This research was undertaken to study the relationships between the performance of locally available asphalts and their physicochemical properties under Iowa conditions with the ultimate objective of development of a locally and performance-based asphalt specification for durable pavements;Physical and physicochemical tests were performed on three sets of asphalt samples including: (a) twelve samples from local asphalt suppliers, (b) six core samples of known service records, and (c) a total of 79 asphalt samples from 10 pavement projects including original, lab aged, and recovered asphalts from field mixes and lab aged mixes. Tests included standard rheological tests, HP-GPC, and TMA. Some specific viscoelastic tests at 5°C were run on (b) samples and some (a) samples. DSC and X-ray diffraction studies were performed on (a) and (b) samples. In addition, NMR techniques were applied to some (a), (b), and (c) samples;Efforts were made to identify physicochemical properties which are correlated to physical properties known to affect field performance. The significant physicochemical parameters were used as a basis for an improved performance-based trial specification for Iowa to ensure more durable pavements.