Cement Mixture For Ultra High Performance Concrete And Manufacturing Method Of Ultra High Performance Concrete Using The Same

Abstract

The present invention solves the problems of conventional carbonation curing methods by supplying carbon dioxide through a cement mixture for ultra-high performance concrete that includes dry ice. By utilizing the cement mixture for ultra-high performance concrete containing dry ice and the method for manufacturing ultra-high performance concrete using the present invention, carbon dioxide can be effectively supplied simply by crushing and adding dry ice without using expensive equipment or skilled technicians for carbon dioxide injection. This enables the production of sustainable ultra-high performance concrete with high compressive strength and low carbon dioxide emissions, thereby promoting the sustainability, durability, and engineering performance of ultra-high performance concrete.

Description

Technology Field

[0001] The present invention relates to a cement mixture for ultra-high performance concrete and a method for manufacturing ultra-high performance concrete using the same. Background Technology

[0003] Ultra High Performance Concrete (UHPC) possesses a very dense structure and high compressive strength, offering advantages such as excellent freeze-thaw resistance. However, the cement used in UHPC production has an average Global Warming Potential (GWP) of 0.981 t CO2eq and generates a significant amount of carbon dioxide during the production process, presenting negative disadvantages in terms of sustainability. Methods to minimize the environmental impact of UHPC include optimizing cement production technology; replacing cement with fillers or additives; carbonation curing; and forced wet carbonation. Cement production can be divided into five stages: raw material extraction and crushing, transportation, fuel and energy consumption, calcination, and grinding; minimizing carbon dioxide emissions at each stage can reduce the carbon footprint of cement production. However, the method of optimizing cement production technology has the disadvantage of having minimal effectiveness due to technical limitations.

[0004] The method of replacing cement with fillers involves replacing a portion of the cement with cementitious materials (SCM) or fillers. However, the use of this method was limited because the chemical composition of the cementitious materials (SCM) or fillers differs, which affects the physical properties of the concrete.

[0005] Carbonation curing is a method of manufacturing concrete by exposing mortar to carbon dioxide to hydrate and induce a carbonation reaction. However, this carbonation curing method is primarily limited to general concrete with a high water-to-cement ratio, and its application to high-strength concrete with a low water-to-cement ratio is currently restricted. In particular, ultra-high performance concrete (UHP) has the characteristic of having an extremely low water-to-cement ratio and a dense pore structure that limits the diffusion of carbon dioxide, thus posing limitations to the application of carbonation curing methods.

[0006] Unlike conventional carbonation curing methods, the forced wet carbonation method promotes carbonation by directly injecting gaseous carbon dioxide into cement paste, and is characterized by not being limited by the diffusion coefficient of carbon dioxide. Therefore, using the forced wet carbonation method allows the carbonation rate of the cement paste to reach a high level within a few hours, which has the advantage of saving processing time and energy. However, the forced wet carbonation method has limitations in that it is difficult to apply in actual construction sites due to the disadvantage of requiring expensive equipment for the storage, transportation, and injection of carbon dioxide.

[0007] The patent documents and references mentioned in this specification are incorporated by reference into this specification to the same extent that each document is individually and clearly identified by reference. Prior art literature

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Shao, Review on carbonation curing of cement-based materials, J. CO2 Util. 21 (2017) 119-131. The problem to be solved

[0011] The present invention aims to provide a method for manufacturing sustainable ultra-high performance concrete with high compressive strength and low carbon dioxide emissions, without using expensive equipment or skilled technicians, by supplying the carbon dioxide required for curing solely by adding crushed dry ice without injecting carbon dioxide gas.

[0012] Other objects and technical features of the present invention are more specifically presented by the following detailed description of the invention, claims, and drawings. means of solving the problem

[0014] The present invention provides a cement mixture for ultra-high performance concrete comprising cement, metakaolin, and dry ice.

[0015] The cement mixture for ultra-high performance concrete according to the present invention is characterized by comprising 70 to 90 parts by weight of cement, 15 to 25 parts by weight of metakaolin, 12 to 17 parts by weight of dry ice, and 2 to 4 parts by weight of a fluidizing agent, based on 100 parts by weight of sand.

[0016] The cement is characterized by having an intermediate particle size of 15 to 18 µm and the mechakaolin by having a particle size of 2 to 4 µm; when the cement mixture for ultra-high performance concrete is mixed with water to produce a molded body and cured for 28 days, the compressive strength is 130 to 135 MPa and the carbon dioxide emission per unit strength is 4 to 5 kg·CO2·m³ -3 ·MPa -1 It is characterized by being.

[0017] The present invention provides a method for manufacturing ultra-high performance concrete comprising: a first step of preparing a cement mixture by mixing cement, metakaolin, and sand; a second step of preparing a cement mixture for ultra-high performance concrete by crushing dry ice and adding it to the cement mixture; a third step of preparing a cement paste for ultra-high performance concrete by adding water and a high-performance water reducer to the cement mixture for ultra-high performance concrete and mixing them; and a fourth step of preparing ultra-high performance concrete by curing the cement paste for ultra-high performance concrete. Effects of the invention

[0019] The present invention solves the problems of conventional carbonation curing methods by supplying carbon dioxide through a cement mixture for ultra-high performance concrete that includes dry ice.

