Lightweight concrete members

Abstract

An object is to provide a lightweight concrete member that can reduce CO2 emissions and has excellent crack resistance. 【Solution means】The lightweight concrete member according to the present invention includes lightweight concrete and steel materials. The lightweight concrete contains only blast furnace cement type B as cement, and 300 to 400 L / m 3 of lightweight coarse aggregate, normal fine aggregate, 150 to 185 kg / m 3 of water, and a chemical admixture for concrete having a weight ratio of 0.2 to 2.0% with respect to the blast furnace cement type B. Let the Young's modulus of the lightweight concrete at 28 days of effective age be E W (N / mm 2 ), the cross-sectional area of the lightweight concrete be A W (mm 2 ), the Young's modulus of the steel material be E B (N / mm 2 ), and the cross-sectional area of the steel material be A B (mm 2 ). When calculated as such, the axial rigidity ratio calculated by E B ×A B / (E B ×A B +E W ×A W ) is 0.02 to 0.90.

Description

[Technical Field]

[0001] The present invention relates to a lightweight concrete member comprising lightweight concrete and steel. [Background technology]

[0002] In the field of concrete materials, technological development is underway with the aim of reducing environmental impact. Specifically, this involves using blast furnace cement type B as a concrete material to reduce the amount of Portland cement used and thereby reduce CO2 emissions during cement production. Furthermore, the following are examples of technologies that use blast furnace cement type B as a concrete material.

[0003] Non-patent document 1 explains that with respect to ordinary concrete (as defined in JIS A 5308:2024) using blast furnace cement type B, shrinkage strain increases with rising temperature, and crack resistance (especially crack resistance at high temperatures of 30°C) decreases. Furthermore, Non-Patent Literature 2 indicates that the crack resistance of ordinary concrete using blast furnace cement type B (especially crack resistance at high temperatures of 30°C) can be improved by replacing a portion of the coarse aggregate in the ordinary aggregate with lightweight aggregate. It also states that concrete cured in a wet environment with lightweight aggregate has a grain density of 0.2-0.3 N / mm². 2 While the introduction of a certain degree of compressive stress is effective in reducing shrinkage-restraining stress, it has been explained that this compressive stress does not change significantly when the replacement rate of lightweight aggregate is 25% by volume or more. In addition, it has been explained that a replacement rate of lightweight aggregate of 25% by volume or less is desirable, even considering the decrease in compressive strength, stagnation of shrinkage-restraining stress, and decrease in the critical stress-to-strength ratio due to an increase in the replacement rate. Furthermore, Non-Patent Document 3 indicates that, with respect to ordinary concrete using blast furnace cement type B, replacing some or all of the fine aggregate with lightweight aggregate, or replacing some of the fine aggregate and coarse aggregate with lightweight aggregate, improves crack resistance and introduces compressive stress after wet curing, similar to Non-Patent Document 2. Furthermore, Patent Document 1 proposes a technique for ordinary concrete compositions in which a portion of the Portland cement is replaced with blast furnace cement type B, and a portion or all of the coarse aggregate is replaced with lightweight aggregate. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Japan Concrete Institute, "Report of the Research Committee on Shrinkage Cracking Reduction and Durability Improvement from the Perspective of Admixtures," pp. 273-276, 2010.9 [Non-Patent Document 2] Momose, Kanda, Yoda, Kasai, "Experimental Study on the Effect of Lightweight Aggregates on Improving Shrinkage Crack Resistance of Blast Furnace Cement Type B Concrete," Annual Proceedings of the Concrete Engineering Society, Vol. 35, No. 1, pp. 589-594, 2013. [Non-Patent Document 3] Kiyohara, Imamoto, Arai, Ishikawa, "Experimental Study on Shrinkage Cracking Characteristics of Blast Furnace Cement Concrete Using Artificial Lightweight Aggregates," Annual Proceedings of the Concrete Engineering Society, Vol. 37, No. 1, pp. 457-462, 2015. [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2011-116612 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] When weighing materials in ready-mixed concrete plants or precast concrete plants, cement and admixtures must be weighed using separate weighing instruments for each material. Therefore, if two types of binders, Portland cement and blast furnace cement type B, are to be used as described in Patent Document 1, separate weighing instruments must be secured for each. However, since the combination of each weighing instrument and the storage facilities connected to it, such as material silos and storage bins, is fixed, applying the technology of Patent Document 1 would occupy these facilities, preventing the production of other types of concrete or limiting the number of plants that can handle it.

[0007] Non-patent documents 1-3 and the technology described in patent document 1 relate to ordinary concrete, and therefore involve replacing ordinary aggregate with lightweight aggregate. In this case, as the replacement rate of lightweight aggregate, which has low rigidity and strength, increases, the decrease in elastic modulus and initial strength development becomes greater. Therefore, in order to ensure performance comparable to that of general ordinary concrete, prior experiments are necessary to determine the optimal replacement rate that balances the required strength properties with improved crack resistance, as described in non-patent document 2.

[0008] The concrete materials using blast furnace cement type B described in Non-Patent Documents 1-3 and Patent Document 1 are more effective in reducing CO2 emissions when applied to above-ground structures where a large amount of concrete is used, rather than when applied to underground structures of buildings. However, for above-ground structures, the member cross-sections are small and they dry out easily. Furthermore, concrete made with blast furnace cement type B has a large shrinkage restraint force during drying, making it prone to cracking. Therefore, concrete made with blast furnace cement type B was rarely used for above-ground structures.

