Method for Three-Dimensional Printing of Column-Free Span Members through Combined Operation of Reinforcement-Free Cementitious Curing Material and Polymeric Melt Material

Abstract

The present invention is a construction method for integrally printing slabs, sloping roofs, window lintels, and stairs of a box-shaped building on-site by alternately printing unreinforced cement-based curing materials and polymer-based molten materials on a single output platform within the same construction cycle. In areas where the self-supporting of the curing material is difficult, the molten material is printed first to form a molten support layer that provides a stacking work surface, and the curing material is printed subsequently on top of this to form the main body of the component. While the curing material undergoes chemical curing, the subsequent molten support layer is printed, thereby operating the two materials in time synchronization. The molten support layer is printed in a multi-arch rib structure by entering simultaneously from multiple entry points on the outer edge of the component, and it ensures the stability of the unreinforced structure by transferring the self-weight and live load of the unreinforced curing material main body to the wall as compressive force. The permanently remaining molten support layer is coupled to the curing material main body using pin anchors and line anchors to additionally form an insulation layer and a design finish.

Description

Technology Field

[0001] The present invention relates to a three-dimensional printing method for construction, and more specifically, to a method of integrally printing on-site a rigid member including a slab, sloping roof, window lintel, and stairs of a box-shaped building by combining and operating a cement-based curing material and a polymer-based molten material within the same construction cycle on a single printing platform. Background Technology

[0002] 3D printing is a process of layering materials within a gravitational field. If there are areas (overhangs, bridges) that cannot be self-supported during printing, a separate support structure is required to support the layering in those areas. This area is referred to as a “column-free space” in this specification. If the shape of a building is designed as a diagonal or free-form surface and all members are self-supported by their own lower portions, a separate support structure is not required. However, due to the demand for human living spaces, buildings are generally designed in a rectangular box shape, and horizontal slabs are essential in multi-story buildings. Box-shaped horizontal slabs, window lintels, and stair cantilevers are representative examples of column-free spaces that lack self-supporting sources directly beneath them.

[0003] Meanwhile, in this specification, “curing material” refers to construction materials such as cementitious mortar that gradually harden through a chemical curing reaction after extrusion, and “molten material” refers to thermoplastic polymers that form a self-supporting shape through physical cooling after extrusion. These two materials have developed independently in distinct industrial fields.

[0004] Since curing materials for 3D printing must pass through a nozzle, it is inherently difficult to place reinforcing bars integrally within the material. Conventional curing materials for 3D printing have evolved into a series of unreinforced concrete, incorporating reinforcing materials such as polypropylene short fibers to partially supplement tensile strength. However, short fiber reinforcement alone does not resolve the inherent weakness in tensile strength of unreinforced curing materials, and the self-weight deflection of the area directly beneath the slab cannot be resolved by short fiber reinforcement.

[0005] A conventional method to compensate for the tensile weakness of unreinforced curing materials is a stress conversion mechanism designed in the shape of an arch or dome that transmits compressive force to the column-free space, thereby transferring self-weight and live loads to the wall through compression rather than tension. This stress conversion principle is the same principle used by the Romans to construct the Colosseum about 2,000 years ago and was refined in the rib vault structures of Gothic architecture from the 12th to 15th centuries. Therefore, constructing a column-free space with unreinforced curing materials essentially requires an arch or rib shape.

[0006] However, since arch and rib shapes inherently include overhang sections that cannot stand on their own during construction, a separate auxiliary support structure is required to support the arch and rib shapes. In other words, the issue of constructing column-free spaces using unreinforced curing materials must simultaneously address two aspects: stress transfer after construction (arch and rib shapes) and auxiliary support during construction (formwork or supports holding the arch and ribs).

[0007] Conventional construction of column-free spaces has addressed these two aspects in the following two ways. First, a method in which temporary supports are installed directly beneath the column-free space during construction, concrete is poured over them, and the temporary supports are removed upon completion of curing. Second, a method in which a pre-manufactured permanent formwork (Stay-in-Place Form) is transported to the construction site and installed directly beneath the column-free space, after which concrete is poured over it (see Patent Document 10). This pre-manufactured formwork method is merely a pre-manufactured formwork of the conventional RC (reinforced concrete) method using 3D printing, and the construction stages consist of separate construction steps: (i) pre-manufacturing of formwork + (ii) transportation to the site + (iii) installation of formwork + (iv) separate concrete pouring. Consequently, this pre-manufactured formwork method has inherent limitations, such as a skyrocketing cost for pre-manufacturing injection molds for irregularly shaped formwork, the occurrence of logistics costs for transporting formwork, increased construction time due to the separation of construction stages, and limited freedom for design changes at the construction site.

[0008] Meanwhile, Fused Deposition Modeling (FDM), one of the standard methods in the 3D printing industry, has solved the similar problem of open space in the field of precision printing by combining dual nozzles with heterogeneous material supports. In other words, a support nozzle is placed separately from the main print nozzle, and support material (water-soluble polymers such as PVA or BVOH, or homogeneous polymers) is deposited in the areas of the main print that cannot be self-supported; the supports are then removed upon completion of construction. This dual nozzle + heterogeneous material support operation has evolved into a standard technology in the FDM industry over approximately 30 years, and the Independent Dual Extruder (IDEX) equipment has established itself as the standard form. In FDM, molten material stands upright through physical cooling within seconds of nozzle extrusion, making it advantageous for overhang printing.

[0009] Conventional 3D printing for construction has not been able to extend the concept of dual nozzles + heterogeneous material supports of the above FDM to the construction industry. Conventional 3D printing for construction has been limited to the operation of curing materials alone, and due to the inherent constraint of the chemical curing time of curing materials (minutes to hours), column-free spaces such as slabs, pitched roofs, window lintels, and cantilevers could not be constructed using only curing materials. Although there have been attempts to operate two types of identical curing materials with separate nozzles (see Patent Document 9), the division within the same curing material series has not resolved the inherent constraint of the chemical curing time of the curing materials, and the residual effect of permanent formwork has not been achieved due to the absence of a mechanism to separate and remove a single nozzle print after construction is completed.

[0010] Conventional 3D printing for construction, due to the limitations of the operation flow of curing materials alone and the transport and installation flow of prefabricated formwork, has not been able to provide an integrated method for printing slabs, sloping roofs, window lintels, and stairs of box-shaped buildings as a single unit on-site within a single construction cycle.

[0011] To overcome the limitations of the two aforementioned flows, the present invention extends the dual nozzle + heterogeneous material support concept of the FDM industry to the construction industry, providing a unique time synchronization sequence of this method that combines a plain cementitious curing material (subject body) and a polymer-based molten material (molten support layer) within the same construction cycle on a single output platform. The curing material of this method possesses higher viscosity and shape-maintaining flowability compared to general ready-mix concrete, and is laminated onto a molten support layer in the shape of a multi-arch rib formed by the inclined output of the molten material in the range of 30° to 60° (approx. 45° in one embodiment), thereby standing independently as a column-free body. This method compensates for the tensile weakness of the plain curing material after construction through stress conversion in the shape of the multi-arch rib, and has a stress distribution essentially identical to the rib vault structure of 12th to 15th-century Gothic architecture.

