The invention relates to a method as defined in the preamble of claim 1 for the production from recycled aggregate of wet concrete intended for 3D printing.

The invention also relates to a method the 3D printing of concrete components used in construction industry, especially in house construction, or for the 3D printing of concrete parts for a building by using wet concrete.

The invention further relates to wet concrete for 3D printing, as well as to an apparatus for executing the method of claim 1.

In the prior art there are hardly any known uses for demolished concrete except in earth construction, resulting inevitably in a low recycling rate of demolished concrete. House construction by 3D printing wet concrete, e.g. for fabricating foundations and/or producing walls by means of casting in situ, or for manufacturing wall elements or other parts of a building such as foundation elements, is nevertheless in increasing demand.

Concrete structures to be demolished, as well as concrete components, such as apartment buildings, manufacturing plants, bridges, concrete floors in industrial halls, and the like structures, are difficult to utilize because of hazardous materials, such as halogen compounds, contained in these concrete structures, or because of foreign substances in concrete, such as wool, plaster, tiles, bricks, pieces of wire, glass, etc. Concrete industry also produces a considerable amount of surplus concrete, such as surplus concrete elements and other similar components, possibly with the presence of hazardous materials and foreign substances.

It is an objective of the present invention to eliminate or at least to alleviate the problems occurring in the foregoing prior art.

Accordingly, the purpose of the invention is to improve the recyclability of demolished concrete by providing new 3D printing-related possibilities in house construction for the reuse of crushed concrete obtained from demolition rubble. The quality of concrete waste as well as surplus concrete can be influenced first and foremost by applying a proper demolition technique and grading technique to concrete structures comprising concrete waste or surplus concrete, such as buildings, foundations, concrete floors and walls. The purpose is to separate useful coarse-crushed concrete aggregate and concrete blocks from foreign substances as well as from excessive hazardous materials. The proper type of crushing and grading technique applied to concrete structures has a significant effect on the end-product quality.

In the event that crushed concrete derived from demotion rubble is used for the production of wet concrete, which is intended for the 3D printing of concrete components used in house construction or for cast-in-situ manufacturing the walls or foundations of an actual building by means of 3D printing, attention must be paid not only to the foreign substances and hazardous materials left in demolition concrete but also to the requirements on the workability of wet concrete with regard to 3D printing.

In the production of wet concrete, it is further necessary to consider the strength requirements for products manufactured by 3D printing.

Especially in the manufacturing of concrete components such as concrete elements, used in construction sector or in the casting of walls and foundations for structures in situ by means of the 3D printing of wet concrete, it is further necessary to make sure that the filler for concrete is sufficiently finely divided.

Accordingly, the invention relates to a method as defined in claim 1 for the production of wet concrete, which is intended for 3D printing.

More specifically, the invention relates to a method for the production of wet concrete applicable to 3D printing by mixing a binder, especially cement, a filler comprising reclaimed aggregate, and water, as well as possible admixtures such as a plasticizer, in such a way that from the dry matter of concrete is the portion of a binder, especially cement 10-40% by weight, preferably 25-30% by weight, the portion of a filler, especially aggregate, is 90-60% by weight, the total amount of filler (i.e. aggregate) being nevertheless not more than 80% of the wet concrete’s total weight, and said aggregate comprising reclaimed aggregate, such as cleaned crushed concrete 10-100% by weight, preferably 30-50% by weight, and other ag- gregate, such as sand or crushed stone, 90-0% by weight, preferably 50-70% by weight.

The production of reclaimed aggregate comprises the following method steps of:

A) producing cleaned crushed concrete from surplus concrete or concrete waste by removing hazardous materials from said surplus concrete or concrete waste and, if necessary, by crushing the surplus concrete or concrete waste in such a way that, as for organic hazardous materials, the cleaned crushed concrete contains polychlorinated phenyls not more than 1 mg/kg, polyaromatic hydrocarbons not more than 30 mg/kg, and mineral oils (C10-C40) not more than 200 mg/kg;

B) evaluating or determining the target strength (compressive strength) in any of classes (1-3) for a concrete structure made of surplus concrete or concrete waste, or for demolition concrete produced from said concrete structure, especially coarse crushed concrete, or for cleaned crushed concrete obtained from said demolition concrete, in order to produce cleaned and strength-graded crushed concrete:

- strength class 1 , crushed concrete, structural target strength not more than 45 N/mm ² ;

- strength class 2, crushed concrete, structural target strength not more than 45 N/mm ² , yet higher than 30 N/mm ² ,

- strength class 3, crushed concrete, no structural target strength,

C) crushing the cleaned and strength-graded crushed concrete, if necessary, into finer particles, followed by screening the finely crushed and cleaned crushed concrete with a sieving device for producing strength-graded, finely crushed and screened, cleaned crushed concrete included in one of the sieve classes C1-C4;

- class C1 , cleaned, strength-graded, finely crushed and screened crushed concrete, particle size more than 32 mm,

- class C2, cleaned, strength-graded, finely crushed and screened crushed concrete, particle size 16-32 mm,

- class C3, cleaned, strength-graded, finely crushed and screened crushed concrete, particle size 8-16 mm,

- class C4, cleaned, strength-graded, finely crushed and screened crushed concrete, particle size 0-8 mm; D) selecting, for reclaimed aggregate in wet concrete, cleaned, strength-graded, finely crushed and screened crushed concrete, which comprises crushed concrete in strength class 1 or 2 and whose particle size is included in class C3 or C4, preferably in class C4.

