JPH04276546A - Strength testing method for cement structure using ultrasonic wave - Google Patents

Abstract

PURPOSE:To make it possible to evaluate strength close to actual compressive strength by adding the sound speed of a transversal wave, an aggregate ratio, a water-cement ratio, an elapsed period from the construction of a structure and the like with respect to the structure as the factors, and evaluating the compressive strength. CONSTITUTION:A longitudinal-wave generating probe and a transversal-wave generating probe are used, and the sound speed VL and the attenuating factor alphaL of a longitudinal wave and the sound speed VS and the attenuating factor alphaS of a transversal wave are measured by an ultrasonic-wave transmitting method across a test body (cement structure). Furthermore, the components of the concrete material (amount of water (w), amount of cement (c), amount of fine aggregate (s) and total (a) in placing) and the elapsed days A after the construction of the structure are obtained. The evaluation of the compressive strength sigma of the structure is performed by obtaining the strength by the expression sigma=K1.VL+K2.alphaL+K3.VS+K4.alphaS+K5N-A+K6.s/a+K7.w/c+K8. In the expression, K1-K7 are coefficients, and K8 is a correcting term. The values are determined by actually measuring a sample and the like corresponding to the kind of the test body.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] This invention relates to a method for testing the strength of structures using cement such as concrete and mortar (hereinafter referred to as cement structures). This invention relates to a strength testing method using ultrasonic waves that can be used to evaluate strength with relatively high accuracy. [Prior Art] A non-destructive and simple method for determining the strength of a concrete structure, especially for determining the strength of a concrete structure that has deteriorated over time, in order to diagnose the durability of a building. There is a strong demand for the development of accurate evaluation methods in various fields, including the construction industry and the materials industry. Currently, the most direct method used to determine concrete strength is to take a core sample directly from a concrete structure and perform a strength test on it. However, this results in partial damage to the structure, and is not a preferable method in terms of labor and cost. [0003]Problems to be Solved by the Invention Currently, methods for on-site strength testing of structures that can be easily and non-destructively carried out without using such means include the repulsion hardness measurement method using a Schmidt hammer and the ultrasonic pulse velocity method. , and combination methods of these are also used. Among these methods, the ultrasonic pulse velocity method uses longitudinal sound velocity and has high utility value as a relatively simple method. However, this is currently in the realm of theoretical or experimental research and has not been put to practical use. The frequency of ultrasonic waves transmitted through structures such as concrete is about 8 kHz to 800 kHz, which is more than two orders of magnitude lower than that of metal materials. For this reason, the directivity of ultrasonic waves is very blunt, and since pulses are used, it is difficult to logically analyze them, which has hindered their practical use. Therefore, strength evaluation of concrete structures using ultrasonic waves is far from practical in terms of accuracy and reliability. [0004] The present invention solves the problems of the prior art, and aims to provide a simple and reliable method for testing the strength of cement structures using ultrasonic waves. purpose. Means for Solving the Problems [0005] The characteristics of the ultrasonic strength testing method for cement structures of the present invention are as follows:
The sound speed (VS ) and attenuation rate (αS ) of the transverse wave are measured, and these measured values and the aggregate ratio M, water-cement ratio N, and elapsed period A since the construction of the cement structure are measured. The compressive strength σ of the cement structure is evaluated according to the following relational expression using σ as an element. σ=K1 ・VL +K2 ・αL +K3 ・VS
+K4 ・αS+K5 ・A+K6 ・M+K7 ・N