[0012] 3D printing is essentially an additive manufacturing process based on modeling. Unlike the carving method, which produces a result by removing material from an existing mass, the modeling method forms a result by accumulating material in empty spaces. In the modeling method, the print head must always be positioned outside the print object during printing, and printing is impossible if the head's entry path is blocked by the print object. The inherent limitations of this modeling method critically influence the sequence design of the present invention. Prior art literature

[0013] Korean Patent Application 10-2026-0007769 (Applicant's prior application, priority examination in progress, polar coordinate-based 3D printing device for construction) Korean Patent Application 10-2026-0030174 (Applicant's prior application, priority examination in progress, pellet-type construction material composition capable of dry transfer) Korean Patent Application 10-2026-0030184 (Applicant's prior application, priority examination in progress, inline mixing type 3D printing head for construction) Korean Published Patent 10-2016-0049040 (Method for manufacturing a concrete structure using a 3D concrete print system) Korean Published Patent 10-2017-0146562 (3D printing nozzle for constructing a construction structure having upper and lower layer bonding reinforcement and shape control functions of cementitious materials) Korean Published Patent 10-2018-0147959 (3D printer Window formwork and window frame fabricated using) Korean Published Patent 10-2019-0059488 (3D printing device for constructing a 3D structure with a vertical reinforcement installation configuration using 3D printing additive manufacturing by a separable nozzle and nozzle module for the same) Korean Published Patent 10-2019-0070476 (3D printing nozzle device and 3D printing equipment equipped with the same) Korean Registered Patent 10-2679179 (Concrete discharge nozzle device and construction method using the same) US Registered Patent US 12,516,522 B2 (Stay-in-Place Concrete Floor and Ceiling System Without Steel Reinforcing) US Registered Patent US 12,331,518 B1 (3D Printed Construction Element) Korean Published Patent 10-2021-0104220 (Using a 3D printing construction robot Method for constructing a reinforced concrete structure) Korean Published Patent 10-2022-0141554 (Multi-nozzle-based 3D printer for construction and method for controlling the same) Korean Published Patent 10-2023-0184230 (3D printing device using a disc having protrusions and method for manufacturing a structure using the same)

[0014] Espalin, D., Ramirez, JA, Medina, F., & Wicker, R. (2014). “Multi-material, multi-technology FDM: exploring build process variations”. Rapid Prototyping Journal, Vol. 20, No. 3, pp. 236-244. DOI: 10.1108 / RPJ-12-2012-0112. Vaezi, M., Chianrabutra, S., Mellor, B., & Yang, S. (2013). “Multiple material additive manufacturing-Part 1: are review”. Virtual and Physical Prototyping, Vol. 8, No. 1, pp. 19-50. BASF Forward AM, “Ultrafuse® BVOH Technical Data Sheet” (Technical Data Sheet for Butenediol Vinyl Alcohol Copolymer Water-soluble Support Material). The problem to be solved

[0015] The present invention solves the following problems.

[0016] (1) A method is provided that maintains the utility of the conventional Stay-in-Place form system, which includes permanent formwork, plain slabs, and arch ceilings, while achieving integration into a single construction cycle at the site without separate construction stages of pre-manufacturing, transportation, and installation. In this method, the molten support layer is not used in all areas of the member, but is applied for self-supporting purposes only in areas where it is difficult for the curing material body to stand on its own.

[0017] (2) The conventional 3D printing technology for construction was limited to the operation of curing materials alone, so it was not possible to construct box-shaped multi-story slabs, window lintels, stairs, and sloping roofs. The integrated method provided allows for the printing of these structures on-site as a single unit through the combined operation of curing materials and molten materials.

[0018] (3) Provides an operation sequence that synchronizes the essentially different time constants of cementitious curing materials (chemical curing) and polymeric molten materials (physical cooling) within a single construction cycle.

[0019] (4) By permanently retaining the molten support layer in the combined operation of the two materials and stacking the curing material on top of it in the shape of multiple arch ribs, a secondary effect is achieved in which the structural strength of the non-reinforced structure is secured without separate reinforcement.

[0020] (5) A general method that can be performed on any IDEX-compatible output platform that does not rely on the kinematics of the output platform (gantry, delta, SCARA, cantilever, 6-axis industrial robot arm, polar coordinates, etc.) or nozzle attitude control function is provided. means of solving the problem

[0021] To solve the above problem, the present invention provides a 3D printing method for construction that operates cement-based curing materials and polymer-based molten materials in time synchronization within the same construction cycle through two types of heads mounted on a single output platform.

[0022] The essence of the inventiveness of this method lies not in the combined operation of the curing material and the molten material itself, but in the operation sequence that synchronizes the fundamentally different time constants of the two materials within the same construction cycle. The self-standing of the molten material is a physical cooling process that occurs within seconds immediately after nozzle discharge, while the self-standing of the curing material is a chemical curing process that occurs over minutes to hours after nozzle discharge. The difference between the two time constants is fundamental, and conventionally, the two material series could not be combined and used within a single construction cycle due to this difference. This method forms a permanent remaining molten support layer by discharging the molten material at an inclination of 30° to 60° (approx. 45° in one embodiment) relative to the normal of the work surface, and then layers a curing material having higher viscosity and shape-maintaining flowability compared to ordinary ready-mix concrete on top of it, thereby forming self-standing even in areas where the curing material body is difficult to stand on its own.

[0023] This method synchronizes two time constants through the combination of the following four mechanisms.

[0024] (a) Asymmetric N:1 sequential alternating stacking: The output frequencies of the two heads are distributed according to the asymmetric ratio of stacking N layers of molten material followed by stacking 1 layer of curing material. Here, N is determined based on the ratio (N ? t_C / t_M) of the thickness of 1 layer of curing material (t_C) and the thickness of 1 layer of molten material (t_M).

[0025] (b) Control of N-layer output within curing material head stagnation limit time: The nozzle diameter and output speed are controlled so that the time required to output N molten material layers in step (a) does not exceed the stagnation limit time inside the curing material head.

[0026] (c) Simultaneous multi-arch rib output: In wide areas such as slabs or pitched roofs, a multi-arch rib structure consisting of multiple arched curved surfaces arranged in parallel rather than a single frame is output simultaneously at multiple entry points on the outer boundary of the member, thereby reducing the output time of N layers per cycle.

[0027] (d) Operation of the gap between the curing material and the molten support layer: When the curing material nozzle is printed close to the pre-printed molten support layer, the stacking position of the curing material is separated from the outer edge of the molten support layer by a distance corresponding to the diameter of the molten material nozzle, and the unfilled area resulting from this separation is filled by reinforcing the extrusion amount of the curing material.

[0028] Each of these four mechanisms is not significantly different from conventional technology when used individually, but in the combined operation, they operate as a unique sequence of this method that synchronizes the time constants of the two materials. This synchronization is the core inventive step of this invention, which cannot be achieved even if a person skilled in the art attempts a simple combination of the two material series.

[0029] This method is operated by classifying it into two categories according to the shape of the applied member.

[0030] The Aligned Extrusion mechanism is applied when the length direction of the member aligns with the length direction of the wall and the member thickness is equal to the wall thickness. The molten support layer forms a flat or inclined support starting from both side walls and meeting at the center of the member, while the cured material body is extruded in a stacking mode along the length direction of the member. Applicable members include window lintels and treads for Rahmen stairs.

[0031] The Spreading Extrusion mechanism is applied when a member is thicker than the wall or cantilevered, making it difficult to support itself using only the two side walls. The molten support layer is printed in a multi-arch rib + permanent retention form, while the main body of the curing material is printed in an inclined horizontal stacking mode, gradually narrowing from the periphery toward the center. In this category, all of the core mechanisms of this method—asymmetric N:1 sequential alternation, simultaneous multi-arch rib printing, and spacing management between the curing material and the molten support layer—are applied. Applicable members include slabs, pitched roofs, and treads for cantilever stairs.

[0032] In addition, this method employs anchor outputs to assist in the bonding between the curing material and the molten material. Anchor outputs are classified into two types: pin anchors (fixing the molten support layer to the main body of the curing material at the starting position of the member) and line anchors (penetrating into the main body of the curing material at regular intervals along the length of the permanently remaining molten support layer to prevent long-term delamination). Line anchors are applied only to the permanently remaining molten support layer, while only pin anchors are applied to molten support layers that are removable after construction (e.g., window lintels).

[0033] The present invention also provides the resulting effects of a building constructed using this method. In a building constructed using this method, the permanent remaining molten support layer and the main body of the curing material member are integrally combined, and structural strength without reinforcement is provided by the multi-arch rib shape, an insulation layer is provided by the low thermal conductivity of the polymer material, and a ceiling finish surface is incidentally formed by the exposure of the permanent remaining molten support layer.

