Method for estimating stress and strain history in cement-based composite materials and calcite particle aggregates

Abstract

The present invention relates to a method for estimating the stress and strain history in a cement-based composite material and an aggregate of calcite particles. In order to be widely applied to various structural materials with different elastic moduli and to measure the stress and strain history in a simple form, a plurality of calcite particles are embedded as stress sensors, the twin density of the calcite particles in the composite material mainly composed of cement that can elastically deform under an external force is measured after the composite material is subjected to an external force, and the twin density is converted into strain using an approximate formula set for the strain ε (%) generated in the composite material and the twin density Dtw (number / mm) of the calcite particles. Then, the strain is converted into stress using the elastic modulus of the composite material, thereby estimating the stress and strain history generated in the composite material. The approximate formula for strain-twin density is a common formula regardless of the elastic modulus of the composite material.

Description

Technical Field

[0001] The present invention relates to a method for estimating the stress and strain history in a composite material mainly composed of cement, and an aggregate of calcite particles. Background Art

[0002] In order to evaluate the stress and damage generated in a structural material mainly composed of cement, a method of inferring based on the impact sound or cracking sound has been carried out, but this depends on human intuition and experience and has low reliability.

[0003] For a concrete structural material, due to natural disasters such as earthquakes, tornadoes, typhoons, or accidents such as collisions by vehicles, a large external force may sometimes be temporarily applied. In this case, if the structural material does not break and undergoes deformation within the elastic limit, the structural material will recover after the external force is released, and thus it is impossible to correctly judge the magnitude of the force received by the structural material or what kind of stress is generated in which part.

[0004] In order to measure the internal stress in a structural material, a method of previously setting marks or sensors in the structural material to measure the existing stress, or a method of collecting cores and estimating the stress based on the rebound amount or the acoustic emission (AE) Kaiser effect (elastic waves generated during deformation and microdamage caused by external actions) is known.

[0005] When performing a safety evaluation of a concrete structure, it is important to know what kind of stress is generated in the structural material. Therefore, it is conceivable to obtain a stress history by setting strain sensors on the surface of the concrete material and continuously monitoring. However, it can be said that it is not realistic to continuously monitor such general structures as high-rise buildings, bridges, and tunnels for a long time. In addition, an electrical sensor is a foreign object for such a structural material, and it can be considered that it becomes a different mechanical property from the original structural material.

[0006] Accordingly, if the structural material itself has the ability to record old stresses and insights into large stresses that have occurred in the structural material in the past are obtained by measuring when necessary, it is considered that it will contribute greatly to the safety evaluation of the structure, and a technique for this has been proposed.

[0007] Patent Document 1 discloses the following: A test specimen of concrete is repeatedly sandwiched between pressure plates, a load exceeding the past stress history is applied to detect the Kaiser effect, and this operation is used to measure the stress history. Patent Document 2 discloses the following: For a measurement object containing calcite particles and capable of elastic deformation under an external force, the stress history of the measurement object is measured based on the change in the twin density of the calcite particles after being subjected to the external force.

[0008] Patent Document 3 discloses the following: For a measurement object embedded with a large number of calcite particles and capable of elastic deformation under an external force, the stress history of the measurement object is measured based on the proportion of calcite particles that undergo twin deformation after being subjected to an external force, improving the technology of Patent Document 2 for application under low-stress conditions.

[0009] Non-Patent Document 1 is related to Patent Document 2 and discloses the following method: From the results of a compression test on a sandstone specimen, a proportional relationship between twin density and differential stress was found. Additionally, the stress-strain relationship of a virtual rock was simulated using the distinct element method (DEM). Patent Document 4 discloses a technique for synthesizing calcite required for verification in Patent Document 2, Patent Document 3, and Non-Patent Document 1.

[0010] In a device using the Kaiser effect as in Patent Document 1, a load is applied to generate cracks, but cracks are also generated for various main reasons other than the material's history. Therefore, as a presumption of the history, it lacks reliability, and it cannot be used in a low-stress region where cracks do not occur.

[0011] In Patent Document 2 and Non-Patent Document 1, it was verified that the twin density of calcite particles changes according to the magnitude of the external force applied to the measurement object, and based on this, the stress history of the measurement object was measured. However, the relationship between stress and twin density varies depending on the elastic modulus of the measurement object. Therefore, it is necessary to find an appropriate relationship between stress and twin density for each measurement object. Additionally, in Patent Document 3, based on the proportion of calcite particles that undergo twin deformation among the calcite particles embedded in a measurement object that is embedded with a large number of calcite and capable of elastic deformation under an external force after being subjected to an external force, the stress history of the measurement object is measured. Similarly, in this case, it is also necessary to find an appropriate relationship between stress and the proportion of calcite particles that undergo twin deformation for each measurement object.

[0012] Prior Art Documents

[0013] Patent Documents

[0014] Patent Document 1: Japanese Patent Publication No. 2876007

[0015] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2008 - 286689

[0016] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2014 - 228511

[0017] Patent Document 4: International Publication No. 2012 / 108473

[0018] Non-Patent Documents

[0019] Non-Patent Document 1: Sakaguchi et al., "Elastic stress indication in elastically rebounded rock", Geophysical Research Letters, Vol. 38, L09316, doi: 10·1029 / 2011GL047055, 2011 (Sakaguchi et al. "Elastic stress indication in elastically rebounded rock", Geophysical Research Letters, vol. 38, L09316, doi: 10·1029 / 2011GL047055, 2011) Summary of the Invention

[0020] Problems to be Solved by the Invention

[0021] For an object to be measured of a structural material such as concrete, the following has been proposed: Measuring the stress history of the object to be measured based on the relationship between the stress caused by the applied external force and the twin density (Patent Document 2), or based on the relationship between the stress caused by the applied external force and the proportion of calcite particles that have undergone twin deformation (Patent Document 3). However, these methods cannot use the same relationship for objects to be measured with different elastic moduli. The object of the present invention is to provide a method that can be widely applied to various structural materials as long as the twin density and the elastic modulus are known, and can measure the stress history in a simple form.

