JP5947036B2 - Method of measuring materials such as concrete whose elastic modulus is unknown by the UCI method - Google Patents

Description

  The present invention is a natural material (stone, aggregate, wood, earth, etc.) or an alloy whose material is unknown, or a cured material (such as ready-mixed concrete, mortar, cement paste, gypsum, plaster, resin before curing), etc. The present invention relates to a method of measuring a material whose elastic modulus cannot be grasped with sufficient accuracy in advance, such as a semi-finished product, by a UCI (Ultrasonic Contact Impedance) method.

  Important physical properties as the mechanical properties of the material are elastic modulus and strength. If these two physical properties are known, a basic design is possible, and methods for accurately measuring these have been established by various tests.

  There are two types of test methods for measuring the elastic modulus and strength, roughly divided into (1) destructive test and (2) non-destructive test. Among these, the destructive test (1) is a test that is performed until the material is destroyed, and the measurement accuracy is generally high, but the material used in the test cannot be used again. Cannot be tested. On the other hand, the nondestructive test (2) is a test performed without destroying the material, and the measurement accuracy is generally low. However, since the material used for the test can be reused, the actual material itself is tested. can do.

  For materials manufactured under highly controlled conditions, such as industrial products, there is little variation in the physical properties of the material actually used and the specimen to be destructively tested. It is done.

  On the other hand, natural materials (stone, aggregate, wood, soil, etc.) and hardened materials (fresh concrete, mortar, cement paste, gypsum, plaster, resin before hardening, etc.) are collected, temperature history, age, etc. Therefore, a non-destructive test that can test the actual material itself is desirable.

  For example, taking concrete as an example, technologies related to concrete strength estimation methods based on nondestructive and microfractures.Conventional technologies for concrete strength estimation methods based on nondestructive and microdestructive methods include the rebound method, scratch method, pin penetration method, There are many types such as needle penetration method, ultrasonic method, shock elastic wave method, resonance method and so on.

  The rebound degree method is a non-destructive inspection method that hits the concrete surface with a rebound hammer, measures the surface hardness of the concrete from the rebound distance of the weight, and estimates the strength using a conversion formula. Yes. However, since this method requires the skill of an inspector, the Schmidt hammer method developed by Dr. Schmidt in Switzerland in 1948 is an example of its application. The built-in hammer uses a spring force to move the concrete surface. Stroke, the degree of repulsion (R value) is substituted into the strength estimation formula, and the compression strength is estimated.

  The shock elastic wave method applies a shock to the surface of a concrete structure and receives internal defects and stress waves reflected on the back of the structure with a receiving sensor. Defects are determined.

  In the ultrasonic method, a reflected wave or transmitted wave from an ultrasonic structure radiated from a piezoelectric element brought into contact with the surface of a concrete structure is received, and an internal defect or thickness of the structure is inspected.

The following patent document describes an application of this ultrasonic method as a laser ultrasonic exploration method [applying a pulsed laser beam to the exploration target to cause rapid thermal expansion on or near the surface of the exploration target, This is a method of propagating the expansion strain as an elastic wave (ultrasonic wave) into the object to be searched. By observing elastic waves, it is possible to detect defects in the exploration target and to measure physical properties (Kazuji Yamanaka “Principle and Application of Laser Ultrasound Method” Nondestructive Inspection, Vol. 49, No. 5, p292- 299)].
JP 2002-296244 A

  In this patent document 1, the surface of a concrete structure to be diagnosed is irradiated with a pulsed laser beam to generate an elastic wave due to thermal expansion, and the surface during irradiation is collimated by a laser interferometer that collimates the surface of the part to be diagnosed. Waves and elastic waves are detected over time, and the presence or absence of internal defects or buried objects in the concrete structure at the diagnosis site is diagnosed from the change in waveform from the detection of the surface wave to the detection of the final elastic wave.