[0034] In accordance with the nature of the claim as a construction method, the mechanism during construction (formation of column-free members through the combined operation of heterogeneous materials and the horizontal expansion of molten materials) and the construction result (maintenance of permanent compressive force through the multi-arch rib shape of curing materials) are integrated within a single method claim in chronological order. The periods during and after construction constitute two consecutive stages in the chronological flow of the method and are not separated into separate system claims or structural claims. This integrated claim structure is directly derived from the nature of the invention as a construction method. Effects of the invention

[0035] The present invention simultaneously provides effects of construction efficiency at the time of construction and effects of the results after construction. The effect at the time of construction is the integration of conventional construction stages through the combined operation of curing materials and molten materials in a single cycle, while the effect after construction is the structural strength, insulation layer, and design finish of the unreinforced structure incidentally formed by the permanently remaining molten support layer and the multi-arch rib shape. The specific effects of the present invention are as follows.

[0036] (a) Integrated output of column-free space of a box-shaped building: The first-floor walls, windows, stairs, multi-story slabs, and sloping roof of a box-shaped building are output as a single unit in a single construction cycle. The limitations of conventional 3D printing for construction, which was limited to wall-centered construction, are overcome, and column-free space components are output directly on-site through the combined operation of curing materials and molten materials in a single cycle.

[0037] (b) Achievement of a single-cycle efficiency comparable to conventional prefabricated formwork systems: Buildings constructed using this method achieve the same level of proven efficiency for permanent formwork, plain slabs, and arched ceilings provided by conventional prefabricated formwork systems (Stay-in-Place form system). However, this efficiency is achieved through a single construction cycle integrated on-site using a single output platform, without the separate construction stages required by conventional systems: factory prefabrication, on-site transportation, formwork installation, and separate concrete pouring. As a result, this method provides the following additional benefits compared to conventional systems: (i) elimination of costs for pre-fabricating irregularly shaped formwork, (ii) elimination of logistics costs for formwork transportation, and (iii) increased design freedom at the construction site.

[0038] (c) Utilization of FDM industry assets in the construction industry: IDEX equipment and dual nozzle operation know-how from the FDM industry can be extended and applied to the construction industry through this method.

[0039] (d) Generalization of output platform: This method can be implemented using a G-code inclined path following method even on conventional 3-axis orthogonal coordinate IDEX equipment (gantry, delta, etc.) that does not have nozzle attitude control functions, and does not rely on the kinematics of the output platform.

[0040] (e) Structural strength without reinforcement as a side effect: By layering curing material in a multi-arch rib shape on a permanently remaining molten support layer, structural strength without reinforcement is secured without the need for separate rebar placement. The multi-arch rib cross-sectional shape of a building constructed using this method has a stress distribution essentially identical to the rib vault structure of 12th to 15th-century Gothic architecture. This method automates the construction principles of irregular curved surfaces, which were virtually discontinued due to the skyrocketing costs of pre-fabricating formwork in the past, using modern 3D printing technology.

[0041] (f) Simultaneous achievement of ceiling and roof design finishes: The undersides of slabs, roofs, and stair treads, where the permanent residual molten support layer is exposed, form the ceiling finish surface themselves. A separate ceiling finishing process is unnecessary.

[0042] (g) Additional assurance of construction convenience: The spaces between the multiple arch ribs of this method can be simultaneously utilized as passageways for equipment such as pipe sleeves and electrical pipe conduits during the construction phase. As a result, separate structural work for equipment is not required after construction.

[0043] (h) Additional securing of thermal insulation performance: Since the polymer material of the permanent remaining molten support layer has a low thermal conductivity of about 1 / 100 to 1 / 200 compared to cementitious curing materials, an additional insulation layer is formed on the underside of the sloping roof, the underside of the inter-story slab, etc.

[0044] (i) Compatibility with irregular shapes: This method can be applied using the same principle not only to regular buildings with straight exteriors but also to irregular buildings with curved exteriors or freeform surfaces. Brief explanation of the drawing

[0045] FIG. 1 is a perspective view of a construction target model according to one embodiment of the present invention, showing a box-shaped building with a plan of 5m × 5m, a first-floor wall height of 2.5m, a second-floor wall height of 1m, and a maximum sloped roof height of 5m. FIG. 2 is a cross-sectional perspective view of the construction target model of FIG. 1, visualizing the result of all of the application areas of this method—windows (800), frame stairs (930), cantilever stairs (940), slabs (400), and sloped roofs (1000)—being output as a single unit in the same model. Figure 3 is a flowchart of the four cycles of the construction sequence of the present method, showing the progression order of cycles 1 to 4 and the three-dimensional shape of the member constructed in each cycle. FIG. 4 is a cross-sectional view showing an embodiment of the asymmetric N:1 sequential alternating stacking of the present method, wherein stacking sequences 1 to 4 represent the accumulation of N layers (N=4) of molten material in one cycle, 5 represents the stacking of 1 layer of curing material above it, 6 to 9 represent N layers of molten material in the next cycle (C2), and 10 represents 1 layer of curing material in the next cycle, the left area (A) represents the accumulated main body of the previous cycles, and the nozzle offset (G) on the right represents the separation so that the curing material nozzle (310) avoids the corner of the pre-stacking molten support layer (500), and the progress time (t_lim) of stacking sequences 1 to 5 is controlled within the curing material stagnation limit time. FIG. 5 is a drawing illustrating the output of a window lintel to which the alignment output mechanism of the present method is applied, FIG. 5a is a cross-sectional perspective view and FIG. 5b is a cross-sectional view. FIG. 6 is a cross-sectional perspective view illustrating the output of one stage of a rigid frame staircase (930) to which the alignment output mechanism of the present method is applied. FIG. 7 is a cross-sectional perspective view illustrating the output of one step of a cantilevered staircase (940) to which the expansion output mechanism of the present method is applied. FIG. 8 is a perspective view illustrating the construction progress sequence of a slab to which the expanded output mechanism of the present method is applied, FIG. 8a is a perspective view of the slab outer starting stage and FIG. 8b is a perspective view of the intermediate progress stage, showing the output progress stages over two cycles in stacking order 1 to ?, with odd numbers representing molten material output and even numbers representing curing material output. FIG. 9 is a cross-sectional view and partial enlarged view illustrating a slab to which the expansion output mechanism of the present method is applied, in which a curved deck plate shape formed by multiple arch ribs (510), a pin anchor (550), and a line anchor (560) are simultaneously exposed, and reference numerals 400-③, 400-④, 400-⑥ and 500-③, 500-⑤ represent the combined stacking time sequence of the slab area (400) and the molten support layer (500). FIG. 10 is a cross-sectional view and a partial enlarged view illustrating the output of a sloping roof (1000) to which the expanded output mechanism of the present method is applied, wherein stacking order 1 to 6 indicates the output progress steps according to the simultaneous entry of four sides of the gable surface and gable wall, and the symbols 1000-① to 1000-④ and 700-⑥ represent the combined stacking time order of the sloping roof (1000) and the wall (700). Specific details for implementing the invention

[0046] 1. Scope of the Method and Definition of Terms

[0047] This method is a 3D printing method for construction that operates two types of print heads on a single print platform. By combining a curing material (second material, cement-based) and a molten material (first material, polymer-based) within a single construction cycle, it integrally prints the walls, windows, stairs, slabs, and sloping roofs of a box-shaped building on-site. The technical significance of this method becomes clear when the construction event is divided into two phases along the time axis: during construction and post-construction. During construction, the key is the combined operation of heterogeneous materials where the molten material provides auxiliary support in areas where the curing material is difficult to stand on its own, while post-construction, the key is securing structural stability where the main body of the curing material remains permanently in a non-reinforced state.

