CN105823685A - Experimental method for determining concrete tensile strength through transverse splitting method - Google Patents

Abstract

The invention belongs to the technical field of concrete performance tests, and particularly relates to an experimental method for determining the concrete tensile strength through a transverse splitting method.The transverse splitting method is the method that the splitting tension acts on the cross section of cylindrical concrete, the cylinder is subjected to tension in the busbar direction, the transverse splitting face of the cylinder is destroyed through splitting, and the concrete tensile strength is determined.By means of the experimental method for determining the concrete tensile strength through the transverse splitting method, much tensile strength data can be obtained from few concrete core samples compared with an existing technical regulation of detecting the concrete tensile strength through a coring method, the concrete samples do not need to be processed, experiments are very convenient and rapid, detection can be conducted on concrete samples which are several centimeters long, and core sample detection on the tensile strength of a concrete thin-slab structure is achieved.Meanwhile, by combining a concrete splitting tensile strength calculation formula, the average value of the ratio of a measured value to a calculated value of the concrete splitting tensile strength is 1.09, and it is shown that the data obtained through the experimental method is reasonable and reliable.

Description

A kind of traction therapy of laterally splitting measures the test method of concrete tensile strength

Technical field

The invention belongs to testing concrete performance technical field, be specifically related to a kind of traction therapy of laterally splitting and measure the test method of concrete tensile strength.

Background technology

At present in the quality testing of large-sized concrete structure, core drilling method is generally considered one of the highest detection method of precision.Core drilling method is the test method of half breakage, though having the advantages such as testing result is directly perceived, reliable, but structure can be caused a certain degree of destruction by drill core, and coring quantity is severely limited, and core sample is wasted seriously during drilling through and be processed into standard specimen.Additionally, many concrete with long age structure, the concrete carbonizations the most on component top layer, carbonation depth is the least, several centimeters, when core boring sampling measures the intensity of carbonizing zone concrete by conventional resistance to compression and splitting tensile test, carbonizing zone concrete core sample length is often unsatisfactory for code requirement so that conventional cylindrical specimens cannot use.

The method measuring concrete tensile strength has axial tension test method, concrete girder bend test method and splits and draw test method(s).Axial tension test method measures the tensile strength of concrete and need not make any theoretic it is assumed that measurement result is close to the actual value of concrete, but in test, stress eccentricity issues is difficult to overcome, and brings difficulty to the popularization and application of test；Concrete girder bend test method is a kind of method of indirect determination concrete tensile strength, it assumes that the upper and lower compressive strain of natural axis and stretching strain are linear change, tensile modulus of elasticity is equal to modulus of elasticity in comperssion, but actually, when concrete pulling stress reaches 0.35ft (ft is axle center tension test ultimate strength), the most non-linear relation of ess-strain, elastic modelling quantity begins to decline simultaneously, this calculation assumption used in deriving with this law theory has certain discrepancy, and the actual tensile strength values measured is often much higher than axial tension test result；Splitting and drawing test method(s) is also a kind of non-immediate assay method, the major defect of the method is to there will be the biggest stress at loading point to concentrate, for improving this phenomenon, bakelite filler strip is disposed between testing machine bearing plate and test specimen, straight line load on cylinder is replaced to the load along filler strip width distribution, this is not bery consistent by the supposition of line load with test specimen, and result of the test is the most often higher than axial tension test value.

Summary of the invention

For overcoming above-mentioned weak point present in prior art, the invention provides a kind of cylinder and laterally split traction therapy and measure the test method of concrete tensile strength.

For achieving the above object, the technical solution used in the present invention is, a kind of traction therapy of laterally splitting measures the test method of concrete tensile strength, comprises the following steps:

(1) with pencil and slide calliper rule, cylinder concrete core sample test specimen draws the circle parallel with its transverse section to determine the position of splitting surface, splitting surface distance >=35mm away from core sample test specimen both ends of the surface；

(2) two test pressing elements are taken, test pressing element includes increased pressure board, increased pressure board center is provided with ogee section push type broach, the push type broach face width degree of ogee section push type broach is 5 ± 2mm, central angle is 90 ± 3 °, ogee section push type broach both sides are provided with several ribbed panels, two test pressing elements are individually placed to the center of the upper and lower pressing plate of pressure testing machine, then cylinder concrete core sample test specimen are placed between the upper and lower ogee section push type broach of two test pressing elements；According to the position of the splitting surface determined, adjust upper and lower ogee section push type broach, ensure that upper and lower ogee section push type broach upwards aligns vertical simultaneously；Before loading, adjust ball seat, make the upper and lower pressing plate of pressure testing machine be in close contact with the increased pressure board of corresponding test pressing element；

