System and method for extruding beads of construction material for a robot for additive manufacturing of architectural structures

Abstract

The invention relates to a system for extruding beads of construction material for a robot (60) for additive manufacturing of architectural structures (70), the system comprising: a printhead (30) for printing beads of construction material, comprising an intake opening (31), an extrusion nozzle (34) and a mixing chamber (35) arranged between the intake opening (31) and the extrusion nozzle (34); a supply circuit (20) for supplying construction material; a device (40) for accelerating setting, which device opens into the mixing chamber (35); and a device (50) for retarding curing comprising a reservoir (52) of retarding additive, a duct (54) fluidically connecting the reservoir and the mixing chamber (35), and a positive displacement pump (56) arranged on the duct (54) and controlled so as to be able to meter the amount of retarder injected into the mixing chamber (35).

Description

[0001] DESCRIPTION

[0002] SYSTEM AND METHOD FOR EXTRUDING BUILDING MATERIAL STRANDS FOR A ROBOT FOR ADDITIVE MANUFACTURING OF ARCHITECTURAL STRUCTURES

[0003] Technical field of the invention

[0004] The invention relates to additive manufacturing (or 3D printing) of construction material. The invention relates more particularly to a system for extruding construction material cords for a robot for additive manufacturing of architectural structures by stacking successive layers of extruded cords.

[0005] Technological background

[0006] 3D printing of construction materials is a booming activity for which the applicant has already proposed numerous innovations to improve manufacturing processes.

[0007] Thus, the applicant has already proposed, in particular in applications WO20 18 / 051370, WO2018 / 229419, WO2019 / 048752, WO2019 / 038491 and WO2019 / 025698, systems for extruding beads of cementitious material for a robot for the additive manufacturing of architectural structures.

[0008] Throughout the text, the term "architectural structures" refers to both individual building elements (bridges, pillars, walls, street furniture, etc.), complete structures (buildings, houses, apartment blocks, etc.) and various architectural pieces (artistic works, sculptures, etc.).

[0009] The systems already proposed by the applicant provide numerous advantages over traditional techniques, including the possibility of creating complex shapes by adding successive layers of construction materials, the speed of construction operations, the reduction of costs and labor, improved safety on construction sites, etc.

[0010] These systems generally comprise a print head equipped with a construction material inlet and an extrusion nozzle (also referred to in the text as an "outlet nozzle") for extrusion beads of construction material, a circuit for supplying the inlet of the print head with construction material comprising a construction material storage tank, a pipe connecting the storage tank and the inlet of the print head, and a pump for feeding the pipe with construction material from the storage tank.

[0011] One of the difficulties in 3D printing construction materials is that the material must be supplied in a rheological state compatible with pumping this material, i.e. sufficiently fluid to be able to be pumped from the storage tank and conveyed to the outlet nozzle, while its state must be consistent enough (i.e. less fluid) at the outlet of the extrusion nozzle to be able to form a self-supporting layer capable of supporting the next layer.

[0012] There is thus a duality between the fluidity of the material during extrusion and the evolution of its consistency (hardening speed of the material). This duality is however naturally present in pasty materials such as cementitious materials where fluidity and consistency exist simultaneously and are quantified respectively by viscosity and shear threshold. The hardening or increase in consistency, however, goes hand in hand with a decrease in fluidity. The hardening speed is all the more critical for high-speed printing where it is necessary for the extruded beads to harden quickly to be able to support the following layers. In particular, a high printing flow rate leads to a rapid evolution of the mechanical loading on the previously deposited layers, their mechanical properties must therefore increase more quickly to support the loading at all times.Furthermore, complex geometries can generate bending forces due to the presence of overhangs, which generates significant stresses and requires rapid hardening of the previous layers.

[0013] The productivity of a cement printing system and the variety of possible shapes of the printed parts are therefore closely linked to the speed of hardening of the material after extrusion.

[0014] To accelerate the hardening of the cementitious material, it is now known to add an adjuvant such as a setting accelerator to the print head, just before the extrusion of the cementitious material.

[0015] The shear threshold of the material increases by adding this setting accelerator upstream of extrusion. This change in the shear threshold occurs during the dispersion of the setting accelerator within the print head. The change in the shear threshold depends in particular on the mixing time of the admixture with the cementitious material.