[0048] From the perspective of construction, the curing material forms the main body of the building (walls, slabs, roofs, lintels, stairs), and the molten material is produced as a lower auxiliary structure in areas where the curing material is difficult to support (under the slab, under the lintel, under the stairs, under the sloping roof). In this specification, this auxiliary structure is consistently referred to as a “molten support layer.” In this specification, the term “molten support layer” refers to an auxiliary structure formed by the molten material to secure the self-supporting rigidity of the curing material, and expressions such as “formwork,” “auxiliary frame,” and “permanently remaining formwork” used in conventional specifications are all unified as “molten support layer” in this specification.

[0049] From the perspective of post-construction, the curing material body remains permanently in an unreinforced state without internal rebar reinforcement. The compressive strength of the curing material is combined with the multi-arch rib geometry of this method (see

[0112] ), converting tensile stresses from self-weight and live loads into compressive stresses that are transferred to the wall. Additionally, the permanently remaining molten support layer secondarily forms an insulation layer on the underside of the slab and the underside of the sloping roof due to the low thermal conductivity of the polymer material (approximately 1 / 100 to 1 / 200 compared to cementitious curing materials). In other words, the molten support layer of this method performs a dual function: as an auxiliary support structure during construction, and as an insulation structure and design finish after construction.

[0050] The present method can be configured in any form as long as the coupling method of the two heads satisfies IDEX (Independent Dual Extruder) compatibility, and there are no restrictions on the kinematics of the output platform (gantry, delta, SCARA, cantilever, 6-axis industrial robot arm, polar coordinates, etc.). The present method can also be implemented by simultaneously mounting two or more output heads on a single output platform or by configuring two or more output platforms to cooperatively output in the same work area, and specific mechanical forms of multi-head or multi-platform configurations are not the subject of claims in this specification.

[0051] In this specification, "reinforcement-free" refers to a state in which there is no integral arrangement of reinforcing steel within the body of the curing material, and does not restrict the incorporation of polymer fiber reinforcements such as polypropylene staple fibers (see

[0064] ) or the use of external reinforcement (anchors, outer coverings, fixing materials, etc.). In this method, molten material anchors remaining within the body of the curing material do not constitute reinforcing steel, and the reinforcement-free nature of this method is maintained.

[0052] Methods of supplying molten materials and curing materials before arrival at the head (pellet heated extrusion, filament heated extrusion, ground pre-mixing + pump transfer, inline mixing immediately before or inside the head, etc.) are not claimed in this specification, and the inventive step of the present method lies in the output sequence after nozzle discharge. The present method allows the use of polymer-based molten materials and cement-based curing materials used in conventional 3D printing for construction, and does not require the development of separate new materials.

[0053] 2. Two types of heads and materials

[0054] 2.1 Molten Material Head

[0055] The first head is a head that discharges a molten polymer at the nozzle end, and immediately after discharge, the molten material self-contains its shape through natural or forced cooling. This self-containment is a simple physical action rather than a chemical reaction. The specific form of the molten material head applicable to this method is a general conventional polymer-based 3D output head and is not the subject of claims in this specification.

[0056] In this method, the nozzle diameter of the first head is operated within a range of approximately 5mm to 20mm. If the nozzle diameter is less than 5mm, the output time required for N layers of molten material in one cycle exceeds the curing material head stagnation limit time; consequently, the curing material begins chemical curing inside the second head, leading to head clogging or output interruption. Within the nozzle diameter range of 5mm to 15mm, self-supporting rigidity is secured through natural convection or cooling by a standard blower fan. Within the nozzle diameter range of 15mm to 20mm, natural cooling is insufficient, requiring forced cooling such as the direct injection of cooling airflow from an air conditioner. If the nozzle diameter exceeds 20mm, the extrusion cross-sectional area exceeds the natural or forced cooling rate, causing self-weight sagging before self-supporting rigidity is formed.

[0057] The thickness of one layer of molten material is operated in the range of approximately 20% to 30% of the nozzle diameter. In conventional FDM 0.4mm nozzles, it was possible to build up to 50%, but in nozzles thicker than 5mm of this method, natural cooling time increases, making it difficult to build up to 50%, and a ratio similar to that of curing material is adopted.

[0058] The molten material applicable to this method is a general thermoplastic polymer that forms a self-standing shape by physical cooling after extrusion. In one embodiment, the molten material is PETG (polyethylene terephthalate glycol-modified) or ASA (acrylonitrile styrene acrylate). This polymer withstands the curing heat generation temperature (approx. 60°C to 80°C) of the curing material, has low odor during printing, and is suitable for use as a molten support layer due to its unit cost. In other embodiments, other thermoplastic polymers such as ABS, PE, and PLA may be used, and are selected based on the shrinkage rate, heat resistance during curing, and unit cost of the polymer used.

[0059] 2.2 Curing Material Head

[0060] The second head is a head that discharges a liquid curing material (such as cementitious mortar) from the nozzle end, and the chemical curing reaction of the curing material begins immediately after discharge from the nozzle, causing it to gradually harden.

[0061] In this method, the nozzle diameter of the second head is operated in a range of approximately 30 mm to 100 mm. If the nozzle diameter is less than 30 mm, the strength distribution of the main body is insufficient, and the number of output cycles per unit area increases, resulting in an impractical increase in construction time. If the nozzle diameter exceeds 100 mm, the volume of one layer is excessive, causing self-weight sagging. In one preferred embodiment, the nozzle diameter of the second head is approximately 50 mm.

[0062] The thickness of one layer of curing material is applied at two ratios depending on the printing mode. In stacking mode (aligned printed part + general wall), it is approximately 30% of the nozzle diameter (about 15mm for a 50mm nozzle), and in inclined horizontal stacking mode (extended printed part), it is approximately 20% of the nozzle diameter (about 10mm for a 50mm nozzle). This reduction in thickness is a conservative measure to prevent sagging due to self-weight during inclined printing.

[0063] The curing material applicable to this method is cementitious 3D printing mortar (hereinafter collectively referred to as “polymer mortar”), which has become the industry standard in conventional construction 3D printing. This method does not require the development of a separate new curing material and is applied when the printing mortar possesses higher viscosity and shape-maintaining flowability than ordinary ready-mix concrete. This flowability prevents the curing material from leaking or flowing down even when one side of the molten support layer is in an unfinished state.

[0064] Reinforcements such as polypropylene staple fibers are incorporated into the curing material to partially supplement tensile strength. The staple fibers are distributed in random directions within the curing material and are not aligned in any specific direction. This random distribution contributes uniformly to the multiaxial stress distribution of the member.

[0065] 3. Nozzle Operating Conditions

[0066] In this specification, “slanted output” refers to a result in which the output is deposited in a shape inclined with respect to the work surface normal, and does not require the nozzle orientation itself to be inclined. Slanted output is implemented by any one of the following two methods, or a combination of both.

[0067] (a) Nozzle tilt attitude control method: When the output platform has a head gimbal or a multi-axis wrist joint, the nozzle attitude itself is controlled in a tilted direction relative to the work surface normal. This is applicable to 6-axis industrial robot arms, cantilever arms of 5 axes or more, etc.

[0068] (b) G-code inclined path following method: In the case where the output platform is a conventional 3-axis orthogonal coordinate system (gantry, delta, etc.) or IDEX equipment that does not have nozzle attitude control function, the nozzle is maintained in a vertical position and the G-code path is controlled to proceed along a plane inclined with respect to the normal of the work surface.

[0069] This method can selectively adopt either of the two methods mentioned above and can be sufficiently implemented using conventional IDEX equipment. The inventive step of this invention lies not in the method of implementing gradient output, but in the time-synchronized operation of the two materials.

[0070] The inclined output angle of this method is operated in a range of about 30° to 60° relative to the normal of the work surface, and in one embodiment, it is about 45°. This angle range is not a mandatory limitation, and depending on the shape of the printed object, the viscosity and self-standing speed of the material used, and the nozzle diameter, it can be operated at an angle outside this range.

