Method for measuring the amount of expansion of hydraulically hardened concrete and method for estimating the amount of restrained expansion of expansive concrete

Abstract

To provide a simple measurement method that can obtain a measurement result equivalent to the amount of constrained expansion of expansive concrete obtained by the test method of JIS A 6202 without requiring a large number of people or a lot of labor.SOLUTION: A method for measuring an expansion amount of a hydraulic hardening body includes: pasting strain gauges, along the circumference at the center of the height direction, on the outer surface of a cylindrical formwork of φ5×10 cm; filling the cylindrical formwork with hydraulic material containing cement, expansive material, fine aggregate and coarse aggregate with a maximum dimension of 10 mm or less; and measuring the amount of expansion strain after curing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the amount of expansion of expansive concrete. [Background technology]

[0002] The amount of expansion of expansive concrete is typically measured in accordance with the Restrained Expansion Test Method for Expansion Concrete in a Uniaxially Confined State (Method A) specified in Appendix B (Reference) of JIS A 6202. However, because specialized measuring equipment is required, this method is only available in limited institutions, and the measurement requires skill, so the number of people who can perform the measurement is often limited. For this reason, new methods for confirming the amount of expansion of expansive concrete have recently been proposed (Patent Document 1). However, both of these methods require mixing the concrete and molding a test specimen for measurement, which requires a significant amount of preparation and manpower. Therefore, a simple method for measuring the amount of expansion of expansive concrete that does not require a large number of people or a great deal of effort has been desired. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-15382 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a simple measurement method that can obtain measurement results equivalent to the restrained expansion amount of expansive concrete obtained by the test method of JIS A 6202, without requiring a large number of people or a great deal of effort. [Means for solving the problem]

[0005] The present inventors have conducted extensive research into measurement methods to solve the above problems and have found a simple measurement method that can provide test results equivalent to those of the JIS method. That is, the present invention provides the following [1] to [4]. [1] A method for measuring the expansion of a hydraulically hardened body, characterized by attaching a strain gauge to the outer surface of a φ5 x 10 cm cylindrical formwork along the circumferential direction at the center position in the height direction, filling the cylindrical formwork with hydraulic material containing cement, expansive agent, fine aggregate, and coarse aggregate with a maximum dimension of 10 mm or less, and measuring the amount of expansion strain after hardening. [2] The method for measuring the expansion of a hydraulically hardened body according to claim 1, wherein the gauge length of the strain gauge is 6 mm or less. [3] The method for measuring the expansion of a hydraulically hardened body according to claim 1 or 2, wherein the mass ratio of the fine aggregate to the coarse aggregate (mass of fine aggregate / mass of coarse aggregate) is 1.0 to 3.5. [4] A method for estimating the restrained expansion of expansive concrete, characterized in that the same expansive additive, the same type of cement, and the same type of aggregate as the materials used in the expansive concrete are used, and the amount of restrained expansion of the expansive concrete is estimated by the restrained expansion test method specified in Appendix B of JISA 6202 using the amount of expansion strain measured by the expansion amount measurement method described in any one of claims 1 to 3. [Effects of the Invention]

[0006] According to the present invention, the expansion amount of a hydraulically hardened body can be measured by a simple method without requiring many people or a great deal of effort, and the restrained expansion amount of expansive concrete can thereby be estimated. [Brief explanation of the drawings]

[0007] [Figure 1] An explanatory diagram showing the external shape of the cylindrical formwork and the position where the strain gauges are attached. DETAILED DESCRIPTION OF THE INVENTION

[0008] A first invention is a method for measuring the amount of expansion of a hydraulically hardened body. Specifically, this method for measuring the expansion of a hydraulically hardened body involves attaching strain gauges to the outer surface of a cylindrical formwork measuring φ5 x 10 cm along the circumferential direction at the center position in the height direction, filling the formwork with hydraulic material containing cement, expansive additive, fine aggregate, and coarse aggregate with a maximum dimension of 10 mm, and measuring the amount of expansion strain after hardening. This method is described in detail below.

