Method for recycling plastics for use in construction industry

Abstract

The present invention relates to a process for manufacturing a carbonized plastic aggregate, said process comprising the steps of: (i) mixing plastic particles with at least one gelling binder comprising at least one metal oxide or metal silicate to form a first composition, (ii) providing a second composition comprising water; (iii) mixing together the first composition and the second composition to form a pre-mixture; (iv) agglomerating the pre-mixture to form a plastic aggregate; and (v) carbonizing the at least one metal oxide or metal silicate by an active carbonization process to obtain the carbonized plastic aggregate.

Description

TECHNICAL FIELD

[0001] The present invention relates to reusing plastics for use in the construction industry. BACKGROUND

[0002] Currently, approximately 45% of the carbon dioxide (CO2) emitted by humans remains in the atmosphere, which is a significant factor behind global warming. While the largest source of CO2 emissions is the burning of fossil fuels for electricity, heat, and transport, significant amounts of CO2 are also released into the atmosphere as a result of waste incineration.

[0003] For example, approximately 25% of all plastic waste is incinerated, and it is estimated that 5 million tonnes of CO2 equivalent is released in the UK alone (2.44 kg CO2 equivalent / kg for polyurethane (PUR) incineration alone). In order to help achieve net zero emissions, it is vital that the incineration of plastic waste, particularly PUR, is stopped or limited.

[0004] While recycling plastics can avoid some of the environmental damage associated with plastic use, currently certain types of plastics are difficult to recycle, particularly foam materials. For example, one of the most commonly used plastic foams is polyurethane (PUR); this type of foam is currently not recyclable, primarily because PUR is a thermoset plastic. Furthermore, the only known recycling process is very expensive and time consuming. As a result, waste PUR is either incinerated or landfilled.

[0005] Therefore, for environmental reasons (i.e. limiting the impact of CO2 equivalent emissions associated with climate change), there is a need to reuse plastics, such as waste plastic-based foams. Furthermore, such reuse would also generate economic value, as it can use waste products (which would otherwise be incinerated or landfilled) to produce valuable products.

[0006] Plastic (such as PUR) powders can be reused in concrete, however, it has proven that using plastic, either without pre-treatment or with some pre-treatment, in concrete results in poor mechanical properties, primarily because the plastic is less compatible with the concrete matrix and has a large surface area. Incompatibility typically results in the plastic being distributed unevenly in the matrix, with the two materials partially or completely separating. The result is that the strength of the concrete is greatly reduced compared to using composite sourced aggregates.

[0007] Therefore, it would be beneficial to reuse waste plastics into plastic aggregates for use in concrete, such that the aggregates would be associated with low CO2 emissions, as emissions resulting from plastic burning would be avoided. However, it is vital that the plastic aggregates are compatible with the concrete matrix, such that once incorporated into the concrete, there is no detrimental effect on the strength of the resulting concrete.

[0008] In addition to, or as an alternative to, first avoiding CO2 emissions, methods have been developed to remove some of the CO2 already present in the atmosphere or to prevent further emissions that contribute to global warming, such as carbon sequestration.

[0009] Carbon sequestration refers to the capture, removal and storage of carbon dioxide (CO2) from the Earth's atmosphere. It is considered a key method for removing carbon from the Earth's atmosphere.

[0010] In particular, CO2 from sources rich in CO2, such as flue gas, can be sequestered and used for other purposes. For example, CO2 can be reacted with minerals such as magnesium oxide or calcium oxide to form stable carbonates. These minerals can be reused for a variety of purposes, such as use in the construction industry.

[0011] Thus, new plastic aggregates for use in concrete (as described above), for example by being able to sequester CO2, will ideally be able to further help reduce CO2 emissions. SUMMARY

[0012] The present invention aims to address the above problems by sequestering CO2 into carbonated plastic aggregates. The sequestered CO2 would otherwise be released into (or continue to exist in) the atmosphere.

[0013] Additionally, the present invention also provides for the reuse of waste plastics, including waste plastic-based foams, which would otherwise typically be incinerated or landfilled, into useful carbonated plastic aggregates for the manufacture of valuable concrete compositions. It has proven that the use of "virgin" plastics (with or without some pre-treatment) in concrete results in poor mechanical properties, primarily due to the low compatibility of the plastics with the concrete matrix and the large surface area. The present invention pre-treats the plastics to make them suitable for use in substances such as concrete.

[0014] The manufacturing method and carbonated plastic aggregates of the present invention provide environmental benefits as the plastic aggregates sequester CO2 that would otherwise be released into (or continue to exist in) the atmosphere; and additionally avoid CO2 equivalent emissions associated with incinerating waste plastic-based foams. Additionally, as the carbonated plastic aggregates are intended to replace at least a portion of natural aggregates, the concrete compositions of the present invention also have environmental benefits as the environmental impact associated with sourcing natural aggregates is lower. As natural aggregates become scarce and more costly due to overuse, reducing the use of natural aggregates has further benefits.

[0015] The carbonated plastic aggregates are primarily intended to replace at least a portion of natural aggregates used in concrete.

[0016] The concrete composition of the present invention can be used, for example, in the construction industry, to manufacture a construction element having a compressive strength (according to British Standard) similar to that of existing blocks but advantageously having a lower thermal conductivity and density.

[0017] A first aspect of the present invention is a method of manufacturing a carbonated plastic aggregate, the method comprising the steps of:

[0018] (i) mixing plastic particles with at least one cementitious binder comprising at least one metal oxide or at least one metal silicate to form a first composition;

[0019] (ii) providing a second composition comprising water;

[0020] (iii) mixing the first composition and the second composition together to form a premix;

[0021] (iv) agglomerating the premix to form a plastic aggregate; and

[0022] (v) carbonating the at least one metal oxide or at least one metal silicate by an active carbonation process to obtain a carbonated plastic aggregate

[0023] A second aspect of the present invention is a method of carbonating a plastic aggregate granulate, comprising:

[0024] (i) providing a plastic aggregate granulate, the plastic aggregate granulate comprising a) plastic particles, b) at least one cementitious binder comprising at least one metal oxide or at least one metal silicate, and c) water; and

[0025] (ii) carbonating the at least one metal oxide or at least one metal silicate by an active carbonation process to obtain a carbonated plastic aggregate.

[0026] A third aspect of the present invention is a concrete composition comprising a carbonated plastic aggregate obtainable by the method of the first or second aspect of the present invention. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 Compressive strengths of precast concrete after 2 and 7 days of curing are shown, wherein 25% by volume of the large aggregate has been replaced by a corresponding volume of plastic aggregate granulate, plastic aggregate mixture, pure PUR granulate and PUR powder.

[0028] Figure 2 An example of the separation of plastic powder into a concrete matrix is shown.

[0029] Figure 3 Compressive strengths of GGBS-based concrete with added sodium hydroxide, sodium carbonate or both over time are shown.

[0030] Figure 4 Rolling resistance of graphene-containing plastic aggregates is shown.

[0031] Figure 5 Compressive strength of concrete comprising graphene-plastic aggregate pellets is shown.

[0032] Figure 6 Rolling resistance of colored 4 mm aggregate pellets is shown.

[0033] Figure 7 Rolling resistance of colored 6 mm aggregate pellets is shown.

[0034] Figure 8 Rolling resistance of colored 8 mm aggregate pellets is shown.

[0035] Figure 9 and Figure 10 Setup of concrete cubes used for the sunlight exposure experiment described in Example 4 is shown.

[0036] Figure 11 Schematic of active carbonation using flue gas / DAC is shown.

[0037] Figure 12 Schematic of improved pelletizer involving pelletization under CO2 atmosphere is shown.

[0038] Figure 13 Schematic of improved disc pelletization under CO2 atmosphere is shown. DETAILED DESCRIPTION

[0039] Unless otherwise defined, all technical and scientific terms used herein will have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0040] The term "comprising" or variations thereof will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The term comprising will include the term consisting of.

[0041] The term "consisting of" or variations thereof will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, and the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0042] The term“about” as used herein when qualifying a numerical value or a value is used herein to refer to a value that is within ±5% of the stated value. For example, if a range of particle sizes is stated to be about 60 pm to about 4 mm, then particle sizes of 57 pm to 4.2 mm are included.

[0043] “wt%” is a commonly used abbreviation in the art to mean“weight %” relative to the total weight of the item / material referred to.

[0044] “Thermoset polymer” refers to a polymer that irreversibly forms a non-melting, non- dissolving polymer network upon curing, known as thermosetting.

[0045] A first aspect of the present application is a method of manufacturing a carbonated plastic aggregate, the method comprising the steps of:

[0046] (i) mixing plastic particles with at least one cementitious binder comprising at least one metal oxide or at least one metal silicate to form a first composition;

[0047] (ii) providing a second composition comprising water;

[0048] (iii) mixing the first composition and the second composition together to form a premix;

[0049] (iv) agglomerating the premix to form a plastic aggregate; and

[0050] (v) carbonating the at least one metal oxide or metal silicate by an active carbonation process to obtain a carbonated plastic aggregate.

[0051] The term“aggregate” as used herein refers to a particulate material.

[0052] As used herein, a“carbonated plastic aggregate” refers to a plastic aggregate that contains more metal carbonate species (e.g. CaC03or MgC03) compared to the same plastic aggregate without the carbonation step. For example, the metal carbonate species can be produced from the reaction of an oxide (e.g. calcium oxide, magnesium oxide) or a silicate (calcium silicate, magnesium silicate) with carbon dioxide.

[0053] “Plastic” as used herein includes synthetic or semi-synthetic plastics, which are materials in which polymers are the main component. Semi-synthetic polymers are obtained from natural polymers by chemical modification. Plastics can be classified by the chemical structure of the main and side chains of the polymers. Important groups classified in this way include acrylic plastics, polyester plastics, silicone plastics, polyurethane plastics, and halogenated plastics. Most plastics contain organic polymers.

[0054] As used herein, “plastic” includes rubber, such as natural rubber or vulcanized rubber. Natural rubber is a polymer of isoprene (polyisoprene).

[0055] In some embodiments, the plastic used to form the plastic aggregate is a synthetic or semi-synthetic plastic, or a rubber.

[0056] In some embodiments, the plastic used to form the plastic aggregate is a synthetic or semi-synthetic plastic, preferably a synthetic plastic.

[0057] Suitably, the plastic used to form the plastic aggregate is a thermoset plastic. Thermoset plastics are obtained by irreversibly hardening (also called “curing”) a soft solid or viscous liquid pre-polymer (resin).

[0058] Suitably, the plastic used to form the plastic aggregate is derived from a plastic-based foam.

[0059] As used herein, “foam” refers to a plastic-based material comprising a cell structure, such as closed cells, open cells, or a mixture thereof. Due to the cell structure, a foam is a porous material. The porosity is inversely related to the density. Generally, when considering the density, foams are classified into high, medium, and low density foams. High density foams have a density between 0.5 g / cm3and 1000 kg / m3, medium density foams have a density between 100 kg / m3and 500 kg / m3, and low density foams have a density below 100 kg / m3. Low density foams are mainly used for insulation applications, while medium density foams are widely used in the packaging, construction, and building industries. High density foams have significantly higher strength and modulus, and thus, can generally replace conventional plastics in applications where lower electrical / thermal conductivity, bulk weight, dielectric constant, compressive modulus, and higher flexibility and damping are required or desired.

[0060] Due to its porosity, a foam is characterized by a large surface area. One particular advantage of using a foam in the present invention is that the surface area of the plastic in the plastic aggregate is larger, such that there is more exposed surface area comprising metal oxides, and thus, more metal oxides or silicates (i.e., at least one of the metal oxides or silicates in the cementitious binder) are available for carbonization. In some embodiments, the plastic used to form the plastic aggregate is a foam.

[0061] “Rigid foam” refers to a plastic-based foam material that generally has a closed cell structure. Its density is generally adjusted by the addition of a blowing agent. Generally, the density of rigid foams is up to 800 kg / m3. 3 “Flexible foam” refers to a plastic-based material that generally has an open cell structure. Generally, the density of flexible foams is about 15 kg / m3 3 to 150 kg / m3 3 . Due to the very fine cell structure of rigid and semi-rigid foams, mechanical treatments such as drilling, milling, or grinding can be performed.