[0016] One of the disadvantages of this solution is that increasing the shear threshold too quickly can cause extrusion problems and deteriorate the quality of the cementitious material deposit (appearance of microcracks, deformation of previous layers). It is therefore necessary in practice to limit the quantity of accelerator injected into the cementitious material to avoid an increase in the extrusion pressure. This dosage limit therefore reduces the possible hardening speed and therefore the permitted printing speed.

[0017] The inventors therefore sought to propose a new solution which makes it possible to reconcile aspects which are a priori incompatible, namely printing speed, pumpability and fluidity of the cementitious material before extrusion, speed of hardening of the material after extrusion and quality of the extruded beads.

[0018] Objectives of the invention

[0019] The invention therefore aims to provide a construction material extrusion system which overcomes at least some of the drawbacks of known solutions.

[0020] The invention aims in particular to provide such a system which makes it possible to overcome the printing speed / material pumpability duality within the system.

[0021] The invention also aims to provide, in at least one embodiment, such a system which makes it possible to quickly print architectural structures without impacting the quality of the extruded cords.

[0022] The invention also aims to provide, in at least one embodiment, such a system which makes it possible to maintain the quality of the extruded bead regardless of the fluidity of the cementitious material delivered to the print head.

[0023] The invention also aims to provide, in at least one embodiment, such a system which makes it possible to decouple the quantity of accelerator used within the system from the shear threshold of the material at the outlet nozzle.

[0024] The invention also aims to provide, in at least one embodiment, such a system which makes it possible to obtain identical extruded cords throughout the printing of the structure.

[0025] The invention also aims to provide a method for extruding construction material.

[0026] Statement of the invention

[0027] To this end, the invention relates to a system for extruding construction material cords for a robot for additive manufacturing of architectural structures comprising: a construction material cord printing head comprising a construction material inlet mouth, an extrusion nozzle configured to form an extruded cord of material, and a mixing chamber arranged between the inlet mouth and the extrusion nozzle and extending in one direction, called the longitudinal direction, said printing head being intended to be moved by the additive manufacturing robot along a predetermined trajectory to form an architectural structure by stacking layers of said extruded cords,a construction material supply circuit for said print head comprising a construction material storage tank and a construction material supply line fluidly connecting said storage tank and said inlet of said print head, a setting accelerator device comprising an accelerator additive tank and a line fluidly connecting said tank and said mixing chamber of said print head so as to be able to inject the accelerator additive into the material present in the mixing chamber, upstream of the extrusion.,

[0028] The system according to the invention is characterized in that it further comprises a hardening retarding device comprising a retarding additive reservoir, a pipe fluidly connecting said retarding additive reservoir and said mixing chamber, and a volumetric pump arranged on said pipe and controlled to be able to dose the quantity of retarder injected into said mixing chamber.

[0029] The system according to the invention therefore has the particularity of combining the use of a setting accelerator device and a hardening retarder device.

[0030] The build material delivered to the inlet of the print head has a given consistency and therefore a stable shear threshold which depends on the intrinsic constitution of the build material. The addition of the setting accelerating admixture in the mixing chamber makes it possible to modify and increase the shear threshold of the build material. The shear threshold of the build material present in the mixing chamber therefore depends, in the absence of a retarding admixture, on the initial shear threshold of the material, the quantity of accelerating admixture injected into the mixing chamber and the mixing time required to disperse the accelerating admixture in the build material.

[0031] Injecting a hardening retarding additive into the mixing chamber can delay the effect of the setting accelerator additive, and even lower the initial shear threshold without impacting the increase in the shear threshold of the construction material, once extruded. Thus, the combined use of a setting accelerator and a hardening retarder eliminates the duality between the shear threshold of the material and the extrusion capacity of the construction material. It is therefore possible to precisely adjust the consistency of the construction material extruded by the print head by controlling the quantity of hardening retarding additive, for a given dosage of setting accelerator additive. Furthermore, it is also possible to compensate for any variability in the consistency of the construction material before adding the accelerator and thus obtain a consistent deposition quality.

[0032] The invention therefore makes it possible to choose the quantity of setting accelerator adjuvant by taking into account only the hardening needs of the architectural structure that one wishes to print and the desired printing speed, without worrying about the extrusion capacities of the corresponding material required.

