The present application claims priority from the Singapore patent application no. 10202012256X, the contents of which are incorporated herein in entirety by reference.

TECHNICAL HELD

[0001] The present disclosure relates to the field of additive manufacturing, and more particularly to concrete additive manufacturing.

BACKGROUND

[0002] Extrusion-based 3D concrete printing (3DCP) or concrete additive manufacturing refers to the buildingof a structure by extruding materials lay er-atop-lay er through a nozzle. One of the main benefits of the 3DCP technology is that it can perform formwork-free concrete construction with enhanced design freedom without additional labor and cost. In comparison to precast prefabrication of a structural unit, such as a prefabricated bathroom unit, concrete additive manufacturing advantageously enables smaller batches to be fabricated economically and has greater flexibility for customization. One hurdle to broader applications of 3DCPin the construction sector however is the need to improvethe structural integrity of end products.

SUMMARY

[0003] In one aspect, the present disclosure provides an apparatus for concrete additive manufacturing, the apparatus comprising: a housing coupleable to an actuator, the housing defining: a main nozzle defining a main axis, the main nozzle being configured to extrude a flowable concrete material to form a concrete extrudate; and a first peripheral nozzle disposed adjacent to the main nozzle, the first peripheral nozzle configured to extrude a first bonding agent to form a first bonding agent extrudate, wherein the housing is configured to be moveable by the actuator to undergo a movement along a curvilinear printing path, wherein the movement includes a translational movement concurrent with a rotational movement about the main axis.

[0004] The apparatus as described above, wherein the first peripheral nozzle and the main nozzle are configured to undergo the rotational movement about the main axis as a rigid body.

[0005] The apparatus according to any described above, wherein the first peripheral nozzle is coupled to the main nozzle at one of a leading side and a trailing side of the main nozzle.

[0006] The apparatus according to any described above, wherein the first bonding agent is a viscous material.

[0007] The apparatus according to any described above, wherein the apparatusis configured to selectively: deposit the concrete extrudate ahead of depositing the first bonding agent extrudate relative to the printing path, responsive to the apparatus being in a first configuration ; or deposit the concrete extrudate behind that of laying the first bonding agent extrudate relative to the printing path, responsive to the apparatus being in a second configuration.

[0008] The apparatus according to any described above, wherein the first bonding agent extrudate has a width smaller or equal to a width of the concrete material extrudate. The apparatus according to any described above, wherein the first bonding agent extrudate is formed substantially in line with the printingpath. The apparatus accordingto any described above, wherein the first bonding agent extrudate is deposited parallel to the printing path.

[0009] The apparatus according to any described above, wherein the main nozzle is configured with a polygonal outlet. The apparatus according to any described above, wherein the polygonal outlet is a rectangular outlet.

[0010] The apparatus according to any described above, wherein the housing is configured to be rotatably coupleable to the actuator, wherein the apparatus is rotatable about the main axis.

[0011] The apparatus according to any described above, further comprising a first spreader disposed adjacent to the first peripheral nozzle, wherein the first spreader is configured to redistribute the first bonding agent extrudate. The apparatus according to any described above, wherein the first bonding agent extrudate is spread on a selected surface of the concrete extrudate. The apparatus according to any described above, wherein the main nozzle and the first spreader are disposed on opposing sides of the first peripheral nozzle. The apparatus according to any described above, wherein the main nozzle and the first peripheral nozzle are disposed on opposing sides of the first spreader.

[0012] The apparatus according to any described above, wherein the housingfurther defines a main channel in fluid communication with the main nozzle, the main channel being configured to receive the flowable concrete material from a concrete source. The apparatus according to any described above, wherein the housing further defines a first peripheral channel in fluid communication with the first peripheral nozzle, the first peripheral channel being configured to receive the first bonding agent from a first bonding agent source. The apparatus according to any described above, wherein the first peripheral channel is configured as a funnel, the first peripheral channel includes a receiving opening substantially larger than the first peripheral nozzle.

[0013] The apparatus according to any described above, further comprising a flow splitter, the flow splitter being in fluid communication with the first bonding agent source, the flow splitter having at least two flow outlets, wherein the at least two flow outlets are configured to direct the first bonding agent from a first bonding agent source into respective distinct regions of the receiving opening of the first peripheral channel. The apparatus according to any described above, wherein the distinct regions of the receiving opening are diametrically disposed about the main axis.

[0014] The apparatus according to any described above, wherein the firstperipheral channel is sealingly connected to the first bonding agent source to form a pressurized chamber in the first peripheral channel.

[0015] The apparatus according to any described above, wherein the housingfurther defines a second peripheral nozzle configured to extrude a second bonding agent as a second bonding agent extrudate, wherein the second peripheral nozzle and the first peripheral nozzle are disposed on opposing sides of the main nozzle in line with the printing path. The apparatus according to any described above, further comprising a second spreader disposed adjacent to the second peripheral nozzle, wherein the second spreader is configured to redistribute the second bonding agent extrudate. The apparatus according to any described above, wherein the housing further defines a second peripheral channel, the second peripheral channel being in fluid communication with the second peripheral nozzle, and wherein the second peripheral channel is configured to receive a second bonding agent from a second bonding agent source.