[0062] Suitablely, the plastics used in this invention, such as plastic-based foams, can be rigid or flexible foams. Preferably, the plastic-based foam is a rigid foam.

[0063] Appropriately, plastic-based foam can be waste plastic-based foam. "Waste plastic-based foam" refers to plastic-based foam materials that have been used for the first time, such as in electrical appliances, insulation, or furniture. These materials are subsequently disposed of and not recycled. As described in the background section, they are typically incinerated or landfilled after initial use. Waste plastic-based foam is typically gray or yellow, beige or cream-colored, and its density differs from that of other plastics (PE, PP, and PS) by approximately 901 kg / m³. 3 895 kg / m 3 and 1050 kg / m 3 Compared to ), it has a lower density (at 48 kg / m³). 3 and 961 kg / m 3 (between). Waste plastic-based foams have a honeycomb structure (closed-cell or open-cell, depending on hardness), belong to thermosetting plastics, and typically contain urethane bonds.

[0064] The most commonly used plastic foams contain isocyanates. Polymer foams containing isocyanate monomers are referred to herein as "isocyanate-based foams." Those skilled in the art can determine whether a given polymer contains isocyanate monomers using standard techniques known in the art. Isocyanates are compounds containing isocyanate groups (-N=C=O). They react with nucleophiles such as alcohols (containing hydroxyl groups), amines, or water. Isocyanates treated with alcohols form urethane bonds. If diisocyanates are treated with compounds containing two or more hydroxyl groups (such as diols or polyols), polymer chains are formed, which are called polyurethanes. Common isocyanates used to form foamed plastics include methylene diphenyl diisocyanate (MDI) and toluene diisocyanate (TDI).

[0065] Suitablely, the plastics used in this invention, such as plastic-based foams (e.g., waste plastic-based foams), include isocyanate-based foams, such as polyurethane (PUR), polyisocyanurate (PIR), or polyurea.

[0066] In a preferred embodiment, the plastic, such as plastic-based foam (e.g., waste plastic-based foam), comprises polyurethane or polyisocyanurate. More preferably, the plastic, such as plastic-based foam (e.g., waste plastic-based foam), is polyurethane.

[0067] The plastic particles can be derived from a plastic-based foam (such as a waste plastic-based foam). Suitably, the plastic particles can have a size distribution of about 0.1 mm to about 6 mm, preferably about 0.2 mm to about 5 mm, such as about 0.2 mm to about 3 mm or about 0.2 mm to about 2 mm. It will be appreciated that the size range given refers to the longest dimension of the plastic particles. At least some of the dimensions of the plastic particles are within this size range. For example, some of the plastic particles can have a dimension of about 1 mm and the remaining plastic particles can have a dimension greater than about 6 mm. According to particular embodiments, substantially all (more than 90% by weight, typically more than 95% by weight, for example more than 98% or 99% by weight) of the plastic particles have a dimension of about 0.1 mm to about 6 mm, preferably about 0.2 mm to about 5 mm, more preferably about 0.2 mm to about 2 mm.

[0068] In some embodiments, the plastic particles (such as plastic particles derived from a plastic-based foam (e.g. a waste plastic-based foam)) can have a dimension greater than about 0.1 mm, such as greater than about 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1 mm, 1.5 mm or 2 mm. In some embodiments, the plastic particles (such as plastic particles derived from a plastic-based foam (e.g. a waste plastic-based foam)) can have a dimension less than about 6 mm, such as less than about 5.5 mm, 5 mm, 4.5 mm, 4 mm, 3.5 mm or 3 mm. For the avoidance of doubt, any one of the lower range endpoints described above can be combined with any one of the higher range endpoints described above.

[0069] “Cementitious binder” refers to a material or substance that binds other materials together to enable the resulting concrete composition to form, set and harden. “Cementitious binder” includes cement, ground granulated blast furnace slag (GGBS), ground fly ash (also known as fly ash), Portland cement, pozzolanic material or geopolymer.

[0070] Typically, cement comprises any one or mixture of calcium oxide, calcium hydroxide and calcium silicate. Typically, cement is a hydraulic cement, such as Portland cement, which reacts with water through a pozzolanic reaction to solidify and set. Portland cement is typically made by heating limestone and clay minerals to form clinker, which is then ground and contacted with gypsum. Portland cement is typically composed of at least two-thirds of its mass as calcium silicate, with the remainder composed of aluminium- and iron-containing compounds. The ratio of CaO to Si02in Portland cement is at least 2:1.

[0071] “Geopolymer” is an amorphous aluminosilicate binder material. “Geopolymer” includes metakaolin.

[0072] The at least one cementitious binder comprises at least one metal oxide or metal silicate. In some embodiments, the at least one cementitious binder comprises at least one metal oxide.

[0073] Suitably, the cementitious binder can comprise cement (such as Portland cement and / or high strength cement (HSC)), slag (such as ground granulated blast furnace slag (GGBS)), fly ash (also known as pulverized fly ash), pozzolans, geopolymer, or a mixture of two or more thereof. In one embodiment, the cementitious binder can comprise cement and / or slag (such as GGBS). Preferably, the cementitious binder comprises slag (such as GGBS), more preferably GGBS.

[0074] In alternative embodiments, the cementitious binder comprises cement. In one embodiment, the cement comprises Portland cement.

[0075] The preferred binder GGBS represents a low-carbon alternative to ordinary Portland cement (OPC). The use of GGBS can reduce the embodied carbon of aggregates and final concrete compared to the use of OPC. GGBS is characterised by an extremely slow rate of setting when hydrated, and is typically activated by an alkaline solution, which increases the rate of setting and compressive strength.

[0076] While the slow setting rate of GGBS can constitute a barrier, during the production of composite aggregates (such as by pelletisation, which generates high pressure and temperature), the pressure and heat increase the strength of the aggregate due to the compaction of the particles.

[0077] The premix is agglomerated to form the plastic aggregate. “Agglomerating” refers to the process of gathering materials into larger cohesive units. Suitably, agglomerating comprises pressure or non-pressure agglomeration of the premix to form the plastic aggregate.

[0078] In some embodiments, agglomerating comprises compression and heating. Thus, the premix can be compressed and heated to form the plastic aggregate.

[0079] The compression of the plastic powder into coarser particles can improve the performance of the plastic in uses such as concrete. The larger particles will exhibit a lower surface area in contact with the concrete matrix, reducing the weakening effect of adverse contact between the two. However, the larger plastic particles still tend to separate, albeit to a lesser extent than compared to the powder, and as there is no connectivity between the PUR powder in the larger particles, they still constitute weaker material regions in the concrete matrix.

[0080] In the present invention, the plastics (e.g. PUR plastics) are agglomerated (e.g. compressed) into larger particles and bound together by a cementitious binder and water. Without wishing to be bound by theory, it is believed that the larger particles will have a smaller contact surface area with the concrete matrix, but due to the similar or identical material, the presence of the binder will improve the interfacial interaction between the aggregate and the cementitious matrix. The effect of the cementitious binder, which will cure upon contact with water in the pre-mix, will also result in the overall strengthening of the plastic aggregate, thereby reducing the overall weakening effect of pure plastic (e.g. pure PUR) granules on the final concrete matrix.

[0081] Compression is achieved by applying a force to the powder mixture to cause it to bind. Heat can be generated from the compression process, or heat can be applied after the aggregate has been formed by compression.

[0082] Suitably, the compression and heating can be a single process. Preferably, the agglomeration (such as compression) and optionally heating comprises granulation. Typically, during the specific compression method comprising granulation, the required heat is naturally generated by friction during the compression of the mixture as it is extruded through a die. However, further heating can also be applied after compression to keep the granules in an oven for a longer period of time to further increase the speed of curing.

[0083] “Granulation” is the process of compressing a material into granule form. Suitably, granulation comprises die plate granulation, disc granulation, briquetting or extrusion granulation. Die plate granulation refers to the conversion of finely ground material into free-flowing granules. “Disc granulation” refers to mixing a material (e.g. finely ground material or seed granules) with a binder and agitating the resulting mixture until granules of the desired size are formed. The centrifugal force experienced by the granules at the edge of the disc compresses the particles into granules. Furthermore, as each aggregate falls as the disc rotates, the continued rotation and falling compresses the granules and increases the density of the granules. “Briquetting” refers to the compression of a material into a desired form, such as a granule. “Extrusion granulation” (also known as “compounding”) refers to the extrusion of a mixture, and then feeding the mixture into a granulator (such as a pelletiser) to convert the extrudate into granules.

[0084] Preferably, the granulation is die plate granulation.

[0085] Alternatively, the compression and heating can be separate, such that they are performed as part of independent processes, and / or are performed at different locations or at different times. In such cases, the compression is performed first, and then the heating is performed. Thus, in some embodiments, the compression and heating are independent processes, wherein the compression is performed before the heating. The heating is required to increase the curing of the granules.

[0086] The plastic aggregate is exposed to an active carbonation process to obtain a carbonated plastic aggregate.

[0087] As used herein, "active carbonation" refers to a carbonation process in which the carbonation rate is increased compared to the "passive carbonation rate." Passive carbonation of plastic aggregates refers to carbonation that occurs by exposing the plastic aggregate to ambient conditions (the atmosphere contains about 420 ppm of CO2). Thus, the passive carbonation rate refers to the carbonation rate of the plastic aggregate exposed to ambient conditions only, i.e., without increasing the concentration of CO2 in the surrounding atmosphere, without heating, or without watering, etc.

[0088] Suitably, the active carbonation process can include adding water to the cementitious binder or plastic aggregate, such as using artificial watering, an automatic watering system, or exposing the plastic aggregate to rain. Adding water to the aggregate increases the carbonation reaction rate.

[0089] Suitably, the active carbonation process can include heating the plastic aggregate, such as by using heating elements or a heat exchange system. Heating the plastic aggregate increases the carbonation reaction rate.

[0090] Intentionally increasing airflow through the aggregate, especially when the aggregate is exposed to an atmosphere containing CO2, increases the carbonation rate and thus belongs to the "active carbonation" process. In some embodiments, active carbonation includes increasing airflow through the plastic aggregate, such as by placing the aggregate on an elevated false floor. In some particular embodiments, increasing airflow through the plastic aggregate can be combined with a heat exchange system, whereby waste heat in the form of gases or water produced in industrial processes can be transported out through pipes that conduct the airflow. These additional heat increases the carbonation rate. In some embodiments, active carbonation includes increasing airflow through the aggregate and exposing the plastic aggregate to an atmosphere containing an increased concentration of CO2 (i.e., a higher concentration of CO2 than in a typical ambient atmosphere, such as more than 450 ppm).

[0091] All equipment used for the watering, heating, or increasing airflow processes can be operated using renewable electricity sources and energy plans to ensure that the damage to the environment does not exceed the removal of carbon dioxide from the atmosphere by the aggregate.

[0092] "Active carbonation" can also refer to exposing plastic (such as plastic aggregate) to a source enriched in CO2. A source enriched in CO2 refers to an air source with a concentration of CO2 higher than that found in the atmosphere (i.e., more than about 420 ppm), such as at least 450 ppm. Such a source enriched in CO2 can be flue gas captured from a site such as a power plant, a cement kiln, and a chemical plant. Suitably, the CO2 concentration of the source enriched in CO2 is 0.5% or more, preferably 1% or more, more preferably 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, or 100% higher than the CO2 concentration in the atmosphere.

[0093] In some embodiments, the CO2 source has a CO2 concentration of at least 0.05%, 0.5%, 1%, 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 99%, or 100%.

[0094] “Active carbonation” can also refer to direct air capture (DAC), whereby CO2 is extracted directly from the atmosphere ( Figure 11 ). Once CO2 has been captured from the atmosphere, it needs to be permanently stored to prevent leakage back into the environment. Carbonation of plastic aggregates can be used to store these CO2. Thus, in some embodiments, the active carbonation process comprises direct air capture (DAC).