[0033] The extrusion capacity is regulated by injecting the curing retarder upstream of the extrusion. This curing retarder makes it possible to delay the hydration reaction of the construction material caused by the addition and dispersion of the accelerator and thus increase its working time.

[0034] Throughout the text, unless otherwise stated, the terms "upstream" and "downstream" are used to refer to the flow of cementitious material within the extrusion system. In other words, the material upstream of the extrusion nozzle refers to the material in the print head (or in the feed circuit) while the material downstream of the extrusion nozzle refers to the extruded material, which has been deposited by the print head.

[0035] Advantageously and according to the invention, said pipe of said setting accelerator device and said pipe of said hardening retarder device open into a common pipe which itself opens into said mixing chamber so as to be able to mix together the setting accelerator additive and the hardening retarder additive before injection into the construction material present in the mixing chamber.

[0036] In other words, and according to this advantageous variant, the setting accelerator and hardening retarder additives are mixed together prior to dispersion in the construction material present in the mixing chamber of the print head. This mixing takes place in a pipe into which both the pipe of the setting accelerator device and the pipe of the hardening retarder device open. This common pipe opens directly into the mixing chamber.

[0037] Advantageously and according to another variant of the invention, said pipe of said setting accelerator device and said pipe of said hardening retarder device each open directly and separately from one another into said mixing enclosure.

[0038] According to this variant, the injections of the setting accelerator and the hardening retarder are carried out separately from each other. Preferably, the injection of the setting accelerator into the mixing chamber is carried out upstream of the injection of the hardening retarder into the mixing chamber. In other words and according to this variant, the setting accelerator is injected in the vicinity of the cementitious material inlet mouth in the print head and the hardening retarder is injected in the vicinity of the extrusion nozzle or closer to the extrusion nozzle than the injection of the setting accelerator.

[0039] Advantageously and according to the invention, the system further comprises an extrusion pressure sensor mounted on said print head and configured to measure the pressure of the material present in said mixing chamber, and said volumetric pump of said curing retarder device is controlled by said pressure measurement provided by said pressure sensor, so as to be able to automatically adjust the dosage of the curing retarder to the extrusion pressure.

[0040] According to this advantageous variant, the amount of hardening retardant additive is determined based on the material pressure measured in the mixing chamber. The combination of the pressure sensor and the control of the volumetric pump of the hardening retardant device forms a feedback loop that allows the amount of retardant additive to be modified based on the measured pressure. Thus, the system according to this variant ensures the quality of the extruded bead and the uniformity of the extruded bead. If the measured pressure reveals a thick material, a larger amount of hardening retardant additive is injected into the mixing chamber to delay the setting of the material and ensure the quality of the extruded bead.

[0041] Advantageously and according to this variant, the system comprises a control unit configured to receive the pressure measurement provided by said pressure sensor and to determine a command for said volumetric pump of said hardening retarding device.

[0042] The control unit may incorporate a software program which precisely determines the quantity of retarding admixture to be injected based on the pressure measurement provided by the pressure sensor and any information relating to the construction material present in the storage tank of the supply circuit (for example the initial shear threshold of the material, its fluidity, etc.).

[0043] Advantageously and according to the invention, said mixing chamber further comprises a dynamic mixer configured to be able to mix said cementitious material and said additives provided by said setting accelerator device and said hardening retarder device in said mixing chamber.

[0044] In this advantageous variant, the dynamic mixer allows the building material and additives (accelerator and retarder) to be mixed homogeneously upstream of the extrusion nozzle. The building material is fed to the mixing chamber, for example, by a eccentric screw metering pump, which allows the material to be conveyed to the chamber at a constant flow rate, without generating pulsations. In addition, this pump reduces any pulsations created by the feed pump.

[0045] The dynamic mixer comprises, for example, a shaft extending longitudinally in the mixing enclosure, and carrying radial fingers distributed along the shaft, and a motor configured to be able to drive this shaft in rotation so as to be able to provide a homogeneous mixture of the construction material and the additives.