[0022] Furthermore, the object of the present invention is also to provide a method of burying multiple calcite particles as stress sensors removably inside the object to be measured, collecting the multiple buried calcite particles from the object to be measured, and measuring the twin density of the collected multiple calcite particles, as well as a morphological example of multiple calcite particles suitable for implementing the above method.

[0023] Technical Means for Solving the Problems

[0024] In the method for estimating the stress and strain history in the cement-based composite material of the present invention for achieving the above object, a plurality of calcite particles 11 having a particle diameter of a specified size are embedded in the object to be measured 50 as stress sensors, and the stress and strain history of the object to be measured 50 is estimated. The method for estimating the stress and strain history is characterized in that the plurality of calcite particles 11 are non-twinned calcite particles, which are mixed in the cement composite material 12 at a specified mixing ratio and form an aggregate 10 of calcite particles integrally formed into a specified shape. The cement composite material 12 is pre-prepared such that the elastic modulus in the cured state becomes a specified value. One or more of the aggregates 10 of calcite particles are embedded in the object to be measured 50 in a form that can be taken out, such as non-shrinking mortar 60 or concrete structural material.

[0025] The second feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is a method for estimating the stress and strain history. A plurality of calcite particles 11 having a particle diameter of a specified size are embedded in the object to be measured 50 as stress sensors, and the stress and strain history of the object to be measured 50 is estimated. In the method for estimating the stress and strain history, the plurality of calcite particles 11 are non-twinned calcite particles, which are mixed in the non-shrinking mortar 60 at a specified mixing ratio and form an aggregate 10' of calcite particles having fluidity. The non-shrinking mortar 60 is pre-prepared such that the elastic modulus in the cured state becomes a specified value.

[0026] The aggregate 10' of calcite particles is embedded in the object to be measured 50 in a form that can be taken out while being filled into a recess 51 provided in the object to be measured 50.

[0027] The third feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is that the specified shape is a sphere, a polyhedron, or a flat plate.

[0028] The fourth feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is that the calcite particles 11 included in the aggregates 10 and 10' of calcite particles are colored.

[0029] The fifth feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is that for the aggregates 10 and 10' of calcite particles taken out from the object to be measured 50, the surface is ground until the twins of the calcite particles 11 can be observed.

[0030] The sixth feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is that for the ground calcite particle aggregates 10, 10', the twin density Dtw of the calcite particles is measured on one or more surfaces.

[0031] The seventh feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is that the relationship between the twin density Dtw of the calcite particles and the stress history σ generated in the object to be measured 50 is configured to correspond one-to-one for each elastic modulus of the cement composite material 12 or the non-shrinking mortar 60.

[0032] The eighth feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is that when the elastic modulus of the cement composite material 12 or the non-shrinking mortar 60 is uniquely fixed, the relationship between the twin density Dtw of the calcite particles and the stress history σ is configured to be linearly approximated.

[0033] The ninth feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is that in the conversion from the twin density Dtw of the calcite particles to the stress history σ, an approximate formula set for the strain ε generated in the object to be measured 50 and the representative value of the twin density Dtw of the calcite particles is used.

[0034] ε = 0.0094Dtw - 0.2 ············ (1)

[0035] The measured twin density Dtw of the calcite particles is converted into strain ε, and then the strain ε is converted into stress through the elastic modulus of the cement composite material 12 or the non-shrinking mortar 60, thereby estimating the stress history σ generated in the object to be measured 50.

[0036] The tenth feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is that the calcite particle aggregates 10, 10' contain untwinned synthetic calcite particles 11 with a particle size of 5 μm to 1.50 mm.

[0037] The eleventh feature of the method for estimating the stress and strain history in the cement-based composite material of the present invention is that the mixing ratio of the untwinned synthetic calcite particles 11 in the calcite particle aggregates 10, 10' is 0.3 vol% to 10 vol%.

[0038] In addition, the calcite particle aggregates 10, 10' of the present invention for implementing the method for estimating the history of stress and strain in the cement-based composite material are characterized in that a plurality of calcite particles 11 having a particle diameter of a specified size and serving as stress sensors are mixed and dispersed in a cement composite material 12 as a base material.

[0039] In addition, regarding the second feature of the calcite particle aggregate 10 of the present invention, it is characterized in that a plurality of calcite particles 11 having a particle diameter of a specified size and serving as stress sensors are mixed and dispersed in a cement composite material 12 as a base material, and the whole forms a specified shape.

[0040] The third feature of the calcite particle aggregate 10 of the present invention is that the specified shape is a sphere, a polyhedron or a flat plate.

[0041] The fourth feature of the calcite particle aggregates 10, 10' of the present invention is that the calcite particles 11 are colored.

[0042] The fifth feature of the calcite particle aggregates 10, 10' of the present invention is that it contains synthetic calcite particles 11 without twins and having a particle diameter of 5 μm to 1.50 mm.

[0043] The sixth feature of the calcite particle aggregates 10, 10' of the present invention is that the mixing ratio of the synthetic calcite particles 11 without twins is 0.3 vol% to 10 vol%.

[0044] Effects of the Invention

[0045] In the method for estimating the history of stress and strain of the present invention, for a cement-based composite material in which a large number of calcite particles are embedded as stress sensors and which can elastically deform under an external force, the twin density of the calcite particles after the composite material is subjected to an external force is measured, and the twin density is converted into strain through an approximate formula representing the relationship between strain and twin density, and then the strain is converted into stress. Thus, the stress and strain history of the composite material can be simply carried out in a common form regardless of the material.

[0046] In addition, in the method for estimating the history of stress and strain of the present invention, a plurality of calcite particles serving as stress sensors can be buried in the object to be measured in a retrievable manner, and the plurality of buried calcite particles are collected from the object to be measured, and the twin density of the collected plurality of calcite particles is measured.