It is the basis of the invention that, when wet concrete applicable to 3D printing is produced from crushed concrete, attention is paid both to the purity requirements of crushed concrete and to the strength requirements of wet concrete applicable to 3D printing. The strength class of reusable crushed concrete or surplus concrete should be 1 or 2, because the structural compressive strength of wet concrete used in 3D printing is at least 45 N/mm ² or at most 45 N/mm ² , but more than 30 N/mm ² . The strength requirements of products manufactured by 3D printing are taken into consideration in such a way that the actual recyclable concrete waste or surplus concrete will be subjected to a strength class requirement as regards the compressive strength of concrete waste or surplus concrete. The reusable concrete waste or surplus concrete, or the crushed concrete obtained therefrom, should fulfill the strength class requirement 1 or 2, because the concrete products fabricated from wet concrete used in 3D printing should have a structural target strength (with regard to compressive strength) of not less than 45 N/mm ² or not more than 45 N/mm ² , yet more than 30 N/mm ² .

In the selection of crushed concrete, attention is further paid to the requirements imposed on wet concrete by 3D printing, such that the 3D printing is preferably conducted by using wet concrete with relatively low moisture and the employed filler comprises aggregate which contains finely divided sand and possibly finely divided crushed stone with a particle size of 8-16 mm, as well as recycled (reused) crushed concrete which is finely crushed and screened to a particle size not less than 0-8 mm and/or 8-16 mm.

The result of using a method, wet concrete and/or an apparatus according to the invention is that a new building, or components such as walls of a structure, used in the building process, will have a carbon handprint which is considerably smaller than that of buildings, components or walls constructed with traditional methods. The invention expedites the execution period of construction processes. In addition, the amount of debris at demolition sites will be significantly reduced. Hence, the invention enhances circular economy in construction sector. The invention relates also to wet concrete for 3D printing, said wet concrete having been produced with a method as set forth in claim 1 by mixing cement 10-40% by weight, preferably 25-30% by weight, a filler, especially aggregate, which contains reclaimed aggregate 90-60% by weight, water, as well as possible admixtures such as a plasticizer, whereby, as for the dry matter of wet concrete, the total amount of filler (i.e. aggregate) is not more than 80% by weight of the total weight of wet concrete, and as for said aggregate, the amount of reclaimed aggregate, such as cleaned crushed concrete derived from a demolished concrete structure, is 10-100% by weight, preferably 30-50% by weight, and other aggregate such as artificial aggregate or natural aggregate, especially sand or crushed stone, 90-0% by weight, preferably 50-70% by weight. The reclaimed aggregate selected for wet concrete is crushed concrete, which has been cleaned, strength-graded, finely crushed and screened as defined in claim 1 , and which comprises crushed concrete included in strength class 1 or 2 and has its particle size included in class C3 or C4, preferably in class C4. In addition, the cleaned crushed concrete contains, per kilogram of crushed concrete, either

A) one or more organic hazardous materials, selected from a group (concentration limits for hazardous material presented as total content), including: polychlorinated phenyls 0,01-1 mg/kg, polyaromatic hydrocarbons 0,1-30 mg/kg, and mineral oils (C10-C40) 1-200 mg/kg, or

B) metallic or non-metallic hazardous materials, selected from a group (the content of hazardous material presented as soluble concentration), including fluorides (F) 1-12 mg/kg, sulfates (SC ^2- ) 10-300 mg/kg, and chlorides (CT) 10-200 mg/kg.

What is implied here by hazardous materials are organic and inorganic hazardous substances not included in concrete material.

What is perceived by concrete or concrete material is a hard, stone-like material used for construction work, which typically consists of a filler, cement, water, and possible admixtures. The filler comprises typically a hard, chemically non-reactive substance such as stone or sand of varying particle sizes. The cement comprises typically limestone, clay, and gypsum. Cement reacts with water in such a way that the cement hardens and, upon hardening, binds the maturating concrete together. The properties of maturating concrete can be modified by changing the mixing ratios and the filler’s particle size distribution as well as, for example, by supplement- ing the concrete mix with admixtures, such as plasticizers, a hardening accelerator (e.g. calcium formate, triethanolamine, finely divided silica, etc.), hardening retarders, a deaeration promoter, a corrosion inhibitor, a microbicidal additive, water absorption inhibitors. With regard to the more specific composition and amount of admixtures, reference is made to the compositions and usages of additives commonly known to a person skilled in the art and employed in concrete production, and to prior art technology, such as the industry standards and publications (e.g. publications issued by Betoniteollisuus (Concrete Industry) ry, as well as ASTM Co494/C494M-17).

The design of concrete structures proceeds generally along the lines of Eurocodes EN 1990-1992 and materials of concrete are mainly CE marked and each has its designated European standard. From these standards are further derived limit values for the quality and usage of the materials (cement and cement mixture ingredients, concrete admixtures and aggregate).

Typically, concrete contains cement about 10-30% by weight, a filler 50-80% by weight, water 5-20% by weight, and possible admixtures about 0,5-3% by weight.

The most important ingredients for cement are iron sulfate, fly ash, gypsum, nickel grain and copper slag, blast furnace slag, limestone and silica. Admixtures for cement also often contain non-metallic and metallic compounds considered as hazardous materials, the concentrations of which must be held within acceptable limits when concrete produced from such cement is used as reclaimed aggregate.

The concrete structure, on the other hand, refers to a structure or construction, such as a house, a hall, or a component or part of the structure or construction made mostly of concrete, such as a foundation, stairs, a floor, a ceiling or wall made of concrete.

In the invention, the surplus concrete of concrete industry or dismantled concrete (concrete blocks and coarse crushed concrete) are processed to remove not only foreign substances but also hazardous materials. The hazardous materials are generally removed prior to crushing the surplus concrete or concrete waste into cleaned crushed concrete.

Hazardous materials refer here to organic or inorganic hazardous substances not included in concrete material. Demolition concrete refers here to concrete blocks and/or coarse crushed concrete resulting from the demolition of a concrete structure consisting of concrete waste or surplus concrete.

An alternative embodiment involves analyzing or assessing first the hazardous materials and foreign substances present in surplus concrete or concrete waste used for producing clean crushed concrete. It is after the removal of foreign substances and the removal/reduction the amount of hazardous materials that the surplus concrete or concrete waste is processed into cleaned crushed concrete.