(3) load continuously and equably with the speed of 0.04MPa/s～0.06MPa/s, when cylinder concrete core sample test specimen is close to when destroying, stops adjusting throttle, until concrete core sample test specimen destroys, record failing load；

(4) concrete split tensile strength it is calculated as follows:

$f_{ts,cu}=0.53\frac{P}{A}$

In formula: f_ts,cuConcrete cube test specimen split tensile strength, MPa；

The horizontal failing load of splitting of P cylinder concrete core sample test specimen, kN；

A cylinder concrete core sample test specimen cross-sectional area, mm²。

Diameter 100 ± 10mm, the highly >=70mm of described cylinder concrete core sample test specimen, the height of core sample test specimen is not less than 3 times of concrete coarse aggregate maximum particle diameter simultaneously.

Test fixture center is provided with ogee section push type broach, and the push type broach face width degree of ogee section push type broach is 5 ± 2mm, central angle is 90 ± 3 °.

Described cylinder concrete core sample be the ratio of mud be normal concrete or the rubber concrete of 0.38～0.74.

The method filling rubber grain in rubber concrete is that equal-volume replaces sand, and rubber grain volume is 0～15%, and rubber grain particle diameter is 0～6mm.

The design principle of the computing formula of concrete split tensile strength is as follows:

Assuming that horizontal intensity fcts of splitting of concrete core sample uses following formula to represent:

$f_{cts}=\mathrm{\γ}\frac{P_2}{A}---\left(1\right)$

In formula: P₂For the horizontal failing load of splitting of cylinder test specimen, kN；A is the cross-sectional area of test specimen, mm²；γ is coefficient of colligation, with relating to parameters such as push type broach face width degree, push type broach central angles；

" concrete for hydraulic structure testing regulations " SL352 2006 cube is vertical splits intensity fts, and cu uses following formula to try to achieve:

$f_{ts,cu}=\frac{2P_1}{{\mathrm{\πa}}^2}---\left(2\right)$

In formula: P₁For the vertical failing load of splitting of concrete cube test specimen, kN；A is the length of side of cube specimen splitting surface, mm；

Identical concrete material, in theory vertical intensity fts of splitting of cube, certain internal relation should be there is in cu and horizontal intensity fcts of splitting of cylinder, it may be assumed that

$f_{ts,cu}={\mathrm{\βf}}_{cts}=\mathrm{\β}\mathrm{\γ}\frac{P_2}{A}---\left(3\right)$

In formula: β is both correlation coefficienies.Make Ψ=β γ, and convolution (2), then have:

$\frac{2P_1}{{\mathrm{\πa}}^2}=\mathrm{\ψ}\frac{P_2}{A}---\left(4\right)$

When concrete cube test specimen length of side a=100mm, during a diameter of 100mm of cylinder test specimen, formula (4) can be reduced to:

P₁=2 ψ P₂(5)

Ψ=0.53 can be deduced according to test data；Therefore, concrete split tensile strength can be calculated as follows:

$f_{ts,cu}=0.53\frac{P}{A}.$

The beneficial effect comprise that: the horizontal method of splitting is a kind of to act on splitting pulling force on the cross section of cylinder concrete, makes cylindrical generatrix direction tension, cause the horizontal right in the face of cylinder to split and pull open the bad method measuring concrete tensile strength.The present invention can obtain relatively large number of Tensile strength data (compared with existing unbearable method detection concrete strength technical regulation) from less concrete core sample, and concrete core sample is without processing, it is the most convenient to test, and the long concrete core sample of logarithm centimetre also can detect, it is achieved that the core sample of concrete thin plates structure tensile strength is detected.In combination with concrete split tensile strength computing formula of the present invention, concrete split tensile strength measured value is 1.09 with the meansigma methods of the ratio of value of calculation, illustrates that the test method of the present invention obtains data the most reliable.

Accompanying drawing explanation

Fig. 1 is the structural representation of test pressing element used in the present invention；

Fig. 2 is the use view testing pressing element in the present invention.

Detailed description of the invention

Below in conjunction with specific embodiment, the present invention is described in further detail.

Embodiment 1

Test pressing element used is as shown in Figure 1: include the increased pressure board 1 of square shape, increased pressure board 1 center is provided with ogee section push type broach 2, the push type broach face width degree W of ogee section push type broach 2 is 5mm, central angle θ is 90 °, and ogee section push type broach 2 is symmetrically arranged on two with four ribbed panels 3.The material of the test each parts of pressing element (i.e. increased pressure board 1, ogee section push type broach 2, ribbed panel 3) is carbon structural steel Q235A.