[0009] <Hydraulic materials> The hydraulic material in the measurement method of the present invention includes cement, expansive materials, fine aggregates, and coarse aggregates having a maximum size of 10 mm or less.

[0010] The cement used for the hydraulic material is not particularly limited as long as it is a cement generally used in mortar concrete, and examples thereof include Portland cements such as ordinary Portland cement and high-early-strength Portland cement, and mixed cements such as blast-furnace cement and fly ash cement.

[0011] The expansive material used in the hydraulic material is not particularly limited as long as it is an expansive material for concrete, and specific examples include lime-based expansive materials, ettringite-based expansive materials, ettringite-lime composite expansive materials, etc. The amount of expansive material to be mixed is preferably 3 to 10 parts by mass per 100 parts by mass of the total of cement and expansive material.

[0012] The fine aggregate used in hydraulic materials is the same as that generally used in mortar concrete. Specifically, the aggregate should contain 85% or more particles of 5 mm or less. It is preferable that the content of particles larger than 5 mm is 5% or less, and that the content of particles smaller than 1.2 mm is 50% or more, and that the content of particles smaller than 2.5 mm is 70% or more.

[0013] The coarse aggregate used for hydraulic materials is the same as that generally used in concrete, with a maximum size of 10 mm or less. Using coarse aggregate with a size exceeding 10 mm increases the variability in measured strain values. Furthermore, sizes of 1.2 to 10 mm are preferred, with 2.5 to 6 mm being more preferable. For example, No. 7 crushed stone can be used.

[0014] The ratio of the fine aggregate to the coarse aggregate is preferably 1.0 to 3.5 in terms of mass ratio (mass of fine aggregate / mass of coarse aggregate), and more preferably 1.2 to 2.75.

[0015] The amount of aggregate (fine aggregate and coarse aggregate) mixed is preferably 170 to 380 parts by mass, more preferably 200 to 350 parts by mass, and even more preferably 250 to 300 parts by mass, per 100 parts by mass of the total of cement and expansive additive.

[0016] The hydraulic material of the present invention can further contain water. There are no particular limitations on the water used, as long as it is water that is commonly used in mortar concrete, and tap water, for example, can be used. The amount of water to be added is preferably 40 to 60 parts by mass per 100 parts by mass of the total of cement and expansive material.

[0017] In addition to the above materials, the hydraulic material of the present invention may contain an admixture as appropriate. Examples of the admixture include a water-reducing agent, a high-performance water-reducing agent, an air-entraining agent, an air-entraining water-reducing agent, and a high-performance air-entraining water-reducing agent. The amount of the admixture added is preferably 0.2 to 2.0% by mass based on the total amount of cement and expansive agent.

[0018] <Formwork> The formwork used in the measurement method of the present invention is a cylindrical formwork of φ5×10 cm. The formwork is preferably thin, with a thickness of 2.0 mm or less. If it exceeds 2 mm, there is a risk of a decrease in the measurement sensitivity of the strain gauge. A thickness of 0.3 to 1.0 mm is more preferable. The material of the cylindrical formwork is not particularly limited, but steel is preferred from the standpoint of strength, etc.

[0019] <Strain gauge> The strain gauge is attached to the outer surface of the cylindrical formwork, along the circumferential direction, at the center position in the height direction of the formwork. The gauge length of the strain gauge is preferably less than 10 mm. If it is 10 mm or more, there is a risk that the amount of expansion strain will be overestimated relative to the amount of restrained expansion of the expansive concrete. The gauge length is more preferably 6 mm or less, and even more preferably 5 mm or less. The lower limit is preferably 1 mm or more.

[0020] <Preparation of hydraulic hardened body> A hydraulically hardened body is produced by filling a cylindrical formwork with hydraulic material, which is made by mixing cement, expansive agent, and aggregate with water, and curing and hardening it until the specified age. A normal mortar mixer can be used to mix the hydraulic material. The mixing time is preferably 2 to 5 minutes. It is preferable to thoroughly mix the cement and expansive agent beforehand. The hydraulic material is filled into the cylindrical formwork without leaving any gaps. After filling, the surface is leveled, and the top of the formwork is sealed with a lid or plastic film to prevent moisture evaporation from the surface. The material is then cured until the specified age. Curing is carried out at a temperature of 20±2°C and a humidity of 50% or higher.