In one embodiment of the method according to the invention, surplus concrete or concrete waste is processed into crushed concrete. The crushed concrete is analyzed and subjected to the removal of foreign substances and possibly also hazardous materials in order to produce cleaned crushed concrete.

As pointed out above, with regard to organic hazardous materials, the acceptable amount of polychlorinated phenyls in cleaned crushed concrete is not more than 1 mg/kg, such as 0,01-1 mg/kg, the acceptable amount of polyaromatic hydrocarbons in cleaned crushed concrete is not more than 30 mg/kg, such as 0,1-30 mg/kg, and the acceptable amount of mineral oils (C10-C40) in cleaned crushed concrete is not more than 200 mg/kg, such as 1-200 mg/kg.

A hazardous materials analysis (hazardous materials survey) is conducted on a to- be-demolished concrete structure of concrete waste prior to its demolition during its material review. The Ministry of the Environment has on November 15, 2019 published a pre-demolition audit guide (Demolition survey - guide for the auditor), which provides information about the best practices for assessing construction and demolition waste flows, i.e. for a pre-demolition survey, to be conducted prior to the demolition or renovation of a building or structure.

Polychlorinated phenyls, i.e. PCB compounds, refer to chlorinated biphenyl products. The general formula of PCB compounds is Ci2Hio- _x Cl _x , wherein x stands for the number (integer) of chlorine atoms, which is within the range of 1-10. The amount of polychlorinated phenyls in crushed concrete is not allowed to be more than 1 mg/kg of crushed concrete. The presence and amount of PCB compounds can analyzed from concrete waste or surplus concrete, or from demolition concrete or crushed concrete obtained therefrom, with the method set forth in standard SFS EN 17322:2020.

Polyaromatic hydrocarbons (PAH) refer to polycyclic aromatic hydrocarbons. These are organic compounds, comprising several fused aromatic rings and having no heteroatoms on the ring. Examples of polyaromatic hydrocarbons include naphthalene, anthracene, phenanthrene, chrysene, benzo(a)pyrene, ben- zo[e]pyrene, benzo[b]fluoranthene, etc.

The amount of polyaromatic hydrocarbons allowed in crushed concrete is not more than 30 mg/kg of crushed concrete. The presence and amount of polyaromatic hydrocarbons can be analyzed from concrete waste or surplus concrete, or from demolished concrete obtained therefrom, especially from concrete rubble, with the method set forth in standard EN 17322:2020.

The presence of polyaromatic hydrocarbons (PAH compounds) in a concrete material can be determined with an appropriate determination method, such as in accordance with standard SFS-EN 15527:2022 or SFS-ISO 18287:2006.

Mineral oils (C10-C40) refer to petroleum hydrocarbons, wherein the carbon chain has a length of 10-40 carbon atoms (C10-C40). Mineral oil is an oil refined by distillation from crude oil.

The amount of mineral oils (C10-C40) allowed in crushed concrete is not more than 200 mg/kg of crushed concrete.

The presence and amount of mineral oils in concrete waste or surplus concrete, or in demolition concrete, such as crushed concrete, obtained therefrom, can be determined with the method defined by standard EN 14039:2004.

Mineral oils (C10-C40), among others, find their way into concrete waste (e.g. a concrete floor to be demolished) generally during use or along with surface materials. Hence, such hazardous substances stay in the surface layer of a concrete structure and can be removed therefrom by grinding or shot blasting.

In one preferred embodiment of the invention, the cleaned crushed concrete is allowed to contain fluoride compounds (F) not more than 12 mg/kg, sulfate ions (SO ₄ ² ’) not more than 300 mg/kg, and chloride ions (Cl) not more than 200 mg/kg. In one preferred embodiment of the invention, the cleaned crushed concrete is allowed to contain hazardous substances as selected from among fluoride ions (F) not more than 12 mg/kg, such as 0,1-12 mg/kg, sulfate ions (SO4 ² ') not more than 300 mg/kg, such as 1-300 mg/kg, and chloride ions (Cl) not more than 200 mg/kg, such as 1-200 mg/kg.

These hazardous substances find their way into surplus concrete or concrete waste, or into demolition concrete obtained therefrom during demolition, often along with a concrete binder, especially cement (e.g. chlorine compounds), whereby the removal thereof from concrete cannot be achieved except by separating the contaminated concrete waste or surplus concrete, or the contaminated demolition concrete, such as crushed concrete, obtained therefrom, out of the clean concrete material.

Alternatively, it is possible to employ a so-called HAS classification technology (Heating Air Classification System), based on the use of hot air (600°C), for removing the hazardous substances of concrete, and especially those of cement, from demolished concrete. In HAS technology, the concrete waste recycling is conducted by heating the concrete in combination with the classification of concrete rubble at high temperature, the process time being 25-40 s. The HAS classification technology has been described e.g. in article Moreno-Juez et al.; Journal of Cleaner Production, Vol 263,1 August 2020, 121515.

The presence and amount of these hazardous materials, containing halogen compounds, in a concrete structure, or in crushed concrete obtained therefrom, can be measured with a percolation test std CEN/TS 14405:2004 conducted on a concrete sample, with a batch test SFS-EN- 12457-3:2012, or with a method as defined in technical report CEN/TR 16192:2020.