[0009] Taking these circumstances into consideration, the inventors of this invention aimed to create a lightweight concrete member with excellent crack resistance that could be applied to above-ground structures, in addition to simply reducing CO2 emissions.

[0010] Therefore, an object of the present invention is to provide a lightweight concrete member that can reduce CO2 emissions and has excellent crack resistance.

Means for Solving the Problems

[0011] The above problems can be solved by the following means. The lightweight concrete member according to the present invention is a lightweight concrete member including lightweight concrete and steel. The lightweight concrete contains only blast furnace cement type B as cement, and lightweight coarse aggregate of 300 to 400 L / m 3 , normal fine aggregate, water of 150 to 185 kg / m 3 , and a chemical admixture for concrete having a weight ratio of 0.2 to 2.0% with respect to the blast furnace cement type B. When the Young's modulus of the lightweight concrete at an effective age of 28 days is E W (N / mm 2 ), the cross-sectional area of the lightweight concrete is A W (mm 2 ), the Young's modulus of the steel is E B (N / mm 2 ), and the cross-sectional area of the steel is A B (mm 2 ), the axial rigidity ratio calculated by E B × A B / (E B × A B + E W × A W ) is 0.02 to 0.90. According to the present invention, since only blast furnace cement type B is used as cement, the amount of Portland cement used can be reduced, and the CO2 emissions during the production of cement can be reduced. Further, according to the present invention, since the content of lightweight coarse aggregate, the axial rigidity ratio, etc. are specified, excellent crack resistance can be exhibited. Furthermore, according to the present invention, since it is based on the premise of using lightweight concrete and lightweight coarse aggregate is used as the coarse aggregate, there is no need for extra considerations such as optimizing the replacement rate as described in Non-Patent Document 2. Moreover, according to the present invention, the equipment used to manufacture ordinary lightweight concrete can be used, so the equipment problems mentioned above that are expected in the technology described in Patent Document 1 do not occur. In addition, in Non-Patent Documents 2-3 and Patent Document 1, the ordinary aggregate of ordinary concrete is replaced with expensive lightweight aggregate, so the unit price of the concrete fluctuates significantly from the original unit price. However, in the present invention, there is no need to change the aggregate of the lightweight concrete (it remains lightweight coarse aggregate), and the problem of a large change in the unit price of the concrete does not occur. Based on these matters, the present invention can be said to be a more feasible and practical technology compared to the technologies described in Non-Patent Documents 1-3 and Patent Document 1.

[0012] In the lightweight concrete member according to the present invention, it is preferable that the water-to-binder ratio of the lightweight concrete is 40 to 54%. According to the present invention, since the water-binder ratio is specified, it is possible to more reliably suppress the occurrence of cracks while ensuring appropriate fluidity and strength. As a result, according to the present invention, concrete placement and finishing work becomes easier, and high-quality lightweight concrete members can be provided.

[0013] The lightweight concrete member according to the present invention has a maximum restraining stress of 0.5 to 1.5 N / mm² during the drying period. 2 It is preferable that this be the case. According to the present invention, since the maximum value of the restraining stress generated during the drying period is specified, superior crack resistance can be more reliably achieved. [Effects of the Invention]

[0014] The lightweight concrete member according to the present invention can reduce CO2 emissions and has excellent crack resistance. [Brief explanation of the drawing]

[0015] [Figure 1]This is a schematic diagram of the specimen used to calculate the compressive stress. [Figure 2] This graph shows the measurement results of the constraining stress for each test specimen. [Figure 3] This graph shows the measured and calculated values ​​of the work done per unit of lightweight coarse aggregate in a specimen with a restraining material ratio of 4.0%. [Figure 4A] This graph plots the restraint ratio and measured restraint stress for each specimen, along with the calculated values ​​when the reduction factor in Equation 1 is disabled. [Figure 4B] This graph plots the restraint ratio and measured restraint stress for each specimen, along with the calculated values ​​when the reduction factor in Equation 1 is enabled. [Figure 5A] This graph shows the results of the confinement stress for specimen a4 and specimen a in the crack resistance test. [Figure 5B] This graph shows the results of the confinement stress for specimen b4 and specimen b in the crack resistance test. [Figure 6] This graph adds the restraint stress results for a restraint ratio of 8.0% to the graph in Figure 4B. [Figure 7] This is a schematic diagram of the specimen used in the drying shrinkage crack test. [Figure 8] This graph shows the results of the confinement stress for specimens a5 and c in the drying shrinkage crack test. [Figure 9] This graph shows the crack width results for specimens a5 and c in the drying shrinkage crack test. [Modes for carrying out the invention]

[0016] The following describes an embodiment for implementing the lightweight concrete member according to the present invention. [Lightweight concrete members] The lightweight concrete member according to this embodiment is a lightweight concrete member comprising lightweight concrete and steel, wherein the lightweight concrete contains only blast furnace cement type B as cement, and also contains lightweight coarse aggregate, ordinary fine aggregate, water, and a chemical admixture for concrete, and the axial stiffness ratio is within a predetermined range. The following describes each element constituting the lightweight concrete member according to this embodiment.