[0095] In some embodiments, active carbonation comprises using a reaction chamber, whereby the CO2 source is pumped into a container containing plastic aggregates. The temperature, pressure, and humidity within the reaction chamber can be controlled. In some embodiments, the plastic aggregates in the container have been hardened after production. Alternatively, the plastic aggregates can also be introduced into the container immediately after having been formed, such as by compression granulation or disc granulation.

[0096] After production of the plastic aggregates, they can be transported using a sealed system comprising a CO2-enriched atmosphere. The sealed system can be an enclosed belt conveyor or a vibrating screw conveyor.

[0097] One or more of the above-described “active carbonation” processes can be used sequentially or simultaneously in the methods of the present application.

[0098] The agglomeration and carbonation steps can be performed simultaneously or sequentially in any order. In some embodiments, the compression, heating, and carbonation steps are performed simultaneously or sequentially in any order.

[0099] Thus, the active carbonation step can be performed: before the aggregate is formed (i.e., before the agglomeration step (such as the compression or heating step), i.e., during step (iii) and / or between step (iii) and step (iv)), during the formation of the aggregate (i.e., during the agglomeration step (such as the compression or heating step)), immediately after the plastic aggregate is formed (i.e., as a subsequent step after agglomeration, such as after compression and heating), and / or after the plastic aggregate has hardened, such as a few days later.

[0100] In some embodiments, the agglomeration and carbonation steps are simultaneous. Thus, in some embodiments, the method comprises preparing the plastic aggregate under a CO2 atmosphere (at ambient temperature and pressure or at elevated temperature and pressure) in step (iv) to directly obtain a carbonated plastic aggregate. Figure 12 A schematic of an improved granulator is shown, which involves granulation under a CO2 atmosphere.

[0101] In embodiments where agglomeration comprises compression and heating, the compression and active carbonation (and optionally heating) steps can be performed simultaneously.

[0102] The carbonated plastic aggregate can then be fed into a granulator to granulate the carbonated plastic aggregate. This process has the advantage that the compression of the plastic aggregate generates heat which accelerates the carbonation process.

[0103] Suitably, the plastic aggregate is tumbled in a disc granulator modified to be sealed from the atmosphere to form the aggregate (e.g. spherical aggregate) under a CO2 atmosphere. Figure 13 During this process, carbonation is accelerated.

[0104] Water absorption is critical to the carbonation process. Therefore, in embodiments where the plastic aggregate comprises plastic foam (such as waste plastic foam), the carbonation process is particularly effective because the aggregate is able to absorb a large amount of moisture through the network of pores which aids the carbonation process because the more moisture absorbed, the more CO2 is available to be converted to carbonic acid for the carbonation process.

[0105] The carbonation process is directly related to the surface area. Since the plastic aggregate described herein is porous (particularly in embodiments where the plastic used to form the aggregate is a plastic-based foam), it allows for greater surface area and therefore exposes more metal oxide or silicate of the cementitious binder and therefore aids the carbonation of the plastic aggregate.

[0106] Additionally, without wishing to be bound by theory, in embodiments where sodium hydroxide is used as the inorganic base, it is expected that the NaOH will react with the carbonic acid to produce sodium bicarbonate. According to Iversen et al (ACS Applied Materials & Interfaces 2015 7 (9), 5258-5264), sodium bicarbonate is able to act as a catalyst for the carbonation of magnesium silicate.

[0107] Therefore, in some embodiments, the method can comprise adding to the pre-mix or the plastic aggregate a catalyst (such as sodium bicarbonate) which is able to increase the rate of carbonation of the aggregate.

[0108] Without wishing to be bound by theory, it is believed that the plastic aggregate described herein exhibits an increased rate of carbonation due to the use of plastic. Carbon dioxide is hydrophobic and due to the hydrophobic nature of the plastic, it is expected that the concentration of CO2 at the surface of the plastic will be higher. This can then result in a higher concentration of CO2 at the water / air interface, increasing the rate of dissolution of CO2 and leading to faster carbonation.

[0109] Suitably, in embodiments where the plastic used to form the plastic aggregate is a waste plastic-based foam, the method of the present application can further comprise the following pre-step:

[0110] (i). receiving waste plastic-based foam, such as from a recycler or a manufacturer.

[0111] In pre-step (i), the waste plastic-based foam can be received in the form of pellets, powder, board, or briquettes. Preferably, the waste plastic-based foam is received in the form of pellets or powder.

[0112] In one embodiment, the waste plastic-based foam can be contaminated with demolition rubble. For example, in pre-step (i), the waste plastic-based foam can be received in the form of pellets, powder, board, or briquettes, and the pellets, powder, board, or briquettes are mixed with or contain demolition rubble. Suitably, the method can include an additional pre-step (i-a) of separating the plastic-based foam from the demolition rubble.

[0113] In some embodiments, the second composition further comprises at least one inorganic base. Early and final strength can be improved by using an activator solution, which is preferably obtained by adding sodium hydroxide, sodium carbonate, calcium oxide, or a combination thereof. A second advantage of this process is that when scaled up (>0.5 T), the aggregates can retain the heat generated by the process as well as the heat generated by the hydration reaction for multiple days due to the inherent thermal insulation properties of the plastic (e.g., PUR), which improves the compressive strength.

[0114] An “inorganic base” acts as an activator. Inorganic bases include a class of inorganic compounds that are capable of reacting with (i.e., neutralizing) acids to form salts. These compounds include strong bases and weak bases, such as metal hydroxides, alkali metal hydroxides, ammonium hydroxides, alkali metal carbonates, or bicarbonates. The term is also intended to include substances that produce bases (i.e., hydroxides) when in contact with water, such as metal and alkali metal oxides, alkaline silicates.

[0115] Suitably, the at least one inorganic base includes an alkali metal hydroxide, an alkali metal oxide, an alkali metal carbonate, an alkaline silicate, or a mixture thereof. In some embodiments, the base is sodium, potassium, or calcium.

[0116] Preferably the at least one inorganic base includes sodium hydroxide, sodium carbonate, calcium oxide, or a mixture thereof.

[0117] Additionally, the inventors have found that when combined with a particular cementitious binder (e.g. GGBS) to form a concrete composition or concrete block, the unreacted inorganic alkali in the plastic aggregate diffuses out. This diffused inorganic alkali significantly accelerates the setting of the particular cementitious binder (e.g. GGBS), resulting in a harder concrete more quickly. This is beneficial as it is known in the industry that some cementitious binders (e.g. GGBS) take a long time to set, which leads to slow and impractical manufacturing. Accordingly, the method can further comprise the step of mixing the carbonated plastic aggregate with at least one cementitious binder to form a concrete composition. Preferably the at least one cementitious binder comprises GBBS. The at least one cementitious binder can be a mixture of GGBS and cement.

[0118] In some aspects of the method, no inorganic alkali is required to set the binder when a particular cementitious binder is used. Accordingly, there is suitably provided a method which does not require inorganic alkali in step ii and the second composition. Exemplary cementitious binders include Portland cement.

[0119] In some embodiments, the carbonated plastic aggregate is in the form of granules.

[0120] The width of the carbonated plastic aggregate granules can be 0.05 mm to 10 mm, preferably 0.5 mm to 10 mm, such as 1 mm to 9 mm, 2 mm to 8 mm, 2 mm to 7 mm, 2 mm to 6 mm or 2 mm to 5 mm, preferably 2 mm to 8 mm. The length of the carbonated plastic aggregate granules can be 0.5 mm to 10 mm, such as 1 mm to 9 mm, 2 mm to 8 mm, 2 mm to 7 mm, 2 mm to 6 mm or 2 mm to 5 mm, preferably 2 mm to 8 mm.

[0121] The “aspect ratio” is a well-known ratio and is the proportional relationship between the length and the width of the aggregate. The aspect ratio between the length of the granules and the width of the granules can be 0.05 to 20, such as 0.1 to 10, 0.2 to 8, 0.25 to 6, 0.25 to 4, preferably 0.25 to 4. Suitably, the carbonated plastic aggregate is circular and so it is difficult to distinguish between length and width. Accordingly, the aspect ratio is suitably about 1 : 1.

[0122] The ratio between the plastic and the cementitious binder is critical to achieving the desired strength and density of the resulting aggregate. In some embodiments, the weight ratio of the plastic to the cementitious binder in the pre-mixture and / or the plastic aggregate and / or the carbonated plastic aggregate is 2: 1 to 1 : 10, such as 2: 1 to 1 : 7, 1 : 1 to 1 : 5 or 1 : 1 to 1 : 4, preferably 2: 1 to 1 : 7.

[0123] The amount of water is critical to enable hydration of the cementitious binder and to assist the granulation process. If the amount of water is too high, the resulting mixture will not be processed efficiently, and if the amount of water is too low, the mixture can jam in the mould and not be processed correctly. In some embodiments, the weight ratio of water in the premixture and / or the plastic aggregate and / or the carbonised plastic aggregate to the cementitious binder is 0.1 to 1, such as 0.2 to 0.6 or 0.3 to 0.5, preferably 0.3 to 0.5.

[0124] In some embodiments, the amount of inorganic alkali is critical to activate the hydration of the cementitious binder and to enable higher final strength of the resulting granules. In some embodiments, the weight % of inorganic alkali in the premixture and / or the plastic aggregate and / or the carbonised plastic aggregate is 0% w / w to 15% w / w of the cementitious binder, 0.1 % w / w to 15% w / w of the cementitious binder, such as 0.5% w / w to 12% w / w, 1 % w / w to 10% w / w or 2% w / w to 10% w / w of the cementitious binder, preferably 2% w / w to 10% w / w of the cementitious binder.

[0125] A strength enhancer can be used to increase the strength of the carbonised plastic aggregate and the resulting concrete. In some embodiments, the method further comprises a step of adding a strength enhancer, preferably graphene, during or between any of steps (i), (ii) or (iii). In particular embodiments, the strength enhancer, preferably graphene, is added to the first composition during or after step (i), preferably after step (ii) and before step (iii).

[0126] A pigment can be used to colour the carbonised plastic aggregate. In some embodiments, the method further comprises a step of adding a pigment during or between any of steps (i), (ii) or (iii). In particular embodiments, the pigment is added to the first composition during or after step (i), preferably after step (i) and before step (iii).

[0127] Fillers can improve the performance and microstructure of the concrete. In some embodiments, the method further comprises a step of adding a filler during or between any of steps (i), (ii) or (iii), preferably wherein the filler is limestone and / or clay and / or microsilica. In particular embodiments, the filler is added to the first composition during or after step (i), preferably after step (i) and before step (iii).

[0128] Suitably, the method of the application can further comprise the following pre-step:

[0129] (ii). pelletising the plastics, such as plastic-based foams or waste plastic-based foams, to form a mixture of plastic particles; and / or

[0130] (iii). sieving the mixture to separate the plastic particles by size;

[0131] Suitably, the mixture of plastic particles according to step (ii) can be produced by pelletising the larger size waste plastic-based foams. It will be appreciated that larger size plastic-based foams refers to bulk plastics, i.e. large pieces of plastic-based foams, such as rigid or flexible foam boards, and plastic foam particles having a size larger than the desired size of the plastic aggregate particles.

[0132] The term “pelletising” refers to forming particles, i.e. discrete solid pieces, and can be achieved by chopping (tearing or cutting), grinding (pressing, crushing and / or milling) and flaking (shaving pieces).

[0133] Pelletising can be achieved by any method that reduces the size of the larger size plastics and forms them into the desired smaller particles. Pelletising can be carried out by any one or a combination of chopping, grinding and flaking. In some embodiments, pelletising comprises chopping. In other embodiments, pelletising comprises chopping and grinding. Typically, pelletising comprises chopping followed by grinding. The surface texture of the plastic particles after pelletising depends on the method used to pelletise the larger size plastics. It is reported that a rougher surface produces better bonding properties, so a pelletising method that produces more textured surfaces is preferred. Over grinding of the larger size plastics is generally avoided as this can smooth the surface of the resulting particles to an undesirable extent.