In one preferred embodiment of the invention, the cleaned crushed concrete may contain, per kilogram of crushed concrete (presented as the soluble amount of each hazardous substance per kilogram of crushed concrete), antimony (Sb) not more than 0,2 mg/kg, such as 0,001-0,1 mg/kg, arsenic (As) not more than 0,1 mg/kg, such as 0,001-0,1 mg/kg, barium (Ba) not more than 5 mg/kg, such as 0,01-5 mg/kg, cadmium (Cd) not more than 0,02 mg/kg, such as 0,0001-0,02 mg/kg, chromium (Cr) not more than 0,6 mg/kg, such as 0,001-0,6 mg/kg, copper (Cu) not more than 1 mg/kg, such as 0,01-1 mg/kg, mercury (Hg) not more than 0,01 mg/kg, such as 0,0001-0,01 mg/kg, lead (Pb) not more than 0,1 mg/kg, such as 0,001-0,1 mg/kg, molybdenum (Mo) not more than 0,7 mg/kg, such as 0,001- 0,7 mg/kg, nickel (Ni) not more than 0,3 mg/kg, such as 0,001-0,3 mg/kg, vanadium (V) not more than 0,3 mg/kg, such as 0,001-0,3 mg/kg, zinc (Zn) not more than 4 mg/kg, such as 0,01-4 mg/kg, selenium (Se) not more than 0,2 mg/kg, such as 0,001-0,2 mg/kg, fluorides (F-) not more than 12 mg/kg, such as 0,01-12 mg/kg, sulfates (SO4 ² ') not more than 300 mg/kg, such as 1-300 mg/kg, and chlorides (CT) not more than 200 mg/kg, such as 1-200 mg/kg.

Several of the discussed hazardous materials find their way into concrete structures by way of various coatings such as paints (lead, zinc, among others). These hazardous materials often stay in the surface layer of concrete and can be removed therefrom, as necessary, by grinding or shot blasting.

According to the Ministry of the Environment’s publication (Demolition survey - Guide for the auditor), the recommendation for the hazardous materials survey and review is to use the instruction RT 18-11245 Haitta-ainetutkimus. Rakennus- tuotteet ja rakenteet (Survey of hazardous materials. Building products and structures) published by Rakennustietosaatid RTS sr (Construction Information Foundation) and Rakennustieto Oy (Construction Information Ltd.).

The amount of heavy metals, non-metals, and metalloids in surplus concrete or in concrete waste, or in demolition concrete obtained therefrom, can be determined with the method set forth in technical report CEN/TR 16192:2020. The amount of mineral oils in surplus concrete or in concrete waste, or in demolition concrete obtained therefrom, can be determined with the method set forth in standard SFS-EN 14039:2014. The amount of polychlorinated hydrocarbons (PCB) in surplus concrete or in concrete waste, or in demolition concrete obtained therefrom, can be determined with the method set forth in standard SFS-EN 17322:2020. The amount of polyaromatic hydrocarbons (PAH) in surplus concrete or in concrete waste, or in demolition concrete obtained therefrom, can be determined with the method set forth in standard SFS-EN 15527:2022 or SFS-ISO 18287:2006. The material distribution, the amount of impurities and floating impurities in surplus concrete or in concrete waste, or in demolition concrete obtained therefrom, can be determined with the method set forth in standard EN 933-11 :2009. The amount of hazardous substances as well as the material distribution in cleaned surplus concrete or in concrete waste, or in demolition concrete obtained therefrom, espe- cially in cleaned crushed concrete, can likewise be determined with the methods set forth in said standards.

The removal/reducing the amount of hazardous materials from surplus concrete or concrete waste can be performed by analyzing the foreign substances and hazardous materials present in the surplus concrete or concrete waste, or in demolished concrete obtained therefrom, followed by either separating/classifying out of concrete structures of surplus concrete or concrete waste, or out of demolition concrete obtained therefrom, the concrete fractions containing foreign substanc- es/hazardous material, prior to finely crushing the surplus concrete or concrete waste, or demolition concrete obtained therefrom, into crushed concrete.

Alternatively, in case it is known about a concrete structure of surplus concrete or concrete waste, or about demolition concrete obtained therefrom, on the basis of its demolition site or origin or the like, that it does not contain hazardous materials at least in such quantities that would cause problems regarding the use of 3D printed concrete, such a demolition concrete/surplus concrete structure/concrete waste structure can be crushed directly into clean crushed concrete.

The structural target strength of concrete products, concrete waste, and surplus concrete refers in this disclosure to the structural compressive strength of concrete.

Concrete waste and surplus concrete refer here to a concrete structure about to be demolished I crushed into crushed concrete. The concrete structure is for example a concrete floor, a concrete element, concrete stairs, a structure or building consisting mainly of concrete.

Demolition concrete stands for coarse crushed concrete, as well as for concrete blocks, obtained in a demolition process.

Reclaimed aggregate refers to aggregate, which is produced from an inorganic material that has served as a building material and which mainly comprises crushed, cleaned and screened concrete, and which is further about to be used as aggregate in the production of concrete (BY 43: 2008).

In some embodiments, the quality of reclaimed aggregate meets the requirements of European product standard SFS EN 12620 + A1. In another embodiment, the reclaimed aggregate meets the requirements of National application standard SFS 7003:2022.

Other aggregate refers here to an aggregate, which is used for the production of concrete and is other than the reclaimed aggregate. The other aggregate may consist of an artificial aggregate or natural aggregate, such as crushed stone, sand, etc., which are used in this field for the production of concrete and reference is indeed made in this respect to the relevant prior known technology.

The cleaned crushed concrete refers to a structure, which is composed of concrete waste or surplus concrete and from which has been removed at least the hazardous materials cited in claim 1 , and which has been crushed into crushed concrete.

The cleaned crushed concrete stands also for coarse concrete rubble, which is made up of demolished concrete and from which has been removed at least the hazardous materials cited in claim 1 , and which coarse concrete rubble has been further crushed, if necessary, into even finer crushed concrete.

The strength class requirement of recyclable concrete waste or surplus concrete is fulfilled for example by subjecting a recyclable structure, composed of surplus concrete or waste concrete, or demolition concrete obtained therefrom, to a strength class test according to standard SFS EN 12390-3:2019 or the like.

The unit employed for concrete strength is megapascal (1 MPa = 1 N/mm ² ) and the compressive strength of concrete is influenced, among other things, by the water cement ratio in a concrete production recipe, by the quality and amount of cement, by the aggregate and its granularity, by mix ingredients and admixtures, by the age of cured concrete, etc.

