| The anti-stripping performance of hot mix asphalt(HMA)is decided by adhesion between asphalt and aggregate.And the adhesion capacity is not only related to characteristics of asphalt and aggregate,but also affected by external environment.Currently,there are several kinds of test methods about anti-stripping performance of HMA,such as boiling water,immersion test,tracer salt,Lottoman test,immersion wheel-tracking test and so on.However,there are some disadvantages in all these methods.Both boiling water and immersion test are influenced greatly by human factors.Tracer salt is complicated operation.Lottoman test doesn’t consider the evaluation in different air void of HMA.Reproducibility about the test results from immersion wheel-tracking test is very poor.Vehicles loads all borne by asphalt pavement.A certain amount of hydrodynamic pressure will produce during impact by tires to asphalt pavement when ponding existed in pavement.Researches have shown that hydrodynamic pressure will accelerate stripping in asphalt mixture.From above all tests about anti-stripping performance of HMA,there are none could reflect the hydrodynamic pressure factors.According to the hydrodynamic pressure characteristic and measurement data from asphalt pavement,a new experimental method was developed in this paper,and considering the factor of hydrodynamic pressure effect to evaluating anti-stripping performance of HMA.This method simulated the hydrodynamic pressure formed on pavement and test system mainly composed of air compressor,single phase asynchronous motor and measuring equipment about theoretical maximum density.Firstly,airproof container after a certain amount of asphalt mixture loosely was put in the container that had existed water appropriately.And positive pressure and negative pressure was applied alternately in certain frequency,to simulate pressure and suction on pavement was produced by repeated loading.Then calculated concentration of suspended substance(SS)after proper suspensions was selected had been mixed evenly and filtered.The concentration of SS as evaluation index would be used for evaluating anti-stripping performance of HMA.A lot of test results showed that anti-stripping performance of HMA of different raw material could be distinguished by this method by the concentration of SS.Namely anti-stripping performance of HMA would be poor with greater concentration of SS,otherwise anti-stripping performance was better with lower concentration of SS.In addition,several conclusions were shown by test results.Testing data were steady and effect obviously when positive pressure was 0.2MPa and negative pressure was-0.08 MPa.It would be meeting requirements that used 0.5min as index of single circulation time of hydrodynamic pressure because there is litter influence from circulation time to anti-stripping performance of HMA.Stripping in asphalt mixture increases with the increment of the number of cycles,however,obvious experimental effect was gained with 15 cycle number. |