[0016] The apparatus according to any described above, wherein the secondbonding agent is characterized by a different composition from the first bonding agent.

[0017] In another aspect, a system for concrete additive manufacturing comprises: the apparatus according to any described above; an actuator coupled to the apparatus; and an actuator controller configured to control the actuator to move the apparatus along the printing path to lay the concrete extrudate and the first bonding agent extrudate.

[0018] The system according to any described above, wherein the actuator controller is configured to control the actuator to rotate the apparatus along a curved portion of the curvilinear printing path.

[0019] The system according to any described above, wherein at least one of the bonding agents is a viscous material.

[0020] The system according to any described above, wherein at least one of the bonding agents is a cement paste with a 0.26 water-to-cement ratio.

[0021 ] The system according to any described above, wherein the at least one of the bonding agents comprises a superplasticizer.

[0022] In another aspect, the present document discloses a method of concrete additive manufacturing, the method comprising: extruding a flowable concrete material via a main nozzle to form a concrete extrudate, the main nozzle defining a main axis; extruding a first bonding agent via a first peripheral nozzle to form a first bonding agent extrudate; and providing a movement of the main nozzle and the first peripheral nozzle along a curvilinear printing path, wherein the movement includes a translational movement concurrent with a rotational movement about the main axis, and wherein the movement is concurrent with the extruding of the flowable concrete material and the extrusion of the first bonding agent.

[0023] The method according to any described above, wherein the first peripheral nozzle and the main nozzle are configured to undergo the rotational movement about the main axis as a rigid body.

[0024] The method according to any described above, wherein the first bonding agent is a viscous material.

[0025] The method according to any described above, the method comprising one of: depositing the concrete extrudate ahead of depositing the first bonding agent extrudate relative to the printing path, responsive to the apparatus being in a first configuration; and depositing the concrete extrudate behind that of laying the first bonding agent extrudate relative to the printing path, responsive to the apparatus being in a second configuration.

[0026] The method according to any described above, wherein the first bonding agent extrudate is deposited parallel to the concrete extrudate, the concrete extrudate being extruded via a rectangular outlet of the main nozzle.

[0027] The method according to any described above, further comprising: spreading the first bonding agent extrudate on a selected surface of the concrete extrudate.

[0028] The method according to any described above, wherein the first bonding agent is spread concurrently with the movement of the main nozzle and the first peripheral nozzle.

BRIEF DESCRIPTION OF DRAWINGS

[0029] Fig. 1 is a schematic diagram of a system for concrete additive manufacturing according to an embodiment of the present disclosure;

[0030] Fig. 2 is an example of a concrete structure 3D printed by the system of Fig. 1 ;

[0031] Fig. 3 A is an isometric view of an apparatus according to an embodiment of the present disclosure;

[0032] Fig. 3B is a sectional view of the apparatus of Fig. 3A

[0033] Fig. 4 A is a side view of the apparatus of Fig. 3 A in a first configuration;

[0034] Fig. 4B is a side view of the apparatus of Fig. 3A in a second configuration; [0035] Fig. 5 is a sectional view of the apparatus of Fig. 3 A;

[0036] Fig. 6 is a top isometric view of the apparatus of Fig. 3 A;

[0037] Fig. 7A is a top view of a curved portion of a printing path according to an embodiment;

[0038] Fig. 7B shows a sectional view of a rectangular concrete extrudate according to Fig. 7A;

[0039] Fig. 7C is a top view of the apparatus at different positions of the curved portion of Fig. 7A;

[0040] Fig. 7D is a top view of the apparatus rotating between the first orientation and the second orientation;

[0041] Fig. 8 is a side view of an apparatus according to another embodiment of the present disclosure;

[0042] Fig. 9 is an isometric view of the apparatus according to one embodiment;

[0043] Fig. 10 is a detailed view of the apparatus according to another embodiment;

[0044] Fig. 11 is a side view of the apparatus of Fig. 10;

[0045] Fig. 12 is an isometric view of an apparatus according to yet another embodiment;

[0046] Fig. 13 is a detailed view of the apparatus of Fig. 12;

[0047] Fig. 14 is a side view of the apparatus of Fig. 12;

[0048] Figs. 15A and 15B are images of cross sections showing defects in a specimen of a printed structure;

[0049] Figs. 15C and 15D are images of cross sections of a specimen 3D printed using an embodiment of the present disclosure;

[0050] Fig. 16 is a plot of the relative bond strength of the printed structures of Figs. 15A to 15D;

[0051 ] Fig. 17 is a sectional view of an apparatus according to another embodiment;

[0052] Fig. 18 is a side view of the apparatus of Fig. 17;

[0053] Fig. 19 is a sectional view of an apparatus according to yet another embodiment;

[0054] Fig. 20 is a side view of an apparatus according to Fig. 19; and

[0055] Fig. 21 is a schematic flow diagram of a method of concrete additive manufacturing according to the present disclosure.

DETAILED DESCRIPTION

[0056] Reference throughout this specification to “one embodiment”, “another embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, that the various embodiments be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, some or all known structures, materials, or operations may not be shown or described in detail to avoid obfuscation.

[0057] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. As used herein, the singular ‘a’ and ‘an’ may be construed as includingthe plural “one or more” unless apparent from the context to be otherwise.

