CN101699267A - Loading device for testing concrete chloride ion permeability by coulometry and testing method thereof - Google Patents

Abstract

The invention provides a loading device for testing the chloride ion permeability of concrete by the electric quantity method. Two screw holes are arranged on the steel base plate, and two parallel screw rods are inserted into the screw holes, and the screw rods are successively covered with pressing steel plates parallel to the steel base plate, The upper pressure plate and the top plate; a jack is set between the top plate and the upper pressure plate; a force measuring device is set between the upper pressure plate and the lower pressure plate; A protruding steel pressure head is arranged on the lower part; the screw rod on the upper part of the upper pressing plate is covered with a positioning bolt cap of the upper pressing plate, and the screw rod on the upper part of the top plate is covered with a top plate positioning bolt cap. The invention also provides a method for testing the chloride ion permeability of concrete by using the loading device. The loading device of the invention solves the problems that the conventional concrete chloride ion permeability testing device cannot apply bending load to the tested piece, cannot simulate the actual load state of the concrete member in service, and cannot measure the concrete chloride ion permeability under the bending load condition.

Description

Concrete chloride ion permeability coulometric test loading device and test method

technical field

The invention relates to a loading device for testing the chloride ion permeability of concrete by the electrical method, in particular to a loading device for performing the chloride ion permeability electrical method test on the concrete under a bending load condition, and the invention also relates to a test using the loading device method.

Background technique

Chloride ion permeability is not only an important index to characterize the permeability of concrete, but also an indicator for the corrosion resistance of steel bars in reinforced concrete in environments with high chloride ion content (such as seaport terminals, underground engineering, hydraulic structures and reinforced concrete poles in coastal areas). important sign. The current methods for measuring the chloride ion permeability of concrete mainly include the electric quantity method and the rapid chloride ion migration method, but the test pieces in the two methods do not involve the effect of load. However, concrete in actual service is not only affected by external factors such as water pressure and chloride ion concentration difference that affect chloride ion penetration. It is affected by the bending load and the erosion of surface chloride ions. Loading tends to affect the generation and propagation of micro-cracks in concrete, affecting the permeability of concrete, including chloride ion permeability. The standard (ASTM C1202) adopted by many countries for evaluating the resistance of concrete to chloride ion penetration (ASTM C1202) formulated by the American Society for Standards and Testing of Materials is to apply a DC voltage of 60V at both ends of a Φ95×50mm concrete sample, and pass the test for 6h The permeability of concrete is evaluated by the amount of electricity flowing through it. The devices and methods used do not consider and cannot realize the simultaneous application of bending loads to the test pieces. Therefore, due to the constraints of conventional test equipment, the test method for the chloride ion permeability of concrete under bending load conditions is still blank.

Contents of the invention

The object of the present invention is to address the deficiencies of the prior art, and provide a loading device capable of applying bending loads to concrete for testing the chloride ion permeability of concrete by galometric method.

Another object of the present invention is to provide a method for testing the chloride ion permeability of concrete using the loading device.

The purpose of the present invention is achieved like this: concrete chloride ion permeability electrometry test loading device, two screw holes are arranged on the steel base plate, insert two parallel screw rods in the screw holes, and described screw rods are sleeved with the described screw rods successively. The lower pressure plate, the upper pressure plate and the top plate parallel to the steel bottom plate;

A jack is arranged between the top plate and the upper pressing plate; a force measuring device is arranged between the upper pressing plate and the lower pressing plate, and the force measuring device includes a pressure sensor and a display instrument;

A protruding steel support is set upward on the steel bottom plate; a protruding steel pressure head is set downward on the lower pressure plate; Has top plate set bolt caps.

Two screw holes on the steel base plate are arranged symmetrically at both ends of the steel base plate; there are two steel supports, which are symmetrically arranged between the two screw holes.

There are two steel pressure heads, which are respectively arranged at the two screw openings where the lower pressing steel plate is connected with the screw rod.

The working principle of the loading device of the present invention is as follows: the pressure load is applied to the upper pressing plate by the jack, and the pressure is measured by the dynamometer; the pressure generated by the jack is applied to the concrete test by the steel pressure head of the upper pressing plate, the dynamometer, and the lower pressing plate. Two parallel steel pressure heads and two parallel steel supports make the concrete specimen subjected to two equal concentrated bending loads acting at the third point between the fulcrums; when the dynamometer displays the set pressure value, Tighten the positioning bolt cap of the upper compression steel plate, and the concrete specimen will bear a stable bending load at this time.

