System and method for three-dimensional printing of fibre-reinforced concrete structures

Abstract

A system (1) and a method for three-dimensional printing of a fibre-reinforced concrete structure, the system comprising: - a mortar mixing unit (3); - a print head (5) comprising a nozzle (7), a concrete mixing unit (9), a driving unit (12) arranged for driving said concrete mixing unit, an extruding unit (13), a further driving unit (15) arranged for driving said extruding unit; - a first transport means (17) for transporting the mortar; - an aggregate dosing unit (19); - a fibre dosing unit (21); - a second transport means (23) for transporting the aggregates and fibres; - a robot arrangement (25), comprising a static framework (27) and a robot (29) attached to said static framework, wherein the system comprises sensor means (31, 32, 33) for measuring and a control unit (34) for controlling the output flow rate of the mortar, the aggregate dosing rate and the fibre dosing rate. A computer program product with program code for performing the method is also claimed.

Description

[0001] Title: SYSTEM AND METHOD FOR THREE-DIMENSIONAL PRINTING OF FIBRE-REINFORCED CONCRETE STRUCTURES

[0002] Field of the invention

[0003] The present invention relates to a system for three-dimensional printing concrete structures and to a method of three-dimensional printing concrete structures.

[0004] Background of the invention

[0005] Sustainability and digitisation are becoming more and more important challenges and spearheads within European and global policies. In addition to zero emissions and circularity, reducing raw material consumption is a priority within the various objectives and digitisation is necessary to keep national or regional economies - in all sectors - competitive in the world. Digitisation for a smarter and more efficient society and industry includes the use of ICT, Al, robotisation and other digital control of processes and products.

[0006] Concrete production is environmentally harmful, because it releases greenhouse gases (about 8% of the total emissions of these gases in the world). To reduce the overall carbon dioxide (CO2) foot print in the concrete construction industry, there is high demand to reduce or replace the cement usage in concrete. In addition, formwork (moulds) must be made and a lot of material is used to achieve a certain strength, instead of the use of other shapes and / or constructions. In addition to cement, lime and other materials, steel - as reinforcement - is also used and a lot of energy is needed for the production of these materials.

[0007] Conventional concrete products, such as parts of bridges or buildings, are made with formwork and are reinforced with steel reinforcement bars. The construction process from design to realization has many steps in which many mistakes can be made because there is still a lot of (human) handicrafts. The design should be translated into a mould, and in the mould the reinforcement should be applied, then the reinforcement should remain in the right place during concrete casting. In the case of prefabricated concrete from a factory, the concrete products must be moved and assembled on site Three-dimensional concrete printing (3DCP) can be used much more in the infrastructure, construction and design industries, where almost every project requires customization of advanced designs with multiple functionalities. The challenges of this industry with regard to sustainability and productivity with 3DCP can also be addressed. The rapid development in 3DCP comes as no surprise, as concrete is the most widely used construction and construction material worldwide. Due to the wide range of functionalities such as strength, durability, fire resistance and the high use in the global construction sector, the use of concrete as a three-dimensional printed material makes it very attractive for the construction sector. Furthermore the advantages offered by 3DCP to reduce the overall concrete usage makes 3DCP technology a highly attractive solution to address the issues related to sustainability in the building and construction industry.

[0008] Concrete is a brittle material that can handle a lot of pressure, but little pulling force. To prevent cracking and improve its tensile strength and ductility, it is therefore important to reinforce concrete with rebar and to reduce the cost and CO2 footprint in the concrete, it important to introduce coarse aggregate into the concrete.

[0009] Though 3DCP technology offers a more efficient solution for concrete construction, the conventional method of applying steel reinforcement to 3DCP structures is not efficient and, in some cases, not possible. Hence the application of 3DCP technology for the construction industry is limited and not yet strong enough for large-scaled structural applications. An alternative to reinforcing concrete with rebars is by strengthening the concrete with small metallic fibres such as steel fibres and non-metallic fibres such as hemp fibres, basalt fibres, polypropylene fibres, glass fibres etc. However with the current 3DCP setups used in the industry only small micro fibres can be introduced to the printed concrete. These fibres are used to prevent shrinkage in the concrete rather than structural application related to improving ductility and tensile strength.

[0010] Furthermore, current 3DCP technology cannot introduce coarse aggregates to the 3D printable concrete to reduce the cement in the concrete mix. As a result of the above- mentioned issues, the material used in conventional 3D concrete printers is unreinforced and therefore unsuitable for the construction of multi-story buildings and / or large infrastructure projects. There is a desire to improve the strength and sustainability of three-dimensional printed concrete such that 3DCP becomes a suitable and viable option for the construction of multi-story buildings and / or large infrastructure projects. A generic concept to achieve this, is through the selective addition of materials such as stone aggregates and / or fibres to the concrete. There are various possibilities to apply such aggregates and / or fibres in three- dimensional printed concrete. Of all the alternatives explored by knowledge institutions, only a few have shown potentially good results.

