CN108802196B - Concrete prism test block static elastic modulus detection method based on impact echo - Google Patents

Concrete prism test block static elastic modulus detection method based on impact echo Download PDF

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CN108802196B
CN108802196B CN201810602801.3A CN201810602801A CN108802196B CN 108802196 B CN108802196 B CN 108802196B CN 201810602801 A CN201810602801 A CN 201810602801A CN 108802196 B CN108802196 B CN 108802196B
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elastic modulus
static
dynamic
concrete
test piece
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CN108802196A (en
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郭学兵
韩之江
刘志华
汪永强
赵雷
郭文龙
王磊
陈栋栋
傅莉
郭琪
何国花
寇伟
刘建勋
刘媛媛
卢鹏
吕立宁
李卓然
毛敏
申雁鹏
汪贤安
王望春
王潇楠
王琪
吴佳佳
吴焱
谢利安
赵芳
赵晓晋
赵文溥
郑彪
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Shanxi Province Transport Science Research Institute
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Abstract

The invention discloses a static elastic modulus detection method of a concrete prism test block based on impact echo, which comprises the following steps of cutting the concrete prism test block into test pieces with the slenderness ratio of more than or equal to 2; polishing two end faces of the cut test piece along the length direction to be smooth; detecting the dynamic elastic modulus of the test piece by using an impact echo method; and deducing the static elastic modulus of the test piece by using the measured dynamic elastic modulus of the test piece according to the numerical relationship of the dynamic-static elastic modulus, and obtaining the static elastic modulus of the concrete prism test block. The method can quickly and accurately detect the real-time static elastic modulus of the concrete prism test block, and avoid a large number of redundant test block static pressure tests; the operation is simple, the cost is low, the purchase of large-scale pressure testing machines and other testing equipment can be avoided, and the engineering cost can be effectively reduced; the formula used can reduce the error caused by indirect data derivation.

