Who can tell me some common test steps and precautions for concrete?

1. Compressive strength test

1. Instruments and equipment

Compression testing machine, and meet the following requirements:

(1) The accuracy is ±1, and the failure load of the specimen should be greater than 20% of the full range of the press and not less than 80% of the full range of the press.

(2) It should have a loading speed indicating device or a loading speed control device, and should be able to load evenly and continuously.

(3) There should be a valid metrological verification certificate.

Note: Unless otherwise specified, the requirements for the pressure testing machine used in the following test items are the same.

2. Test steps

(1) The test piece should be tested in time after being taken out from the maintenance location, and the surface of the test piece and the upper and lower pressure-bearing plates should be wiped clean.

(2) Place the test piece on the lower pressure plate or backing plate of the testing machine. The pressure-bearing surface of the test piece should be perpendicular to the top surface during molding. The center of the test piece should be aligned with the center of the lower pressure plate of the testing machine. Start the testing machine. When the upper pressure plate is close to the test piece or steel backing plate, adjust the ball seat to make the contact balanced.

(3) Loading should be continued and evenly during the test. When the concrete strength grade is

(4) When the specimen is close to destruction and begins to deform sharply, the throttle of the testing machine should be stopped until it is destroyed. The failure load is then recorded.

3. Data processing and result judgment

(1) The concrete cube compressive strength should be calculated according to the following formula:

Where - the concrete axial resistance Compressive strength (MPa);

——Failure load of the specimen (N);

——Pressure-bearing area of ??the specimen (mm?).

The calculation of concrete cube compressive strength should be accurate to 0.1MPa.

(2) The determination of the strength value should comply with the following regulations:

The arithmetic mean of the measured values ??of the three test pieces is used as the strength value of the group of test pieces (accurate to 0.1MPa) ;

If the difference between the maximum or minimum value among the three measured values ??and the middle value exceeds 15, the maximum and minimum values ??will be rounded off and the middle value will be taken as The compressive strength value of this group of specimens;

If the difference between the maximum value, the minimum value and the middle value exceeds 15 of the middle value, the test results of this group of specimens are invalid.

When the concrete strength grade is

2. Flexural strength test

1. Instruments and equipment

Pressure testing machine:

(1) The testing machine should comply with this specification Requirements for testing machines in joint compressive strength tests;

(2) The testing machine should be able to apply a uniform, continuous, speed-controllable load, and have a device that can enable two equal loads to act on the specimen at the same time. The flexural test device at the 3rd minute point of the span is shown in Figure 4.2.2:

(3) The support and loading head of the test piece should be 20 to 40mm in diameter and not less than b in length. 10mm hard steel cylinder, the footing of the support is a fixed hinge, and the others should be rolling fulcrums.

2. Test steps

(1) The test piece should be tested in time after being taken out from the maintenance location, and the surface should be wiped clean.

(2) Install the test piece according to the drawing, and the installation size deviation shall not be greater than 1mm. The pressure-bearing surface of the test piece shall be the side surface of the test piece when it is formed. The contact surface between the support and the pressure-bearing surface and the cylinder should be smooth and even, otherwise it should be padded flat.

(3) The applied load should be uniform and continuous.

When the concrete strength grade is

3. Data processing and result judgment

(1) If the fracture position of the lower edge of the specimen is between two concentrated load action lines, the flexural strength of the specimen is Calculation by formula:

In the formula - concrete flexural strength (MPa);

- specimen failure load (N);

- support The span between the specimens (mm);

——The height of the specimen section (mm);

—The width of the specimen section (mm);

Bending resistance The intensity should be accurate to 0.1MPa.

(2) The determination of the flexural strength value shall comply with the provisions of Article 3, paragraph 2, of the compressive strength test in this section.

(3) If one of the three specimens has a fracture surface located outside the two concentrated loads, the concrete flexural strength value will be calculated based on the test results of the other two specimens. If the difference between the two measured values ??is not greater than 15% of the two measured values, the flexural strength value of the set of specimens shall be calculated based on the average of the two measured values, otherwise the test of the set of specimens shall be invalid. If the fracture position of the lower edge of two specimens is outside the two concentrated load action lines, the test of this group of specimens will be invalid.

(4) When the size of the test piece is 100mm×100mm×400mm non-standard test piece, it should be multiplied by the size conversion factor 0.85; when the concrete strength grade ≥C60, the standard test piece should be used; use non-standard test piece When using standard test pieces, the size conversion factor should be determined by testing.

3. Impermeability test

1. Instruments and equipment

Concrete impermeability meter: It should be able to stabilize the water pressure according to the prescribed system during the test. device on the device.

Pressure device: spiral or other form, the pressure should be enough to press the test piece into the test piece sleeve.

2. Preparation of specimens

The impermeability test should use a truncated cone with a top diameter of 175mm, a bottom diameter of 185mm, and a height of 150mm, or a truncated cone with a diameter and height of 150mm. Cylindrical specimen (depending on the requirements of anti-seepage equipment).

The impermeability test pieces are divided into groups of 6.

The specimen is removed from the mold 24 hours after it is formed, and the cement slurry film on both ends is brushed with a wire brush, and then sent to the standard curing room for curing.

The test pieces are generally maintained until they are 28 days old for testing. If there are special requirements, they can be tested at other ages.

3. Test steps

(1) Maintain the specimen until it is taken out one day before the test, dry the surface, and then apply a layer of molten sealing material on its side, and then put it on the spiral Or other pressurizing devices, press the test piece into the test piece set preheated in the oven. After cooling slightly, the pressure can be released and the test piece set together with the test piece set can be tested on the impermeability meter.

(2) The test starts with the water pressure being 0.1MPa. From now on, increase the water pressure by 0.1MPa every 8 hours, and pay attention to the water seepage on the end face at all times.

(3) When there is water seepage on the end faces of 3 of the 6 test pieces, the test can be stopped and the water pressure at that time is recorded.

(4) During the test, if water is found to seep out from around the test piece, the test should be stopped and resealed.

4. Data processing and result judgment

The anti-permeability mark of concrete is calculated based on the maximum water pressure when 4 specimens in each group of 6 specimens do not see water seepage. The formula is:

S=10H-1

In the formula, S——the anti-seepage mark;

H——when 3 of the 6 specimens see water. pressure (MPa).