[0011] A commonly used system is to mix fine aggregates and micro fibres in the printed concrete, either in the dry mortar mixture or in the fresh mortar mixture. The biggest limitation of this process is that most large-scale coarse aggregates / macro fibres - which are crucial for improving material properties - cannot pass through the current pumping system for 3DCP. The pump or hose becomes clogged by the fibres or larger aggregates.

[0012] A second process is to sprinkle aggregates and fibres during the printing process between each layer. This system is easier to implement in the concrete printing system. However, proper control of the system is difficult and the quality of the printed output is not homogeneous when using various aggregates / fibres.

[0013] A third process is to carry fibres / aggregates using an additive system at the nozzle. Another process is the addition of fibres to the concrete matrix that are randomly distributed. Here you can choose to add fibres to the mortar or to add fibres to the print head. A drawback of these known systems is that quality of the printed output may vary too much, resulting in inconsistency of the printed concrete, which may for example result in printed layers of concrete to not sufficiently bond to each other resulting in reduced strength.

[0014] Object of the invention

[0015] It is therefore an object of the invention to provide for a solution to allow printing of a concrete structure using a fibre reinforced concrete mixture with larger aggregates, having an improved consistency resulting in a three-dimensional printed fibre reinforced concrete structure having improved material and mechanical properties (e.g., tensile strength, flexural strength and ductility).

[0016] The foregoing object is achieved according to a first aspect of the present invention that relates to a system for three-dimensional printing of a concrete structure with a fibre reinforced concrete mixture, comprising: a mortar mixing unit arranged for mixing dry mortar mixture with an aqueous liquid into a fresh mortar mixture; a print head comprising: a nozzle ; a concrete mixing unit arranged for mixing said fresh mortar mixture with aggregates and fibres in a mixing chamber into said fibre reinforced concrete mixture; a driving unit arranged for driving said concrete mixing unit; an extruding unit arranged for extruding said fibre reinforced concrete mixture out of said mixing chamber and through said nozzle; a further driving unit arranged for driving said extruding unit thereby controlling a flow-rate of said fibre reinforced concrete mixture through said nozzle; a first transport means arranged for transporting said fresh mortar mixture from said mortar mixing unit to said concrete mixing unit; an aggregate dosing unit arranged for introducing said aggregates to said concrete mixing unit; a fibre dosing unit arranged for introducing said fibres to said concrete mixing unit; a second transport means arranged for transporting said aggregates and said fibres from said respective aggregate dosing unit and fibre dosing unit to said concrete mixing unit; a robot arrangement, comprising a static framework and a robot attached to said static framework, said robot having said print head attached thereto as an end effector, and wherein said robot is arranged to move said print head in a predefined space in respect of said static framework; wherein said system comprises one or more first sensor means for measuring an output flow rate of said fresh mortar mixture, one or more second sensor means for measuring an aggregate dosing rate and one or more third sensor means for measuring a fibre dosing rate, and wherein said system further comprises a control unit for controlling said output flow rate of said fresh mortar mixture, said aggregate dosing rate and said fibre dosing rate.

[0017] In a second aspect, the invention relates to a method of three-dimensional printing of a fibre reinforced concrete structure, comprising the steps of: mixing, with a mortar mixing unit, a dry mortar mixture with an aqueous liquid into a fresh mortar mixture; transporting, with a first transport means, said fresh mortar mixture from said mortar mixing unit to a concrete mixing unit of a print head; transporting, with a second transport means, aggregates and fibres from a respective aggregate dosing unit and a fibre dosing unit to said concrete mixing unit of said print head; mixing, with said concrete mixing unit, said fresh mortar mixture with said aggregates and said fibres in a mixing chamber of said concrete mixing unit into a fibre reinforced concrete mixture; extruding, with an extruding unit, said fibre reinforced concrete mixture out of said mixing chamber and through a nozzle; driving, with a driving unit, said extruding unit thereby controlling a flow-rate of said fibre reinforced concrete mixture through said nozzle; measuring, with one or more first sensor means, an output flow rate of said fresh mortar mixture; measuring, with one or more second sensor means, an aggregate dosing rate; measuring, with one or more third sensor means, a fibre dosing rate; controlling, with a control unit, said output flow rate of said fresh mortar mixture, said aggregate dosing rate and said fibre dosing rate.

[0018] In a third aspect, the invention relates to a computer program product, comprising a data storage device storing computer program code arranged for performing the method according to the second aspect of the invention, when said computer program code are loaded onto a memory of an electronic processing unit when executed by said electronic processing unit. In 3DCP, also known as concrete additive manufacturing (AM), objects are built layer by layer in 3D using a robot system, such as a gantry robot, robotic arm, or other automated system. AM makes formwork unnecessary and is therefore attractive for the construction sector. Construction and construction engineers and architects were limited in designing efficient concrete buildings and (art) works with complex and optimized shapes and constructions, due to the high cost of custom formwork. The application of 3DCP in construction can significantly reduce the occurrence of construction waste from formwork and limit the impact on the environment with less production waste. AM’s inherent ability to optimize material use could further contribute to reducing the environmental impact due to high carbon dioxide (CO2) emissions from the use of cement in concrete.