[0058] Terms such as “first” and “second” are used in the description and claims only for the sake of brevity and clarity, and do not necessarily imply a priority or order, unless required by the context. The terms "about" and "approximately" as applied to a stated numeric value encompasses the exact value and a reasonable variance as will be understood by one of ordinary skill in the art, and the terms “generally” and “substantially” are to be understood in a similar manner, unless otherwise specified.

[0059] For the sake of brevity, the terms “3D concrete printing”, “concrete additive manufacturing”, “3D concrete manufacturing”, “concrete additive printing”, and “3D concrete printing” are used interchangeably. The terms “concrete extrudate”, “concrete layer”, “concrete extrudate layer”, “concrete printing material”, and “concrete deposit”, etc. are used interchangeably. Similarly, terms “bonding agent extrudate”, “bonding agent layer”, “bonding agent material”, and “bonding agent deposit”, etc. are also used interchangeably.

[0060] In this disclosure, the term “extrude” or “extrusion” refers to the action or process of molten/semi-solid/solid material passing through an outlet of an apparatus to be shaped and formed as a continuous material with a generally uniform cross section. The terms “extrude”, “deposit”, “lay”, “print”, and “form” maybe used interchangeably as the context will make clear. Similarly, “extrudate” refers to an end product of extrusion, namely, a continuous molten/semi-solid/solid material, of a viscosity enabling the material to be flowable and generally taking on a cross section or profile determined by the outlet of the nozzle/app aratu s .

[0061] To aid understanding, the various embodiments of the present disclosure will refer to a concrete extrudate as the primary extrudate for use in fabricating a structure/building structure. However, it will be understood from the context that the present apparatus can similarly be used with other types of viscous materials. The term “viscous material” is used herein to describe materials that is flowable for use in 3D printing of large structural products (such as building units) and viscous enough to hold a pre-determined shape for the purpose of forming products requiring a certain degree of structural strength and integrity. A conventional apparatus designed to deliver a spray or jet of materials would therefore not be suitable for use with a viscous material as the viscous material will clog up the jet/spray outlet, in the context of the term “viscous material” as used herein.

[0062] Further, the terms “concrete printing material”, “concrete material”, “molten concrete material”, and “flowable concrete material” as used herein refer to flowable cement or concrete material suitable for 3D concrete printing. Such flowable concrete material may encompass different materials of differing physical and chemical properties, such as differing viscosity, water content, expansion/contraction coefficients, thermal conductivity, etc. Upon the concrete printed material setting or hardening, the respective hardened concrete printed material may have differing physical and chemical properties (as compared to its flowable state). The concrete printed material may be described in terms of properties, such as but not limited to Young’s Modulus (E), strength, hardness, fracture toughness, Poisson ratio, etc., relative to the properties of the material prior to its setting or hardening.

[0063] The bonding agents disclosed herein may encompass different materials of different chemical compositions with differing physic al and chemical properties. As an example, a bonding agent suitable for used with the present disclosure may be selected from a range of bonding agents having a large range of viscosity, ranging from low viscosity free flowing material to a high viscosity slow flowing material. Examples of bonding agents include, but are not limited to, water, cement strengthener, polymer solution, cement paste, etc.

[0064] Various embodiments of an apparatus for concrete additive manufacturing are disclosed. As shown in Fig. 1, disclosed is an embodimentof a system 100 for concrete additive manufacturing, for example 3DCP. For the sake of brevity and clarity, selected portions of the system 100 are shown and described in detail. The system 100 includes an apparatus 200; an actuator 300 coupled to the apparatus 200; and a pump system 400 in fluid communication with the apparatus 200. The actuator 300 may be coupled to and controllable by an actuator controller 310. The pump system 400 includes a concrete source 410. The concrete source 410 may be coupled to a concrete pump 420 which is configured to provide a flowable concrete material to the apparatus 200. The pump 400 may further include a first bonding agent source 430 coupled to a first bonding agent pump 440. The first bonding agent pump 440 is configured to provide a first bonding agent to the apparatus 200. One or more pump controller 490 is configured to control the concrete pump 420 and the first bonding agent pump 440. In some embodiments, there is more than one bonding agent source and more than one respective bonding agent pump. The actuator controller 310 is configured to control the actuator 300 such that the apparatus 200 travels along a curvilinear printing path 80 to lay a concrete extrudate and a first bonding agent extrudate. [0065] Fig. 2 illustrates a concrete structure printable by the system 100 according to an example of a curvilinear printing path 80. The printing path 80 may be configured as a closed loop. The printing path 80 may include straight portions 80a and curved portions 80b. The printing path 80 may iteratively pass through a point in space multiple times. It may be appreciated that printing path 80 may include overlapping closed loops such that concrete extrudates are formed on top of previously concrete extrudate layers.