[0134] In some embodiments, the mixture is sieved to separate the plastic particles by size. Particle sieves of different mesh sizes are used to separate the plastic particles by size. The person skilled in the art is able to determine which mesh size is suitable for the size range covered by a certain size category. For example, if it is preferred to separate the plastic particles by longest dimension into the following size categories: <63 pm, >63 pm to <125 pm, >125 pm to <250 pm, >250 pm to <500 pm, >500 pm to <2 mm, >2 mm to <4 mm, >4 mm to <6 mm, >6 mm to <10 mm, >10 mm to <20 mm, >20 mm to <40 mm, then mesh sizes of 230, 120, 60, 35, 10, 5 should be used. The plastic particles can be separated by sieving in order of increasing or decreasing mesh size. Typically, the plastic particles are separated by sieving through particle sieves of decreasing mesh size (increasing mesh size number).

[0135] Suitably, different sized plastic particles can be in contact with each other. Typically, contact requires the particles to be bound, and typically the particles are mixed. Herein, particles should be considered to have different sizes when their longest dimension differs by more than 5%. For example, if the longest dimension of a first particle is 0.5 mm, and the longest dimension of a second particle is 0.48 mm, the longest dimensions of these two particles differ by 5% or less, and herein they are considered to have similar sizes. Conversely, if the longest dimension of a first particle is 0.5 mm, and the longest dimension of a second particle is 0.53 mm, the longest dimensions of these two particles differ by more than 5%, and herein they are considered to have different sizes.

[0136] In one embodiment, the carbonised plastic aggregate has a size distribution of from 0 mm to about 2 mm, preferably from 0 mm to about 1 mm. Preferably, the carbonised plastic aggregate is in the form of a powder. It will be appreciated that the size range given refers to the longest dimension of the plastic particles. At least some of the aggregate particles have a size within this size range. For example, some of the aggregate particles can have a size of about 1 mm, and the remaining aggregate particles can have a size greater than about 2 mm. According to particular embodiments, substantially all (more than 90% by weight, typically more than 95% by weight, for example more than 98% or 99% by weight) of the plastic particles in the carbonised aggregate have a size of from about 0 mm to about 2 mm, or from 0 mm to about 1 mm.

[0137] In one embodiment, the carbonised plastic aggregate has a size distribution of from about 2 mm to about 40 mm, preferably from about 5 mm to about 10 mm. Preferably, the carbonised plastic aggregate is in the form of granules. It will be appreciated that the size range given refers to the longest dimension of the plastic particles. At least some of the aggregate particles have a size within this size range. For example, some of the aggregate particles can have a size of about 2 mm, and the remaining aggregate particles can have a size greater than about 40 mm. According to particular embodiments, substantially all (more than 90% by weight, typically more than 95% by weight, for example more than 98% or 99% by weight) of the plastic particles in the carbonised aggregate have a size of from about 2 mm to about 400 mm, or from 5 mm to about 10 mm.

[0138] Suitably, the method can include a step such as adding at least one additive prior to step (iv). The resulting carbonised plastic aggregate will comprise at least one additive.

[0139] The additive includes an admixture, a strength enhancer, a rheology modifier, a pigment, a fibre or a mineral.

[0140] "Admixtures" include materials such as air entraining agents, water-reducing agents, set retarders, set accelerators, or plasticizers. Admixtures include rosin resins, alkyl sulfonates, fatty alcohol sulfonates, proteinates and petroleum sulfonates, soluble inorganic salts of alkali and alkaline earth metals (sodium or potassium hydroxides, calcium chlorides, bromides and fluorides, sodium and calcium nitrites, potassium carbonates, sodium and calcium thiocyanates, sulfates, thiosulfates, perchlorates, silicates, aluminates), carboxylic acids (formic, acetic, propionic and butyric, oxalic) and their salts (calcium formate, calcium oxalate), lignin sulfonates, sulfonated naphthalene formaldehyde (PNS), sulfonated melamine formaldehyde (PMS), vinyl copolymers (VCP), and polycarboxylate ethers (PCE). Suitably, the method can comprise a step such as adding at least one admixture prior to step (iv).

[0141] "Strength enhancers" are materials used to increase the strength of concrete. Strength enhancers include graphene and alkanolamines, such as triisopropanolamine (TIPA) and triethanolamine (TEA). Suitably, the at least one additive comprises a strength enhancer. Suitably, the method can comprise a step such as adding at least one strength enhancer prior to step (iv).

[0142] In some embodiments, the strength enhancer is graphene. Graphene increases the strength of the plastic aggregate and the resulting concrete comprising the plastic aggregate. Graphene can be functionalized with surface groups such as graphene oxide and other forms of functionalized graphene, dispersed in a liquid using a surfactant, or used in pure carbon form without any dispersing aids.

[0143] Modifying the rheological properties of concrete can improve the performance of the concrete in fresh and hardened states, which is particularly important for the production and placement of special architectural applications such as underwater concrete or self-compacting concrete. A "rheology modifier" is a material capable of modifying the rheology (i.e. the deformation or flow response to an applied force or stress) of a fluid composition to which it is added. Rheology modifiers include viscosity modifiers such as cellulose ethers, natural gums (xanthan gum, welan gum), and starches. Suitably, the method can comprise a step such as adding at least one rheology modifier prior to step (iv).

[0144] Cement can be colored using pigments. "Pigments" refer to colored materials that are completely or almost insoluble in water. Pigments include iron oxide, cobalt, titanium dioxide, and chromium oxide pigments, and carbon black. Suitably, the method can comprise a step such as adding at least one pigment prior to step (iv).

[0145] Fiber reinforced concrete has a higher tensile strength compared to plain concrete. Fibers include cellulose fibers, natural fibers, carbon fibers, polyester fibers, glass fibers, polypropylene fibers and steel fibers. Suitably, the method can comprise a step of adding at least one fiber, such as prior to step (iv).

[0146] In some embodiments, the method can comprise a step of adding at least one additive, such that the pre-mixture and / or the carbonized plastic aggregate comprises 0.01 wt% to 5 wt% of the at least one additive, such as 0.1 wt% to 5 wt%, 0.1 wt% to 3 wt%, or 1 wt% to 3 wt%.

[0147] Fillers can improve the performance and microstructure of the concrete. Suitably, the method can comprise a step of adding at least one filler, such as prior to step (iv). The filler can be gypsum, limestone, sand, wood, wood chips, clay, concrete dust, microsilica or charcoal, preferably clay, limestone, microsilica or mixtures thereof, preferably clay.

[0148] In some embodiments, the clay is calcined clay. The calcined clay can be natural or synthetically produced by high-temperature kiln.

[0149] In particular embodiments, the method can comprise a step of adding calcined clay, such as prior to step (iv), and the cementitious binder comprises high-strength cement. In particular such embodiments, the plastic aggregate further comprises a coarse aggregate, preferably limestone.

[0150] In some embodiments, the method can comprise a step of adding at least one filler, such that the pre-mixture and / or the carbonized plastic aggregate comprises 0.01 wt% to 40 wt% of the at least one filler, such as 0.1 wt% to 30 wt%, 0.1 wt% to 25 wt%, 0.5 wt% to 20 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt%.

[0151] As porosity and water absorption are considered important for assisted carbonization, the method can comprise adding a further material, such as prior to step (iv), to achieve a higher porosity and water absorption.

[0152] The further material can be a filler, such as biochar.

[0153] The further material can also be a mineral, such as a finely ground mineral. In some embodiments, the mineral comprises a substantial amount of calcium and magnesium oxides and silicates.

[0154] In some embodiments, the mineral can be selected from the group consisting of: oxides, portlandite, brucite, silicates, periclase, silicates.

[0155] These minerals can be mined and ground into a powder or sand to increase its surface area.

[0156] In a second aspect of the application, there is provided a method of carbonizing a plastic aggregate granulate, the method comprising:

[0157] i. providing a plastic aggregate granulate comprising a) plastic particles, b) at least one cementitious binder comprising at least one metal oxide or at least one metal silicate, and c) water,

[0158] ii. carbonizing the at least one metal oxide or the at least one metal silicate by an active carbonization process to obtain a carbonized plastic aggregate.

[0159] For the avoidance of doubt, the method of the second aspect of the application can comprise any of the features described above in relation to the first aspect of the application.

[0160] For example, in some embodiments, the plastic aggregate granulate further comprises an inorganic base.

[0161] In a third aspect of the application, there is provided a concrete composition comprising a carbonized plastic aggregate such as obtainable by the method of the first or second aspect of the application. For the avoidance of doubt, the concrete composition can comprise any of the features described above in relation to the first or second aspect of the application.

[0162] Suitably, the concrete composition can further comprise a cementitious binder, a natural aggregate and / or water. Suitably, the concrete composition can further comprise a secondary aggregate.

[0163] Suitably, the concrete composition can be used to produce a concrete building element. The concrete building element can be a precast concrete element such as a column, beam, slab or block. Preferably, the concrete building element is a concrete block.

[0164] In some embodiments, the concrete composition comprises a strength enhancer, preferably wherein the strength enhancer is graphene. The strength enhancer can be present in the concrete composition by the concrete composition comprising a plastic aggregate comprising said strength enhancer.

[0165] Suitably, the concrete composition can have a carbon footprint of -0.5 kg to 0.2 kg CO2 equivalent per kg of the concrete composition, preferably -0.35 kg to 0.05 kg CO2 equivalent per kg of the concrete composition. The skilled person is able to determine the carbon footprint of a given composition using standard techniques known in the art, such as by performing industry standard life cycle assessments (LCAs) and using environmental product declarations (EPDs).

[0166] Suitably, the thermal conductivity of the concrete composition can be 0.1 W / mK to 1 W / mK, preferably 0.2 W / mK to 0.8 W / mK, more preferably 0.3 W / mK to 0.5 W / mK. Alternatively, the thermal conductivity of the concrete composition can be 0.5 W / mK to 1.6 W / mK, preferably 0.6 W / mK to 1.4 W / mK, more preferably 0.7 W / mK to 1.2 W / mK. The thermal conductivity can be measured using standard techniques known in the art, such as using a thermal conductivity meter.

[0167] Suitably, the compressive strength of the concrete composition can be 1 N / mm 2 to 60 N / mm 2 , preferably 3 N / mm 2 to 40 N / mm 2 , more preferably 3.6 N / mm 2 to 22.5 N / mm 2 .

[0168] Suitably, the density of the concrete composition can be 600 kg / m 3 to 2500 kg / m 3 , preferably 1200 kg / m 3 to 1600 kg / m 3 , more preferably 1350 kg / m 3 to 1550 kg / m 3 . Alternatively, the density of the concrete composition can be 1500 kg / m 3 to 2500 kg / m 3 , preferably 1600 kg / m 3 to 2200 kg / m 3 , more preferably 1700 kg / m 3 to 2100 kg / m 3 . The density can be recorded using standard techniques known in the art, such as British Standard, which involves drying and weighing the concrete composition.

[0169] The plastic particles within the carbonated plastic aggregate can be surface modified to improve the interaction of the aggregate with the cement. Surface modification can be achieved by exposing the particles to chemicals, gamma irradiation, electron beams or plasma. Surface modification by chemical treatment will typically result in new chemical groups being bound at the surface of the particles.

[0170] Atmospheric pressure plasma treatment is limited to ionizing chemical species that are gaseous at atmospheric pressure, which in turn limits the type of plasma that can be generated. Low pressure plasma treatment can be used as an alternative. In low pressure plasma treatment, the reaction chamber is evacuated to a pressure below atmospheric pressure at which the target plasma source becomes gaseous. The plasma source is ionized to generate a low pressure plasma stream that flows through the reaction chamber (A. Yanez-Pacios and J. Martin-Martinez, supra; L. Gerenser, J. Adhesion Sci. Technol., 1987, 1(4), 303-318; L. Gerenser, J. Adhesion Sci. Technol., 1993, 7(10), 597-614; R. Foerch, J. Izawa, and G. Spears, J. Adhesion Sci. Technol., 1991, 5(7), 549-564; and E. Occhiello et al., J. Appl. Polym. Sci., 1991, 42(2), 551-559).