Moreover, the concrete strength estimation method like the following patent document 2 is also proposed.
Japanese Patent No. 3672527

  This Patent Document 2 collects a plurality of concrete samples, and measures a Vickers hardness HV of a portion not affected by neutralization and measures a compressive strength Fc for each of the collected samples. Based on the measurement results of the hardness HV and the compressive strength Fc, the relationship between the Vickers hardness HV of concrete and the compressive strength Fc is obtained in advance, and the compressive strength Fc is affected by the neutralization of the concrete to be estimated. The concrete in which the compressive strength Fc is estimated using the relationship obtained in advance from the measurement result of the Vickers hardness HV of the concrete in which the Vickers hardness HV is measured for a portion that is not the target and the compressive strength Fc is to be estimated The compressive strength Fc is estimated.

  Patent Document 2 has an effect that the compressive strength of concrete can be estimated with high accuracy over a wide strength range without being affected by the neutralized portion of the concrete.

  The prior art related to the non-destructive / micro-destructive concrete strength estimation method can be mainly divided into two, one is to give vibrations such as ultrasonic waves and shock waves, to estimate the elastic modulus of the material, This is a method of estimating the strength from the elastic modulus, and the other is a microdestructive test in which the strength is estimated by scratching the concrete surface with a nail or a needle.

  In general, the elastic modulus and strength of concrete have a positive correlation, but are not proportional, so there is a limit to the accuracy in estimating strength from the elastic modulus. Therefore, it is necessary to perform a destructive test in order to estimate an accurate strength. However, the method of damaging the surface is difficult to apply unless the concrete has low strength, and sufficient accuracy cannot be ensured at the concrete strength level that is generally used at present. In addition, it is important to have a short measurement time and portability of the testing machine, taking into account the on-site measurement.

  In Patent Document 2, a plurality of concrete samples are collected and measurements are performed on the collected samples. A small cylindrical concrete core is sampled, and the sampled core is removed by a concrete cutter. A test piece having a thickness of about 10 mm is cut out by cutting the sample parallel to the surface, and the measurement surface (cut surface) is polished to a mirror finish. In addition, in order to eliminate the influence of the neutralized part of the concrete surface on the measurement of the Vickers hardness HV, for example, a phenolphthalein solution is applied to the concrete piece separated from the test piece by the above-mentioned cutting, and the color changes. The neutralization depth C, which indicates how much neutralization is progressing from the concrete surface, is measured by confirming the region in which the neutralization occurs (the neutralized portion is not discolored) or the like.

  By the way, UCI (Ultrasonic Contact Impedance) method is known as a method for estimating the hardness of a measurement material from a change in resonance frequency before and after contact with a measurement sensor. According to this UCI method, measurement is possible with a portable testing machine, measurement on site is easy, and one measurement time is short.

  In the UCI method, when a rod vibrating at a constant frequency is brought into contact with a material, the frequency changes in accordance with the indentation area and the elastic modulus, and the indentation area is back-calculated from the change in frequency, and the hardness (= (Load / indentation area). The actual measurement is performed by pressing the rod tip with Vickers diamond against the measurement material.

  However, in the UCI method, the indentation area can be calculated backward from the change in frequency because the elastic modulus of the measurement material is known. That is, the hardness can be estimated by the UCI method because the value of the elastic modulus needs to be known in advance with sufficient accuracy. However, the case where the elastic modulus can be grasped in advance as described above is limited to a material that is highly controlled and manufactured such as an industrial product as described above.

  On the other hand, natural materials and hardened materials cannot grasp the elastic modulus with sufficient accuracy in advance. For natural materials such as stone, the elastic modulus may vary greatly depending on slight differences in the sampling position, and for concrete, the elastic modulus varies greatly depending on the curing conditions (temperature, humidity, demolding time, etc.) and age. . Therefore, in order to obtain an accurate result, it is necessary to measure the elastic coefficient of the material itself, and the elastic coefficient cannot be determined in advance.

  From the above, it can be said that the UCI method is originally a test method for industrial products, and it is difficult to apply to natural materials and cured materials. These difficulties are caused by the fact that the elastic modulus is indefinite depending on conditions (it cannot be measured with sufficient accuracy unless the material itself is measured).

