Effect of temperature and air void on mixed mode fracture toughness of modified asphalt mixtures

• Mixed mode fracture toughness of different modified asphalt mixtures was determined.
• Effects of temperature changes and air-void were studied on fracture toughness values.
• The mixtures modified with CR and SBS additives had the most KIc and KIIc values.
• Critical mode of fracture was not noticeably sensitive to the type of modifier.

The use of modified asphalt mixtures is a suitable solution for preventing low temperature cracking of pavements in cold regions. In this paper, mixed mode I/II fracture toughness of five modified asphalt mixtures containing poly phosphoric acid (PPA), Styrene Butadiene Styrene (SBS), anti-stripping agent, crumb rubber (CR) and F-T paraffin wax (Sasobit) and an unmodified one (with no additive) is investigated experimentally using a large number of cracked semi-circular bend (SCB) specimens. The effects of four different mode mixities from pure mode I to pure mode II, temperature changes, and air void percentage are also studied on fracture toughness values of modified asphalt mixtures. The obtained result showed that the fracture toughness of tested mixtures depends noticeably on the modifier type, air void content and the test temperature. It is shown that the performance grade (PG) of the tested binders has significant effect on the low temperature fracture resistance of the investigated modified asphalt mixtures. Also, according to the test results, mixed mode loading cases were more critical than the pure modes I and II situations.