The asphalt pavement permeability tester is used to quantify the permeability of road structures, and its calibration directly affects the accuracy and comparability of the detection results. The following systematically explains the standardized calibration method from four aspects: calibration principle, operation process, key parameter control, and precautions.

1、 Basic principles of calibration

This device simulates rainfall conditions and measures the volume of water that seeps into asphalt mixture per unit time. The core calibration basis is the consistency between flow measurement accuracy and test conditions. It is necessary to focus on verifying the opening of the inlet valve, the synchronization of the timer, and the accuracy of the graduated cylinder scale to ensure that the measurement error under the collaborative work of the three is ≤± 2%.

2、 Preparation of standard instruments

1. Standard measuring cylinder: Select a 1L glass measuring cylinder verified by the metrology department, with a minimum division value of 5mL, used for calibrating the instrument's built-in measuring tools;

2. Electronic stopwatch: with an accuracy of 0.01 seconds, used for calibrating timing modules;

3. Pressure regulating device: can accurately control the water source pressure to 0.1MPa ± 0.01MPa;

4. Standard test mold: Marshall test mold that meets the requirements of the "Test Code for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), with an inner diameter of 101.6mm ± 0.2mm.

3、 Calibration implementation steps

1. Sealing pre inspection

-Install blank test mold (without sample), close the drain valve, and fill the container with water until the overflow pipe is opened;

-Maintain for 30 minutes and observe the decrease in water level. If it exceeds 1mL, replace the sealing ring.

2. Flow calibration

-Connect the constant pressure water supply system and set the water pressure to 0.1MPa;

-Open the inlet valve to the maximum opening, use a measuring cylinder to take the amount of water flowing out within 1 minute, repeat 3 times and take the average;

-Adjust the valve screw to ensure that the deviation between the measured flow rate and the theoretical value (such as 500mL/min) is ≤ ± 1%.

3. Timing system calibration

-Start the built-in timer of the device and synchronously trigger the external electronic stopwatch;

-Record the actual time taken from the start of water injection to reaching the preset time (such as 3 minutes), and correct the timer error.

4. Verification of graduated cylinder scale

-Inject a known volume of standard solution (such as 200mL) into the measuring cylinder of the instrument using a pipette;

-Compare the displayed value of the measuring cylinder with the actual injection amount, and the error of each range segment should be less than 1%.

5. Comprehensive performance verification

-Prepare standard compacted specimens (porosity 4%~6%) and conduct water permeability tests according to specifications;

-The relative deviation of the water seepage of the same specimen before and after calibration should be ≤ 5%.

4、 Calibration cycle and records

It is recommended to conduct complete calibration every quarter, and additional verification is required before major projects. Establish a calibration log to record the environmental temperature (20 ± 5 ℃), water temperature (15-25 ℃), and various correction factors to ensure data traceability.

Through the multidimensional calibration mentioned above, equipment system errors can be effectively eliminated, and the reliability of water permeability coefficient detection can be improved. In practical operation, it is necessary to strictly follow the "On site Testing Regulations for Highway Roadbeds and Pavements" and develop personalized calibration plans in conjunction with equipment manuals.