[0171] Suitably, the plastic aggregate can comprise plastic particles that have been treated with low pressure plasma or electron beam. In one embodiment, the carbonized plastic aggregate comprises plastic particles that have been treated with low pressure plasma. As described above, low pressure plasma is capable of reacting with and bonding to the surface of plastic. In an alternative embodiment, the plastic aggregate comprises plastic particles that have been treated with electron beam.

[0172] In particular embodiments, the plastic aggregate comprises plastic particles that have been treated with low pressure plasma, wherein the plasma comprises ions formed from any one or combination selected from the group consisting of: carboxylic acid, alcohol, amine, ester, aldehyde, amide, ketone, epoxide, ammonia, and peroxide.

[0173] In particular embodiments, the plastic aggregate is untreated (such as substantially untreated). As used herein, “untreated plastic aggregate” refers to plastic aggregate that has not been treated with plasma, electron beam, and / or inorganic compound. In particular embodiments, the plastic aggregate has not been treated with inorganic compound.

[0174] Clause

[0175] 1. A method of manufacturing a carbonized plastic aggregate, the method comprising the steps of:

[0176] (i) mixing plastic particles with at least one cementitious binder comprising at least one metal oxide or metal silicate to form a first composition;

[0177] (ii) providing a second composition comprising water;

[0178] (iii) mixing the first and second compositions together to form a pre-mix;

[0179] (iv) agglomerating the pre-mix to form a plastic aggregate; and

[0180] (v) carbonating at least one metal oxide or metal silicate by an active carbonation process to obtain a carbonated plastic aggregate.

[0181] 2. The method according to Clause 1, wherein agglomerating comprises pressure or non-pressure agglomeration of the pre-mix to form the plastic aggregate.

[0182] 3. The method according to Clause 1 or 2, wherein agglomerating comprises compression and heating of the pre-mix.

[0183] 4. The method according to any one of the preceding Clauses, wherein agglomerating comprises briquetting or pelletizing of the pre-mix, preferably die-die, disc-die or extrusion pelletizing of the pre-mix.

[0184] 5. The method according to any one of the preceding Clauses, wherein the agglomerating and carbonating steps are simultaneous.

[0185] 6. The method according to any one of the preceding Clauses, wherein the active carbonation process comprises adding water to the cementitious binder or plastic aggregate, such as by manual watering, an automated watering system or exposing the plastic aggregate to rain.

[0186] 7. The method according to any one of the preceding Clauses, wherein the active carbonation process comprises providing an increased airflow through the plastic aggregate.

[0187] 8. The method according to any one of the preceding Clauses, wherein the active carbonation process comprises heating the plastic aggregate.

[0188] 9. The method according to any one of the preceding Clauses, wherein the active carbonation process comprises exposing the plastic aggregate to a source of C02-enriched gas.

[0189] 10. The method according to Clause 9, wherein the source of C02-enriched gas is obtained by direct air capture.

[0190] 11. The method according to Clause 9, wherein the source of C02-enriched gas is an industrial flue gas.

[0191] 12. The method according to any one of the preceding Clauses, wherein the second composition further comprises at least one inorganic base.

[0192] 13. The method according to any one of the preceding clauses, wherein the size distribution of the particles of plastic is between 0.1 mm to 6 mm, preferably 0.2 mm to 5 mm, more preferably 0.2 mm to 4 mm, even more preferably 0.2 mm to 3 mm, yet more preferably 0.2 mm to 2 mm.

[0193] 14. The method according to any one of the preceding clauses, wherein the at least one cementitious binder is selected from GGBS, cement or fly ash, Portland cement or mixtures thereof, preferably GGBS.

[0194] 15. The method according to clauses 12 to 14, wherein the at least one inorganic base comprises an alkali metal hydroxide, an alkali metal oxide or an alkali metal carbonate or mixtures thereof, preferably sodium hydroxide, sodium carbonate, calcium oxide or mixtures thereof.

[0195] 16. The method according to any one of the preceding clauses, wherein the carbonated plastic aggregate is in the form of granules.

[0196] 17. The method according to clause 16, wherein the width of the carbonated plastic aggregate granules is 0.05 mm to 10 mm, preferably 0.06 mm to 8 mm.

[0197] 18. The method according to clause 16 or 17, wherein the aspect ratio between the length of the granules and the width of the granules is 0.05 to 20, preferably 0.25 to 4.

[0198] 19. The method according to any one of the preceding clauses, wherein the plastic is a synthetic or semi-synthetic plastic, or a rubber, preferably a synthetic or semi-synthetic plastic, more preferably a synthetic plastic.

[0199] 20. The method according to any preceding clause, wherein the plastic is derived from a plastic-based foam, preferably the plastic-based foam comprises polyurethane (PUR) or polyisocyanurate (PIR), preferably PUR.

[0200] 21. The method according to any preceding clause, wherein the plastic is derived from waste plastic, such as a waste plastic-based foam.

[0201] 22. The method according to any preceding clause, wherein the weight ratio of plastic to cementitious binder in the pre-mix and / or the plastic aggregate is 2: 1 to 1 :7.

[0202] 23. The method according to any preceding clause, wherein the weight ratio of water to cementitious binder in the pre-mix and / or the plastic aggregate is 0.2 to 0.6, preferably 0.3 to 0.5.

[0203] 24. The method according to any one of clauses 12 to 23, wherein the weight % of inorganic base in the pre-mix and / or the plastic aggregate is between 0.1 % w / w and 15% w / w of the cementitious binder, preferably between 2% w / w and 10% w / w of the cementitious binder.

[0204] 25. The method according to any preceding clause, further comprising the step of adding an additive (preferably a mineral) during or between any of steps (i), (ii) or (iii).

[0205] 26. The method according to clause 25, wherein the additive is added to the first composition during or after step (i), preferably after step (ii) and before step (iii).

[0206] 27. The method according to any preceding clause, further comprising the step of adding a pigment during or between any of steps (i), (ii) or (iii).

[0207] 28. The method according to clause 27, wherein the pigment is added to the first composition during or after step (i), preferably after step (i) and before step (iii).

[0208] 29. The method according to any preceding clause, further comprising the step of adding a filler during or between any of steps (i), (ii) or (iii), preferably wherein the filler is limestone and / or calcined clay and / or microsilica.

[0209] 30. The method according to clause 29, wherein the filler is added to the first composition during or after step (i), preferably after step (i) and before step (iii).

[0210] 31. A method of carbonating a plastic aggregate pellet, the method comprising:

[0211] i. providing a plastic aggregate pellet, the plastic aggregate pellet comprising a) plastic particles, b) at least one cementitious binder comprising at least one metal oxide or at least one metal silicate, and c) water,

[0212] ii. carbonating the at least one metal oxide or at least one metal silicate by an active carbonation process to obtain a carbonated plastic aggregate.

[0213] 32. The method according to clause 31, wherein the weight ratio of plastic to cementitious binder is between 2: 1 and 1 :7.

[0214] 33. The method of clause 31 or 32, wherein the size distribution of the particles of plastic is between 0.2 mm to 5 mm, preferably 0.2 mm to 4 mm, more preferably 0.2 mm to 3 mm, even more preferably 0.2 mm to 2 mm.

[0215] 34. The method of any one of clauses 31 to 33, wherein the at least one cementitious binder is selected from GGBS, cement or fly ash, Portland cement or mixtures thereof, preferably GGBS or cement, preferably cement.

[0216] 35. The method of any one of clauses 31 to 34, wherein the plastic aggregate particles comprise at least one inorganic base.

[0217] 36. The method of clause 35, wherein the at least one inorganic base comprises an alkali metal hydroxide, an alkali metal oxide or an alkali metal carbonate or mixtures thereof, preferably sodium hydroxide, sodium carbonate or mixtures thereof.

[0218] 37. The method of any one of clauses 31 to 36, wherein the plastic is a synthetic or semi-synthetic plastic, or a rubber, preferably a synthetic or semi-synthetic plastic, more preferably a synthetic plastic.

[0219] 38. The method of any one of clauses 31 to 37, wherein the plastic is a plastic-based foam, preferably the plastic-based foam comprises polyurethane (PUR) or polyisocyanurate (PIR), preferably PUR.

[0220] 39. The method of any one of clauses 31 to 38, wherein the plastic is derived from waste plastic, such as waste plastic-based foam.

[0221] 40. The method of any one of clauses 31 to 39, wherein the weight ratio of water to cementitious binder is 0.2 to 0.6, preferably 0.3 to 0.5.

[0222] 41. The method of any one of clauses 35 to 40, wherein the weight % of inorganic base is 0% w / w to 15% w / w of the cementitious binder, 0.1% w / w to 15% w / w of the cementitious binder, preferably 2% w / w to 10% w / w of the cementitious binder.

[0223] 42. The method of any one of clauses 31 to 41, wherein the plastic aggregate particles further comprise at least one additive, preferably the at least one additive is an admixture, a strength enhancing agent, a rheology modifier, a pigment or a fibre, preferably a pigment.

[0224] 43. The method of clause 42, wherein the at least one additive is a mineral.

[0225] 44. The method of any one of clauses 31 to 43, wherein the plastic aggregate granules comprise 0.01 wt% to 5 wt% of at least one additive.

[0226] 45. The method of any one of clauses 31 to 44, wherein the plastic aggregate granules further comprise at least one filler, preferably at least one filler is limestone, sand, wood, clay, concrete dust, microsilica or charcoal, preferably limestone and / or calcined clay and / or microsilica.

[0227] 46. The method of clause 45, wherein the plastic aggregate granules comprise 0.01 wt% to 40 wt% of at least one filler.

[0228] 47. The method of any one of clauses 31 to 46, wherein the plastic aggregate granules comprise calcined clay, limestone, high strength cement.

[0229] 48. A concrete composition comprising carbonated plastic aggregate obtained by any one of clauses 1 to 47.

[0230] 49. A concrete block comprising carbonated plastic aggregate obtained by any one of clauses 1 to 47.

[0231] Example

[0232] Materials

[0233] The following supplied materials were used:

[0234] • Cement supplied by Hanson

[0235] • Ground Granulated Blast Furnace Slag (GGBS) supplied by Hanson

[0236] • Ground Granulated Blast Furnace Slag (GGBS) supplied by Lkab

[0237] • Coarse aggregate (10mm limestone) supplied by MKM Building Supplies

[0238] • Fine aggregate (sharp sand - 0-4mm) supplied by MKM Building Supplies

[0239] • Water

[0240] • PUR plastic aggregate (derived from PUR rigid foam)

[0241] • NaOH supplied by Inovyn

[0242] • Na2C03 supplied by DirectChem

[0243] • Graphene suspension supplied by Graphene Star

[0244] • Limestone powder supplied by Longcliffe

[0245] • Calcined clay supplied by Materials Marketing

[0246] • High strength cement (HSC) supplied by Hanson

[0247] Example 1 - Manufacture of plastic aggregate

[0248] Mix design:

[0249] • Preferred mix proportions

[0250] PUR: GGBS 1 : 1.2

[0251] Water / GGBS 0.4

[0252] Sodium hydroxide at 5% w / w of GGBS

[0253] Sodium carbonate at 5% w / w of GGBS

[0254] Method:

[0255] Upon receipt of the PUR rigid foam pellets / powder from the recycler or manufacturer, the plastic is processed (pelletised, sieved and re-formulated to the desired size distribution (greater than 0.2 mm and less than 4 mm)).

[0256] The desired amount of plastic powder (20.8 kg) and GGBS (25 kg) is added to a paddle mixer and stirred together for a few minutes to ensure the two materials are fully dispersed.

[0257] The activators (sodium hydroxide 150 g and sodium carbonate 150 g) are added to the required water (10 kg). The solution is stirred vigorously until the chemicals are fully dissolved. At room temperature (20-25 °C), this sodium carbonate solution can be unstable as the concentration is above the solubility limit. However, the solubilisation of the NaOH generates enough heat to increase the solubility of the sodium carbonate and fully dissolve the chemicals.

[0258] Once the solution is prepared (before it cools and causes the sodium carbonate to precipitate), it is added to the PUR and GGBS in the mixer while the stirring continues.