The sampling is generally conducted by taking a test sample from a concrete structure of surplus concrete or concrete waste either with a diamond drill, such as a chuck drill, or by chipping. The test sample is generally cubical, cylindrical, or a core sample extracted from inside the concrete structure.

The sampling must be carried out as determined in any of standards EN-12350- 1 :2019, EN 12390-1 :2021 or EN 12390-2:2019. Likewise, other methods known in the art can be used for determining the structural strength of those concrete structures where the concrete waste originates from. With regard to these detemination methods, reference is made to technology prior known in the art.

Alternatively, the classification of concrete waste or surplus concrete can be conducted by using strength-indicating documents such as structure type drawings. In the event that a concrete structure of concrete waste or surplus concrete is originally designed for example for strength class (compressive strength) 1 or 2, it can often be considered confidently that the demolition concrete (crushed concrete as well as concrete blocks), obtained from the discussed concrete structure (surplus concrete or concrete waste), shall also match the structural target strength (compressive strength) of not less than 45 N/mm ² (class 1 ) or not more than 45 N/mm ² , yet more than 30 N/mm ² (class 2).

The compressive strength of demolition concrete obtained from surplus concrete or concrete waste, crushed concrete or concrete blocks made up of demolition concrete, as well as cleaned and non-cleaned crushed concrete, can also be determined directly with the method set forth in standard Pank 9003 Fl or the like. Even though the Pank 9003 Fl standard is intended primarily for earth construction or green construction purposes for the classification of crushed concrete along the lines of standard SFS 5884, the method described in said standard can also be used for assessing the compressive strength of crushed concrete in the present method.

According to standard Pank 9003 Fl, the crushed concrete to be tested is not allowed to contain more than 10% of brick or tile waste and 1 % of other impurities. Thus, from 7 as well as 28 days old crushed concrete are extracted test specimens in the size of at least 100 mm. After all, in the present wet concrete production method, on the brick and tile waste contained in cleaned crushed concrete, as well as other impurities (foreign substances), have been imposed considerably lower limits than those in standard Pank 9003 Fl.

The purity requirements of recycled crushed concrete, applicable to the 3D printing of concrete, are fulfilled by first removing from concrete waste or surplus concrete, or from crushed concrete obtained therefrom, if necessary, foreign substances such as asbestos and miscellaneous construction waste.

Foreign substances refer here to non-floating matter (X), not included in a concrete structure or in crushed concrete obtained therefrom, such as non-floating clay and other cohesive soil and earth, miscellaneous metals, wood, rubber, plastic, glass, gypsum plaster, etc. (Government decree 466/2022 as well as Ell directive 2008/98/EC)

Foreign substances further refer here to floating particles (FL), not included in crushed concrete, i.e. floating impurities (Government decree 466/2022 as well as Ell directive 2008/98/EC). The floating particles, i.e. the floating impurities, are made up of matter not included in crushed concrete and capable of floating in water (material lighter than water), such as plastics and insulation materials.

Foreign matter further refers to brick and tile waste, such as bricks and clinkers, sand lime bricks and blocks, as well as other burnt bricks as well as non-floating foamed concrete (Rb).

In terms of material, the foreign substances present in concrete structures are typically microbes, wood, plastic, brick, tile, asbestos, glass, gypsum board, etc.

The cleaned crushed concrete is allowed to contain foreign substances as follows:

The portion of floating particles (FL) comprising a foreign substance is not more than 5 cm ³ /kg of crushed concrete, preferably 0 cm ³ /kg of crushed concrete, and the portion of non-floating matter comprising a foreign substance in crushed concrete is less than 1 % by weight, such as 0-1 % by weight, and the portion of brick and tile wastes (Rb) in crushed concrete is less than 30% by weight, preferably less than 10% by weight, such as 0-10% by weight, especially 0-2% by weight, especially favorably 0% by weight.

The foreign substances can be removed from surplus concrete or concrete waste, or from demolition concrete produced therefrom, such as from crushed concrete, by first analyzing the type and amount of foreign substances in concrete or surplus concrete and by then separating the contaminated concrete waste or surplus concrete containing foreign substances, or the demolition concrete obtained therefrom, from the cleaner concrete material or demolition concrete.

The amount of foreign substances can be reduced from a structure by using light demolition. Light demolition is a voluntary process conducted on a structure to be demolished or renovated. An appraisal visit involves reviewing the movable property, furniture, and other light structural components such as lighting, wet area fixtures and room dividers. Alternatively, it is from demolition concrete such as crushed concrete, produced from surplus concrete or concrete waste, that foreign substances are separated magnetically (metals), by airflow separation or by some other separation method based on different specific weights of objects and crushed stone obtained therefrom. Airflow separation must generally be preceded by crushing the demolition concrete into crushed concrete. The foreign substances can also be removed from crushed concrete by screening or by some other separation method based on the shape or surface area of the foreign substances.

The demolition of concrete structures and the removal of foreign substances can also be conducted by using methods known from the prior art such as, among others, EP application 2949632 and Chinese published application CN113277772.

In terms of a more detailed execution of the removal of foreign substances (microbes, dust, dirt, rebar steel, wood, asbestos, plastic, etc.), reference is also made to practices and methods known in the art. The analysis of foreign substances from surplus concrete or waste concrete, or from crushed concrete obtained therefrom, can also be carried out by using the method set forth in standard EN 933-11 :2009. This particular method comprises a method for clarifying the constitution of a coarse material and is therefore applicable to identifying the relative proportions of foreign substances and concrete/crushed concrete.

A prior known process, among others, is the removal of impurities and microbial contaminants from concrete rubble or crushed concrete by means of water-wash, the removal of ferromagnetic compounds (e.g. reinforcing steel) by water-wash, magnetically, the sorting of materials based on a dissimilar specific weight thereof (centrifugation, cyclone) the sorting of particles based on the size and specific surface area of particles.