[0047] In addition, according to the calcite particle aggregate of the present invention, the method for estimating the history of stress and strain in the cement-based composite material of the present invention can be suitably implemented. Description of the Drawings

[0048] Figure 1 It is a diagram showing the relationship between stress and twin density for various composites containing calcite particles and having different elastic moduli, which is clear as a prerequisite for the method of the present invention.

[0049] Figure 2 It is a diagram showing the relationship between stress and twin density for various composites containing calcite particles and having different elastic moduli, which is clear when applied to the method of the present invention.

[0050] Figure 3 It is a diagram explaining the concept of a method for measuring the stress and strain history of a composite containing calcite particles as a stress sensor. Figure 3 (a) thereof shows a state where no external force is acting. Figure 3 (b) thereof shows a state where a compressive force acts on the composite and the composite is compressed and deformed. Figure 3 (c) thereof shows a state where the external force is removed and the composite elastically recovers.

[0051] Figure 4 It is a flowchart showing the procedure for embedding synthetic calcite particles into an existing building.

[0052] Figure 5 It is an explanatory diagram showing an example of the shape of the aggregate of synthetic calcite particles of the present invention.

[0053] Figure 6 It is a main part sectional explanatory diagram showing an example of the embedding construction of the aggregate of synthetic calcite particles into an existing building as an object to be measured.

[0054] Figure 7 It is a flowchart showing the procedure for embedding synthetic calcite particles into a novel building.

[0055] Figure 8 It is a flowchart showing the procedure for collecting the aggregate of synthetic calcite particles of the present invention from an existing building.

[0056] Figure 9 It is a main part sectional explanatory diagram showing an example of the construction for extracting a part of the non-shrink mortar containing the aggregate of synthetic calcite particles from an existing building.

[0057] Figure 10 It is a main part sectional explanatory diagram showing the collected core extracted from a building, the aggregate of synthetic calcite particles cut out from the collected core, and the flat-shaped aggregate of synthetic calcite particles embedded in the collected core coplanar with the surface of the building.

[0058] Explanation of symbols

[0059] 10: Aggregate of synthetic calcite particles (aggregate of calcite particles)

[0060] 10': Aggregate of synthetic calcite particles (aggregate of calcite particles)

[0061] 11: Synthetic calcite particle (calcite particle)

[0062] 12: Cement composite material

[0063] 50: Building (object to be measured)

[0064] 50': Part of the building

[0065] 51: Bottom hole (depression)

[0066] 52: Drilling hole

[0067] 60: Non-shrinking mortar

[0068] 60': Part of the non-shrinking mortar

[0069] 70: Embedded part mark (mark)

[0070] 100: Sampling core

[0071] 200: Core drill

[0072] 210: Peripheral edge

[0073] 220: Center drill

[0074] P1 - P5: Programs Detailed implementation manners

[0075] Hereinafter, a method for estimating the stress and strain history in structural materials such as concrete according to an embodiment of the present invention will be described with reference to the accompanying drawings. The method for estimating the stress and strain history in structural materials such as concrete according to the present invention is common to the prior arts in Patent Document 2 or Non-Patent Document 1 in terms of containing calcite particles as stress sensors in the structural materials and focusing on the relationship between the stress generated by the external force applied to the structural materials and the twin density in the calcite particles (hereinafter referred to as "calcite twin density") to measure the stress history, but improves the problems of these prior arts.

[0076] For example, in Non-Patent Document 1, it was found through the compression test of sandstone that the calcite twin density is proportional to the differential stress. However, in the further research process, the proportional coefficient here contains elements related to strain and elastic modulus. Therefore, it can be considered that there are problems as a practical evaluation method. Furthermore, it is known that in the case where the structural material is a composite material mainly composed of cement, the elastic modulus changes according to the cement-water ratio. Ideally, a stress history measurement method that can be applied to structural materials with different elastic moduli should be provided.

[0077] By Figure 3 way of explaining the concept of a method for measuring the stress history of an object to be measured that includes calcite particles as stress sensors in a structural material. In Figure 3 each of (a) to Figure 3 (c), the left-side diagram shows a partial cross-section of the object to be measured in which strong particles and weak particles coexist. The stronger the particle, the darker the color, and the weaker the particle, the lighter the color. The white particles are stress sensors that plastically deform due to stress. The right-side diagram schematically shows that the strong particles elastically support the overall load using the connecting springs between the particles, and shows that the stress sensors are interposed therebetween.

[0078] Figure 3 (a) shows a state where no external force is acting, Figure 3 (b) shows a state where a compressive force acts on the object to be measured and the entire object to be measured elastically deforms in the compression direction, and the stress sensors also deform. Figure 3 (c) shows a state after the external force is removed. The entire object to be measured elastically recovers, and the stress and deformation disappear, but the stress sensors do not recover their shape and the stress history still exists. The measurement of the stress history in the object to be measured is completed based on the above concept. In calcite particles as stress sensors, due to the deformation when subjected to an external force, crystal planes that deform between simple crystal structures are generated as deformation twins. In addition, the so-called "calcite twin density" refers to the number of deformation twins per 1 mm length in the axial direction orthogonal to the e-plane where the twins are generated.

[0079] The magnitude of the deformation of the object to be measured when subjected to an external force in the compression direction depends on the elastic modulus of the entire object to be measured, which corresponds to Figure 3 the strength of the springs of the frame connecting the hard particles in each of the right-side diagrams of (a) to Figure 3 (c). That is, depending on the strength of the said springs, the remaining twin deformation in the calcite particles as stress sensors is different. Therefore, it is considered that if the elastic modulus of the object to be measured is different, the relationship between the stress and the twin deformation when subjected to an external force is also different. In Non-Patent Document 1, a relational expression between the change amount of the calcite twin density and the stress was obtained for sandstone, but it can be considered that the said relationship is not applicable to, for example, the case of a structural material formed of cement. Therefore, in the present invention, research has been conducted from the viewpoint of obtaining an appropriate relational expression when measuring the stress history for a wider range of structural materials.

