Hydraulic components, hydraulic hardeners, and methods for manufacturing hydraulic hardeners

Abstract

To increase the strength of hydraulically hardened materials. [Solution] The hydraulic composition contains cement, water, aggregate, and fibers, with a water-to-binder ratio of 30% to 65%, an average fiber length of 2 mm to 15 mm, an average fiber diameter of 3 μm to 100 μm, and a fiber content of 0.5 kg / m 3 ~5kg / m 3 That is the case.

Description

[Technical Field]

[0001] This disclosure relates to a hydraulic composition, a hydraulic cured body, and a method for producing a hydraulic cured body. [Background technology]

[0002] Patent Document 1 discloses a technique for carbonizing a hydraulically hardened body containing organic fibers by carbonation curing. Patent Document 2 discloses a technology that promotes CO2 fixation by forming voids in the surface layer of concrete using alkali-degradable organic fibers. Patent document 3 discloses concrete mixed with organic fibers. Patent Document 4 discloses a carbonated cement that hardens by carbon dioxide curing. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2018-003612 [Patent Document 2] Japanese Patent Publication No. 2006-265030 [Patent Document 3] Japanese Patent Publication No. 2004-224616 [Patent Document 4] Japanese Patent Publication No. 2010-235410 [Overview of the project] [Problems that the invention aims to solve]

[0004] Traditionally, high-strength concrete (for example, with a water-binder ratio of 30% or less) has been mixed with organic fibers such as polypropylene fibers. Because high-strength concrete has a dense structure, moisture evaporated from within is difficult to dissipate, which can lead to spalling during a fire. To counteract this, organic fibers are mixed in to prevent spalling. On the other hand, it is known that concrete with a water-binder ratio of about 30% to 65% is less prone to spalling during a fire. Concrete with a relatively large water-binder ratio does not have a very dense structure, so evaporated water is easily dissipated, and it is less prone to spalling during a fire. Therefore, it is general that organic fibers are not mixed into such concrete.

[0005] The present inventors have found the technical significance of actively mixing fibers into a hydraulic composition having a water-binder ratio of 30% to 65%. When fibers are mixed into a hydraulic composition, the periphery of the fibers serves as an intrusion path for CO₂ gas and a site for carbonation reaction, so the amount of CO₂ fixed to the hydraulic hardened body increases, and the strength of the hydraulic hardened body increases.

[0006] An object of the present disclosure is to increase the strength of a hydraulic hardened body. [Means for Solving the Problem]

[0007] Specific means for solving the above problem include the following aspects. <1> Comprising cement, water, aggregate, and fibers, having a water-binder ratio of 30% to 65%, wherein the fibers have an average length of 2 mm to 15 mm and an average diameter of 3 μm to 100 μm, a content of the fibers is 0.5 kg / m 3 to 5 kg / m 3 , which is a hydraulic composition. <2> The hydraulic composition according to <1>, wherein the fibers include organic fibers. <3> The hydraulic composition according to <1>, wherein the fibers include polypropylene fibers. <4> A hydraulic hardened body obtained by hardening the hydraulic composition according to any one of <1> to <3>. <5> obtaining the hydraulic composition according to any one of <1> to <3>, molding the hydraulic composition to obtain a molded body, curing the molded body to obtain a hydraulic cured body; and carbonating the hydraulic cured body, a method for producing a hydraulic cured body. Advantageous Effects of the Invention