[0046] A system according to this advantageous variant makes it possible to obtain a homogeneous mixture of the construction material and the additives. The presence of radial fingers distributed along the mixer shaft makes it possible to distribute the material particles evenly in the mixing chamber. Advantageously and according to the invention, said pipe of said hardening retarding device comprises at least one needle opening into said mixing chamber in an additive direction forming with the longitudinal direction, an angle of between 0 and 90°.

[0047] According to this variant, the hardening retardant admixture is added to the construction material in a mixing chamber following an admixture direction which forms a predetermined angle with the longitudinal direction. This longitudinal direction is the main direction of the mixing chamber, which is also the direction of the flow of cementitious material towards the outlet nozzle. The injection of admixtures following a predetermined admixture direction makes it possible to quickly obtain a homogeneous mixture of the cementitious material and the admixture. An admixture at 90°, i.e. a radial admixture, promotes the mixing of the admixtures with the construction material circulating in the vicinity of the central axis of the mixing chamber. An admixture close to 0° promotes the mixing of the admixtures with the material circulating in the vicinity of the walls of the mixing chamber. An admixture at 45° is a good compromise between the two angles previously described.

[0048] Advantageously and according to the invention, said hardening retarder is a material chosen from the group comprising aqueous solutions of polycarboxylate ether, polyacrylate ether, phosphonates, lignosulfonic acids, sulfonates, sugar derivatives and all compositions formed from one or more of these materials.

[0049] Throughout the text, the term "hardening retarder" refers to an admixture for cementitious material that delays the start of hardening of the cementitious material. Such a hardening retarder can be likened to a setting retarder.

[0050] The invention also relates to a method for extruding building material cords for a robot for additive manufacturing of architectural structures comprising: a step of supplying building material to a building material cord printing head comprising a building material inlet mouth, an extrusion nozzle configured to form building material cords, and a mixing chamber arranged between the inlet mouth and the extrusion nozzle, a step of injecting a setting accelerating additive into said mixing chamber to accelerate the setting of the cementitious material after extrusion, a step of injecting a hardening retarding additive into said mixing chamber, a step of extruding building material cords by said printing head.

[0051] The technical advantages and effects of the system according to the invention apply mutatis mutandis to an extrusion process according to the invention.

[0052] A method according to the invention is advantageously implemented by an extrusion system according to the invention and an extrusion system according to the invention advantageously implements a method according to the invention.

[0053] Advantageously and according to the invention, the method further comprises: a measurement of the pressure of the material present in said mixing enclosure, a control of the quantity of retarding adjuvant injected into said mixing enclosure as a function of said measured pressure.

[0054] In this advantageous variant, the amount of curing retardant admixture is determined based on the material pressure measured in the mixing chamber. The combination of the pressure sensor and the control of the amount of curing retardant admixture forms a feedback loop that allows the amount of curing retardant admixture to be modified based on the measured pressure.

[0055] The invention also relates to an extrusion system and an extrusion method characterized in combination by all or part of the features mentioned above or below.

[0056] List of figures

[0057] Other aims, characteristics and advantages of the invention will appear on reading the following description given solely for non-limiting purposes and which refers to the appended figures in which:

[0058] [Fig. 1] is a schematic view of an extrusion system according to one embodiment of the invention,

[0059] [Fig. 2] is a schematic view of a print head of a system according to one embodiment of the invention,

[0060] [Fig. 3] is a schematic view of a print head of a system according to another embodiment of the invention,

[0061] [Fig. 4] is a schematic view of an extrusion process according to one embodiment of the invention.

[0062] Detailed description of an embodiment of the invention

[0063] In the figures, scales and proportions are not strictly observed for the purposes of illustration and clarity. Throughout the detailed description which follows with reference to the figures, unless otherwise indicated, each element of the extrusion system is described as it is arranged when the extrusion system is implemented in the context of the manufacture of an architectural structure by stacking layers of extruded cords.

[0064] Furthermore, identical, similar or analogous elements are designated by the same references in all figures.

[0065] An extrusion system according to the invention comprises, as shown in Figure 1, a print head 30 intended to be moved by a robot 60 to form an architectural structure 70 by stacking beads extruded by the print head, a circuit 20 for supplying construction material to the print head comprising in particular a storage tank 10, a setting accelerator device 40 intended to inject an accelerator adjuvant into the print head, and a setting retarder device 50 intended to inject a setting retarder adjuvant into the print head. As schematically illustrated in Figure 1, the robot 60 carries the print head 30 and ensures the movement of the print head along a predetermined path to form an architectural structure 70 by adding successive layers of beads of construction material extruded from the print head 30.