[0080] The complex as the object to be measured contains a large number of calcite particles, and the calcite particles are synthetic calcite particles. The particle size of natural calcite particles is mostly excessively smaller than that of synthetic calcite particles, and stress cannot be determined. Moreover, there is substantially no twin-free substance in natural calcite particles. Therefore, natural calcite particles are not suitable for the method of estimating the stress and strain history in structural materials such as concrete based on the present invention. Therefore, in the method of estimating the stress and strain history in structural materials such as concrete based on the present invention, it is necessary to use synthetic calcite particles. The synthetic calcite particles are synthesized by the method for manufacturing calcite single crystals shown in Patent Document 4.

[0081] In the present invention, the following conditions are imposed on the synthetic calcite particles contained in the complex.

[0082] (a) Size of synthetic calcite particles

[0083] The shape of the synthetic calcite crystal is a parallelepiped, and the particle size is represented by the short side. If the particle size is too small, detection becomes difficult, and if it is too large, it will affect the strength of the complex. Therefore, as the particle size, the particle diameter is preferably in the range of 5 μm (0.005 mm) to 1.50 mm, more preferably 0.01 mm to 1.20 mm, and still more preferably 0.1 mm to 1.0 mm.

[0084] (b) Mixing ratio of synthetic calcite particles

[0085] In addition, in terms of being able to easily detect the particles without reducing the strength of the complex, as the mixing ratio of the synthetic calcite particles in the complex, it can be 0.3 vol% to 10 vol%, and more preferably set to 1 vol% to 5 vol%.

[0086] [Verification of the relationship between stress and twin density based on elastic modulus]

[0087] In the objects to be measured made of cements with different elastic moduli, the relationship between the stress generated by a compressive load and the twin density of calcite particles was obtained, and a comparative study was conducted on them. As the structural material formed of cement for each object to be measured for obtaining the stress-twin density relationship, a specific proportion of calcite particles was mixed. The calcite particles were synthesized in the following manner.

[0088] [A] Synthesis of calcite particles

[0089] The synthesis of calcite particles follows the method of Patent Document 4 and is carried out in the following steps.

[0090] (1) 5M ammonium adjustment

[0091] Prepare four 1-L beakers, add 400.2 g of ammonium nitrate to each, and add 1 L of water. While heating with a magnetic stirrer, mix until transparent.

[0092] (2) pH adjustment

[0093] Adjust the pH of the solution mixed in (1) to 7.50 before the reaction. Add ammonia when increasing the pH.

[0094] (3) Reaction preparation

[0095] Add 4 L of the pH-adjusted solution to a container. Add 36 g of calcium carbonate (9 g / L) thereto. Attach the handle to Teflon (registered trademark) and set it in an autoclave.

[0096] (4) Autoclave operation

[0097] The autoclave operation is carried out according to a procedure of raising the temperature to 180 °C and maintaining it at 180 °C for 12 hours, and then decreasing the temperature to 30 °C over 60 hours.

[0098] (5) Post-treatment, filtration

[0099] After the autoclave operation, the generated slurry is suction-filtered to obtain synthetic calcite.

[0100] 〔B〕Formation and test of the object to be measured

[0101] Using the cement for high-strength concrete, three types of objects to be measured were prepared with the ratio of cement to water set to 1.5 times the reference amount / 2 times the reference amount of the reference amount. Their respective elastic moduli vary depending on the water ratio, and according to the difference in the average elastic modulus E, they become hard cement (E: 10.1 GPa), medium cement (E: 8.6 GPa), and weak cement (E: 5.9 GPa).

[0102] Mix synthetic calcite particles with a particle size of 0.2 mm to 0.5 mm in each cement as the object to be measured at a ratio of 1 vol% to 5 vol%. After curing for four weeks, form them into a shape with a diameter of about 20 mm and a length of about 40 mm, and conduct a compression test. The test is carried out using a UH-1000 kN type testing machine (manufactured by Shimadzu Corporation) at atmospheric pressure, applying a stress from a low stress to the failure stress, and making a thin slice of the specimen at this time. Use a polarized light microscope to measure the twin density of more than dozens of calcite particles. The measurement is to scan the entire inspection surface with a polarized light microscope and calculate the representative value of the twin density for multiple calcite particles where the presence or absence of twins can be confirmed. The twin density of each specimen containing multiple calcite particles is taken as the representative value of the twin density with the mode value of the frequency distribution.

[0103] For each of the objects to be measured of the three types of cement, the relationship between the applied stress and the generated twin density is as Figure 1 shown. The results of measuring sandstone are also shown together in Figure 1 . From the Figure 1 shown results, it can be seen that the relationship between the stress of the object to be measured and the twin density is represented by a linear relational expression according to each material, but these relational expressions are different according to the elastic modulus of the material. That is, in order to convert the stress according to the twin density, it is necessary to obtain the relational expression for each material.

[0104] On the other hand, if the relationship between the strain and the twin density when a load is applied to each object to be measured is obtained separately, it is as Figure 2 shown. From Figure 2 , it can be seen that including sandstone, the strain ε (%) - twin density Dtw (number of twins / mm) for the objects to be measured made of each type of cement shows a distribution represented by a common straight line. The straight line is represented by

[0105] ε = 0.0094Dtw - 0.2 ············ (1)

[0106] . The twin density Dtw represents the modal value of the frequency distribution as the representative value of the twin density. In Figure 1 , Figure 2 , the Dtw on the horizontal axis represents the representative value (number of twins / mm) of the twin density.

[0107] Thus, as Figure 1 in the stress - twin density relationship, according to the material and elastic modulus of the object to be measured, the approximate expression representing the relationship varies depending on the material. In contrast, in the Figure 2 shown relationship between strain and twin density, it is represented by a single common approximate expression (1) regardless of the material and elastic modulus of the object to be measured.

[0108] In the conventional method based on Non-Patent Document 1, the stress of calcite particles and the twin density are converted to stress to estimate the stress. However, since the conversion formula varies depending on the material of the object to be measured, it cannot be carried out in a common form. In contrast, if the twin density is converted to strain by the approximate expression (1) representing the strain - twin density relationship, it can be carried out in a common form regardless of the material. Moreover, according to the relationship

[0109] σ = εE ············ (2)

[0110] between stress (σ), strain (ε), and elastic modulus (E), the strain can be converted to stress and the stress can be estimated.