[0020] By utilizing the cement mixture for ultra-high performance concrete containing dry ice and the method for manufacturing ultra-high performance concrete using the present invention, carbon dioxide can be effectively supplied simply by crushing and adding dry ice without using expensive equipment or skilled technicians for carbon dioxide injection. This enables the production of sustainable ultra-high performance concrete with high compressive strength and low carbon dioxide emissions, thereby promoting the sustainability, durability, and engineering performance of ultra-high performance concrete. Brief explanation of the drawing

[0022] Figure 1 shows the particle size distribution of cement and metakaolin used in the cement mixture of the present invention. Figure 2 schematically illustrates the method for analyzing a sample of the present invention. Figure 3 shows the results of the hydration heat analysis for the cement paste for ultra-high performance concrete of the present invention. Figure 4 shows the X-ray diffraction analysis results for an embodiment of the present invention. Figure 5 shows the results of attenuated total reflection-Fourier transform infrared spectroscopy analysis for the ultra-high performance concrete specimen of the present invention. Figure 6 shows the results of thermogravimetric analysis for the ultra-high performance concrete specimen of the present invention. Figure 7 shows the results of analyzing the ultra-high performance concrete specimen of the present invention using a scanning electron microscope. Figure 8 shows the results of analyzing the ultra-high performance concrete specimen of the present invention using an optical microscope. Figure 9 shows the compressive strength analysis results for the ultra-high performance concrete of the present invention. Figure 10 shows the results of measuring the electrical resistance of the ultra-high performance concrete specimen of the present invention. Figure 11 shows the results of comparing the carbon dioxide emissions per unit strength of the ultra-high performance concrete of the present invention with the carbon dioxide emissions per unit strength of the ultra-high performance concrete of the prior art. Specific details for implementing the invention

[0023] The present invention provides a cement mixture for ultra-high performance concrete comprising cement, metakaolin, and dry ice.

[0024] More specifically, the cement mixture for ultra-high performance concrete is characterized by comprising 70 to 90 parts by weight of cement, 15 to 25 parts by weight of metakaolin, 12 to 17 parts by weight of dry ice, and 2 to 4 parts by weight of a fluidizing agent, based on 100 parts by weight of sand.

[0025] The cement of the above cement mixture for ultra-high performance concrete is characterized by having an intermediate particle size of 15 to 18 μm, and the metakaolin is characterized by having a particle size of 2 to 4 μm. Therefore, when water is added to the above cement mixture for ultra-high performance concrete to make a paste and then cured, the metakaolin particles are positioned between the cement particles, which has the advantage of improving the density of the ultra-high performance concrete.

[0026] When the cement mixture for ultra-high performance concrete according to the present invention is mixed with water to produce a molded body and cured for 28 days, the compressive strength is 130 to 135 MPa and the carbon dioxide emission per unit strength is 4 to 5 kg·CO2·m³ -3 ·MPa -1 It is characterized by being.

[0027] The present invention provides a method for manufacturing ultra-high performance concrete comprising: a first step of preparing a cement mixture by mixing cement, metakaolin, and sand; a second step of preparing a cement mixture for ultra-high performance concrete by crushing dry ice and adding it to the cement mixture; a third step of preparing a cement paste for ultra-high performance concrete by adding water and a high-performance water reducer to the cement mixture for ultra-high performance concrete and mixing them; and a fourth step of preparing ultra-high performance concrete by curing the cement paste for ultra-high performance concrete.

[0028] The present invention will be described in detail below through examples.

[0030] Examples

[0032] 1. Experimental Method

[0033] 1.1. Preparation of Cement Mixtures and Concrete Specimens

[0034] The cementitious materials used in the cement mixture of the present invention are Type I general Portland cement (Ssangyong Cement Co. Ltd.) and metakaolin (Daewon Materials Co., Ltd.) (see Table 1).

[0035] CaO SiO2 Al2O3 Fe2O3 SO3 MgO Others Loss on ignition cement 64.69 21.18 5.12 3.12 1.64 0.86 2.44 0.95 Metakaolin 0.33 52.21 45.34 0.27 - - 0.87 0.98

[0037] Figure 1 shows the particle size distribution of the cement and metakaolin used in the cement mixture of the present invention. The intermediate particle sizes of the cement and metakaolin were confirmed to be 16.39 μm and 2.73 μm, respectively. The dry ice included in the cement mixture of the present invention has a density of 1.6 g / cm³. 3It had a purity of 99.99% and was purchased from Victex. Table 2 shows the composition of the cement mixture of the present invention.

[0038] cement mixture cementitious materials dry ice water Fluidizing agent sand cement Metakaolin Example 1 DI-0% 80 parts by weight 20 parts by weight 0 parts by weight 20 parts by weight 3 parts by weight 100 parts by weight Example 2 DI-5% 80 parts by weight 20 parts by weight 5 parts by weight 20 parts by weight 3 parts by weight 100 parts by weight Example 3 DI-10% 80 parts by weight 20 parts by weight 10 parts by weight 20 parts by weight 3 parts by weight 100 parts by weight Example 4 DI-15% 80 parts by weight 20 parts by weight 15 parts by weight 20 parts by weight 3 parts by weight 100 parts by weight

[0040] The cement mixture of the present invention was prepared with a ratio of cementitious material to sand of 1:1. Cement and metakaolin were used as the cementitious material and added in a ratio of 9:2. The amounts of cement and metakaolin added were 80 parts by weight and 20 parts by weight, respectively, per 100 parts by weight of sand. Metakaolin has a small particle size, so it acts as a filler in the matrix to increase adhesion. Dry ice was added in amounts of 0, 5, 10, or 15 parts by weight per 100 parts by weight of sand, and was named DI-0%, DI-5%, DI-10%, or DI-15% accordingly. Water was added in an amount of 20 parts by weight per 100 parts by weight of sand, and a polycarbonate-based high-performance fluidizer was added in an amount of 3 parts by weight as a high-performance fluidizer to ensure fluidity.

[0041] A cement mixture was prepared by weighing cement, metakaolin, and sand in the above proportions and mixing them uniformly, and a cement mixture for ultra-high performance concrete was prepared by adding crushed dry ice in the above proportions. A cement paste for ultra-high performance concrete was prepared by adding water and a high-performance fluidizer to the cement mixture for ultra-high performance concrete in the above proportions and mixing. The prepared cement paste for ultra-high performance concrete was slowly mixed for 3 minutes and then rapidly mixed for 5 minutes, poured into a mold, wrapped in plastic wrap, cured for 24 hours, and then demolded to produce a molded body. The molded body was cured at 20°C in a sealed state to produce an ultra-high performance concrete specimen. Table 3 shows the ultra-high performance concrete specimen of the present invention.

