Low temperature fracture properties of polyphosphoric acid modified asphalt mixtures

The low temperature fracture properties of polyphosphoric acid (PPA) modified mixtures are evaluated and compared with those of polymer modified mixtures. Themain objective is to determine whether PPA can partially or completely substitute traditional polymer modifiers, without adversely affecting the mixture's resistance to thermal cracking. Laboratory compacted and field cored test samples from theMinnesota Road Research Project (MnROAD) were tested using traditional methods as well as newly developed fracture testing protocols: indirect tensile test (IDT), semicircular bending test (SCB), and disk-shaped compact tension test (DCT). The effects of temperature, air-void content, comma and long-term aging on low temperature fracture properties were analyzed; and field performance observations of the test cells from MnROAD were discussed. On the basis of the analysis, the fracture resistance of the PPA modified mixture is less than that of the SBS modified mixture. However, when PPA is used to substitute part of the SBS, a mixture with fracture resistance comparable to that of the mixture modified with SBS alone is produced.