[0017] [Lightweight concrete] The lightweight concrete member according to this embodiment comprises "lightweight concrete" and "steel material". The lightweight concrete is concrete using lightweight aggregate as aggregate, and more specifically, it satisfies the requirements specified in JIS A 5308:2024. Preferably, the lightweight concrete is lightweight concrete type 1 (so-called lightweight type 1) which uses lightweight coarse aggregate as coarse aggregate and ordinary fine aggregate as fine aggregate. (Blast furnace cement type B) Lightweight concrete contains only blast furnace cement type B as its cement component. Because lightweight concrete contains blast furnace cement type B, the amount of Portland cement used can be reduced, thereby reducing CO2 emissions during cement production. Here, blast furnace cement type B refers to cement mixed with a specified amount of blast furnace slag, and meets the requirements specified in JIS R 5211:2019. Furthermore, the statement "contains only blast furnace cement type B as cement" means that no other cement, such as Portland cement (JIS R 5210:2019), is used in addition to blast furnace cement type B. In other words, unlike typical lightweight concrete, the lightweight concrete according to this embodiment has all of its cement replaced with blast furnace cement type B. For example, the content (per unit amount) of blast furnace cement type B in lightweight concrete is 280 kg / m³. 3 More than 300kg / m 3 More than 330kg / m 3 That is all, 400 kg / m 3Below 380kg / m 3 Below 360kg / m 3 The following applies:

[0018] (Lightweight coarse aggregate) Lightweight coarse aggregate is coarse aggregate that is lighter than ordinary coarse aggregate and meets the requirements specified in JIS A 5002:2003. The content (unit amount) of lightweight coarse aggregate in lightweight concrete is, for example, 300 L / m³. 3 Above, 305L / m 3 Above, 309L / m 3 That's all, 400 L / m 3 Below, 380L / m 3 Below, 350L / m 3 The following applies: (Ordinary fine aggregate) Ordinary fine aggregates include mountain sand, crushed lime sand, river sand, sea sand, crushed sand, silica sand, and lime sand, and conform to JIS A5308:2024 Annex A. The content (unit amount) of ordinary fine aggregate in lightweight concrete is, for example, 300 L / m³. 3 Above, 320L / m 3 Above, 330L / m 3 That's all, 450 L / m 3 Below, 400L / m 3 Below, 360L / m 3 The following applies:

[0019] (water) The water content (per unit) in lightweight concrete is, for example, 150 kg / m³. 3 More than 170kg / m 3 More than 180kg / m 3 That is all. 185 kg / m 3 The following applies: Furthermore, there are no particular restrictions on the type of water used; tap water, groundwater, industrial water, etc., can be used. (Water binding material ratio) The water-to-binder ratio (= water content (mass) / binder content (mass) × 100) in lightweight concrete is, for example, 40% or more, 45% or more, 48% or more, 54% or less, and 52% or less. Furthermore, a binder is a substance that reacts with water to contribute to the development of concrete strength, and specifically, the aforementioned blast furnace cement type B is an example of this. (Chemical admixture for concrete) Chemical admixtures for concrete, as defined in JIS A 6204:2011, include AE ​​agents, AE water-reducing agents, and high-performance AE water-reducing agents. In lightweight concrete, the weight ratio of the chemical admixture for concrete (at least one of AE water-reducing agents and high-performance AE water-reducing agents) to blast furnace cement type B (= weight of admixture / weight of blast furnace cement type B × 100) is, for example, 0.2% or more, 2.0% or less, 1.5% or less, or 1.0% or less. (others) The lightweight concrete according to this embodiment may appropriately contain conventionally known materials used in general lightweight concrete, to the extent that the desired effects of the present invention are not hindered.

[0020] [Steel] Steel materials primarily serve as reinforcing elements such as structural steel (shaped steel) and reinforcing bars (steel bars) that bear tensile stress, and act as restraining materials that constrain the expansion of lightweight concrete that occurs during the wet curing period. By restraining the expansion of lightweight concrete, the steel materials impart compressive stress (prestress) to the lightweight concrete members. The type of steel used is not particularly limited, as long as it is a general-purpose steel used for the applications described below. Furthermore, the placement of the steel within the lightweight concrete member is not particularly limited; it may be placed inside the lightweight concrete, around the lightweight concrete, or both. Note that when the steel is placed inside the lightweight concrete, internal constraints act upon it, while when the steel is placed around the lightweight concrete, external constraints act upon it.