[0066] Figs. 3A and 3B illustrate an embodiment of an apparatus 200 according to the present disclosure. The apparatus 200 includes ahousing 210 coupleable to the actuator 300 via a coupler 320. The actuator 300 is configured to move the apparatus 200 along the printing path 80 and to rotate the apparatus 200 about a main axis 226. The apparatus 200 is configured to be moveable by the actuator 300 to undergo a movement along a curvilinear printing path 80, wherein the movement includes translational movement concurrent with rotational movement about the main axis 226. The housing 210 defines a main nozzle 220 and a first peripheral nozzle 230 disposed adjacent to the main nozzle 220. The main nozzle 220 is configured to extrude a concrete printing material to form a concrete extrudate 60. The first peripheral nozzle 230 is configured to extrude a first bonding agent to form a first bonding agent extrudate 70. The first peripheral nozzle 230 and the main nozzle 220 are configured to undergo rotational movement about the main axis 226 as a rigid body.

[0067] In an example, the first peripheral nozzle 230 is disposed adjacent to the main nozzle 220 with an offset 223 (OS) therebetween (e.g., as shown in Fig. 4A or Fig. 4B). The apparatus 200 is configured to allow the concrete extrudate 60 and the first bonding agent extrudate 70 to be deposited one ahead of the other, without any obstruction to the concrete printing process. The concrete extrudate 60 and the first bonding agent extrudate 70 can be controllab ly printed in alignment with one another, and in alignment with the printing path 80. In some embodiments, as schematically illustrated in Fig. 4A, the concrete extrudate 60 is deposited ahead of the first bonding agent extrudate 70. While the deposition of the concrete extrudate 60 and the first bonding agent extrudate 70 may be timewise occurring simultaneously or concurrently, spatially the concrete extrudate 60 is deposited ahead of the firstbonding agent 70. In other words, relative to the printing path 80, the concrete extrudate 60 is deposited ahead of the first bonding agent extrudate 70. The first bonding agent extrudate 70 is laid atop the concrete extrudate 60, such that the printed first bonding agent extrudate 70 may be in alignment with both the current layer of concrete extrudate 60 and the next printed layer of concrete extrudate. That is to say, a centerline 70a defined by the first bonding agent extrudate 70 and a centerline 80a defined by the concrete extrudate 60 are substantially parallel to one another or the printing path 80. The printed first bonding agent extrudate 70 may be sandwiched between the current layer of concrete extrudate 60 and the next/subsequently printed layer of concrete extrudate.

[0068] In other embodiments, as schematically illustrated in Fig. 4B, the concrete extrudate 60 is deposited behind that of the first bonding agent extrudate 70, relative to the printing path 80. The first bonding agent extrudate 70 is deposited atop a previously deposited layer of concrete extrudate 60b. The first bonding agent extrudate 70 may be aligned with and sandwiched between the current layer of concrete extrudate 60 and the previously (and most recently) deposited layer of concrete extrudate 60b.

[0069] As shown in Fig. 4A, the apparatus 200 illustrates the first peripheral nozzle 230 coupled to the main nozzle 220 at a trailing side 225 of the main nozzle 220. The apparatus 200 is in a first configuration in which the main nozzle 220 is configured to spatially travel ahead of or in front of the first peripheral nozzle 230 along the printing path 80. The first peripheral nozzle 230 may be configured to be disposed adjacent or proximal to a trailing side 225 of the main nozzle 220, in which the trailing side 225 is defined with reference to the printing path 80. In this first configuration, the apparatus 200 is configured to deposit the concrete extrudate 60 along the printing path 80 ahead of depositing the first bonding agent extrudate 70. In the first configuration, the first bonding agent extrudate 70 is deposited atop the top surface of the concurrently laid concrete extrudate layer 60. Upon depositing the first bonding agent extrudate 70, the first bonding agent extrudate 70 is compressed or spread apart by a subsequent layer of concrete extrudate 60a. For a bonding agent with a lower viscosity, the bonding agent extrudate may first flow under gravity to spread across the concrete extrudate 60. The firstbonding agent extrudate 70 may be formed substantially in line with the printing path 80, or in other words, the first bonding agent extrudate 70 may be laid on or applied generally at a center of the concrete extrudate layer 60. In the first configuration, there is a time interval between the printing of the firstbonding agent extrudate 70 and the printing of a subsequent layer of concrete extrudate 60a (to be stacked atop the printed first bonding agent 70). The first configuration may be selected to allow fora longer hardening/setting time to lapse between depositing the firstbonding agent and depositing a subsequent layer of concrete extrudate. This enables more control over the hardening/setting time for increasing interlayer bond strength. In some embodiments, for example, where the bonding agent properties or effect do not vary or deteriorate quickly upon deposition, the first configuration maybe employed.

[0070] As shown in Fig. 4B, the apparatus 200 illustrates the first peripheral nozzle 230 coupled to the main nozzle 220 at a leading side 227 of the main nozzle 220. The apparatus 200 is in a second configuration in which the first peripheral nozzle 230 is configured to travel in front of or ahead of the main nozzle 220 along the printing path 80. The first peripheral nozzle 230 may be configured to be disposed adjacent or proximal to a leading side 227 of the main nozzle 220, in which the trailing side 227 is defined with reference to the printing path 80. In this second configuration, the apparatus 200 is configured to deposit the concrete extrudate 60 along the printing path 80 behind (after and on top of) the first bonding agent extrudate 70. In the second configuration, the firstbonding agent extrudate 70 is deposited atop a top surface of a previously (and most recently) deposited concrete extrudate layer 60b. The subsequent layer (currently deposited layer) of concrete extrudate 60 is thus deposited after the first bonding agent extrudate 70 is deposited. Upon laying down the first bonding agent extrudate 70, the first bonding agent extrudate 70 is immediately compressed, at least partially redistributed or otherwise spread by the layer of concrete extrudate 60. The second configuration may be selected in some examples, for example, if the first bonding agent extrudate 70 requires a relatively shorter hardening/setting time for a desired interlayer bond strength. The second configuration may also be useful in some embodiments where the first bonding agent extrudate 70 is time sensitive, for example, where the bonding agent properties or interlayer bonding effect varies or deteriorates relatively quickly upon deposition.