[0066] Throughout the following, the invention is described considering that the construction material used is a cementitious material, it being understood that any other viscous paste construction material can be used within the framework of this invention.

[0067] Each of the different subsystems of the extrusion system will now be described in detail, in particular with reference to Figures 1, 2 and 3.

[0068] Storage tank

[0069] The storage tank 10 is preferably a hopper comprising an upper opening 11 adapted to receive batches of cementitious materials and a lower outlet 12 connected to the supply circuit 20. The hopper may further comprise an agitator 13 comprising a shaft 14 carrying a plurality of lateral blades via axes perpendicular to the shaft 14, and a motor 16 for rotating the shaft 14. The motor 16 is for example an electric motor configured to be able to drive at low speed, for example at a speed of six revolutions per minute, the shaft 14 of the agitator 13. The use of a thermal or hydraulic motor is of course possible without modifying the performance of the extrusion system according to the invention. The role of the agitator is to be able to maintain the cementitious material in the hopper in a quasi-constant rheological state before being conducted to the print head by the supply circuit 20.

[0070] The cementitious material used is, for example, a cement-based premix with fine particles, hydrated and fluidified.

[0071] Power supply circuit

[0072] The supply circuit 20 connects the storage tank 10 to the print head 30. This circuit comprises a pipe 21 connecting the outlet 12 of the storage tank 10 to an inlet 31 of the print head 30. The supply circuit 20 further comprises a booster pump 22. This booster pump 22 is for example an eccentric screw pump so as to be able to convey the cementitious material to the print head 30 while minimizing pulsations.

[0073] Print head

[0074] The print head 30 comprises, as schematically represented by FIGS. 2 and 3, an inlet mouth 31 connected to the supply circuit 20 and a nozzle 34 for extruding cementitious material configured to form beads of cementitious material.

[0075] The print head further comprises a mixing chamber 35 arranged upstream of the extrusion nozzle 34. This mixing chamber 35 is equipped with a dynamic mixer 37 adapted to be able to mix the cementitious material and the accelerator and retarder admixtures provided by the accelerator 40 and retarder 50 devices described later.

[0076] The dynamic mixer comprises, for example, a shaft extending longitudinally in the mixing enclosure 35 on which radial fingers are mounted distributed along the shaft 37. The dynamic mixer also comprises a motor 39 configured to be able to drive the shaft 37 in rotation so as to be able to provide a homogeneous mixture of the cementitious material. This motor 39 can be an electric motor, a thermal motor, and generally all types of motors.

[0077] The print head 30 also comprises an eccentric screw metering pump 32 configured to be able to convey the cementitious material from the inlet mouth 31 to the extrusion nozzle 34, passing through the mixing enclosure 35. Such a metering pump is for example an eccentric screw jacket pump. Of course, other pumps can be used without modifying the performance of the invention. This metering pump is for example driven in rotation by an electric motor 38.

[0078] The extrusion nozzle 34 of the print head is preferably removable so as to be able to adapt the shape of the extrusion nozzle 34 to the part to be manufactured. In particular, the section of the extrusion nozzle 34 can be adapted to each type of part manufactured, or even changed during printing to modify the section of the beads of certain portions of the part manufactured. To do this, the extrusion nozzle comprises for example a threaded external wall which cooperates with a threaded internal portion of the wall of the print head delimiting the mixing enclosure 35. According to another variant, the extrusion nozzle comprises a threaded internal wall which cooperates with a threaded external portion of the wall of the print head.

[0079] Setting accelerator device

[0080] The system according to the invention also comprises a setting accelerator device 40 comprising a reservoir of accelerator adjuvant 42 and a pipe 44 fluidly connecting the reservoir 42 and the mixing enclosure 35 of the print head 30. The device 40 also comprises a volumetric pump 46 arranged on the pipe 44. This volumetric pump 46 is controlled by a control unit 80 to meter the quantity of accelerator injected into the mixing enclosure 35.

[0081] According to the embodiment of Figure 2, the pipe 44 opens into a pipe 48 which itself opens into the mixing chamber via an injection needle. This pipe 48 also receives the retarding additive from the setting retarding device 50 described later.