[0008] According to the present disclosure, the strength of a hydraulic cured body can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] [Figure 1] FIG. 1 is a diagram showing the shape and dimensions of a test body and an outline of carbonation. [Figure 2A] FIG. 2 is a graph showing compressive strength. [Figure 2B] FIG. 3 is a graph showing the strength increase ratio of compressive strength. [Figure 3A] FIG. 4 is a graph showing the relationship between the mass increase rate due to carbonation and the strength increase ratio for a test body without fibers. [Figure 3B] FIG. 5 is a graph showing the relationship between the mass increase rate due to carbonation and the strength increase ratio for a test body with fibers. [Figure 4] FIG. 6 is a photograph showing the neutralization depth of mortar after carbonation curing at a CO2 concentration of 90%. [Figure 5A] FIG. 7 is an X-ray diffraction chart for a ordinary Portland cement test body without fibers. [Figure 5B] FIG. 8 is an X-ray diffraction chart for a low-heat Portland cement test body without fibers. [Figure 5C] FIG. 9 is an X-ray diffraction chart for a blast furnace cement Type C test body without fibers. [Figure 6A] FIG. 10 is an X-ray diffraction chart comparing the influence of the presence or absence of fibers in an ordinary Portland cement test body. [Figure 6B] FIG. 11 is an X-ray diffraction chart comparing the influence of the presence or absence of fibers in a low-heat Portland cement test body. [Figure 6C] FIG. 12 is an X-ray diffraction chart comparing the influence of the presence or absence of fibers in a blast furnace cement Type C test body. [Figure 7] This is a comparison of the amount of Ca(OH)2 and CaCO3 in the fiber-free test specimens. [Figure 8A] This graph shows the relationship between depth and CO2 fixation amount for a test specimen without fibers. [Figure 8B] This graph shows the relationship between depth and CO2 fixation amount for test specimens containing fibers. [Figure 9A] This graph shows the relationship between depth and CO2 fixation amount for a test specimen of ordinary Portland cement. [Figure 9B] This graph shows the relationship between depth and CO2 fixation amount for a test specimen of low-heat Portland cement. [Figure 9C] This graph shows the relationship between depth and CO2 fixation amount for a blast furnace cement type C test specimen. [Figure 10] This graph shows the amount of CO2 fixed up to the top 20 mm of the layer. [Figure 11] This graph shows the relationship between the dimensions of organic fibers and the amount of CO2 fixed. [Figure 12] This graph shows the relationship between the organic fiber content and the amount of CO2 fixed. [Figure 13] This graph shows the relationship between the organic fiber content and the 15-dot flow value. [Modes for carrying out the invention]

[0010] Embodiments of the invention are described below. These descriptions and embodiments are illustrative and do not limit the scope of the invention.

[0011] In this disclosure, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range described in stages. In numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced by the values ​​shown in the examples.

[0012] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their objectives are achieved.

[0013] When referring to the amount of each component in a composition in this disclosure, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0014] <Hydraulic composition and hydraulic cured product> The hydraulic composition disclosed herein is a fresh hydraulic composition, and the hydraulic composition disclosed herein hardens to obtain the hydraulic hardened body disclosed herein. The hydraulic composition may be a concrete composition or a mortar composition.

[0015] The hydraulic composition disclosed herein contains cement, water, aggregate, and fibers, with a water-to-binder ratio of 30% to 65%. Details of the materials and composition of the hydraulic composition are as follows.

[0016] [Water binder ratio] The hydraulic composition disclosed herein has a water-to-binder ratio (mass ratio of water to binder, water / binder) of 30% to 65%. The water-to-binder ratio may be, for example, 35% or more, 40% or more, 60% or less, 55% or less, or 50% or less.

[0017] [fiber] In a hydraulically hardened body, the area around the fibers becomes a pathway for CO2 gas to enter and a site for carbonation reactions. As a result, the amount of CO2 fixed to the hydraulically hardened body increases, and the strength of the hydraulically hardened body increases.

[0018] Fibers include organic fibers and inorganic fibers. One type of fiber may be used alone, or two or more types may be used in combination.

[0019] The fibers have an average length of 2 mm to 15 mm and an average diameter of 3 μm to 100 μm. These dimensions result in a high fiber density per unit weight and allow for highly uniform dispersion in the hydraulic composition, creating numerous pathways for CO2 gas penetration and carbonation reactions. Furthermore, these dimensions minimize fiber entanglement, resulting in a well-preserved, fresh hydraulic composition. From the above viewpoint, the average length of the fibers is preferably 3 mm to 12 mm, and more preferably 5 mm to 10 mm. From the above viewpoint, the average diameter of the fibers is preferably 5 μm to 100 μm, more preferably 5 μm to 80 μm, even more preferably 9 μm to 80 μm, and particularly preferably 9 μm to 50 μm. The diameter of the fiber is the equivalent circular diameter of the fiber cross-section.

[0020] From the viewpoint of easily forming gas intrusion pathways around the fibers, water-repellent materials are preferable to hydrophilic materials. From this viewpoint, organic fibers are preferable to inorganic fibers.

[0021] Examples of organic fibers include polypropylene fibers, polyethylene fibers, polyvinyl alcohol fibers, polyvinylidene fibers, polyamide fibers, polylactic acid fibers, and vinylon fibers. From the viewpoint of easily forming gas intrusion pathways around the fibers, water-repellent organic fibers are preferred over hydrophilic materials. From this viewpoint, polypropylene fibers are preferred.

[0022] Organic fibers may be monofilaments or strands. Monofilaments may be cylindrical fibers, hollow fibers, fibers with irregular cross-sections, fibers with pores on the surface, or fibers with fine branching.