[0071] In this method, N layers of molten material are printed first as a molten support layer and 1 layer of curing material is printed later according to an asymmetric N:1 sequential alternating stacking (see

[0086] ). In this printing sequence, a collision may occur if the stacking position of the later curing material is adjacent to the preceding molten support layer. This collision is caused by the difference in diameter between the curing material nozzle and the molten material nozzle. The molten material nozzle has a smaller diameter compared to the curing material nozzle; as a result, the outer edge of the molten support layer is formed relatively sharply with a smaller radius of curvature compared to the curing material output. When the curing material nozzle passes adjacent to this sharp edge, interference occurs between the nozzle's outer diameter and the edge.

[0072] In order to prevent collisions, the stacking position of the curing material is spaced a certain distance from the outer edge of the preceding molten support layer (see FIG. 4). In this specification, the term “gap between the curing material and the molten support layer” refers to this separation distance.

[0073] (a) Spacing distance: The spacing between the outer edge of the curing material and the molten support layer is set to a distance corresponding to the diameter of the molten material nozzle. In one embodiment, for a molten material nozzle diameter of 10 mm, the spacing distance is approximately 10 mm. The reason this spacing distance is determined by the diameter of the molten material nozzle rather than the diameter of the curing material nozzle is that the direct cause of the collision lies in the curvature of the corner of the molten support layer.

[0074] (b) Reinforcement of curing material extrusion volume: To compensate for the unfilled areas occurring in the gaps, the amount of curing material extruded is increased compared to normal operation. As a result, the gap areas are also filled with curing material.

[0075] (c) Normal output in non-adjacent areas: In curing material output areas where the molten support layer is not adjacent, normal output occurs without this gap operation.

[0076] 4. Anchor output of heterogeneous material joint

[0077] In this method, since the curing material and the molten material are heterogeneous materials, the surface bonding strength between the two materials is significantly lower compared to the bonding strength between homogeneous materials. To address this, this method employs two types of anchor outputs: a "pin anchor" (starting anchor) that secures the molten support layer to the wall at the starting position of the member, and a "line anchor" (continuous anti-delamination anchor) that prevents delamination along the entire length of the permanently remaining molten support layer.

[0078] In this construction method, the molten support layer is classified into a permanently retained type and a removable type depending on the type of structural member. The molten support layer for slabs and pitched roofs remains permanently after construction is completed to form an insulation layer and design finish. The molten support layer for window lintels is removed after construction is completed to allow for window installation. For stairs, the molten support layer is selected to remain permanently or be removed according to the design intent. Line anchors are applied only to the permanently retained molten support layer, while only pin anchors are applied to the removable molten support layer.

[0079] 4.1 Pin Anchor (Starting Anchor)

[0080] A pin anchor is formed by a line output in which the molten material penetrates into the interior of the curing material wall for 2 to 5 layers immediately prior to the start of the molten support layer, at a location where the molten support layer originates from the curing material wall. This line consists of a combination of a horizontal penetration section, in which the depth of penetration into the curing material wall is approximately twice the diameter of the curing material nozzle (approximately 100 mm based on a 50 mm curing nozzle), and a vertical protrusion section, in which the height protruding outward from the curing material wall is the thickness of one layer of the molten material itself. The horizontal penetration section is formed by line outputting the molten material on top of it immediately after the curing material is output, and as subsequent curing material is stacked on top of it, the molten material line becomes embedded within the curing material. The vertical protrusion serves as the starting point for the subsequent molten support layer line. This pin anchor forms a mechanical interlock between the two materials as a combination of a line penetrating into the interior of the curing material body and a line protruding outward.

[0081] The pin anchor line is repeatedly printed over 2 to 5 layers. One layer alone is insufficient for bonding strength, and if it exceeds 5 layers, the inherent rigidity of the curing material may decrease. In one embodiment, 3 layers are used.

[0082] 4.2 Line Anchor (Continuous Anti-Peeling Anchor)

[0083] Line anchors are formed as lines that penetrate into the body of the curing material at regular intervals along the longitudinal direction of the permanently remaining molten support layer, such as in slabs and pitched roofs. The bonding strength of the permanently remaining molten support layer must be maintained to prevent delamination from the body of the curing material over a long period after construction is completed. While pin anchors serve to secure the molten support layer to the wall at its starting position, they have limitations in preventing delamination from the body of the curing material along the entire longitudinal direction of the molten support layer. Line anchors are introduced to compensate for this limitation.

[0084] The penetration direction of the line anchor is opposite to the outer normal direction of the molten support layer, and it crosses the molten support layer and the curing material body to connect both sides. The length of the line anchor is operated within a range of approximately 20% to 50% of the curing material nozzle diameter (approximately 10mm to 25mm for a 50mm nozzle), and the spacing between line anchors is approximately 5 to 10 times the curing material nozzle diameter (approximately 250mm to 500mm spacing for a 50mm nozzle). The line anchor remains permanently embedded inside the curing material body even after construction is completed.

[0085] 5. Quantitative Significance of Asymmetric N:1 Sequential Alternating Stacking

[0086] The core mechanism of this method, asymmetric N:1 sequential alternating stacking + N-layer output control within the curing material head stagnation limit time, is explained below.

[0087] The thickness of one layer of molten material (t_M) and one layer of curing material (t_C) are determined independently by the inherent constraints of each head, and generally, t_C is several to tens of times greater than t_M. For one layer of curing material to be output, a molten support layer must be accumulated on the same working surface to a height greater than t_C to form a shape that supports the self-weight of the subsequent curing material. Therefore, the ratio N is determined by the following relationship.

[0088] N?t_C / t_M

[0089] Example 1: In the case of a molten material nozzle of 10 mm + layer thickness of about 2 to 3 mm and a curing material nozzle of 50 mm + layer thickness of about 10 to 15 mm, N is about 4 to 7.

[0090] Example 2: In the case of a molten material nozzle of 15 mm + layer thickness of about 4 to 5 mm and a curing material nozzle of 80 mm + layer thickness of about 16 to 20 mm, N is about 4.

[0091] An example of the asymmetric N:1 sequential alternating stacking of the present method is illustrated in FIG. 4. FIG. 4 represents two cycles of an N=4 example in a single cross-sectional view. Stacking sequences ① through ④ represent the accumulation of N layers (N=4) of molten material in one cycle, and stacking sequence ⑤ represents the stacking of one layer of curing material on top thereof. Subsequently, stacking sequences ⑥ through ⑨ represent N layers of molten material for the next cycle, and stacking sequence ⑩ represents one layer of curing material on top thereof. The left area (A) of FIG. 4 represents a main body formed by the accumulation of multiple cycles completed prior to the point in time of this cross-sectional view. This accumulated main body (A) and the stacking sequences ① through ⑩ visualize that the construction sequence of the present method is applied in a continuous, repetitive manner. The **right nozzle offset (G) of FIG. 4** indicates a separation for the curing material nozzle to avoid the corner of the previously stacked molten support layer (see

[0072] ). The progress time of stacking sequences ① to ⑤ adjacent to region A is controlled within the curing material stagnation limit time (t_lim), and stacking sequences ⑥ to ⑩ represent the next cycle (C2).

[0092] In the sequential alternation of steps (c) and (d) of this method, the time required to output N layers of molten material in step (c) is controlled to be within the curing material retention limit time inside the second head. The retention limit time is determined by the chemical curing rate of the curing material used, the internal retention volume of the curing material head, and the elapsed time since the curing material became liquefied.

[0093] In one embodiment of the present method, when a curing material head adopts a method of inline mixing of pellet-type construction materials and liquid components immediately before or inside the head (see Patent Document 3), the curing material stagnation limit time is extended to approximately 5 minutes. This means that the present method operates stably by controlling the time required to output N molten material layers in step (c) of the present method to within approximately 5 minutes. As shown in FIG. 4, the core operating condition of the present method is that stacking sequences ① to ⑤ proceed within the curing material stagnation limit time (t_lim).