[0019] In addition to reducing costs and positive environmental impact, AM can further automate and digitize the sector and the technology helps transform the construction sector into Industry 4.0. Automating concrete production with AM will also help find a solution to reduce physical labour in on-site concrete structures. Finally, given the current situations due to COVID-19, the global construction, infrastructure and design industry has had a significant impact due to the fact that construction projects were either delayed or stopped fully complying with social distancing rules. In the future, construction and infrastructure must reduce its dependence on manual labour and move towards a more automated solution to address such a crisis.

[0020] The system for 3DCP is complex and by individually monitoring and controlling all components of the system and ingredients of the concrete mixture used for 3DCP, one can obtain concrete mixtures of improved quality, and thereby also three-dimensional printed concrete structures of improved quality.

[0021] The system according to the first aspect of the invention reduces the environmental impact of concrete production. A digital design is sent to a three-dimensional printer (in a factory or on a construction site) and products can be made without formwork and reinforcement bars (rebar). This reduces the impact on the environment because less construction and production waste is generated. Additionally, the system may also reduce the carbon footprint in the construction sector by replacing cement use in concrete with alternative binders such as alkali-activated binders, geopolymer concrete, or by reducing the amount of binder in the concrete by using aggregates or fibres, or by optimizing concrete use with emerging technology such as additive manufacturing or three-dimensional printing for the building and construction industry.

[0022] Furthermore, the system allows to make 3DCP structures stronger. With the system, reinforcing fibres can be added to concrete mortar in a controlled and flexible manner during printing, improving the concrete’s structural properties, e.g. tensile strength, flexural strength and ductility. The improved structural properties allows the manufacture of complex and optimized shapes and constructions. The system according to the present invention enables the use of both microfibres and macrofibres as reinforcing fibres. For example, the macrofibres bridge gaps of possible (small) cracks within the printed concrete structures and thus, provide additional strength to the concrete and / or make sure that the strength of the concrete structure is maintained.

[0023] With the use of such an automated system for manufacturing three-dimensional concrete structures, the manufacturing process is less dependent on manual labour, which may reduce the manufacturing costs.

[0024] Another benefit of the present invention is that variations in the dosing rates of one or more or the ingredients of the fibre reinforced concrete mixture can be corrected such that the ratio between all of the ingredients remains constant. This also provides the possibility to change the recipe during the printing of a three-dimensional concrete structure or in between the printing of different three-dimensional concrete structures.

[0025] The system allows the addition of different types of fibre, such as thick, thin, long, smooth, rough, hooked end, corrugated, circular and / or organic or inorganic, metallic, virgin or recycled fibres, and also allows the addition of multiple admixtures to the fresh mortar to further improve the specifications or appearance of the fresh concrete mixture, such as rheological properties of the fresh concrete, curing speed, open time, stiffness or flow properties of the fresh concrete mixture. List of definitions

[0026] The following definitions are used in the present description and claims to define the stated subject-matter. Other terms not cited below are meant to have the generally accepted meaning in the field.

[0027] “Aggregates” as used in the present disclosure means a granular material suitable for use in concrete, as defined by standard EN 12620. Aggregates may be natural, artificial or re-cycled from material previously used in construction.

[0028] “Aggregate size” as used in the present disclosure means the designation of aggregate in terms of lower (d) and upper (D) sieve sizes expressed as d / D, as defined by standard EN 12620.

[0029] “Fine aggregates” as used in the present disclosure means the designation given to the smaller aggregate sizes with D less than or equal to 4 mm, as defined by standard EN 12620.

[0030] “Coarse aggregates” as used in the present disclosure means the designation given to the larger aggregate sizes with D greater than or equal to 4 mm and d greater than or equal to 2 mm, as defined by standard EN 12620.

[0031] “Additives” as used in the present disclosure means ingredients added to a dry or fresh mortar / concrete mixture to improve the manufacture or properties of the concrete mixture or resulting concrete structure, as defined by standard EN 197-1.

[0032] “Admixtures” as used in the present disclosure means ingredients added during the mixing process of dry of fresh mortar / concrete to modify the properties of the concrete mixture in the fresh and / or hardened state, as defined by standard EN 934-2.

[0033] “Dry mortar mixture” as used in the present disclosure means a mixture of one or more mineral binders and fine aggregates and optionally, one or more additives and / or admixtures. “Fresh mortar mixture” as used in the present disclosure means a printable mixture of dry mortar mixture fully mixed with an aqueous liquid, e.g. water.

[0034] “Fresh concrete mixture” as used in the present disclosure means a printable mixture of dry mortar mixture fully mixed with an aqueous liquid, e.g. water, and coarse aggregates.

[0035] “Fibre reinforced concrete mixture” as used in the present disclosure means a printable mixture of dry mortar mixture fully mixed with an aqueous liquid, e.g. water, coarse aggregates and fibres.

[0036] “Static framework” as used in the present disclosure means that the print head can move relative to the framework, thus the framework being static relative to the print head. The static framework is not fixed to the underground.

[0037] “Macrofibres” as used in the present disclosure means that the fibres have specific size dimensions (e.g., diameter, length). Macrofibres can be divided into small macrofibres and large macrofibres. Small and large macrofibres both have a diameter of more than 300 micrometre. Small macrofibres typically have a length of 12 to 30 mm, whereas large macrofibres typically have a length of more than 30 mm. Macrofibres generally provide strength to the concrete as these fibres tackle micro- and macrocracks that may be present / form in the 3D printed concrete structure.