[0023] Examples of inorganic fibers include metal fibers, carbon fibers, glass fibers, and basalt fibers.

[0024] The fiber content in the hydraulic composition is 0.5 kg / m³ per unit volume of the hydraulic composition. 3 ~5kg / m 3 It is 5 kg / m 3If the content is higher than this, the fresh properties of the hydraulic composition will deteriorate, 0.5 kg / m 3 If the content is lower than this, it is difficult to obtain the enhancement effect of CO2 fixation. When the hydraulic composition contains organic fibers, the content of the organic fibers is 0.5 kg / m 3 to 5 kg / m 3 is preferable.

[0025] When the hydraulic composition is a concrete composition, the content of fibers contained in the hydraulic composition is 0.5 kg / m 3 to 4 kg / m 3 is preferable, and 0.5 kg / m 3 to 3 kg / m 3 is more preferable. When the hydraulic composition is a concrete composition and contains organic fibers, the content of organic fibers contained in the hydraulic composition is 0.5 kg / m 3 to 4 kg / m 3 is preferable, and 0.5 kg / m 3 to 3 kg / m 3 is more preferable.

[0026] When the hydraulic composition is a mortar composition, the content of fibers contained in the hydraulic composition is 0.8 kg / m 3 to 5 kg / m 3 is preferable, and 1 kg / m 3 to 5 kg / m 3 is more preferable. When the hydraulic composition is a mortar composition and contains organic fibers, the content of organic fibers contained in the hydraulic composition is 0.8 kg / m 3 to 5 kg / m 3 is preferable, and 1 kg / m 3 to 5 kg / m 3 is more preferable.

[0027] [Cement] The cement can be selected from various known types of cement according to the purpose. The cement may be cement alone or a mixed cement mixed with fine powder admixtures. Examples of fine powder admixtures include blast furnace slag powder, silica fume, fly ash, limestone powder, stone powder, and expansives.

[0028] Examples of cement include Portland cements such as ordinary Portland cement, rapid-hardening Portland cement, moderate-heat Portland cement, and low-heat Portland cement; and blended cements such as blast furnace cement, fly ash cement, and silica fume cement.

[0029] [aggregate] Examples of fine aggregates include river sand, mountain sand, land sand, sea sand, silica sand, crushed sand, crushed limestone sand, blast furnace slag fine aggregate, and recycled fine aggregate. The type and content of the fine aggregate should be selected according to the target mechanical strength of the hydraulically hardened body.

[0030] Examples of coarse aggregates include crushed andesite, rhyolite, hard sandstone, limestone, river gravel, mountain gravel, land gravel, blast furnace slag coarse aggregate, and recycled coarse aggregate. The rock type, size, and content of the coarse aggregate should be selected according to the target mechanical strength of the hydraulically hardened body.

[0031] [Other materials] The hydraulic compositions disclosed herein may contain expansive agents, chemical admixtures, etc., depending on the purpose. Examples of expansive materials include lime-based expansive materials, ettringite-based expansive materials, and ettringite-lime composite expansive materials. Examples of chemical admixtures include water-reducing agents, AE water-reducing agents, shrinkage-reducing agents, curing accelerators, curing retarders, thickeners, dust-reducing agents, antifreeze / cold-resistant agents, preservatives, waterproofing agents, and rust inhibitors.

[0032] [Method for producing a hydraulic composition] The hydraulic compositions disclosed herein are obtained by mixing the materials described above. The mixing of the materials can be carried out, for example, by kneading using a mixer.

[0033] The order in which materials are mixed when preparing a hydraulic composition is not limited. For example, cement and fine aggregate are mixed first, then water and chemical admixtures are added and mixed, and then fibers (and coarse aggregate as needed) are added and mixed.

[0034] <Method for producing hydraulic cured body> The hydraulically cured body of the present disclosure is obtained by curing the hydraulic composition of the present disclosure. The method for producing a hydraulic hardened body according to the present disclosure includes the following steps (1), (2), (3), and (4).

[0035] Step (1): To obtain the hydraulic composition of the present disclosure. Step (2): Molding the hydraulic composition to obtain a molded body. Step (3): The molded body is cured to obtain a hydraulically hardened body. Step (4): Carbonate the hydraulically hardened body.

[0036] The steps included in the method for manufacturing the hydraulic hardened material disclosed herein will be described in order below.

[0037] [Process (1)] Step (1) is a step to obtain the hydraulic composition of the present disclosure. The hydraulic composition and the method for producing the hydraulic composition are as described above.

