In order to determine whether polyphosphoric acid （PPA） can partially or completely substitute styrene-butadiene- styrene （SBS） modifier while it does not adversely affect the resistance to thermal cracking of the asphalt mixture, the low- temperature fracture properties of the PPA modified mixtures are evaluated and compared to the SBS modified mixtures. First, laboratory compacted test samples were tested by the indirect tensile test （IDT） and the newly developed fracture testing protocol, named as disk-shaped compact tension （DCT）. Then, the effects of the test temperature and air-void ratio on the low-temperature fracture properties of asphalt mixtures were analyzed. The results show that the fracture resistance of the PPA modified mixtures is worse than that of the SBS modified mixtures. However, for those modified mixtures that use the PPA substituting part of the SBS modifier, a relatively low-temperature fracture resistance can be obtained compared with the mixture only using the SBS modifier.
