled aggregates and / or recycled fine powder, a recycling facility for carrying out the method, and recycled aggregates obtained by microwave treatment and mechanical treatment of concrete blocks.

Description

Technical Field

[0001] The present invention relates to a method for recycling concrete waste generated from construction and / or demolition, including at least one step of microwave treatment of concrete blocks, at least one step of mechanical treatment, and at least one step of carbonation of recycled concrete aggregates and / or recycled concrete fine powder. The present invention also relates to a recycling facility for implementing the recycling method, and to recycled concrete aggregates obtained by the steps of microwave treatment and mechanical treatment of concrete blocks.

Background Art

[0002] Concrete is one of the most widely consumed manufactured materials in the world. Concrete mainly contains aggregates (coarse aggregates and gravel), to which cement, sand, and water are mixed. In particular, the annual consumption of aggregates in France is 350 million metric tons, which corresponds to 6 metric tons per inhabitant per year and 17 kg per inhabitant per day. Projections indicate that the demand for aggregates will continue to increase in the future, especially in the construction of new buildings. Natural aggregates (NA) are generally obtained by mining alluvial, terrestrial, or marine sand and gravel deposits. Natural aggregates (NA) are not renewable resources, and although technically infinite, they are becoming increasingly difficult to obtain for social and environmental reasons. In particular, opening new quarries to meet the demand for natural aggregates (NA) is becoming increasingly difficult because it causes nuisances such as noise, dust, and increased traffic volume to neighboring residents.

[0003] At the same time, the amount of materials generated by the demolition or dismantling of buildings and social infrastructure is increasing and will continue to increase in the coming years. In fact, buildings constructed during the post-war reconstruction period in the 1950s are gradually reaching the end of their lifespan, which means that the amount of concrete available for recycling will be significant.

[0004] Furthermore, the calcination of natural limestone mineral resources required for cement production accounts for nearly half of the CO2 emissions associated with concrete production, and concrete is one of the most CO2-emitting materials created by humanity.

[0005] Recycling concrete or stone materials (such as construction waste and demolition waste) has been proposed as a way to avoid landfilling, reduce dependence on natural deposits, and protect natural aggregate resources while manufacturing new concrete structures.

[0006] Concrete waste generated during construction and demolition is generally recycled by crushing concrete blocks to form recycled concrete aggregates (RCA). RCA can also be separated from fine powder by screening. However, current recycling methods are not entirely satisfactory. The separation of NA from residual mortar is far from optimized. Commonly obtained RCA is composed of NA, most of which is bound to a large amount of residual mortar from the original concrete. In particular, most of the residual mortar adheres to the NA or is present in the NA in the form of aggregates at least as large as natural aggregates, thus preventing the production of impurity-free NA. Due to the high proportion of adhered cement paste, such RCA is of inferior quality compared to NA, has a higher water absorption rate than NA, and lower mechanical properties (lower impact resistance and / or higher vulnerability). Concrete produced from RCA mixed under normal conditions may lose workability during transportation in a drum can and may not be suitable for use upon arrival at the destination. The current concrete standard NF EN 206 / CN defines the maximum proportion of RCA that can replace natural aggregates in the production of new concrete, which varies depending on the type of RCA, particularly its composition, and the exposure class of the structure being built. Due to the low quality of these RCA, they are currently mainly used in structures with low added value, particularly as low-value backfill materials in road earthworks, capping layer materials for roads, or backfill materials for quarries. However, there are limits to the recycling capacity in the road construction field, and this form of downcycling cannot fully meet the criteria for sustainable development.

[0007] Furthermore, due to crushing, NA is significantly damaged, the dimensions of NA are reduced compared to the initial particle size distribution, and fine powder containing NA fragments is concentrated. Therefore, the resulting recycled fine powder has a composition that makes recovery and / or recycling more difficult. Finally, since most of the cement paste adheres to or is bound to the RCA, the amount of fine powder produced is small compared to the amount of mortar in the concrete. In current industrial plants, the fine fraction is generally not recovered and is considered waste.

[0008] Solutions have been proposed for the development of standards that improve the performance of RCA and, in particular, increase its proportion in new concrete structures with high added value. Examples include polymer-based chemical treatments, the use of mineral reinforcements, or carbonation (e.g., the use of bacteria that induce the formation of calcium carbonate).

[0009] In particular, International Application No. WO2020 / 217232 describes a fresh concrete mixture comprising a hydraulic cement, water, and carbonated recycled concrete aggregates. The carbonated recycled concrete aggregates are obtained using a method comprising at least one crushing step, at least one sieving step, and a carbonation step, and the carbonation can be carried out simultaneously with the crushing step or the sieving step, or after one of these steps. In an example, to form carbonated recycled concrete, mortar containing sand and cement is crushed to form coarse recycled concrete aggregates of 5 - 20 mm, and then carbonation is carried out by exposing it to an atmosphere with a relative humidity of 55 - 65% rich in carbon dioxide (CO2). This carbonated recycled concrete aggregate is mixed with sand, water, and cement to form new concrete. The recycled concrete aggregate of International Publication No. WO2020 / 217232 has a composition of mortar (a mixture of sand and cement). The RCA obtained after carbonation contains impurities and has inferior quality compared to NA.

[0010] Furthermore, some documents assume the direct use of concrete powder in cement raw materials as a raw material for the production of clinker. For example, Schoon et al. (Cement and Concrete Composites, 58, 2015, 70 - 80) describe mixing recycled concrete powder (5 - 15%) into cement raw materials as an alternative to conventional siliceous materials. Various technical configurations were used to separate the mortar fraction from the aggregates and the generated powder from the recycled sand. However, Schoon et al. point out that it is difficult to collect large amounts of powder.

[0011] As a result, there is still a need for a recycling method that can obtain recycled concrete aggregates that are as free of impurities as possible (i.e., with as little mortar residue as possible) and / or of improved quality, and that can form new concrete structures by using more of them. There is also a need for a recycling method that can produce large quantities of high-quality recycled fine powder of concrete. In particular, there is a need for a recycling method that can recycle all recoverable parts of concrete, i.e., both natural aggregates (NA) and the mortar surrounding them.

[0012] From these results, the present invention aims to overcome the drawbacks of the prior art and, in particular, to enable the use of recycled coarse aggregates (RCA) of better quality in terms of water absorption and / or mechanical properties and / or high levels of purity, and to enable the use of recycled fine powder that is larger in quantity and / or of higher quality, particularly in terms of pozzolanic activity and / or hydraulic activity, from concrete waste resulting from construction and / or demolition. The method is simple, industrially applicable, uses abundant raw materials, and is environmentally beneficial.

Summary of the Invention

[0013] The first main subject of the present invention is a method for recycling concrete from construction and / or demolition, characterized by comprising at least the following steps. i) One or more steps of subjecting concrete blocks of centimeter-scale dimensions from construction and / or demolition to microwave treatment to form micro-crushed concrete blocks. ii) One or more steps of mechanical treatment that enable the extraction of recycled coarse aggregates (hereinafter referred to as RCA), including bare natural aggregates (NA) and natural aggregates (NA) bonded to an adherent residual cementitious matrix (or residual mortar), and recycled fine powder from the micro-crushed concrete blocks. And further comprising the following steps: iii) One or more steps of carbonating the recycled coarse aggregates in the presence of carbon dioxide to form carbonated recycled coarse aggregates (hereinafter referred to as CRCA), and / or iv) in the presence of carbon dioxide, carbonating the recycled fine powder to form a carbonated recycled fine powder in one or more steps.

[0014] The method of the present invention is simple and easy to implement, and brings the following results: - At the end of steps i), ii), and iii), carbonated recycled aggregate (CRCA) is obtained, and the carbonated recycled aggregate has less impurities and / or is of higher quality, especially in terms of water absorption rate and / or mechanical properties, and / or - At the end of steps i), ii), and iv), carbonated recycled fine powder containing a large amount of cement paste and / or with improved quality (especially, after the formation of amorphous silica that is particularly reactive in the cementitious medium by the carbonation step, the quality is improved from the perspective of pozzolanic activity) is obtained.

[0015] This method can include the carbonation of RCA [step iii)], the carbonation of recycled fine powder [step iv)], or the carbonation of both RCA and recycled fine powder [steps iii) and iv)].

[0016] Furthermore, this method is industrially applicable, uses abundant raw materials (concrete waste from construction or demolition), enables the recycling of unused construction concrete or demolition concrete, reduces the environmental impact, and at the same time guarantees the use or recovery of CO2. The method of the present invention is an integrated concrete recycling method in terms of recycling the entire initial concrete, i.e., natural aggregate (NA) and fine powder.

[0017] This method is a method for recycling concrete from construction and / or demolition, especially in the construction and public works sectors. In other words, the concrete can be concrete waste from the construction of buildings and / or paved structures, scraps from concrete production, concrete from the demolition of buildings or paved structures, or a mixture thereof.

[0018] Definitions In the present invention, the term "cement" means a hydraulic binder, i.e., a finely divided inorganic material that forms a paste which hardens and sets by a hydration reaction and process when mixed with water and maintains strength and stability even in water after hardening (as defined by the standard specification EN 197-1).

[0019] The term "cement paste" (hereinafter also referred to as "CP") is used in the present invention to mean a mixture of cement and water that hardens by a hydration reaction. The cement paste may contain one or more additives as required. The amount of cement paste adhering to the RCA is a criterion for determining the purity of the RCA.

[0020] In the present invention, the term "concrete" is used to mean a mixture of cement, aggregates (sand and gravel), and water. This is the initial material that includes all components (aggregates and cement paste) to be recovered.

[0021] In the present invention, the term "natural aggregate (NA)" is used to mean natural sand and gravel particles obtained by mining alluvial deposits, land, or marine sand and gravel sediments.

[0022] In the present invention, the term "recycled concrete aggregate (RCA)" is used to mean sand and gravel particles produced from concrete and used as an alternative to NA or recycled in the manufacture of concrete or other applications. In the present invention, the term "recycled concrete aggregate (RCA)" is also referred to as "recycled aggregate".

[0023] In the present invention, the term "carbonated recycled concrete aggregate (CRCA)" is used to mean concrete aggregate carbonated by a dedicated accelerated carbonation method. In the present invention, the term "carbonated concrete aggregate (CRCA)" is also referred to as "carbonated recycled aggregate".