[0042] cement mixture curing temperature curing time Example 1-1 DI-0% 20℃ 1 day Example 1-2 DI-0% 20℃ 3 days Examples 1-3 DI-0% 20℃ 7 days Examples 1-4 DI-0% 20℃ 28th Example 2-1 DI-5% 20℃ 1 day Example 2-2 DI-5% 20℃ 3 days Example 2-3 DI-5% 20℃ 7 days Example 2-4 DI-5% 20℃ 28th Example 3-1 DI-10% 20℃ 1 day Example 3-2 DI-10% 20℃ 3 days Example 3-3 DI-10% 20℃ 7 days Examples 3-4 DI-10% 20℃ 28th Example 4-1 DI-15% 20℃ 1 day Example 4-2 DI-15% 20℃ 3 days Example 4-3 DI-15% 20℃ 7 days Example 4-4 DI-15% 20℃ 28th

[0044] 1.2. Analysis Method

[0045] Figure 2 schematically illustrates the analysis method for the sample of the present invention. In the present invention, hydration heat analysis using isothermal calorimetry, X-ray diffraction (XRD), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) analysis, thermogravimetric analysis, scanning electron microscopy analysis, optical microscopy analysis, compressive strength analysis, and electrical resistivity analysis were performed.

[0047] 1.2.1. Analysis of Hydration Heat Using an Isothermal Calorimeter

[0048] Samples of the cement paste for ultra-high performance concrete according to the present invention (Examples 1, 2, 3, and 4, 5 g each) were prepared and placed in ampoules, and hydration heat data were collected at 20°C for 168 hours. The analysis was performed using a TAM-air isothermal calorimetry.

[0050] 1.3.2. X-ray Diffraction Analysis

[0051] Cement paste samples for ultra-high performance concrete according to the present invention (Examples 1, 2, 3, and 4) were prepared, and a central portion was taken and ground to a particle size of 75 μm or less. The ground material was dried at 40 °C after stopping hydration by a solvent exchange method to prepare powder samples. The powder samples were analyzed using a PANalytical X'Pert Pro diffractometer (2θ = 5 ~ 45 °λ = 1.5406 Å).

[0053] 1.3.3. Attenuated Total Reflection-Fourier Transform Infrared Spectroscopic Analysis

[0054] Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) analysis was performed using a Fourier transform infrared spectrophotometer. The above analysis had a resolution of 0.4 cm⁻¹. -1 and analysis range 4000 to 400 cm -1 It was performed using the same sample as the X-ray diffraction analysis above.

[0056] 1.3.4. Thermogravimetric Analysis

[0057] Thermogravimetric analysis (TGA) was performed on powder samples prepared using the same method as the X-ray diffraction analysis described above. The analysis was performed using a DSC / DTA / TGA system at a heating rate of 10°C per minute within a temperature range of 20 to 1020°C. Through the thermogravimetric analysis, the mass loss of constituent components occurring during heating was analyzed. The decomposition range of calcium hydroxide (Ca(OH)2) was in the temperature range of 400 to 500°C, and the decomposition range of calcium carbonate (CaCO3) was in the temperature range of 600 to 900°C.

[0058] The content of calcium hydroxide (Ca(OH)2) was calculated using Equation 1, and the content of calcium carbonate (CaCO3) was calculated using Equation 2.

[0059]

[0060]

[0061] The above W 400 represents the mass of calcium hydroxide at the start of decomposition; W 500 represents the mass of calcium hydroxide at the end of decomposition; the above W 600 represents the mass of calcium carbonate at the start of decomposition; W 900 represents the mass of calcium carbonate at the end of decomposition; W 5500 represents the mass of calcium hydroxide at 550°C; 74 represents the molar mass of calcium hydroxide; 18 represents the molar mass of water; 100 represents the molar mass of calcium carbonate; and 44 represents the molar mass of carbon dioxide.

[0063] 1.3.5. Scanning Electron Microscopy Analysis

[0064] The fracture surface and cross-section of the ultra-high performance concrete specimens of the present invention (see Examples 1-1 to 4-4, Table 3) were analyzed using a scanning electron microscope (SEM). After introducing platinum into the cross-section of the ultra-high performance concrete specimens, ultra-high-resolution scanning electron microscope (UHR-SEM) measurements were performed at an acceleration voltage of 15 kV.

[0066] 1.3.6. Optical Microscope Analysis

[0067] The distribution of air bubbles within the matrix of the ultra-high performance concrete specimens of the present invention (see Examples 1-1 to 4-4, Table 3) was analyzed using an optical microscope. After cutting the central portion of the ultra-high performance concrete specimens of the present invention, the cross-section was analyzed using an optical microscope.

[0069] 1.3.7. Compressive Strength and Electrical Resistance Analysis

[0070] Ultra-high performance concrete specimens of the present invention (Examples 1-1 to 4-4, see Table 3) were prepared in a size of 50 × 50 × 50 mm, and their compressive strength was measured according to ASTM C109.

[0071] The above ultra-high performance concrete specimen was prepared with dimensions of Φ100 × 200 mm, and the electrical resistance of the specimen surface was measured using RILEM TC154-EMC.

[0073] 2. Experimental Results

[0074] 2.1. Isothermal Calorimetry Analysis Results

[0075] FIG. 3 shows the results of the heat of hydration analysis for the cement paste for ultra-high performance concrete of the present invention. Panel (a) of FIG. 3 shows the heat flow (mW / g of binder) according to the hydration time of the cement paste for ultra-high performance concrete of the present invention (Examples 1, 2, 3, and 4), and panel (b) shows the cumulative heat of hydration (J / g of binder) of the cement paste for ultra-high performance concrete of the present invention (Examples 1, 2, 3, and 4).