[0038] “Microfibres” as used in the present disclosure means that the fibres have specific size dimensions (e.g., diameter, length). Microfibres typically have a diameter of 300 micrometre or smaller and a length of 12 mm or smaller. Microfibres generally have the function of reducing or preventing shrinkage issues during the drying process of wet concrete. Due to their limited size, the microfibres to not provide strength to the printed concrete structure.

[0039] Examples In an example, the system may comprise a liquid admixture injection unit arranged for introducing one or more liquid admixtures to said concrete mixing unit or to said extruding unit.

[0040] In this example, the system may further comprise a third transport means arranged for transporting said one or more liquid admixtures from said liquid admixture injection unit to said concrete mixing unit or to said extruding unit.

[0041] The liquid admixture will allow for changing the material properties of the concrete near the printing nozzle. The advantage of the changing the material properties at the nozzle allows for better control of the material properties during printing. For example the chemical accelerators can be introduced into the printed concrete at the concrete extruder to improve the setting time of the concrete. The impact of introducing the accelerator to the system is that the open time or fresh concrete properties of the concrete will rapidly change and start hardening in the system. The advantage of introducing the accelerator at the said concrete extruder unit near the nozzle is that the accelerator will impact the concrete near the nozzle and during printing process only the concrete extruder and nozzle needs to be cleaned in quick interval rather than cleaning the complete setup. This will also help in drastically improving the productivity during the printing process. The other advantage is that with accelerators added near the nozzle it allows for on demand instantaneous deposition of concrete with different materials at the desired location during the printing process.

[0042] In another example, the system may further comprise a dust filtration unit arranged for collecting dust from said aggregates before introducing said aggregates to said concrete mixing unit.

[0043] While transporting the coarse aggregates from the aggregate dosing system to the inlet of the concrete mixing chamber with a suction or blower unit, the air in the system needs to be released out of the system. Coarse aggregates during dosing and transportation processes generate fine dust. While releasing the air out of the system will create a hazardous environment if the air contains fine dust particles from the coarse aggregates. To avoid that a dust filtration unit is needed to filter the fine dust particles in the particle transport system before the air is released out of the system. In yet another example, the system may comprise one or more fourth sensor means for measuring one or more of a viscosity of said fresh mortar mixture, a temperature of said fresh mortar mixture, a pressure of said fresh mortar mixture, a level of said fibre reinforced concrete mixture in said mixing chamber, a viscosity of said fibre reinforced concrete mixture, a temperature of said fibre reinforced concrete mixture, a pressure of said fibre reinforced concrete mixture, an output flow rate of said fibre reinforced concrete mixture out of said nozzle, a dosing rate of said liquid admixture, and a pressure rate of said liquid admixture, and the system comprises a control means for controlling at least one of said level of said fibre reinforced concrete mixture in said mixing chamber, said output flow rate of said fibre reinforced concrete mixture and said dosing rate of said liquid admixture. Said control means may comprise the control unit of the system according to the present invention or a different control unit.

[0044] The complete sensor system can be divided into three types of sensors:

[0045] • First type is to control and maintain the overall flow rate in the system by controlling and monitoring the flow rate of the fresh mortar mixture into the concrete mixing unit and controlling the level of the complete concrete mixture in the mixing unit with a level sensor. Simultaneously monitoring the output flow of the fibre reinforced concrete mixture with a flow rate sensor to maintain the dimensions of the concrete filaments. Hence, this type of sensors provides quality insurances for the shape of the printed structures;

[0046] • Second type are weight sensors added to the aggregate dosing unit and fibre dosing unit to control and monitor the desired input proportions of the coarse aggregates and fibres into the said concrete mixing chamber. As well as the desired input of the liquid admixtures from the liquid admixture injection unit into the concrete extrusion chamber with a liquid admixture flow rate sensor. Hence, this type of sensors provides material quality properties (ratio fresh mortar to fibres to coarse aggregates);

[0047] • Third type are viscosity and temperature sensors added to the extruding unit and the concrete mixing unit to monitor the desired quality of the fresh mortar and the fibre reinforced concrete properties such as viscosity and temperature.

[0048] In yet another example, the first transport means comprises a pumping unit. Current mortar mixing and pumping units available in the industry do not allow the continuous pumping of concrete with coarse aggregate and fibres in a constant and stable amount (without any pulses or breaks) with a desired flow rate needed for the extrusion of 3D concrete printing.

[0049] Hence, an independent fresh mortar mixture pumping unit without aggregates and fibres allows the mixing and pumping units to be more robust and flexible to transport fresh mortar to the concrete mixing unit at a desired rate in a continuous controlled process, while fibres and aggregates are transported to the concrete mixing unit with a different transport means. Furthermore, the mortar pumping unit not being attached to the robot offers flexibility during printing.

[0050] In yet another example, the second transport means may comprise a suction or blower unit.