[0024] In the present invention, the term "residual mortar" is used to mean a mixture of cement paste and NA having dimensions smaller than the mesh size of the RCA. Most of the residual mortar adheres to the surface of the RCA. Therefore, the definition of residual mortar varies depending on the particle size fraction of the RCA. G M is the particle size fraction G of the RCA M -G m is the upper limit mesh size, and G m is the lower limit mesh size. When this is the case, the residual mortar bonded to this particle size fraction of the RCA contains a mixture of cement paste and NA having a particle size <G m . In the present invention, the term "residual mortar" is also referred to as "residual cementitious matrix".

[0025] In the present invention, the term "fines" is used to mean a mixture of cement paste and NA having dimensions smaller than the minimum particle size of the finest particle fraction of the RCA produced by the concrete recycling method. m

[0026] In the present invention, the term "accelerated carbonation" is used to mean a carbonation method that functions at a CO2 concentration 250 to 12,000 times that of the Earth's atmosphere (415 ppm). As a result, the carbonation rate is on the order of several minutes, whereas natural carbonation takes several years. In residual mortar, since the NA contained in the residual mortar does not carbonize, only the cement paste carbonizes. In the present invention, when the term "carbonation" is used alone, it is synonymous with "accelerated carbonation". Therefore, the terms "accelerated carbonation" or "carbonation" are opposed to the term "natural carbonation".

[0027] ​In the RCA of the present invention, the terms "bare natural aggregates", "natural aggregates free of impurities", and "RCA free of impurities" are synonymous. The bare natural aggregates in the RCA of the present invention preferably contain less than 5% by weight of CP, more preferably at most 4% by weight of CP, and still more preferably at most 3% by weight of CP, based on the total weight of the bare natural aggregates.

[0028] In the RCA of the present invention, the terms "natural aggregates associated with an adherent residual mortar", "natural aggregates containing impurities", and "RCA containing impurities" are synonymous. The natural aggregates associated with an adherent residual mortar in the RCA of the present invention preferably contain 5% to 30% by weight of CP, more preferably 7% to 25% by weight of CP, and still more preferably 10% to 20% by weight of CP, based on the total weight of the natural aggregates associated with an adherent residual mortar.

[0029] Step i) The centimeter-scale sized concrete blocks from construction and / or demolition used in Step i) include bare natural aggregates (i.e., natural aggregates not bonded to an adherent residual cementitious matrix or without an adherent residual cementitious matrix), such as gravel or sand (i.e., "bare" or gravel or sand not bonded to an adherent residual cementitious matrix or without a residual cementitious matrix), and natural aggregates such as gravel or sand bonded to an adherent residual cementitious matrix. In other words, the centimeter-scale sized concrete blocks from construction and / or demolition used in Step i) include natural aggregates (NA) such as gravel and / or sand and cement paste. Within the said concrete blocks of centimeter-scale size from construction and / or demolition, the NA is bonded to the cement paste to form the said blocks of centimeter-scale size.

[0030] In the present invention, the adherent residual cementitious base material contains, for example, cement, sand, water, and, if necessary, one or more additives. Instead of sand, gravel or a mixture of sand and gravel can be used. As described above, the particle size fraction of sand and / or gravel in the cementitious base material is smaller than the particle size fraction of the natural aggregate NA that is combined with the cementitious base material.

[0031] By step i), a primary fracture network can be formed within the concrete block, more specifically around the natural aggregate (NA) (separation in the tissue structure of the aggregate). Thereafter, a secondary fracture network can be formed within the cement paste CP of the cementitious base material (physical separation of the aggregate and dense fracture of the cement paste CP). As a result, the concrete is selectively fractured, and it becomes possible to separate the natural aggregate (NA) from most of the CP of the cementitious base material without causing significant damage to the natural aggregate (NA).

[0032] In other words, due to the secondary fracture, a dense (secondary) network of microfractures distributed in the cement paste of the cementitious base material is formed, regardless of whether it adheres to the surface of the natural aggregate. As a result, it becomes possible to separate the cement paste of the cementitious base material as a fine particle size fraction. This not only facilitates the subsequent extraction step ii), but also promotes the carbonation step iii) of the cement paste of the cementitious base material that binds to a specific natural aggregate and adheres to its surface, and / or the carbonation step iv) of the cement paste contained in a large amount in the recycled fine powder.

[0033] The formation of the above-mentioned primary and secondary fracture networks promotes the next step ii) of selectively separating the natural aggregate (NA) contained in the construction and / or demolition concrete. As a result, the separation of NA from the fine powder is promoted without deteriorating NA.

[0034] In other words, the greater the number of micro-destructions per unit volume in the cement paste of the cementitious base material, the purer the resulting recycled concrete aggregate (RCA) will be (i.e., the higher the content of NA, the lower the content of the residual cementitious base material or the adhering residual mortar, or the complete absence of the residual cementitious base material or the adhering residual mortar), the greater the amount of CP in the fine powder, and the more efficient the method will be, particularly meaning that the subsequent steps ii), iii), and iv) will be more efficient.

[0035] Different from a crusher that randomly breaks concrete (as shown in FIG. 1), in microwave treatment, the cementitious phase of the cement paste CP is selectively weakened without significantly changing the structure of the natural aggregate NA. Therefore, the integrity of the natural aggregate NA is maintained, and at least 75% by weight of the CP of the centimeter-scale dimension concrete blocks from construction and / or demolition is found in the recycled fine powder by the combination of steps i) and ii).

[0036] The microwave treatment in step i) can be carried out with an incident power sufficient to induce the destruction of the concrete block.

[0037] Preferably, the microwave treatment in step i) is carried out at a power in the range of 1 kW to 50 kW, preferably 5 kW to 40 kW, more preferably 5 kW to 10 kW.

[0038] These powers are particularly suitable for treating 1 ton / hour of concrete blocks.

[0039] Preferably, the microwave treatment in step i) is carried out for a time (exposure time) ranging from about 30 seconds to about 10 minutes, more preferably from about 1 minute to about 5 minutes.

[0040] In the present invention, the term "centimeter-scale dimension" with respect to concrete blocks from construction and / or demolition preferably means that the concrete blocks from construction and / or demolition have dimensions of up to about 10 cm, more preferably up to about 7 cm, and most preferably up to about 5 cm.

[0041] Preferably, the concrete blocks from construction and / or demolition have dimensions of at least about 1 cm, more preferably at least about 2 cm, and most preferably at least about 3 cm.

[0042] Step i) can be carried out by passing the concrete block through a microwave tunnel.

[0043] The microwave treatment i) can be carried out at frequencies from about 915 MHz to about 2450 MHz, more preferably at a frequency of about 915 MHz or about 2450 MHz. These frequencies are the average frequencies in the ranges of 902 - 928 MHz and 2400 - 2500 MHz, respectively.

[0044] The microwave treatment i) can be carried out continuously or in pulse mode (for example, symmetric rectangular wave pulses lasting at least 1 second).

[0045] Depending on the dimensions of the concrete piece to be treated, a traveling wave or standing wave propagation mode can be used (for a concrete piece less than 5 cm: standing wave, for a concrete piece more than 5 cm: traveling wave).

[0046] The microwave treatment i) can be carried out using a waveguide or an antenna in a reflection cavity.

[0047] The microwave treatment i) results in drying of the material and can advantageously recover the evaporated water for subsequent reuse in steps ii) - iv).

[0048] At the end of step i), the concrete block is in a state of "micro-destruction". This is because a large amount of the cement paste contained in the concrete block is in a state of micro-destruction. As a result, the concrete block obtained in step i) contains micro-destroyed cement paste.

[0049] Step ii) In step ii), one or more mechanical treatment steps are performed on the micro-destroyed concrete block obtained in step i).

[0050] By step i), the mechanical stress that promotes the shear force in step ii) propagates the destruction and fragments the micro-destroyed concrete block. At the same time, it limits the destruction of NA and separates the recycled coarse aggregate RCA containing the bare natural aggregate, the adherent residual cementitious matrix, and the natural aggregate bonded to the recycled fine powder.

[0051] By step ii), it becomes possible to extract the recycled coarse aggregate RCA containing the bare natural aggregate and the natural aggregate bonded to the adherent residual cementitious matrix (or adherent residual mortar), and the recycled fine powder from the micro-destroyed concrete block. At the end of step ii), the recycled coarse aggregate is separated from the recycled fine powder, and at least 75% by weight of the CP contained in the initial concrete to be recycled is present in the recycled fine powder.

[0052] At the end of step ii), a fraction F1 of the recycled coarse aggregate RCA containing the bare natural aggregate and the natural aggregate bonded to the adherent residual cementitious matrix (or adherent residual mortar), and a fraction F2 of the recycled fine powder are obtained.

[0053] The recycled coarse aggregate RCA preferably has a particle size of about 1 mm or more.

[0054] The bare natural aggregate preferably has a particle size of about 1 mm or more.

[0055] The natural aggregate bonded to the adherent residual cementitious matrix (or adherent residual mortar) preferably has a particle size of about 1 mm or more.

[0056] According to one preferred embodiment of the present invention, the bare natural aggregates (each natural aggregate bonded to the adhering residual cementitious matrix or adhering residual mortar) are selected from gravel, sand having a particle size of about 1 mm or more, and mixtures thereof.

[0057] Gravel is generally defined as having a particle size of about 4 mm or more.

[0058] Sand is generally defined as having a particle size of 4 mm or less.

[0059] In the present invention, the particle sizes of RCA, gravel, and sand are determined by methods well known to those skilled in the art, in particular, by sieving (for example, according to standard NF EN 933-1) (laboratory method) or sorting (industrial method).

[0060] The adhering residual cementitious matrix (or adhering residual mortar) bonded with the natural aggregate NA preferably contains natural aggregate NA having a particle size of less than about 1 mm.

[0061] Recycled fine powder (fraction F2) generally contains cement paste and preferably natural aggregate NA such as sand having a particle size of less than about 1 mm.

[0062] Recycled fine powder (fraction F2) preferably has a particle size of less than 1 mm.

[0063] In fraction F2, the sand and the cement paste can be in a mortar form, an individual form, or a mixture of a mortar form and an individual form.

[0064] Step ii-1) Step ii) preferably includes at least one step ii-1) of crushing the small-damaged concrete blocks.