The invention provides significant benefits, the reuse of crushed concrete in the production of wet concrete enabling the production of 3D printing-manufactured parts and components (e.g. concrete stairs, floors, walls and components) for a building or structures, as well as the manufacturing of walls, etc. for a building or structures by in-situ-casting.

The use of crushed concrete in the production of wet concrete also reduces the carbon dioxide emissions of concrete grades made from such wet concrete; the concrete grades manufactured in this manner are classified as low-carbon and the BY Low-carbon classification thereof is typically GWP.85% relative to the reference emission rate of this particular concrete grade.

When calculating the carbon dioxide emissions of a concrete grade, attention is paid, among others, to the type and amount of raw materials contained in the concrete recipe, as well as the mode and distance of transporting the raw materials, and to the electrical and heating energy used for the production of concrete.

The most important factors in a concrete recipe with an effect on carbon dioxide emissions are the type and amount of cement and aggregate. The effect of admixtures on the carbon dioxide emission rate is generally relatively modest as the mounts thereof in a concrete recipe are small.

For example, the emission rates of cement are typically within the range of 0,470- 1 ,100 kg CO2e/(kg) and those of aggregate are 0,004-0,006 CO2e/(kg), depending e.g. on the quality and particle size of the aggregate. For sand, among others, the emission rate is 0,004 kg CO2 e/kg and for crushed stone 0,006 CC^e/kg.

The emission rate of crushed concrete obtained from reused concrete is low or even negative. In the production of wet concrete, the portion of cement from emission rates is approximately 40-60% and the portion of reclaimed aggregate from emission rates is approximately 1 % (the rest of emission rates consisting of e.g. other ingredients, water, transports, and the like), whereby the reused crushed concrete reduces concrete emission rates by about 0,3-0, 7%.

In some embodiments, the wet concrete is also supplemented with other screened aggregate, which is produced from natural stone material, such as sand, crushed stone, or from artificial aggregate, and which is included in sieve class C3 and/or C4 and has a particle size within the range of 0-8 mm and/or 8-16 mm.

In some embodiments, the wet concrete is supplemented with biocoal 1-10% by weight of the wet concrete’s dry weight. The addition of biocoal into wet concrete may enhance the compressive strength of the produced concrete. It is by the addition of biocoal that the portion of cement used for concrete can be respectively diminished, thereby reducing the utilization rate of virgin materials in concrete. It is also by the use of biocoal that the climate effects of concrete can be mitigated. In some embodiments, the biocoal has been produced by torrefying biomass, such as wood, in oxygen-free conditions, at a temperature of about 300-800°C (slow pyrolysis).

In some embodiments, the aggregate used for producing wet concrete comprises 30-100% by weight, preferably 30-50% by weight, reclaimed aggregate which consists of cleaned crushed concrete obtained from a demolished concrete structure, which reduces the aggregate’s carbon dioxide emission rate respectively by 30-100%, preferably by 30-50%.

In some embodiments, the production of wet concrete is carried out by using cement 18-30% by weight, as well as sand in particle size of 0-8 mm and/or crushed stone in particle size of 8-16 mm, totaling 50-30% by weight, cleaned crushed concrete obtained from a demolished concrete structure and having particle size of 0-8 mm and/or cleaned crushed concrete in particle size of 8-16 mm, totaling 30-50% by weight, water 8-15% by weight, and possibly concrete production admixtures, such as a plasticizer, a hardening accelerator or water absorption inhibitor, 0,5-2, 5% by weight.

The invention relates to a method for the 3D printing of concrete components used in house construction or for the 3D printing of walls for structures by using wet concrete which is produced as defined in claim 1 . The method hence further comprises the 3D printing of an element with the additive manufacturing process defined in standard SFS-EN ISO/ASTM 52900:2017, either a) by the extrusion or injection of wet concrete layer by layer onto a foundation or into a mold,

- by allowing the wet concrete to dry after its layer-by-layer extrusion or injection onto a foundation or into a mold,

- by removing the cured concrete element from the foundation or the mold, or b) by slip casting technique, by moving a foundation or a mold relative to a nozzle which is adapted to dispense wet concrete onto said foundation or into the mold in such a way that the wet concrete settles in a layer-by-layer fashion on said foundation or in the mold, by allowing the wet concrete to dry after its layer-by-layer placement on the foundation or in the mold, - by removing the cured concrete element from said foundation or mold.

In some embodiment, the cured concrete component is removed from a mold by opening or breaking the mold.

In some embodiments, the method comprises producing one or more building walls by in-situ casting on construction site.

In some embodiments, the method comprises 3D printing one or more products useful as a building’s wall elements.

In some embodiments, the method comprises using a concrete pump truck or a 3D printer loadable with wet concrete mix, said concrete pump truck or 3D printer being fitted with a printing head for delivering wet concrete to each printing location.

In some embodiments, the method comprises using a crane, such as a bridge or boom crane, which is fitted with said 3D printer.

In some embodiments, the method comprises 3D printing a structural component by using a robot arm or a boom crane, which is fitted with a printing head for delivering wet concrete to each printing location.

The invention relates to an apparatus for executing the production method of claim 1. The apparatus comprises a concrete station as well as, in association with the concrete station, either a) a mobile crusher equipped with a mesh screen or b) a pulverizing device or an excavator equipped with a flat screen for crushing the demolished concrete into crushed concrete and for screening the same to desired particle size/sizes.

The invention will be described in more detail with subsequently presented working examples.

Example A

An example of removing foreign substances by sorting from a concrete structure made up of concrete waste. Referring particularly to structures consisting of concrete waste, the foreign substances can be removed, prior to the demolition of concrete waste, as follows: the building is subjected to a material review as well as to a so-called material analysis (in addition to an asbestos and contaminant survey). The Ministry of the Environment has on November 15, 2019 published a demolition survey guide (Demolition survey - Guide for the author), which provides information about best practices as regards the evaluation, i.e. demolition survey, to be conducted prior to the demolition or renovation of a building or a structure and relating to the flows of construction and demolition waste.