Another object of the present invention is achieved like this: utilize above-mentioned loading device to carry out the method for concrete chloride ion permeability coulometric method test, carry out as follows:

Step 1. Put the straight quadrangular prism concrete specimen on the screw rod between the steel base plate and the lower pressure plate through two screw holes, pressurize it with a jack, and the pressure passes through the upper pressure plate, the dynamometer and the lower pressure plate. The steel indenter is transferred to the concrete specimen, and when the dynamometer displays the set load value, the set bolt cap of the upper pressure plate is tightened;

The two steel indenters and the two steel supports act on the concrete specimen together, so that the concrete specimen is subjected to two equal concentrated bending loads acting at the third point between the fulcrums;

The size of the test pressure load is calculated according to the following formula:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&eta;f</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; b</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>$

In the formula: P-test compressive load (N); f _t -bending strength of concrete specimen (MPa); η-set stress level (%); b-specimen width (mm); h-specimen height (mm ); l- the distance between the two pressure heads of the lower pressure plate (mm);

Step 2. Install the test tank with electrodes of the concrete permeability electric tester on two opposite sides of the concrete specimen, inject NaOH solution into the positive test tank, and inject NaCl solution into the negative test tank, and use 50-120V DC , to test the electricity passing through the concrete specimen within a specified time when different bending loads are applied;

Step 3. According to the thickness of the specimen, the applied voltage and the electricity passing through, calculate the equivalent current flow which characterizes the chloride ion permeability of the concrete:

Measure the initial reading of the recorded current I ₀ , then measure and record the current reading I _i every 15 minutes until 6 hours, and calculate the total electricity Q passing through the concrete specimen within 6 hours according to the following formula:

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 300</span>}<span\; class="notranslate">\; \&times;</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 36</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>$

In the formula: the total electricity (C) passing through the concrete specimen within Q-6h;

I _i - current reading (A) measured for the ith time;

I _i-1 - current reading (A) measured for the i-1th time;

Convert the total electric quantity into the equivalent electrified electric quantity when the thickness of the specimen is 50mm and the DC voltage is 60V according to the following formula:

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; b</span>}}{\mathrm{<span\; class="notranslate">\; 50</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 60</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1.2</span>}\mathrm{<span\; class="notranslate">\; bQ</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}$

In the formula: the equivalent electric current (C) passing through the concrete specimen within Q _e -6h;

b-prismatic concrete specimen thickness (mm);

V-DC voltage (V);

Take the average value of the equivalent electricity of the three test pieces in the same group as the equivalent electricity flow of the group of test pieces, and evaluate the chloride ion permeability of the concrete under the loaded state according to Table 1.

Table 1 Chloride ion permeability based on equivalent flux

The beneficial effects of the present invention are:

1. The loading device of the present invention solves the problem that the conventional concrete chloride ion permeability test device cannot apply bending load to the tested piece, so it cannot simulate the actual load state of the concrete member in service and cannot measure the bending load. The problem of chloride ion permeability of concrete;

2. The loading device of the present invention is simple in structure and easy to operate, and the load during the test is stable, can be displayed in real time, and can be adjusted at any time according to needs, and loaded step by step, and the test results are stable and reliable;

3. The inventive method adopts the equivalent electric quantity to characterize the chloride ion permeability of the concrete under the loaded state, which solves the comparability problem of different test piece thicknesses and different test voltage measurement results;

4. The method of the present invention adopts the bending load loading device to apply bending loads of different sizes to the concrete specimens, and can study the influence of bending load conditions on the chloride ion permeability of concrete, thereby revealing the evolution law and damage mechanism of concrete permeability under the multi-factor combination condition And combination mechanism, if popularized and applied to actual engineering, it can provide a basis for the design, health diagnosis and reinforcement of concrete structures.

Description of drawings

Fig. 1 is the structural representation of the loading device of concrete chloride ion permeability electrometry test of the present invention;

Fig. 2 (a) is the assembly schematic diagram of the concrete chloride ion permeability electrical method testing device that the right quadrangular prism concrete specimen and the concrete chloride ion permeability electric measuring instrument test tank are installed;

Fig. 2 (b) is the left view of Fig. 2 (a);

Fig. 3 (a) is the structural representation of the steel floor with two parallel steel supports;

Fig. 3 (b) is the left view of Fig. 3 (a);

Fig. 4 (a) is the structure schematic diagram of the down-pressed steel plate of band steel pressure head at both ends;

Fig. 4 (b) is the left view of Fig. 4 (a);

In the figure: 1. Steel bottom plate; 2. Screw; 3. Lower pressure plate; 4. Force measuring device; 5. Upper pressure plate; 6. Positioning bolt cap of upper pressure plate; 7. Jack; 8. Top plate; Positioning bolt cap; 10. Concrete specimen; 11. Electrode test tank of concrete permeability electric tester; 12. Steel support; 13. Steel pressure head.