[0071] In some instances, the apparatus 200 may be configured such that the firstbonding agent extrudate 70 may be deposited “off-center” relative to a center of the subsequent and/or previously laid concrete extrudate layer 60 (e.g., 70b as shown in Fig. 7A), forming an off-center distance between where the first bonding agent extrudate 70 and the concrete extrudate layer 60 first contact the previously laid layer. [0072] In one example, an outlet 222 of the main nozzle 220 is configured to be larger relative to an outlet 232 of the first peripheral nozzle 230. Thus, the first bonding agent extrudate 70 has a width smaller than a width of the concrete material extrudate 60. This ensures the first bonding extrudate 70 does not spread exterior to an exterior of the concrete extrudate, thus resulting in a change in surface finish or a change in cross-sectional shape of the printed structure. In other examples, where the first bonding agent may be highly viscous and hence exhibits minimal flow upon extrusion, the first bonding agent extrudate 70 may be configured with a width about equal to a width of the concrete material extrudate 60.

[0073] In some embodiments, as the first bonding agent is deposited with the aid of gravitational force, the size of the outlet 232 of the peripheral nozzle 230 is determined based on a viscosity of the first bonding agent. For example, a highly viscous first bonding agent (such as cement paste) may require a larger outlet of the peripheral nozzle 230 (for example, 15 millimeters) in comparison to an outlet (for example, 6 to 8 mm) for a less viscou s first bonding agent (such as a polymer solution) . In other embodiments, the bonding agent forms a viscous bonding agent extrudate which exhibits minimal flow upon deposition. In one example, the bonding agent is a cement paste with 0.26 water-to-cement ratio. In another example, the cement paste includes a superplasticizer (such as ADVA 18 IN) with 0.35 weight percentage of cement content.

[0074] Similarly, the size of an outlet 222 of the main nozzle 220 may also be determined based on a viscosity of the flowable concrete printing material. As an example, a more viscous concrete printing material may require a larger outlet of the main nozzle 220 in comparison to a less viscous flowable concrete printing material. As an example, the main nozzle 220 may include a polygonal outlet, such that the main nozzle 220 is configured to form a polygonal concrete extrudate, i.e., a concrete extrudate having a polygonal cross section. In another example, the polygonal outlet may be configured with a rectangular outlet, such that the resulting concrete extrudate has a substantially rectangular cross section.

[0075] In an embodiment, the housing 210 is configured to be selectively coupleable (releasably engageable) to the actuator 300 in either the first configuration or the second configuration. For example, the housing 210 may initially be coupled to the actuator in one configuration, then decoupled from the actuator 300, and the same housing 210 may be reattached to the same actuator in the other configuration. Therefore, according to various operational considerations, such as the above-described, the housing 210 may be either coupled to the actuator 300 in the first configuration, or alternatively in the second configuration. In this embodiment, once the housing 210 is coupled to the actuator 300 in either of the first configuration or the second configuration, the housing 210 remains in the selected configuration throughout the printing process.

[0076] In another embodiment, the housing 210 is configured to be rotatably coupleable to the actuator 300. This enables the apparatus 200 to be rotated relative to the actuator 300 between the first configuration and the second configuration, i.e., the apparatus 200 may be rotatable to any position between and inclusive of the first configuration and the second configuration. As an example, the actuator 300 may be configured to rotate the apparatus 200 along the curved portion 80b of the printing path 80. This enables the apparatus to form a curved concrete extrudate and a curved first bonding agent extrudate 70 along the curved portion 80b.

[0077] As shown in Figs. 5 and 6, the housing 210 further defines a main channel 224 in fluid communication with the main nozzle 220. The main channel 224 may be disposed in line with the main nozzle 220 along a main axis 226. The main channel 224 is configured to receive a flowable concrete material from a concrete source 410 and to deliver the flowable concrete material to the main nozzle 220. The main channel 224 thus acts as a conduit to flow the flowable concrete material from the concrete source 410 to the outlet 222 of the main nozzle 220. In another example, the main channel 224 may be disposed forming an oblique angle with the main axis 226.

[0078] Further, the housing 210 also defines a first peripheral channel 234 in fluid communication with the first peripheral nozzle 230. The first peripheral channel 234 is configured to receive the first bonding agent from the first bonding agent source 430 and deliver the first bonding agent to the outlet 232 of the first peripheral nozzle 230. The first peripheral channel 234 may be configured as an annular channel surrounding the main channel 224. In one embodiment, the first peripheral channel 234 is configured as a funnel. The funnel 234 includes a receiving opening 236 substantially larger than the outlet 232 of the first peripheral nozzle 230. The funnel 234 defines sloped portions 234a configured to facilitate delivery of the first bonding agent via gravity, such that the first bonding agent in the funnel 234 may be substantially uniformly distributed about the first peripheral nozzle 230. This provides a substantially uniform fluid pressure to the first bonding agent in the funnel 234 and allows a consistent first bonding agent extrudate to be formed by the first peripheral nozzle 230.

