introductionRutting is a major disease form of asphalt pavement, which not only affects the smoothness and performance of pavement, but also seriously endangers driving safety. Because rutting treatment is generally milling and repaving, the maintenance cost is much greater than the repair of pit and other diseases, so the prevention and control of rutting on asphalt pavement has always been the focus of asphalt pavement research. Rutting resistance is the basic requirement of asphalt pavement design, but at present, rutting test is used as the verification of asphalt mixture design results only in the asphalt mix ratio design stage, and there is a lack of detection and evaluation of the rutting resistance of asphalt pavement structural layer, which cannot ensure that the pavement has a good rutting resistance.

Because of the simple operation, short cycle and low cost, indoor rutting test is widely used in scientific research and engineering practice at home and abroad, and there are a variety of rutting testing machines and their testing methods, including the current standard rutting test in China, Hamburg Rutting (HWTD) and asphalt pavement analyzer (APA).

Knowledge sharing: Rut testing on asphalt pavement

The differences between standard rut, HWTD and APA rut test methods are as follows: (1) Different loading times and duration: standard rut test duration is the shortest, less than 2500 times of loading, and the time is about 1 h; HWTD takes the longest time to load 20,000 times, which takes about 7 hours. ② Different loading methods: APA rut test reciprocates the steel wheel on the inflation hose (air pressure 0.69MPa), and standard rut and HWTD directly apply the steel wheel to the specimen surface. ③ Different evaluation indicators: In addition to the maximum rut depth, standard rut, HWTD and APA have other different evaluation indicators. Such as the standard Dynamic Stability (DS), Hamburg rut Creep Slope (CS) and APA test Rate of Rutting depth change (RR).

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The Hamburg Rut experiment

Comparing with the traditional standard rutting test, Hamburg rutting test can reflect the actual rutting resistance of pavement more accurately by carrying out the rutting resistance test directly on the core sample retrieved from the field. The Hamburg Rutting tester was developed in Germany and is now included in the German specification for some heavy traffic roads to evaluate rutting and stripping resistance. Research at home and abroad shows that the Hamburg rutting instrument can carry out dry and immersed, plate and cylindrical test specimens at different temperatures, and is an effective tool to analyze the causes of rutting on asphalt pavement and evaluate the high temperature performance of asphalt mixture. The rutting depth index of pavement structure obtained by the Hamburg rutting test method is of high reliability to evaluate the anti-rutting performance of pavement structure.

Knowledge sharing: Rut testing on asphalt pavement

The main difference between domestic rutting test and Hamburg rutting test:

1. The sample of Hamburg rut uses rotary compaction (SGC) cylinder specimen and field coring specimen, which is closer to the compaction method in actual construction, and has little damage to aggregates, and field coring parts can be used for finished road quality detection. Rutting test specimens are generally 300mmx300mmx50mm, and the void ratio differs greatly from the actual situation, which is limited to the mix ratio test and is not suitable for the quality sampling of finished pavement. The Hamburg rutting test adopts the loading of specimens until the steel wheel moves 20,000 times or produces 20mm deformation. The Hamburg Rut test results report includes: loading times, maximum indentation, test temperature, creep slope, spalling slope, spalling deformation point, which are used as evaluation indicators of the Hamburg Rut test. A large number of foreign studies have shown that there is a good correlation between Hamburg rutting and actual road performance, which can evaluate the quality of aggregates, the hardness of asphalt concrete, the length of short-term aging time, the extraction process of asphalt and the quality of crude oil, the effect of anti-stripping agent, the temperature of compaction and water sensitivity. The conventional rutting in China evaluates the anti-rutting performance by measuring the deformation of rutting in 45min and 60min to calculate the dynamic stability data. The relative detection index is relatively simple and has poor correlation with the actual highway. There is a phenomenon that the laboratory rutting test has met the standard requirements, but the actual road surface performance is not ideal. The evaluation indexes of the Hamburg rutting test are directly derived from the whole process of the rutting test time-deformation curve, and the dynamic stability of the domestic rutting test is less affected by the test accuracy and other factors.

2. Hamburg rutting test can change the test environment, can be tested under submerged and non-submerged conditions, can be carried out in the underwater temperature range of 25 ° C to 70 ° C, of which the most commonly used temperature is 45 ° C or 50 ° C. Domestic conventional rutting is basically tested under 60℃ air bath.

Knowledge sharing: Rut testing on asphalt pavement

3. Hamburg Rut test has been widely used in foreign countries to evaluate the water stability of asphalt mixture. The spalling back bending point is the number of reciprocating movements of the steel wheel corresponding to the intersection of the creep curve and the spalling curve. This value is used to evaluate the resistance of the asphalt mixture specimen to water damage. Most of the water stability tests in China use freeze-thaw splitting as the test index, and the immersion rut test is only a test method being explored to evaluate the water stability of asphalt mixture, and there is no consistent evaluation index at present.

4. Hamburg Rut adopts 11 data collection points, while domestic rut generally adopts single point data collection, so in terms of data accuracy and dispersion, Hamburg Rut is superior to conventional rut.