Description

Concrete prism test block static elastic modulus detection method based on impact echo
Technical Field
The invention belongs to the technical field of civil engineering detection, and particularly relates to a static elastic modulus detection method of a concrete prism test block based on an impact echo.
Technical Field
The concrete elastic modulus is one of the most important mechanical indexes of concrete materials, and not only can directly reflect the rigidity characteristic of the concrete materials and the deformation characteristic of a concrete structure, but also can indirectly reflect the aging characteristic of the concrete materials and the internal destruction characteristic of the concrete structure. Therefore, the real-time accurate detection of the concrete elastic modulus has very important significance.
The existing method for measuring the static elastic modulus of the concrete prism test block mainly comprises two methods. One is a direct measurement, i.e. the modulus of elasticity is measured by the static pressure method in the current specification. However, the static pressure method is harsh, and requires a large-scale pressure tester and other equipment, which results in high engineering cost. Meanwhile, a large amount of time is consumed for the static pressure test, and the engineering cost is further increased. The other method is an indirect measurement method, firstly, the axial compressive strength of the concrete prism test block is detected by a rebound method or an ultrasonic rebound synthesis method, and then the elastic modulus of the concrete prism test block is calculated by utilizing the relation between the elastic modulus of the concrete and the axial compressive strength. However, as the rebound method belongs to a surface hardness method, although the ultrasonic rebound comprehensive method can comprehensively reflect the internal compactness and the external surface hardness of a concrete structure, at present, a uniform quantitative relation between the elastic modulus of concrete and the axial compressive strength is not available. Because the increasing trends of the axial compressive strength and the elastic modulus are not consistent, the elastic modulus of the concrete is probably lower than the design index when the compressive strength of the concrete meets the design requirement. Therefore, the indirect method results in a series of calculation errors, and the elastic modulus of the concrete cannot be accurately measured.
Disclosure of Invention
Aiming at the problems, the invention provides a concrete prism test block static elastic modulus detection method based on an impact echo, which can quickly and accurately detect the existing real-time static elastic modulus of the concrete prism test block and avoid a large number of redundant test block static pressure tests; the operation is simple, the cost is low, the purchase of large-scale pressure testing machines and other testing equipment can be avoided, and the engineering cost can be effectively reduced; the formula used can reduce the error caused by indirect data derivation.
A concrete prism test block static elastic modulus detection method based on impact echo is characterized in that,
cutting the concrete prism test block into a test piece (1) with the slenderness ratio more than or equal to 2 by a cutting machine;
polishing two end surfaces of the test piece (1) along the length direction smoothly by a polishing machine;
detecting the dynamic elasticity modulus of the test piece (1) by using an impact echo method through a concrete multifunctional detector (2) and Vaseline; and deducing the static elastic modulus of the test piece (1) by using the measured dynamic elastic modulus of the test piece (1) through the numerical relationship of the dynamic-static elastic modulus, and obtaining the static elastic modulus of the concrete prism test block.
Preferably, the dynamic elastic modulus E of the test piece (1) is measureddSubstituting the coefficient into a formula (1) to obtain a static elastic modulus/dynamic elastic modulus coefficient corresponding to the dynamic elastic modulus state of the test piece (1), multiplying the coefficient by the dynamic elastic modulus to obtain the static elastic modulus of the test piece (1), and obtaining the static elastic modulus of the concrete prism test block,
Figure BDA0001693677820000021
wherein: edThe dynamic modulus of elasticity is, y is static modulus of elasticity/dynamic modulus of elasticity coefficient, parameter a, b are greater than 0.
Preferably, the dynamic elastic modulus E of the test piece (1) is measureddSubstituting into formula (2) to obtain the dynamic elastic modulus of the test piece (1)The static elastic modulus of the concrete prism test block is obtained by the corresponding static elastic modulus in the state,
Figure BDA0001693677820000022
wherein: edIs a dynamic modulus of elasticity, EcIs static modulus of elasticity, EdIs greater than or equal to the parameter c.
Preferably, the single-sided reflection method in the impact echo method of the multifunctional concrete detector (2) is used for detecting the dynamic elastic modulus of the concrete prism test block above C15.
Vaseline is used for enabling a sensor in the multifunctional concrete detector (2) to be better attached to the test piece (1). Only certain grades of concrete are used in actual engineering, concrete with too small elastic modulus to approach 0 is not discussed, and the invention is suitable for concrete above C15.
Compared with the prior art, the method can quickly and accurately detect the real-time static elastic modulus of the concrete prism test block, and avoid a large number of redundant test block static pressure tests; the operation is simple, the cost is low, the purchase of large-scale pressure testing machines and other testing equipment can be avoided, and the engineering cost can be effectively reduced; the formula used can reduce the error caused by indirect data derivation.
Drawings
FIG. 1 is a theoretical concrete stress-strain relationship.
FIG. 2 shows E in example 1c/EdCoefficient theoretical growth curve with the abscissa being the dynamic modulus of elasticity EdThe ordinate represents the static modulus of elasticity/dynamic modulus of elasticity coefficient y.
FIG. 3 shows E in example 2c/EdCoefficient theoretical growth curve with the abscissa being the dynamic modulus of elasticity EdThe ordinate is the modulus of static elasticity Ec。
FIG. 4 is a schematic diagram of the detection method in the example.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, a concrete prism test block static elastic modulus detection method based on shock echo provided by the present invention is described in detail below with reference to the accompanying drawings.
Fig. 1 shows the stress/strain relationship of a typical concrete material. For most engineering materials, the deformation of the material under uniaxial stress conditions is elastic when the stress is less than the elastic limit of the material, and it is generally believed that there is a simple linear relationship between the stress and the strain, and this class of materials is referred to as linear elastomers. However, for concrete materials, the stress-strain relationship is initially non-linear, and when the stress is relieved below the elastic limit, it will return to the original state along the original load curve. As shown in fig. 1: when the deformation is small, the elastic deformation is realized in the initial stage; when the deformation increases, the material enters a plastic deformation phase. The greater the stress, the smaller the slope of the tangent at that point, which represents the modulus of elasticity. In the static pressure test of the elastic modulus of the concrete, an external force for applying one third of the damage limit load of a prism test piece to the concrete is adopted, and the static elastic modulus of the concrete is calculated by measuring the strain generated by the long axial section in the stress range. The concrete specimen is stressed to generate larger deformation in the process of measuring the static elastic modulus of the concrete, and the aggregate cement slurry in the concrete and the cementing surface between the aggregate cement slurry and the cement slurry are subjected to larger mechanical action. The impact echo method is to generate an elastic wave on the surface of a test piece by using a vibration hammer and determine the elastic modulus through the propagation speed of the elastic wave in the test piece. The elastic modulus obtained by the method in a small strain state belongs to the dynamic elastic modulus. It is generally believed that the dynamic modulus of elasticity of a material is greater than the static modulus of elasticity, i.e., the impact echo method provides greater results than the static pressure test. Meanwhile, the dynamic elastic modulus is the initial tangent modulus of the material, and the static elastic modulus is the tangent modulus of the elastic section in the stress-strain relationship. From the relationship between stress and strain in FIG. 1, it can be seen from the slope of the curve that the dynamic modulus of elasticity of concrete measured by the impact echo method should be equal to or greater than the static modulus of elasticity of concrete.