[0065] Step ii-1) of crushing the small-damage concrete block can be carried out using at least one impact crusher (e.g., jaw crusher, gyratory crusher, cone crusher, or impact crusher), or can be carried out using a non-impact crusher (e.g., single-roller type, double-roller type, or roller mill such as a high-pressure roller mill, also well-known as HPRC, the abbreviation of "High Pressure Roll Crusher").

[0066] Preferably, step ii-1) of crushing the small-damage concrete block is a non-percussive milling step. In this embodiment, step ii-1) of crushing the small-damage concrete block preferably uses at least one non-impact crusher.

[0067] The non-impact crusher has the advantage that it can apply a continuous compressive shear action. Therefore, excessive damage to the natural aggregate NA can be prevented and / or the integrity of its particle size and mechanical properties can be maintained.

[0068] The non-impact crusher is preferably a roller mill such as a single-roller type or a double-roller type. The roller mill can be equipped with smooth rollers or toothed rollers.

[0069] The crusher-type roller mill can generate a specific maximum particle size corresponding to the maximum particle size of the natural aggregate NA contained in the initial concrete to be recycled by appropriately adjusting operating parameters such as the feed rate, the rotational speed of one or more rollers, the roller spacing, and / or the applied hydraulic pressure.

[0070] The roller spacing is adapted to the maximum particle size of the original aggregate (i.e., the natural aggregate NA in the initial concrete to be recycled), especially to minimize its fragmentation.

[0071] This method may include a plurality of grinding steps ii-1), in particular by performing the following: - a plurality of grinding steps ii-1) after the microwave treatment step i), or - a plurality of consecutive sequences of the microwave treatment step i) and the grinding step ii-1).

[0072] When performing a plurality of grinding steps ii-1) after step i), a series of devices of non-impact crushers such as roller mills can be used. In particular, by appropriately adjusting the operating parameters of the consecutive crushers, such as the feed rate, the rotational speed of the rollers, the distance between the rollers and / or the applied hydraulic pressure, it is possible to continuously produce RCA with a finer maximum particle size.

[0073] The distance between the rollers can be continuously narrowed, thereby reducing the particle size of the RCA aggregate and obtaining the highest purity RCA aggregate (i.e., high NA content and low content of residual adhering mortar or cementitious matrix). As a result, the generation of recycled fine powder can be optimized.

[0074] When a plurality of consecutive sequences of steps i) and ii-1) are carried out, a single non-impact crusher such as a roller mill can be used after each step i). By appropriately adjusting its operating parameters, in particular the feed rate, rotational speed, distance between the rollers and / or the applied hydraulic pressure of one or more rollers, it is possible to continuously produce RCA with a finer maximum particle size.

[0075] The grinding step ii-1) is preferably carried out in a dry process. The dry process is particularly suitable because the previous microwave treatment step i) contributes to the drying of the material.

[0076] One or more grinding steps ii-1) result in recycled aggregate RCA (natural aggregate with or without adhering residual cementitious matrix), which preferably has a particle size G of up to about 45 mm, or up to about 25 mm, or up to about 11.2 mm, or up to 8 mm, or up to 4 mmM (corresponding to the maximum particle size of the natural aggregate NA in the original concrete to be recycled), and depends on the intended use and / or the particle size of the natural aggregate NA included in the initial concrete to be recycled (i.e., G M ≤ 45 mm, or G M ≤ 25 mm, or G M ≤ 11.2 mm, or G M ≤ 4 mm).

[0077] Preferably, the recycled aggregate RCA (regardless of the presence or absence of the adhered residual cementitious matrix on the natural aggregate) obtained after the crushing step has a minimum particle size G m of at least about 1 mm (G m ≥ 1 mm).

[0078] Step ii-2) Step ii) may further include at least one sorting step ii-2) (also called sieving), especially after step ii-1). By this step ii-2), the RCA aggregate and the fine powder can be sorted by particle size.

[0079] The sorting step ii-2) can be carried out by a dry or wet process, preferably a wet process.

[0080] The sorting step ii-2) can be carried out using any type of vibrating, gyratory, rotary screen or sieve, preferably a rotary screen or a rotary gyratory sieve. A rotary screen is also called a rotary sieve, a revolving screen, a trommel screen, or a trommel sieve.

[0081] By the sorting step ii-2), it becomes possible to separate the fraction F1 of the recycled aggregate RCA from the fraction F2 of the recycled fine powder, and if necessary, it becomes possible to separate the recycled aggregate RCA according to the particle size within the fraction F1.

[0082] This method preferably includes a plurality of sorting steps ii-2).

[0083] One or more screens used in one or more screening steps ii-2) comprise a mesh having apertures suitable to allow such separation.

[0084] The screen (or series of screens) preferably has a mesh size suitable for the crusher (or series of crushers) used in step ii-1) or the plurality of steps ii-1).

[0085] According to one preferred embodiment of the invention, step ii-2) comprises a first screening step ii-2a) capable of separating recycled coarse aggregate RCA having a particle size fraction G m ≦G1≦G M such that the particle size G1, or G m ≦G 1’ <G1≦G M such that the particle size fraction G 1’ -G1.

[0086] By way of example, the recycled coarse aggregate RCA isolated (i.e., separated) in the first screening step ii-2a) has a particle size G1 of at least about 4 mm.

[0087] By way of example, the recycled coarse aggregate RCA isolated (i.e., separated) in the first screening step ii-2a) has a particle size G1 of up to about 45 mm, or up to about 25 mm, or up to about 11.2 mm, or up to about 8 mm, depending on the intended use and / or the particle size of the natural aggregates included in the original concrete to be recycled.

[0088] By way of example, the first screening step ii-2a) makes it possible to separate RCA having a predetermined particle size fraction of 4 - 8 mm, or 8 - 11.2 mm, or 11.2 - 25 mm, or 25 - 45 mm.

[0089] The limiting values of the particle size fractions are only indicative, and other limiting values may be used depending on the use and / or the particle size of the NA included in the original concrete to be recycled.

[0090] In the first screening step ii-2a), the particle size G1 (fraction F1a ) The recycled coarse aggregate RCA is separated from recycled fine powder (fraction F 2a ), and if necessary, from recycled coarse aggregate RCA (fraction F 1b , fraction F 1c , etc.) with a smaller particle size.

[0091] The recycled coarse aggregate RCA with particle size G1 includes bare natural aggregate and natural aggregate preferably bonded to the residual cementitious matrix (residual mortar) attached to the natural aggregate.

[0092] Step ii-2) may further include a second screening step ii-2b) that enables separation of recycled coarse aggregate RCA having a particle size fraction G m ≦ G2 < G1 or G m ≦ G 2’ < G2 ≦ G1 < G1 ≦ G M such that. 2’ -G2.

[0093] As an example, the recycled coarse aggregate RCA separated in the second screening step ii-2b) has a maximum particle size G2 of about 4 mm.

[0094] As an example, if it was possible to separate RCA with a particle size fraction of 4 to 8 mm by the first screening step ii-2a), it becomes possible to separate RCA with a particle size fraction of 1 to 4 mm by the second screening step ii-2a). If it was possible to separate RCA with a particle size fraction of 8 to 11.2 mm by the first screening step ii-2a), in the second screening step ii-2a), it becomes possible to separate RCA with a particle size fraction of 4 to 8 mm. If it was possible to separate RCA with a particle size fraction of 11.2 to 25 mm in the first screening step ii-2a), in the second screening step ii-2a), it becomes possible to separate RCA with a particle size fraction of 8 to 11.2 mm. If the first screening step ii-2a) can separate RCA with a particle size fraction of 25 to 45 mm, the second screening step ii-2a) can separate RCA with a particle size fraction of 11.2 to 25 mm.

[0095] Preferably, the recycled aggregate RCA separated in the second sorting step ii-2b) has a particle size G2 of at least about 1 mm.

[0096] In the second sorting step ii-2b), the recycled aggregate RCA having a particle size G2 (fraction F 1b ) is separated from the recycled fine powder (fraction F 2b ) and, if necessary, from recycled aggregates having a smaller particle size (fraction F 1c , etc.).

[0097] The recycled aggregate RCA with a particle size G2 includes bare natural aggregates and natural aggregates bonded to a residual cementitious matrix (residual mortar) preferably attached to the natural aggregates.

[0098] 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 necessary to separate the recycled aggregate RCA from the recycled fine powder as much as possible. This may depend in particular on the particle size distribution of the initial natural aggregate NA used in the construction and / or demolition concrete.

[0099] 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).

[0100] In this embodiment, step ii) is - a plurality of sorting steps ii-2) following a plurality of grinding steps ii-1), or - a plurality of consecutive sequences of grinding steps ii-1) and sorting steps ii-2).

[0101] Step ii) preferably includes a plurality of consecutive sequences of grinding steps ii-1) and sorting steps ii-2).

[0102] At the end of step ii), in particular at the end of steps ii-1) and ii-2), the separated or recovered recycled coarse aggregate RCA has a structure as close as possible to that of the natural aggregate NA of the original demolished and / or construction concrete.

[0103] Therefore, by the method of the present invention resulting from steps i) and ii), high-purity RCA aggregates can be obtained, and since most of the RCA is released from the residual mortar (and as a result the cement paste contained in the mortar) attached to the NA, a large amount of fine powder can be obtained.

[0104] After step ii), when the method includes a plurality of screening steps ii-2), the method may further include the step of collecting different fine powder fractions from different screening steps (F 2a 、F 2b 、F 2c etc.).

[0105] Recycling this large amount of fine powder from concrete construction and demolition waste as a mineral additive to reduce the demand for cement in concrete and / or as a component of the raw materials used in the production of cement is a potential means to reduce the CO2 emissions and the demand for natural resources associated with concrete production.

[0106] At the end of step ii), in particular at the end of steps ii-1) and ii-2), the recycled coarse aggregate RCA obtained in a predetermined particle size fraction of 1 mm or more preferably contains, with respect to the total weight of the RCA having the predetermined particle size fraction, 65 wt% to 95 wt%, more preferably 70 wt% to 90 wt%, even more preferably 75 wt% to 85 wt% of the NA having the predetermined particle size fraction. This is also called the recovery rate.

[0107] Preferably, the RCA obtained in a predetermined particle size fraction of 1 mm or more contains, with respect to the total weight of the RCA having the predetermined particle size fraction, at most 10 wt% of CP, preferably at most 8 wt% of CP, even more preferably at most 5 wt% of CP.