  Furthermore, when the concrete strength is estimated by the UCI method, as described above, the measured value by the UCI method depends not only on the hardness of the material but also on the surface roughness and elastic modulus of the material. The modulus of elasticity changes from moment to moment and is difficult to apply to concrete surfaces where the surface roughness is not constant due to diversion of the wooden formwork. Unlike metal materials, concrete changes in strength and elastic modulus over time.

  Moreover, since concrete is a composite material of an aggregate and a cement matrix, if the number of measurement points is small in the local measurement such as the UCI method, the measurement may not be representative of the whole.

  The object of the present invention is to eliminate the inconvenience of the conventional example, and since the elastic modulus cannot be grasped with sufficient accuracy in advance, the hardness of the natural or hardened material using the UCI method, which has been impossible until now, It is possible to measure the strength, so that sufficient measurement accuracy can be ensured, and it is possible to measure with a portable testing machine, easy on-site measurement, and one measurement time is short. It is possible to fully utilize the advantages of the UCI method of Tesumi, and by applying this, it is possible to estimate the strength of the concrete surface by the UCI method. It is to provide a measurement method by the UCI method.

The invention of claim 1, wherein for achieving the object, a method of estimating the hardness from the change in the resonant frequency of the measuring sensor contacts the front and rear of UCI (Ultrasonic Contact Impedance) measured material method involves the use of measurement The indentation area is constant between the material surface and the rod, and natural materials (stone, aggregate, wood, earth, etc.) and alloys with unknown materials, hardened materials (green concrete, mortar, cement paste, plaster) Thickness that can secure a thickness that does not cause indentation on measurement materials whose elastic modulus cannot be determined in advance, such as those after curing of semi-finished products before curing, etc. The gist is to determine the elastic coefficient using a correlation between the vibration frequency and the elastic coefficient prepared in advance from the change in the vibration frequency by measuring with a thin insertion material of an industrial product.

  As described above, the UCI method uses the fact that when a rod that vibrates at a constant frequency is brought into contact with the material, the frequency changes according to the indentation area and the elastic modulus of the material, and the indentation area is determined from the change in frequency. This is a method of calculating the hardness (= load / indentation area) by back calculation.

  In a general UCI testing machine, the tip of a rod with a Vickers diamond has an acute tip, and when the measurement material is a natural material or a cured material, it cannot always be in contact with the same area.

  According to the first aspect of the present invention, without replacing the tip of the rod with the Vickers diamond with a flat tip (the rod cannot be replaced with a general UCI testing machine), the indentation area is always constant. The frequency change value measured through the insert material can be constant and the frequency change value measured through the insert material changes depending on the elastic modulus of the measurement material. And the elastic modulus (data obtained by placing the insertion material on the concrete) are obtained, the elastic modulus can be estimated.

  The present invention according to claim 2 grasps the correlation between the change in the frequency and the elastic coefficient when an insertion material is used in advance, and the change in the frequency of the measurement material is detected by the UCI tester via the insertion material. The measurement method according to claim 1, wherein the elastic coefficient is determined by measuring and using the correlation between the vibration frequency and the elastic coefficient prepared in advance from the change in the vibration frequency. Measure the number change, estimate the indentation area from the change in frequency and elastic modulus, and based on the correlation between the indentation area and the hardness or strength obtained from the same material in advance, hardness or strength The gist of this is to estimate.

  According to the second aspect of the present invention, it is possible to measure the hardness or strength of a natural material or a cured material by the UCI method using the estimation of the elastic modulus of the first aspect.

  The present invention described in claim 3 is a method for estimating the strength of the concrete surface. A thin insert material of an industrial product is pasted on the surface of the concrete formwork at the planned measurement position, and various kinds of concrete are prepared in advance with the same composition as the concrete to be measured. Compressive strength and elastic modulus at the age of the material are measured with a UCI testing machine, a calibration curve is prepared, and the measured value of the surface hardness and the estimated elastic modulus are used to calculate the concrete using the calibration curve. The gist of this is to estimate the intensity.

