Method for shortening construction period of building using pre-construction of key structural members and ultra-rapid hardening concrete

Abstract

The present invention provides a structural methodology to solve the problem of process delays caused by the long curing period of the entire concrete of the basement floor in conventional technology by (a) strategically selecting core vertical members (main columns and core walls) that receive the load of the ground floor, (b) pouring ultra-fast curing nano-reinforced geopolymer concrete only on the members to complete ultra-short-term curing within 1 to 3 days, and (c) immediately starting construction of the ground floor using the cured core vertical members as support points without waiting for the surrounding slabs to cure. The ultra-fast setting nano-reinforced geopolymer concrete composition optimized for the above construction method is prepared by adding nano silica to a binder containing blast furnace slag fine powder, fly ash, and metakaolin to promote reaction and densify the structure, and using an alkali activator of a specific concentration and ratio. According to this configuration, the present invention fundamentally eliminates bottlenecks caused by basement construction, thereby drastically shortening the overall construction period, while simultaneously securing ultra-high strength, low shrinkage, and excellent long-term durability required as core structural members of a building, and has the effect of enhancing eco-friendliness by recycling industrial by-products.

Description

Technology Field

[0001] The present invention relates to construction technology for buildings, and more specifically, to a new construction method for drastically shortening the overall construction period of a building including an underground structure and a concrete composition optimized therefor. Specifically, the present invention relates to a technology that innovates the entire process by organically combining a structural methodology for strategically pre-constructing a specific structural member that forms the main path of the building load with material characteristics that enable ultra-short-term curing of said member, thereby minimizing the waiting time for subsequent processes. Background Technology

[0003] Generally, in the construction of high-rise mixed-use buildings in urban areas, the structural work of underground structures, such as underground parking lots, occupies the initial stage of the entire process and has a decisive impact on the overall duration of the project.

[0004] According to traditional cast-in-place concrete methods, the entire structure of a floor—including slabs, columns, and walls—is poured sequentially starting from the lowest basement level, followed by a long curing process until the poured concrete develops sufficient strength to safely support the loads of the upper floors. However, standard Portland cement-based concrete absolutely requires a curing period of typically three to four weeks before formwork can be removed and subsequent processes can proceed. During this period, subsequent processes, including the construction of the above-ground structural framework, are effectively halted, acting as the biggest bottleneck in the overall project schedule. Such process delays have been a chronic problem, causing serious socioeconomic costs such as increased financial expenses associated with project financing (PF) and massive opportunity cost losses due to the inability to use the building early.

[0005] As an attempt to solve these problems, methods using rapid-hardening cement or ultra-rapid-hardening cement, which simply increase the hardening speed of the material, have been attempted. However, these materials have limitations in terms of safety and reliability, as well as high material costs, cracking problems caused by large drying shrinkage during the rapid hardening process, and reduced long-term durability.

[0006] Meanwhile, as a structural approach to changing the construction sequence, a technology has been proposed to shorten the construction period by first constructing the core of a building and then using it as a support to carry out the construction of the lower frame and upper frame in parallel, such as Korean Registered Patent No. 10-0171873 (hereinafter 'Prior Art 1').

[0007] However, prior art 1 has the following obvious limitations.

[0008] First, prior art 1 merely presents a 'methodology' for changing the construction sequence, but fails to provide specific material solutions regarding 'material technology,' which is the core means for safely and efficiently implementing that methodology in reality; consequently, the effect of shortening the construction period is bound to be limited. In other words, for the pre-constructed core section to safely support the massive load of simultaneous construction of the upper and lower sections, it is essential to have the prerequisite that the core section itself must develop high strength within a very short period. However, since prior art 1 is based on general concrete technology of the time, a considerable period of curing is still unavoidable even after the pre-construction of the core section, so the effect of shortening the construction period is bound to be very limited.

[0009] Second, it fails to resolve fundamental concerns regarding structural safety. If subsequent construction is carried out using a core section as a support without undergoing a sufficient curing period, it may cause deformation or cracking of the core section itself, posing a fatal threat to the safety of the entire building. Prior art 1 lacks specific means to resolve safety issues arising from these material limitations.

[0010] Therefore, there is an urgent need for an innovative construction method that can fundamentally shorten the construction period while perfectly ensuring structural safety. This is achieved by organically combining a structural approach that fundamentally redesigns the flow and sequence of the entire construction—going beyond a piecemeal approach of merely changing the construction order—with high-performance material technology optimized for this approach, which simultaneously satisfies ultra-short-term high strength development and long-term durability. Prior art literature

[0011] Korean Registered Patent No. 10-0171873 (Registered Oct. 21, 1998) (Title of Invention: Method for constructing a high-rise building using a pre-constructed core) Korean Published Patent No. 10-1996-0034606 (Published Oct. 24, 1996) (Title of Invention: Method for shortening the construction period of the frame of a concrete building) The problem to be solved

[0012] The present invention was devised to solve the problems of the conventional technology described above, and its main purpose is to provide a new construction method that drastically shortens the overall construction period of a building by minimizing the waiting time for subsequent processes that inevitably occurs due to the concrete curing period of underground structures.