[0051] An independent particle transport means via said suction or blower unit allows flexibility of the transport hose to move along with the movements of the printhead unit attached to the robot. Furthermore, one integrated transport means allows better control in transporting the desired amounts of both aggregates and fibres without having to calibrate the flow rate of the aggregates and fibres separately. Furthermore, the flow rate of the air in the transport hose is maintained at a high velocity such that all the fibres and aggregates are suspended in the air flow while flowing through the hose. This allows of fibres and aggregates to not get clogged in the hose.

[0052] Preferably, the further transport means transports the aggregates and fibres from the respective aggregate and fibre storage units with a screw conveyor and a belt conveyor to the suction or blower unit.

[0053] The screw conveyor transport means in the aggregate dosing unit allows for the controlled dosing of coarse aggregates into the further transport means by controlling the rotation speed of the screw. The advantage of having separate and independent dosing and transport means for aggregates and fibres allows for prescribed amount of aggregates and fibres to be transported to the concrete mixing unit to produce different mixes of fibre reinforced concrete on demand (dosage can be adjusted during the printing process) in an controlled automated process.

[0054] In yet another example, the nozzle may have a cross-sectional opening for mortar or concrete extrusion that is at least substantially circular-shaped or at least substantially rectangular-shaped.

[0055] In yet another example, the nozzle may be a downflow nozzle having a downward orientation for disposing the fibre reinforced concrete mixture.

[0056] In yet another example, the nozzle may be a backflow nozzle having a backward orientation for disposing the fibre reinforced concrete mixture.

[0057] In yet another example, the nozzle may be a hybrid downflow / backflow nozzle having a combined downward and backward orientation for disposing the fibre reinforced concrete mixture.

[0058] A backflow nozzle allows for a more pronounced fibre orientation along the printing direction following the print path, Having fibres oriented along the printing direction offers more tensile strength of the printed layers along the direction of the print path.

[0059] In yet another example, the fibres may comprise virgin and / or reused material.

[0060] The system being a robust and generic system allows for all types of fibres to be introduced in the printed concrete.

[0061] In yet another example, the fibres may have a length in the range of from 5 mm to 70 mm, preferably from 10 mm to 35 mm, more preferably from 15 mm to 30 mm. In yet another example, the fibres may have a diameter of in the range of from 20 micrometre to 1000 micrometre, preferably from 200 micrometre to 800 micrometre, more preferably from 300 micrometre to 700 micrometre.

[0062] Concrete with fibres with a larger length will offer better mechanical performance over fibres with smaller length, for the equivalent diameter (according to EN 14889-1) and fibre dosage. The ratio between the length of the fibres and the equivalent diameter of the fibre is defined as aspect ratio according to EN 14889-1. Concrete with fibres having a higher aspect ratio offers better mechanical performance. However shorter fibres with low aspect ratio are easier to transport through the further transport means. Furthermore, fibres with the preferred length with a smaller aspect ratio are easier to mix with the concrete and finally extrude out of the concrete nozzle.

[0063] In yet another example, the one or more admixtures are one or more binders, such as Portland cement, alkali-activated binders, geopolymer binders, or limestone calcinated clay cement (LC3). Preferably, the one or more binders are alkali-activated binders or geopolymer binders.

[0064] The system is developed as a generic system with support for different types of 3D mortars and concretes. As long as the rheological properties of the printing material fit the requirements of the system, it does not matter what kind of binder system is used in the printing material composition. However, the CO2 emissions of Portland cement are relatively high compared to alternative binders. By applying alternative binders to printable concrete, the overall carbon footprint of the printable concrete is reduced.

[0065] In yet another example, the robot is a 3 to 4 axis gantry robot, a 6 or more axis robotic arm or cable-driven robot, a telescopic robot or a printing robot in a robot crawler.

[0066] The system is developed as a generic system which is compatible to all types of robotic solutions with slight modifications to fit different robotic solutions.

[0067] In yet another example, the print head is arranged for rotation of the print head to print concrete structures having standard geometric shapes and / or 3 dimensional forms comprising a plurality of layers and / or complex geometries comprising a plurality of layers having organic freeform shapes and / or 3 dimensional forms.

[0068] 3DCP technology offers the possibility to produce freeform complex concrete geometries with ease. Where in case of a traditionally casted concrete construction is sometimes difficult or expensive and in some cases impossible as complex mould needs to be produced upfront.

[0069] In yet another example, the viscosity of the fresh concrete mortar is in the range of from 20 to 2000 Pa s, preferably 200 Pa s to 2000 Pa s, more preferably 500 Pa s to 1500 Pa s.

[0070] In yet another example, the viscosity of the fibre reinforced concrete mixture is in the range of from 20 to 2000 Pa s, preferably 200 Pa s to 2000 Pa s, more preferably 500 Pa s to 1500 Pa s.

[0071] In yet another example, the print head is configured for disposing layers of fibre reinforced concrete mixture having a thickness in the range of from 5 mm to 25 mm, preferably from 8 mm to 20 mm, more preferably of from 10 mm to 15 mm.