The sorting of foreign substances depends on the quality of a concrete structure made up of concrete waste, the building’s interior often housing, mixed within concrete, e.g. gypsum, wood, plastics, glass, tiles, as well as ceramics, metal, fixtures, stone wool and other insulators. On the other hand, the demolition of a concrete structure used as a building’s frame material often involves the presence of bricks, wood waste, metal waste, miscellaneous construction waste, corrugated felt, wool and plastics.

It is at the demolition site of a structure consisting of concrete waste that the following fractions are sorted to separate the same from each other:

- fractions with a content of asbestos and other contaminant-containing wastes, these fractions being removed as set forth in asbestos and other contaminant report (AHA survey report),

- foreign substance-containing fractions contained in concrete waste or surplus concrete, or in crushed concrete obtained therefrom: solid non-floating impurities (X), i.e. non-floating matter, and floating impurities (FL), i.e. floating particles, are separated from clean concrete material,

- fractions, comprising impurities (X) not floatable in water. These include, among others, cohesive soil, miscellaneous metals, non-floating wood, plastic, rubber and gypsum plaster, insulation materials, glass,

- fractions, comprising impurities floatable in water (floating particles). Floating impurities (FL) include, among others, wool, floating wood material.

Alternatively or in addition, some of the foreign substances can be removed after the concrete structure has been demolished into coarse crushed concrete. The foreign substances can be removed from crushed concrete e.g. with water-wash (microbes and other light material) or with methods based on airflow or dissimilar specific surface areas of materials.

Reusable equipment and furniture, metals, pure concrete, timber, roofing felt, miscellaneous construction waste will be salvaged.

Hazardous wastes (e.g. impregnated timber, oils, contaminated concrete, etc.) will be removed.

Example 1

Very finely-divided foundation concrete mix, which is relatively dry and hence has its properties applicable to the 3D printing of a foundation, i.e. to the in-situ mold casting of a foundation.

1 m ³ dry raw materials the moisture contents of raw materials must be taken into consideration when making concrete, crushed concrete must be moistened and aggregates must be moist by nature.

Cement (Plus) 430 kg/m ³

Sand, particle size 0-2 mm 100 kg/m ³

Sand, particle size 0-8 mm 1050 kg/m ³

Cleaned crushed concrete, particle size 0-5 mm 566 kg/m ³ (moist)

Plasticizer 1 ,7 kg/m ³

Into wet concrete is further added water 200 kg/m ³ . Example 2

Very finely-divided foundation concrete mix, which is relatively dry and hence has its properties applicable to the 3D printing of a foundation, i.e. to the in-situ mold casting of a foundation.

1 m ³ dry raw materials the moisture contents of raw materials must be taken into consideration when making concrete, crushed concrete must be moistened and aggregates must be moist by nature.

Oiva-cement 430,00 kg

Sand, particle size 0-8 mm 895,00 kg

Crushed stone, particle size 6-16 mm 150,00 kg

Crushed concrete, particle size 5-16 mm 443,00 kg

Plasticizer 0,7% (Sika MR1 ) 3,01 kg

Into wet concrete is further added water 285,00 kg /m ³

Example 3

The processing of demolition concrete obtained from surplus concrete, or especially from concrete waste, into crushed concrete applicable to 3D printing (general description of the method)

Reusable concrete waste or surplus concrete was classified as follows:

Class 1 - high-strength concrete waste The first class (Class 1) includes demolition concrete (coarse crushed concrete and concrete blocks), which is obtained from concrete waste or surplus concrete, and in which the compressive strength of structure test speciments, extracted from the original concrete structures comprising concrete waste or surplus concrete, has been more than 45 N/mm ² . Alternatively, the demolition concrete (coarse crushed concrete and concrete blocks), which is obtained from concrete waste or surplus concrete, can be classified in class 1 provided that, based on the original design documents, such as construction type drawings, of a building about to be demolished, the concrete structures comprising concrete waste or surplus concrete, and also the demolition concrete obtained therefrom, can be reliably classified in this class.

The reclaimed aggregates included in class 1 (best quality) can be used in recycled concrete which has a target strength of not more than 45 N/mm ² .

The second class (Class 2) includes conventional strength-class concrete waste or surplus concrete, in which the compressive strength of structure test speciments, extracted from the original concrete structures comprising concrete waste- or surplus concrete, has been within the range of 30-45 N/mm ² . Alternatively, the demolition concrete (coarse crushed concrete and concrete blocks), which is obtained from concrete waste or surplus concrete, can be classified in class 3 provided that, based on the original design documents, such as construction type drawings, of a building about to be demolished, the concrete structures comprising concrete waste or surplus concrete, and also the demolition concrete (crushed concrete and concrete blocks) obtained therefrom, can be reliably classified in this class. The reclaimed aggregates/crushed concrete, included in class 2, can be used in recycled concrete which has a target strength of not more than 30 N/mm ² .

The third class (Class 3) includes concrete waste or surplus concrete, in which the compressive strength of structure test speciments, extracted from the original concrete structures comprising concrete waste or surplus concrete, has been less than 30 N/mm ² . Alternatively, the demolition concrete (coarse crushed concrete and concrete blocks), which is obtained from concrete waste or surplus concrete, can be classified in class 3 provided that, based on the original design documents, such as construction type drawings, of a building about to be demolished, the concrete structures (crushed concrete and concrete blocks) comprising concrete waste or surplus concrete, and also the demolition concrete obtained therefrom, can be reliably classified in this class. The reclaimed aggregates, i.e. crushed concrete, included in class 2, can be used in recycled concrete which has no target strength.

The wet concrete applicable to 3D printing is first and foremost produced from demolition concrete (crushed concrete), which is included in first or second strength class.

Subject to national or regional contaminant standards, the hazardous substances removed from concrete waste shall further include heavy metals, non-metals and metalloids.