[0013] In addition, another objective of the present invention is to provide a construction method that satisfies all the requirements for ultra-short-term high strength development, low shrinkage, and excellent long-term durability as a core structural member responsible for the permanent safety of a building, while realizing the aforementioned reduction in construction time, and a high-performance concrete composition optimized therefor.

[0014] Furthermore, another objective of the present invention is to provide a practical construction technology for shortening construction time that ensures eco-friendliness by actively utilizing industrial by-products as primary raw materials to reduce environmental burden, and secures constructability and economic feasibility necessary for on-site application. means of solving the problem

[0015] The construction method for shortening the construction period of a building according to the present invention, which is intended to solve the above problem, comprises: (a) a step of strategically selecting a core vertical member [main column (110a) and core wall (140)] that receives the load of a ground floor structure to be constructed on top within an underground structure; (b) a step of curing by pouring ultra-fast curing nano-reinforced geopolymer concrete onto the selected core vertical member to secure a target initial strength that allows subsequent processes to be started within an ultra-short period of 1 to 3 days; and (c) a step of initiating the frame construction of the ground floor structure by utilizing the core vertical member that secured the target initial strength in step (b) as a direct support point for the load of the ground floor structure, while the slab around the core vertical member is not cured until it exhibits sufficient strength to support the load of the ground floor structure above.

[0016] Preferably, step (a) can be performed by selecting a main column (110a) of a load-concentrating modular structure designed to concentrate the building load at a specific location instead of a number of general columns as the core vertical member, thereby optimizing the use of special concrete and facilitating construction management.

[0017] In addition, the above construction method can maximize the efficiency of subsequent processes by designing the main circulation section (ramp), which is used as the main passage for equipment and materials during the construction period, as an independent structure by structurally separating it from the surrounding slab, and by further including a step of constructing it in advance, either independently or in parallel with steps (a) to (c).

[0018] The ultra-fast setting nano-reinforced geopolymer concrete composition of the present invention for solving the above problem comprises a binder, an alkali activator, aggregates, and key additives as a material optimized for the above construction method, and

[0019] The above binder comprises 65-75 wt% of ground blast furnace slag powder (GGBFS), 15-25 wt% of fly ash, and 5-10 wt% of metakaolin based on the total weight of the binder;

[0020] As the above-mentioned key additive, it further includes 1 to 3 weight percent of nano-silica, which promotes the geopolymer reaction and densifies the structure of the cured body, relative to the total weight of the binder;

[0021] The above alkali activator is composed of a combination of a sodium hydroxide (NaOH) solution with a molar concentration of 12 to 14 M and a sodium silicate solution with a SiO₂ / Na₂O molar ratio (Ms) of 1.5 to 1.8, and is characterized in that the mass ratio (Liquid / Binder ratio) of the total amount of the alkali activator solution to the total amount of the binder is 0.33 to 0.38.

[0022] Another problem to be solved by the present invention and specific means for solving it will be explained in more detail in the 'specific details for implementing the invention' and the attached drawings described below. Effects of the invention

[0024] The present invention having the above configuration and features provides the following excellent and complex effects.

[0025] First, it reduces the conventional process waiting time of several weeks, required for the concrete of the entire basement to harden, to just 1 to 3 days for the curing of core vertical members that serve as the building's framework. In other words, by fundamentally eliminating process bottlenecks, it shortens the overall project duration by at least 10% to over 20%, providing significant economic benefits by reducing substantial financial and indirect costs.

[0026] Second, the 'ultra-fast setting nano-reinforced geopolymer concrete' proposed according to the present invention not only exhibits ultra-short-term strength but also forms a very dense and uniform high-density structure due to the nucleation promotion and pore-filling effects of nano-silica. As a result, its long-term strength and resistance to the penetration of harmful substances such as moisture and chlorides—that is, its durability—are significantly superior to conventional concrete, thereby ensuring the permanent safety of buildings.

[0027] Third, by pre-constructing major traffic routes (ramps) that serve as the arteries for construction equipment and materials and utilizing them as dedicated construction roads, it maximizes the efficiency of material transport and equipment movement, facilitates subsequent processes such as finishing and installation, and optimizes the overall construction flow.

[0028] Fourth, based on a low solution-to-binder ratio (L / B ratio) and a high aggregate filling rate, the shrinkage of the material itself is minimized, and since the robust core members constructed in advance stably support the load of subsequent processes, safety during construction is very high.

[0029] Fifth, by using large quantities of industrial by-products such as blast furnace slag fine powder and fly ash as primary binders, it reduces the massive amount of carbon dioxide emissions generated during the Portland cement production process and increases the resource recycling rate, thereby enabling environmentally friendly construction.