  According to the third aspect of the present invention, since the measured value by the UCI method depends not only on the hardness of the material but also on the surface roughness and the elastic coefficient of the material, the elastic coefficient of the material changes every moment. Difficult to apply to concrete surfaces where the surface roughness is not constant for diverting the formwork, and since concrete is a composite of aggregate and cement matrix, local measurements like UCI method Then, when the number of measurement points is small, it is possible to eliminate the inconvenience that the measurement may not be representative of the whole.

  In the case of concrete, it is possible to accurately estimate the surface strength and elastic modulus of concrete by nondestructive and microdestructive tests. This makes it possible to check the strength of new buildings. Since the local strength can be estimated, it is possible to grasp the strength distribution due to the difference of several centimeters, such as the strength of the concrete surface and the inside.

  As described above, the measurement method by the UCI method of the material having the unknown elastic modulus of the concrete according to the present invention uses the UCI method which has been impossible until now because the elastic modulus cannot be grasped with sufficient accuracy in advance. This makes it possible to measure the hardness or strength of all natural materials and hardened materials, which ensures sufficient measurement accuracy and can be measured with a portable testing machine, facilitating on-site measurement. Furthermore, the advantage of the UCI method that one measurement time is short can be fully utilized.

  By applying this, in the case of concrete, it is possible to accurately estimate the surface strength and elastic modulus of the concrete by nondestructive and microdestructive tests. This makes it possible to check the strength of new buildings. Since the local strength can be estimated, it is possible to grasp the strength distribution due to the difference of several centimeters such as the strength of the concrete surface and the inside. By performing strength estimation using this method, it is possible to indirectly estimate durability.

  In addition, since the elastic modulus can be measured locally with high accuracy, the elastic modulus can be measured without performing a compression test by shaping a compression test piece or the like. It can be used for measuring the elastic modulus of inorganic materials such as aggregates and tiles that cannot be compressed as they are.

Hereinafter, embodiments of the present invention will be described in detail. In the present invention, the UCI (Ultrasonic Contact Impedance) method, which is a method for estimating the hardness of a measurement material from the change in resonance frequency before and after contact with the measurement sensor, is not known for natural materials (stone, aggregate, wood, soil, etc.) and materials. The elastic modulus of the pre-cured semi-finished product such as alloys and hardened materials (such as ready-mixed concrete, mortar, cement paste, plaster, plaster, pre-cured resin, etc.) is grasped with sufficient accuracy in advance. It is used to measure the hardness / strength and elastic modulus of impossible measurement materials.

  The UCI method is a method for estimating the hardness of a measurement material from the change in resonance frequency before and after contact with the measurement sensor. When a rod that vibrates at a constant frequency is brought into contact with the material, the frequency depends on the indentation area and the elastic modulus of the material. This is a method for estimating the hardness (= load / indentation area) by back-calculating the indentation area from the change in frequency using the change in the frequency.

  The UCI method has been published as a well-established technology by 1970. Test machines are also sold by General Electric and JFE Advantech. The test method is defined in ASTM A1038. However, these are methods for measuring the hardness of the material, but are not methods for measuring the strength as in the present invention.

  The measurement principle of the UCI method is as follows. When a contact sensor (vibrating at a certain frequency) is brought into contact with the surface of the measurement sample, a frequency change (Δf) depending on the contact area (A) and the elastic coefficient (E) is generated. That is, Δf = f (A, E) is established with f (x) as a function of frequency change.

  Therefore, the UCI testing machine measures frequency changes and converts them to hardness according to the following relationship. The Vickers hardness (HV) is obtained from the relationship between the load (F) and the contact area (A), and is HV: F / A. HV is an index of hardness, but F / A is the same as the formula of strength, and it is considered that there is a high correlation with strength. Therefore, it is highly possible that the strength can be estimated by using the hardness index.

