I. Product introduction

TD739-1 Four-point bending fatigue tester for asphalt mixture is designed and manufactured by Hebei Tianqi Xingzi Testing Equipment Co., LTD. According to the requirements of T0739-2011 Four-Point Bending Fatigue Test for Asphalt Mixture in standard JTG E20-2011 "Test Regulations for Asphalt and Asphalt Mixture in Highway Engineering" of the Ministry of Communications of the People's Republic of China. It is suitable for measuring the fatigue life of compacted asphalt mixture under repeated bending load under specified test conditions.

The standard test conditions were as follows: test temperature 15℃±0.5℃, loading frequency 10Hz±0.1Hz, continuous partial sinusoidal loading mode controlled by constant strain. Other test conditions can also be selected according to need; The test termination condition was the number of loading cycles corresponding to the bending stiffness modulus decreasing to 50% of the initial bending stiffness modulus; This method is suitable for the asphalt mixture plate specimen formed by the wheel in the laboratory or the plate specimen drilled from the field road surface, and the trabecular specimen with the length of 380mm ±5mm, thickness of 50mm ±5mm and width of 63.5mm is cut.

Two, instrument configuration

1. TDLQHJ-1 asphalt mixture comprehensive test environment.

Technical parameters:

Power supply voltage: 220V±10V

Refrigeration power: 1 piece

Heating power: 2KW

Temperature control range: 0 ~ +60℃

Temperature control accuracy: ±0.2℃

Studio size: 800mm(length)× 500mm(width)×750mm(height)

Dimensions: 1100(L)× 630(W)×1500(H)

Noise level less than 70db (at 2m)

2. TD739-1 asphalt mixture four-point bending fatigue tester

Voltage: 220 v + 10 v

Power: 360 w

Dynamic loading capacity up to 10KN

Loading frequency up to 60Hz

Actuator stroke 30mm

The sample size is 70mm×85mm×380mm

3, others: vernier calipers, day equality.

Three, test steps

1 Preparations

1.1 Specimen preparation: Make asphalt mixture plate specimens according to the method of vibration wheel rolling, or cut plate specimens from the road surface on site. Then, the plate specimen was cut with a high-precision diamond double-sided saw, and the rolling molding direction was taken as the specimen length direction to make the beam specimen. The size of the specimen should meet the requirements of length 380mm±5mm, height 50mm±6mm and width 63mm±6mm. A 400mm×300mm×75mm asphalt concrete plate can usually be cut into 4 trabecular specimens.

1.2 Storage of specimens before test: The storage temperature of asphalt mixture plate specimens and cut specimens shall not exceed 35℃, and the cut specimens shall complete the test within 30 days. During storage, the specimen should be placed horizontally on a hard glass plate (or ceramic tile) with a flat surface and a certain stiffness to prevent deformation of the specimen.

1.3 Specimen size measurement: use vernier calipers to measure the width and thickness of the specimen, and determine five positions, namely, the point position within 20mm of both ends of the specimen, the point position within 10mm of the beam midpoint and the point position 90mm from the beam midpoint, accurate to 0.01mm. The average value of the five measurements was taken as the specimen size, which was accurate to 0.1mm. If any of the five measured values of width or thickness differs from the average value by more than 1.5mm, the beam specimen is discarded.

1.4 Measurement of specimen volume parameters: The fatigue and bending properties of asphalt mixture are largely dependent on the actual compaction level of the mixture. The voids (VV) and mineral voids (VMA) of each trabecular specimen should be measured before the fatigue test. The actual voids of the specimens should be within the range of the target voids ±0.5%, the measured mineral clearance rate (VMA) should be within the range of the target mineral clearance rate ±0.5%, and the specimens exceeding this range should be abandoned.

2 Test Procedure

3.2.1 Specimen health preservation: Trabecular specimens should be directly put into the environmental box for health preservation, and the test should be carried out at a temperature of ±0.5℃ for more than 4 hours.

2.2 Specimen placement: Put the cured specimen into the four-point bending fatigue loading device and fix it with a fixture. Make the displacement sensor LVDT pulley contact the surface of the specimen, adjust the displacement sensor to the middle of the specimen, and the LVDT reading is as close to zero as possible.

2.3 Selection of test parameters: Select partial sinusoidal loading mode, and input parameters such as specimen number and size, target tensile strain, loading frequency and test termination standard on the interface of test parameter setting.

2.4 Under the target test strain level, 50 cycles were preloaded, and the stiffness modulus of the specimen in the 50th loading cycle was calculated as the initial stiffness modulus and used as the benchmark stiffness modulus to determine the fatigue failure criterion of the specimen.

2.5 Start the test: when the initial stiffness modulus is determined, the testing machine should be automatically adjusted and stabilized to the target tension strain level required by the test within 50 cycles, and monitor and record the test parameters and test results according to the selected loading cycle interval to ensure the correct operation of the system. When the specimen reaches the fatigue test termination condition, the loading will stop automatically.