[0030] Another functional effect of the present invention will be explained in more detail in the 'specific details for implementing the invention' described below. Brief explanation of the drawing

[0032] FIG. 1 is a schematic plan view to explain the structural characteristics of an underground parking lot to which the construction method for shortening construction time according to the present invention is applied. FIG. 2 is a schematic construction diagram for sequentially explaining the key steps of the construction method for shortening construction time according to the present invention for the building of FIG. 1. Specific details for implementing the invention

[0033] The present invention is capable of various modifications and may take various forms, and embodiments are to be described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed forms, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0034] The terms used in this specification are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "consisting of" are intended to indicate the existence of the features, numbers, steps, actions, components, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, or combinations thereof.

[0036] Hereinafter, with reference to the attached drawings, the construction method for shortening the construction period of a building according to the present invention and the ultra-fast setting nano-reinforced geopolymer concrete composition used therein will be described in detail.

[0037] The core technical concept of the present invention lies in fundamentally redesigning the entire construction process flow, namely the 'Critical Path'. In particular, as a specific construction methodology for shortening the construction period, it features (1) a structure for pre-construction and separate casting of core vertical members, (2) a load-concentrating modular structure, and (3) an independent structure and pre-construction of major circulation sections (ramps).

[0038] Furthermore, an effective concrete composition is proposed as a key technical means for implementing the aforementioned innovative construction methodology in practice. The content range of each component of the ultra-rapid hardening concrete composition according to the present invention is an essential technical configuration established to optimally realize multiple conflicting performance objectives, such as ultra-rapid hardening, workability, long-term durability, and crack resistance. If the content falls outside the critical range described below, the effects intended by the present invention may not be fully obtained, or serious side effects may occur.

[0040] First, with reference to FIGS. 1 and 2, the 'core vertical member pre-construction and separate casting structure' of the present invention will be described. In the prior art, all columns and slabs shown in this plane were considered as a single process unit, cast simultaneously, and waited for the entire structure to cure.

[0041] However, in the present invention, as shown in FIG. 1, the core vertical members that form the foundation of the building by directly receiving the massive load of the ground floor, namely the main columns (110a) that are partially constructed in advance, and the core walls (140) that constitute the stairwell and elevator shaft are strategically selected first. FIG. 1 schematically illustrates an underground parking lot to which the present invention is applied.

[0042] FIG. 2 clearly illustrates this innovative construction sequence. First, in step S1, the ‘ultra-fast curing nano-reinforced geopolymer concrete’ described later is poured only on the core vertical members (110a, 140) strategically selected as described above, and curing is completed within an ultra-short period of 1 to 3 days. Once these core vertical members secure sufficient strength early on as the permanent framework of the building, even if the surrounding wide slabs are in an arbitrary state where they have not yet reached the design strength to independently support the upper load because curing is still in progress immediately after pouring, the core vertical members directly support the upper load, so the structural work, such as the installation of formwork and shoring to support the upper ground structure, can be started immediately in step S2 without waiting for the curing of the slabs to be completed. In the present invention, the state in which a slab is "still in the process of hardening" or "not fully cured" does not specify whether the slab has just been cast or has achieved a certain strength, but rather encompasses all curing stages until the slab reaches the design strength capable of independently supporting the upper load. Furthermore, in the present invention where the core vertical members bear the load, this means that the specific degree of curing of the slab does not serve as a constraint on the initiation of subsequent processes.

[0043] In other words, the present invention has the decisive effect of ensuring that construction continues continuously without interruption by eliminating the inevitable process gap of several weeks that existed between stage S1 and stage S2.

[0045] The construction method according to the present invention is a preferred embodiment for further maximizing the efficiency of the preceding construction, and instead of uniformly arranging a number of general columns, a structural design can be applied in which main columns (110a) with a larger cross-section and greater rigidity are arranged according to a certain module (e.g., one per 24 parking spaces) as shown in FIG. 1 to concentrate the load of the upper part of the building at a specific location. This configuration has additional advantages, such as optimizing the use of expensive ultra-rapid hardening concrete by limiting it only to essential parts, simplifying construction by reducing management points, and maximizing the effect of shortening the construction period.

[0047] Furthermore, the construction method according to the present invention has another feature in that the independent structure and pre-construction of the main circulation section (ramp) are different.

[0048] The ramp connecting the basement and the ground floor serves as a "vascular" for the movement of materials and equipment during the construction period. In the present invention, as shown in FIG. 1, the ramp (160) is designed as an independent structure that is structurally separated from the surrounding slab (not shown) of the ground floor (e.g., by installing an expansion joint), and can be constructed first as a separate process from the main building frame construction. Once the ramp (160) is completed early, it is no longer a subject of construction but becomes a "construction road," which dramatically improves the overall efficiency of the project by smoothly supplying materials and equipment necessary for subsequent finishing and installation processes.

[0050] The concrete composition of the present invention is the key technological means for realizing the aforementioned innovative construction methodology in practice. The ultra-rapid hardening concrete composition according to the present invention focuses on "maximizing ultra-short-term strength development" of "high-strength vertical members" that bear the load of the entire building.