Theoretically, the dynamic modulus of elasticity of a material is equal to or greater than the static modulus of elasticity. As can be seen from fig. 1, the closer the material approaches the elastomer before the elastic limit is reached, the closer the loading curve approaches a straight line. When the material is entirely elastomeric, the loading curve is a straight line. That is, as the material approaches the elastomer, the static modulus of elasticity approaches the dynamic modulus of elasticity wirelessly. When the material is entirely elastomeric, the static modulus of elasticity is equal to the dynamic modulus of elasticity. In particular, with concrete materials, a closer to an elastomer means a greater static modulus of elasticity, i.e. a greater dynamic modulus of elasticity. Namely, the larger the actual elastic modulus of the concrete (the higher the index is), the closer the static elastic modulus is to the dynamic elastic modulus, and the closer the ratio of the static elastic modulus to the dynamic elastic modulus is to 1.
The invention provides a static elastic modulus detection method of a concrete prism test block based on impact echo, which comprises the following steps of cutting the concrete prism test block into a test piece 1 with the slenderness ratio of more than or equal to 2 through a cutting machine; polishing two end surfaces of the test piece 1 along the length direction by a polishing machine; detecting the dynamic elasticity modulus of the test piece 1 by using an impact echo method through a multifunctional concrete detector 2 and vaseline; and deducing the static elastic modulus of the test piece 1 by using the measured dynamic elastic modulus of the test piece 1 through the numerical relationship of the dynamic-static elastic modulus, and obtaining the static elastic modulus of the concrete prism test block.
The method comprises the following steps:
according to the numerical relationship of the dynamic-static elastic modulus, the static elastic modulus/dynamic elastic modulus coefficient is less than or equal to 1, and the larger the dynamic elastic modulus is, the closer the static elastic modulus/dynamic elastic modulus coefficient is to 1 but not to exceed 1.
The theoretical growth curve of static modulus of elasticity/dynamic modulus of elasticity coefficient should be an exponential curve, as shown in fig. 2, and the asymptote is y ═ 1, and the formula is shown in formula (1).
Figure BDA0001693677820000041
In the formula: ed is the dynamic elastic modulus, y is the static elastic modulus/dynamic elastic modulus coefficient, and parameters a and b are both larger than 0.
Substituting the measured dynamic elastic modulus Ed of the test piece 1 into the formula (1) to obtain the corresponding static elastic modulus/dynamic elastic modulus coefficient in the dynamic elastic modulus state, and multiplying the coefficient by the dynamic elastic modulus to obtain the static elastic modulus of the test piece 1, thus obtaining the static elastic modulus of the concrete prism test block.
In another mode:
according to the numerical relationship of the dynamic-static elastic modulus, the dynamic elastic modulus is larger than or equal to the static elastic modulus, and the larger the dynamic elastic modulus is, the more the static elastic modulus approaches to the dynamic elastic modulus but does not exceed the dynamic elastic modulus.
The theoretical curve of the relationship between static and dynamic elastic moduli is a hyperbolic curve, as shown in fig. 3, and the asymptote of the curve is the static elastic modulus ═ dynamic elastic modulus, that is, Ec ═ Ed, and the formula is shown in formula (2).
Figure BDA0001693677820000042
In the formula: ed is the dynamic elastic modulus, Ec is the static elastic modulus, and Ed is greater than or equal to c.
And (3) substituting the measured dynamic elastic modulus Ed of the test piece 1 into the formula (2) to obtain the corresponding static elastic modulus of the test piece 1 in the dynamic elastic modulus state, namely the static elastic modulus of the concrete prism test block.
Examples
Taking the elastic modulus detection of a concrete standard prism test block (with the size of 150mm multiplied by 300mm) manufactured in a certain laboratory as an example, the method for detecting the static elastic modulus of the concrete prism test block based on the impact echo provided by the invention comprises the following specific steps:
1. polishing two end surfaces of the test block along the length direction by using a polishing machine to manufacture a test piece;
2. detecting the dynamic elasticity modulus of the test piece by using a multifunctional concrete detector and vaseline and using a single-sided reflection method based on an impact echo method;
3. and deducing the static elastic modulus of the test piece by using the measured dynamic elastic modulus of the test piece according to the numerical relationship of the dynamic-static elastic modulus, and obtaining the static elastic modulus of the concrete prism test block.
In this example, the concrete was designated as C55, and 1 group (6) of prism test blocks after standard curing for 28 days was subjected to a static pressure test to determine 3 static elastic moduli. (3 test blocks in 1 group of tests are used for carrying out axial compression strength tests, and 3 test blocks are used for carrying out elastic modulus tests, so that the elastic modulus data is only 3.) the two ends of the 3 test blocks are polished smoothly, and the slenderness ratio requirement is met. The concrete multifunctional detector detects and obtains 3 dynamic elastic moduli, the respective static elastic moduli are obtained through conversion of two functions, and the static elastic moduli are compared with the static elastic modulus measured by the test block static pressure test in the previous stage, and the results are shown in tables 1 and 2.
Because the properties of the concrete of each mark are different, the parameters a, b and c of the concrete with different specifications are different. When the concrete strength grade is C55, a is 12.77046, b is 0.11366, and C is 18.16515.
TABLE 1 exponential curve derivation static modulus of elasticity, GPa
Figure BDA0001693677820000051
TABLE 2 hyperbolically derived static modulus of elasticity, GPa
Figure BDA0001693677820000052
As can be seen from tables 1 and 2, the error of the static elastic modulus of the concrete prism test block detected by the method is small, and the precision requirement can be met within the engineering allowable range.
Compared with the prior art, the method for detecting the static elastic modulus of the concrete prism test block based on the impact echo can quickly and accurately detect the real-time static elastic modulus of the concrete prism test block, and avoid a large number of redundant test block static pressure tests; the operation is simple, the cost is low, the purchase of large-scale pressure testing machines and other testing equipment can be avoided, and the engineering cost can be effectively reduced; the formula used can reduce the error caused by indirect data derivation.
The above embodiments are merely representative embodiments of the present invention, but the technical solution protected by the present invention is not limited thereto, and any changes or substitutions that can be directly derived or easily conceived from the disclosure of the present invention by those skilled in the art within the technical scope of the present invention are included in the protective scope of the present invention.