[0072] Increasing the layer thickness within the layer thickness range will increase the vertical build rate of a printed structure. However, the vertical build rate is limited by the buildability constrains of the printable concrete. Larger layer thickness reduces the printing time of the structure thereby improving the productivity, lowering labour cost, and energy requirements. Whereas lowering the layer thickness in the said layer thickness range increase the printing resolution.

[0073] In yet another example, the method comprise the step of: introducing, with a liquid chemical admixture injection unit, one or more chemical admixtures to said concrete mixing unit or to said extruding unit.

[0074] In yet another example, the method may further comprise the step of: transporting, with a third transport means, said one or more chemical admixtures from a liquid chemical admixture injection unit to said concrete mixing unit or to said extruding unit; and / or collecting, with a dust filtration unit, dust from said aggregates before introducing said aggregates to said concrete mixing unit.

[0075] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope thereof.

[0076] The above-mentioned and other features and advantages of the invention are illustrated in the following description with reference to the enclosed drawings which are provided by way of illustration only and which are not limitative to the present invention. The scope of the present invention is defined by the appended claims. One or more of the objects of the invention are achieved by the appended claims.

[0077] Brief description of the drawings

[0078] The present invention is described hereinafter with reference to the accompanying drawings in which embodiments of the present invention are shown and in which like reference numbers indicate the same or similar elements. The invention is in no manner whatsoever limited to the embodiments disclosed therein. Fig. 1 shows, in a schematic and illustrative manner, a system for three-dimensional printing of a concrete structure with a fibre reinforced concrete mixture according to the present invention;

[0079] Fig. 2 shows, in a schematic and illustrative manner, a print head according to the present invention;

[0080] Fig. 3 shows, in a schematic and illustrative manner, a cross-sectional view of the print head of Fig. 2;

[0081] Fig. 4 shows a method of three-dimensional printing of a fibre reinforced concrete structure according to the present invention.

[0082] Detailed description

[0083] The present invention is elucidated below with a detailed description.

[0084] In Fig. 1 , a schematic and illustrative overview of the system 1 for three-dimensional printing of a concrete structure with a fibre reinforced concrete mixture according to the present invention is shown. The system 1 comprises a mortar mixing unit 3. Said mortar mixing unit 3 is arranged for mixing dry mortar mixture with an aqueous liquid into a fresh mortar mixture.

[0085] The system 1 further comprises a print head 5, as shown in Fig. 2, comprising a nozzle 7, a concrete mixing unit 9 that is arranged for mixing the fresh mortar mixture with aggregates and fibres in a mixing chamber 11 into the fibre reinforced concrete mixture. A driving unit 12 is arranged for driving the concrete mixing unit. The print head 5 further comprises an extruding unit 13 arranged for extruding the fibre reinforced concrete mixture out of the mixing chamber 11 and through the nozzle 7, and a further driving unit 15 arranged for driving said extruding unit 13 thereby controlling a flow-rate of the fibre reinforced concrete mixture through the nozzle 7. The system further comprises a dust filtration unit 39a, 39b arranged for collecting dust from the aggregates before introducing the aggregates to the concrete mixing unit 9. The dust is collected in dust filtration unit 39a, transported via a transport means 49 and air containing said dust is filtrated in dust filtration unit 39b before said air is released into the atmosphere, as shown in Fig. 1. The aggregates enter the dust filtration unit 39a via an aggregate inlet 45 (see Fig. 2). The fresh mortar mixture enters the mixing chamber 11 of the print head 5 via a fresh mortar mixture inlet 47.

[0086] The system 1 as shown in Fig. 1 further comprises an aggregate dosing unit 19 arranged for introducing the aggregates to the concrete mixing unit 9 and a fibre dosing unit 21 arranged for introducing the fibres to the concrete mixing unit 9.

[0087] Furthermore, the system 1 comprises a first transport means 17 arranged for transporting the fresh mortar mixture from the mortar mixing unit 3 to the concrete mixing unit 9, and a second transport means 23 arranged for transporting the aggregates and fibres from their respective aggregate dosing unit 19 and fibre dosing unit 21 to the concrete mixing unit 9. Said first transport means 17 comprises a pumping unit 43. The pumping unit 43 pumps the fresh mortar mixture from the mortar mixing unit 3 to the print head 5. Said second transport means 23 comprises a suction or blower unit 44. The suction or blower unit 44 transports the aggregates and fibres via the hose of the second transport mean 23 to the print head 5.

[0088] The system 1 further comprises a robot arrangement 25. Said robot arrangement 25 comprises a static framework 27 and a robot 29 attached to said static framework 27. Said robot 29 has the print head 7 attached thereto as an end effector and the robot 29 is arranged to move the print head 7 in a predefined space in respect of the static framework 27.

[0089] One or more first sensor means 31 are comprised in the system 1 as shown in Fig. 1. The one or more first sensor means 31 are for measuring an output flow rate of the fresh mortar mixture. The system 1 also comprises one or more second sensor means 32 for measuring an aggregate dosing rate of the fresh mortar mixture and one or more third sensor means 33 for measuring a fibre dosing rate. Said system 1 further comprises a control unit 34 for controlling the output flow rate of the fresh mortar mixture, the aggregate dosing rate and the fibre dosing rate.

