The cement compression testing machine is a key equipment used to determine the compressive strength of cement mortar or concrete test blocks, and its operating specifications directly affect the accuracy of the test results. The following are detailed usage instructions and precautions:
1、 Usage method
1. Preparation before the experiment
Equipment inspection:
Confirm that the power supply, pressure sensor, and hydraulic system (or motor drive system) of the testing machine are normal.
Check if the pressure gauge or digital display screen is reset to zero, and if the loading rate adjustment device is flexible.
Preparation of test specimens:
Cement sand test piece: Form a 40mm × 40mm × 160mm prism according to standard methods, and cure it to the specified age (such as 28 days).
Concrete test block: The standard size is 150mm × 150mm × 150mm, and it needs to be taken out of the curing room in advance and wiped dry of surface moisture.
Measurement of specimen size:
Measure the edge length or diameter of the compression surface of the specimen with a vernier caliper, accurate to 0.1mm, and calculate the actual compression area.
2. Calibration of testing machine
Zero point calibration:
Turn on the testing machine and run the pressure head with no load to the position where it contacts the specimen. Adjust the pressure gauge or digital display to zero.
Standard block calibration (optional):
Use standard test blocks of known strength for verification to ensure that the indication error of the testing machine is within ± 1%.
3. Installation of test specimens
Alignment operation:
Place the specimen at the center of the pressure plate of the testing machine, ensuring that the axis of the specimen coincides with the axis of the press.
For prismatic specimens, the compression surface should be the side surface at the time of forming; The surface of the cube specimen needs to be kept flat.
Contact adjustment:
Slowly lower the pressure head to make slight contact with the surface of the specimen (the pressure gauge shows about 0.5kN) to avoid impact.
4. Loading test
Load rate control:
Cement sand: According to GB/T 17671, the loading rate is 2400N/s ± 200N/s.
Concrete test block: According to GB/T 50081, the loading rate is 0.3~0.5MPa/s (adjusted according to the strength grade).
Data recording:
Observe the process of specimen failure and record the maximum pressure value (P).
The digital testing machine can automatically collect data and generate stress-strain curves.
5. Result calculation
Revision rules:
The strength result of cement mortar is accurate to 0.1MPa;
The concrete strength result is accurate to 0.1 MPa, rounded according to the standard (such as rounding to five pairs).
2、 Precautions
1. Safe operation
Protective measures:
Wear goggles and gloves during the experiment to prevent the specimen from shattering and splashing.
Set up protective barriers around the testing machine to prevent non operators from approaching.
Emergency shutdown:
Familiarize yourself with the position of the emergency stop button and immediately stop the test in case of abnormal situations (such as abnormal noise or oil leakage).
2. Equipment maintenance
Daily maintenance:
Clean the pressure plate and specimen residue after the experiment to prevent corrosion.
Regularly check the hydraulic oil level (hydraulic type) or the operating status of the motor (electric type).
Regular calibration:
Every 6 months or after 1000 uses, the pressure sensor and loading rate should be calibrated by a professional organization.
3. Test piece requirements
Appearance inspection:
The test piece must not have missing corners, cracks, or uneven surfaces, otherwise it needs to be re prepared.
Moisture content control:
After the concrete test block is taken out of the curing room, it needs to be left to stand at 15-25 ℃ for 1 hour before testing.
4. Environmental conditions
Temperature and humidity control:
The laboratory temperature should be maintained at 20 ℃± 2 ℃, and the humidity should be ≥ 50% (for cement testing).
Avoid direct sunlight or excessive ventilation to prevent moisture evaporation from the specimen.
5. Operating standards
Prohibited behavior:
Overloading is not allowed (80% of the testing machine range is the upper limit).
Avoid frequent start stop or rapid adjustment of loading rate.
Data backup:
The digital testing machine needs to export data regularly to prevent loss.
3、 Common problem handling
Large fluctuations in pressure values:
Check the sealing of the hydraulic system or the stability of the motor, replace the hydraulic oil or repair the sensor.
Abnormal form of specimen failure:
If the specimen fails obliquely, it needs to be re centered; If it breaks prematurely, check if the loading rate is too fast.
The device cannot reset to zero:
Clean the contact points of the pressure sensor or contact the manufacturer for repair.
4、 Standard basis
Cement compression test: GB/T 17671 "Test Method for Strength of Cement Mortar (ISO Method)";
Concrete compression test: GB/T 50081 "Standard Test Method for Mechanical Properties of Ordinary Concrete".
By strictly following the above methods and precautions, the accuracy of the test results and the service life of the equipment can be ensured. Operators need to undergo professional training and regularly participate in equipment operation assessments.