[0079] The apparatus 200 is further provided with a flow splitter 241 in fluid communication with the first bonding agent source 430. The flow splitter 241 has two flow outlets 242 disposed diametrically on opposing sides of the main channel 224. The two flow outlets 242 are configured to direct the first bonding agent from the first bonding agent source 430 into respective distinct regions 236a/236b of the receiving opening 236. This allows the first bonding agent to be uniformly delivered to the first peripheral channel 230 regardless of the configuration of the apparatus 200, therefore allowing uniform distribution of firstbonding agent within the first peripheral channel 230. The funnel 234enables a more uniform delivery of the first bonding agent despite the different respective distances from each of the flow channels 242 to the first peripheral channel 230. The concrete delivery speed and the bonding agent conveying speed is coordinated such that the concrete deposition and the bonding agent deposition may be in a synchronized manner. In other embodiments, the flow splitter 241 may have more than two flow outlets, for example, a total of six flow outlets. The six flow outlets may be distributed symmetrically about the main axis 226 defined by the main channel 224.

[0080] Fig. 7 A illustrates the apparatus 200 navigating a curved portion of the printing path 80b. It can be seen that the concrete extrudate 60 follows the printing path 80b with a first radius (Rl), while the firstbonding agent extrudate follows a second printingpath 70a with a second radius (R2). The apparatus 200 includes a rectangular outlet configured to lay a corresponding rectangular concrete extrudate as shown in Fig. 7B. The printing path 80b and second printing path 70a may form a printing offset 70b between the firstbonding agent extrudate 70 and the concrete extrudate layers 60. For the purposes of the present disclosure, the printing path 80b and the second printing path 70 are described as being aligned or in alignment (that is, they are substantially parallel). In one aspect, the printing path 80b and the second printing path 70a are substantially parallel for most if not all of the printing path 80b. In another aspect, the firstbonding agent 70 is wholly deposited within an area covered by the concrete extrudate 60. In some examples, the outlet 232 of the first peripheral nozzle 230 may be configured smaller and closer to the main nozzle 220, for example, when a smaller printing offset 70b is desired. In other examples, the outlet 232 may be provided with a larger cross-sectional area to enable a suitable flow rate for a more viscous first bonding agent. The concrete deposition and the bonding agent deposition is synchronized in real-time 3D concrete printing, which also provide enhanced interlayer bond strength.

[0081] Fig. 7C illustrates the apparatus 200 navigating a curvilinear printing path 80b. It can be seen that the apparatus 200 concurrently undergoes both a translation 82 and a rotation 84 about the main axis, to move along the curvilinear printing path 80b. The apparatus 200 concurrently deposits the concrete extrudate along the curvilinear printing path 80b and deposits the bonding agent extrudate along the second printing path 70a. Fig. 7D further illustrates the apparatus 200 undergoing a rotation 86 to switch from the first configuration in which the main nozzle 220 is configured to travel ahead of or in front of the first peripheral nozzle 230 along the printing path 80, to the second configuration in which the first peripheral nozzle 230 is configured to travel in front of or ahead of the main nozzle 220 along the printing path 80.

[0082] Fig. 8 shows an alternative embodiment in which the funnel 234 is sealed or closed 239 to form a hydraulic slip ring 239. The hydraulic slip ring 239 defines a chamber 238 to receive the first bonding agent from the first bonding agent source 430 via one or more flow outlets 242. The chamber 238 may be pressurized to facilitate extrusion of the first bonding agent from the chamber 238 via the first peripheral nozzle 230.

[0083] Fig. 9 shows an embodiment of the apparatus 200 coupled to the actuator 300 in which the first peripheral nozzle is partially recessed into a leading side or a trailing side of the main nozzle 220, with the first peripheral nozzle ending at a higher elevation than the main nozzle.

[0084] Figs. 10 and 11 show another embodiment of in which the apparatus 200 includes a first spreader 240 disposed adjacent to the first peripheral nozzle 230. As shown, the main nozzle 220 and the first spreader 240 are disposed on opposing sides of the first peripheral nozzle 230. In other words, the first peripheral nozzle 230 is disposed between the main nozzle 220 and the first spreader 240. The first peripheral nozzle 230 may be disposed proximal to the trailing side 225 of the main nozzle 220. Upon deposition of the first bonding agent from the first peripheral nozzle, the first spreader 240 follows to level off and/or redistribute the first bonding agent extrudate 70 on a top surface of the concrete extrudate 60. The first spreader 240 is configured as a trailing spreader in this example. The first spreader 240 may be configured with a leveling surface 246 to spread or redistribute the first bonding agent extrudate 70, on a selected surface of the concrete extrudate, immediately following or concurrently with the deposition of the first bonding agent extrudate 70. The leveling surface 246 of the spreader 240 may be arranged at a higher elevation than a rim 228 of the main nozzle 220. For the sake of convenience, a datum 85 may be defined as a plane coincidental surface on which the current extrudates are printed on. In this example, the datum can be defined at a lower surface of the concrete extrudate. The peripheral nozzle 230 may be located at a higher elevation relative to the leveling surface 246 of the spreader 240.