  A portable hardness tester manufactured by GE Inspection Technology can be used as the UCI testing machine. The model numbers of the measuring instruments are MIC-2101 and MIC-2103.

  In addition, in order to estimate hardness (= load / indentation area) by the UCI method, the indentation area can be calculated backward from the change in frequency because the elastic modulus of the measurement material is known. That is, the hardness can be estimated by the UCI method because the value of the elastic modulus needs to be known in advance with sufficient accuracy. However, the case where the elastic modulus can be grasped in advance as described above is limited to materials that are manufactured under high control such as industrial products as described above.

  On the other hand, natural materials and hardened materials cannot grasp the elastic modulus with sufficient accuracy in advance. For natural materials such as stone, the elastic modulus may vary greatly depending on slight differences in the sampling position, and for concrete, the elastic modulus varies greatly depending on the curing conditions (temperature, humidity, demolding time, etc.) and age. . Therefore, in order to obtain an accurate result, it is necessary to measure the elastic coefficient of the material itself, and the elastic coefficient cannot be determined in advance.

  In the present invention, data on strength and elastic modulus obtained from a test specimen of the same composition is obtained in advance, and based on this data, the elastic modulus and strength are estimated from the measured values of the UCI method.

  First, the estimation method of the elastic modulus is described. Since it is difficult for the UCI method to measure a natural material or a cured material, a non-destructive elastic modulus measurement method capable of measuring the material itself in-situ can be considered as a means for solving this. As this method, there are existing techniques such as an ultrasonic method and a rebound hardness method (Schmidt hammer). However, these require a measuring instrument, and it is necessary to separately examine the correlation with the elastic modulus of the UCI method. There are some problems. Therefore, in order to measure with a UCI test machine in the following, the present invention applies an insertion material such as a metal plate to the surface of the measurement material, and makes the indentation area constant by bringing the rod into contact therewith. To measure.

Here, the insertion material has the following properties, specifically, a metal flake, a thin resin, and the like.
1. It must be thin enough that the difference in elastic modulus of the measurement material affects the frequency change of the rod. In addition, the thickness of the insert material should not reach the measurement material below.
2. Industrial products that have a constant indentation area.

  The optimum material and thickness of the insertion material differ depending on the elastic coefficient of the material to be measured. As a general tendency, the material is a material with a small indentation area (metal rather than resin), and the thinner the better, as long as the thickness can be secured so that no indentation is formed on the lower measurement material. Thus, the insertion material can be changed depending on the measurement material.

  Thus, the change value of the vibration frequency measured through the insertion material changes according to the elastic coefficient of the measurement material. If the correlation between the change value of the frequency measured through the insertion material and the elastic coefficient is obtained in advance, the elastic coefficient can be estimated. In this case, for example, it is data obtained by placing an insertion material on concrete.

  Next, a method for estimating hardness and strength will be described. Since the elastic modulus can be estimated even with the natural material and the cured material, the hardness and strength can be estimated by combining with the conventional UCI method.

That is, the hardness and strength of the material can be estimated through the following steps.
1. The correlation between the change in the frequency and the elastic modulus when using an insertion material in advance is grasped.
2. The change in frequency of the measurement material is measured by the UCI tester through the insertion material.
3. From the change in the frequency, the elastic coefficient is determined using the correlation between the prepared frequency and the elastic coefficient.
4). The frequency change of the measurement material is directly measured without using the insertion material.
5. Indentation area is estimated from frequency change and elastic modulus.
6). The hardness or strength is estimated from the indentation area. The correlation between the indentation area and the hardness or strength is grasped in advance using the same material.

Specific measurement methods and results using the UCI testing machine (MIC20) are as follows.
The tester used is named Krautkramer MIC20, a General Electric tester. There are several types of testing machines all over the world, but they are basically the same equipment, so other testing machines are omitted.
The general usage of the equipment is as follows.
(1) When the main body is turned on, it starts and becomes ready for measurement.
(2) Select the type of measurement material and determine the elastic modulus (E).
(3) The rod is pressed against the surface of the measurement material with a constant load (F).
(4) The amount of change in frequency (Δf) is measured inside the testing machine.
(5) Calculate and display the value of HV from the relationship of the two formulas A = f (E, Δf) and HV = F / A inside the testing machine.