+K8 However, K1 to K7 are coefficients, and K8 is a correction term, and these are numerical values determined by actually measuring a sample etc. corresponding to the type of object to be measured. [Operation] In this way, in addition to the conventional measurement using only the longitudinal sound velocity, the longitudinal sound velocity and its attenuation rate, the transverse sound velocity and its attenuation coefficient, and also the cement structure as a correction factor for these measured values. The actual compressive strength σ is calculated by adding the aggregate ratio (s/a), water-cement ratio (w/c), and elapsed period A since the construction of the cement structure to the evaluation factors. Ultrasonic measurement enables strength evaluation close to compressive strength. [Example] FIG. 1 is an explanatory diagram of the relationship between the actually measured value of compressive strength and the theoretical formula in the ultrasonic strength testing method for cement structures of the present invention, and FIG. FIG. FIG. 1 shows the measured values for 18 concrete samples indicated by ● and the graph (solid line) of the multiple regression equation obtained based on the logical equation according to the present invention, which is calculated using the estimation equation (σreal= σEst). The compressive strength evaluation line shown as this solid line graph is
The difference from actual measurements can be kept to about ±10%. In addition to the conventional longitudinal wave sound speed VL, the transverse wave sound speed VS, ultrasonic attenuation rate α (longitudinal wave attenuation rate αL, shear wave attenuation rate αS), and the components of concrete materials (amount of water w, amount of cement This is because an evaluation formula could be obtained by adding c, amount of fine aggregate s, total a), temporal condition correction value (number of days A), etc. The evaluation formula for the compressive strength σ is shown below: σ=K1 ・VL +K2 ・αL +K3
・VS +K4 ・αS +K5 ・A
+K6 ・S/a+K7 ・w/c+K8...
...(1) becomes. Here, K1 ・VL +K2 ・
αL +K3 ・VS +K4 ・αS is condition evaluation data obtained by actually measuring the concrete structure using ultrasonic measurement. What is different from the conventional method is that here, the longitudinal wave attenuation rate, the transverse wave sound velocity, and the attenuation rate are added to the ultrasonic measurement value. K5·A at the beginning of the next line is a time correction term based on the elapsed time from when the measurement target was constructed to the present for the measurement data in the first line. This was introduced in connection with the fact that the components of cement undergo gradual reactions and change in quality as time passes, and the value of the ultrasonic measurement data shown in the first line of equation (1) above is not linear. This improves measurement accuracy by correcting measurement information that cannot be fully grasped. The next K6 ・S/a
+K7 ・w/c is a characteristic correction term according to the characteristics of the concrete structure at the time of pouring. This was introduced because it is thought that the condition of aggregate is actually related to the shear strength of concrete structures. In other words, because the frequency of ultrasonic waves used is low, the effect on the strength of aggregate cannot be easily expressed by the value obtained from the measurement data expressed by the first line of equation (1) above. This correction term corrects the missing parts. K8 is a correction term for the entire equation determined depending on the measurement target. As can be understood from this formula, this compressive strength evaluation formula involves actually measuring the attenuation rate, the sound velocity of the transverse wave, and its attenuation rate, in addition to the longitudinal sound velocity of the ultrasonic wave, which is the conventional compressive strength evaluation. In addition to measuring compressive strength in a more practical manner, the results of these measurements are added by applying a load, and the results are then corrected for elapsed time and state characteristics at the time of construction of the measurement target. This technology has advanced the compressive strength evaluation of concrete structures using ultrasonic waves, which has not yet reached a practical state, to the stage where it can be put to practical use. [0010] The inventors have found through numerous experiments and studies that selecting such evaluation elements is effective in evaluating the compressive strength of concrete structures, and in order to prove this, As a typical example, we will introduce the following basic data. Before that, let's first consider the strength of concrete structures. It is empirically known that this is controlled by the maximum shear force and shear strain energy. Therefore, among the various moduli of elasticity of a concrete structure, the parameter most closely related to failure is considered to be G', which governs shear deformation. Focusing on this G', the following relational expression is derived from the equation of motion when a plane wave propagates in the X-axis direction in a semi-infinite isotropic elastic body. VL = {(K'+(4/3)G')/ρ}1
/2 ......(2) E'=K
'+(4/3)G'
......(3) VS = (G
'/ρ) 1/2
......(4) Here, E' is the complex modulus of longitudinal elasticity, K' is the complex modulus of bulk elasticity, and G' is the complex shear modulus. Since the term can be eliminated, in reality, E', K', and G' each have only real parts, and become the dynamic longitudinal modulus, dynamic bulk modulus, and dynamic shear modulus. As can be understood from this equation, the dynamic shear modulus G', which is related to compressive strength evaluation, is the longitudinal wave VL, the shear wave VS, the dynamic longitudinal modulus E', and the dynamic bulk modulus K'