[0094] In the conventional ground mixer + pump truck method, approximately 10 minutes have already elapsed during the process in which the curing reaction begins in the ground mixer and is transported through the pump truck hose to the head, so the stagnation limit time from the time of arrival at the head is essentially very short. Therefore, with the conventional ground mixing method, it is difficult to complete the output of N layers in step (c) of the present method within the stagnation limit time. However, the scope of the claims of the present method is not limited to the inline mixing method, and if another curing material supply method is derived in the future in which sufficient stagnation time inside the curing material head is secured, the present method can be applied to such a method as well.

[0095] 6. Category Classification of Application Area and Output Sequence

[0096] This method is operated by classifying it into an alignment output mechanism and an expansion output mechanism depending on the shape of the applied member.

[0097] 6.1 Alignment Output - Installation of Window Lintels + Frame Stairs

[0098] The alignment output mechanism is applied when the length direction of the member aligns with the length direction of the wall and the thickness of the member is equal to or similar to the thickness of the wall. The member is output in the form of a short, simple support spanning between the two side walls.

[0099] The output sequence of the alignment output is as follows (see FIGS. 5 and FIGS. 6).

[0100] (a) Pin anchors on both sides: Pin anchors are output on the walls on both sides where the member begins. Since the member is short, 1 to 2 anchor lines are sufficient.

[0101] (b) Formation of molten support layer - Inclined horizontal expansion of molten material: The active head switches to the first head (molten material), and the molten material originates from the pin anchors on both sides and is output in an inclined horizontal expansion mode. The molten support layers originating from the two sides meet at the center of the member to form a flat or inclined support that defines the lower surface of the member.

[0102] (c) Body Formation - Lamination of Curing Material: The active head switches to the second head (curing material), and the curing material is output in a lamination mode onto the molten support layer. The member body is output in a straight line along the length direction (left-right) of the member using vertical lamination, identical to that of a standard wall. Short fiber reinforcement incorporated into the curing material is dispersed in random directions, contributing to the multi-axial stress distribution of the member.

[0103] (d) Classification of Molten Support Layer Operation - Permanent Retention or Removal: Depending on the type of member, the molten support layer in this category is selected to be permanently retained or removed after construction. The molten support layer of window lintels is removed after construction for window installation. Depending on the design intent, the molten support layer of rigid frame stairs is either permanently retained to be preserved as a finish on the underside of the treads, or removed to be used as an exposed concrete finish.

[0104] The alignment output is applied to the next member.

[0105] (α) Window lintel (see Fig. 5): A lintel that spans between the two side walls, which is an area that required a separate formwork in conventional RC construction methods. In this method, pin anchors are printed on the upper part of the main wall on both sides, and a molten support layer of the lintel is formed by the inclined horizontal expansion of molten material, and the main body of the lintel is formed by stacking curing material on top of it.

[0106] (β) Rahmen Stairs (see FIG. 6): These are treads of straight stairs with walls on both sides, representing an embodiment of a Rahmen structure in which the side walls and the treads are integrally joined. In this specification, they are referred to as “Rahmen Stairs.” The molten support layer of the treads is produced as a flat or inclined support that crosses between the side walls, and the tread body is produced in a straight line in the stair width direction (wall-to-wall direction) by stacking. The risers are directly vertically stacked on top of the tread body by stacking curing materials, and the separate formwork required for risers in conventional RC construction methods is unnecessary due to the shape-maintaining flowability of the curing material in this method. The construction speed of the stairs is the same as that of general wall stacking, and since the curing material of this method has rapid hardening characteristics, no separate curing time is required after each step is produced.

[0107] 6.2 Extended Output - Construction of Slabs + Sloped Roofs + Cantilever Stairs

[0108] The extended output mechanism is applied when a member is thicker than the wall or cantilevered, making it difficult to stand independently using only the two side walls. The member is wide or cantilevered, and a multi-arch rib + inclined horizontal stacking mechanism is applied.

[0109] The output sequence of the extended output is as follows (see FIGS. 8 and 9).

[0110] (a) Exterior Pin Anchors + Simultaneous Wall-Slab Output: The wall portion of the member (slab) starting area is essentially interpreted as an area where the slab extends in the direction of the wall thickness, and the wall and slab are output simultaneously within the same construction cycle. In this area, the curing material is processed simultaneously in an aligned output (vertical stacking) mode on the wall side and in an inclined horizontal stacking (slanted extension) mode on the slab side. The layer thickness of the slab-side extension output is operated to be slightly slimmer compared to the wall-side aligned output (see

[0062] ), which is a conservative approach to prevent self-weight deflection during inclined output. The wall output in this area is converted from an envelope + infill format to an infill finish that fills the entire cross-section with curing material, and multiple pin anchor lines are output on the wall immediately after the infill finish.

[0111] (b) Multiple Entry - Simultaneous Start from Multiple Walls: Entry occurs simultaneously from multiple entry points on the outer boundary of the member. In the case of a regular slab where the member area is divided by four walls, simultaneous entry in four directions is applied; however, if it is further divided by internal walls or has an irregular outer shape, the number of entry points and the direction of entry are determined according to the shape of the divided area. This method is not limited to four directions. Through this simultaneous multiple entry output, the time required to output N layers of molten material in one cycle is reduced to within the curing material head stagnation limit time.

[0112] (c) Cross-sectional shape - Multi-arch rib: The molten support layer of a slab or pitched roof has a shape similar to the curved deck plate of a conventional steel structure and is produced as a multi-arch rib structure in which multiple arched curved surfaces are arranged in parallel. This multi-arch rib is a double-curved structure in which short-period arched ribs reinforce the cross-sectional stiffness of the member (increase moment of inertia), while the entire member forms a large curvature (arch) over the span to transmit self-weight and live load to the wall as compressive force. This multi-arch rib forms a working surface in which one layer of curing material can be stacked in the gap between adjacent ribs, as shown in the stacking sequences ①~④ and ⑥~⑨ in FIG. 4. The thickness distribution of the member is not uniform and may have a distribution that is thicker at the wall-adjacent part and thinner in the center. The specific ratios and rise values ​​of this thickness distribution are determined based on the member span, the compressive strength of the curing material, and live load assumptions, and structural safety review for multi-story applications is subject to consultation with a structural engineer.

[0113] (d) Formation of the main body - Inclined horizontal stacking of curing material (extended output): After the multi-arch ribs are formed, the active head is switched to the second head (curing material), and one layer of curing material is stacked in the gap area between adjacent ribs. As shown in FIG. 4, one layer of curing material (⑤·⑩) is stacked in an inclined direction on the multi-arch ribs (①~④, ⑥~⑨), and the space between adjacent ribs is filled in the lateral direction due to the shape-maintaining flowability of the curing material. The main body of the member is formed as a continuous body without lateral separation by the polymer. In this step, the curing material nozzle avoids collision with the previously outputted molten support layer area by applying the spacing operation between the curing material and the molten support layer (see

[0072] ). In this specification, “inclined horizontal stacking” and “extended output” are used interchangeably with equivalent meanings.

[0114] (e) Asymmetric N:1 alternating sequence: The cycles of steps (b) through (d) are repeated in an asymmetric N:1 ratio.

[0115] (f) After outer closure - expansion output only: After the outer closure, the wall output is finished, and the multi-arch ribs narrow from the outer to the center and meet at the center of the member plane to close (see Fig. 8).

[0116] (g) Center finish - Vertex bridge output: The remaining space between opposing multi-arch ribs in the center closure area of ​​the member is traversed by a molten material bridge output. After the bridge closure, the curing material is finished over it by a layered output with increased extrusion volume (see Fig. 6530).

[0117] (h) Line Anchor: Since the molten support layer of this category remains permanently, line anchors are output at regular intervals along the length of the molten support layer (see

[0083] ).

[0118] Extended output is applied to the following members.

[0119] (α) Slab: An inter-story slab in a multi-story building. In the case of a regular slab separated by walls on four sides, simultaneous entry in four directions is applied. The slab cross-section is output in a multi-arch rib shape, and when applied to multiple stories, the slab thickness distribution and rise are subject to consultation with a structural engineer.