In the implementation of the present invention, it is assumed that (2) the type of measurement material in the above-described general usage method is selected and the elastic modulus (E) cannot be determined. In this case, since the value of HV cannot be calculated in (5), this problem will be specifically solved below.
(1) When the main body is turned on, it starts and becomes ready for measurement.
(2) Temporarily set the type of measurement material to steel (E) or the like, and specify the elastic coefficient used in the internal calculation. This is only necessary to display the HV and may be specified independently of the elastic modulus of the measurement material.
(3) Press the insertion material between the measurement material and the rod from above the insertion material with a constant load (F).
(4) The change in frequency (Δf) is measured inside the testing machine.
(5) Calculate and display the value of HV from the relationship of the two formulas A = f (E, Δf) and HV = F / A inside the testing machine. However, it should be noted that the magnitude of the HV value measured through the insertion material in this way does not depend on the value of A as in the general usage described above, but depends on the value of E. is necessary. This is because the value of A is almost constant due to the influence of the insertion material.
(6) (5) Since the value of HV is a function of E (E = G (HV)), if this function is grasped in advance by calibration, the elastic modulus E of the material can be determined. .
(7) Press with a constant load (F) from above the insertion material without passing through the insertion material.
(8) The change in frequency (Δf) is measured inside the testing machine.
(9) Calculate and display the value of HV from the relationship of the two formulas A = f (E, Δf) and HV = F / A inside the testing machine. However, since the elastic coefficient E used for the internal calculation at this time is the temporary elastic coefficient determined in (2), the value of HV is not a correct value. Recalculate the value of HV using the correct elastic modulus obtained in (6). As described above, the hardness when the elastic modulus is indefinite can be measured with high accuracy.
(10) Since HV and intensity Fc have a relationship of a certain function (Fc = H (HV)), if this function is grasped in advance by calibration, the intensity Fc of the material can be determined.

  An example of measurement results of materials having different elastic coefficients and strengths is shown in FIGS. FIG. 1 shows the correlation between the elastic modulus and the HV via the insertion material, and FIG. 2 shows the correlation between the strength and the HV (the numerical value in the legend is age (day), and the measurement material is concrete).

  It can be seen that a certain correlation is established between HV, which is the display value of the testing machine, and the elastic modulus and strength, and the elastic modulus and strength can be estimated by measurement. Note that the value of HV in the “correlation between strength and HV” is a value calculated with a temporary elastic coefficient as it is, and is corrected by multiplying the square of the elastic coefficient obtained by the measurement. Note that the correction method (such as multiplication by the square of the elastic modulus) differs depending on the testing machine.

  Next, a method for estimating the strength of concrete will be described. The measured value by the UCI method depends not only on the hardness of the material but also on the surface roughness and elastic modulus of the material. Therefore, the elastic modulus of the material changes from moment to moment, and the surface roughness is reduced in order to divert the wooden formwork. It is difficult to apply to non-constant concrete surfaces. Unlike metal materials, concrete changes in strength and elastic modulus over time.

  Furthermore, since concrete is a composite material of an aggregate and a cement matrix, if the number of measurement points is small in the local measurement such as the UCI method, the measurement may not be representative of the whole.

  In order to solve this problem, the present invention obtains in advance data on strength and elastic modulus (data on the strength and elastic modulus of concrete with the same composition) from the specimens of the same composition, and the hardness of the specimen by the UCI method. A correspondence with the measured value is given, and the elastic modulus and strength are estimated from the measured value of the UCI method using this correspondence.

  It is generally accepted that the strength of concrete is also highly correlated with the durability of concrete. Therefore, it is possible to estimate durability indirectly by performing strength estimation using the method of the present invention. When the durability is estimated, a calibration curve of the correlation between the durability and the strength is acquired again, and the durability is estimated according to the calibration curve.