[0021] (shaft stiffness ratio) In this embodiment, the upper limit of the axial stiffness ratio of the lightweight concrete member is preferably 0.90 or less. By setting the axial stiffness ratio of the lightweight concrete member to a predetermined value (0.90) or less, the expansion of the crack width after crack formation can be suppressed. On the other hand, the lower limit of the axial stiffness ratio of the lightweight concrete member according to this embodiment is set to 0.02 or higher, referring to the range of axial stiffness ratios of the six test specimens shown in Table 2, and the provision in Article 13 of the Architectural Institute of Japan's Reinforced Concrete Structural Calculation Standards and Commentary, which states that the minimum tensile reinforcement ratio for floor slabs should be 0.2% or higher. The axial stiffness ratio of a lightweight concrete member is, in detail, determined by the Young's modulus of the lightweight concrete at an effective age of 28 days, E W (N / mm 2 ) and the cross-sectional area of ​​the lightweight concrete in the direction of the principal stress is A W (mm 2 ) and the Young's modulus of the steel material is E B (N / mm 2 ) and the cross-sectional area of ​​the steel material in the direction of the principal stress is A B (mm 2 If we set it to E, B ×A B / (E B ×A B +E W ×A W It is calculated as follows. Furthermore, each index used to calculate the axial stiffness ratio is an index for the state at an effective age of 28 days, and is the state during the drying period described below (the state after demolding, when the formwork used during the wet curing period is removed). The axial stiffness ratio is as described in Momose and Kanda, "Quantification of Shrinkage Reduction Effect by Expanding Agents," Journal of Structural Engineering, Architectural Institute of Japan, Vol. 76, No. 666, pp. 1367-1373, 2011. Furthermore, the effective age is the age converted so that the effect of curing temperature on the hydration reaction is equivalent to the degree of hydration when the curing temperature is 20°C, as defined on page 68 of the "Design and Construction Guidelines and Commentary for Temperature Cracking Control of Mass Concrete, 2nd Edition" by the Architectural Institute of Japan.

[0022] (Ratio of restraining material) In this embodiment, the lightweight concrete member may specify the following "restraint ratio" (more precisely, the restraint ratio during the wet curing period) instead of, or in combination with, the "axial stiffness ratio" described above. The restraining material ratio, which is the area ratio of the cross-sectional area of ​​the steel material to the cross-sectional area of ​​the lightweight concrete, is preferably 0.2% or higher. More preferably, the restraining material ratio is 8.0% or lower, 5.0% or lower, or 4.0% or lower. By having the restraining material ratio within the specified range, appropriate compressive stress is generated (the compressive stress described later is within the specified range), and excellent crack resistance can be achieved. Furthermore, the restraint ratio is, in detail, the ratio of each cross-sectional area in the direction of principal stress (= cross-sectional area of ​​steel / cross-sectional area of ​​lightweight concrete × 100). For example, if the cross-section of the steel in the direction of principal stress is 200 mm 2 The cross-section of the lightweight concrete member (lightweight concrete + steel) is 8200 mm 2 In that case, the restraint ratio would be 2.5% (=200 / (8200-200)×100). Furthermore, when calculating the restraint ratio, "steel material" is a concept that includes all steel materials, and naturally, this also includes main reinforcing bars.

[0023] [Constraining stress generated during the drying period] The upper limit of the maximum restraining stress generated during the drying period after the wet curing period is 1.5 N / mm². 2 The following is preferable. This makes it possible to suppress cracking of the lightweight concrete member during the drying period. On the other hand, although there is no particular lower limit to the maximum value of the restraining stress that occurs during the drying period after the wet curing period, for example, 0.5 N / mm 2 That's all. The drying period refers to the drying period after the wet curing period. For example, if the wet curing period is 22 days of effective age, the drying period will be from 22 to 60 days of effective age. If the wet curing period is 7 days of effective age, the drying period will be from 7 to 60 days of effective age.

[0024] [Compressive stress] The compressive stress generated during the wet curing period of 3 to 22 days is 0.01 N / mm². 2 The above is preferable. By having a compressive stress above a predetermined value, it is possible to more reliably achieve superior crack resistance. Furthermore, the compressive stress is 0.33 N / mm². 2The following is preferable: By keeping the compressive stress below a predetermined value, it is possible to avoid situations such as a decrease in compressive strength. The effective age is as described above.

[0025] The compressive stress can be calculated in detail based on the following equations 1 and 2. Furthermore, equations 1 and 2 below were derived by the inventors based on experimental results, with reference to the equations described in Yukikazu Tsuji's "Basic Research on the Use of Chemical Prestress in Concrete" (Transactions of the Japan Society of Civil Engineers, No. 235, March 1975). ≪Formula 1≫ σex = -α[{2 × Er × (pr / 100)} 0.5 ]×[(Ug×Vg) 0.5 ]+β (Explanation of symbols in Equation 1) σex: Compressive stress (N / mm²) caused by expansion during the wet curing period of lightweight concrete restrained by steel. 2 [Negative constraint stress is defined as compressive stress] Er: Young's modulus (N / mm²) of the restraining material (steel). 2 ) pr: restraining material ratio (%) [=Ar / Ac×100] Ar: Cross-sectional area (mm²) of the restraining material (steel) in the direction of the principal stress. 2 ) Ac: Cross-sectional area of ​​lightweight concrete in the direction of principal stress (mm²) 2 ) Ug: Unit of wet curing period te (days) Work rate per lightweight coarse aggregate ([N / mm 2 ]·[L / m 3 ] -1 ), (Here, "work done per unit of lightweight coarse aggregate" specifically refers to "the amount of work done by lightweight coarse aggregate per unit volume on the restraining material.") Vg: Lightweight concrete 1m 3 Volume of lightweight coarse aggregate per unit (L / m³) 3 ) α, β: Reduction factors when considering safety for compressive stress To disable the reduction factor, use α=1.0 and β=0.0. To enable the reduction factor, use, for example, α=0.9 and β=-0.03. In the above formula 1, the amount of work Ug per unit lightweight coarse aggregate during the wet curing period te can be calculated based on the following formula 2.