[0259] Once all the solution has been added, the mixture is left to stir for a few minutes until a uniform wet powdery mixture (aggregate mix) is obtained.

[0260] The process of the pelletiser begins with the "base mix" (sand, flour, wood chips and vegetable oil) being passed through the machine and pre-heated. In this way, the temperature of the processing mould is already high enough to produce the desired accelerated curing effect on the pellets when the aggregate mix is processed. Typically, the temperature range is 50°C to 100°C. The pelletising mould is typically a disc or ring with a series of countersunk holes of a set compression ratio, the mould hole diameter being 6mm. A knife is used to cut the formed plastic aggregate to the desired length and produce a size distribution. The compression value of the mould is the ratio of the mould hole diameter to the mould thickness, which is 27mm, so the compression value is 4.5. Depending on the aggregate produced and the desired application, the compression value ranges from 4 to 8.

[0261] The aggregate mix is processed through the pelletiser (screened at the un-cured and wet stage to remove fines (<2mm) and the fines are collected for recycling back into the system. The pellets >2mm come out of the screen and onto a conveyor belt and into bulk bags, which are kept warm for a few days and left to cure for at least 4 days.

[0262] Once the plastic aggregate is fully cured, it is again screened using a 2mm screen to remove any fines, which are then collected into bulk bags and ready for use in concrete applications, however, the curing process of the GGBS in the aggregate continues for several weeks and undergoes carbonation, which further increases the strength of the aggregate. Any un-reacted GGBS remaining in the aggregate before use is expected to react with the cementitious binders present in the concrete, such as Portland cement, due to the high alkalinity of Portland cement.

[0263] Compressive strength testing

[0264] The compressive strength of precast concrete made using plastic aggregate pellets (25% by volume of the large aggregate) was compared to precast concrete in which the same volume (25%) of large aggregate was replaced with:

[0265] • plastic aggregate mix cured directly without pelletising to show that forming the aggregate without the heating and pressing of the present invention results in concrete with worse performance than the concrete of the present invention,

[0266] • pure PUR pellet aggregate without GGBS and chemicals to show that the cementitious binders can increase the strength of the concrete of the present invention,

[0267] • PUR powder to demonstrate that adding PUR to concrete without forming it into larger particles results in concrete with worse performance than the concrete of the present invention.

[0268] The mix design used for the preparation of the precast concrete is summarized in Table 1.

[0269] Table 1. Mix design of the precast concrete.

[0270]

[0271] The concrete was cast in 10 x 10 cm molds and crushed after 2 and 7 days of curing (3 molds each time). Figure 1 The results are summarized in Table 3.

[0272] Figure 1 It is shown that the concrete comprising plastic aggregates has a higher compressive strength compared to concrete comprising (i) a plastic aggregate mixture (i.e. cured without granulation), or (ii) pure PUR granules or (iii) PUR powder. The concrete comprising plastic aggregates has a higher compressive strength after 2 and 7 days of curing.

[0273] To better show the segregation of PUR in the concrete and the better dispersibility of the plastic aggregate, two more mixtures were made in which only PUR plastic or plastic aggregate granules were used as aggregates.

[0274] The mixtures were prepared by putting 2 kg of cement in a 5 L bucket and then filling the bucket with plastic aggregate granules or PUR powder to achieve the same volume of ingredients. The amount of water needed to reach a similar consistency was added to the mixtures. More water was needed for the powdered PUR. The mix design used is summarized in Table 2.

[0275] Table 2. Mix design of the precast concrete with plastic aggregate granules or PUR powder.

[0276]

[0277] The compressive strength and density of the concrete are summarized in Table 3.

[0278] Table 3. Compressive strength and density of the concrete.

[0279]

[0280] Figure 2 Pictures of concrete cubes are shown, showing mix 1 (left), mix 2 (middle bottom) and mix 3 (right). The top picture is of a concrete cube corresponding to mix 2.

[0281] Figure 2 Mix 1, mix 2 and mix 3 in Table 2 and Table 3 correspond to mix 1, mix 2 and mix 3 shown in Table 2 and Table 3.

[0282] From Figure 2It can be seen that the concrete cubes corresponding to mix 2 and mix 3 contain more cracks on the surface compared to the concrete cubes corresponding to mix 1. In addition, due to segregation, the top picture in Figure 1 shows the top picture in Figure 1. Figure 2

[0283] These results show that the addition of plastic aggregate pellets improves the dispersion of the plastic in the concrete and increases the strength of the concrete.

[0284] The effect of the activators sodium hydroxide and sodium carbonate was tested by measuring the compressive strength of GGBS-based concrete over time using sodium hydroxide or sodium carbonate alone (10% by weight of GGBS) and a mixture of both (5% by weight of GGBS each). The mix design of the three samples is summarised in Table 4.

[0285] Table 4. Mix design of GGBS-based concrete.

[0286]

[0287] The concrete was cast in 10 x 10 cm moulds and crushed after 1 day, 3 days and 7 days of curing (3 moulds each time). Figure 3 The results are summarised in Figure 1.

[0288] Figure 3 The effect of sodium hydroxide and sodium carbonate (“activators”) on the curing of GGBS is shown. The use of sodium hydroxide alone can accelerate the growth of early strength, with the strength after one day comparable to the strength when both chemicals are used simultaneously. But after this, the strength remains lower. The addition of sodium carbonate does not affect the early strength (after 1 day) but significantly increases the final strength. Thus, a technical advantage can be obtained when one chemical, or a combination of two or more chemicals, such as sodium hydroxide and sodium carbonate as shown, is present. In summary, the activator solution for GGBS enables faster early strength growth and higher final strength.

[0289] Conclusion

[0290] The compressive strength of concrete made with the same volume of plastic aggregate pellets, plastic aggregate mixture, pure PUR pellets and PUR powder replacing 25% by volume of the large aggregate was significantly higher than the plastic aggregate pellets of the present invention. This demonstrates that the method, in particular the presence of heat and pressure (e.g. a pelletiser), cementitious binder and inorganic alkali activator, improves the properties of the final concrete obtained when incorporating waste plastic. The method is essentially an effective way of improving the dispersion and compatibility of the waste plastic in the concrete matrix.

[0291] Example 2 - Manufacture of graphene-containing plastic aggregate​

[0292] Method

[0293] The PUR rigid foam was treated (pelletized, sieved and re-formulated to the desired size distribution (between 0.2 mm and 4 mm) as described in Example 1 to Example 3.

[0294] The desired amount of plastic powder and GGBS were added to a paddle mixer and stirred together for a few minutes to ensure the two materials were well dispersed. While continuing to stir, the graphene was added by weighing in different amounts of the dispersion suspension and then adjusting the amount of water added, taking into account the water already added in the graphene suspension, so that the total amount of water added was always the same for all granules. Sample 1 was prepared as a control sample with no graphene added. The amounts of materials used are summarised in Table 5.

[0295] Table 5 - Mix design for graphene containing plastic aggregates

[0296]

[0297] Once all the required amount of water had been added, the mixture was continued to be stirred for a few minutes until a uniform wet powdery mixture (aggregate mix) was obtained.

[0298] Each aggregate mix was processed through a pelletiser and collected into a plastic tub and left to cure for at least 4 days. Once the graphene reinforced plastic aggregates were fully cured, they were analysed and used for concrete testing.

[0299] Resistance to rolling

[0300] As an in-house modification of the Los Angeles test (BS EN 1097-2), a tumbler was used to test the strength and resistance to rolling of the aggregates.

[0301] The aggregates were tumbled for 20 hours and the % change in mass of the fines (<2mm) was measured. The results are shown in Figure 4 .

[0302] The less fines there are after tumbling, the higher the strength of the granules tested.

[0303] Figure 4 It is shown that the strength of Sample 2, Sample 5 and Sample 6 were higher than the control (Sample 1) which did not contain graphene. The strength of Sample 3 and Sample 4 were slightly lower than the control. Nonetheless, as described below, all the plastic aggregates containing graphene produced stronger concrete compared to the appropriate comparison without graphene.

[0304] Compressive strength of precast concrete

[0305] Precast concrete was prepared by replacing 25% and 50% of the bulk aggregate with graphene-plastic aggregate pellets. Concrete samples were labeled CX_Y, where X corresponds to the plastic aggregate sample numbers given above (samples 1 to 6 in Table 5), and Y is the volume percentage of the bulk aggregate replaced. The mix design is shown in... Figure 6 middle.

[0306] Table 6 – Mix Design for Concrete Containing Graphene-Plastic Aggregate

[0307]

[0308] The compressive strength recorded after 7 days of curing is shown in Figure 5 middle.

[0309] Figure 5 It was shown that the strength of all compositions C2_25 to C6_25 (i.e. graphene-containing) was higher than that of C1_25 (graphene-free). Figure 5 The study also showed that the highest replacement rate of large aggregates (50% - C1_50 and C3_50) resulted in lower-than-expected strength. However, concrete made from the samples that achieved the best results in the tumble test (Samples 2, 5, and 6) also had higher strength than concrete made using the control aggregate (Sample 1). This indicates that adding graphene increases strength by 10% to 17%.

[0310] Conclusion

[0311] Adding graphene as an additive to plastic aggregates improves the strength of the plastic aggregates and increases the strength of concrete containing graphene-containing plastic aggregates by 10% to 17%.

[0312] Example 3 - Manufacturing plastic aggregates using binders and without alkaline activator solutions

[0313] method

[0314] As illustrated in the previous example, the PUR rigid foam was processed (granulated, sieved, and reformulated to the desired size distribution (between 0.2 mm and 4 mm).

[0315] Add the desired amounts of plastic powder and binder (GGBS, limestone, calcined clay, and HSC) to a paddle mixer and stir for several minutes to ensure thorough dispersion of the two materials. While continuing to stir, add the required amount of water and continue stirring the mixture for several minutes until a homogeneous wet powder mixture (aggregate mixture) is obtained. Prepare a sample with a binder:PUR ratio of 1:5. The amounts of materials used are summarized in Table 7.

[0316] Table 7 - Mix design of plastic aggregates without the use of an alkaline activator solution

[0317]

[0318] The aggregate mixture was processed through the granulator as described above and sieved in a non-cured and wet state to remove fines (<2 mm). The granules >2 mm collected from the sieve were collected in a plastic tub and left to cure for at least 4 days. Once the plastic aggregate was fully cured, it was analysed.

[0319] Resistance to tumbling

[0320] The mass change % of fines (<2 mm) was measured to be 40.6% after 20 hours of tumbling. If the aggregate had not experienced some degree of curing within 4 days, it would be expected that more than 90% of the fines would have been completely broken down.

[0321] Due to the use of HSC, it is expected that the strength of the aggregate will increase further over time.

[0322] This result shows that the curing of the binder mixture can be achieved using a substance similar to HSC in place of a water-soluble alkaline activator.

[0323] Example 4 - Manufacture of coloured aggregates

[0324] Method

[0325] Coloured granules were prepared by preparing the aggregate as described above, but with the addition of pigment to the powder in the paddle mixer and mixing together for a few minutes to ensure the material was fully dispersed. For each colour, 2 levels of pigment were used, 1% and 3.7% of the total mass, replacing part of the PUR. The granules were labelled XY-1 or XY-2, where X represents the colour of the pigment used (R: red, G: green, B: blue, Y: yellow, BK: black) and Y is the mould aperture (4 mm, 6 mm or 8 mm) and -1 or -2 refers to the level of pigment in the mixture (1 corresponds to the lower percentage, 1%; 2 corresponds to the higher percentage, 3.7%).

[0326] The amounts of materials used are summarised in Table 8.

[0327] Table 8 - Mix design for the manufacture of coloured plastic aggregates

[0328]

[0329] Once all the required water has been added, the mixture is left to continue mixing for a few minutes until a uniform wet powdery mixture (aggregate mixture) is obtained.

[0330] Each aggregate mixture was processed through the granulator using 4 mm, 6 mm, and 8 mm dies, then collected into plastic tubs and left to cure for 7 days.