  Since the UCI method is affected by the surface roughness of the measurement sample, it is necessary to uniformly adjust the surface roughness of the measurement sample. However, the wooden formwork is diverted at the construction site, so the surface of the formwork that has been repeatedly diverted is rough and the surface roughness is different.

  Therefore, in the present invention, the surface roughness of the concrete surface is made uniform by pasting a smooth plate such as a metal plate such as a thin iron piece or a vinyl sheet as an insertion material on the mold surface of the measurement location in advance. It was made to become. Further, the number of measurement points is at least 10 points. Unlike an aluminum tape, a vinyl sheet does not cause a chemical reaction with concrete, so it is suitable as a material to be attached to the surface of a wooden formwork.

  The measured value of hardness by the UCI method is an index including hardness and elastic modulus, but when an insertion material such as a metal plate is sandwiched between the contact sensor of the UCI method tester and the sample, Since the hardness measurement value has a high correlation with the elastic modulus, the elastic modulus can also be measured.

  As described above, the hardness measurement value of the UCI testing machine has a constant contact area when a material such as a metal thin plate is sandwiched between the contact sensor and the measurement sample. Since the frequency change measured by the testing machine has a correlation of Δf = f (E, A) as described above, if A is a constant value, the measured value depends only on E, and the elastic modulus Can be estimated. If the correlation between the elastic coefficient and the amount of change in frequency is obtained in advance, the elastic coefficient can be estimated with high accuracy.

  Further explaining the unification of the surface roughness, the result of the strength test is used for the calibration curve creation data, but the test specimen for the strength test is generally a steel formwork such as a summit mold. Therefore, the surface roughness is different. Therefore, it is necessary to unify the surface roughness to a wooden formwork or a steel formwork. From the point of view of measurement, it is desirable to unify the steel formwork because data with higher accuracy is obtained when the surface roughness is smaller. Therefore, as described above, this problem is solved by sticking a smooth body such as a metal plate or a vinyl sheet as an insertion material to the surface of the wooden formwork at the planned measurement position.

The flow of measurement is shown below.
(1) A commercially available testing machine is used as the UCI testing machine.
(2) For concrete of the same composition as concrete to be measured in advance, compressive strength at the age of 3, 7, 14, 28, 56, 91 days, elastic modulus, hardness measurement by UCI testing machine, and calibration Prepare an action curve.

  It is necessary to determine the range of compressive strength and elastic modulus so that the hardness measurement value to be measured in the future will be within the range of the calibration curve. For this reason, data acquisition from weak materials is the standard. The specimen curing method used in the compression test at this time is standardly sealed sealing or standard water curing. When concrete is dried, moisture is dissipated from the surface, resulting in different strength and elastic modulus between the surface and the interior. Only the surface can be measured by the UCI method, and a calibration curve cannot be obtained accurately with a specimen having a strength different between the inside and the surface.

(3) A smooth body such as a metal plate or a vinyl sheet is attached to the surface of the concrete formwork at the measurement planned position.
Since the surface roughness affects the measured value, a metal plate or the like is pasted as an insertion material on the mold surface at the measurement position so that the surface roughness is uniform.

(4) The surface hardness is measured with a UCI testing machine. Measure 10 or more points at one location. When measuring the elastic modulus, measurement is performed with a smooth body such as a thin metal plate or a vinyl sheet interposed therebetween.
If the UCI testing machine is a measurement of a metal surface, measurement of several points is sufficient because there is little variation in measured values. However, in the case of a composite material having a large local strength such as concrete, the measurement values vary greatly, so that a large number of measurements are indispensable.

(5) The concrete strength is estimated using the calibration curve from the measured value of the surface hardness and the estimated value of the elastic modulus.
The concrete strength is estimated from the measured surface hardness using a calibration curve.