Detailed ways

The technical solution of the present invention will be described in detail below by means of embodiments in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the embodiments.

Example 1

Loading device and loading method for galometric test of chloride ion permeability of concrete under bending load

Concrete chloride ion permeability electric method test loading device, which is composed of a steel base plate 1 with two parallel supports 12, a screw rod 2, a lower pressing steel plate 3 with steel pressure heads 13 at both ends, a force measuring device (including a pressure sensor and a display instrument) 4, upper pressure plate 5, upper pressure plate positioning bolt cap 6, jack 7, top plate 8 and top plate positioning bolt cap 9;

The steel bottom plate 1 is 400mm long, 300mm wide, and 30mm thick. The height of the two parallel supports on the top is 70mm, and the width is 30mm. The top of the support is semicircular, and the distance between the centers of the two supports is 100mm. M24 screw holes with a spacing of 200mm; the dimensions of the lower pressure plate 3, the upper pressure plate 5 and the top plate 8 are all 360mm in length, 70mm in width, and 30mm in thickness. The top of the head is semicircular, and the distance between the centers of the two indenters is 300mm; the size of the prismatic concrete specimen 10 is 100mm×70mm×400mm; There are two symmetrically distributed round holes on the axis, and the distance between the centers of the holes is 300mm.

Screw two 700mm long, M24 screw rods 2 into the two screw holes of the steel base plate, respectively pass the screw rods 2 through the prismatic concrete specimen 10 and the lower pressure steel plate 3, and place the maximum capacity of 30kN in the middle of the lower pressure steel 3 For the sensor 4 of the dynamometer, insert the screw 2 into the upper pressure plate 5, screw on the positioning bolt cap 6 of the upper pressure plate, place a 30kN jack 7 in the middle of the upper pressure plate 5, and then insert the screw 2 into the top plate 8. Screw on the top plate fixing bolt cap 9. Use the jack 7 to pressurize the upper pressure plate 5, and the pressure is displayed by the dynamometer display. When it reaches 7840N, tighten the upper pressure plate positioning bolt cap 6. At this time, the lower pressure plate 3 bears a stable pressure of 7840N; The two indenters on the steel plate 3 exert a stable and uniform pressure of 3920N on both ends of the prismatic concrete specimen 10 respectively. Under the simultaneous action of the two parallel supports on the steel base plate 1, the concrete specimen bears 3.36MPa within a width range of 100mm in the middle Uniform flexural tensile stress.

The device described in this embodiment can be used to effectively perform the galometric test of the chloride ion permeability of hydraulic concrete under bending load conditions.

Example 2

Coulometry test method for chloride ion permeability of hydraulic concrete under complex compressive load conditions

Use P II 42.5 grade cement, river sand with a fineness modulus of 2.4, limestone artificial gravel with a maximum particle size of 20mm, and tap water to prepare concrete according to the mix ratio shown in the table, and form it into a prismatic concrete of 100mm×70mm×400mm Test pieces, 21 test pieces for each ratio. After the specimens were cured in water in the standard concrete curing room for 28 days, three of each proportioned specimens were selected to measure the four-point flexural strength, which was used as a reference for the loading size of the remaining specimens in the chloride ion permeability test.

Table 2 Concrete mix ratio and flexural strength of specimens

Each ratio is divided into 6 groups, according to the bending load levels of 0, 20%, 40%, 50%, 60%, and 70% six loading methods are measured, and 3 test pieces are measured in each group.

