Bitumens are currently modelled as a colloidal system and are the most used materials for road paving. Despite this large application, asphalts are still affected by some inconveniences that bring to road deterioration. This is prevalently due to temperature cycling which is related to the given local climate conditions and to the incident traffic load. In the last decades bitumen performances have been improved by means of different types of additives in order to match various expectations. This improvement is often the result of the indications given by traditional empirical standardized tests like penetration grade, temperature ductility and Fraas breaking point. The comprehension of the chemical mechanism that regulates the action of the used additives can greatly help in designing new and better performance materials. By means of a Stress Controlled Rheometer we present a laboratory evaluation of the rheological properties of a 70/100 bitumen which has been doped by different percentage of Polyphosphoric acid (PPA). In addition H-1-NMR measurements of proton transverse relaxation time ( T-2) have been exploited in order to corroborate the rheological data. As a novel approach to the knowledge of bitumen macro-structures, we applied an Inverse Laplace Transform (ILT) to the measured echo decay. The results show the effect of PPA addition on bitumen mechanical behaviour.