[0038] [Process (2)] Step (2) is a step of molding the hydraulic composition. Step (2) can be carried out, for example, by pouring the hydraulic composition into a mold. The hydraulic composition poured into the mold may be subjected to treatment such as degassing in accordance with conventional methods.

[0039] [Process (3)] Step (3) is a step in which the hydration reaction of the molded body is advanced and the molded body is hardened to obtain a hydraulically hardened body. The molded body may be removed from the mold before or during step (3).

[0040] Step (3) is carried out, for example, by curing the molded body. Examples of curing include standard curing carried out in water, wet sand, or saturated steam while maintaining the temperature at 20±3℃. It is also preferable to combine standard curing with one or more other curing methods. Examples of other curing methods include steam curing carried out in a temperature range of 40℃ to 100℃ for 2 hours to 14 days, high-temperature curing carried out in a temperature range of 100℃ to 400℃ for 2 hours to 72 hours, and high-temperature and high-pressure curing using an autoclave or the like.

[0041] [Process (4)] Step (4) is a step of carbonizing the hydraulic curing body. In this disclosure, step (4) is also referred to as "carbonation curing". Carbonation curing may be carried out by simply placing the hydraulic curing body in the atmosphere, or by exposing it to a CO2-containing gas. By using a CO2-containing gas, CO2 fixation in the hydraulic curing body is accelerated and increased, and the strength of the hydraulic curing body can be increased rapidly.

[0042] Examples of CO2-containing gases used for carbonation curing include CO2-containing gases with a volume concentration of 1% to 20%. The exposure time to the CO2-containing gas may be, for example, 1 day or more, 3 days or more, or 7 days or more, or 14 days or less.

[0043] As the CO2-containing gas used for carbonation curing, exhaust gas generated from coal-fired power plants, LNG-fired power plants, cement plants, steel mills, oil refineries, waste incineration plants, etc., may be used. Preferably, the CO2-containing gas is obtained by removing soot, NOx, and SOx from these exhaust gases.

[0044] The carbonation process of hydraulic hardening materials can reduce the amount of CO2 in the environment, or reduce the amount of CO2 emitted into the atmosphere from power plants, factories, treatment plants, etc. [Examples]

[0045] The hydraulic compositions and hydraulic cured products of this disclosure will be described in detail below with reference to examples. The hydraulic compositions and hydraulic cured products of this disclosure are not limited to the following examples.

[0046] Hereafter, the curing process in step (3) will be referred to as "pre-curing," meaning that it is performed before the carbonation curing.

[0047] <<Investigation into increasing the strength of hydraulically hardened materials through carbonation>> <Materials and preparation> Table 1 shows the materials used in the experiment. Three types of cement were used: ordinary Portland cement (hereinafter N), low-heat Portland cement (hereinafter L), and improved blast furnace cement type C (hereinafter BC) with adjusted cement components. Polypropylene fibers with a fiber length of 5 mm and a fiber diameter of 9 μm were used as organic fibers.

[0048] [Table 1]

[0049] Table 2 shows the mortar mixes. Experiments were conducted with a total of six mixes, each containing either fiber or polypropylene fibers. In all mixes, the water-cement ratio was 50%, the cement-sand ratio was 1.5%, and the polypropylene fiber content was calculated per 1 m³ of mortar. 3 The amount was set at 3 kg per unit. The amount of air was adjusted using an AE enhancer and an antifoaming agent to fall within the target range.

[0050] [Table 2]

[0051] <Test Items> The test items are shown in Table 3. The weight change rate was calculated by measuring the weight of a φ5 × 10 cm test specimen before and after carbonation, and dividing the difference by the weight before carbonation. The amount of Ca(OH)2 was calculated from the weight loss at around 450°C using thermogravimetric analysis. The amount of CO2 fixed was calculated by total carbon content analysis using a carbon-sulfur analyzer EMIA-Step (Horiba, Ltd.). The calculation method was as follows: First, the measured total carbon content was converted to CO2 per unit cement. Then, the amount of CO2 fixed per unit cement was calculated by taking the difference between the amount of CO2 converted per unit cement and the amount with and without carbonation curing.

[0052] [Table 3]

[0053] <Method for preparing and curing test specimens> (1) Preparation of test specimens and pre-curing After mixing the mortar according to the formulations shown in Table 2, the mortar was poured into φ5 × 10 cm steel formwork and 4 × 4 × 16 cm steel formwork. The test specimens were demolded after 2 days and immediately subjected to steam curing at 65°C for 14 days to allow sufficient hydration to proceed.