is related to. The velocities of longitudinal waves and transverse waves can be obtained by ultrasonic measurements, but the latter, dynamic longitudinal elastic modulus E' and dynamic bulk elastic modulus K', cannot be adequately measured using ultrasonic measurements. I can't. Therefore, first of all, attention was focused on the combination of the sound speed and attenuation rate of ultrasonic waves. This is because the sound speed and attenuation rate of ultrasonic waves are related to the volume and elastic modulus (internal material) of the object through which it passes. [0012] From this point of view, we have attempted many experiments using actual concrete samples, but it is difficult to put them into practical use by measuring the sound velocity and attenuation rate of longitudinal waves of ultrasonic waves, and the sound velocity and attenuation rate of transverse waves. It was difficult to understand the relationship between compressive strength evaluation to the extent possible. Therefore, the next consideration was a correction term in the temporal sense and a correction based on the compositional state of the concrete structure at the time of construction. We introduced this idea, and in order to prove it, experimental values and theoretical values were verified using the apparatus shown in FIG. The samples used here were 60 specimens prepared by the Concrete NDT Committee of the Japan Nondestructive Testing Association, as shown in Table 1. [Table 1] The test specimens in Table 1 have a water/cement ratio (ratio (%) of water kg/m3, cement kg/m3), fine aggregate ratio (aggregate k
g/m3, the ratio (%) of the total weight kg/m3), etc., are changed. Separately, in order to understand the temporal relationship, we conducted an experiment by changing the curing method (in water, in air) for samples with a constant formulation as shown in Table 2. The timber age on the measurement date is from 7th to 38th. The dimensions of the test specimen are 100 mm in diameter and 200 mm in height.
It is a cylinder. This is based on JIS-R-5210 cement strength testing method. The material was demolded after 1 day of age, and cured as shown in Table 3. [0014] [Table 2] [0015] [Table 3] [0016] Measurements for each test specimen were performed using the configuration shown in FIG. That is, the measurement is performed by a transmission method in which a transmitting probe and a receiving probe are placed one above the other with the transmitting probe on the lower side, and the test specimen is sandwiched between them. The sound speed and attenuation rate of longitudinal waves and the sound speed and attenuation rate of transverse waves were measured using a longitudinal wave generation probe and a shear wave generation probe, respectively. Note that the frequency of the ultrasonic waves used was 100 kHz, as an example. FIGS. 3 to 6 show the relationship between the actual compressive strength and each measured value for 60 test specimens prepared by the Concrete NDT Committee of the Japan Nondestructive Testing Association. The age of the material was 28 days, the sound velocity was calculated by dividing the thickness of the test specimen by the propagation time measured by the relative amplitude method, and the attenuation constant was calculated by dividing the thickness of the specimen by the propagation time measured by the relative amplitude method. It is the difference (dB) between the maximum amplitude value of the wave pulse and the maximum amplitude value of the received pulse when measuring the test object, divided by the thickness of the test object. Note that the equations in each figure are regression equations, and γ indicates a correlation coefficient. Figure 3 shows the longitudinal wave sound velocity VL (m/
s) and the actual compressive strength σc (kg/cm2), and Figure 4 shows an example of the measurement results of the longitudinal wave attenuation constant (αL [d
B/mm]) and the actual compressive strength. In addition, Figure 5 shows the transverse wave sound speed VS (m/s) and compressive strength σc
(kg/cm2), and FIG. 6 shows the relationship between longitudinal wave attenuation constant (αS [dB/mm]) and compressive strength. Here, for each measured value, the compressive strength σ is defined as the reference variable and the ultrasonic measurement value as the explanatory variable.
When calculating the multiple regression equation for c, σc =0.1594 ・VL −2374 ・α
L +0.3934 ・VS +74502・αS +
250.4...(5) Furthermore, (1)
When a multiple regression equation is obtained by adding concrete mixing conditions (component information) to the explanatory variables according to the concept of the equation, the compressive strength σc is calculated as follows: σc = 0.03543・VL −1255・α
L +0.1932 ・VS +472.2・αS
+0.2182 ・(s/a)-8.97