[0051] The ultra-fast setting nano-reinforced geopolymer concrete composition according to the present invention is characterized by comprising: a binder comprising 65-75% by weight of ground blast furnace slag powder (GGBFS), 15-25% by weight of fly ash, and 5-10% by weight of metakaolin, based on the total weight of the binder; 1-3% by weight of nano-silica relative to the total weight of the binder; and an alkali activator comprising a sodium hydroxide (NaOH) solution with a molar concentration of 12-14 M and a sodium silicate solution with a SiO₂ / Na₂O molar ratio (Ms) of 1.5-1.8, wherein the mass ratio (L / B ratio) of the total amount of the alkali activator solution to the total amount of the binder is 0.33-0.38.

[0053] The binder of the ultra-rapid hardening concrete composition according to the present invention is characterized by being composed of 65 to 75 weight% of ground granulated blast furnace slag (GGBFS), 15 to 25 weight% of fly ash, and 5 to 10 weight% of metakaolin. The binder of the present invention composed of these components can simultaneously satisfy two goals of 'shortening the construction time' and 'structural stability' because metakaolin triggers the initial reaction and GGBFS and fly ash complement long-term strength and durability, resulting in a superior speed of initial strength development compared to Portland cement, a low shrinkage rate, and high durability.

[0054] The blast furnace slag fine powder (GGBFS) among the binder components mentioned above is a component that forms the basis of long-term strength and durability. If its content is less than 65 weight%, the formation of dense cash gel is insufficient, which may result in insufficient long-term stability and salt resistance required for underground structures. On the other hand, if it exceeds 75 weight%, the proportion of GGBFS, which reacts relatively slowly, becomes excessive, diluting the ultra-rapid hardening effect imparted by metakaolin, making it difficult to achieve the target 'ultra-short curing'.

[0055] Fly ash among the binder components improves the fluidity of the mixture through its spherical particle shape, thereby ensuring workability and controlling the heat of reaction. If the content is less than 15 weight%, it is difficult to secure the fluidity required for pump pouring, and if it exceeds 25 weight%, the development of initial strength may be significantly delayed due to the influence of fly ash, which has low initial reactivity.

[0056] Metakaolin, among the binder components mentioned above, acts as a key trigger for the 'ultra-fast curing' of the present invention. If its content is less than 5 weight%, it is insufficient to actively initiate the geopolymer reaction, resulting in a negligible effect in securing ultra-fast curing. On the other hand, if it exceeds 10 weight%, the reaction becomes excessively fast, which can cause a flash set phenomenon where it is impossible to secure working time. Furthermore, due to excessive reaction heat, the risk of thermal cracking increases rapidly, and self-shrinkage increases, which can be fatal to durability.

[0058] The ultra-fast setting concrete composition according to the present invention contains 1 to 3 weight percent of nano-silica as a key additive. In particular, nano-silica is an ultrafine particle with a size of tens of nanometers (nm), and when incorporated into concrete, it exhibits two powerful effects.

[0059] Nano-silica is a key component that provides the technical differentiation of the present invention. Nano-silica, which consists of nano-sized ultrafine particles, simultaneously exhibits a nucleation-promoting effect that provides countless seeds for the growth of hydrates during the geopolymer reaction, and a pore-filling effect that fills the fine pores between binder particles. Through this, it explosively increases initial strength and makes the structure ultra-high density. If the content is less than 1 weight%, the above effects are negligible and there is no meaning in adding more; if it exceeds 3 weight%, the viscosity of the mixture increases rapidly due to the enormous specific surface area, making casting impossible and causing material costs to skyrocket.

[0060] The composition containing nano silica can achieve a strength of 20 to 25 MPa or higher within 3 hours. This enables a reduction in construction time, allowing subsequent work, such as the installation of shoring for upper floor construction, to begin just a few hours after the casting of the core main columns of the underground parking lot. Furthermore, considering that the main columns of the underground parking lot are critical components that must support the entire building for decades, the ultra-high-density structure reinforced with nano silica not only increases strength but also drastically enhances resistance to the penetration of harmful substances, such as moisture and chlorides, thereby ensuring the long-term stability and reliability of the structure.

[0062] In addition, the ultra-rapid hardening concrete composition according to the present invention is characterized by further including an NaOH solution with a concentration of 12 to 14 M as an alkali activator. The NaOH solution initiates a reaction by providing a strong alkaline environment to dissolve the binder raw materials. If the concentration of the NaOH solution is less than 12 M, the activation energy is insufficient, causing the reaction rate to slow down significantly and failing to secure ultra-rapid hardening properties. On the other hand, if the concentration of the NaOH solution exceeds 14 M, the reaction becomes uncontrollably fast, making it impossible to secure working time and posing a serious threat to the safety of workers.