[0082] According to the embodiment of Figure 3, the pipe 44 opens directly into the mixing enclosure 35.

[0083] Hardening retardant device

[0084] The system according to the invention further comprises a curing retarder device 50 comprising a retarder additive reservoir 52 and a pipe 54 fluidly connecting the reservoir 52 and the mixing enclosure 35 of the print head 30. The device 50 also comprises a volumetric pump 56 arranged on the pipe 54. This volumetric pump 56 is controlled by the control unit 80 to meter the quantity of retarder injected into the mixing enclosure 35.

[0085] According to the embodiment of Figure 2, the pipe 54 opens into the pipe 48 which itself opens into the mixing chamber via an injection needle. This pipe 48 also receives the accelerator additive from the setting accelerator device. Thus, the setting accelerator additive and the hardening retardant additive are mixed together before injection into the mixing chamber 35.

[0086] According to the embodiment of Figure 3, the pipe 54 opens directly into the mixing enclosure 35.

[0087] Feedback loop

[0088] The system according to the invention preferably further comprises a feedback loop formed by a pressure sensor 82, the control unit 80 and the volumetric pump 56.

[0089] The pressure sensor 82 is mounted on the print head and configured to measure the pressure of the material present in the mixing chamber 35.

[0090] The control unit 80 is configured to acquire the pressure measurement provided by the pressure sensor 82 and determine a command for the volumetric pump 56 of the retarder device 50 which makes it possible to modify the pressure value of the cementitious material present in the mixing enclosure 35.

[0091] In Figures 2 and 3, the solid lines that start from the control unit 80 and arrive at the control unit 80 represent the measurement reception lines and the control lines. These may be wired or wireless lines depending on the nature of the components concerned.

[0092] The control unit comprises, for example, a regulator known by the acronym PID (Proportional, Integral, Derivative) having as a setpoint a sliding average of the extrusion pressure measured by the pressure sensor 82.

[0093] The system according to the invention also preferably comprises a pressure sensor 84 arranged in the vicinity of the inlet mouth 31 of the print head. This pressure measurement provided by the sensor 84 can for example be used to control the feed pump 22 of the cement material supply circuit of the print head. This pressure measurement can also be used to control the volumetric pump of the setting accelerator device 40.

[0094] The flow rate of the feed pump is controlled for example, by the use of a PID regulator, on the pressure measurement provided by the sensor 84 having as a setpoint a constant target inlet pressure, or possibly equal to a sliding average of the extrusion pressure measured by the sensor 82.

[0095] Figure 4 is a schematic view of a process for extruding beads of cementitious material for an additive manufacturing robot for architectural structures according to the invention.

[0096] Such a method comprises a first step E1 of supplying construction material, such as a cementitious material, to a print head of construction material cords from a construction material storage tank connected to the print head by a supply line equipped, for example, with a booster pump.

[0097] The method also includes a step E2 of injecting a setting accelerator additive into the mixing chamber to accelerate the setting of the cementitious material after extrusion. The quantity of accelerator is determined in particular according to the specifications of the targeted architectural structure.

[0098] The method also includes a step E3 of measuring the pressure of the material present in the mixing chamber.

[0099] The method comprises a subsequent step E4 of controlling the volumetric pump of the delay device.

[0100] The method comprises a subsequent step E5 of injecting a hardening retarding admixture into the mixing chamber, so as to delay the start of hardening of the cementitious material present in the mixing chamber.

[0101] The process finally includes a step E6 of extrusion of construction material beads by the print head.

[0102] A method according to the invention makes it possible to obtain quality beads, uniform regardless of the consistency of the material feeding the print head. Controlling the quantity of retarder directly in the mixing chamber makes it possible to obtain quality extrusion without impacting the consistency of the extruded material. The invention therefore makes it possible to obtain uniform beads for a given flow rate of material and setting accelerator additive by monitoring the pressure of the material in the mixing chamber.

[0103] The robot used to move the print head can be of any type. It can be a six-axis robot, mounted on rails or not, on a gantry or not. The robot can also be a cable-driven robot or any type of robot whose positioning system, such as an articulated arm, can be controlled by a computer.