8・(w/c)+233.1……
(6) becomes. FIGS. 7 to 11 show the relationship between the actual compressive strength and the measured values including each evaluation element for the latter test specimen that was cured. Figure 7 shows the relationship between the number of elapsed days A (days) and compressive strength, Figure 8 shows an example of the measurement results of longitudinal wave sound velocity VL and compressive strength σc, and Figure 9 shows the longitudinal wave attenuation constant (αL [dB/ mm]) and compressive strength. Figure 10 shows the measurement results of shear wave sound velocity VS (m/s) and compressive strength σc (kg/cm2), and Figure 11 shows the relationship between longitudinal wave attenuation constant (αS [dB/mm]) and compressive strength. ing. From these measurement results (1)
The compressive strength σ for the concrete specimen according to the formula
When calculating the multiple regression equation for evaluation, σc = 0.3188 ・VL +5091 ・α
L +0.05518・VS +108.2・αS −
1146...(7) When adding the time elapsed element to this, σc =0.03899・A+0.31
81 ・VL +513.1・αL +0.05407
・VS +108.1・αS -117
2
………………(
8) It becomes. Next, FIGS. 12 to 22 show the results of measuring the above two systems of test specimens under different conditions in order to obtain a general formula for concrete structures according to the concept of formula (1). From these measurement results, we used compressive strength as the reference variable and the variable increase/decrease method using information criterion (AIC) using longitudinal wave sound speed, its attenuation rate, transverse wave sound speed, its attenuation rate, elapsed days, condition of aggregate, etc. as explanatory variables. When performing multiple regression analysis using σc =0.2204 ・VL +3313
・αL +0.2117 ・VS +472.4・αS
-5.389・A+2.796・
(s/a)-9.255・(w/c)-422.9...
(9) FIG. 1 shows the correlation between this multiple regression equation and the actually measured compressive strength, and as shown in the figure,
The measured value of compressive strength is approximately ± based on the regression line mentioned above.
It is in the range of 10%. That is, it can be said that the estimation error in compressive strength evaluation using this formula is within this range. Equation (9) is a general compressive strength evaluation formula for concrete structures, but for mortar and other cement structures, if the coefficients are calculated for each sample, it can be used as a general compressive strength evaluation formula. A regression equation can be found. Therefore, for concrete structures, an arithmetic expression or tabulated data using equation (9) as a criterion is stored in the memory of the ultrasonic measuring device, and after the concrete structure to be measured is constructed. Enter the year and month, aggregate ratio (s/a), water-concrete ratio (w/c), etc. from the keyboard in advance, and calculate the longitudinal wave sound velocity VL, shear wave sound speed VS, and longitudinal wave attenuation rate (
By actually measuring αL ) and shear wave attenuation coefficient (αS ) by ultrasonic measurement, it becomes possible to automatically calculate the compressive strength evaluation value σ for the concrete structure. [0021] As explained above, the coefficient values in the examples are based on actual test specimen measurements, and the number of digits and magnitude of the coefficient values change depending on how the dimension is taken, so the coefficient values are The units of numerical values are not fixed. Moreover, this coefficient value is considered to be influenced to some extent by the quality of cement. For example, there is a difference in strength between domestically produced cement and imported cement, and each requires some correction by mixing blast furnace ash or other reinforcing materials. In addition, although 100 kHz is used in the example as the measurement frequency, it is possible to use a range of about 8 kHz to 800 kHz, which is the range where ultrasonic waves can be used for structures such as concrete, which is a so-called low frequency range. . [0022] As explained above, in the present invention, in addition to the conventional measurement using only the sound velocity of longitudinal waves, the sound velocity and attenuation rate of longitudinal waves, the sound velocity and attenuation rate of transverse waves, and these measurements are also carried out. The aggregate ratio (s/a), water-cement ratio (w/c), and elapsed period A since the cement structure was constructed are added as correction terms to the measured value of the cement structure. By evaluating the compressive strength σ, strength evaluation close to the actual compressive strength becomes possible through ultrasonic measurement.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the relationship between actually measured values of compressive strength and theoretical formulas in the ultrasonic strength testing method for cement structures of the present invention.