Test test specimen

(1) cylinder core diameter 100mm, cuts into the core sample test specimen of height >=70mm, and the height of core sample test specimen is not less than 3 times of concrete coarse aggregate maximum particle diameter simultaneously, and core sample test specimen can not have crackle or other bigger defects；

(2) described cylinder concrete core sample be the ratio of mud be normal concrete or the rubber concrete of 0.38～0.74.

Test method (uses state as shown in Figure 2), comprises the following steps:

(1) with pencil and slide calliper rule, cylinder concrete core sample test specimen 4 draws the circle parallel with its transverse section to determine the position of splitting surface, splitting surface distance >=35mm away from core sample test specimen both ends of the surface；

(2) take two test pressing elements, be individually placed to the center of the upper and lower pressing plate of pressure testing machine, then cylinder concrete core sample test specimen be placed between the upper and lower ogee section push type broach of two test pressing elements；According to the position of the splitting surface determined, adjust upper and lower ogee section push type broach, ensure that upper and lower ogee section push type broach upwards aligns vertical simultaneously；Before loading, adjust ball seat, make the upper and lower pressing plate of pressure testing machine be in close contact with the increased pressure board of corresponding test pressing element；

(3) load continuously and equably with the speed of 0.04MPa/s～0.06MPa/s, when cylinder concrete core sample test specimen is close to when destroying, stops adjusting throttle, until concrete core sample test specimen destroys, record failing load；

(4) concrete split tensile strength it is calculated as follows:

$f_{ts,cu}=0.53\frac{P}{A}$

In formula: f_ts,cuConcrete cube test specimen split tensile strength, MPa；

The horizontal failing load of splitting of P cylinder concrete core sample test specimen, kN；

A cylinder concrete core sample test specimen cross-sectional area, mm²。

Concrete split tensile strength measured value is 1.09 with the meansigma methods of the ratio of value of calculation, illustrates that the test method of the present embodiment obtains data the most reliable.

Claims (4)

1. the test method laterally splitting traction therapy mensuration concrete tensile strength, it is characterised in that comprise the following steps:

(1) with pencil and slide calliper rule, cylinder concrete core sample test specimen draws the circle parallel with its transverse section to determine the position of splitting surface, splitting surface distance >=35mm away from core sample test specimen both ends of the surface；

(2) two test pressing elements are taken, test pressing element includes increased pressure board, increased pressure board center is provided with ogee section push type broach, the push type broach face width degree of ogee section push type broach is 5 ± 2mm, central angle is 90 ± 3 °, ogee section push type broach both sides are provided with several ribbed panels, two test pressing elements are individually placed to the center of the upper and lower pressing plate of pressure testing machine, then cylinder concrete core sample test specimen are placed between the upper and lower ogee section push type broach of two test pressing elements；According to the position of the splitting surface determined, adjust upper and lower ogee section push type broach, ensure that upper and lower ogee section push type broach upwards aligns vertical simultaneously；Before loading, adjust ball seat, make the upper and lower pressing plate of pressure testing machine be in close contact with the increased pressure board of corresponding test pressing element；

(3) load continuously and equably with the speed of 0.04MPa/s～0.06MPa/s, when cylinder concrete core sample test specimen is close to when destroying, stops adjusting throttle, until concrete core sample test specimen destroys, record failing load；

(4) concrete split tensile strength it is calculated as follows:

$f_{ts,cu}=0.53\frac{P}{A}$

In formula: f_ts,cuConcrete cube test specimen split tensile strength, MPa；

P cylinder concrete core sample test specimen failing load, kN；

A cylinder concrete core sample test specimen cross-sectional area, mm²。

2. test method as claimed in claim 1, it is characterised in that: diameter 100 ± 10mm, the highly >=70mm of described cylinder concrete core sample test specimen, the height of core sample test specimen is not less than 3 times of concrete coarse aggregate maximum particle diameter simultaneously.

3. test method as claimed in claim 1, it is characterised in that: described cylinder concrete core sample be the ratio of mud be normal concrete or the rubber concrete of 0.38～0.74.

4. test method as claimed in claim 3, it is characterised in that: the method filling rubber grain in rubber concrete is that equal-volume replaces sand, and rubber grain volume is 0～15%, and rubber grain particle diameter is 0～6mm.