[0111] In the method for estimating stress and strain based on the present invention described above, by simply adding synthetic calcite particles to a cement-based composite material, the stress generated in the composite material can be estimated by measuring the twin density of the calcite particles. When an electrical sensor is attached to the composite material as described above, this will become a foreign object for the composite material and inevitably affect the mechanical properties. However, in the case of the present invention, the mixed calcite particles originally exist in the cement and will not become foreign objects when added in small amounts.

[0112] Industrial applicability

[0113] The method for estimating the stress and strain history based on the present invention can be effectively applied to the following situations: checking whether a device or structure that is constantly stressed maintains a specified strength or whether the structure itself deteriorates after being subjected to an action that will not cause damage due to an earthquake or the like, or monitoring local stress concentration accompanying the deterioration of a device or structure.

[0114] As described above, according to the method for estimating the stress and strain history of a cement-based composite material based on the present invention, by measuring the twin density Dtw of the synthetic calcite particles contained in the object to be measured after an external force is applied, the stress and strain history generated in the object to be measured can be quantitatively estimated. Hereinafter, for the synthetic calcite particles as stress sensors, the embedding into a cement-based building (concrete structural material) as the object to be measured, the collection (recovery) of the embedded synthetic calcite particles from the building for measuring the twin density Dtw, and the measurement of the twin density of the collected synthetic calcite particles will be described respectively.

[0115] [Embedding of synthetic calcite particles into a building]

[0116] Figure 4 It is a flowchart showing the procedure for embedding synthetic calcite particles into an existing building.

[0117] First, as procedure P1, a synthetic calcite particle aggregate 10 is produced. As Figure 5As shown, the so-called synthetic calcite particle aggregate 10 described herein is formed by mixing a plurality (multiple) of synthetic calcite particles 11 serving as stress sensors into a cement composite material 12 as a base material and solidifying the whole into a specified shape. The cement composite material 12 as the base material (solid agent) is a composite material mainly composed of cement that can elastically deform under an external force. Specifically, it is equivalent to a composite material mainly composed of cement with a known average elastic modulus E prepared by changing the ratio of cement to water in the "〔B〕 Formation and test of the object to be measured" described above. For example, hard cement (E: 10.1 GPa), medium cement (E: 8.6 GPa), or weak cement (E: 5.9 GPa), etc.

[0118] In addition, in addition to being able to use the mixture of the cement and water, mortar can also be used as the cement composite material 12. In this case, the ratio of cement to sand in the mortar is, for example, 1:2 by mass, and the adjustment of the elastic modulus is carried out according to the water content. Synthetic calcite particles 11 with a particle diameter of, for example, 0.2 mm to 0.5 mm are mixed into the mortar adjusted to a specified elastic modulus in a content ratio of, for example, 1 vol% to 5 vol%.

[0119] Furthermore, the synthetic calcite particles 11 included in the synthetic calcite particle aggregate 10 are synthetic calcite particles without twins. The synthetic calcite particles without twins 11 can be synthesized by the "〔A〕 Synthesis of calcite particles" described above. By using the synthetic calcite particles without twins 11, the initial value of the twin density Dtw of the synthetic calcite particles becomes zero, so the estimation of the stress history generated in the object to be measured described later ( Figure 8 procedure P4) becomes easier.

[0120] Regarding the particle diameter (grain size) of the synthetic calcite particles 11 when the cement composite material 12 is mortar, it is preferably the same size as the grain size of the sand serving as the aggregate constituting the mortar. Specifically, for example, it is 63 μm (0.063 mm) to 2000 μm (= 2 mm). In addition, the so-called "particle diameter of the synthetic calcite particles" described in this specification refers to the short diameter of the rectangle circumscribing the largest projection plane. When the particle diameter of the synthetic calcite particles 11 is too large, the obtained synthetic calcite particle aggregate 10 is likely to not have sufficient strength required. On the other hand, when the particle diameter of the synthetic calcite particles 11 is too small, it becomes difficult to measure the twin density Dtw of the synthetic calcite particles in the crystal plane.

[0121] In addition, regarding the content ratio of the synthetic calcite particles 11 in the synthetic calcite particle aggregate 10, for example, it is preferably 0.3 vol% to 10 vol%, more preferably 1 vol% to 5 vol%. Thereby, while reliably preventing the strength reduction of the obtained synthetic calcite particle aggregate 10, the desired stress measurement (inspection) can be reliably performed.

[0122] Figure 5 (a) of which shows the synthetic calcite particle aggregate 10 formed into a spherical shape. Figure 5 (b) of which shows the synthetic calcite particle aggregate 10 formed into a cubic shape. Figure 5 (c) of which shows the synthetic calcite particle aggregate 10 formed into a flat plate shape. By using the synthetic calcite particle aggregate 10, the number of synthetic calcite particles required for measuring the twin density Dtw of the synthetic calcite particles can be ensured on the inspection surface. An example of the forming method of the synthetic calcite particle aggregate 10 will be described below.

[0123] [Forming Method of Synthetic Calcite Particle Aggregate 10]

[0124] For example, in the case of forming a spherical shape, synthetic calcite particles 11 with a particle diameter of 0.2 mm to 0.5 mm are mixed in the cement composite material 12 at a content ratio of 1 vol% to 5 vol%, and the mixture is placed in a mold having a spherical depression (cavity), and cured for a prescribed time (for example, four weeks), thereby forming the spherical synthetic calcite particle aggregate 10. Therefore, by changing the mold, the synthetic calcite particle aggregate 10 having a shape other than a sphere can also be suitably formed. In addition, in order to easily detect the occurrence of twin deformation in the measurement of the twin density Dtw during stress estimation, the synthetic calcite particles 11 can also be colored with a reagent such as alizarin red before being mixed in the cement composite material 12.