[0085] Figs. 12 to 14 illustrate an alternative embodiment with the apparatus 200 coupled to the actuator 300 in the second configuration. In addition to the main nozzle 220 and the first peripheral nozzle 230, the apparatus 200 further includes a first spreader 240 disposed adjacent to the first peripheral nozzle 230. As shown, the main nozzle 220 and the first peripheral nozzle 230 are disposed on opposing sides of the first spreader 240, or in other words, the first spreader 240 is disposed between the main nozzle 220 and the firstperipheral nozzle 230. The first spreader 240 is configured to spread out or redistribute the firstbonding agent extrudate 70 on a selected surface of the concrete extrudate, immediately after or concurrently with the deposition of the first bonding agent extrudate 70. In this example, the first spreader 240 is configured as a leading spreader. The leveling surface 246 of the spreader 240 may be arranged at a higher elevation than a rim 228 of the main nozzle 220. For the sake of convenience, a datum 85 may be defined as a plane coincidental surface on which the current extrudates are printed on. In this example, the datum can be defined at a lower surface of the first bonding agent extrudate or an upper surface of a previous layer of concrete extrudate. The peripheral nozzle 230 may be located at a higher elevation relative to the leveling surface 246 of the spreader.

[0086] Figs. 15A and 15B are images taken of a cross sections of a specimen of a printed structure. The printed structure was made using a viscous material such as a cement paste as a bonding agent between layers of concrete extrudates. Cement paste is widely adopted in the construction industry as a cost-effectivebonding agent. However, dueto the relatively high viscosity of cementpaste, an upper surface of the cementpaste extrudate tends to show a relatively small radius of curvature, with the cement paste having a tendency to form a tube-like extrudate, even when under the pressure of the subsequent concrete extrudate layer. Defects (as pointed out in Fig. 15B) can be found at the interfaces between the cement paste and the concrete extrudates, adversely affecting interlayer bond strength.

[0087] Figs. 15C and 15D are images taken of a cross section of a specimen of another printed structure, 3D printed using the apparatus 200 according to an embodiment of the present disclosure. In this experiment, cementpaste was used as the firstbonding agent. The cement paste was spread substantially evenly across the width of the concrete extrudate by the spreader 240. No defects were observed either in the first bonding agent extrudate, or at the interfaces between the firstbonding agent extrudate and the concrete extrudate. This is consistent with a structure having a higher interlayer bonding strength. Additionally, the overall profile of the concrete extrudate also improves with the use of the apparatus 200 of the present disclosure.

[0088] Fig. 16 shows a plot of the relative bond strength of a structure 3D printed using an embodiment of the present disclosure (using a spreader with cement paste as the bonding agent), compared to that of a conventionally 3D printed reference specimen. The relative bond strength of specimens formed using an apparatus according to an embodiment of the present disclosure is higher (267%) compared to the reference specimen (100%). The results confirm that embodiments of the present disclosure provide improvements in the interlayer bonding strength.

[0089] Figs. 17 and 18 illustrate another embodiment of an apparatus 500. The apparatus 500 includes a housing 510 coupleable (releasably engageable) to the actuator 300. The housing 510 defines a main nozzle 520 configured to extrude a concrete printing material to form a concrete extrudate 60. The apparatus 500 includes a first peripheral nozzle 530 and a second peripheral nozzle 550. The first peripheral nozzle 530 and the second peripheral nozzle 550 are disposed on opposing sides of the main nozzle 520. In one example, the main nozzle 520, first peripheral nozzle 530 and the second peripheral nozzle 550 are disposed in line with the printing path 80. The first peripheral nozzle 530 is configured to extrude a first bonding agent to form a first bonding agent extrudate 70. The second peripheral nozzle 550 is configured to extrude a second bonding agent to form a second bonding agent extrudate 72. The apparatus 500 is thus configured to deposit the first bonding agent extrudate 70 and the second bonding agent extrudate 72 concurrently ahead of and following the concrete extrudate 60.

[0090] Further, as illustrated in Fig. 17, the housing 510 further defines a first peripheral channel 534 in fluid communication with the first peripheral nozzle 530 and the second peripheral nozzle 550. The first peripheral channel 534 is configured to receive the first bonding agent from the first bonding agent source 430 via a pair of flow outlets 542. The first bonding agent is delivered to the first peripheral nozzle 530 and the second peripheral nozzle 550, and extruded to form the first bonding agent extrudate 70 and second bonding agent extrudate 72. The first peripheral channel 534 may be configured as an annular channel. In an embodiment, the first peripheral channel 534 is configured as a funnel.