FIG. 2 is an explanatory diagram of test specimen measurement for determining a logical formula.

FIG. 3 is an explanatory diagram of the measurement results of longitudinal sound velocity and compressive strength for test specimens created by the Japan Nondestructive Testing Association Concrete NDT Committee.

FIG. 4 is an explanatory diagram of measurement results showing the relationship between longitudinal wave attenuation constant and compressive strength.

FIG. 5 is an explanatory diagram of measurement results showing the relationship between the transverse sound velocity and compressive strength.

FIG. 6 is an explanatory diagram of measurement results showing the relationship between the transverse wave attenuation constant and compressive strength.

FIG. 7 is an explanatory diagram illustrating the measurement results of the age and compressive strength of a cured specimen.

FIG. 8 is an explanatory diagram of measurement results of longitudinal sound velocity and compressive strength for a cured test specimen.

FIG. 9 is an explanatory diagram of measurement results showing the relationship between longitudinal wave attenuation constant and compressive strength for a cured test specimen.

FIG. 10 is an explanatory diagram of measurement results showing the relationship between transverse wave sound velocity and compressive strength for a cured test specimen.

FIG. 11 is an explanatory diagram of measurement results showing the relationship between transverse wave attenuation constant and compressive strength for a cured test specimen.

FIG. 12 is an explanatory diagram of measurement results showing the relationship between material age and compressive strength for a cured test specimen.

FIG. 13 is an explanatory diagram of measurement results showing the relationship between longitudinal sound velocity and compressive strength for a cured test specimen.

FIG. 14 is an explanatory diagram of measurement results showing the relationship between longitudinal wave attenuation constant and compressive strength for a cured test specimen.

FIG. 15 is an explanatory diagram of measurement results showing the relationship between transverse wave sound velocity and compressive strength for a cured test specimen.

FIG. 16 is an explanatory diagram of measurement results showing the relationship between shear wave attenuation constant and compressive strength for a cured test specimen.

FIG. 17 is an explanatory diagram of measurement results showing the relationship between fine aggregate ratio and compressive strength for a cured test specimen.

FIG. 18 is an explanatory diagram of measurement results showing the relationship between water/cement ratio and compressive strength.

FIG. 19 is an explanatory diagram of measurement results showing the relationship between longitudinal sound velocity and material age.

FIG. 20 is an explanatory diagram of measurement results showing the relationship between longitudinal wave attenuation constant and material age.

FIG. 21 is an explanatory diagram of measurement results showing the relationship between transverse wave sound velocity and material age.

FIG. 22 is an explanatory diagram of measurement results showing the relationship between transverse wave attenuation constant and material age.

Claims (2)

[Claims] [Claim 1] The sound velocity of longitudinal waves (
VL), attenuation rate (αL), sound velocity of transverse waves (VS), and attenuation rate (αS), and these measured values and the aggregate ratio M, water-cement ratio N, and water-cement ratio N of the cement structure are measured. A method for testing the strength of a cement structure using ultrasonic waves, characterized in that the compressive strength σ of the cement structure is evaluated according to the following relational expression using the elapsed period A since the construction as an element. σ=K1 ・VL +K2 ・αL +K3 ・VS
+K4 ・αS+K5 ・A+K6 ・M+K7 ・N
+K8 However, K1 to K7 are coefficients, and K8 is a correction term, and these are numerical values determined by actually measuring a sample etc. corresponding to the type of object to be measured. Claim 2: Aggregate ratio M is fine aggregate ratio, and compressive strength σ
The relational expression for σc =0.2204 ・VL +3313
・αL +0.2117 ・VS +472.4・αS
-5.389・A+2.796・
(s/a)-9.255・(w/c)-422.9, and in this formula, a range of ±10% is taken as the compressive strength evaluation value. Strength testing method using ultrasonic waves.