[0125] Regarding the size of the synthetic calcite particle aggregate 10 formed, for example, it is about 10 mm to 50 mm in terms of the maximum outer diameter. In addition, the size of the formed product varies according to the size of the bottomed hole 51 described later.

[0126] Return Figure 4 , as the program P2, select the embedding part of the synthetic calcite particle aggregate 10. As the embedding part of the synthetic calcite particle aggregate 10 into the existing building 50, it is preferably to select a place where stress concentration occurs in the design.

[0127] As the program P3, form a bottomed hole 51 for embedding the synthetic calcite particle aggregate 10 at the selected embedding part Figure 6(a)). Regarding the shape and size of the bottomed hole 51, it is a shape and size that does not affect the strength of the building 50. For example, for the synthetic calcite particle aggregate 10 with a maximum outer diameter of about 10 mm to 50 mm, a cylindrical bottomed hole with a diameter of 120 mm and a depth of 60 mm can be formed.

[0128] As the procedure P4, the synthetic calcite particle aggregate 10 is embedded into the bottomed hole 51 using the non-shrinking mortar 60 ( Figure 6 (b)). Specifically, the synthetic calcite particle aggregate 10 is mixed in midway when backfilling the bottomed hole 51 with the non-shrinking mortar 60.

[0129] As the procedure P5, a buried part mark (label) 70 is attached to the embedding part of the synthetic calcite aggregate 10 ( Figure 6 (d)). The buried part mark 70 can be attached to the center of the bottomed hole 51, for example. In addition, the size of the bottomed hole 51 (Φ120×60), the date of embedding the synthetic calcite particle aggregate 10 into the building 50, etc. can be noted.

[0130] The above is the embedding procedure of the synthetic calcite particles 11 of the synthetic calcite particle aggregate 10 into the existing building 50. Incidentally, it is also possible to embed the synthetic calcite particles 11 into the existing building 50 without using the synthetic calcite particle aggregate 10.

[0131] As Figure 6 (c) shows, when not using the synthetic calcite particle aggregate 10, the synthetic calcite particles 11 are mixed into the non-shrinking mortar 60 at a content ratio of, for example, 1 vol%, and then water is added to backfill the bottomed hole 51 with a pre-prepared mixture of synthetic calcite and mortar (synthetic calcite particle aggregate 10') to achieve a specified elastic modulus, thereby embedding the synthetic calcite particles 11 into the existing building 50.

[0132] In addition, as Figure 7 shown, regarding the embedding procedure of synthetic calcite particles into a novel building, instead of the Figure 4 procedure P3 and procedure P4, a procedure of "putting the synthetic calcite particle aggregate 10 into the stress concentration part in design during concrete pouring" is implemented. Next, the collection procedure of the synthetic calcite particle aggregate 10 embedded in the building 50 will be described.

[0133] Figure 8 is a flowchart showing the collection of the synthetic calcite particle aggregate 10 from the building 50 and the estimation of the stress history. In addition, for the sake of easy explanation, it is assumed that the synthetic calcite particles 11 are buried in the building 50 in the form of the synthetic calcite particle aggregate 10.

[0134] First, as program P1, a part of the non-shrinking mortar 60 containing a plurality of synthetic calcite particle aggregates 10 is extracted from the existing building 50. For the extraction, for example, a commercially available core drill 200 for concrete structural materials ( Figure 9 ) can be used to extract a part of the non-shrinking mortar 60 in a core shape. Hereinafter, a simple description will be given of the extraction of the embedded part of the synthetic calcite particle aggregate 10 using the core drill 200.

[0135] As Figure 9 (a) of FIG. shows, the core drill 200 (the illustration of the motor for rotationally driving the core drill 200 is omitted) includes a circumferential blade 210 at the front end of the hollow cylindrical body and a center drill 220 on the central axis inside the body. The circumferential blade 210 and the center drill 220 rotate integrally. The circumferential blade 210 is used to cut the building 50 into a core shape, and the center drill 220 is used to screw into the collected core cut into a core shape and capture the collected core into the core drill 200.

[0136] First, for example, the core drill 200 is positioned such that the embedding position mark 70 of the synthetic calcite particles is on the central axis of the center drill 220. While maintaining the relative positional relationship between the embedding position mark 70 and the center drill 220, the core drill 200 is rotated and advanced toward the building 50 side.

[0137] As Figure 9 (b) of FIG. shows, while rotating the core drill 200, it is penetrated into the building 50 to a predetermined depth until a plurality of synthetic calcite particle aggregates 10 are taken into the inside of the core drill 200.

[0138] As Figure 9 (c) of FIG. shows, when the core drill 200 is penetrated into the building 50 to a predetermined depth, the rotation of the core drill 200 is stopped and it is moved in the opposite direction. In this case, since the center drill 220 is screwed into the collected part 50' of the building and the part 60' of the non-shrinking mortar, by moving the core drill 200 in the non-rotating state in the opposite direction, the embedded part of the synthetic calcite particle aggregate 10 can be extracted from the building 50, and a drilled hole 52 is left in the building 50.

[0139] Return Figure 8 , as program P2, the synthetic calcite particle aggregate 10 is cut out from the collected core 100 extracted from the building 50. As Figure 10 (a) of FIG. shows, the collected core 100 extracted from the building 50 includes a part 60' of the non-shrinking mortar containing the synthetic calcite particle aggregate 10 and a part 50' of the building.

[0140] like Figure 10 As shown in (b), the portion 60' of the non-shrinkage mortar is cut out, and then the synthetic calcite particle assembly 10 is cut out to expose the crystal surfaces of multiple synthetic calcite particles 11. The cut surface of the synthetic calcite particle assembly 10 where the crystal surfaces of the synthetic calcite particles 11 are exposed becomes the inspection surface. The size of the inspection surface can be appropriately set according to the purpose.