[0054] (2) Carbonation curing After steam curing was completed, the test specimens were subjected to carbonation curing under the conditions shown in Table 4 and Figure 1. The CO2 concentration was set to three levels: 0% (air), 10%, and 90%, and the test specimens were left undisturbed for 7 days in an environment with a temperature of 20°C and a relative humidity of 60%. For the φ5×10cm test specimens, carbonation was performed by introducing CO2 gas from all sides. For the 4×4×16cm test specimens, the four sides other than the end face were sealed with aluminum tape, and carbonation was performed by introducing CO2 gas from the two side faces.

[0055] [Table 4]

[0056] (3) Preparation of samples for measurement After the carbonation curing was complete, the φ5 × 10 cm specimens were subjected to gravimetric and compressive strength tests. The 4 × 4 × 16 cm specimens were wet-cut into 20 mm square sections in the depth direction, as shown in Figure 1, to prepare powder samples for various analyses. The cut specimens were treated with acetone to stop hydration and allowed to dry thoroughly for 7 days in an environment of 20°C and 11% relative humidity. The samples were then pulverized using a pulverizer to a particle size of 150 μm or less, and the powder samples were subjected to XRD, thermogravimetric analysis, and total carbon content analysis. The carbonation depth was measured according to JIS A 1152 by wet-cutting the portion shown in Figure 1.

[0057] <Experimental Results> (1) Compressive strength Figure 2A is a graph showing the compressive strength of each test specimen. Figure 2B is a graph showing the strength enhancement ratio relative to a CO2 concentration of 0%. The average compressive strength of each cement type is 75.7 N / mm² at L. 2 , at N, 55.9 N / mm 2 39.1 N / mm² in BC 2 The strength of L was high despite the water-cement ratio being 50%, which is presumed to be due to accelerated hydration by steam curing. When comparing the effects of CO2 concentration, there was a tendency for compressive strength to be higher with higher CO2 concentration. The cement that provides the greatest increase in strength, relative to a CO2 concentration of 0%, is N, which has a strength of approximately 25-30 N / mm² at a CO2 concentration of 90%. 2 Strength enhancement was confirmed. The cement with the largest strength enhancement ratio was N, and no significant difference in strength enhancement ratio was observed between L and BC.

[0058] (2) Mass increase rate due to carbonation Figures 3A and 3B are graphs showing the relationship between the mass increase rate due to carbonation and the strength increase ratio. The mass increase rates due to carbonation in Figures 3A and 3B are calculated from the difference between the mass change rate at a concentration of 0% and the mass change rates at concentrations of 10% and 90%. Figures 3A and 3B show that the mass increase rate due to carbonation and the strength increase ratio are generally positively correlated, regardless of the type of cement. Assuming that the mass increase rate due to carbonation corresponds to the increase in pure mass due to CO2 fixation, the increase in compressive strength can be attributed to the carbonation of the cement structure. In other words, it is inferred that as carbonation progresses, the structure becomes denser, resulting in increased strength. When fibers were mixed in, the slope of the regression equation became smaller, the mass increase rate was larger relative to the strength increase ratio, and there was a tendency for the amount of CO2 fixed to increase.

[0059] (3) Neutralization depth Figure 4 shows the measurement results of the neutralization depth at a CO2 concentration of 90%. In the N and L regions, almost no non-colored area of ​​phenolphthalein was observed even at a CO2 concentration of 90%, and the neutralization depth was 0 mm, suggesting that Ca(OH)2 remained in the tissue. The neutralization depth in BC was 16.5 mm without fibers and 14.0 mm with fibers.

[0060] (4) Powder X-ray diffraction Figures 5A, 5B, and 5C are graphs showing the XRD results for samples up to 20 mm from the surface, without fibers, for each cement type. The diffraction peaks of calcite, vaterite, and aragonite are shown in the figures. In both N and L, a large amount of calcite was observed to be produced by carbonation at a CO2 concentration of 90%. The presence of a large amount of calcite at a CO2 concentration of 0% in N is due to the influence of a small amount of 5% mixed component in the cement. In BC, the amount of calcite produced was greater than in L and N, and the formation of vaterite and aragonite was also observed. Figures 6A, 6B, and 6C show the XRD results comparing the effects of fiber contamination. In samples N and L, the calcite peak is larger with fiber than without. In sample BC, the calcite and vaterite peaks are smaller with fiber.