[0021] <Method for measuring expansion strain> The amount of expansion strain of the hydraulically hardened body at a specified age is measured with a strain gauge. Three hydraulically hardened body specimens are used for the test under the same conditions, and the average value is used as the amount of expansion strain of the hydraulically hardened body.

[0022] The second invention is a method for estimating the amount of restrained expansion of expansive concrete. When the restrained expansion amount of expansive concrete is estimated by the measurement method of the present invention, the same expansive additive, the same type of cement, and the same type of aggregate as those used in the expansive concrete are used.

[0023] In the present invention, the same expansive additive means the same product from the same manufacturer. For example, if "Taiheiyo Expan" manufactured by Taiheiyo Materials Corporation is used for the expansive concrete, "Taiheiyo Expan" is also used in this measurement method.

[0024] Here, expansive additives are classified into type 20 and type 30 depending on their performance. When used for shrinkage compensation in ordinary concrete, the standard amount is 20 kg / m 3 This type of expanding material is called type 20, and the standard usage amount is 30 kg / m 3 The expanding agent with this formula is called Expansive Agent Type 30. When Expansive Agent Type 20 is used, the standard amount of the expanding agent to be mixed in the hydraulic material of the present invention is 6.7 parts by mass per 100 parts by mass of the total of cement and expanding agent. On the other hand, when Expansive Agent Type 30 is used, the standard amount is 10 parts by mass per 100 parts by mass of the total of cement and expanding agent.

[0025] In the present invention, the term "same type of cement" refers to the same type of cement. For example, when ordinary Portland cement is used in expansive concrete, ordinary Portland cement is also used in this measurement method.

[0026] In the present invention, "same type of aggregate" refers to aggregate of the same rock type. For example, if limestone aggregate is used in expansive concrete, limestone aggregate should also be used in this measurement method. Furthermore, it is preferable to use aggregate from the same source, but if it is difficult to obtain, aggregate of the same rock type can be used.

[0027] Regarding aggregate, the amount of fine aggregate mixed is preferably 170 to 380 parts by mass per 100 parts by mass of the total of cement and expansive additive. Furthermore, the ratio of fine aggregate to coarse aggregate of 10 mm or less is preferably 1.0 to 3.5 in mass ratio (mass of fine aggregate / mass of coarse aggregate) from the viewpoint of error with the restrained expansion rate of expansive concrete, and more preferably 1.2 to 2.75. The standard is 2.0.

[0028] The standard amount of water (water volume) is 50 parts by mass per 100 parts by mass of cement and expansive additive combined. If the amount of water in the expansive concrete is in the range of 40 to 60 parts by mass per 100 parts by mass of cement and expansive additive combined, there is no particular problem with setting the amount of water in this measurement method to 50 parts by mass per 100 parts by mass of cement and expansive additive combined. However, if the amount of water in the expansive concrete is less than 40 parts by mass or more than 60 parts by mass, it is preferable to take the amount of water in the expansive concrete into consideration and set the amount of water in this measurement method so that it is approximately the same mass ratio.

[0029] According to the present invention, the amount of restrained expansion of expansive concrete can be estimated by measuring the amount of expansion strain of the hydraulically hardened concrete using this measurement method. Usually, the amount of restrained expansion of expansive concrete is estimated by measuring the amount of expansion strain at an age of 7 days. [Example]

[0030] The present measurement method will be described in detail below with reference to examples, but is not limited to these examples.

[0031] (1) Preparation of cylindrical formwork The cylindrical formwork used was a φ5 × 10 cm steel formwork (manufactured by Maeda Manufacturing Co., Ltd., thickness: 0.3 mm). Strain gauges (manufactured by Tokyo Measuring Instruments Research Institute Co., Ltd.) 2 with gauge lengths of 5 mm and 10 mm were attached circumferentially to the center of the outer surface of this cylindrical formwork 1, and the lead wires 3 of the strain gauges were connected to a strain measurement device 4 (Figure 1).