[0090] The system 1 shown in Fig. 1 further comprises a liquid admixture injection unit 35 arranged for introducing one or more liquid admixtures to the extruding unit 13. The one or more liquid admixtures may also be introduced to the concrete mixing unit 9.

[0091] Furthermore, the system 1 comprises a third transport means 37 arranged for transporting the one or more liquid admixtures from the liquid admixture injection unit 35 to the extruding unit 13. The third transport means 37 may also be arranged for transporting the one or more liquid admixtures from the liquid admixture injection unit 35 to the concrete mixing unit 9.

[0092] The system 1 further comprises one or more fourth sensor means 41a,41b,41c,41i,41j for measuring one or more of a viscosity of said fresh mortar mixture, a temperature of said fresh mortar mixture, a pressure of said fresh mortar mixture, a dosing rate of the liquid admixture, and a pressure rate of the liquid admixture. The print head 5 of said system 1 also comprises one or more fourth sensor means 41d,41e,41f,41g,41 h for measuring one or more of a level of said fibre reinforced concrete mixture in said mixing chamber 11 , a viscosity of said fibre reinforced concrete mixture, a temperature of said fibre reinforced concrete mixture, a pressure of said fibre reinforced concrete mixture, and an output flow rate of said fibre reinforced concrete mixture out of said nozzle 7. The system further comprises a control means for controlling at least one of the level of the fibre reinforced concrete mixture in the mixing chamber 11 , the output flow rate of the fibre reinforced concrete mixture and the dosing rate of the liquid admixture.

[0093] Fig. 3 shows a cross sectional view of the print head 5 of Fig. 2. It clearly shows the mixing screw inside the mixing chamber 11 and the extruding screw inside the extruding unit 13. The mixing screw is driven by the driving unit for mixing the fibre reinforced concrete mixture and transporting said mixture to the extruding unit 13. The extruding screw is driven by the further driving unit 15 for transporting the fibre reinforced concrete mixture through the extruding unit 13 and out of the nozzle 7. A method 101 of the three-dimensional printing of a fibre reinforced concrete structure according to the present invention is shown in Fig. 4. The method comprises the steps of: mixing 103, with a mortar mixing unit 3, a dry mortar mixture with an aqueous liquid into a fresh mortar mixture; transporting 105, with a first transport means 17, said fresh mortar mixture from said mortar mixing unit 3 to a concrete mixing unit 9 of a print head 5; transporting 107, with a second transport means 23, aggregates and fibres from a respective aggregate dosing unit 19 and a fibre dosing unit 21 to said concrete mixing unit 9 of said print head 5; mixing 109, with said concrete mixing unit 9, said fresh mortar mixture with said aggregates and said fibres in a mixing chamber 11 of said concrete mixing unit 9 into a fibre reinforced concrete mixture; extruding 111 , with an extruding unit 13, said fibre reinforced concrete mixture out of said mixing chamber 11 and through a nozzle 7; driving 113, with a driving unit 12, said extruding unit 13 thereby controlling a flowrate of said fibre reinforced concrete mixture through said nozzle 7; measuring 115, with one or more first sensor means 31 , an output flow rate of said fresh mortar mixture; measuring 117, with one or more second sensor means 32, an aggregate dosing rate; measuring 119, with one or more third sensor means 33, a fibre dosing rate; controlling 121 , with a control unit 34, said output flow rate of said fresh mortar mixture, said aggregate dosing rate and said fibre dosing rate; introducing 123, with a liquid chemical admixture injection unit 35, one or more chemical admixtures to said concrete mixing unit 9 or to said extruding unit 13; transporting 125, with a third transport means 37, said one or more chemical admixtures from a liquid chemical admixture injection unit 35 to said concrete mixing unit 9 or to said extruding unit 13; collecting 127, with a dust filtration unit 39a, 39b, dust from said aggregates before introducing said aggregates to said concrete mixing unit 9. Modifications and additions to the method and arrangement disclosed above are obvious to those skilled in the art and covered by the scope of the appended claims.

[0094] Embodiments and examples of the first aspect of the present invention are also applicable to the second or further aspects of the present invention.

Claims

Claims1. A system (1) for three-dimensional printing of a concrete structure with a fibre reinforced concrete mixture, comprising: a mortar mixing unit (3) arranged for mixing dry mortar mixture with an aqueous liquid into a fresh mortar mixture; a print head (5) comprising: a nozzle (7); a concrete mixing unit (9) arranged for mixing said fresh mortar mixture with aggregates and fibres in a mixing chamber (11) into said fibre reinforced concrete mixture; a driving unit (12) arranged for driving said concrete mixing unit; an extruding unit (13) arranged for extruding said fibre reinforced concrete mixture out of said mixing chamber and through said nozzle; a further driving unit (15) arranged for driving said extruding unit thereby controlling a flow-rate of said fibre reinforced concrete mixture through said nozzle; a first transport means (17) arranged for transporting said fresh mortar mixture from said mortar mixing unit to said concrete mixing unit; an aggregate dosing unit (19) arranged for introducing said aggregates to said concrete mixing unit; a fibre dosing unit (21) arranged for introducing said fibres to said concrete mixing unit; a second transport means (23) arranged for transporting said aggregates and said fibres from said respective aggregate dosing unit and fibre dosing unit to said concrete mixing unit; a robot arrangement (25), comprising a static framework (27) and a robot (29) attached to said static framework, said robot having said print head attached thereto as an end effector, and wherein said robot is arranged to move said print head in a predefined space in respect of said static framework; characterized in that said system comprises one or more first sensor means (31) for measuring an output flow rate of said fresh mortar mixture, one or more second sensor means (32) for measuring an aggregate dosing rate and one or more third sensor means (33) for measuring a fibre dosing rate, and wherein said system further comprises a controlunit (34) for controlling said output flow rate of said fresh mortar mixture, said aggregate dosing rate and said fibre dosing rate.