FIG. 2 shows experimental data on the correlation between E ² · HV and compression strength. E is an elastic modulus of the sample at the time of measurement, and HV is a measured value of Vickers hardness by a UCI tester. A mortar sample is used as a test specimen. From the figure, there is a proportional relationship between E ² · HV and compressive strength, and strength can be estimated by measuring HV with a UCI tester. The value of E is grasped in advance or estimated from the value of Vickers hardness measured with a thin metal plate or the like sandwiched between the sample and the sample.

  In addition, experimental data are data of the sample of W / C = 65, 55, 45%, and the measurement material age is also different from 3 days, 7 days, and 14 days after placement. Nevertheless, the fact that all data are generally in a straight line indicates that differences in blending and age do not significantly affect strength estimation. Therefore, it can measure without worrying about the age at the time of measurement and the difference in preparation.

  FIG. 1 is a graph showing a correlation between an elastic coefficient and a measured value HV ′ sandwiching a smooth body such as a metal thin plate or a vinyl sheet. By using this correlation, the elastic coefficient of the measurement material can be estimated.

  Regarding the durability of concrete, it is generally accepted that the strength of concrete has a high correlation with the durability of concrete, so it is possible to estimate the durability indirectly by estimating the strength using this method. It is thought that it becomes. When the durability is estimated, a calibration curve of the correlation between the durability and the strength is acquired again, and the durability is estimated according to the calibration curve.

When the elastic modulus is estimated, the measurement is made through the insertion material, while when the strength and hardness are measured, the measurement is made without using the insertion material. (However, when measuring strength and hardness, an elastic modulus is required, and therefore measurement through an insertion material is also required.

  Since the physical properties being measured are different, when the strength is estimated, the measurement is performed without using an insertion material.

It is a correlation diagram of HV through an elastic coefficient and an insertion material by the measuring method by the UCI method of a material with an unknown elastic coefficient of concrete of the present invention. It is a measurement method by UCI method of the material whose elastic modulus is unknown, such as concrete according to the present invention, and is a correlation diagram of strength and HV not using an insertion material (the numerical value in the legend is age (day), and the measurement material is mortar).

Claims (3)

The UCI (Ultrasonic Contact Impedance) method is used to estimate the hardness of the measurement material from the change in resonance frequency before and after contact with the measurement sensor . The indentation area is constant between the measurement material surface and the rod. Semi-finished products such as natural materials (stone, aggregate, wood, soil, etc.) and alloys whose materials are unknown, and hardened materials (such as ready-mixed concrete, mortar, cement paste, plaster, plaster, and resin before curing) Measured with a thin insert material of industrial products sandwiched between the measurement materials whose elastic modulus cannot be grasped in advance, such as those in the state after curing, that can secure a thickness that does not cause indentation. A method of measuring a material having an unknown elastic coefficient, such as concrete, using the UCI method, wherein an elastic coefficient is determined from a change in frequency using a correlation between a previously prepared frequency and an elastic coefficient. Understand the correlation between the change in frequency and the elastic modulus when using an insert material in advance, measure the change in frequency of the measurement material with the UCI tester via the insert material, Using the measurement method according to claim 1, wherein the elastic coefficient is determined using the correlation between the frequency and the elastic coefficient prepared in
Measure the frequency change of the measurement material directly without using the insertion material, estimate the indentation area from the frequency change and elastic modulus,
The UCI method for materials with unknown elastic modulus, such as concrete, characterized by estimating the hardness or strength based on the correlation between the indentation area and the hardness or strength obtained from the same material in advance. Measurement method.   As a method for estimating the strength of the concrete surface, a thin insert of an industrial product is affixed to the surface of the concrete formwork at the planned measurement position, and the compressive strength and elastic modulus at various ages for concrete of the same composition as the concrete to be measured in advance. The hardness measurement by the UCI test machine is performed, a calibration curve is prepared, and the strength of the concrete is estimated using the calibration curve from the measured value of the surface hardness and the estimated value of the elastic modulus. The measuring method by the UCI method of the material whose elastic modulus is unknown, such as concrete according to claim 2.

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