[0108] Preferably, the recycled concrete aggregate RCA obtained with a predetermined particle size fraction of 1 mm or more contains 5 wt% to 20 wt%, and more preferably 7 wt% to 15 wt% of NA having a particle size smaller than the predetermined particle size fraction, with respect to the total weight of the RCA having the predetermined particle size fraction.

[0109] In particular, the recycled concrete aggregate RCA obtained with a predetermined particle size fraction of 1 mm or more contains 5 wt% to 35 wt% of residual mortar, preferably 10 wt% to 30 wt% of residual mortar, and even more preferably 15 wt% to 25 wt% of residual mortar, with respect to the total weight of the RCA having the predetermined particle size fraction.

[0110] As defined herein, the CP of the RCA obtained with a predetermined particle size fraction of 1 mm or more, the NA having the predetermined particle size fraction, the NA having a particle size smaller than the predetermined particle size fraction, and the content of the residual mortar are determined by selectively dissolving the CP contained in the RCA with hydrochloric acid and weighing and measuring the various above-mentioned contained components.

[0111] At the end of step ii), in particular at the end of steps ii-1) and ii-2), the recycled fine powder is separated or recovered. They preferably contain at least 75 wt% of the CP contained in the initial concrete to be recycled, while the conventional crushing step and, optionally, the subsequent screening step(s) result in recycled fine powder containing less than 25 wt% of the CP contained in the initial concrete to be recycled.

[0112] Preferably, the recycled fine powder further contains NA having a particle size of less than 1 mm.

[0113] In the recycled fine powder, the NA having a particle size of less than 1 mm and the cement paste can be dissociated, bonded, or partially bonded, and generally are partially bonded.

[0114] Steps i) and ii) of the method are very effective, and with the cement paste adhering to the NA in the RCA, only a very small amount remains. This enables optimization of the subsequent carbonation step iii), particularly by promoting the access and diffusion of carbon dioxide into the pore volume of the cement paste of the adherent residual cementitious matrix containing carbonatable reactive phases, particularly portlandite, lime, and calcium silicate hydrate (C-S-H).

[0115] Similarly, steps i) and ii) of the method are very efficient, with most of the cement paste present in the recycled fine powder, which has a very fine particle size and sufficient distribution of micro-damage. In particular, the recycled fine powder has the shape of very fine particles (at least 45% by weight of the total weight of the recovered recycled fine powder has a particle size less than 0.25 mm) and is fully available for carbonation. This enables optimization of the subsequent carbonation step iv), particularly by promoting the access and diffusion of carbon dioxide into the pore volume of the cement paste containing carbonatable reactive phases, particularly portlandite, lime, and calcium silicate hydrate (C-S-H).

[0116] Finally, the recycled aggregates obtained by the combination of steps i) and ii) contain only the bare natural aggregates and the natural aggregates bonded to the adherent residual cementitious matrix. On the other hand, if one or more sorting steps are carried out following the crushing step as required, recycled aggregates with a high content of cementitious matrix are obtained, and some of the recycled aggregates are composed only of the cementitious matrix (residual mortar), containing little or no natural aggregates NA, which may have an adverse effect on the subsequent carbonation step.

[0117] The method of the present invention is efficient in that it enables the obtaining of high-purity RCA for each predetermined particle size fraction of 1 mm or more.

[0118] In the RCA of this invention, the mortar (CP + NA having a particle size smaller than the predetermined particle size fraction) is unevenly distributed / adhered around the NA having the predetermined particle size fraction. In fact, this results in obtaining a majority of RCA without impurities (i.e., bare natural aggregate or natural aggregate without impurities), and a minority of RCA containing a small amount of impurities (i.e., natural aggregate bonded to the adhered mortar or aggregate containing impurities).

[0119] In particular, at the end of step ii), in particular at the end of steps ii-1) and ii-2), the recycled concrete aggregate RCA obtained with a predetermined particle size fraction of 1 mm or more, with respect to the total weight of the RCA having the predetermined particle size fraction, preferably at least 50% by weight is natural aggregate without impurities having the predetermined particle size fraction (i.e., bare natural aggregate having the predetermined particle size fraction or RCA without impurities), more preferably 55% to 85% by weight is natural aggregate without impurities having the predetermined particle size fraction (i.e., bare natural aggregate having the predetermined particle size fraction or RCA without impurities), and even more preferably 60% to 75% by weight is natural aggregate without impurities having the predetermined particle size fraction (i.e., bare natural aggregate having the predetermined particle size fraction or RCA without impurities).

[0120] As a concomitant result, at the end of step ii), in particular at the end of steps ii-1) and ii-2), the recycled concrete aggregate RCA obtained with a predetermined particle size fraction of 1 mm or more, with respect to the total weight of the RCA having the predetermined particle size fraction, preferably has a content of natural aggregate containing impurities having the predetermined particle size fraction (i.e., natural aggregate bonded to the adhered residual mortar having the predetermined particle size fraction or RCA containing impurities) of less than 50% by weight, more preferably 15% to 45% by weight of natural aggregate containing impurities having the predetermined particle size fraction (i.e., natural aggregate bonded to the adhered residual mortar having the predetermined particle size fraction or RCA containing impurities), and even more preferably 25% to 40% by weight of natural aggregate containing impurities having the predetermined particle size fraction (i.e., natural aggregate bonded to the adhered residual mortar having the predetermined particle size fraction or RCA containing impurities).

[0121] In the case of RCA without impurities and RCA containing impurities as defined in this specification, the content of RCA obtained in a predetermined particle size fraction of 1 mm or more is obtained by separating RCA without impurities and RCA containing impurities by optical sorting and / or visual sorting, and then selectively dissolving CP contained in the RCA without impurities and the RCA containing impurities with hydrochloric acid, followed by weighing and measurement to examine the proportion of CP in the RCA without impurities and the RCA containing impurities.

[0122] The method of the present invention may include a plurality of microwave treatment steps i), a plurality of grinding steps ii-1), and a plurality of sorting steps ii-2), preferably including a plurality of consecutive sequences of microwave treatment steps, grinding steps ii-1), and sorting steps ii-2).

[0123] Step a) The method may further include at least one step a) of removing impurities from the recycled aggregate RCA. As a result, the proportion of the cementitious matrix (residual mortar) in the recycled aggregate RCA is reduced, the purity ratio of the recycled aggregate RCA is further increased, and the proportion of the recycled fine powder recovered is increased.

[0124] Step a) is preferably carried out by polishing, particularly using a rotary screen or a gyratory sieve.

[0125] Polishing is a well-known mechanical method for removing surface impurities.

[0126] Step a) is preferably carried out after the grinding step ii-1).

[0127] Step a) can be carried out simultaneously with (i.e., concomitantly with), before or after the sorting step ii-2), preferably simultaneously with the sorting step ii-2).

[0128] When steps a) and ii-2) are carried out simultaneously, it can be carried out using a rotary screen or a gyratory sieve.

[0129] If steps a) and ii-2) are not carried out simultaneously, the polishing step a) can be carried out in a rotating drum regardless of the presence or absence of a lifter.

[0130] If a plurality of sorting steps (for example, steps ii-2a) and ii-2b)) are carried out, the method may include a plurality of impurity removal steps a), in particular carried out simultaneously with each sorting step, before or after each sorting step.

[0131] In order to facilitate step a), in particular the polishing of the cementitious base material (residual mortar), natural aggregate NA can be added to recycled aggregate RCA before step a).

[0132] The added natural aggregate NA can be up to 99.5% by weight, preferably up to 95% by weight, more preferably up to 50% by weight, based on the total weight of the aggregate (NA + RCA) used in step a).

[0133] Step b) The method may further include at least one step b) of washing the recycled aggregate RCA. Thereby, the proportion of sand and cement paste (fine powder) residues in the recycled aggregate RCA (i.e., which can adhere to the surface of the recycled aggregate RCA) is reduced.

[0134] Step b) is preferably carried out by washing with water, more preferably by spraying or atomizing water.

[0135] Step b) can be carried out simultaneously with (i.e., concomitantly with) the impurity removal or polishing step a), and / or simultaneously with the sorting step ii-2), and / or between the impurity removal or polishing step a) and the sorting step ii-2), preferably simultaneously with the sorting step ii-2), and if necessary, simultaneously with the impurity removal or polishing step a).

[0136] This also makes it possible to promote the entrainment of recycled fines and the separation of recycled fines from the recycled aggregate RCA.

[0137] When a plurality of sorting steps (e.g., steps ii-2a) and ii-2b)) are carried out, the method may include a plurality of washing steps b), in particular carried out simultaneously with each sorting step ii-2) and / or each impurity removal step a), or between each impurity removal step a) and each sorting step ii-2).

[0138] In one preferred embodiment of the present invention, steps ii-2) and a) are carried out simultaneously, in particular using a rotary screen or a gyratory sieve, and particularly preferably in a wet process. The wet process is preferably carried out by spraying or atomizing water (for example, the water spray evaporates in step i) and the condensed water can then be reused). In other words, in this wet process, steps ii-2), a) and b) are carried out simultaneously. This removes the recycled fines that may adhere to the surface of the natural aggregate and prevents them from being entrained in the recycled aggregate (RCA), and as a result, concentrates them in the final fraction of the recycled fines. Step iv) of the method of the present invention is selective in that, according to step iii), only the RCA can be carbonated at the end of step ii) (first variant). The recycled fines obtained at the end of step ii) can be used directly in cement raw materials, such as for the production of calcium clinker, by adding other raw materials to the cement raw material to adjust the composition (for example, to obtain a specific silicon or hydraulic ratio). By replacing part of the natural limestone used in the cement raw materials with recycled fines, it contributes to the conservation of natural limestone resources and also reduces the carbon footprint of the clinker because no additional CO2 is emitted in the clinker production stage compared to using natural limestone (calcination).

[0139] Step iii) of the method of the present invention is selective in that, according to step iv), it is also possible to carbonate only the recycled fine powder at the end of step ii) (second variant). In fact, as a result of steps i) and ii), the RCA is in a very impurity-free state, so carbonation in step iii) may not be necessary (the CP content of the RCA obtained in a predetermined particle size fraction of 1 mm or more is low).