[0076] The hydration reaction of cement consists of an initial reaction, an induction phase, an accelerator, a decelerator, and a slow reaction phase. The initial hydration reaction occurs for approximately 30 minutes at the beginning, during which C3A and gypsum react to form ettringite. As a result of analysis, in Examples 1, 2, 3, and 4 of the present invention, in addition to the peak generated by the initial reaction, a peak appearing after 1 to 2 hours of the hydration reaction was also identified. The cement paste for ultra-high performance concrete (DI-5%) of Example 2 of the present invention contains dry ice added at 0.89 mW / g; the cement paste for ultra-high performance concrete (DI-10%) of Example 3 of the present invention contains dry ice added at 1.00 mW / g; and the cement paste for ultra-high performance concrete (DI-15%) of Example 4 of the present invention contains dry ice added at 1.15 mW / g.

[0077] The above results show that dry ice influences the formation of ettringite. When dry ice is added to the cement mixture for ultra-high performance concrete according to the present invention, both physical effects that negatively affect the formation of ettringite and chemical effects that positively affect the formation of ettringite are exhibited. The physical effect means that the formation of ettringite is reduced because a rapid decrease in internal temperature occurs at the beginning of the reaction due to the dissolution of dry ice; the chemical effect means that as dry ice dissolves and bicarbonate is generated, the acidity of the solution increases, thereby increasing the solubility of gypsum and promoting the formation of ettringite.

[0078] According to panel (a) of FIG. 3, a sharp exothermic hydration peak is observed at 24 to 30 hours of hydration reaction. The peak is formed by the superposition of the hydration reaction peak of C3S (main peak) and the secondary reaction peak of aluminate (shoulder peak), and it is determined that it includes the aluminum phase released from metakaolin in addition to the aluminum phase dissolved in C3A and C4AF of the cement.

[0079] According to panel (b) of Fig. 3, when dry ice was added at 0%, 5%, 10%, or 15%, the peaks of maximum calorific value were 2.13 mW / g (Example 1, DI-0%), 1.92 mW / g (Example 2, DI-5%), 1.81 mW / g (Example 3, DI-10%), and 2.10 mW / g (Example 4, DI-15%), respectively. It was confirmed that the calorific value peaks decreased as the amount of dry ice added increased, which is attributed to the dry ice promoting cement hydration.

[0080] The relationship between dry ice and the heat of hydration is summarized as follows.

[0081] First, dry ice dissolves to become bicarbonate, and the bicarbonate reacts with calcium ions to become calcium carbonate (CaCO3). The calcium carbonate covers the surface, which hinders the reaction of C3S, thereby reducing the release of heat of hydration.

[0082] Second, calcium carbonate (CaCO3) formed by the dissolution and reaction of dry ice is used as a nucleation factor for the precipitation of hydration products, which promotes the formation of ettringite and promotes the release of heat of hydration.

[0083] According to panel (b) of Fig. 3, it was confirmed that the cement paste for ultra-high performance concrete containing dry ice has a low cumulative heat of hydration at a hydration time of 1 to 2 hours, which is attributed to the physical effect of the dry ice. When the dry ice melts, it absorbs the heat generated during cement hydration and lowers the internal temperature of the matrix, so the cumulative heat of hydration at the initial hydration stage (hydration time 1 hour) decreases, but the cumulative heat of hydration increases thereafter.

[0085] 2.2. X-ray Diffraction Analysis Results

[0086] Figure 4 shows the results of X-ray diffraction analysis for an embodiment of the present invention. The cement paste for ultra-high performance concrete of the present invention produces hydration products including ettringite, AFm (Hc, Mc) and calcium hydroxide (Ca(OH)2) due to hydration reactions; produces C2S and C3S as unhydrated mineral clinker; produces metakaolin-derived quartz; and produces calcium carbonate (CaCO3).

[0087] According to Figure 4, the diffraction peaks of ettringite (2θ = 9.1° and 15.8°), AFm (2θ = 10.8° and 11.6°), and calcium carbonate (2θ = 23.0° and 29.5°) were found to gradually increase as the dry ice content increased. The above results indicate that dry ice promotes the formation of hydrates such as ettringite and AFm. Additionally, the diffraction peak of calcium carbonate was also observed in a cement paste for ultra-high performance concrete without added dry ice (Example 1, DI-0%), which is attributed to the small amount of limestone contained in the cement.

[0088] It is determined that dry ice contained in cement paste for ultra-high performance concrete promotes the formation of hydrates, namely ettringite and AFm. According to the results in Figure 4, the diffraction peak of calcium carbonate increases as the dry ice content increases, which is attributed to the dry ice dissolving and converting into calcium carbonate (see Chemical Formulas 1 and 2).

[0089]

[0090]

[0091] The formation of calcium carbonate due to the addition of the above dry ice serves as an additional nucleation site for the formation of hydrates, and since this reacts with the aluminum phase to form AFm, the formation of ettringite and AFm is promoted.

[0092] According to Figure 4, it is confirmed that the diffraction peaks of calcium hydroxide (2θ = 18.1° and 34.1°) decrease as the dry ice content increases, which is attributed to the consumption of calcium hydroxide during the dry ice melting process (see Chemical Formulas 3 and 4).

[0093] According to Figure 4, the cement mixture for ultra-high performance concrete containing dry ice is confirmed to have a weak calcium hydroxide peak intensity. This result is attributed to the fact that the cement mixture for ultra-high performance concrete of the present invention has a very low water-to-binder ratio (w / b = 0.2), which limits the formation of hydration products by micronizing the pore space where reactants dissolve and hydration products precipitate.

[0094] It is confirmed that the metakaolin pozzolanic reaction and dry ice dissolution reaction of the present invention consume most of the calcium hydroxide generated through the hydration reaction. Therefore, it is determined that specimens prepared by curing the cement paste for ultra-high performance concrete containing dry ice of the present invention will have a low calcium hydroxide content.