[0061] (5) Amount of Ca(OH)2 and CaCO3 Figure 7 shows the amounts of Ca(OH)2 and CaCO3 calculated from the TG curve of thermogravimetric analysis. For N50, the amount of CaCO3 originally present in small amounts of mixed components in the cement was calculated from the thermogravimetric analysis results of the unhydrated cement, and the value obtained by subtracting this amount was used. At a CO2 concentration of 0%, the amount of Ca(OH)2 is highest in nitrogen (N), followed by lutein (L). In BC (Breakfast and Brucolite), the amount of Ca(OH)2 produced is low because the cement contains a large amount of blast furnace slag. In all formulations, carbonation at a CO2 concentration of 90% results in a decrease in Ca(OH)2 and an increase in CaCO3 compared to a CO2 concentration of 0%. Comparing N and L, N, which initially produces a larger amount of Ca(OH)2, produces a larger amount of CaCO3 through carbonation. Despite having a low initial amount of Ca(OH)2, BC produces the most CaCO3 when carbonated at a CO2 concentration of 90%. Toyomura et al. reported that cement with a high substitution rate of admixtures such as blast furnace slag is prone to carbonation of CSH (Eri Toyomura, Takeshi Iyoda: Study on Carbonation Mechanisms under Different Carbon Dioxide Concentration Environments, Annual Proceedings of Concrete Engineering, Vol.35, No.1, pp769-774, 2013), and Harasawa et al. reported that the crystalline form of the generated CaCO3 changes with changes in the substitution rate of blast furnace slag fine powder, potentially leading to coarsening of the voids in the structure (Yoko Harasawa, Kazuhiro Honda, Takeshi Iyoda: Effects of Different Carbonation Tolerances on Void Characteristics and Carbonation Products, Annual Proceedings of Concrete Engineering, Vol.36, No.1, pp808-813, 2014). In this experiment, the high production of CaCO3 in BC, leading to the formation of vaterite and aragonite, and the relatively small increase in strength due to carbonation in BC, are presumed to be due to similar factors.

[0062] (6) CO2 fixed amount Figures 8A and 8B are graphs showing the relationship between carbonation depth and CO2 fixation amount. Figures 9A, 9B, and 9C are graphs showing the relationship between carbonation depth and CO2 fixation amount for each type of cement. When comparing the effects of cement type in the fiber-free specimens shown in Figure 8A, the amount of CO2 fixed was high for all cements from 0 to 20 mm, while the amount of CO2 fixed from 20 mm to 80 mm was similar regardless of depth. As shown in Figures 9A and 9B, in both N and L, the amount of CO2 fixed was greater with fibers than without fibers at both depths. In BC, as shown in Figure 4, carbonation was sufficiently advanced in the surface layer even without fibers, so the effect of fiber incorporation was not clearly observed as a difference in CO2 fixed amount at 0-20 mm, but the effect of fiber incorporation was confirmed at deeper depths. Figure 10 is a graph comparing the amount of CO2 fixed up to the top 20 mm of the layer, calculated from the results of total carbon content analysis. When comparing different cement types, BC cement had the highest CO2 fixation capacity, while L cement had the lowest. As mentioned earlier, BC cement has a low Ca(OH)2 content due to the high amount of blast furnace slag substitution, making it more susceptible to CSH decomposition. XRD and thermogravimetric analysis results also suggest that the high CO2 fixation capacity was achieved through the decomposition and carbonation of CSH. It is presumed that L had less CO2 fixation compared to N, due to a lower amount of Ca(OH)2 before carbonation curing and reduced carbonation progress due to increased strength (densification) from steam curing. Comparing the effects of fiber contamination, it was confirmed that the amount of CO2 fixed increased in N and L due to fiber contamination, which is consistent with the XRD results in Figures 6A, 6B, and 6C. In BC, a tendency for the amount of fixed CO2 to decrease with fiber inclusion was observed. This is thought to be because carbonation had progressed sufficiently in the top 20 mm of BC, so the effect of the fibers was not apparent. From the results of the neutralization depth in Figure 4, it can be confirmed that neutralization was progressing in the surface layer of BC, and from Figure 7, it can be inferred that there was a very small amount of Ca(OH)2 remaining in the top 20 mm. From this, it is thought that carbonation in the top 20 mm of BC was almost complete, and therefore the effect of fiber inclusion on the amount of CO2 fixed in the surface layer of BC could not be confirmed.