[0026] ≪Formula 2≫ Ug = Uref × exp[1.15 × {1 - (7 / te) 0.65}] (Explanation of symbols in Equation 2) Uref: Standard work volume (N / mm) 2 )·(L / m 3 ) -1 te: Wet curing period converted to effective age (days) The standard work load Uref represents the value for a wet curing period (effective age) of 7 days when the restraint material ratio is 4.0%, and is calculated as 9.27 × 10⁻⁶. -9 (N / mm 2 )·(L / m 3 ) -1 Let's assume that. The values ​​of Uref in Equation 2 and the constants (1.15, 0.65) were determined by the least squares method so that the solid line (calculated value of Ug) in Figure 3 (calculated value of Ug) and the plot in Figure 3 (measured value of Ug) would be close together.

[0027] [Application] The lightweight concrete members according to this embodiment have excellent crack resistance and can be suitably applied to above-ground structures such as floor slabs, beams, columns, and walls. Furthermore, they can be applied to precast concrete structures (such as precast concrete curtain walls) that are manufactured in advance at a factory. For example, when manufacturing a curtain wall, it is acceptable to use general manufacturing methods, but to prevent the surface of the components from drying out, a formwork with low water permeability must be left in place or covered with a watertight sheet, and the components must be subjected to a specified period of moist curing. [Examples]

[0028] [Example 1: Test to confirm the effectiveness of the method for calculating compressive stress] (Preparation of test specimens) Figure 1 is a schematic diagram of the specimen used to calculate the compressive stress. The shape of the test specimen is as shown in Figure 1, based on Method B of Annex B, "Test Method for Restrained Expansion and Shrinkage of Expanding Concrete," of JIS A 6202:2017. In detail, lightweight concrete 1 measured 100mm in height, 100mm in width, and 385mm in length. A restraining material 2 (SS400) was embedded inside lightweight concrete 1, and both ends of lightweight concrete 1 were restrained with nuts 3 (NACH10T) and end plates 4 (SS400, 19mm in length). A strain gauge 5 was placed near the center of the restraining material 2. By using restraining materials 2 of different diameters (nominal diameters: M6, M12, M24), the restraining material ratio and axial stiffness ratio were changed. The materials used in the lightweight concrete specimens are shown in Table 1, and their compositions are shown in Table 2. As shown in Table 2, the temperature during the wet curing period of the concrete after mixing (simply referred to as "temperature" in the table) was set to two levels: 20°C and 30°C, and the restraint material ratio was set to three levels: 0.2%, 0.9%, and 4%. Two specimens were prepared for each of the six types of test specimens (a1-a3, b1-b3). The axial stiffness ratios of the six types of test specimens are shown in Table 2. Furthermore, the test specimens were covered after placement to prevent their surfaces from drying out.

[0029] [Table 1]

[0030] [Table 2]

[0031] The axial stiffness ratio of each specimen shown in Table 2 can be calculated in detail using the following formula (E B ×A B / (E B ×AB +E W ×A W Calculated based on )) Axial stiffness ratio of a1: 0.023 = 205000 × 20.1 / (205000 × 20.1 + 17777 × 9979.9) Axial stiffness ratio of a2: 0.089 =205000×84.3 / (205000×84.3+17777×9915.7) Axial stiffness ratio of A3: 0.297 =205000×353 / (205000×353+17777×9647) Axial stiffness ratio of b1: 0.022 = 205000 × 20.1 / (205000 × 20.1 + 18762 × 9979.9) Axial stiffness ratio of b2: 0.085 =205000×84.3 / (205000×84.3+18762×9915.7) Axial stiffness ratio of b3: 0.286 =205000×353 / (205000×353+18762×9647)

[0032] (Exam content: Regarding Figure 2) Figure 2 is a graph showing the measurement results of the constraining stress for each specimen. The "restraining stress" of each specimen during the wet curing period is calculated by multiplying the strain of the restraining material measured by strain gauges by the Young's modulus of the restraining material (20.5 kN / mm²). 2 The strain was calculated by multiplying the cross-sectional area of ​​the steel material by the ratio of the cross-sectional area of ​​the steel material to that of the lightweight concrete (= cross-sectional area of ​​steel material / cross-sectional area of ​​lightweight concrete), and then averaging the values ​​obtained for the two bodies. The strain of the restraining material was measured up to 14 days of age. To evaluate the effect of different wet curing temperatures on this "constrained stress" at an equivalent age, the age was converted to an effective age. Note that when the measurement period up to 14 days is converted to an effective age, it becomes 14 days at 20°C and 22 days at 30°C. Figure 2 shows the results of plotting the "constrained stress" and "effective age" of each specimen calculated in this way. Note that the compressive stress in Figure 2 is shown as a negative constraint stress.