[0096] 2.3. Results of Fourier Transform Infrared Spectroscopic Analysis

[0097] Figure 5 shows the results of attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) analysis performed on the ultra-high performance concrete specimen of the present invention. In the ATR-FTIR analysis, 3644 cm⁻¹ -1 The absorption peak corresponds to the OH stretching vibration of calcium hydroxide; 1644 cm⁻¹ -1 The absorption peak corresponds to the OH bending vibration of C-SH; 1412 cm⁻¹ -1 The absorption peak corresponds to the asymmetric stretching vibration of CO2-3; 1066 cm⁻¹ -1 The absorption peaks correspond to the symmetric stretching vibration of CO2-3; 875 and 711 cm⁻¹ -1 The absorption peaks correspond to the out-of-plane bending vibrations of CO2-3; 946 and 665 cm⁻¹ -1 The absorption peaks correspond to the asymmetric stretching and bending vibrations of Si-O, respectively.

[0098] According to the results of Fig. 5, the ultra-high performance concrete specimens of the present invention (Examples 1-4, 2-4, 3-4, and 4-4) have an absorption peak of calcium hydroxide (3644 cm⁻¹). -1 It was confirmed that ) is weak, which is consistent with the results of the X-ray diffraction analysis above. The above results indicate that the cement paste for ultra-high performance concrete containing dry ice according to the present invention consumed most of the calcium hydroxide as the reaction between metakaolin, pozzolan, and dry ice proceeded.

[0099] Also, absorption peak associated with CO2-3 (1412 cm⁻¹) -1 , 1066 cm -1 , 875 cm -1 and 711 cm -1 It was confirmed that the strength increased significantly as the dry ice content increased, and this became even more evident as the dry ice content increased from 5% to 15%. The above results indicate that the addition of dry ice promoted the formation of calcium carbonate, which in turn led to the micronization of the pores.

[0100] C-SH absorption peak (1644 cm⁻¹) -1 It was confirmed that the intensity gradually increased as the dry ice content increased, which means that dry ice promotes the formation of CSH gel.

[0102] 2.4 Thermogravimetric Analysis Results

[0103] Figure 6 shows the results of thermogravimetric analysis for the ultra-high performance concrete specimens of the present invention. Regarding the derivative TG (DTG) peaks, the DTG peak at 142 ℃ is determined to be due to the dehydration of AFt and CSH; the DTG peak at 195 ℃ is determined to be due to the dehydration of AFm and CSH; the DTG peak at 456 ℃ is determined to be due to the decomposition of Ca(OH)2; and the DTG peak at 750 ℃ ​​is determined to be due to the decomposition of CaCO3. Table 4 shows the content of calcium hydroxide or calcium carbonate in concrete specimens prepared using the cement mixture of the present invention.

[0104] cement mixture curing temperature curing period Calcium hydroxide (wt%) Calcium carbonate (wt%) Examples 1-4 DI-0% 20℃ 28th 5.83 4.61 Example 2-4 DI-5% 20℃ 28th 5.64 5.57 Examples 3-4 DI-10% 20℃ 28th 3.74 5.60 Example 4-4 DI-15% 20℃ 28th 3.63 5.80

[0105] Analysis results confirmed that as the dry ice content increases, the weight of calcium hydroxide decreases and the weight of calcium carbonate increases. The above results are consistent with the XRD and FTIR analysis results, which means that dry ice reacts with calcium hydroxide, a hydration product, to produce calcium carbonate.

[0107] 2.5. Scanning Electron Microscope Analysis Results

[0108] Figure 7 shows the results of analyzing the ultra-high performance concrete specimen of the present invention using a scanning electron microscope.

[0109] As a result of the analysis, it was confirmed that the ultra-high performance concrete specimens prepared by curing the cement paste for ultra-high performance concrete containing dry ice of the present invention for 28 days exhibited a dense structure. This result is attributed to the low water-to-binder ratio (w / b = 0.2) and the formation of fine pore spaces due to the high pozzolanic reactivity of metakaolin during the curing process.

[0110] In the ultra-high performance concrete specimens prepared by curing the cement paste for ultra-high performance concrete containing dry ice of the present invention for 28 days, hydration products such as AFt, AFm, and calcium hydroxide were hardly observed. Based on these results, it is determined that dry ice did not have a significant effect on the microstructure of the cured samples.

[0112] 2.6. Optical Microscope Analysis Results

[0113] FIG. 8 shows the results of analyzing the ultra-high performance concrete specimens of the present invention using an optical microscope. Panels (a), (b), and (c) of FIG. 8 show the results of analyzing the cross-section of Example 1-1, an ultra-high performance concrete specimen, using an optical microscope; panels (d), (e), and (f) of FIG. 8 show the results of analyzing the cross-section of Example 4-1, an ultra-high performance concrete specimen, using an optical microscope.

[0114] When cement paste for concrete is mixed, a small number of pores (~3 mm) are formed, and when an admixture is added, a small amount of fine bubbles (50 ~ 200 μm) are further formed. The pores formed in the concrete cement paste are much larger than capillary pores. Therefore, if the amount of the above pores increases, the strength of the concrete specimen decreases.

[0115] According to Fig. 8, it was confirmed that the ultra-high performance concrete specimen prepared by curing the cement paste for ultra-high performance concrete containing dry ice of the present invention for one day had more pores than the ultra-high performance concrete specimen prepared by curing a cement mixture without dry ice for one day. However, it was confirmed that the pores of the ultra-high performance concrete specimen prepared by curing the cement paste for ultra-high performance concrete containing dry ice for one day had a radius of 76.4 μm, whereas the pores of the ultra-high performance concrete specimen prepared by curing the cement paste for ultra-high performance concrete without dry ice for one day had a larger radius of 93.9 μm. In summary, as dry ice was added, the number of pores increased but their size decreased; therefore, it is judged that the effect on overall strength should be explained through an analysis of actual compressive strength.