[0120] (β) Sloped roof: In this specification, “sloped roof” encompasses all roof types (gable roof, hip roof, hipped gable, slit roof, curved roof, etc.) excluding flat roofs (=slabs). In one embodiment of a gable roof, the left and right gable slopes and the two gable walls (front and back) enter simultaneously and close simultaneously at the ridge (see FIG. 10). Since the gable surface is essentially a sloped area, the risk of self-weight deflection is lower compared to horizontal slope stacking such as a slab, and the slope output is more natural as the angle of inclination increases. The gable walls are stacked in a triangular pattern along the slope of the gable surface, and the gable surface is subjected to the same expansion output mechanism of horizontal slope stacking of cured material + permanent remaining multi-arch ribs. In other roof types, the direction of entry and the location of closure are determined by the shape—in the case of a hip roof, the four sloped sides are simultaneously closed at one point, in the case of a flat roof, the same mechanism as a slab, and in the case of a curved roof, multiple arch ribs are replaced by a meridian or latitude line skeleton.

[0121] (γ) Cantilever Stairs (see FIG. 7): A tread of a cantilever staircase in which only one side is attached to a wall and the other side is a free end, referred to herein as a “cantilever staircase.” Since the tread is difficult to stand on its own, a multi-arch rib + inclined horizontal stacking mechanism with an extended output is applied. The molten support layer of the tread proceeds in a cantilever form to the free end through the multi-arch rib + inclined horizontal extension, and the tread body also proceeds with inclined horizontal stacking. Line anchors are applied along the length of the molten support layer.

[0122] 7. One Example of a Construction Sequence - Grouping 4 Cycles

[0123] One embodiment of the present method is a box-shaped building with a floor plan of 5m × 5m, a first-floor wall height of 2.5m, a second-floor wall height of 1m, and a maximum pitched roof height of 5m (see Fig. 1). This model is an example to visualize a construction cycle in which all application areas of the present method (slab, pitched roof, window lintel, stairs) appear. The specific dimensions, pitched roof type, window locations, etc. of this model are examples, and the scope of rights of the present method is not limited to the specifications of this model.

[0124] The cross-section of the construction result of this model is shown in Fig. 2. Fig. 2 is a cross-sectional perspective view of the model after construction is completed, visualizing the result of the four application areas of this method (slab, sloping roof, window lintel, and stairs) all being printed as a single unit in one model. As shown in Fig. 2, a curved deck plate shape is formed in the slab area by multiple arch ribs, and a permanent residual molten support layer is exposed at the bottom of the sloping roof to form the design finish. The window lintel on the front of the first floor is the result of an alignment printing mechanism, and the two types of stairs inside the model—an alignment-printed rigid frame staircase and an extended-printed cantilever staircase—demonstrate the versatility of this method's application.

[0125] The construction sequence of this model consists of the following four cycles (see Fig. 3).

[0126] Cycle 1 - 1st floor wall + window / door lintel (aligned output, height 0 ~ 2.5m): This cycle proceeds with an aligned output mechanism, the 1st floor wall is printed in curing material stacking mode, and the lintel in the window / door area is printed in an aligned output.

[0127] Cycle 2 - 1st Floor Stairs (Alignment or Extension Parallel Progress, Parallel Progress with Cycle 1): This cycle proceeds in parallel with Cycle 1, and two types of rigid frame stairs (alignment output type) and cantilever stairs (extension output type) can be operated.

[0128] Cycle 3 - 2nd Floor Slab (Alignment + Expansion Integration, Height 2.5m): In this cycle, the 1st floor wall and the 2nd floor slab are not separated but integrated. Slab output begins when the 1st floor wall reaches the 2.5m position, and construction of the slab thickness area (approx. 250 ~ 300mm) proceeds as follows. In this integrated process, the 1st floor wall portion of the slab thickness area is interpreted as an area where the slab is expanded in the direction of the wall thickness, and curing materials proceed simultaneously in the same layer: alignment output (vertical stacking) on ​​the wall side and inclined expansion output with inclined horizontal stacking on the slab side (see

[0110] ). The column-free space portion within the slab plane enters expansion output mode with multiple arch ribs, and curing materials are stacked on top of it with expansion output. In this integrated process, the first-floor walls and slabs are printed together within the same construction cycle to form a single unit, and are separated as if stacked in the order of first-floor walls → second-floor slab → second-floor walls. Once the printing of the slab thickness area is completed, this cycle switches to a single expansion printing process within the slab plane, and the slab body is formed by the expansion printing of curing material as the multi-arch ribs narrow from the outer to the center. When the center of the slab plane is reached, it is finished with a vertex bridge printing (see

[0116] ). As a result of this cycle, a solid slab is placed on top of the first-floor walls, and the construction of the second-floor walls proceeds in the next cycle.

[0129] Cycle 4 - Sloped Roof + Vertical Wall (Simultaneous alignment or expansion, height 2.5 ~ 5.0m): In this cycle, the 2nd floor walls (vertical walls) and the sloped roof proceed in succession. The 2nd floor walls are stacked up to a height of 1m using an alignment output mechanism, after which the sloped roof proceeds using an expansion output mechanism, allowing both left and right gable faces + both gable walls to enter simultaneously and close simultaneously at the ridge. The window areas of the 2nd floor walls (such as skylights under the eaves of the sloped roof) are output using the same alignment output mechanism as in Cycle 1.

[0130] This construction sequence is the standard cycle of this method. When this cycle is applied to a single-story building, Cycle 3 is omitted, and Cycle 4 proceeds directly immediately after Cycles 1 and 2. For multi-story buildings, Cycles 1 through 3 are repeated and end with Cycle 4 at the top floor. Structural safety reviews regarding slab thickness, rise, and live load distribution when applied to multi-story buildings are subject to consultation with a structural engineer.

[0131] 8. Modified Examples

[0132] This method can be applied using the same principle not only to column-free slabs enclosed by walls but also to irregular walls with severe overhangs, such as sloping roofs. In other words, the molten support layer provides an auxiliary support structure for any section of irregular wall where self-support of curing materials is difficult, and the sloping roof embodiment described herein is a representative example of this application to irregular walls. This method can be extended to various irregular wall shapes not specified herein using the same mechanism.

[0133] Slabless single-story single-space structure: This variation is a simplified variation in which cycle 3 is omitted from one embodiment (see

[0123] ) and cycle 4 proceeds directly immediately after cycles 1 and 2. This variation is suitable for a simple single-space structure in which the roof directly forms the ceiling surface without having a slab inside.

[0134] Limitation of Application Area: This method applies to buildings with shapes where structural safety without reinforcement is ensured. In other words, buildings constructed using this method are limited to shapes where structural strength is secured through a combination of the compressive strength of curing materials, the tensile auxiliary contribution of the permanent remaining molten support layer, and tensile-to-compressive stress transition shapes such as arches, ribs, and domes. Areas where tensile stress is dominant in straight flat slabs, areas where rebar reinforcement against seismic or wind loads is legally mandatory, and structural members of multi-story residential buildings are outside the scope of this method; construction in these areas must utilize conventional RC methods or other reinforcement techniques. The boundary between the applicable and non-applicable areas of this method is determined by structural safety review and is subject to consultation with a structural engineer. Structural safety certification for buildings constructed using this method is planned to be secured through a separate certification procedure in the future; in the United States, there are cases of certification for conventional 3D-printed buildings based on the ICC-ES AC509 evaluation criteria.

[0135] Various modifications of curing materials: The curing materials of this method include, but are not limited to, cement-based mortar, the following: inline mixing results of pellet-type construction materials (see Patent Document 3), conventional cement-based output mortar pre-mixed on the ground, geopolymer-based materials, lime mortar, etc. Depending on each curing material, the stagnation limit time, pouring flowability, curing heat generation, etc., differ, and the determination of N and the selection of nozzle diameter are adjusted accordingly.