[0032] (2) Preparation of hydraulic hardened body Hydraulic materials were prepared using the materials listed below. The cement and expansive additive were thoroughly mixed in advance. The hydraulic material was mixed using a mortar mixer for 3 minutes. The mixed hydraulic material was filled into a cylindrical formwork fitted with a strain gauge. After filling, the top was covered with plastic film and left to cure in air for 7 days at 20°C and 60% humidity to prepare specimens of the hardened hydraulic body. Three specimens were prepared for each level.

[0033] <Materials used> 1) Cement: Ordinary Portland cement (manufactured by Taiheiyo Cement Corporation, density: 3.16 g / cm 3 ) 2) Fine aggregate: Kakegawa mountain sand, particle content of 0.15 to 5 mm is 85% or more, 2.5 mm or less is 82%, density is 2.58 g / cm 3 3) Coarse aggregate: Sakuragawa No. 7 crushed stone, size 2.5-6 mm, density 2.64 g / cm 3 4) Expansive material: "Taiheiyo Hyperexpan" concrete expansive material, manufactured by Taiheiyo Materials Co., Ltd. 5) Water: Tap water 6) Admixture: AE water reducer "Master Polyhede 15S", manufactured by Pozzolith Solutions

[0034] (3) Measurement of expansion strain After the hydraulic material hardened, the strain of the hydraulically hardened body at the age of 7 days was measured with a strain gauge, and this strain was taken as the expansion strain of the hydraulically hardened body.

[0035] (4) Measurement of the amount of restrained expansion of expansive concrete according to the JIS method The restrained expansion amount (length change rate) of the expansive concrete was measured in accordance with the test method of JIS A 6202. Table 1 shows the mix proportions of the expansive concrete. The cement, expansive additive, and fine aggregate used were the same as those used above. The coarse aggregate was Sakuragawa crushed stone (size 5-20 mm; density 2.64 g / cm). 3 The amount of expansion restraint of this expansive concrete was 206 × 10 -6 It was.

[0036] [Table 1] *P is the total amount of cement and expansive material

[0037] (5) Measurement results The blending amounts of each material used and the measurement results are shown in Table 2. It was found that the expansion strain values ​​in Test Examples 1 to 6 were within 10% error of the restrained expansion value measured by the test method of JIS A 6202. Therefore, the aggregate ratio is preferably approximately 1.0 to 3.5. Furthermore, the gauge length of the strain gauge is preferably 5 mm. When the gauge length was 10 mm (Test Example 9), the expansion strain value was 10% or more larger than the restrained expansion value.

[0038] [Table 2] [Explanation of symbols]

[0039] 1 Cylindrical formwork 2 Strain gauges 3 Lead Wires 4. Strain measurement device 5 Hydraulic hardening body

Claims

1. A simple method for measuring the amount of expansion of a hydraulically hardened body, characterized in that a hydraulic material containing cement, expansive material, fine aggregate, coarse aggregate with a maximum dimension of 10 mm or less, and water, wherein the maximum dimension of the coarse aggregate contained is 10 mm or less, is filled into a φ5 x 10 cm cylindrical formwork having a strain gauge with a gauge length of 5 mm or less attached circumferentially to the outer surface at the center position in the height direction, and the amount of expansion strain after hardening is measured.

2. 2. The simplified method for measuring the expansion of a hydraulically hardened body according to claim 1, wherein the mass ratio of the fine aggregate to the coarse aggregate (mass of fine aggregate / mass of coarse aggregate) is 1.0 to 3.

5.

3. A method for estimating the restrained expansion of expansive concrete, characterized in that the same expansive additive, the same type of cement, and the same type of aggregate as the materials used in the expansive concrete are used, and the amount of restrained expansion of the expansive concrete is estimated by the restrained expansion test method specified in Appendix B of JIS A 6202 using the amount of expansion strain measured by the simplified method for measuring the amount of expansion as described in claim 1 or 2.

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