[0117] 2.7. Compressive Strength Analysis Results

[0118] Figure 9 shows the results of the compressive strength analysis for the ultra-high performance concrete of the present invention. The specimens were divided into four groups according to curing time (ultra-high performance concrete specimens cured for 1, 3, 7, or 28 days) and analyzed according to ASTM C109. The compressive strength error between the groups was 0.3 to 1.6 MPa. The early curing group was divided into 1 day of curing, the intermediate curing group into 3 and 7 days of curing, and the long curing group into 28 days of curing.

[0119] The compressive strength of ultra-high performance concrete specimens in the early or intermediate curing groups was measured, and the results showed a tendency for the compressive strength to decrease as the dry ice content increased, followed by an increase again. Additionally, it was confirmed that the compressive strength of ultra-high performance concrete specimens in all curing groups increased with increasing dry content.

[0120] It was confirmed that the compressive strength of the ultra-high performance concrete specimens of Example 2-2 (DI-5%) and Example 3-2 (DI-5%), which correspond to the initial curing group, and the ultra-high performance concrete specimens of Example 3-2 (DI-10%) and Example 3-3 (DI-10%), which correspond to the intermediate curing group, was lower than that of the ultra-high performance concrete specimens without dry ice (Examples 1-1 to 1-4). However, it was confirmed that the compressive strength of the ultra-high performance concrete specimens of Examples 4-1 to 4-4 (DI-15%) was higher than that of the ultra-high performance concrete specimens without dry ice (Examples 1-1 to 1-4).

[0121] It is determined that this is the result of the combined action of strength-increasing and strength-decreasing factors caused by dry ice.

[0122] The increase in strength caused by dry ice is explained by the increased formation of ettringite and the refinement of pores. When dry ice is added, strength increases due to increased gypsum solubility (low pH of the pore solution due to dry ice dissolution) and the formation of additional nucleation sites (provided by CaCO3 from the bicarbonate reaction formed by dry ice dissolution). Additionally, when dry ice is added, strength increases because the calcium carbonate formed by the dry ice reaction reacts with the aluminum phase to produce Hc and Mc, which can further refine the pores.

[0123] The decrease in strength caused by dry ice is explained by an increase in the number of pores and a decrease in the reactivity of metakaolin. When dry ice is added, the number of pores increases, leading to a decrease in strength, and the consumption of calcium hydroxide reduces the reactivity of metakaolin, resulting in a decrease in strength.

[0124] In summary, it is determined that the ultra-high performance concrete specimen produced by curing a cement mixture containing less than 15% dry ice according to the present invention is dominated by strength reduction factors during the initial and intermediate curing, whereas the ultra-high performance concrete specimen produced by curing a cement mixture containing 15% dry ice is dominated by strength increase factors regardless of the curing period.

[0125] Ultra-high performance concrete (Example 1-4, DI-0%) prepared by curing the cement paste for ultra-high performance concrete containing no dry ice of the present invention for 28 days showed a compressive strength of 125.4 MPa; ultra-high performance concrete (Example 2-4, DI-5%) prepared by curing the cement paste for ultra-high performance concrete containing 5% dry ice for 28 days showed a compressive strength of 125.9 MPa; ultra-high performance concrete (Example 3-4, DI-10%) prepared by curing the cement paste for ultra-high performance concrete containing 10% dry ice for 28 days showed a compressive strength of 126.3 MPa; and ultra-high performance concrete (Example 4-4, DI-15%) prepared by curing the cement paste for ultra-high performance concrete containing 15% dry ice for 28 days showed a compressive strength of 132.0 MPa.

[0126] It is determined that the compressive strength of the ultra-high performance concrete specimens produced by curing the cement paste for ultra-high performance concrete of the present invention for 28 days is proportional to the dry ice content. This result is attributed to the fact that the factors increasing compressive strength were dominant in the case of late curing. In particular, it was confirmed that calcium carbonate in the cement mixture containing dry ice gradually precipitates as the curing time increases, which refines the pore space and weakens the decomposition effect caused by the addition of dry ice. Therefore, the increase in compressive strength due to dry ice is proportional to the amount of dry ice and the curing time.

[0128] 2.8. Results of Electrical Resistance Analysis

[0129] 2.8.1. Change in Electrical Resistance Due to Addition of Dry Ice

[0130] Figure 10 shows the results of measuring electrical resistance for the ultra-high performance concrete specimen of the present invention. Analysis results indicate that changes in electrical resistance are closely related to changes in the pore structure of the matrix. Therefore, it is believed that the water permeability resistance of ultra-high performance concrete can be evaluated by analyzing the relationship between the microstructure and electrical resistance.

[0131] According to the results in Fig. 10, it was confirmed that the electrical resistance of the ultra-high performance concrete specimen of the present invention is proportional to the curing time. This result is attributed to the fact that cement hydration and hydration products precipitated in proportion to the curing time, and that the pore network connected to the pore structure within the matrix gradually decreased as the curing time increased. In particular, the electrical resistance of the ultra-high performance concrete specimen of Examples 1-4 (DI-0%, cured for 28 days) was confirmed to be 632.5 kΩ·cm; the electrical resistance of the ultra-high performance concrete specimen of Examples 2-4 (DI-5%, cured for 28 days) was confirmed to be 679.0 kΩ·cm; and the electrical resistance of the ultra-high performance concrete specimen of Examples 3-4 (DI-10%, cured for 28 days) was confirmed to be 840.0 kΩ·cm; The electrical resistance of the ultra-high performance concrete specimen (DI-15%, cured for 28 days) of Example 4 was confirmed to be 865.0 kΩ·cm.

[0132] The electrical resistance of a high-performance concrete specimen prepared by curing the cement paste for high-performance concrete containing dry ice according to the present invention increases as the water-binder ratio decreases. The cement paste for high-performance concrete containing dry ice according to the present invention has a very low water-binder ratio (w / b = 0.2). Therefore, it is determined that the high-performance concrete specimen of the present invention exhibits high electrical resistance due to the very low water-binder ratio.

