EVALUATION OF FRACTURE TOUGHNESS OF WARM-MIX ASPHALT CONTAINING NATURAL AND SYNTHESIS FIBERS AT LOW TEMPERATURES

Compared to typical hot-mix asphalt (HMA), Warm-mix asphalt (WMA) is produced at a lower temperature; therefore, it can be a good alternative for pavement located in cold climates. On the other hand, the low-temperature cracking is one of the main concerns of highways agencies in cold climates. Many different additives including fibers have been used for improving hot-mix asphalt performance; however, a few types of research have been conducted to investigate the effects of fibers on warm-mix asphalt performance. In this paper, warm-mix asphalt containing Sasobit and different percentages of natural and synthesis fibers (0.7%, 0.5% and 0.3% by weight of the total warm mix asphalt) were prepared by gyratory compactor. The cylinder specimens were cut to prepare semi-circular bending (SCB) specimens to determine the critical intensity factor (fracture toughness) of the warm-mix asphalt specimens. Using ABAQUS software the finite element analysis was conducted to determine the geometry factors and crack positions for pure tension (mode I), pure shear (mode II) and mixed modes (I/II). The cracked specimens were loaded at a constant rate (3 mm/min) at 0 oC, -10 oC and -20 oC until they were fractured; then the fracture toughness of each specimen was calculated. Analysis of testr esults indicated that the fracture toughness of warm-mix asphalt specimens containing natural or synthesis fibers increased when the temperature test decreased. In addition, the tests results showed that fracture toughness of warm mix specimens containing natural or synthesis fibers in mixed mode (with the same portion of tension and shear) and pure tension mode are higher than that of the control asphalt mixtures. However, this trend was not observed for loading modes with the higher portion of shear, especially for specimens containing natural fibers. Furthermore, in the same percentages of fibers, the effect of synthesis fibers to improve the fracture toughness of the mixtures was higher than that of the natural fibers.