[0140] The RCA obtained at the end of step ii) can be used directly in the preparation of new concrete. Since their residual mortar ratio is very low, their water absorption and polishing properties are 2 to 3 times better than those of the RCA obtained by the methods of the prior art.

[0141] In a third variant of the method, the recycled fine powder and the RCA are carbonated. This makes it possible to recover / store a larger amount of CO2 and further improve the properties of the RCA.

[0142] Step iii) The method may further include a carbonation step iii) of one or more RCAs in the presence of carbon dioxide [corresponding to the fraction F1 recovered at the end of step ii), ii-1), ii-2), ii-2a), or ii-2b)].

[0143] Step iii) enables the carbonation of the recycled coarse aggregate RCA obtained in the previous step ii) in the presence of carbon dioxide, and in particular, one or more of the particle sizes described in the present invention, in particular G m from G M to G1 and / or G2, enabling the carbonation of the recycled coarse aggregate RCA having one or more particle sizes in the range in the presence of carbon dioxide.

[0144] During step iii), the CP attached to the surface of the RCA is carbonated.

[0145] At the end of step ii), particularly at the end of steps ii-1) and ii-2), the RCA contains NA bound to a small amount of CP distributed within the volume due to the microporosity resulting from step i). This enables optimization of the carbonation step iii), particularly by facilitating the access and diffusion of carbon dioxide into the volume of the cement paste containing a carbonatable reaction phase, particularly portlandite, lime, and calcium silicate hydrate (C-S-H).

[0146] Step iii) is preferably carried out in the presence of a CO2-containing gas comprising at least 1 mol% CO2, more preferably at least 10 mol% CO2, and most preferably at least 15 mol% CO2, based on the total molar amount of the gas.

[0147] Step iii) is preferably carried out in the presence of a CO2-containing gas comprising preferably at least 5 vol% CO2, more preferably at least 10 vol% CO2, based on the total volume of the gas.

[0148] Carbon dioxide can be obtained from a CO2-containing flue gas, for example, from a biogas stream rich in CO2 generated in a methanator or a biomass power plant, or from a flue gas generated from industrial emission sources such as a cement plant or a thermal power plant. Alternatively, it can also be prepared from a CO2 source. The CO2 source may or may not be pre-stored.

[0149] The flue gas containing CO2 preferably contains at least 15 mol% CO2 based on the total molar amount of the gas contained in the flue gas, or at least 15 vol% CO2 based on the total volume of the gas contained in the flue gas.

[0150] The flue gas containing CO2 may contain other elements, particularly molecular nitrogen N2, molecular oxygen O2, and optionally water.

[0151] The biogas stream may contain about 70 mol% to about 90 mol% of CO2, or about 70 vol% to about 90 vol% of CO2, based on the total moles or total volume of the biogas, respectively.

[0152] During step iii), the recycled aggregate RCA can be introduced into a rotary drum or other reactor where it can be contacted with a gas containing carbon dioxide.

[0153] Step iii) can be carried out at a CO2 partial pressure of about 0.1 bar to about 100 bar, preferably about 0.1 bar to about 5 bar (i.e., about 250 to about 12,000 times the partial pressure of 415 ppm of CO2 in the Earth's atmosphere).

[0154] Step iii) can be carried out at a temperature of about 18°C to about 100°C, preferably about 20°C to about 80°C.

[0155] Step iii) can be carried out at a relative humidity in the range of about 0% to about 100%, preferably about 10% to about 90%, more preferably about 40% to about 70%.

[0156] At the end of step iii), the carbonated recycled aggregate or CRCA complies with standard NF EN 12620, particularly in terms of water absorption, and / or fragmentation resistance, and / or density after oven drying, and / or abrasion resistance, and advantageously complies at least in terms of water absorption and abrasion resistance.

[0157] By carbonating the recycled aggregate RCA, a homogeneous and quality-improved carbonated recycled aggregate CRCA is obtained, which can be used in particular for the preparation of new concrete for the manufacture of new structures. Steps ii-2) and iii) may be carried out simultaneously.

[0158] Carbonation is directed towards the reaction phase, i.e., the cement paste CP of the adherent residual cementitious base material. At the end of step iii), carbonated recycled aggregate or CRCA is obtained, which comprises the bare natural aggregate and, preferably, the natural aggregate NA with the cement paste carbonated residual cementitious base material to which the carbonated cement paste is bonded.

[0159] Step iv) The method may further comprise one or more of step iv) of carbonation of the recycled fines [corresponding to fraction F2 recovered at the end of step ii), ii-1), ii-2), ii-2a), or ii-2b)] in the presence of carbon dioxide.

[0160] Carbonation is directed towards the reaction phase, i.e., the CP contained in the recycled fines. At the end of step iv), carbonated recycled fines containing a mixture of NA < 1 mm and carbonated CP are obtained.

[0161] Carbonation of the recycled fines not only enables the storage of carbon dioxide but also allows for the production of carbonated fines that potentially have pozzolanic and / or hydraulic activity. These can then be used as mineral additives in concrete as an alternative to cement (e.g., CEM I or CEM II), or as components of cement for the production of blended cement. For example, in the formulation of structural concrete (buildings) or non-structural concrete (lightweight concrete blocks, blocks, slabs, coping stones, technical mortars), replacing Portland cement with carbonated fine powder and using the carbonated fines as mineral additives reduces the concrete's carbon footprint. This reduction is due to the lower proportion of Portland cement in the concrete and the amount of carbon captured by the carbonated fines, acting as a carbon sink.

[0162] In other words, the regenerated carbonated fine powder obtained by the above-described method can be used as a means for storing CO2 and / or as an alternative to all or part of cement. By using this carbonated fine powder as a reactive mineral additive in a concrete formulation, the carbon footprint of the concrete is reduced according to the proportion in which the cement is replaced by the carbonated fine powder.

[0163] When using the regenerated fine powder derived from step ii) as a mineral additive, preferably, the regenerated fine powder is ground before the carbonation step iv), for example, until a particle size of less than about 80 μm, preferably about 5 μm to about 20 μm is obtained.

[0164] Step iv) is preferably carried out in the presence of a CO2-containing gas containing at least 1 mol%, more preferably at least 5 mol%, and most preferably at least 10 mol% of CO2, based on the total number of moles of the gas.

[0165] Step iv) is preferably carried out in the presence of a CO2-containing gas containing preferably at least 5% by volume, more preferably at least 10% by volume of CO2, based on the total volume of the gas.

[0166] Carbon dioxide can be obtained from a CO2-containing flue gas, for example, from a biogas stream rich in CO2 generated in a methanator or a biomass power plant, or from a flue gas generated from industrial emission sources such as a cement plant or a thermal power plant. Alternatively, it can also be prepared from a CO2 source. The CO2 source may or may not have been stored in advance.

[0167] The flue gas containing CO2 preferably contains at least 10 mol% of CO2 based on the total number of moles of the gas contained in the flue gas, or at least 10% by volume of CO2 based on the total volume of the gas contained in the flue gas.

[0168] The flue gas containing CO2 may contain other elements, especially molecular nitrogen N2, molecular oxygen O2, and optionally water.

[0169] The biogas stream may contain from about 70 volume % to about 90 volume % of CO2, or from about 70 mole % to about 90 mole % of CO2, based on the total volume or total number of moles of the biogas.

[0170] During step iv), the recycled fines can be introduced into a rotary drum or any other reactor and contacted with a gas containing carbon dioxide.

[0171] Step iv) can be carried out at a partial pressure of CO2 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 partial pressure of CO2 in the atmosphere of 0.415 millibar).

[0172] Step iv) can be carried out at a temperature of about 18 °C to about 100 °C, preferably about 20 °C to about 80 °C.

[0173] Step iv) can be carried out at a relative humidity in the range of 0% to about 100%, preferably about 10% to about 90%.

[0174] By accelerated carbonation of the fines, carbonated recycled fines are produced that can store up to about 15 wt % of CO2, i.e., up to about 150 kg of CO2 per metric ton of fines.

[0175] Step i0) The method may further include step i0) of crushing construction and / or demolition concrete prior to step i) to form concrete blocks of centimeter-scale dimensions from construction and / or demolition as carried out in step i).

[0176] The crushing step i0) can be carried out using a crusher such as a gravel crusher or jaw crusher, cone crusher, gyratory crusher, impact crusher, impactor crusher, hammer crusher, or centrifugal rotor crusher.

[0177] In one preferred embodiment of the present invention, step i) is carried out immediately after step i0) (without intermediate steps).

[0178] In one preferred embodiment of the present invention, the method does not include a step containing a liquid phase between step i0) and step i).

[0179] By the method of the present invention, from the concrete blocks from construction and / or demolition, a distribution of aggregates and fine powder close to the initial distribution of the original concrete is obtained, that is, with respect to the total weight of the concrete blocks from construction and / or demolition, about 70% to 90% by weight of recycled coarse aggregate RCA or carbonated recycled coarse aggregate CRCA (fraction F1, regardless of the presence or absence of carbonation), and 10% to 30% by weight of fine powder (fraction F2, regardless of the presence or absence of carbonation), and it is understood that at least one of fraction F1 or F2 is carbonated.

[0180] In particular, by combining the use of microwaves, mechanical treatment, and carbonation of fine powder and / or RCA in the presence of carbon dioxide, it becomes possible to recycle concrete waste generated from construction and / or demolition.

[0181] The second subject of the present invention is a recycling facility for carrying out the recycling method according to the first subject of the present invention, characterized in comprising: - at least one microwave tunnel for forming micro-destroyed concrete blocks from concrete blocks from construction and / or demolition of centimeter-scale dimensions, - at least one roller mill for fragmenting the micro-destroyed concrete blocks and separating recycled coarse aggregate (RCA) containing natural aggregate free of coating and natural aggregate bonded to the adherent residual cementitious matrix, and recycled fine powder, - at least one vibrating, swiveling, or rotating screen or sieve for separating the recycled coarse aggregate and the recycled fine powder and, if necessary, removing impurities therefrom and, if necessary, washing them, and - at least one carbonation reactor for forming carbonated recycled coarse aggregate (CRCA) and / or carbonated recycled fine powder.

[0182] For separating recycled aggregates and recycled fine powder and removing impurities therefrom and washing them, a rotary or revolving screen is preferable.

