Abstract:

To study the performance evolution of asphalt mixture under the impact of multiple pore water pressure cycles, three kinds of SBS modified asphalt mixture specimens with different asphalt content (3.5%, 4.5% and 5%) were prepared. Different cycles of pore water pressure (500 to 7000 cycles) were applied on specimens by Moisture Induced Sensitivity Tester (MIST), and then the change of internal structure of asphalt mixture is characterized by the physical indicators (volume, bulk relative density) of the moisture conditioned specimens. Indirect Tensile Strength (ITS) and Tensile Strength Ratio (TSR) under different times of pore water pressure measured by Indirect Tensile Test (IDT) are used to characterize the evolution of mechanical properties of asphalt mixture. The results show that the volume of the specimens increases first and then decreases, the Bulk Relative Density (BRD) slightly decreases with the pore water pressure cycles. ITS and TSR results show that the mechanical properties decrease first and then improve. It is found that 500 pore water pressure cycles are the critical times for specimens to change from unsaturated state to saturated state. When cycles are less than 500, the specimens are unsaturated and the pore water pressure produced by MIST is large, so the mechanical properties are continuously reduced. When cycles are higher than 500, the specimens are saturated, MIST cycle has little contribution to pore water pressure and the effect of temperature becomes the main impact, resulting in the improvement of mechanical properties. Thus, for the small dense asphalt mixture specimen with porosity of about 4%, it is recommended to use 500 MIST cycles as moisture condition to evaluate the water damage resistance of asphalt mixture.

Key words: multiple pore water pressure, moisture induced sensitivity test, indirectly tensile test, performance evolution