[0331] After 7 days of curing, each sample was subjected to the anti-rolling test to verify that the presence of pigment did not affect the stability of the pellets. Results are discussed below.

[0332] In another test, concrete cubes made with the colored pellets were also exposed to sunlight for several days to test the ultraviolet light stability of the pigments. Results are discussed below.

[0333] Anti-rolling

[0334] After 20 hours of rolling, the mass change % of the fines (<2 mm) was measured. Results are shown in Figures 6 to 8

[0335] Figure 6 Results obtained using 4 mm pellets are shown.

[0336] Figure 7 Results obtained using 6 mm pellets are shown.

[0337] Figure 8 Results obtained using 8 mm pellets are shown.

[0338] Overall, Figures 6 to 8 Strength of the 4 mm pellets was higher than the other 2 sizes (less fines after rolling) because the smaller die diameter results in greater pressure on the material as it passes through the granulator. There was not much difference between 6 mm and 8 mm. For both 4 mm and 6 mm pellets, the 2 different percentages of pigment did not seem to affect the strength of the pellets, with the amount of fines after rolling comparable to the control without pigment for most of the pellets. The red pigment in both 4 mm and 6 mm pellets, the black pigment for 4 mm pellets, and the green pigment for 6 mm pellets resulted in 10% to 30% more fines after rolling than the control. However, this effect did not strengthen with increasing amounts of the same pigment in the mixture, suggesting that it can not be related to the pigment itself, but to an error in the testing method.

[0339] For 8 mm pellets, the addition of pigment resulted in stronger pellets for each color and percentage of pigment in the mixture.

[0340] Sunlight exposure

[0341] Some of the colored pellets and control pellets were used as aggregate to make concrete, and the cubes were partially exposed to sunlight and partially not exposed to sunlight to verify the stability of the plastic and color in the sunlight. Setup is shown in Figure 9 and Figure 10 ​Mid.

[0342] Figure 9 Four stacks of cubes, two cubes per stack, and a control cube are shown.

[0343] Figure 10 The top cubes and the upper half of the control cube are shown partially exposed to sunlight; and the bottom cubes and the lower half of the control cube are shaded.

[0344] The cubes were exposed for 2 months. The contrast between the exposed and unexposed cubes reveals that the color of the pigments is not affected by sunlight. The concrete surface exposed to sunlight but containing pigmented plastic aggregates did not observe a yellowing.

[0345] However, the control concrete (without pigments) yellowed in the sunlight.

[0346] Conclusion

[0347] Concrete blocks containing plastic will yellow over time when exposed to sunlight, which is undesirable. Coloring the plastic aggregate is an advantage because the yellowing of the concrete containing the colored aggregate will be diminished or no longer visible, while the color of the pigments is not affected by sunlight.

[0348] Example 5 - Manufacture of carbonated plastic aggregate

[0349] Theoretical calculation of carbonation:

[0350] - mass of calcium oxide (kg)

[0351] - percentage of calcium oxide present in the sample

[0352] - mass of plastic aggregate (kg)

[0353] - moles of calcium oxide in the sample

[0354] - molar mass of calcium oxide

[0355] - maximum mass of carbon dioxide that can react with the sample

[0356] - moles of carbon dioxide in the sample

[0357] - mass of magnesium oxide (kg)

[0358] - percentage of magnesium oxide present in the sample

[0359] - moles of magnesium oxide in the sample

[0360] - molar mass of magnesium oxide

[0361] - maximum sum of masses of carbon dioxide that can react with the calcium oxide and magnesium oxide components

[0362]

[0363] Moles of CaO:

[0364]

[0365] Stoichiometric ratio of 1:1

[0366] CaO + H2O Ca(OH)2

[0367] H2O + CO2 ⇌ H2CO3

[0368] Ca(OH)2 + H2CO3 CaCO3 + 2H2O

[0369] Overall equation

[0370] CaO + CO2 CaCO3

[0371] =

[0372]

[0373]

[0374]

[0375] Stoichiometric ratio of 1:1

[0376] MgO + H2O Mg(OH)2

[0377] H2O + CO2 ⇌ H2CO3

[0378] Mg(OH)2 + H2CO3 MgCO3 + 2H2O

[0379] Overall equation:

[0380] MgO + CO2 MgCO3

[0381] =

[0382]

[0383] Results

[0384] In a similar manner to that described in Example 1 and Example 2, an aggregate made from GGBS and sand was prepared using a granulator. After curing for 24 hours, the sample was separated into Sample 5-01, Sample 5-02 and Sample 5-03.

[0385] Sample 5-01 was a control and was vacuum packed to minimise exposure to the atmosphere. Sample 5-02 was the aggregate as it came from the granulator, unmodified (such as sieved) and contained larger particles. Sample 5-03 was granulated to reduce the particle size to increase the carbonation rate and was spread out on a plastic tray and placed next to Sample 5-02.

[0386] The aggregate was left in its various containers for 4 weeks before being sent for external analysis.

[0387] Calculation Example

[0388] 1 kg of aggregate contains 4.38% CO2. The ratio derived is 95.62:4.38 (sample:CO2)

[0389] The maximum amount of CO2 that 1 kg of the mixture can absorb is 0.3825 kg CO2, the ratio derived is 1:0.3825 (sample:CO2).

[0390] The maximum percentage of CO2 derived is CO2 content

[0391] The % of the total maximum that can then be calculated is

[0392]

[0393] The same calculation method was used for Sample 5-02 and Sample 5-03.

[0394] Table 9: % CO2 measured by external testing and % compared to maximum theoretical result

[0395]

[0396] As the % CO2 content of Sample 5-01 was lower than the other samples, this indicates that a significant degree of passive carbonation occurs when aggregate is made from GGBS when exposed to air for 4 weeks.

[0397] The amount of C02% for sample 5-01 was surprisingly high, which can be caused by a number of factors, such as the carbonation reaction occurring at a faster rate, and significant carbonation occurring within the first 24 hours after sample preparation. Alternatively, it can also be due to external testing, as it is not possible to determine whether the sample was exposed to atmosphere for about a week prior to testing.

[0398] Conclusion

[0399] This experiment shows that the aggregate according to the present application has suitable properties so that it can undergo carbonation, and using only passive carbonation, a carbonation rate of up to 27% is achieved within 4 weeks. This demonstrates the potential of plastic aggregate carbonation. With the adoption of an active carbonation step, in addition to or instead of passive carbonation, the carbonation rate of the aggregate is expected to increase to 100%. Furthermore, active carbonation will greatly increase the carbonation rate, enabling faster storage of C02, and enabling the aggregate to be subsequently used in products / applications.

[0400] Example 6 - Active carbonation of GGBS-based aggregate

[0401] A GGBS-based aggregate (sample 8) was produced using a die pelletiser.

[0402] The sample was prepared by mixing the dry components, then adding the inorganic alkali solution and water. The resulting mixture can be described as able to be "snowballed", i.e. the mixture is able to stick together when squeezed by hand.

[0403] The die pelletiser was preheated using a "clean mix" consisting of non-hardening material, such as a mixture of wood chips, sand and water. The die consisted of holes of 6 mm in diameter. The samples were bagged immediately after production and sealed for curing.

[0404] Table 10: Material specification for producing sample 8.

[0405]

[0406] After 1 day of curing (hardening), 25 wt% water was added to the samples (relative to the sample weight), after which they were placed in a metal bowl in a reaction vessel to be exposed to carbon dioxide.

[0407] During the test, the air in the vessel was completely removed using a vacuum pump, after which 99.9% carbon dioxide was slowly injected into the vessel until a pressure of 2 bar was reached. Once the pressure was reached, the connection to the carbon dioxide was closed. The samples were then exposed to room temperature for 76 hours to react.

[0408] After 76 hours, the samples were removed from the vessel and dried at 100°C for 24 hours.

[0409] The samples were then analysed by placing them in dilute HC1 which releases CO2 from CaCC and MgCC in the sealed containers. The increase in pressure generated by the CO2 is directly proportional to the amount of carbonate in the sample and this is compared to a calibration curve to obtain the total carbonate % in the sample.

[0410] Table 11: Total carbonate % and maximum carbonation for sample 8

[0411]

[0412] The GGBS used in sample 8 has a typical CaO content of 40% and a MgO content of 10%. Based on the mix design, the maximum carbonation that can occur is 0.19 kg CO2 / kg sample 8.

[0413]

[0414] At 100% carbonation, the weight of the aggregate would increase by 19% giving a maximum CO2 uptake of 16% or carbonate % of 36%.

[0415] This experiment shows that GGBS based aggregates are able to undergo active carbonation. Sample 8 achieved significant carbonation, reaching 44.2% of the maximum carbonation possible. Therefore, active carbonation results in increased carbonation and a faster carbonation rate compared to passive carbonation (see Example 5 where samples 5-02 and 5-03 only achieved 27% of the maximum carbonation after a significantly longer period of time (i.e. 4 weeks)).

[0416] Example 7A: Active carbonation using added water (bulk aggregate carbonation)

[0417] Four different samples were prepared using the same mix as sample 8 (Example 6) but were investigated with different parameters such as time and additional water content. The samples were prepared using the same method described in Example 6. After hardening for 24 hours, 60 kg of the sample was loaded into a bulk bag.

[0418] For sample 9, 10% additional water (6 kg) was sprayed evenly over the material. Due to the absorbency of the mix, the water was able to penetrate throughout the 60 kg sample.

[0419] For samples 10 and 11, the 60 kg of sample was fully immersed in water and drained so that the moisture content was 42%.

[0420] After the specified time period, the top 30 kg of material in the bulk bag was removed from the surface and 4 kg of material was taken from the deepest part of the bag. This was to ensure that carbonation was occurring in the deep parts of the aggregate pile.

[0421] 4kg of material was placed in an oven at 100°C for 24 hours to stop the carbonation process (as moisture is required to dissolve atmospheric carbon dioxide to allow the carbonation reaction to occur).

[0422] It should be noted that sample 8 had no additional water added but retained the natural moisture content of 10% remaining from the initial mix.

[0423] Table 12: Carbonation results for samples made using the mix described for sample 8

[0424]

[0425] After drying, the samples were sent for carbonate testing in accordance with the BS EN 196: Part 2: 2013 standard. The carbonate was then converted to maximum carbonation possible.

[0426] The results show that a significant amount of carbonation occurs to the mix during storage of the aggregate for up to a week. This can be increased by adding additional moisture. This is thought to allow more carbon dioxide to dissolve in the aggregate which then reacts with the calcium and magnesium on the GGBS.

[0427] Example 7B: Surface active carbonation with added water

[0428] In another example, the aggregate was spread over a larger area increasing the available surface area for carbon dioxide dissolution. 4kg of aggregate made using the same mix as sample 8 (see example 6) was spread evenly over a plastic tray. Initially 1.5kg of water was sprayed over the surface of sample 12 and 200ml of water was sprayed every 2 days to keep the surface wet.

[0429] Both samples were left for 14 days after which both samples were dried at 100°C for 24 hours. After this, the samples were tested for carbonate in accordance with the BS EN 196: Part 2: 2013 standard.

[0430] Table 13: Maximum carbonation results for spread aggregate.

[0431]

[0432] The results show that adding water to the sample increases the amount of carbonation that has occurred (in line with the bulk aggregate carbonation results). Overall, the maximum carbonation results are higher. This is thought to be mainly due to the aggregate being spread over a larger area increasing the exposed surface area of the aggregate (rather than increasing the time exposed to CO2).

[0433] Example 8: Environmental impact of carbonated GGBS based and cement based aggregates

[0434]

[0435] Note: The skilled person will be aware that in calculating the carbon footprint of a material, Al refers to the raw material, A2 refers to the transportation of the material to the supplier site, and A3 refers to emissions due to manufacturing.

[0436] The carbonation potential of both of these aggregates used in this example (GGBS and CEM II aggregate) at 100% carbonation is 0.19 kg CO2 / kg, so the 0.084 kg CO2 / kg for sample 8 is based on 0.442*0.19 = 0.084. The carbonation rate for sample 8 (GGBS based) is 44.2%, which means that 1 kg of product will absorb 0.084 kg CO2. Once this sequestered carbon is removed from the total emissions of the raw material (0.0387 kg CO2e / kg), the carbon footprint of the GGBS based aggregate is -0.0453 kg CO2e / kg.