[0033] (Exam content: Regarding Figure 3) Figure 3 is a graph showing the measured and calculated values ​​of the work done per unit of lightweight coarse aggregate in specimens with a restraining material ratio of 4.0%. For specimens a3 and b3 with a restraining material ratio of 4.0%, data was extracted from the time-series data of restraining stress (values ​​shown in Figure 2) obtained by the method described above for predetermined wet curing periods (effective age of 3, 5, 7, 11, and 22 days), and the average restraining stress of specimens a3 and b3 was calculated. Then, the extracted data was substituted into the compressive stress σex in equation 1 (α=1.0, β=0.0) to calculate the work Ug per unit lightweight coarse aggregate. The Ug values ​​calculated in this way were plotted as measured values ​​in Figure 3. Furthermore, the calculated work rate Ug per unit lightweight coarse aggregate, obtained based on Equation 2, is shown as a line in Figure 3.

[0034] (Exam content: Regarding Figure 4) Figure 4 is a graph plotting the restraint ratio and measured restraint stress for each specimen. Figure 4A shows the calculated values ​​when the reduction factor in Equation 1 is disabled, and Figure 4B shows the calculated values ​​when the reduction factor in Equation 1 is enabled. For each specimen, data was extracted from the time-series data of confinement stress (values ​​shown in Figure 2) obtained by the method described above, for predetermined wet curing periods (effective age of 3, 5, 7, 11, and 22 days). Then, for specimens with the same confinement material ratio, the average value of the confinement stress (i.e., the average value of the confinement stress for a1 and b1, a2 and b2, and a3 and b3) was calculated for each predetermined wet curing period. The restraint material ratio and restraint stress for each specimen calculated in this way were plotted in Figures 4A and 4B. Furthermore, Figure 4A shows the curve between the restraint material ratio and restraint stress obtained based on Equation 1 with the reduction factor disabled (α=1, β=0). On the other hand, Figure 4B shows the curve between the restraint material ratio and restraint stress obtained based on Equation 1 with the reduction factor enabled (α=0.9, β=-0.03).

[0035] (Discussion of the results shown in Figure 2 of Example 1) As shown in Figure 2, it was confirmed that compressive stress increases as the restraint ratio increases, and that compressive stress increases as the effective age of the material increases. Furthermore, as shown in Figure 2, it was confirmed that the compressive stress was almost the same for specimens a1 and b1, a2 and b2, and a3 and b3, which had different temperatures during the wet curing period. Therefore, it was confirmed that compressive stress can be expressed as "restraint ratio" and "effective age" by considering the effect of temperature during the wet curing period using the effective age. (Discussion of the results shown in Figure 3 of Example 1) As shown in Figure 3, the measured and calculated values ​​of the work rate Ug per unit lightweight coarse aggregate matched, confirming that Ug can be appropriately calculated based on Equation 2. (Discussion of the results shown in Figure 4 of Example 1) As shown in Figure 4A, the measured compressive stress and the calculated value (when the reduction factor in Equation 1 is disabled) were in almost agreement. However, it was confirmed that in cases where the restraint ratio was less than 1%, the calculated value was higher. On the other hand, as shown in Figure 4B, it was confirmed that, for any restraint ratio, the calculated compressive stress (when the reduction factor in Equation 1 is enabled) was consistently lower than the measured value. In other words, the results in Figures 4A and 4B show that compressive stress can be appropriately calculated based on Equation 1 when the reduction factor is disabled. However, if you want to calculate the compressive stress on the safe side (i.e., if you want the actual compressive stress to be greater than the calculated compressive stress), it is preferable to enable the reduction factor in Equation 1. Based on the results shown in Figures 2-4 of Example 1, it was confirmed that compressive stress can be calculated very simply using Equations 1 and 2.

[0036] [Example 2: Test to confirm crack resistance, etc.] (Preparation of test specimens) The lightweight concrete materials used for specimens a4 and b4 were those shown in Table 1. On the other hand, the lightweight concrete materials for specimens a and b were "ordinary Portland cement (density: 3.16 g / m³)" as the cement. 3 ), specific surface area 3250(cm 2 Except for the use of " / g))" (symbol N in the table), the specimens shown in Table 1 were used. The composition of each specimen was as shown in Table 3. The axial stiffness ratio of each specimen was also as shown in Table 3.

[0037] (Test content: Crack resistance test) The crack resistance test was conducted in accordance with the "Concrete Shrinkage Crack Evaluation Test Method" described in Non-Patent Document 2 mentioned above, and the details were as follows. The specimen used in the crack resistance test consisted of lightweight concrete with dimensions of 100 mm in height, 100 mm in width, and 1,100 mm in length. A threaded steel bar with a nominal diameter equivalent to M33 (8.0% of the restraint ratio) was embedded in the center of the 100 mm x 100 mm cross section as a restraint. The central 300 mm section of the restraint was then sealed with a Teflon sheet to remove adhesion to the lightweight concrete, and a strain gauge was placed in the center of the restraint. The specimen was in the form of lightweight concrete 1 shown in Figure 1, without nuts 3 and end plates 4 at both ends. The prepared specimens were demolded after 7 days of wet curing, and then covered with aluminum tape on all sides except for two sides measuring 100 mm in height and 1,100 mm in length, and dried under the conditions shown in Table 3. The "restraining stress" of each specimen was calculated by multiplying the strain of the restraining material measured with a strain gauge by the Young's modulus of the restraining material (20.5 kN / mm²). 2 The cross-sectional area was calculated by multiplying the cross-sectional area of ​​the steel material by the ratio of the cross-sectional area of ​​the steel material to that of the lightweight concrete (= cross-sectional area of ​​steel material / cross-sectional area of ​​lightweight concrete). Furthermore, for the crack resistance test, two specimens were tested for each test sample.