[0183] The various elements used in the system are as defined in the first main subject of the present invention.

[0184] The third main subject of the present invention is a method for recycling concrete from construction and / or demolition, characterized by including the following steps: i) one or more steps of microwave-treating concrete blocks of centimeter-scale dimensions from construction and / or demolition to form micro-crushed concrete blocks, and ii) one or more mechanical treatment steps enabling extraction of recycled coarse aggregate (RCA) and recycled fine powder including natural coarse aggregate bonded to bare natural coarse aggregate and adherent residual cementitious matrix (or residual mortar) from the micro-crushed concrete blocks, The method lacks steps iii) and iv) as defined in the present invention (i.e., the step(s) of carbonating the RCA and recycled fine powder obtained in step ii)).

[0185] As described above in the first main subject of the invention, by the combination of steps i) and ii), particularly steps i), ii-1) and ii-2), it becomes possible to obtain recycled coarse aggregate RCA having a structure as close as possible to the natural coarse aggregate NA of the initial demolition and / or construction concrete, and thus having a high purity.

[0186] By the method according to the third main subject of the present invention resulting from steps i) and ii), it becomes possible to obtain RCA aggregates of high purity, and furthermore, since most of the RCA has been released from the residual mortar (and as a result, the cement paste contained in the mortar) adhering to the NA, it also becomes possible to obtain a large amount of fine powder.

[0187] Steps i) and ii) of the method according to the third subject of the present invention are very effective, and the amount of cement paste adhering to the NA in the RCA is very small. Similarly, steps i) and ii) of the method according to the third subject of the present invention are very efficient, and most of the cement paste exists in the recycled fine powder with a very fine particle size.

[0188] Step ii) preferably includes at least one step ii-1) of crushing the micro-damaged concrete blocks. The method may include a plurality of crushing steps ii-1).

[0189] Step ii) may further include at least one sorting step ii-2), particularly after step ii-1). Step ii) may include one or more sorting steps ii-2).

[0190] The method of the present invention, particularly step ii), may include a plurality of crushing steps ii-1) and a plurality of sorting steps ii-2).

[0191] The method may further include at least one step a) of removing impurities from the RCA.

[0192] The method may further include at least one step b) of washing the RCA.

[0193] The method may further include a step i0) of crushing the construction and / or demolition concrete before step i) to form concrete blocks of centimeter-scale dimensions from the construction and / or demolition as performed in step i).

[0194] Steps i), ii), ii-1), ii-2), a), b), and i0) of the method according to the third subject of the present invention are as defined in the first subject of the present invention.

[0195] Therefore, by the method according to the third subject of the present invention, it becomes possible to separate the RCA directly obtained in step ii). In other words, this corresponds to a method for manufacturing RCA.

[0196] The recycled fine powder obtained at the end of step ii) of the method according to the third subject can be used directly in cement raw materials, for example, by adding other raw materials of the materials used in the raw materials and adjusting the composition (for example, to achieve a specific silicon or hydraulic ratio) for the production of calcium clinker. By replacing a part of the natural limestone used in the cement raw materials with the recycled fine powder, it contributes to the conservation of natural limestone resources, and also reduces the carbon footprint of the clinker because it does not emit additional CO2 in the clinker production step compared to the case of using natural limestone (calcination).

[0197] The RCA obtained at the end of step ii) of the method according to the third subject can be used directly in the preparation of new concrete.

[0198] The fourth subject of the present invention is recycled coarse aggregate (RCA) obtained by the method according to the first subject of the present invention or RCA obtained by the method according to the third subject of the present invention, and with respect to the total weight of the RCA having a predetermined particle size fraction, the RCA having a predetermined particle size fraction of 1 mm or more is at least 50% by weight of natural coarse aggregate without impurities having the predetermined particle size fraction (that is, bare natural coarse aggregate having the predetermined particle size fraction or RCA without impurities), more preferably 55% to 85% by weight of natural coarse aggregate without impurities having the predetermined particle size fraction (that is, bare natural coarse aggregate having the predetermined particle size fraction or RCA without impurities), and even more preferably 60% to 75% by weight of natural coarse aggregate without impurities having the predetermined particle size fraction (that is, bare natural coarse aggregate having the predetermined particle size fraction or RCA without impurities).

[0199] As a concomitant result, preferably, recycled concrete aggregate RCA of 1 mm or more has, with respect to the total weight of RCA having a predetermined particle size fraction, a content of natural aggregate containing impurities having the particle size fraction (i.e., natural aggregate bound to adherent residual mortar having the predetermined particle size fraction or RCA containing impurities) of less than 50% by weight, more preferably, a content of natural aggregate containing impurities having the predetermined particle size fraction (i.e., natural aggregate bound to adherent residual mortar having the predetermined particle size fraction or RCA containing impurities) of 15% to 45% by weight, and even more preferably, a content of natural aggregate containing impurities having the predetermined particle size fraction (i.e., natural aggregate bound to adherent residual mortar having the predetermined particle size fraction or RCA containing impurities) of 25% to 40% by weight.

[0200] In particular, RCA having a predetermined particle size fraction of 1 mm or more contains, with respect to the total weight of RCA having the predetermined particle size fraction, a maximum of 10% by weight of CP, preferably, a maximum of 8% by weight of CP, and even more preferably, a maximum of 5% by weight of CP.

[0201] Recycled concrete aggregate RCA having a predetermined particle size fraction of 1 mm or more preferably contains, with respect to the total weight of RCA having the predetermined particle size fraction, 65% to 95% of NA having the predetermined particle size fraction, more preferably, 70% to 90% of NA having the predetermined particle size fraction, and even more preferably, 75% to 85% of NA having the predetermined particle size fraction.

[0202] Preferably, recycled concrete aggregate RCA having a predetermined particle size fraction of 1 mm or more contains, with respect to the total weight of RCA having the predetermined particle size fraction, 5% to 20% of NA having a particle size smaller than the predetermined particle size fraction, and more preferably, 7% to 15% of NA having a particle size smaller than the predetermined particle size fraction.

[0203] In particular, recycled concrete aggregate RCA having a predetermined particle size fraction of 1 mm or more contains 5 wt% to 35 wt%, preferably 10 wt% to 30 wt%, and more preferably 15 wt% to 25 wt% of residual mortar, based on the total weight of the RCA having the predetermined particle size fraction.

[0204] The accompanying drawings illustrate the present invention.

Brief Description of the Drawings

[0205]

Figure 1

Figure 2

Figure 3

Figure 4a

Figure 4b

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0206] Further features and advantages of the present invention will become apparent from the description of non-limiting embodiments of the method according to the present invention.

Examples

[0207] Example 1: Description of the method according to the present invention and the prior art method not according to the present invention

[0208] Figure 1 includes an explanation of concrete destruction by the prior art method (Figure 1a)) and an explanation of concrete destruction using the method of the present invention (Figure 1b)).

[0209] In Figure 1a), the destruction is random and not selective between NA and mortar. This produces RCA with a high probability of intragranular destruction of the original natural aggregate NA, a low NA content (less than 60% by weight of NA with respect to the total weight of RCA), and a high CP content (more than 10% by weight of CP with respect to the total weight of RCA). As a result, aggregates composed only of the cementitious matrix are formed, while the original structure-preserved natural aggregate NA is separated only to a limited extent. After destruction, mainly one type of recycled concrete aggregate (RCA) is obtained. That is, it is a mixed aggregate composed of fragments of natural aggregate and the cementitious matrix or mortar in the mixed aggregate at a high ratio. As an accompanying result, almost no recycled fine powder is generated by the destruction, and the recycled fine powder does not exceed 25% of the CP of the initial concrete to be recycled.

[0210] In Fig. 1b), since the destruction of concrete by the method of the present invention is selectively carried out between NA and mortar, the destruction of the original natural aggregate NA is avoided, and separation while maintaining the original structure of the natural aggregate NA, and separation of the cementitious matrix are promoted. The cement paste in the slightly damaged cementitious matrix can become fine powder with a particle size that can be easily separated from the aggregate particle size, whether carbonated or not. There may be a small amount of residual cementitious matrix adhering to the surface of the separated natural aggregate, and the residual cementitious matrix may or may not be carbonated in order to obtain recycled aggregate RCA or carbonated recycled aggregate CRCA having the same performance as the original natural aggregate. In other words, the destruction of concrete by the method of the present invention promotes both the concentration of NA into RCA with a low content of adhering mortar without changing the particle size and mechanical properties of NA, and the recovery of the fine powder fraction of CP contained in the initial concrete to be recycled. Due to the micro-destruction of CP, most of the CP in the initial concrete to be recycled is concentrated in the fine powder, and the carbonation of CP adhering in a small amount on the surface of the CP and / or RCA in the fine powder is promoted. By the carbonation of RCA, CRCA having the same performance level as NA is produced.

[0211] Fig. 2 shows step i) of subjecting concrete blocks from construction and / or demolition to microwave treatment in a microwave tunnel to form slightly damaged concrete blocks. Next, in step ii-1), these are ground by a roller mill to form a mixture of recycled aggregates RCA and recycled fine powder with different particle sizes. By grinding in ii-1), it becomes possible to obtain, for example, a particle size of 8 mm or less. Next, a first sorting or sieving step ii-2a) is carried out using a rotary screen, and recycled aggregates having a particle size fraction G 1’ -G1 (for example, a particle size fraction of 4 mm to 8 mm), and a mixture of recycled fine powder and recycled aggregates having a particle size <G1 (a particle size of less than 4 mm) are extracted.

[0212] Particle size fraction G 1’- The impurity-free recycled coarse aggregate RCA having G1 is then carbonated in a carbonation reactor by step iii), and a first CRCA fraction is formed. The recycled fine powder and recycled coarse aggregate having a particle size smaller than G1 are separated using a rotary screen into particle size fraction G 2’ - The recycled coarse aggregate RCA having G2 (e.g., a particle size or particle size fraction of 1 mm to 4 mm) undergoes a further sorting or screening step ii-2b) to extract it. Similarly, recycled fine powder (particle size less than 1 mm) is also extracted.

[0213] Particle size fraction G 2’ - The impurity-free recycled coarse aggregate having G2 is then carbonated in a carbonation reactor by step iii) to form a second CRCA fraction, and / or the recycled fine powder is carbonated in the carbonation reactor in step iv).