[0104] A system according to the invention can be used to manufacture all types of architectural parts. Such an architectural part can be a reinforcement part, a building, and generally, any part made of cementitious material. The architectural parts manufactured by the use of an extrusion system according to the invention can be of various scales. It can be a portion of a post, an entire post, a wall, a slab element, a building, street furniture, a sculpture, etc.

Claims

CLAIMS 1. System for extruding building material cords for a robot (60) for additive manufacturing of architectural structures (70) comprising: a print head (30) for building material cords comprising an inlet mouth (31) for building material, an extrusion nozzle (34) configured to form an extruded cord of material, and a mixing chamber (35) arranged between the inlet mouth and the extrusion nozzle and extending in one direction, called the longitudinal direction, said print head (30) being intended to be moved by the additive manufacturing robot (60) along a predetermined trajectory to form an architectural structure (70) by stacking layers of said extruded cords,a supply circuit (20) for building material for said print head comprising a reservoir (10) for storing building material and a supply line (21) for building material connecting said storage reservoir (10) and said inlet of said print head (30), a setting accelerator device (40) comprising a reservoir of accelerator adjuvant (42) and a line (44) fluidly connecting said reservoir and said mixing chamber (35) of said print head so as to be able to inject the accelerator adjuvant into the material present in the mixing chamber, characterized in that it further comprises a curing retarder device (50) comprising a reservoir of retarder adjuvant (52), a line (54) fluidly connecting said reservoir and said mixing chamber (35),and a volumetric pump (56) arranged on said pipe (54) and controlled to be able to dose the quantity of retarder injected into said mixing chamber (35)., 2. System according to claim 1, characterized in that said pipe (44) of said setting accelerator device (40) and said pipe (54) of said hardening retarder device (50) open into a common pipe (48) which itself opens into said mixing chamber (35) so as to be able to mix together the setting accelerator additive and the hardening retardant additive before injection into the construction material present in the mixing chamber (35).

3. System according to claim 1, characterized in that said pipe (44) of said setting accelerator device (40) and said pipe (54) of said hardening retarder device (50) each open directly and separately from one another into said mixing enclosure (35).

4. System according to one of claims 1 to 3, characterized in that it further comprises an extrusion pressure sensor (82) mounted on said print head (30) and configured to measure the pressure of the material present in said mixing chamber (35), and in that said volumetric pump (56) of said curing retarder device (50) is configured to be controlled by said pressure measurement provided by said pressure sensor (82), so as to be able to automatically adjust the dosage of the curing retarder to the extrusion pressure.

5. System according to claim 4, characterized in that it comprises a control unit (80) configured to receive the pressure measurement provided by said pressure sensor (82) and to determine therefrom a command of said volumetric pump (56) of said curing retarding device (50).

6. System according to one of claims 1 to 5, characterized in that said mixing enclosure (35) further comprises a dynamic mixer (37) configured to be able to mix said cementitious material and said additives provided by said setting accelerator device (40) and said hardening retarder device (50) in said mixing enclosure.

7. System according to one of claims 1 to 6, characterized in that said pipe (54) of said hardening retarding device (50) comprises at least one needle opening into said mixing enclosure (35) in an adjuvantation direction forming with the longitudinal direction, an angle of between 0 and 90°.

8. System according to one of claims 1 to 7, characterized in that said curing retarder is selected from the group comprising aqueous solutions of polycarboxylate ether, polyacrylate ether, phosphonates, lignosulfonic acids, sulfonates, sugar derivatives and any combinations formed from one or more of these materials 9. Method for extruding building material cords for a robot for additive manufacturing of architectural structures comprising: a step (El) of supplying building material to a building material cord printing head comprising a building material inlet mouth, an extrusion nozzle configured to form building material cords, and a mixing chamber arranged between the inlet mouth and the extrusion nozzle, a step (E2) of injecting a setting accelerating additive into said mixing chamber to accelerate the setting of the cementitious material after extrusion, a step (E5) of injecting a hardening retarding additive into said mixing chamber, a step (E6) of extruding building material cords by said printing head.

10. Extrusion method according to claim 9, characterized in that it further comprises: a pressure measurement (E3) of the material present in said mixing chamber, a control (E4) of the quantity of hardening retardant additive injected into said mixing chamber as a function of said measured pressure.

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