[0038] (Test content: Test related to strength properties) Regarding lightweight concrete at 28 days of age for each specimen, the compressive strength test was conducted according to the method described in JIS A 1108:2018, the static elastic modulus test was conducted according to the method described in JIS A1149:2017, and the splitting tensile strength test was conducted according to the method described in JIS A 1113:2018. In addition, for each of these tests, three tests were carried out for each specimen, and the average value was calculated.

[0039]

Table 3

[0040] The axial rigidity ratios of each specimen shown in Table 3 were calculated based on the following calculation formula (E B ×A B / (E B ×A B +E W ×A W )). Axial rigidity ratio of a4: 0.480 = 205000×742 / (205000×742 + 17777×9258) Axial rigidity ratio of b4: 0.467 = 205000×742 / (205000×742 + 18762×9258) Axial rigidity ratio of a: 0.468 = 205000×742 / (205000×742 + 18711×9258) Axial rigidity ratio of b: 0.477 = 205000×742 / (205000×742 + 18010×9258)

[0041]

Table 4

[0042] [[ID=​​According to the test results on the strength properties in Table 4, for specimens a4 and b4 that meet the requirements of the present invention, although the splitting tensile strength of specimen a4 was slightly lower, the other values were equivalent to those of conventional lightweight concrete (specimens a and b).

[0043] (Discussion on the results of the crack resistance test shown in Table 4 and Figure 5 of Example 2) Figure 5 shows the results of the restraint stress in the crack resistance test. Figure 5A shows the results of specimen a4 and specimen a, and Figure 5B shows the results of specimen b4 and specimen b. Note that "×" in Figure 5 indicates that cracks have occurred. According to the results in Figures 5A and 5B, although the compressive stress during the wet curing period also occurred in conventional lightweight concrete (specimens a and b), it was found that specimens a4 and b4 that meet the requirements of the present invention were slightly larger. And the tensile stress after the start of drying was 2 - 2.5 N / mm for conventional lightweight concrete (specimens a and b) 2 whereas for specimens a4 and b4 that meet the requirements of the present invention, it was 0.5 - 1.5 N / mm 2 and it was confirmed that it was significantly suppressed. Therefore, as shown in Table 4 and Figures 5A and 5B, the period until cracks occurred in specimen a4 (experimental condition temperature 20°C) that meets the requirements of the present invention was significantly extended compared to conventional lightweight concrete (specimen a). Also, even when the experimental condition was 30°C at high temperature, the period until cracks occurred in specimen b4 that meets the requirements of the present invention was equal to or longer than that of conventional lightweight concrete (specimen b). That is, it was confirmed that by the lightweight concrete member meeting the requirements of the present invention, excellent crack resistance can be exhibited.

[0044] (Discussion on the results shown in Figure 6 of Example 2) Figure 6 is a graph obtained by adding the results of the restraint stress when the restraint material ratio is 8.0% to the graph of Figure 4B. The results added to Figure 6 are the average values ​​of the restraining stress obtained in the test of Example 2 for specimens a4 and b4 used in the crack resistance test, calculated for each predetermined wet curing period (effective age of 3, 5, 7, 11, and 22 days). As shown in Figure 6, it was confirmed that the calculated compressive stress was lower than the measured value, even when the restraint ratio was 8.0%. Therefore, from the results in Figure 6, it was found that even when the restraint ratio is 8.0%, the compressive stress can be calculated to be on the safer side when the reduction factor is enabled (α=0.9, β=-0.03) based on Equation 1. In other words, if the compressive stress calculated based on Equation 1 (when the reduction factor is enabled) is greater than the lower limit specified in this invention, the actual compressive stress will naturally be greater than that lower limit, thus making the excellent crack resistance more reliable.

[0045] [Example 3: Test when the axial stiffness ratio and restraint ratio are larger than in Example 2] (Preparation of test specimens) The lightweight concrete material used for specimen a5 is shown in Table 1. On the other hand, the lightweight concrete material used for specimen c was "ordinary Portland cement (density: 3.16 g / m³)" as the cement. 3 ), specific surface area 3250(cm 2 Except for the use of " / g))" (symbolized as N in the table), the samples shown in Table 1 were used. The composition of each specimen was as shown in Table 5.

[0046] [Table 5]

[0047] The axial stiffness ratio of each specimen shown in Table 5 can be calculated in detail using the following formula (E B ×A B / (E B ×A B +E W ×A W Calculated based on )) Axial stiffness ratio of A5: 0.807 =205000×3924.33 / (205000×3924.33+19400×9928.67) Axial stiffness ratio of c: 0.807 =205000×3924.33 / (205000×3924.33+19400×9928.67)