[0141] In addition, if Figure 10 As shown in (c), when the flat-plate-shaped synthetic calcite particle aggregate 10 is coplanar with the surface (wall) of the building 50 or buried slightly shallower than the surface, it is not necessary to cut out the synthetic calcite particle aggregate 10 from the collection core 100, and the crystal faces of a plurality of synthetic calcite particles 11 can be appropriately exposed by grinding the surface to a degree that does not affect the strength of the object to be measured. In addition, since the measurement can be performed non-destructively, continuous observation such as comparison before and after the occurrence of an accident or the like can be performed.

[0142] return Figure 8 As a program P3, the twin density is measured for a plurality of synthetic calcite particles 11 with crystal faces exposed on the inspection surface. As described above, the "twin density of synthetic calcite particles" is defined by the number of twins contained in each predetermined length (e.g., 1 mm) in the axial direction perpendicular to the e-plane that generates twins, so it is necessary to measure the number of twins for each of the plurality of synthetic calcite particles 11 with crystal faces exposed on the inspection surface. The number of twins is measured, for example, by scanning the inspection surface in its entirety with an optical microscope and performing image analysis on the synthetic calcite particles 11 with crystal faces exposed. That is, since the refractive index or reflectivity changes with the deformation of the crystal lattice of the synthetic calcite particles 11, it is easy to determine whether there are twins in the synthetic calcite particles 11 by analyzing the change in the refractive index or reflectivity. Thus, for each of the plurality of synthetic calcite particles 11 with crystal faces exposed, the number of twins contained in each predetermined length (e.g., 1 mm) in the axial direction perpendicular to the e-plane that generates twins is measured. The average value of the number of twin crystals contained per the measured predetermined length is the twin density Dtw of the synthetic calcite.

[0143] Subsequently, as program P4, the stress history generated in the object to be measured is estimated. As described above, the average twin density Dtw of multiple synthetic calcite particles present in the inspection object area of a specified size depends on the magnitude of the external force. As the external force increases, the average twin density of the synthetic calcite particles tends to increase. Specifically, the average twin density Dtw of the synthetic calcite particles is in a proportional relationship with the magnitude of the external force. Therefore, based on the degree of change of the obtained average twin density Dtw with respect to the initial value (e.g., 0), the stress history generated in the object to be measured (building 50) can be estimated.

[0144] Therefore, for example, when the elastic modulus E of the cement composite material 12 of the synthetic calcite particle aggregate 10 is adjusted to 10.1 GPa, the twin density Dtw of the synthetic calcite particles measured in the program P3 is substituted into Figure 1 the stress-calcite twin density relationship for hard cement E: 10.1 GPa therein, whereby the stress history σ generated in the object to be measured (building 50) can be estimated.

[0145] Incidentally, the elastic modulus E of the cement composite material 12 is known, but in the case where there is no stress-calcite twin density relationship (linear approximation formula) in Figure 1 (for example, when 10.1 GPa < E < 29.3 GPa), the twin density Dtw of the synthetic calcite particles measured in the program P3 is substituted into Figure 2 the strain-calcite twin density relationship of the (1) shown therein, whereby the strain history ε generated in the object to be measured (building 50) is estimated. Subsequently, the estimated strain history ε is multiplied by the elastic modulus E of the cement composite material 12, whereby the stress history σ generated in the object to be measured (building 50) can be estimated.

[0146] In addition, for the buried synthetic calcite particle aggregate 10' ( Figure 6 of (c)), the stress history generated in the building 50 can also be appropriately estimated by appropriately recovering it from the building 50 according to the collection procedure of the synthetic calcite particles shown in Figure 8 and the measurement procedure of the twin density Dtw of the synthetic calcite particles for the collected core.

[0147] As described above, according to the method for estimating the stress and strain history in the cement-based composite material based on the present invention, the plurality of synthetic calcite particles 11 are untwinned calcite particles, which are mixed in the cement composite material 12 at a prescribed mixing ratio and form an aggregate 10 of calcite particles integrally formed into a prescribed shape (e.g., sphere, polyhedron, flat plate). The cement composite material 12 is pre-prepared such that the elastic modulus in the cured state becomes a prescribed value. Moreover, one or more of the aggregates 10 of calcite particles are buried in the building 50 in a form that can be taken out, such as non-shrinkage mortar 60 or a concrete structural material. Thus, the embedding of the synthetic calcite particles 11 as stress sensors into the building 50 and the collection (recovery) from the building 50 become easy, and the measurement of the twin density Dtw of the recovered synthetic calcite particles becomes easy.

[0148] In addition, a plurality of untwinned synthetic calcite particles 11 are mixed in the non-shrinkage mortar 60 at a prescribed mixing ratio and form a flowable aggregate 10' of calcite particles. The non-shrinkage mortar 60 is pre-prepared such that the elastic modulus in the cured state becomes a prescribed value. Even when it is filled into the bottomed hole 51 provided in the building 50 and can be buried in the building 50 in a form that can be taken out, the embedding of the synthetic calcite particles 11 as stress sensors into the building 50 and the collection (recovery) from the building 50 also become easy, and the measurement of the twin density Dtw of the recovered synthetic calcite particles becomes easy.

[0149] When the synthetic calcite particles 11 are colored with a reagent such as alizarin red, it becomes easy to confirm whether the synthetic calcite particles 11 with crystal faces exposed on the inspection surface have twins.

[0150] Furthermore, according to the method for estimating the stress and strain history in the cement-based composite material based on the present invention, the relationship between the twin density Dtw of the synthetic calcite particles and the stress history σ generated in the building 50 is configured to be linearly approximated to each other for each elastic modulus of the cement composite material 12 or the non-shrinkage mortar 60. Therefore, the stress history σ generated in the building 50 can be uniquely estimated based on the measured twin density Dtw of the synthetic calcite particles.