[0063] (7) Summary 1) Carbonation curing of mortar increased the compressive strength of all cement types. The ratio of increase in compressive strength was largest for N and smallest for BC. 2) The ratio of increase in compressive strength due to carbonation curing and the rate of mass increase were positively correlated, with a larger rate of mass increase indicating a greater increase in compressive strength. 3) XRD analysis confirmed the formation of calcite due to carbonation in all cement types. The amount of calcite formation was particularly high in BC, and the formation of vaterite and aragonite was also confirmed in BC. 4) The amount of CaCO3 produced in BC significantly exceeds the amount of Ca(OH)2 before carbonation, suggesting that CSH decomposition occurred in BC. 5) The amount of CO2 fixed by carbonation was particularly high in the surface layer, and in the absence of fibers, almost no CO2 fixed was observed below 40 mm from the surface. An increase in CO2 fixed amount was confirmed with the addition of fibers in all cement types. However, in BC, the effect of fiber addition was not observed up to 20 mm from the surface, but this is thought to be because the neutralization of the surface layer was almost complete. The amount of CO2 fixed was smallest in L and largest in BC.

[0064] <<Investigation of Strength Enhancement of Hydraulic Hardened Bodies Based on Fiber Dimensions>> <Materials and preparation> Table 5 shows the materials used in the experiment. Two types of cement were used: ordinary Portland cement (hereinafter referred to as N) and low-heat Portland cement (hereinafter referred to as L). Four types of polypropylene fibers were used as organic fibers.

[0065] [Table 5]

[0066] Table 6 shows the mortar mixes. Two types of polypropylene fibers were set for N, and four types of polypropylene fibers were set for L, and experiments were conducted with a total of six mixes. In all mixes, the water-cement ratio was 50%, and the polypropylene fiber content was 1 m³ of mortar.3 The amount was set at 3.0 kg per unit. The amount of air was adjusted using high-performance AE water-reducing agents, defoaming agents, and AE auxiliary agents to fall within the target range.

[0067] [Table 6]

[0068] <Method for preparing and curing test specimens> (1) Preparation of test specimens and pre-curing Mortar was mixed according to the formulation shown in Table 6. First, sand, cement, and polypropylene fibers were placed in a mortar mixer and dry-mixed at low speed for 15 seconds. Next, water and admixtures were added and mixed at low speed for 90 seconds. After scraping off the excess, the mixture was mixed at high speed for 180 seconds. The resulting mortar was then poured into a 4 x 4 x 16 cm steel formwork.

[0069] After casting, the material was left undisturbed in a sealed state at a temperature of 20°C for 24 hours. From 24 hours of age, steam curing was performed at a temperature of 65°C for 14 days. After steam curing was completed, the material was removed from the mold, placed in a sealed plastic bag, and left undisturbed at a temperature of 20°C until the start of carbonation curing.

[0070] (2) Carbonation curing After steam curing was completed, the test specimens were subjected to carbonation curing under the conditions shown in Table 7 and Figure 1. The CO2 concentration was set to two levels: 0% (in air) and 90%. The test specimens were left undisturbed for 7 days in an environment with a temperature of 20°C and a relative humidity of 60%. The four sides of the 4×4×16cm test specimen, excluding the end face, were sealed with aluminum tape, and CO2 gas was introduced from the two side faces to induce carbonation.

[0071] [Table 7]

[0072] (3) Preparation of samples for measurement After the carbonation curing was completed, a 4 × 4 × 16 cm specimen was wet-cut into 20 mm squares in the depth direction, as shown in Figure 1, to prepare a powder sample for analysis. The cut specimen was treated with acetone to stop hydration, and then left to dry thoroughly for 7 days in an environment of 20°C and 11% relative humidity. Next, it was pulverized using a pulverizer to a particle size of 150 μm or less, and the powder sample was subjected to thermogravimetric analysis.

[0073] <Experimental Results> (1) CO2 fixed amount The mass loss in the thermogravimetric analysis TG curve between 500°C and 800°C was considered to be the decomposition of calcium carbonate, and the amount of CO2 fixed by carbonation curing was calculated from the difference in the amount of calcium carbonate at CO2 concentrations of 0% and 90%. Figure 11 shows the relationship between the dimensions of the polypropylene fibers and the amount of CO2 fixed. Comparing N-fiber A and N-fiber B, fiber A fixed more CO2 at deeper locations than fiber B. Comparing L-fibers A, B, C, and D, fiber A fixed more CO2 at deeper locations than fibers B, C, and D. In other words, thinner fibers fixed more CO2 at deeper locations. Comparing L-fiber B and L-fiber C, fiber B fixed more CO2 than fiber C. In other words, shorter fibers fixed more CO2. It is presumed that when fibers are thin and / or short, the number of fibers per unit weight is high, and they can be dispersed with high uniformity in the hydraulic composition, creating many pathways for CO2 gas to enter and many sites for carbonation reactions.