[0048] (Test content: Drying shrinkage crack test) The drying shrinkage crack test was conducted in accordance with JIS A 1151:2011, "Test method for drying shrinkage cracks in confined concrete," and the details are as follows. Figure 7 is a schematic diagram of the specimen used in the drying shrinkage crack test. The left side of Figure 7 is a cross-sectional view of the specimen, and the right side is a side view. All dimensions in the diagram are in millimeters (mm). The specimen used for the drying shrinkage crack test is shown in Figure 7. Unlike the aforementioned JIS standard, the length of the test section of concrete 10 was set to 1000 mm (300 mm in JIS), and the overall dimensions of the test section were 1000 mm in length, 100 mm in height, and 100 mm in width. Furthermore, a single deformed steel bar 30 (D10) was placed inside the concrete 10 that was constrained by the constrained steel section 20. In addition, to clearly evaluate the crack resistance, the cross-sectional area of ​​the constrained steel section 20 was made larger than in the aforementioned JIS standard, and the axial stiffness ratio was increased. A strain gauge 40 was attached to the center of the constrained steel section 20 in the longitudinal direction to measure the change in strain. The temperature (simply indicated as "temperature" in the table) was kept at 20°C from the time the concrete was mixed until the 7-day wet curing period, and again after demolding at 7 days. During the 7-day wet curing period, the finished surface was covered with a polyester film and then covered with a damp cloth in a 20°C environment. After demolding at 7 days, the entire surface of the test specimen was dried in an environment with a temperature of 20°C and a relative humidity (RH) of 60%. Then, the "total crack width" and the "time until crack occurrence" up to 60 days of age were confirmed, and the "restraining stress" up to 60 days of age was calculated. This "restraining stress" is calculated by multiplying the average strain of the restraining steel (restraining material) measured with strain gauges by the Young's modulus of the restraining material (20.5 kN / mm²). 2 The cross-sectional area was calculated by multiplying the cross-sectional area of ​​the steel material by the ratio of the cross-sectional area of ​​the steel material to that of the lightweight concrete (= cross-sectional area of ​​steel material / cross-sectional area of ​​lightweight concrete). Furthermore, for the drying shrinkage crack test, two tests were conducted on each specimen.

[0049] [Table 6]

[0050] (Discussion of the crack resistance test results shown in Table 6 and Figures 8 and 9 of Example 3) Figure 8 is a graph showing the results of the confinement stress for specimens a5 and c in the drying shrinkage crack test. Figure 9 is a graph showing the results of the crack width for specimens a5 and c in the drying shrinkage crack test. In Figures 8 and 9, "a5(1)" and "a5(2)" represent the results for two specimens of specimen a5, and similarly, "c(1)" and "c(2)" represent the results for two specimens of specimen c. In Figure 8, the thick line represents the result of a5(2), the solid line represents the result of c(2), the dotted lines with small spacing represent the result of c(1), and the dotted lines with large spacing represent the result of a5(1).

[0051] According to Figure 9 and Table 6, specimen c (conventional lightweight concrete) showed a total crack width of 0.4 mm up to 60 days of age. On the other hand, specimen a5 (concrete satisfying the requirements of the present invention) showed a total crack width of 0.08 to 0.13 mm up to 60 days of age, indicating that cracking was significantly suppressed compared to specimen c. Furthermore, the time until cracking occurred was 19 days for specimen c, compared to 49 days for specimen a5, demonstrating a significant delay in cracking. These results confirm that even if the axial stiffness ratio is larger than the value in Example 2 (axial stiffness ratio of "0.480" for specimen a4 and "0.467" for specimen b4 shown in Table 3, and axial stiffness ratio of "0.807" for specimen a5 shown in Table 5), the lightweight concrete member can exhibit excellent crack resistance if it satisfies the requirements of the present invention. According to Figure 8, the maximum restraining stress generated in specimen a5 during the drying period (age 7-60 days) is 0.5-1.5 N / mm². 2 It was confirmed that it falls within the specified range. On the other hand, the maximum restraining stress generated during the drying period of specimen c was slightly higher than that of specimen a5, and in particular, one of specimen c (c(1) in Figure 8) was 1.5 N / mm 2 It was confirmed that it exceeded the limit. [Explanation of Symbols]

[0052] 1. Lightweight concrete 2 Restraint material (steel material) 3 nuts 4 End plate 5. Strain Gauges 10 Concrete 20 Restraint section steel 30 Deformed steel bar 40 strain gauges

Claims

1. A lightweight concrete member comprising lightweight concrete and steel, The aforementioned lightweight concrete contains only blast furnace cement type B as cement, and has a density of 300 to 400 L / m³. ３ Lightweight coarse aggregate and ordinary fine aggregate, 150-185 kg / m ３ It contains water and a concrete chemical admixture in a weight ratio of 0.2 to 2.0% relative to the blast furnace cement type B, Let the Young's modulus of the lightweight concrete at 28 days of effective age be E Ｗ (N / mm ２ ), let the cross-sectional area of the lightweight concrete be A Ｗ (mm ２ ), let the Young's modulus of the steel be E Ｂ (N / mm ２ ), let the cross-sectional area of the steel be A Ｂ (mm ２ ), when, the axial rigidity ratio calculated by E Ｂ × A Ｂ / (E Ｂ × A Ｂ + E Ｗ × A Ｗ ) is 0.02 to 0.90, a lightweight concrete member characterized by this.

2. The lightweight concrete member according to claim 1, characterized in that the water-binding ratio of the lightweight concrete is 40 to 54%.

3. The maximum restraining stress generated during the drying period is 0.5 to 1.5 N / mm². ２ The lightweight concrete member according to claim 1 or 2, characterized in that it is the same as the lightweight concrete member according to claim 1 or 2.

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