[0133] The cement paste for ultra-high performance concrete containing dry ice according to the present invention contains metakaolin as a binder. Metakaolin exhibits low electrical resistance as the pozzolanic reaction proceeds, the pores decrease, and as calcium hydroxide is consumed, the ion concentration decreases.

[0134] In summary, it is determined that the ultra-high performance concrete specimen prepared by curing the cement paste for ultra-high performance concrete containing dry ice according to the present invention exhibits high electrical resistance because it has a low water-to-binder ratio and the pozzolanic reaction of metakaolin is carried out.

[0135] According to the results of Figure 10, as the dry ice content increases, the electrical resistance increases, which means that dry ice affects the microstructure change of the sample.

[0136] The factors by which dry ice affected the microstructure can be summarized as follows:

[0137] First, the addition of dry ice promotes the formation of ettringite, calcium carbonate, and AFm, which densifies the matrix and increases electrical resistance. These results are supported by XRD, FTIR, and TG analysis results.

[0138] Second, dry ice reacts with CH4, a hydration product, to form calcium carbonate. The molar volume of calcium carbonate is greater than that of the reactant CH4. Therefore, as the calcium carbonate content increases, the volume of permeable pores gradually decreases and the microstructure becomes denser, thereby increasing the durability of ultra-high performance concrete.

[0139] Third, when dry ice is dissolved and reacts, the CH formed by cement hydration is consumed, and the pH and ion concentration decrease, thereby improving electrical resistance.

[0140] Electrical resistance is a characteristic of concrete materials. The aforementioned changes are closely related to the degree of saturation, the evolution of the pore structure of the matrix, and the ion concentration of the pore solution. Regarding durability against chloride penetration, high electrical resistance is considered to indicate a low chloride diffusion coefficient, low corrosion current, and a long service life. Therefore, it is believed that the addition of dry ice improves electrical resistance and durability by increasing the calcium carbonate content.

[0141] According to an embodiment of the present invention, it was confirmed that the compressive strength of ultra-high performance concrete specimens increases as the dry ice content increases. Since the compressive strength is an approximate indicator of durability, an increase in compressive strength signifies an improvement in durability.

[0143] 2.8.2. Effects of Dry Ice on Rebar Corrosion

[0144] Attack by chloride ions is a major cause of rebar corrosion in marine concrete structures. Ultra-high performance concrete produced by curing the cement paste for ultra-high performance concrete containing dry ice according to the present invention has the advantage of improved resistance to corrosion caused by chlorides. According to the results of the present invention, as the amount of dry ice added increases, the electrical resistance and chloride ion diffusion coefficient decrease.

[0145] Therefore, it is believed that using dry ice in the manufacture of ultra-high performance concrete will improve the service life of reinforcing steel during the early stages of corrosion. Additionally, as the electrical resistance of ultra-high performance concrete decreases, the current density of corrosion also decreases, thereby improving the service life of reinforcing steel.

[0146] When dry ice is added, the pH of the pore solution decreases due to the generation of bicarbonates by the dry ice. Furthermore, since the bicarbonate generation reaction caused by the dry ice consumes a portion of CH, it weakens carbonation resistance and increases the tendency for carbonation. However, if the curing time is prolonged, the dissolved dry ice reacts within the matrix to form calcium carbonate; this calcium carbonate acts as a pore filler, causing the pores to become denser, which reduces the carbon dioxide diffusion coefficient and leads to an increase in carbonation resistance.

[0148] 2.9 Sustainability Analysis Results

[0149] 2.9.1. Carbon dioxide emissions per unit intensity

[0150] Reducing carbon dioxide emissions is a way to improve the sustainability of concrete. However, a reduction in carbon dioxide emissions leads to a decline in concrete performance, and a rapid deterioration in performance actually lowers the sustainability of concrete.

[0151] In this invention, to evaluate the sustainability of sustainable ultra-high performance concrete, carbon dioxide emissions related to the production and transportation of concrete materials and the strength of the concrete were used as sustainability indicators.

[0152] The carbon dioxide emissions per unit intensity were calculated using Equation 3.

[0153]

[0154] The above C i represents the carbon dioxide emissions per unit strength; C represents the total carbon dioxide emissions generated during the production and transportation of concrete raw materials; and p represents the compressive strength of the concrete.

[0155] To evaluate the total carbon dioxide emissions generated during the production and transportation of concrete raw materials, the emission factors and mixing ratios of the concrete raw materials were calculated. The emission factors of the concrete raw materials are as shown in Table 5 below.

[0156] cement Metakaolin dry ice water High-performance fluidizing agent sand Emission factor (CO2 / kg) 0.86 0.21 -1 0.000196 0.0026 Density (kg·m²) -3 ) 3150 2600 1600 1000 1220 2600 Mass per unit volume (kg·m²) -3 ) 851 213 - 213 32 1064

[0157] The sum of the concrete volumes is 1m 3 Assuming that, the mass per unit volume of each component was calculated using Equation 4, and the carbon dioxide emissions per unit volume of the mixture were calculated using Equation 5.

[0158]

[0159]

[0160] The above m i is the mass per unit volume of a component (kg·m³) -3 It means ); ρ i is the density of the component (kg·m²) -3 It means )) and; CO 2i represents the carbon dioxide emission factor of the component.

[0161] Table 6 shows the total carbon dioxide emissions and carbon dioxide emissions per unit strength of ultra-high performance concrete specimens prepared by curing the cement paste for ultra-high performance concrete containing dry ice of the present invention for 28 days.

[0162] Examples 1-4 (DI-0%) Examples 2-4 (DI-5%) Examples 3-4 (DI-10%) Example 4-4 (DI-15%) Compressive strength (MPa) 125.4 125.9 126.3 132.0 Total carbon dioxide emissions (kg CO2·m³) -3 ) 809.3 782.6 757.7 734.2 Carbon dioxide utilization (kg CO2·m²) -3 ) 0.0 51.4 99.6 144.8 Carbon dioxide emissions per unit intensity (kg CO2·m³) -3 ·MPa -1 ) 6.5 5.8 5.2 4.5

[0163] Analysis results confirmed that carbon dioxide emissions per unit strength increased as the amount of dry ice added increased. The above results indicate that the sustainability of the concrete increases as the amount of dry ice added increases. In particular, Example 4-4, an ultra-high performance concrete specimen of the present invention, was confirmed to have excellent performance, having the lowest carbon dioxide emissions, which minimizes environmental impact, as well as the highest strength.