[0437] This shows that using GGBS as the binder for the aggregate allows for the production of a negative carbon aggregate when the aggregate has been actively carbonated.

[0438] The aggregate produced using CEM II (sample 13) that has undergone the same carbonation has a carbonation of 51.4%, which means that 1 kg of aggregate will absorb 0.098 kg CO2. Once this sequestered carbon is removed from the total emissions of the raw material (0.35 kg CO2e / kg), the carbon footprint of the CEM II based aggregate will be 0.25 kg CO2 / kg.

[0439] This shows that using cement as the binder for the aggregate allows for the production of a low carbon aggregate when the aggregate has been actively carbonated compared to not actively carbonating the aggregate. It is noted that the aggregate described herein is a high strength lightweight aggregate. Crucially, this means that while similar carbon footprints can occur for other types of lightweight cement-binder aggregate, the carbon footprint of the aggregate of the present invention is significantly lower than other High Intensity The carbon footprint of the aggregate of the present invention is significantly lower than other aggregates. The strength of the aggregate is assessed in example 9 below.

[0440] Example 9: Aggregate strength

[0441] A typical carbon footprint for a synthetic lightweight aggregate (LWA) ranges from 0.1 kg CO2 / kg to 0.3 kg CO2 / kg. An example of a synthetic LWA is expanded clay. The carbon footprint of the cement based aggregate in example 8 after active carbonation is 0.25 kg CO2e / kg, with the potential to further absorb around 0.1 kg CO2e / kg.

[0442] While the carbon footprint is similar, the strength of the granules is significantly different. The high strength of the aggregate of the present invention makes it useful for other applications where current LWA cannot be used due to lack of required strength.

[0443] To compare the strength of the aggregate, a standard 10% fines test was performed. This test investigates how much force is required to break the aggregate to produce 10% of the material as "fines". The higher the number, the stronger the material.

[0444] Table 15: Strength comparison results for expanded clay and sample 13

[0445]

[0446] The results show that the strength of the cement-based aggregate is 15.5% higher than the expanded clay. This strength increase can be used to increase the strength of concrete produced using the cement aggregate, or to allow for a reduction in cement usage.

[0447] Example 10: PUR vs sand (passive carbonation)

[0448] The rate of carbonation of a mineral is affected by the available surface area it has to react with carbon dioxide. The initial service life of PUR stems from the use of rigid foam. After the polyurethane has broken down, part of the foam structure is retained. This irregularly angular particle shape of the waste PUR increases the porosity of the aggregate. The increased porosity allows for faster penetration of carbon dioxide into the aggregate compared to using a comparative material.

[0449] To demonstrate this, an aggregate was produced (sample 14) in the same way as sample 8 (example 6), but with the PUR component replaced with sand. Sample 14 can then be subjected to passive carbonation.

[0450] Table 16: Material specification used to produce sample 14.

[0451]

[0452] After 7 days of atmospheric carbonation, the carbonate content of the aggregate was 6.22% resulting in a total carbonate % of 16.4%.

[0453] The GGBS used in sample 14 has a typical CaO content of 40% and a MgO content of 10%. Based on the mix design, the maximum carbonation that can occur is 0.2 kg CO2 / kg sample 8.

[0454]

[0455] At 100% carbonation, the weight of the aggregate will have increased by 20% resulting in a maximum CO2 uptake of 16.7% or carbonate % of 38%.

[0456] Table 17: Carbonate % and maximum carbonation achieved by aggregates produced using PUR and sand after 7 days of passive carbonation.

[0457]

[0458] Table 17 shows that the addition of PUR in the sample improves the passive carbonation of GGBS over the same time period.

[0459] This shows that the potential for carbonation of the PUR based aggregate is greater than the sand based analogue. Importantly, the carbonation of the PUR based aggregate will further increase when active carbonation is used instead of passive carbonation.

[0460] It should be noted that the sand used in sample 14 does have a moisture content of 15%, which was not accounted for in these calculations. If this was accounted for, this would result in a higher concentration of GGBS in the sample, which would subsequently increase the possible maximum carbonation, which would reduce the maximum carbonation occurring in the sand, which would further increase the difference between the sand and the PUR samples.

[0461] The additional moisture in sample 14 would also increase the carbonation rate compared to sample 8, however, the PUR provides a faster carbonation over the same time period compared to achieving this by adding moisture.

[0462] This is a useful property of the aggregate as certain applications desire moisture contents as low as possible, such as in polymer bound concrete or asphalt concrete. These applications can require further drying of the aggregate, which is typically done in fossil fuel fired heating kilns, which is not only costly, but also environmentally damaging.

[0463] The water absorption of the samples can be used as an indication of the porosity of the aggregate. The samples are dried at 100°C for 24 hours until completely dry, then 100g of material is placed in 1 litre of water for 24 hours, then the water is drained from the sample and weighed to determine the water absorption of the material.

[0464] Table 18: Water absorption of samples made from sand and PUR.

[0465]

[0466] Table 18 shows that the water absorption of the materials made with PUR is much higher than the materials made with sand, indicating that the irregular shape of the PUR provides pores for water to penetrate into the material, thus the materials have a higher porosity. The increase in porosity and subsequent increase in surface area allows for faster carbonation. Overall, Example 10 shows that due to the increased porosity of the plastic foam PUR, the carbonation potential of the PUR-based aggregate is higher compared to the sand-based analogue. Importantly, the carbonation % of the PUR-based aggregate is expected to further increase when using active carbonation instead of passive carbonation used to generate the data in Table 17.

[0467] Example 11 : PUR vs. sand (active carbonation)

[0468] In another example, active carbonation was performed on aggregates made with sand and PUR. The samples were produced in the same way as Example 10. After 7 days of curing, the samples were dried at 100°C for 24 hours, after which 25% extra water was added to the samples. The samples were then placed together in a reaction vessel at room temperature and exposed to a 100% carbon dioxide atmosphere at 2 bar pressure for 16 hours. After this, the samples were dried at 100°C for 24 hours and the carbonate % was measured using the procedure described in the BS EN 196: Part 2: 2013 standard.

[0469] Table 19: Active carbonation results for samples made from sand and PUR.

[0470]

[0471] The results in Table 19 show that the aggregate made with sand does not react rapidly with CO2 during the short 16 hour period, but the samples prepared using PUR show significant levels of carbonation.

[0472] The samples made from sand also appear to have similar results to the passive carbonation of the samples, which can indicate that the extent of CO2 penetration into the sand samples does not exceed the extent that has already occurred during the 7 days of passive carbonation.

[0473] This indicates that the plastic (foam PUR) significantly increases the amount of carbonation that can occur during the active carbonation reaction. This can be due to the PUR increasing the porosity, thus enabling other fillers such as sand to be compacted, reducing the penetration of CO2 into the sample.

[0474] The improvement in carbonation due to the PUR cementing the aggregate means that there is a higher reaction efficiency when using more carbon dioxide during the reaction, requiring a reduced pressure, which leads to lower operating costs, energy usage, increased productivity.

Claims

1. A method for manufacturing carbonized plastic aggregate, the method comprising the following steps: (i) Mixing plastic granules with at least one gelling binder comprising at least one metal oxide or metal silicate to form a first composition, wherein the plastic is derived from plastic-based foam; (ii) providing a second composition comprising water; (iii) The first composition and the second composition are mixed together to form a premix; (iv) Aggregate the premix to form plastic aggregate; as well as (v) Carbonizing the at least one metal oxide or metal silicate by an active carbonization process to obtain the carbonized plastic aggregate.

2. The method of claim 1, wherein the agglomeration comprises pressure or non-pressure agglomeration of the premix to form the plastic aggregate.

3. The method according to claim 1 or 2, wherein the agglomeration comprises compressing and heating the premix.

4. The method according to any one of the preceding claims, wherein the agglomeration comprises briquetting or granulation of the premix, preferably die granulation, disc granulation or extrusion granulation of the premix.

5. The method according to any one of the preceding claims, wherein the agglomeration and carbonization steps are simultaneous.

6. The method according to any one of the preceding claims, wherein the active carbonization process comprises adding water to the gelling binder or the plastic aggregate (e.g., by manual watering, an automatic water spraying system, or exposing the plastic aggregate to rain).

7. The method according to any one of the preceding claims, wherein the active carbonization process includes providing an increased airflow through the plastic aggregate.

8. The method according to any one of the preceding claims, wherein the active carbonization process includes heating the plastic aggregate.

9. The method according to any one of the preceding claims, wherein the active carbonization process comprises exposing the plastic aggregate to a CO2-enriched gas source.

10. The method of claim 9, wherein the source of enriched CO2 is obtained by direct air capture or industrial flue gas.

11. The method according to any one of the preceding claims, wherein the second composition further comprises at least one inorganic base, preferably the inorganic base comprising an alkali metal hydroxide, an alkali metal oxide, or an alkali metal carbonate, or a mixture thereof, preferably sodium hydroxide, sodium carbonate, calcium oxide, or a mixture thereof.

12. The method according to any one of the preceding claims, wherein the size distribution of the plastic particles is between 0.1 mm and 6 mm, preferably between 0.2 mm and 5 mm, more preferably between 0.2 mm and 4 mm, even more preferably between 0.2 mm and 3 mm, and even more preferably between 0.2 mm and 2 mm.

13. The method according to any one of the preceding claims, wherein the at least one cementitious binder is selected from GGBS, cement or fly ash, Portland cement or mixtures thereof, preferably GGBS.

14. The method according to any one of the preceding claims, wherein the plastic is a synthetic or semi-synthetic plastic, or rubber, preferably a synthetic or semi-synthetic plastic, more preferably a synthetic plastic.

15. The method according to any of the preceding claims, wherein the plastic-based foam comprises polyurethane (PUR) or polyisocyanurate (PIR), preferably PUR.

16. The method according to any of the preceding claims, wherein the plastic is derived from waste plastics, such as waste plastic-based foam.

17. A method for carbonizing plastic aggregate pellets, the method comprising: i. Providing plastic aggregate pellets, said plastic aggregate pellets comprising a) plastic particles, b) at least one binder comprising at least one metal oxide or at least one metal silicate, and c) water, ii. Carbonizing the at least one metal oxide or at least one metal silicate by an active carbonization process to obtain carbonized plastic aggregate.

18. The method of claim 17, wherein the size distribution of the plastic particles is between 0.2 mm and 5 mm, preferably between 0.2 mm and 4 mm, more preferably between 0.2 mm and 3 mm, and even more preferably between 0.2 mm and 2 mm.

19. The method according to any one of claims 17 to 18, wherein the at least one cementitious binder is selected from GGBS, cement or fly ash, Portland cement or mixtures thereof, preferably GGBS or cement, and more preferably cement.

20. The method according to any one of claims 17 to 19, wherein the plastic aggregate granules comprise at least one inorganic alkali, preferably an alkali metal hydroxide, alkali metal oxide, or alkali metal carbonate, or a mixture thereof, preferably sodium hydroxide, sodium carbonate, or a mixture thereof.

21. The method according to any one of claims 17 to 20, wherein the plastic is a synthetic or semi-synthetic plastic, or rubber, preferably a synthetic or semi-synthetic plastic, more preferably a synthetic plastic.

22. The method according to any one of claims 17 to 21, wherein the plastic is a plastic-based foam, preferably the plastic-based foam comprising polyurethane (PUR) or polyisocyanurate (PIR), preferably PUR.

23. The method according to any one of claims 17 to 22, wherein the plastic is derived from waste plastic, such as waste plastic-based foam.

24. The method according to any one of claims 17 to 23, wherein the plastic aggregate further comprises at least one filler, preferably limestone, sand, wood, clay, concrete dust, silica fume or carbon, preferably limestone and / or calcined clay and / or silica fume.

25. A concrete composition comprising carbonized plastic aggregate obtained by any one of claims 1 to 24.

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