[0064] Generally, the solution-to-binder ratio (L / B Ratio) of an ultra-rapid hardening concrete composition is the most important factor determining the strength, shrinkage, and workability of the concrete. The solution-to-binder ratio (L / B Ratio) of the ultra-rapid hardening concrete composition according to the present invention is characterized by being in the range of 0.33 to 0.38. If the solution-to-binder ratio (L / B Ratio) is less than 0.33, the mixture lacks fluidity, making casting and compaction impossible; if it exceeds 0.38, the excess moisture causes a large number of voids after hardening, which lowers strength and increases drying shrinkage, becoming a direct cause of cracking.

[0066] The following describes the manufacturing process of ultra-fast setting nano-reinforced geopolymer concrete according to the present invention.

[0067] The manufacturing process of the ultra-rapid hardening concrete according to the present invention is broadly divided into ① a material preparation and precision weighing stage, ② a pre-preparation stage of an alkali activator solution, ③ a mixing stage, and ④ a quality control and transportation stage. Since each stage is an important variable determining the performance of the final concrete, strict control is required.

[0068] (a) Step 1: Material preparation and precise weighing

[0069] Prior to all mixing processes, the first step of preparing and weighing each material specified in the mix design without error is the first step in ensuring quality. The above first step includes the preparation of powdered materials (binders and additives) and the aggregate preparation process.

[0070] In the preparation stage for powder materials (binders and additives), the main raw materials—blast furnace slag fine powder, fly ash, and metakaolin—must be used after being stored in a state where moisture is completely blocked. If any hardened or lumpy parts are present, sieving must be performed prior to use to ensure a homogeneous powder state. Furthermore, nano silica, a key additive, is highly susceptible to moisture as it consists of ultrafine particles. As a general rule, it should be used immediately after opening, and weighing should be done carefully to prevent loss due to static electricity or other factors. All powder materials must be accurately weighed according to the formulation design table using a precision electronic scale within an error range of ±0.5%, and stored in separate containers.

[0071] Furthermore, in the aggregate preparation process, clean fine aggregate (sand) and coarse aggregate (gravel) free from impurities such as soil and organic matter must be used. Since the moisture content of the aggregates directly affects the amount of mixing water, it is most ideal to manage them based on the Surface Dry Saturated State (SSD). It is essential to measure the moisture content of the aggregates on-site in advance and adjust the amount of mixing water based on the results. This is a necessary step to accurately match the final solution-to-binder ratio (L / B Ratio).

[0072] (b) Step 2: Pre-preparation of alkali activator solution

[0073] The second step involves preparing the alkali activator solution, which is the core solution for triggering the geopolymer reaction. Since this solution involves a powerful chemical reaction, it is crucial to prepare and stabilize it at least 24 hours in advance. In particular, sodium hydroxide (NaOH) is a strong alkaline substance that generates intense heat when reacting with water; therefore, the work must be carried out while fully wearing personal protective equipment, such as chemical-resistant gloves, safety glasses, and dust masks.

[0074] The preparation process of the sodium hydroxide solution is explained in more detail as follows. First, place the required amount of distilled or deionized water into a stainless steel container. Then, add the measured amount of high-purity sodium hydroxide (in flake or pellet form) to the water very slowly in portions while continuously stirring with a stirrer. At this stage, water must absolutely not be poured onto the sodium hydroxide, as an explosive reaction could cause the solution to splatter. Next, continue stirring until the sodium hydroxide is completely dissolved. During this stirring step, the temperature of the solution rises rapidly to 80–90°C due to an exothermic reaction. After preparing the sodium hydroxide solution, seal it with a lid and allow it to cool completely to room temperature (10–30°C). This cooling process is crucial, as using the solution while hot can cause instantaneous setting during concrete mixing. Next, pour the measured amount of sodium silicate solution (water glass) into the sodium hydroxide solution that has completely cooled to room temperature, and stir with a stirrer for about 5–10 minutes until the two solutions become a single, completely homogeneous solution. It is recommended to let the completed alkali activator solution sit for at least several hours to stabilize before use.

[0075] (c) Step 3: Concrete Mixing

[0076] The third step is the concrete mixing step, and the mixing order is very important to induce homogeneous dispersion of materials and optimal reaction.

[0077] The mixing sequence of the ultra-fast setting nano-reinforced geopolymer concrete according to the present invention consists of: ① a dry mixing step, ② a wet mixing step, ③ a nano silica addition and final mixing step, and ④ a mixing completion step.

[0078] In the above dry mixing step, the weighed fine aggregate and coarse aggregate are first introduced into the mixer. Then, finely ground blast furnace slag powder, fly ash, and metakaolin, which are powder binders, are introduced on top. The mixer is operated for about 2 to 3 minutes to ensure that the aggregate and binder powders are uniformly mixed together. Through this process, the binder is evenly coated on the surface of all aggregates.

[0079] In the above wet mixing step, the mixer is continuously operated while slowly adding the alkali activator solution, which has been prepared in advance and cooled, to the mixture from which the above dry mixing is completed. Since the geopolymer reaction begins when the solution is added, the mixture is thoroughly mixed for about 3 to 5 minutes to become a paste with uniform viscosity throughout.