[0074] <<Investigation of increasing the strength of hydraulic hardened materials by increasing fiber content>> <Materials and preparation> The materials used in the experiment are the same as those shown in Table 5. However, only one type of cement, low-heat Portland cement (hereinafter referred to as L), was used, and two types of polypropylene fibers, A and D, were used.

[0075] Table 8 shows the mortar mix designs. Experiments were conducted with a total of five mix designs, each with a specified type and unit amount of polypropylene fiber. The water-cement ratio was set to 30% in all mix designs. Air content was adjusted using high-performance AE water-reducing agents, defoamers, and AE additives to fall within the target range.

[0076] [Table 8]

[0077] <Method for preparing and curing test specimens> (1) Preparation of test specimens and pre-curing Mortar was mixed according to the formulation shown in Table 8. First, sand, cement, and polypropylene fibers were placed in a mortar mixer and dry-mixed at low speed for 15 seconds. Next, water and admixtures were added and mixed at low speed for 90 seconds. After scraping off the excess, the mixture was mixed at high speed for 300 seconds. The resulting mortar was then poured into a 4 x 4 x 16 cm steel formwork.

[0078] After casting, the material was left undisturbed in a sealed state at a temperature of 20°C for 24 hours. From 24 hours of age, steam curing was performed at a temperature of 65°C for 3 days. After steam curing was completed, the material was removed from the mold, placed in a sealed plastic bag, and left undisturbed at a temperature of 20°C until the start of carbonation curing.

[0079] (2) Carbonation curing After steam curing was completed, the test specimens were subjected to carbonation curing under the conditions shown in Table 9 and Figure 1. The CO2 concentration was set to a single level of 90%, and the test specimens were left undisturbed for 7 days in an environment with a temperature of 20°C and a relative humidity of 60%. The four sides of the 4×4×16cm test specimen, excluding the end face, were sealed with aluminum tape, and CO2 gas was introduced from two side faces to induce carbonation.

[0080] [Table 9]

[0081] (3) Preparation of samples for measurement After the carbonation curing was completed, a 4 × 4 × 16 cm specimen was wet-cut into 20 mm squares in the depth direction, as shown in Figure 1, to prepare a powder sample for analysis. The cut specimen was treated with acetone to stop hydration, and then thoroughly dried for 7 days in an environment of 20°C and 11% relative humidity. Next, the specimen was pulverized using a pulverizer to a particle size of 150 μm or less, and the powder sample was subjected to total carbon content analysis.

[0082] <Experimental Results> (1) CO2 fixed amount The amount of CO2 fixed was calculated by total carbon content analysis using the EMIA-Step carbon-sulfur analyzer (Horiba, Ltd.). The calculation method involved first converting the measured total carbon content to CO2 per unit cement. Then, the amount of CO2 fixed per unit cement was calculated by taking the difference between the amount of CO2 per unit cement when carbonation curing was not performed and when carbonation curing was performed. Figure 12 shows the relationship between the polypropylene fiber content and the amount of CO2 fixed. Comparing L30-1A and L30-5A, L30-5A fixed more CO2. Comparing L30-1D and L30-2D, L30-2D fixed more CO2. In other words, materials with a higher fiber content fixed more CO2.

[0083] (2) Freshness A flow test of the mortar was conducted in accordance with JIS R 5201:2015. Figure 13 shows the relationship between the polypropylene fiber content and the 15-count flow value. The higher the organic fiber content, the greater the amount of chemical admixture required to adjust the 15-count flow value to an appropriate level. Furthermore, above a certain organic fiber content, fiber balls formed from entangled organic fibers began to form. The organic fiber content was 5 kg / m³. 3 The following is appropriate.

Claims

1. It contains cement, water, aggregate, and fibers. The water-binding ratio is 30% to 65%. The average length of the aforementioned fibers is 2 mm to 15 mm and the average diameter is 3 μm to 100 μm. The fiber content is 0.5 kg / m ３ ~5 kg / m ３ That is, Hydraulic composition.

2. The hydraulic composition according to claim 1, wherein the aforementioned fibers include organic fibers.

3. The hydraulic composition according to claim 1, wherein the aforementioned fibers include polypropylene fibers.

4. A hydraulically cured body obtained by curing a hydraulic composition according to any one of claims 1 to 3.

5. To obtain the hydraulic composition described in any one of claims 1 to 3, The hydraulic composition is molded to obtain a molded body, The molded body is cured to obtain a hydraulically hardened body, This includes carbonating the hydraulic hardened body. A method for producing a hydraulic cured body.

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