Claims (2)

1. A concrete prism test block static elastic modulus detection method based on impact echo is characterized in that,
cutting the concrete prism test block into a test piece (1) with the slenderness ratio more than or equal to 2 by a cutting machine;
polishing two end surfaces of the test piece (1) along the length direction smoothly by a polishing machine;
detecting the dynamic elasticity modulus of the test piece (1) by using an impact echo method through a concrete multifunctional detector (2) and Vaseline; deducing the static elastic modulus of the test piece (1) by using the measured dynamic elastic modulus of the test piece (1) through the numerical relationship of the dynamic-static elastic modulus to obtain the static elastic modulus of the concrete prism test block;
the dynamic elastic modulus E of the test piece (1) to be measureddSubstituting the coefficient into a formula (1) to obtain a static elastic modulus/dynamic elastic modulus coefficient corresponding to the dynamic elastic modulus state of the test piece (1), multiplying the coefficient by the dynamic elastic modulus to obtain the static elastic modulus of the test piece (1), and obtaining the static elastic modulus of the concrete prism test block,
Figure FDA0002603772330000011
wherein: edIs dynamic elastic modulus, y is static elastic modulus/dynamic elastic modulus coefficient, and both parameters a and b are greater than 0;
or the dynamic elastic modulus E of the test piece (1) to be measureddSubstituting the static elastic modulus of the test piece (1) in the dynamic elastic modulus state into the formula (2) to obtain the static elastic modulus of the concrete prism test piece,
Figure FDA0002603772330000012
wherein: edIs a dynamic modulus of elasticity, EcIs static modulus of elasticity, EdIs greater than or equal to the parameter c.
2. The method for detecting the static elastic modulus of the concrete prism test block based on the impact echo as claimed in claim 1, wherein the dynamic elastic modulus of the concrete prism test block above C15 is detected by using a single-sided reflection method in the impact echo method of the multifunctional concrete detector (2).
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CN102116716A (en) * 2010-08-10 2011-07-06 中国水利水电第十四工程局有限公司 Method for determining modulus of elasticity of plastic concrete
CN104807983A (en) * 2015-04-23 2015-07-29 山东大学 Determination method for elasticity modulus of early-stage concrete

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