[0080] Next, in the nano silica addition and final mixing step, the last metered nano silica is added when the mixture becomes homogeneous. To prevent clumping, it is effective to add the nano silica by spreading it widely over the entire mixture. After adding the nano silica, high-speed mixing is performed for an additional 2 to 3 minutes to ensure that the nano particles are perfectly dispersed throughout the entire matrix without clumping.

[0081] The total mixing time in the above mixing completion step is approximately 10 minutes, and the mixing is completed when the material has a uniform color and viscosity without separation when checked visually.

[0082] (d) Phase 4: Quality Inspection and Transportation

[0083] Upon completion of mixing, the concrete is immediately tested for slump flow to verify that it meets the target workability (fluidity). Additionally, the concrete's temperature and air content are measured and recorded. Concrete that passes these inspections is then loaded onto a ready-mix concrete truck and transported to the site. Since the viscosity of geopolymer concrete increases rapidly over time, the principle is to complete on-site pouring within 60 minutes of mixing completion. During transport, the truck's drum is rotated at a low speed to prevent sedimentation or separation of the materials.

[0085] In the manufacturing and casting process of the ultra-fast setting nano-reinforced geopolymer concrete according to the present invention, temperature is a key variable determining the chemical reaction rate. During the winter season, when the temperature is below 10°C, the geopolymer reaction is significantly delayed, and the ultra-fast setting properties of the present invention may not be exhibited. Conversely, during the summer season, when the temperature exceeds 30°C, the reaction is excessively accelerated, and there is a risk of condensation during transport of ready-mix concrete or immediately after casting, which makes it impossible to guarantee construction quality.

[0086] In addition, the initial moisture supply is absolutely critical for the geopolymer reaction of the ultra-fast setting nano-reinforced geopolymer concrete according to the present invention. If the surface is not covered with vinyl or the like for at least 24 hours after pouring to maintain a high humidity of 95% or more, the moisture on the surface will evaporate rapidly, causing plastic shrinkage cracks and incomplete strength development, which can lead to a serious decrease in surface durability.

[0088] To demonstrate the effects of the present invention, experiments were conducted by setting up one example and three comparative examples as follows. The concrete mixes of all examples were designed based on identical aggregate conditions and water-to-binder ratios (or solution-to-binder ratios), and their performance was evaluated under the assumption that they would be applied to the 'pre-construction of core members' method.

[0089] Table 1 below shows the experimental results of a preferred embodiment according to the present invention (hereinafter referred to as 'Example 1'), Comparative Example 1, and Comparative Example 2. Example 1 according to the present invention is an example in which an ultra-fast setting nano-reinforced geopolymer concrete according to the present invention is used, that is, a binder composed of 70% blast furnace slag, 20% fly ash, and 10% metakaolin, 2% nano silica (relative to the binder), and an alkali activator (13M NaOH + Ms 1.65 sodium silicate, L / B=0.35). Comparative Example 1, which is used in contrast to this, was based on 100% ultra-fast setting Portland cement (without alkali activator and nano silica), which is the most widely used fast-setting concrete. In addition, to demonstrate the effect of nano silica, a geopolymer concrete composition without nano silica added to the ultra-fast setting nano-reinforced geopolymer concrete composition according to the present invention was set as Comparative Example 2. That is, the concrete composition applied in Comparative Example 2 is an example using a binder composed of 70% blast furnace slag, 20% fly ash, and 10% metakaolin, and an alkali activator (13M NaOH + Ms 1.65 sodium silicate, L / B=0.35). The above-mentioned Comparative Example 2 is an example established to clearly identify the role of 'nano silica' in comparison with the present invention (Example 1).

[0090] Performance items Example 1 Comparative Example 1 Comparative Example 2 compression robbery 1 day 28 MPa 20 MPa 15 MPa 3 days 52 MPa 40 MPa 35 MPa 28th 85 MPa 55 MPa 70 PMa Drying shrinkage rate (90 days) 0.038 % 0.095 % 0.050 % Workability (Slump Flow) 650 mm 550 mm 650 mm Subsequent process start Possible timing Within 24 hours of pouring 3 days after pouring 5 days after pouring Structural stability (Cracks / Durability) Very excellent High risk of cracking excellence Overall evaluation Achieved shortened airflow, safety, and durability. Timeline can be shortened, but quality / safety risks are high. Limited air shortening effect, delayed intensity development

[0092] The experimental results in Table 1 above clearly show that the present invention has an unpredictable and significant effect compared to the prior art and the subject of comparison.

[0093] Example 1 exhibited an astonishing strength of 28 MPa in just one day of pouring. This is a sufficient strength to allow for the immediate commencement of subsequent construction, and is 40% higher than Comparative Example 1 (ultra-rapid hardening cement) and nearly twice as high as Comparative Example 2 (nano-silica removal). This is because the alkali activator system of the present invention is significantly faster than the cement hydration reaction, and the nano-silica promotes the nucleation of the geopolymer reaction, thereby maximizing the reaction speed and initial strength.