2. The system according to claim 1 , wherein the system comprises: a liquid admixture injection unit (35) arranged for introducing one or more liquid admixtures to said concrete mixing unit or to said extruding unit.

3. The system according to claim 2, wherein the system comprises a third transport means (37) arranged for transporting said one or more liquid admixtures from said liquid admixture injection unit to said concrete mixing unit or to said extruding unit.

4. The system according to any of the previous claims, wherein the system further comprises: a dust filtration unit (39a, 39b) arranged for collecting dust from said aggregates before introducing said aggregates to said concrete mixing unit.

5. The system according to any of the previous claims, wherein the system comprises one or more fourth sensor means (41 a, 41 b,41 c,41 d,41 e,41f,41 g,41 h,41 i,41j) for measuring one or more of a viscosity of said fresh mortar mixture, a temperature of said fresh mortar mixture, a pressure of said fresh mortar mixture, a level of said fibre reinforced concrete mixture in said mixing chamber, a viscosity of said fibre reinforced concrete mixture, a temperature of said fibre reinforced concrete mixture, a pressure of said fibre reinforced concrete mixture, an output flow rate of said fibre reinforced concrete mixture out of said nozzle, and, when dependent to claim 2 or 3, a dosing rate of said liquid admixture, a pressure rate of said liquid admixture, and wherein a control means for controlling at least one of said level of said fibre reinforced concrete mixture in said mixing chamber, said output flow rate of said fibre reinforced concrete mixture and said dosing rate of said liquid admixture.

6. The system according to any of the previous claims, wherein the first transport means comprises a pumping unit (43).

7. The system according to any of the previous claims, wherein the second transport means comprises a suction or blower unit (44).

8. The system according to any of the previous claims, wherein the robot is a 3 to 4 axis gantry robot, a 6 or more axis robotic arm or cable-driven robot, a telescopic robot or a printing robot in a robot crawler.

9. The system according to any of the previous claims, wherein the print head is arranged for rotation of the print head to print concrete structures having standard geometric shapes and / or 3 dimensional forms comprising a plurality of layers and / or complex geometries comprising a plurality of layers having organic freeform shapes and / or 3 dimensional forms.

10. The system according to any of the previous claims, wherein the print head is configured for disposing layers of fibre reinforced concrete mixture having a thickness in the range of from 5 mm to 25 mm, preferably from 8 mm to 20 mm, more preferably of from 10 mm to 15 mm.

11. A method (101) of three-dimensional printing of a fibre reinforced concrete structure, comprising the steps of: mixing (103), with a mortar mixing unit, a dry mortar mixture with an aqueous liquid into a fresh mortar mixture; transporting (105), with a first transport means, said fresh mortar mixture from said mortar mixing unit to a concrete mixing unit of a print head; transporting (107), with a second transport means, aggregates and fibres from a respective aggregate dosing unit and a fibre dosing unit to said concrete mixing unit of said print head; mixing (109), with said concrete mixing unit, said fresh mortar mixture with said aggregates and said fibres in a mixing chamber of said concrete mixing unit into a fibre reinforced concrete mixture; extruding (111), with an extruding unit, said fibre reinforced concrete mixture out of said mixing chamber and through a nozzle;driving (113), with a driving unit, said extruding unit thereby controlling a flow-rate of said fibre reinforced concrete mixture through said nozzle; measuring (115), with one or more first sensor means, an output flow rate of said fresh mortar mixture; measuring (117), with one or more second sensor means, an aggregate dosing rate; measuring (119), with one or more third sensor means, a fibre dosing rate; controlling (121), with a control unit, said output flow rate of said fresh mortar mixture, said aggregate dosing rate and said fibre dosing rate.

12. The method according to claim 11 comprising the step of: introducing (123), with a liquid chemical admixture injection unit, one or more chemical admixtures to said concrete mixing unit or to said extruding unit.

13. The method according to claim 12, comprising the step of: transporting (125), with a third transport means, said one or more chemical admixtures from a liquid chemical admixture injection unit to said concrete mixing unit or to said extruding unit.

14. The method according to claim 12 or 13, comprising the step of: collecting (127), with a dust filtration unit, dust from said aggregates before introducing said aggregates to said concrete mixing unit.

15. A computer program product, comprising a data storage device storing computer program code arranged for performing the method according to any of the claims 11 to 14, when said computer program code are loaded onto a memory of an electronic processing unit when executed by said electronic processing unit.

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