[0214] If necessary, the concrete blocks used in step i) have centimeter-scale dimensions (e.g., ≤ 30 mm) and can preferably be obtained from the crushing of construction and / or demolition concrete using a gravel crusher or a jaw crusher [step i0)].

[0215] Between steps ii-2a) and ii-2b), the steps of polishing a) and washing b) (water spraying) are preferably carried out simultaneously with each step of steps ii-2a) and ii-2b).

[0216] Example 2: Recycling of concrete from construction and / or demolition using the method according to the invention 2.1 Preparation and properties of concrete samples Concrete was prepared from cement and crushed siliceous natural aggregate (NA) with a particle size less than 8 mm at a water / cement ratio of 0.6.

[0217] 2.1.1 The cement used was Lafarge CEM I from the Le Teil factory. Its strength class is 52.5R, i.e., it is rapid-hardening. This meets the European requirements of standard EN 197-1. The physical and mechanical properties of the cement used are as follows: - Blaine specific surface area = 4160 cm 2 / g, and - Density = 3.15 g / cm 3 .

[0218] 2.1.2 The natural aggregates (NA) used are a mixture of sand (S) and gravel (G) from the Palvadeau quarry of the crushed siliceous type, Saint-Christophe-du-Ligneron. The properties of these aggregates are as follows: - Density = 2640 kg / m 3 , - Water absorption = 0.7%, - Chloride < 0.001%, - Water-soluble sulfate < 0.01%, and - Active alkali content = 0.0022%.

[0219] The following Table 1 shows the particle size distribution of the NA used in making the concrete, and more specifically, the weight % (mass fraction) of five different particle size fractions of 4 / 8 mm, 2 / 4 mm, 1 / 2 mm, 0.25 / 1 mm, and 0 / 0.25 mm with respect to the total weight of the natural aggregate NA used in formulating the concrete.

[0220]

Table 1

[0221] These mass fractions are interpreted as the average values of the actual NA composition of the concrete used below. In the last row of Table 1, the NA particle size fraction of 0 / 1 mm referred to below is defined. This ratio is a combination of 0.25 / 1 mm and 0 / 0.25 mm NA.

[0222] 2.1.3 Production of Concrete The ratios of the binder (cement and high-performance water reducer), water, and NA used in manufacturing the concrete are as shown in Table 2 below.

[0223]

Table 2

[0224] A plurality of concrete samples are mixed at low speed (62 rpm) for 60 seconds, at high speed (125 rpm) for 40 seconds, rested for 90 seconds, and then at high speed (125 rpm) for 60 seconds to form a mixture by mixing the components with a mortar mixer. Then, the mixture is poured into a gray polypropylene cylindrical mold with a diameter of 25 mm and a height of 30 mm. The mold is vibrated on a vibrating table for 2 × 10 seconds. As a result, a plurality of concrete cylinders with a controlled composition and shape are formed, and their maximum dimension is about 30 mm.

[0225] These concrete cylinders are stored for 28 days in a room adjusted to 19 °C to cure the concrete while wrapped in cellophane.

[0226] After curing for 28 days in a temperature-controlled room, the cylindrical concrete samples are oven-dried at 80 °C for 48 hours. This time was determined based on a series of aggregate tests weighed at regular intervals until a constant mass was reached (Δm < 0.1%). This drying method controls the moisture content to be approximately equivalent to that of naturally matured concrete, ensuring the reproducibility of the manufactured concrete samples.

[0227] The composition of the concrete in the samples after curing and storage is measured by dissolving the CP in 19 wt% hydrochloric acid. The values in Table 3 below show the range of composition values measured for a plurality of 30 mm concrete samples, and each sample is dissolved individually. This makes it possible to evaluate the variation in the composition of the concrete samples used.

[0228]

Table 3

[0229] 2.2 Implementation of the method of the present invention 2.2.1 Microwave destruction step i) The microwave bench used is a single-mode cavity waveguide manufactured by SAIREM and has the following characteristics: - Frequency = 2450 ± 25 MHz, - Output power = 2000 ± <0.1%W, - Maximum operating power = 1700 W, - Waveguide = WR340 (rectangular cross-section 86x43 mm), - Wave ripple < 0.3% RMS, and - Magnetron cooling system: water.

[0230] This microwave bench can process one 30-mm concrete sample at a time with a predetermined power and for a predetermined time. The cylindrical concrete sample is placed in a quartz tube (which functions as a sample holder), and the quartz tube is placed inside the chimney tube of the microwave bench. Each sample is processed at an incident microwave power of 1.5 kW for 4 minutes. The temperature reached on the concrete surface ranges from 450°C to over 600°C (the limit value measurable with the infrared thermometer used).

[0231] 2.2.2 Mechanical processing step ii) 2.2.2.1 Non-impact crushing (step i-1) Non-impact crushing after 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 at a position 8 mm from the surface where the RCA is placed, corresponding to the maximum dimension of the NA of the concrete sample.

[0232] 2.2.2.2 Screening (step ii-2) Next, the crushed samples are dry-screened using standard 8-mm, 4-mm, 2-mm, 1-mm, 0.25-mm square mesh sieves to produce particle size fractions of 4 / 8 mm, 2 / 4 mm, 1 / 2 mm, 0.250 / 1 mm, 0 / 0.25 mm.

[0233] 2.2.2.3 Polishing (step a)) The 1 / 4 mm and 4 / 8 mm fractions of recycled concrete aggregates (RCA) generated by crushing and subsequent screening are separately polished for a short time for 2 minutes each while being rotated at a speed of 100 rpm in a cylindrical metal container with an inner diameter of 10 cm. The polishing filler consists of 336 g of 20 mm alumina beads and 200 ml of water. Thereafter, the products are re-screened at 8 mm and 4 mm, and the 8 mm and 4 mm RCA are separated from the polishing fine powder respectively.

[0234] At the end of steps ii-1), ii-2) and a), multiple fractions of fine powder are collected and gathered.

[0235] 2.2.3 Carbonation of fine powder (step iii)) The obtained fine powder is crushed to 80 μm using an automatic mortar and pestle, and the average particle size d 50 is about 10 μm. This fineness is appropriate for using the carbonated fine powder as a mineral additive. The carbonation step of the crushed fine powder is carried out in a suspended state in a stirred reactor with an effective volume of 300 ml. The suspension used consists of a mixture of 15 g of recycled concrete fine powder and 150 ml of distilled water. Mixing is ensured by a movable stirrer rotating at 800 rpm. The carbonation reactor operates at a temperature controlled at 60 °C under a CO2 partial pressure of 5 bar. The carbonation test lasts for 20 hours, during which the consumption of CO2 by the fine powder is continuously measured. The final carbonation rate of the carbonated fine powder is obtained by thermogravimetric analysis (TGA) or total carbon measurement (CHNS analysis).

[0236] Comparative Example 3: Recycling of concrete from construction and / or demolition by a method not according to the present invention The method of the present invention was compared with the non-impact crushing method, which is the most efficient current technology in the production of recycled concrete aggregates. This comparative method, hereinafter referred to as the "reference method", was carried out using the same concrete samples as those described in section 2.1. The reference method consists of mechanical treatment by non-impact crushing and screening steps, and the conditions are the same as those described in section 2.2.

[0237] The carbonation step of the fine powder is carried out as described in Example 2, section 2.2.3.

[0238] Example 4: Performance of the method of the present invention 4.1 Performance evaluation criteria The performance criteria used to characterize the performance of this method are related to the quality and use characteristics of recycled concrete aggregates (RCA) and recycled concrete fine powder.

[0239] For recycled concrete aggregates (RCA): □ Quality: ◆ Content of CP (weight %) in a given RCA particle size fraction, ◆ Content of impurity-free RCA (i.e., RCA with a CP content of less than 5% by weight) in a given RCA particle size fraction, and ◆ Content of natural aggregates (NA) having the same particle size fraction as RCA (weight %).

[0240] □ Use characteristics: ◆ Water absorption of RCA by the WA24 test method. This test measures the water content of RCA after drying in accordance with the NF EN 1097-5 standard. The result is expressed as a weight percentage. ◆ Abrasion resistance of RCA measured by the Micro Deval (MDE) test. This test measures the resistance to abrasion due to friction between RCA and the abrasive load of steel balls in accordance with the NF EN 1097-1 standard. The test result is expressed as a percentage and represents the weight percentage of particles less than 1.6 mm generated during the test.

[0241] For recycled concrete fine powder (less than 1 mm): □ Quality: ◆ Content of mortar concentrated by this method in the generated fine powder (less than 1 mm) (weight %) ◆ Content of CP concentrated by this method in the generated fine powder (weight %) ◆ Carbonation rate of the fine powder (CO2 capture weight %)

[0242] 4.2 Purity of recycled concrete aggregates Attached Figure 3 shows the measured values of the purity of RCA in the method of the present invention (solid circle) and the reference method (hollow circle) with the change in the residual CP content rate (wt%) according to the particle size of RCA (left). This content rate is measured by dissolving RCA having 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.

[0243] The fact that the 95% confidence intervals of the mass fraction of residual CP do not overlap up to an RCA particle size of 0.5 mm indicates that the RCA produced by the method of the present invention is significantly more impurity-free than the RCA produced by the reference method up to an RCA dimension of 0.5 mm.

[0244] Attached Figure 3 also shows the measured values of the water absorption rate (%) of RCA according to the dimension of RCA by the method of the present invention (long dotted curve) and the reference method (short dotted curve) (right). This content rate is measured by dissolving RCA having 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.

[0245] 4.3 Chemical species identification of the product during the method of the present invention The precise analysis of the quality of the product during the method of the present invention (comparison with the reference method) is based on the measurement of the chemical species (NA and CP, see Example 2, Part 2.1) of the initial components of the concrete before and after the method of the present invention (comparison with the reference method) (Example 2, Part 2.2 and Example 3). Chemical species identification (speciation) is used to track and manage the initial components in the product by the method of the present invention (comparison with the reference method).

[0246] For the sake of caution, the products used to characterize the performance of the concrete recycling method are 4 / 8 RCA, 2 / 4 RCA, 1 / 2 RCA, and fine powder (particles less than 1 mm). The components noted in the chemical species measurement are fine powders represented by natural aggregates 4 / 8 NA, 2 / 4 NA, 1 / 2 NA, and 0.25 / 1 NA, 0 / 0.25 NA, and CP.