[0164] Assuming that the compressive strength of a high-performance concrete specimen produced by curing the cement paste for high-performance concrete containing dry ice according to the present invention is the same as that of a high-performance concrete specimen produced by curing the cement paste for high-performance concrete without dry ice, it is determined that the binder content required for the production of the cement paste for high-performance concrete decreases as the dry ice content increases. Therefore, in the case of high-performance concrete with a high binder content, using dry ice is considered a viable method to improve the sustainability of concrete, as it can not only reduce carbon dioxide emissions per unit strength but also replace the binder.

[0166] 2.9.2. Carbon Dioxide Emission Analysis

[0167] Ultra-high performance concrete (UHPC) uses a significantly larger amount of cement compared to standard concrete, resulting in much higher carbon dioxide emissions. Therefore, to develop sustainable UHPC, it is necessary to reduce carbon dioxide emissions caused by its manufacturing.

[0168] In this invention, carbon dioxide emissions per unit strength (kg·CO2·m³) are used as an indicator to evaluate the sustainability of ultra-high performance concrete. -3 ·MPa -1 ) was used. For comparison, the carbon dioxide emissions and compressive strength of ultra-high performance concrete were referenced from prior studies.

[0169] Figure 11 shows the results of comparing the carbon dioxide emissions per unit strength of the ultra-high performance concrete of the present invention with the carbon dioxide emissions per unit strength of the ultra-high performance concrete of the prior art. The high compressive strength of the ultra-high performance concrete and the carbon dioxide emissions are proportional to each other. One of the ultra-high performance concretes with a compressive strength of approximately 150 MPa has a carbon dioxide emission of 7.1 kg·CO2·m³ per unit strength. -3 ·MPa -1It has been confirmed that this has a significant impact on the environment.

[0170] According to known results, sustainable ultra-high performance concrete has 850 kg·CO2·m³ -3 It is known to have carbon dioxide emissions exceeding [amount]. In contrast, the ultra-high performance concrete of the present invention has lower carbon dioxide emissions (734.2 kg·CO2·m³). -3 ) and carbon dioxide emissions per unit intensity (4.5 kg·CO2·m³ -3 It was confirmed that it maintains a higher compressive strength (132.0 MPa) while maintaining )

[0171] Therefore, it is believed that adding dry ice to ultra-high performance concrete can realize sustainable ultra-high performance concrete with high compressive strength and low carbon dioxide emissions.

[0173] 3. Conclusion

[0174] In the present invention, it was confirmed that adding 0, 5, 10, and 15 wt% of dry ice to a cement mixture for ultra-high performance concrete resulted in lower carbon dioxide emissions and higher compressive strength compared to conventional ultra-high performance concrete. The method for manufacturing ultra-high performance concrete according to the present invention is intended to solve the problems of carbonation curing technology, which was difficult to use in the manufacture of ultra-high performance concrete, and has the advantages of being simple to operate, having low technical difficulty, and not requiring separate equipment.

[0175] Therefore, the method for manufacturing ultra-high performance concrete using dry ice according to the present invention is expected to effectively utilize carbon dioxide and serve as an important method for achieving carbon neutrality in the concrete industry, and is judged to promote the sustainability, durability, and engineering performance of ultra-high performance concrete.

[0176] The specific embodiments described herein represent preferred embodiments or examples of the invention and do not limit the scope of the invention. It is evident to those skilled in the art that variations and other uses of the invention do not deviate from the scope of the invention as described in the claims of this specification.

Claims

Claim 1 A cement mixture for ultra-high performance concrete comprising cement, metakaolin, and dry ice, wherein the cement mixture for ultra-high performance concrete comprises, per 100 parts by weight of sand, 70 to 90 parts by weight of cement having an intermediate particle size of 15 to 18 μm, 15 to 25 parts by weight of metakaolin having an intermediate particle size of 2 to 4 μm, 12 to 17 parts by weight of dry ice, and 2 to 4 parts by weight of a fluidizing agent; wherein, when the cement mixture for ultra-high performance concrete is mixed with water to produce a molded body and cured for 28 days, the compressive strength is 130 to 135 MPa and the carbon dioxide emission per unit compressive strength is 4 to 5 kg·CO2·m -3 ·MPa -1 A cement mixture for ultra-high performance concrete characterized by being. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 A first step of preparing a cement mixture by mixing 100 parts by weight of sand, 70 to 90 parts by weight of cement having an intermediate particle size of 15 to 18 μm relative to 100 parts by weight of sand, and 15 to 25 parts by weight of metakaolin having an intermediate particle size of 2 to 4 μm relative to 100 parts by weight of sand; a second step of preparing a cement mixture for ultra-high performance concrete by crushing 12 to 17 parts by weight of dry ice relative to 100 parts by weight of sand and adding it to the cement mixture; and a third step of preparing a cement paste for ultra-high performance concrete by adding 2 to 4 parts by weight of a fluidizing agent and water relative to 100 parts by weight of sand to the cement mixture for ultra-high performance concrete and mixing. and a fourth step of manufacturing ultra-high performance concrete by curing the cement paste for ultra-high performance concrete; wherein, when ultra-high performance concrete is manufactured by mixing the cement mixture for ultra-high performance concrete with water to produce a molded body and then curing it for 28 days, the compressive strength is 130 to 135 MPa and the carbon dioxide emission per unit compressive strength is 4 to 5 kg·CO2·m -3 ·MPa -1 A method for manufacturing ultra-high performance concrete characterized by the following.

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