[0136] Modification of a temporary melt support layer using a water-soluble polymer: In another modified embodiment of the present invention, a water-soluble polymer (PVA, BVOH, etc.) may be used as a temporary melt support layer when a protective film treatment or a separate separation structure is applied to block the influence of the mixing water of the curing material. This modification is not the standard claimed in this specification and requires separate technical processing.

[0137] Extension to multi-story buildings: The construction sequence according to one embodiment of this specification is extended to the construction of any multi-story building by repeatedly applying this cycle. However, the lifting mechanism of the output platform required for multi-story construction is not the subject of claims in this specification.

[0138] 9. Results of the Present Method - Comparison with Conventional Prefabricated Formwork Systems

[0139] Buildings constructed using this method achieve the same level of proven utility as the conventional prefabricated permanent formwork system (see Patent Document 10), which provides permanent formwork + plain slab + arch ceiling. However, this method achieves this utility through a construction method that is fundamentally different from the conventional prefabricated system. That is, while the conventional system consists of separate construction stages of (i) factory prefabrication + (ii) on-site transportation + (iii) formwork installation + (iv) separate concrete pouring, this method integrates the above four stages into a single construction cycle on-site using a single output platform.

[0140] Through the achievement of this integration, this method provides the following additional benefits compared to conventional systems. First, there are no pre-fabrication costs for irregularly shaped formwork. In conventional systems, irregular formwork requires injection molds or separate manufacturing facilities, whereas this method enables the realization of any shape without additional cost through the kinematics of the output platform. Second, there are no logistics costs for transporting formwork. Third, the design freedom at the construction site is increased. With this method, design changes can be made at the construction site simply by modifying the output data.

[0141] Buildings constructed using this method have the following integrated characteristics.

[0142] Column-free space integral output: In buildings constructed using this method, the box-shaped first-floor walls, windows, stairs, multi-story slabs, and sloping roofs are integrally output in a single construction cycle. The limitations of conventional 3D printing for construction, which was restricted to wall-centered construction, are overcome, and column-free space components are directly output on-site through the combined operation of curing materials and molten materials.

[0143] Automatic formation of openings: All window openings are automatically formed by the integrated output of both side posts + lintels, and the disconnection of integrity caused by the indirect support method that borrows part of the formwork in conventional RC construction methods is eliminated.

[0144] Simultaneous achievement of ceiling and roof design finishes: The underside of the slab, the underside of the roof, and the underside of the stair treads simultaneously form a ceiling finish surface through the exposure of the permanently remaining molten support layer. The shape in which the multi-arch ribs on the underside of the slab are exposed in the form of curved rafters has a stress distribution and visual expression essentially identical to the rib vault structure of 12th to 15th-century Gothic architecture. This method automates the construction principles of irregular curved surfaces, which were virtually discontinued due to the skyrocketing costs of pre-fabricating formwork in the past, using modern 3D printing technology.

[0145] Additional assurance of construction convenience: The spaces between the multiple arch ribs of this method can be simultaneously utilized as passageways for equipment such as pipe sleeves and electrical pipe conduits during the construction phase. As a result, separate structural work for equipment is not required after construction.

[0146] Additional securing of thermal insulation performance: Since the polymer material of the permanent remaining molten support layer has a low thermal conductivity of about 1 / 100 to 1 / 200 compared to cementitious curing materials, an additional insulation layer is formed on the underside of the sloping roof, the underside of the inter-story slab, etc.

[0147] Structural Strength of Reinforced Structure: The structural strength of a building constructed using this method is secured by a combination of (i) the compressive strength of the curing material, (ii) the tensile auxiliary contribution of the permanent remaining molten support layer, and (iii) the tensile-to-compressive stress conversion of the multi-arch rib shape.

[0148] Compatibility with irregular shapes: This method can be applied using the same principle not only to regular buildings with straight exteriors but also to irregular buildings with curved exteriors or freeform surfaces. Explanation of the symbols

[0149] 100: Output base 200: 1st Head (Molten Material Head) 210: 1st head nozzle 300: 2nd Head (Curing Material Head) 310: Second head nozzle 400: Slab 500: Molten material 510: Molten Material Extended Output Body 520: Molten material rib structure 530: Molten material center horizontal finish 540: Molten material multi-parallel framework 550: Molten material output insertion anchor (start anchor) 560: Anchor for preventing continuous molten material peeling 600: Curing materials 610: Curing Material Alignment Output Main Body 620: Curing Material Extended Output Main Body 700: 1st floor wall 710: 2nd floor wall 800: Window opening 900: Stairs 930: Ramen Stairs 940: Cantilever stairs 1000: Sloped roof A: The accumulated body of previous cycles t_lim: Progress time for stacking sequence ① to ⑤ (within the curing material stagnation limit time) C2: Next cycle G: Nozzle offset ① to ⑩ (Fig. 4): Stacking order of asymmetric N:1 sequential alternating stacking ① to ? (Fig. 8): Stacking order of slab output progress (odd order is molten material) Output, even numbers indicate curing material output) ① to ⑥ (Fig. 10): Stacking sequence of sloped roof printing process

Claims

Claim 1 A method for 3D printing of a building member on-site having a region where self-standing of a non-reinforced cementitious curing material is difficult, comprising: (a) a step of printing a polymer-based molten material in the region where self-standing is difficult to form a molten support layer having a multi-arch rib structure that enters simultaneously at multiple entry points on the outer boundary of the member; (b) a step of printing the curing material in the gap region between the multi-arch ribs to form the main body of the member as a continuous body without lateral separation; and (c) a step of performing the steps (a) and (b) alternately within the same construction cycle on a single printing platform to form a member in which the molten support layer and the main body of the member are integrally combined; wherein the subsequent printing of the molten support layer in step (a) proceeds while the curing material in step (b) undergoes chemical curing, so that the molten material and the curing material are operated in time-synchronized, and the multi-arch ribs transmit the self-weight and live load of the main body of the member to the wall as a compressive force. Claim 2 A method for on-site 3D printing of a building member according to claim 1, wherein the multi-arch rib is a shape in which a plurality of arch-shaped curved surfaces are arranged in parallel, and is a double-curved surface structure that simultaneously forms a short-period arch-shaped rib that reinforces the cross-sectional rigidity of the member and a large curvature of the entire span, and the period of the short-period arch-shaped rib is in the range of 5 to 30 times the diameter of the curing material nozzle. Claim 3 A method for on-site 3D printing of a building member according to claim 1, wherein the molten support layer of step (a) is stacked at an inclination of 30° to 60° with respect to the normal of the work surface, and steps (a) and (b) are sequentially alternately repeated in an asymmetric N:1 ratio, wherein N is determined based on the ratio of the thickness of one layer of curing material (t_C) to the thickness of one layer of molten material (t_M) (N - t_C / t_M), and the time required to output N layers of molten material in step (a) is controlled to be within approximately 5 minutes. Claim 4 A method for on-site 3D printing of a building member according to claim 1, wherein the curing material stacking position in step (b) is spaced apart from the outer edge of the previously stacked molten material by a distance corresponding to the diameter of the molten material nozzle, and the unfilled area resulting from this separation is filled by reinforcing the extrusion amount of the curing material. Claim 5 A method for on-site 3D printing of a building member according to claim 1, wherein the molten support layer is not removed after construction is completed and remains as a permanent component of the member, and additionally forms an insulating layer on the lower surface of the member due to a lower thermal conductivity compared to the curing material body, and a pin anchor is formed at a position where the molten support layer starts from the member body, wherein the pin anchor forms a mechanical interlock between the two materials by combining a horizontal penetration part that penetrates into the member body and a vertical protrusion part that protrudes outside the member body, and a line anchor is formed at regular intervals along the length direction of the molten support layer, wherein the length of the line anchor is in the range of 20% to 50% of the diameter of the curing material nozzle and the spacing between the line anchors is in the range of 5 times to 10 times the diameter of the curing material nozzle.

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