Step 1: Install the prismatic concrete specimen (10) on the loading device according to the method described in Example 1 and apply the load according to the bending load level required by the test setting. The value of the compressive load applied each time is calculated according to the following formula:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&eta;f</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}\mathrm{<span\; class="notranslate">\; b</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 70</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 100</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&eta;f</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}{\mathrm{<span\; class="notranslate">\; 300</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2333</span>}{\mathrm{<span\; class="notranslate">\; \&eta;f</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; )</span>$

Step 2: Install a pair of test tanks (11) with electrodes of the concrete permeability electric tester on two opposite free surfaces of the test piece. Fill the positive test tank with 0.3mol/L NaOH solution, fill the negative test tank with 3% NaCl solution, connect the positive and negative electrodes of the test tank to the concrete permeability electric meter, switch on the power supply, and test the above two test tanks. Apply a constant voltage of 80V DC to the positive and negative electrodes, measure the initial reading of the recorded current I0, and then measure the recorded current reading _Ii every 10 minutes until 6h. Calculate the total electricity Q passing through the concrete specimen within 6 hours according to the following formula:

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 300</span>}<span\; class="notranslate">\; \&times;</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 36</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>$

In the formula: the total electricity (C) passing through the concrete specimen within Q-6h; I _i - the current reading (A) measured for the ith time.

The total energization Q is converted into the equivalent energization Q _e according to the following formula:

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1.2</span>}\mathrm{<span\; class="notranslate">\; bQ</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1.2</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 70</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; Q</span>}}{\mathrm{<span\; class="notranslate">\; 80</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1.05</span>}\mathrm{<span\; class="notranslate">\; Q</span>}$

Take the average value of the passing electricity of the three test pieces in the same group, and use it as the passing electricity of the group of test pieces to evaluate the chloride ion penetration resistance of the concrete under the loaded state. The results are shown in Table 3.

Table 3 The results of coulometric determination of chloride ion permeability of hydraulic concrete under different compressive loads

It can be seen from the test results that:

The electrical flux (ie, chloride ion permeability) of the two concretes with different strengths showed the same variation law under bending load. As the loading level increases, the chloride ion permeability of concrete increases gradually. This is due to the expansion of the original micro-cracks in the concrete under the bending load, and the generation of new micro-cracks, thereby improving the permeability of the concrete. When the loading level reaches more than 60%, the chloride ion permeability of the specimen increases rapidly, which is due to the rapid increase of various crack propagation degrees when the maximum loading level is higher.

Claims (4)

1. Concrete chloride ion permeability electric method test loading device, it is characterized in that: two screw holes are arranged on the steel base plate (1), insert two parallel screw rods (2) in the screw holes, on the screw rod (2) A lower pressure steel plate (3), an upper pressure steel plate (5) and a top plate (8) parallel to the steel bottom plate (1) are sequentially covered; A jack (7) is arranged between the top plate (8) and the upper pressing steel plate (5); a force measuring device (4) is arranged between the upper pressing steel plate (5) and the lower pressing steel plate (3); A protruding steel support (12) is arranged upward on the steel base plate (1); a protruding steel pressure head (13) is provided downward on the lower pressure plate (3); 2) upper pressure plate set bolt cap (6) is set on, and the top plate set bolt cap (9) is set on the screw rod (2) on the top plate (8). 2. the concrete chloride ion permeability coulometric method test loading device according to claim 1 is characterized in that: two screw holes are symmetrically arranged at the two ends of described steel base plate (1); Described steel support (12) There are two, symmetrically arranged between the two screw holes. 3. the concrete soil chloride ion permeability electric quantity test loading device according to claim 2, is characterized in that: described steel indenter (13) is two, is respectively arranged on described lower pressing steel plate (3) and described The two screw ports where the screw rod (2) is connected. 4. utilize the loading device described in claim 3 to carry out the method for concrete chloride ion permeability coulometric method test, it is characterized in that: Step 1. Put the straight quadrangular prism concrete specimen (10) on the screw rod (2) between the steel base plate (1) and the lower pressure plate (3) through two screw holes, pressurize it with a jack (7), The pressure is transmitted to the concrete specimen (10) through the steel pressure head (13) on the upper pressure plate (5), the dynamometer (4), and the lower pressure plate (3); when the dynamometer (4) Tighten the positioning bolt cap (6) of the upper pressure plate when the set load value is displayed; Step 2: Install the electrode test tank (11) of the concrete permeability electric tester on two opposite sides of the concrete specimen (10), inject NaOH solution into the positive test tank, and inject NaCl solution into the negative test tank , using 50-120V direct current to test the electric quantity passing through the concrete specimen (10) within a specified time when different bending loads are applied; Step 3, according to the thickness of the test piece, the applied voltage and the electricity passing through, calculate the equivalent current flow representing the chloride ion permeability of the concrete.

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