[0151] In addition, the relationship between the twin density Dtw of the synthetic calcite particles and the strain history ε generated in the building 50 is configured to be linearly approximated without depending on the respective elastic moduli of the cement composite material 12 or the shrinkage-compensating mortar 60. Therefore, even though the elastic modulus E of the cement composite material 12 or the shrinkage-compensating mortar 60 is known, even when the relationship between the twin density Dtw of the synthetic calcite particles and the stress history σ generated in the building 50 is not configured to be linearly approximated, the strain history ε generated in the building 50 can be uniquely estimated based on the measured twin density Dtw of the synthetic calcite particles. Moreover, by multiplying the estimated strain history ε by the known elastic modulus E, the stress history σ generated in the building 50 can be uniquely estimated.

Claims

1. A method for estimating the stress and strain history in a cement-based composite material, in which a plurality of calcite particles (11) having a specified particle diameter are embedded as stress sensors in an object to be measured (50), and the stress and strain history of the object to be measured (50) is estimated. The method for estimating the stress and strain history is characterized in that the plurality of calcite particles (11) are untwinned calcite particles, which are mixed in a cement composite material (12) at a specified mixing ratio and form an aggregate (10) of calcite particles integrally formed into a specified shape, and the cement composite material (12) is pre-prepared such that the elastic modulus in the cured state becomes a specified value. one or more of the aggregates (10) of calcite particles are embedded in the object to be measured (50) in a form that can be taken out, such as non-shrink mortar (60) or a concrete structural material. The twin density Dtw of the calcite particles in the aggregate (10) of calcite particles after being subjected to an external force is measured, and the twin density Dtw is converted into the strain ε according to an approximate formula representing the relationship between the strain ε generated in the object to be measured (50) and the twin density Dtw, and then the strain ε is converted into the stress σ.

2. A method for estimating the stress and strain history in a cement-based composite material, in which a plurality of calcite particles (11) having a specified particle diameter are embedded as stress sensors in an object to be measured (50), and the stress and strain history of the object to be measured (50) is estimated. The method for estimating the stress and strain history is characterized in that the plurality of calcite particles (11) are untwinned calcite particles, which are mixed in non-shrink mortar (60) at a specified mixing ratio and form an aggregate (10') of calcite particles having fluidity, and the non-shrink mortar (60) is pre-prepared such that the elastic modulus in the cured state becomes a specified value. the aggregate (10') of calcite particles is embedded in the object to be measured (50) in a form that can be taken out while being filled into a recess (51) provided in the object to be measured (50). The twin density Dtw of the calcite particles in the aggregate (10') of calcite particles after being subjected to an external force is measured, and the twin density Dtw is converted into the strain ε according to an approximate formula representing the relationship between the strain ε generated in the object to be measured (50) and the twin density Dtw, and then the strain ε is converted into the stress σ.

3. The method for estimating the stress and strain history in a cement-based composite material according to claim 1, characterized in that the specified shape is a sphere, a polyhedron or a flat plate.

4. The method for estimating the stress and strain history in a cement-based composite material according to claim 1 or 2, characterized in that the calcite particles (11) included in the aggregates (10, 10') of calcite particles are colored.

5. The method for estimating the stress and strain history in a cement-based composite material according to claim 1 or 2, characterized in that For the calcite particle aggregate (10, 10') taken out from the object to be measured (50), the surface is polished until the twins of the calcite particles (11) can be observed.

6. The method for estimating the stress and strain history in a cement-based composite material according to claim 5, characterized in that For the polished calcite particle aggregate (10, 10'), the twin density Dtw of the calcite particles is measured on one or more surfaces.

7. The method for estimating the stress and strain history in a cement-based composite material according to claim 6, characterized in that When claim 1 is cited, in the case where the elastic modulus of the cement composite material (12) is uniquely fixed, the relationship between the twin density Dtw of the calcite particles and the stress history σ is approximated by a straight line. When claim 2 is cited, in the case where the elastic modulus of the non-shrinkage mortar (60) is uniquely fixed, the relationship between the twin density Dtw of the calcite particles and the stress history σ is approximated by a straight line.

8. The method for estimating the stress and strain history in a cement-based composite material according to claim 6, characterized in that In the conversion from the twin density Dtw of the calcite particles to the stress history σ, an approximate formula set for the representative value of the strain ε generated in the object to be measured (50) and the twin density Dtw of the calcite particles is used. ε = 0.0094Dtw - 0.2 ············ (1) The measured twin density Dtw of the calcite particles is converted into strain ε. When claim 1 is cited, the strain ε is converted into stress through the elastic modulus of the cement composite material (12), thereby estimating the stress history σ generated in the object to be measured (50). When claim 2 is cited, the strain ε is converted into stress through the elastic modulus of the non-shrinkage mortar (60), thereby estimating the stress history σ generated in the object to be measured (50).

9. The method for estimating the stress and strain history in a cement-based composite material according to claim 1 or 2, characterized in that The calcite particle aggregate (10, 10') contains synthetic calcite particles (11) without twins having a particle diameter of 5 μm to 1.50 mm.

10. The method for estimating the stress and strain history in a cement-based composite material according to claim 1 or 2, characterized in that The mixing ratio of the synthetic calcite particles (11) without twins in the calcite particle aggregate (10, 10') is 0.3 vol% to 10 vol%.

11. A calcite particle aggregate, characterized in that A plurality of calcite particles (11) having a particle diameter of a specified size and serving as stress sensors are mixed and dispersed in a cement composite material (12) as a base material, and the whole forms a specified shape and can be embedded in an object to be measured (50) and taken out. The base material is pre-prepared such that the elastic modulus in the cured state becomes a specified value. The calcite particle aggregate can easily ensure the number of calcite particles (11) required for measuring the twin density Dtw of the calcite particles (11) after being subjected to an external force.

12. The calcite particle aggregate according to claim 11, wherein: The specified shape is a sphere, a polyhedron, or a flat plate.

13. The calcite particle aggregate according to claim 11, wherein: The calcite particles (11) are colored.

14. The calcite particle aggregate according to claim 11, wherein: It contains twin-free synthetic calcite particles (11) having a particle diameter of 5 μm to 1.50 mm.

15. The calcite particle aggregate according to claim 14, wherein: The mixing ratio of the twin-free synthetic calcite particles (11) is 0.3 vol% to 10 vol%.

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