[0247] Figures 4a) and 4b) respectively show this chemical species identification in detail for the reference method and the method of the present invention. In these figures: - Xi and X´i represent the initial composition of the concrete sample before conducting the test method. This composition is the same for both the reference method and the method of the present invention. - Columns A and A´ respectively show the mass distributions of the products (4 / 8RCA, 2 / 4RCA, 1 / 2RCA, and fine powder) after conducting the methods according to the reference method and the present invention. The said products are separated after crushing and screening for the reference method (Example 3), and after steps ii) and a) for the method of the present invention (Example 2, Part 2.2), and their mass fractions are determined by weighing. - Columns B and B´ show the chemical species (in the form of mass percentages) of each product, in other words, each fraction of Columns A and A´. B1 (or B´1) corresponds to the chemical species of 4 / 8RCA of A1 (or A´1), B2 (or B´2) corresponds to the chemical species of 2 / 4RCA of A2 (or A´2), and so on. In the chemical species measurement, it includes selective dissolution of CP in each product with 23 wt% hydrochloric acid, and then screening (and polishing if necessary), weighing, and drying of the particle size fractions of NA found after dissolution. The mass loss after dissolution gives a direct measurement of the mass of CP found in the product. - Columns C and C´ show the amounts of NA without observed impurities (or bare or impurity-free RCA) and NA bound to the adhering residual mortar (or RCA containing impurities or with impurities), and the amount of CP in the selected fractions. C1 (or C´1) corresponds to the observation and measurement of the 4 / 8NA fraction of B1 (or B´1), C2 (or C´2) corresponds to the 2 / 4NA fraction of B2 (or B´2), and C3 (or C´3) corresponds to the 1 / 2NA fraction of B3 (or B´3). - Xr and X´r respectively represent the recalculated composition of the concrete sample after conducting the reference method and the method of the present invention. This is established based on the values of Columns B and B´ showing the chemical species of the initial components of the concrete in the products.

[0248] Since the fraction of fine powder is defined as all particles less than 1 mm (0.25 / 1 RCA + 0 / 0.25 RCA), it can be seen that by chemical species analysis of the components, in the reference method, only 12% (Column A: A4 is 8% + A5 is 4%) is present, while in the method of the present invention, 31% of the mass of the concrete is collected in this fine powder fraction (Column A': A'4 is 16% + A'5 is 15%) (Figure 4b). Therefore, in the method of the present invention, it is possible to concentrate almost three times more fine powder compared to the reference method, and the fine powder can be recycled as a cement raw material if not carbonated, or as a mineral additive if carbonated.

[0249] 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. This can be explained by the fact that the recovery rate of NA in RCA exceeds 75% or reaches 80%. In other words, the RCA produced by the method of the present invention contains less than 20% by weight of residual mortar, that is, a CP mass fraction of 5% - 8% (see B'1, B'2, B'3 in Figure 4b).

[0250] In comparison, the NA recovery rate of the RCA of the reference method is 40% - 60% by weight. Therefore, the mass fraction of the residual mortar in the RCA is 60% - 40% by weight, that is, the CP mass fraction is 11% - 21% (see B1, B2, B3 in Figure 4a).

[0251] By recalculating the compositions Xr and X'r of the concrete samples, it is shown that the method of the present invention better maintains the complete state (size integrity) of the initial NA dimensions than the reference method. In fact, the 4 / 8 NA content in the recalculated composition X'r of the reference method is significantly lower than that obtained by the method of the present invention, and in fact, the 2 / 4 NA content will increase more significantly in the reference method. This is because the CP induced by the microwave step is micro-destroyed, thereby avoiding excessive fragmentation of NA in the subsequent crushing step.

[0252] The separation degree (or purity) of NA in RCA was measured by visual sorting while verifying the CP content of the separated fractions (columns C and C´). This measurement demonstrates the selectivity of the method of the present invention regarding NA recovery, which is brought about by the fine destruction of concrete induced by the microwave treatment step. Due to this selectivity, a non-uniform distribution of residual CP occurs, which is concentrated in a very small part of NA, while the CP content of most of the RCA is particularly low. These are herein referred to as impurity-free (or bare) NA. The very high proportion of impurity-free NA in RCA is a distinctive feature of the method of the present invention. The measurement of separation by visual sorting was carried out for 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). As shown in column C´ on the right side of Figure 4b, more than 60 - 70% of the RCA produced by the method of the present invention is impurity-free (i.e., RCA with a CP content of 1.6% - 3.2%), and the remaining 30 - 40% is concentrated with a CP content of 3.9% - 10.7%. As shown in column C of Figure 4a), the separation degree (or purity) of the RCA of the reference method is only in the range of 16% - 42%. In summary, for the three RCA particle size classes analyzed, the separation degree (or purity) of NA is twice as high for the method of the present invention as for the reference method.

[0253] The performance of the method of the present invention was compared with the reference method and the theoretical limit. As an example, the purity of the theoretical limit of RCA from the perspective of the residual CP content is 0%, while the maximum % of 4 / 8 mm NA in 4 / 8 mm RCA is 100%. All percentages are shown by weight %.

[0254] Figure 5 shows the performance of the method of the present invention compared with the reference method and the theoretical limit.

[0255] 4.4 Carbonation property evaluation In the aqueous solution carbonation method, at most, it can achieve about 80% of the theoretical carbonation limit of solids calculated based on the chemical composition.

[0256] The theoretical carbonation limit of the fine powder is directly related to the amount of calcium (Ca) it contains. This theoretical limit per unit mass of the fine powder is the same for the fine powder of the method of the present invention and the reference method because they have the same chemical composition as shown by the measurement results. This theoretical limit is 170 kg to 200 kg of CO2 per metric ton of fine powder. Conversely, in the method of the present invention, since it is possible to produce 2.6 times more fine powder than the reference method, up to 2.6 times more CO2 can be stored in the recycled concrete per metric ton than the reference method. This means that the reference method can store 20 kg of CO2 per metric ton of recycled concrete, while the method of the present invention can store 60 kg of CO2 per metric ton of recycled concrete. It should be borne in mind that the maximum possible amount of carbonation of concrete is estimated to be 70 kg of CO2 per metric ton of recycled concrete on the same basis. Therefore, for fine powder, for 1 metric ton of recycled concrete, the method of the present invention can store up to 3 times more CO2 than the reference method (Table 4 below).

[0257]

Table 4

[0258] The final carbonation rate of the carbonated fine powder can be obtained by measuring the total carbon (CHNS analysis).

[0259] Table 5 below shows the results of the obtained fine powder according to the reference method and the method of the present invention.

[0260]

Table 5

[0261] Experimental measurements confirm that the carbonation potential of the fines is similar for the method of the present invention and the reference method due to similar chemical compositions. However, the results show a 1.3-fold increase in carbonation for the fines by the reference method, which is substantially preferred for the fines produced by the method of the present invention. This result, along with the observation during the carbonation test that the carbonation of the fines by the method of the present invention is kinetically superior to that of the fines by the reference method, is probably the result of the micro-destruction of the CP induced by the microwave treatment step, which promotes the transfer of carbon dioxide (CO2) to the carbonatable elements (calcium) contained in the CP.

[0262] Figure 6 shows the performance of the method of the present invention compared to the reference method and the theoretical limit.

[0263] In all measured performance criteria, the method of the present invention is on average 2.3 times more efficient than the reference method.

Claims

1. A method for recycling concrete from construction and / or demolition, comprising at least the following steps: i) Microwave treatment of concrete blocks of centimeter-scale dimensions from construction and / or demolition to form micro-destroyed concrete blocks in one or more steps, ii) One or more mechanical processing steps that enable the extraction of recycled aggregate, including bare natural aggregate and natural aggregate bound to the adhering residual cementitious matrix, and recycled fine powder from the micro-broken concrete block, And, iii) One or more steps of carbonating the recycled aggregate in the presence of carbon dioxide to form carbonated recycled aggregate, and / or iv) A method further comprising one or more steps of carbonating the regenerated fine powder in the presence of carbon dioxide to form carbonated regenerated fine powder.

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

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

4. The method according to claim 1, characterized in that the microwave processing i) is carried out at a frequency of 915 MHz to 2450 MHz.

5. The method according to claim 1, characterized in that the bare natural aggregate is selected from gravel, sand with a particle size of 1 mm or more, and a mixture thereof, and the natural aggregate bonded to the adhering residual cementitious matrix is ​​selected from gravel, sand with a particle size of 1 mm or more, and a mixture thereof.

6. The method according to claim 1, characterized in that the adhering residual cementitious matrix material bonded to the natural aggregate includes natural aggregate having a particle size of less than 1 mm.

7. The method according to claim 1, characterized in that step ii) includes at least one step iii-1) of crushing the micro-broken concrete block.

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

9. The method according to claim 1, characterized in that the recycled aggregate has a maximum particle size GM of 45 mm, 25 mm, 11.2 mm, 8 mm, or 4 mm.

10. The method according to claim 1, characterized in that the recycled aggregate has a particle size Gm of at least 1 mm.

11. The method according to claim 1, further comprising at least one step a) of removing impurities from the recycled aggregate.

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

13. The method according to claim 1, characterized in that step iii) is carried out in the presence of a gas containing at least 10 mol% CO2 relative to the total number of moles of gas.

14. Recycling equipment for carrying out the recycling method described in any one of claims 1 to 13, - At least one microwave tunnel for forming micro-destroyed concrete blocks from concrete blocks of centimeter-scale dimensions from construction and / or demolition, - At least one roller mill for fragmenting the micro-broken concrete blocks and separating the recycled aggregate, which includes bare natural aggregate and natural aggregate bound to a cementitious matrix, and the recycled fine powder. - At least one of vibrating, swirling, or rotary screens or sieves for separating the recycled aggregate from the recycled fine powder, removing impurities as necessary, and washing them as necessary, and - A recycling facility characterized by comprising at least one carbonation reactor for forming carbonated recycled aggregate and / or carbonated recycled fine powder.

15. Recycled aggregate (RCA) obtained by the method of any one of claims 1 to 13, wherein the RCA having a predetermined particle size fraction of 1 mm or more contains at least 50% by weight of bare natural aggregate having the predetermined particle size fraction, relative to the total weight of the RCA having the predetermined particle size fraction.

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