[0091] Alternatively, as illustrated in Fig. 19, the housing 510 further defines a first peripheral channel 534 in fluid communication with the first peripheral nozzle 530; and a second peripheral channel 554 in fluid communication with the second peripheral nozzle 550. The first peripheral channel 534 is configured to receive the first bonding agent from the first bonding agent source 430 via a first flow outlet 544. The first bonding agent is delivered to the first peripheral nozzle 530 to be extruded to form the first bonding agent extrudate 70. The second peripheral channel 554 is configured to receive a second bonding agent from a second bonding agent source via a second flow outlet 546. The second bonding agent is delivered to the second peripheral nozzle 550 to be extruded to form the second bonding agent extrudate 72. The apparatus 500 is configured to deposit the first bonding agent extrudate 70 and the second bonding agent extrudate 72 concurrently ahead of and behind that of the concrete extrudate 60. In this embodiment, the second bonding agent may have a different chemical composition from the first bonding agent. Therefore, the second bonding agent extrudate 72 have a different chemical composition from the first bonding agent extrudate 70. In some embodiments, the first bonding agent extrudate 70 and the second bonding agent extrudate 72 are configured to react chemically to form a strong interlayer bonding agent extrudate.

[0092] In another embodiment of the apparatus 500, as shown in Fig. 20, the apparatus 500 further includes a first spreader 540 disposed adjacent to the first peripheral nozzle 530; and a second spreader 560 disposed adjacent to the second peripheral nozzle 550. The main nozzle 520 is disposed between the first spreader 540 and the second spreader 560 along the printing path 80. The first spreader 540 is configured to spread the first bonding agent extrudate 70 concurrently with the deposition of the first bonding agent extrudate 70. The first spreader 560 is configured to spread the second bonding agent extrudate 72 concurrently with the deposition of the second bonding agent extrudate 72. In some embodiments, the first bonding agent extrudate 70 have a different composition from the second bonding agent extrudate 72. As an example, they may be configured to chemically react to form a bonding agent extrudate.

[0093] Fig. 21 is a schematic flow diagram of a method 900 of concrete additive manufacturing (3DCP) according to embodiments of the present disclosure. The method 900 includes extruding 910 a concrete material via a main nozzle to form a concrete extrudate, the main nozzle defining a main axis; extruding 920 a first bonding agent via a first peripheral nozzle to form a first bonding agent extrudate; and providing a movement of the main nozzle and the first peripheral nozzle along a curvilinear printing path 930. The movement (of the main nozzle and the first peripheral nozzle) includes a translational movement concurrent with a rotational movement about the main axis, and wherein the movement is concurrent with the extruding of the flowable concrete material and the extrusion of the first bonding agent. The first peripheral nozzle and the main nozzle maybe configured to undergo the rotational movement about the main axis as a rigid body. The method 900 is suitable for use with a flowable concrete material. The method 900 is suitable for use with a first bonding agent that is a viscous material. The method 900 may involve selectively depositing the concrete extrudate ahead of depositing the first bonding agent extrudate relative to the printing path, responsive to the apparatus being in a first configuration; or depositing the concrete extrudate behind that of laying the first bonding agent extrudate relative to the printing path, responsive to the apparatus being in a second configuration . The method 900 enables depositing the first bonding agent such that the first bonding agent extrudate is deposited parallel to the concrete extrudate, even if the concrete extrudate is being extruded via a rectangular outlet of the main nozzle. The method 900 may include spreading or distributing the first bonding agent extrudate on a selected surface of the concrete extrudate. The first bonding agent extrudate may be spread or distributed concurrently with the movement of the main nozzle and the first peripheral nozzle.

[0094] Due to the nature of 3DCPin which each concrete extrudate layer is extruded atop a previously extruded concrete layer, the interlayer bond strength between the interfaces of the extrudates is one of the factors determining the overall integrity and strength of the final concrete structure. While the interlayer bond strength may be improved by the provision of a bonding agent between layers of concrete extrudates , it has been shown that bonding agents may themselves contribute to the formation of defects and negatively impact both the overall interlayer bond strength as well as the overall profile of the concrete structure. The apparatus and method according to any of the embodiments of the present disclosure described herein advantageously address these technical challenges such that improved interlayer bonding strength can be achieved. The apparatus disclosed herein may be used with various types of extrudates and bonding agents. Even in cases where the bonding agent has a relatively low viscosity, the present apparatus can facilitate a more accurate application of the bonding agent. In one aspect, the bonding agent can be applied in a more selective or targeted manner, such that the bonding agent extrudate is aligned with the concrete extrudate, relative to the printing path, even if the printing path require s continuous printing around a corner or along a curvilinear path. In another aspect, the bonding agent can be applied in a more selective or targeted manner to coat only the upper and/or lower surfaces of opposing surfaces of the extrudates. This would be an improvement over indiscriminate spraying of bonding agents via a jet/spray on all surfaces of the extrudate as there will be significantly less wastage. A more targeted and controlled application of the bonding agent also avoids problems associated with the bonding agent affecting surface quality of the side surfaces of the concrete extrudate, e.g., the surface quality of a wall of a building structure. Further, embodiments of the apparatus of the present disclosure are also suitable for use with flowable materials with different viscosities, even in combination with bonding agents with relatively higher viscosities, such as cement paste.

[0095] All examples described herein, whether of apparatus, methods, materials, or products, are presented for the purpose of illustration and to aid understanding, and are not intended to be limiting or exhaustive. Various changes and modifications may be made by one of ordinary skill in the art without departing from the scope of the invention as claimed.