[0094] In particular, the drying shrinkage rate is noteworthy. Comparative Example 1 (ultra-fast hardening cement) exhibited a very high drying shrinkage rate of 0.095% due to the side effects of rapid hardening, suggesting that cracking and reduced durability are inevitable in the long term. On the other hand, Example 1 had a drying shrinkage rate of only 0.038% thanks to the characteristics of the geopolymer reaction and the pore-filling effect of nano-silica. This implies that the technical challenge of the conflicting relationship between 'ultra-fast hardening' and 'low shrinkage stability' has been simultaneously resolved, and this is a unique effect of the present invention that could not have been predicted in the prior art.

[0095] The only difference between Example 1 and Comparative Example 2 is the addition of nano silica. Comparative Example 2, which lacks nano silica, showed significantly slower initial strength development and long-term strength that was more than 15% lower. This clearly demonstrates that nano silica acts not merely as a micro-filler, but also as a 'chemical catalyst' that promotes geopolymer reactions and a 'structural reinforcing agent' that densifies the hardened body structure from the nanoscale.

[0097] Table 2 below is the result of a comparative experiment to confirm the importance of the nano-silica content range in the ultra-fast setting nano-reinforced geopolymer concrete composition according to the present invention. Geopolymer concrete with a nano-silica content below the range proposed by the present invention was designated as Comparative Example 3, and geopolymer concrete with an excessive amount of nano-silica was selected as Comparative Example 4, and compared with a preferred embodiment according to the present invention (hereinafter referred to as 'Example 1'). The concrete mixes of all examples were designed based on the same aggregate conditions and water-to-binder ratio (or solution-to-binder ratio), and their performance was evaluated assuming application to the 'core member pre-construction' method.

[0098] Performance items Example 1 Comparative Example 3 Comparative Example 4 compression robbery 1 day 28 MPa 18 MPa 12 MPa 3 days 52 MPa 40 MPa 25 MPa 28th 85 MPa 75 MPa 50 PMa Drying shrinkage rate (90 days) 0.038 % 0.045 % 0.065 % Workability (Slump Flow) 650 mm 650 mm 400 mm Subsequent process start Possible timing Within 24 hours of pouring 4 days after pouring 7 days or more after pouring Structural stability (Cracks / Durability) Very excellent excellence Risk of cohesion and cracking

[0100] The experimental results in Table 2 above confirm that the nano silica content is a very important factor in determining the effect of the invention. When the content falls below the range of the present invention, as in Comparative Example 3 (nano silica 0.5%), the nucleation promotion and pore filling effects are insufficient, resulting in a decrease in both initial and long-term strength development compared to Example 1. Conversely, when the content is excessive, as in Comparative Example 4 (nano silica 5%), the fluidity of the mixture decreases rapidly (slump flow 400 mm) due to the high specific surface area of ​​the nanoparticles, leading to deterioration in workability. Furthermore, due to the aggregation of nanoparticles, the strength enhancement effect is actually reduced, and the risk of forming a non-uniform hardened body increases. This clearly demonstrates that the nano silica content range defined in the present invention is the optimal range for simultaneously achieving the 'maximum strength enhancement effect' and 'securing stable workability'.

[0102] In addition, Table 3 below is a comparative experiment to clearly elucidate the role and significance of the content of the 'alkali activator' in the ultra-rapid hardening nano-reinforced geopolymer concrete composition according to the present invention. Geopolymer concrete with only water added and without the use of the 'alkali activator' in the ultra-rapid hardening nano-reinforced geopolymer concrete composition according to the present invention was designated as Comparative Example 5, geopolymer concrete with an alkali activator content below the range proposed by the present invention was designated as Comparative Example 6, and geopolymer concrete with an excessive amount of alkali activator added was selected as Comparative Example 7. These results were compared with a preferred embodiment according to the present invention (hereinafter referred to as 'Example 1'). The concrete mixes of all examples were designed based on identical aggregate conditions and water-to-binder ratios (or solution-to-binder ratios), and their performance was evaluated under the assumption that they would be applied to the 'core member pre-construction' method.

[0103] Performance items Example 1 Comparative Example 5 Comparative Example 6 Comparative Example 7 compression robbery 1 day 28 MPa Hardening defects 10 MPa 16 MPa 3 days 52 MPa (Unmeasurable) 22 MPa 30 MPa 28th 85 MPa (Unmeasurable) 45 MPa 60 MPa Drying shrinkage rate (90 days) 0.038 % (Unmeasurable) 0.055 % 0.080 % Workability (Slump Flow) 650 mm (Unmeasurable) 450 mm 750 mm Subsequent process start Possible timing Within 24 hours of pouring Unfair 7 days or more 5 days Structural stability (Cracks / Durability) Very excellent Failure of structure formation Reaction delay Whitening, reduced durability

[0105] It can be confirmed from the experimental results of Table 3 above that the alkali activator component of the ultra-fast setting nano-reinforced geopolymer concrete composition according to the present invention is an indispensable element for initiating the geopolymer reaction.