The European Parliament and Council Directive 2008/98/EC, regarding wastes, determines acceptable limit values for hazardous substances such as heavy metals, non-metals and metalloids. In Finland, the limit values consistent with Directive 2008/98/EC have been determined in Government Decree 466/2022, relating to evaluation criteria for terminating the classification of crushed concrete as waste. The limit values for the solubility of heavy metals, non-metals and metalloids in cleaned crushed concrete are (mg/kg) antimony (Sb) 0,2, arsenic (As) 0,1 , barium (Ba) 5, cadmium (Cd) 0,02, chromium (Cr) 0,6, copper (Cu) 1 , mercury (Hg) 0,01 , lead (Pb) 0,1 , molybdenum (Mo) 0,7, nickel (Ni) 0,3, vanadium (V) 0,3, zinc (Zn) 4, selenium (Se) 0,2, fluoride (F) 12, sulfate (SO4 ² ') 300, and chloride (Cl) 200.

It is from concrete waste included in first or second strength class that cleaned crushed concrete, applicable to 3D printing, is produced by removing, as necessary, asbestos, hazardous materials, as well as foreign substances, from crushed concrete waste in such a way that the portion of floating particles (FL) in cleaned crushed concrete is 0 cm ³ /kg of crushed concrete, the content of non-floatable matter, comprising a foreign substance, in crushed concrete is less than 1 % by weight, the portion of brick and tile wastes (Rb) in crushed concrete is 0% by weight and, as for hazardous materials, the amount of polychlorinated phenyls is not more 1 mg/kg, the amount of polyaromatic hydrocarbons is not more than 30 mg/kg, and the amount of mineral oils (C10-C40) is not more than 200 mg/kg.

Thereafter, the thus obtained cleaned crushed concrete is crushed and screened to a desired particle size either (a) with a sieve-equipped mobile crusher capable of screening a batch of crushed concrete into several fractions, or (b) with a pulverizing device or with a flat screen attached to an excavator.

The appropriate particle size for crushed concrete in 3D printing is preferably within the range of 0-16 mm.

Example 4

3D-printable wet concrete.

Example 4A

30% of the sand is replaced with cleaned crushed concrete

Cement (Plus) 430 kg/m ³

Sand, particle size 0-2 mm 100 kg/m ³

Sand, particle size 0-8 mm 1050 kg/m ³

Cleaned crushed concrete, particle size 0-2 mm 30 kg/m ³ (moist)

Cleaned crushed concrete, particle size 2-16 mm 530 kg/m ³ (moist)

Water 200 kg/m ³

Plasticizer 1 ,7 kg/m ³ and is replaced with cleaned crushed concrete s) 430 kg/m ³

Sand, particle size 0-2 mm 50 kg/m ³

Sand, particle size 0-8 mm 800 kg/m ³

Cleaned crushed concrete, particle size 0-2 mm 50 kg/m ³ Cleaned crushed concrete, particle size 2-16 mm 800 kg/m ³ (moist)

Water 200 kg/m ³

Plasticizer 1 ,7 kg/m ³ Example 4C

30% of the sand is replaced with cleaned crushed concrete

Cement (Plus) 430 kg/m ³

Sand, particle size 0-2 mm 100 kg/m ³

Sand, particle size 0-8 mm 1050 kg/m ³ Cleaned crushed concrete, particle size 0-5 mm 30 kg/m ³ (moist)

Cleaned crushed concrete particle size 5-16 mm 530 kg/m ³ (moist) Water 200 kg/m ³

Plasticizer 1 ,7 kg/m ³

50% of the sand is replaced with cleaned crushed concrete

Cement (Plus) 430 kg/m ³

Sand, particle size 0-2 mm 50 kg/m ³

Sand, particle size 0-8 mm 800 kg/m ³

Cleaned crushed concrete, particle size 0-5 mm 50 kg/m ³

Cleaned crushed concrete, particle size 5-16 mm 800 kg/m ³ (moist)

Water 200 kg/m ³

Plasticizer 1 ,7 kg/m ³

Production of wet concrete as 50% of the sand replaced with cleaned crushed concrete

Cement (Plus) 430 kg/m ³

Sand, particle size 0-8 mm 850 kg/m ³

Cleaned crushed concrete, particle size 0-5 mm 50 kg/m ³

Cleaned crushed concrete, particle size 5-16 mm 800 kg/m ³ (moist)

Water 200 kg/m ³

Plasticizer 1 ,7 kg/m ³ All concrete recipes presented in examples 4A-4E are suitable for the production of wet concrete, which is applicable to the casting of 3D printable concrete cubes whose strength class is 1 or 2.

Wet concrete, which had been produced in accordance with a recipe described in examples 4A-4E, was used for the 3D printing of cube-shaped test specimens 150 x 150 x 150 mm ³ into a mold.

The crushed concrete used in the recipes consisted of cleaned crushed concrete, from which had been removed foreign substances as well as hazardous materials, and which crushed concrete had thereafter been crushed and screened to a desired particle size.

The strength tests on the cast, cube-shaped test specimen made of concrete were performed in keeping with standard SFS-EN 12390-3: 2019 against mold surfaces. The concrete testing machine was ELE International ADR Auto 2000, which fulfilled the requirements of standard EN 12350-1 :2019. The mold and sample, used in measuring the compressive strength of cured concrete, satisfied the requirements of standard SFS-EN-12390-1 :2021 .

The carbon dioxide emission rates of wet concrete produced in accordance with examples 4A-4E decreased by about 5-15% relative to wet concrete that had been produced from virgin raw materials. The degree of reduction in carbon dioxide emission rates depends on how much of the aggregate is replaced with recycled cleaned crushed concrete (the aggregate may contain 30-50% by weight of cleaned crushed concrete), because the emission rate of recycled as well as cleaned crushed concrete is zero or even negative. The produced objects (concrete cubes) are hence classified as low carbon and have a BY Low-carbon classification of about GWP.85%, depending on the type of concrete and the amount of recycled concrete contained therein.