JP7762038B2 - Method for measuring the amount of expansion of hydraulically hardened concrete and method for estimating the amount of restrained expansion of expansive concrete - Google Patents

Description

The present invention relates to a method for measuring the amount of expansion of expansive concrete.

The amount of expansion of expansive concrete is typically measured in accordance with the Test Method for Restrained Expansion of Expansive Concrete in a Uniaxially Confined State (Method A) specified in Appendix B (Reference) of JIS A 6202. However, because specialized measuring equipment is required, only a limited number of institutions can perform this test, and the measurement requires skill, so the number of people who can perform the test 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, and mixing the concrete 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.

JP 2013-15382 A

The present invention provides a simple measurement method that can obtain measurement results equivalent to the restrained expansion of expansive concrete obtained using the JIS A 6202 test method, without requiring a large number of people or significant effort.

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, comprising: attaching a strain gauge 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 cylindrical formwork with a 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 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] A 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 amount 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 expansion amount measurement method described in any one of claims 1 to 3.

According to the present invention, the amount of expansion of a hydraulically hardened body can be measured using a simple method without requiring a large number of people or significant effort, thereby making it possible to estimate the amount of restrained expansion of expansive concrete.

An explanatory diagram showing the external shape of the cylindrical formwork and the position where the strain gauges are attached.

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 cylindrical formwork with a 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 to determine the amount of expansion. This method will be explained in detail below.

<Hydraulic material>
The hydraulic material in the measurement method of the present invention includes cement, expansive material, fine aggregate, and coarse aggregate having a maximum dimension of 10 mm or less.

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

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

The fine aggregate used in hydraulic materials is the same as that typically used in mortar concrete. Specifically, the aggregate should contain 85% or more particles of 5 mm or less. It is also preferable that the content of particles greater than 5 mm is 5% or less, and it is even more preferable that the content of particles less than 1.2 mm is 50% or more, and that the content of particles less than 2.5 mm is 70% or more.

The coarse aggregate used for hydraulic materials is the same as the coarse aggregate typically used in concrete, with a maximum size of 10 mm or less. Using coarse aggregate larger than 10 mm will result in greater variance in measured strain values. Furthermore, sizes between 1.2 and 10 mm are preferred, with 2.5 to 6 mm being even more preferable. For example, No. 7 crushed stone can be used.

The ratio of fine aggregate to coarse aggregate by mass (mass of fine aggregate/mass of coarse aggregate) is preferably 1.0 to 3.5, and more preferably 1.2 to 2.75.

The amount of aggregate (fine aggregate and coarse aggregate) mixed is preferably 170 to 380 parts by mass per 100 parts by mass of cement and expansive agent combined. 200 to 350 parts by mass is more preferable, and 250 to 300 parts by mass is even more preferable.

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; for example, tap water can be used. The amount of water to be added is preferably 40 to 60 parts by weight per 100 parts by weight of the total of cement and expansive agent.

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

<Formwork>
The formwork used in the measurement method of the present invention is a cylindrical formwork with a diameter of 5 cm and a length of 10 cm. The formwork is preferably thin, with a thickness of 2.0 mm or less. If the thickness exceeds 2 mm, there is a risk of the measurement sensitivity of the strain gauge decreasing. A thickness of 0.3 to 1.0 mm is more preferable. There are no particular restrictions on the material of the cylindrical formwork, but steel is preferred in terms of strength, etc.

<Strain gauge>
The strain gauge is attached to the outer surface of the cylindrical formwork in 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.

<Preparation of hydraulic hardened body>
A hydraulically hardened body is produced by filling a cylindrical formwork with a hydraulic material 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.

<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 taken as the amount of expansion strain of the hydraulically hardened body.

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.

In this 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 expansive concrete, "Taiheiyo Expan" should also be used in this measurement method.

Here, expansive additives are classified into type 20 and type 30 based on their performance. When used for the purpose of shrinkage compensation in ordinary concrete, an expansive additive with a standard usage amount of 20 kg/ ^m³ is called type 20, and an expansive additive with a standard usage amount of 30 kg/ ^m³ is called type 30. The mixing amount of expansive additive in the hydraulic material of the present invention is based on 6.7 parts by mass per 100 parts by mass of the total of cement and expansive additive when type 20 is used. On the other hand, when type 30 is used, the mixing amount is based on 10 parts by mass per 100 parts by mass of the total of cement and expansive additive.

In this invention, the term "same type of cement" refers to the same type of cement. For example, if ordinary Portland cement is used in expansive concrete, ordinary Portland cement should also be used in this measurement method.

In this invention, "the same type of aggregate" means 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 this is difficult to obtain, aggregate of the same rock type can be used.

Regarding aggregate, the amount of fine aggregate mixed is preferably 170 to 380 parts by mass per 100 parts by mass of cement and expansive additive combined. Furthermore, from the perspective of the error with the restrained expansion rate of expansive concrete, the ratio of fine aggregate to coarse aggregate of 10 mm or less is preferably a mass ratio (fine aggregate mass/coarse aggregate mass) of 1.0 to 3.5, more preferably 1.2 to 2.75. 2.0 is used as the standard.

The standard amount of water to be mixed (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 roughly the same mass ratio.

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

The following provides a detailed explanation of this measurement method using examples, but the method is not limited to these examples.

(1) Preparation of the cylindrical formwork A steel formwork measuring φ5 × 10 cm (manufactured by Maeda Manufacturing Co., Ltd., thickness: 0.3 mm) was used as the cylindrical formwork. 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).

(2) Preparation of hydraulically hardened body Hydraulic materials were prepared using the materials shown 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 to which a strain gauge was attached. After filling, the top surface was covered with plastic film and the formwork was left to cure in air for 7 days under conditions of 20°C and 60% humidity to prepare hydraulically hardened body specimens. Three specimens were prepared for each level.

<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/ ^cm3
3) Coarse aggregate: Sakuragawa No. 7 crushed stone, size 2.5-6 mm, density 2.64 g/ ^cm3
4) Expansive material: concrete expansive material "Taiheiyo Hyperexpan", manufactured by Taiheiyo Materials Co., Ltd. 5) Water: tap water 6) Admixture: AE water reducer "Master Polyhede 15S", manufactured by Pozzolith Solutions Co., Ltd.

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

(4) Measurement of the amount of restrained expansion of expansive concrete by JIS method The amount of restrained expansion (rate of change in length) 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. Sakuragawa crushed stone (dimensions 5-20 mm; density 2.64 g/cm ³ ) was used as the coarse aggregate. The amount of restrained expansion of this expansive concrete was 206×10 ^-6 .

*P is the total amount of cement and expansive material

(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 amounts in Test Examples 1 to 6 were values within an error of 10% of the restrained expansion amount 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 amount was 10% or more larger than the restrained expansion amount.

1 Cylindrical formwork 2 Strain gauge 3 Lead wire 4 Strain amount measuring device 5 Hydraulic hardened body

Claims (3)

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, where the maximum dimension of the coarse aggregate contained is 10 mm or less, is filled into a φ5 x 10 cm cylindrical formwork on the outer surface of which a strain gauge with a gauge length of 5 mm or less is attached along the circumferential direction at the center position in the height direction, and the amount of expansion strain after hardening is measured. 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. 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.