[0106] In other words, when an alkali activator was not added as in Comparative Example 5, blast furnace slag and the like did not react at all, and hardening itself did not occur, resulting in a failure to form a structure. Furthermore, the content is also very important. If the amount of activator is insufficient, as in Comparative Example 6 (L / B=0.25), the dissolution of the raw material is insufficient, causing the reaction rate to slow down significantly and the final strength to decrease greatly. Conversely, if the activator is excessive, as in Comparative Example 7 (L / B=0.50), although the initial fluidity is high, the excessive alkali component actually weakens the structure of the hardened body, increases the drying shrinkage rate, and causes efflorescence and reduced durability in the long term. This demonstrates that the content of the alkali activator (L / B ratio) specified in the present invention is the optimal condition that induces the 'fastest and most complete geopolymer reaction' without compromising 'long-term stability'.

[0108] In conclusion, the present invention combines the structural methodology of 'pre-construction of core components' with the best material, 'ultra-fast setting nano-reinforced geopolymer concrete,' in which ① 'nano silica' within an optimal range and ② an 'alkali activator' in an optimal content are organically combined. The results of the comparative experiments above clearly demonstrate that each component of the present invention and its content range exhibit a close synergy effect with one another, and that only within this numerical range can it produce unpredictable and remarkable effects, simultaneously achieving world-class levels of groundbreaking construction time reduction ('initiation of subsequent processes within 24 hours') and potentially conflicting goals ('long-term stability and durability').

[0110] As explained in detail above, the present invention scientifically designs and organically combines 'how to build (structural methodology)' and 'what to build with (material technology).' In other words, the present invention is a highly advanced invention with high industrial utility value that fundamentally overcomes the limitations of conventional technology and safely and dramatically shortens the construction period of buildings.

[0111] The embodiments of the present invention described so far are exemplary, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the scope of the present invention should be determined by the claims set forth below rather than by the detailed description of the specification, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts should be interpreted as being included within the scope of the present invention. Explanation of the symbols

[0113] 110a: Pre-constructed Column 140: Core Wall S1: Step of constructing the core vertical members (110a, 140) in advance and curing them in an ultra-short period. S2: Subsequent step of commencing construction of the above-ground structure based on the produced core vertical members.

Claims

Claim 1 In a construction method for shortening the construction period of a building, the method comprises: (a) selecting one or more of a pre-constructed main column (110a) and a core wall (140) as core vertical members that receive the load of a ground floor structure to be constructed on top within an underground structure; (b) pouring ultra-fast curing nano-reinforced geopolymer concrete onto the selected core vertical members and performing ultra-short-term curing to secure a target initial strength that enables the commencement of construction of the ground floor structure within a period of 1 to 3 days; and (c) a step of initiating the frame construction of the ground floor structure by utilizing the core vertical member, which has secured the target initial strength in step (b), as a direct support point for the load of the ground floor structure, while the slab surrounding the core vertical member is not cured until it exhibits sufficient strength to support the load of the upper ground floor structure, wherein the ultra-fast setting nano-reinforced geopolymer concrete composition of step (b) comprises: a binder comprising 65-75 wt% of ground furnace slag powder (GGBFS), 15-25 wt% of fly ash, and 5-10 wt% of metakaolin based on the total weight of the binder; and 1-3 wt% of nano-silica based on the total weight of the binder. and an alkali activator comprising a sodium hydroxide (NaOH) solution of 12 to 14 M (molar concentration) and a sodium silicate solution having a SiO₂ / Na₂O molar ratio (Ms) of 1.5 to 1.8; wherein the mass ratio (L / B ratio) of the total amount of the alkali activator solution to the total amount of the binder is 0.33 to 0.

38. A construction method for shortening the construction period of a building, characterized by the following steps: the step of preparing an alkali activator solution in advance, cooling it to room temperature (10~30℃), and then adding it to prevent flash set caused by the heat of hydration generated when mixing a high concentration sodium hydroxide solution of 12~14 M and a sodium silicate solution; the step of first mixing aggregate, binder, and the cooled alkali activator to form a paste to prevent clumping of nano particles, and then adding and mixing the nano silica last; and curing while maintaining a moist state of at least 95% relative humidity for at least 24 hours to suppress plastic shrinkage cracks caused by initial moisture evaporation after pouring. Claim 2 A construction method for shortening the construction period of a building according to claim 1, wherein step (a) is characterized by selecting a main column of a load-concentrating modular structure designed to concentrate the building load at a specific location instead of a plurality of general columns as the core vertical member. Claim 3 A method for shortening the construction period of a building, characterized in that, in claim 1 or 2, a ramp which is a major circulation section used as a passage for construction equipment and materials is structurally separated from the surrounding slab and constructed in advance, either independently or in parallel with steps (a) to (c). Claim 4 delete Claim 5 delete Claim 6 delete

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