Analisi sperimentale e modellazione reologica della lavorabilità dei conglomerati bituminosi

In recent years pavement engineering has considerably evolved from many perspectives, with a general improvement of field performance. This improvement should attributed to the development of new materials and technologies and to a more careful management of resources in every stage of infrastructure life, from design to maintenance, through construction. The laying and compaction of hot-mix asphalt (HMA) is one of the most important issues to be taken into account since it is a stage that can negatively influence the whole life of a pavement. It is advisible to pay attention to the workability properties of HMA because only with the control of these and with a careful study of the factors that affect compaction it is possible to prevent unexpected performance problems during service life. This research work is set in this general framework, trying to give a further contribution to the actual knowledge of HMA workability. The aim of the research is to analyse critically the factors that affect compaction of HMA by means of laboratory investigations carried out with a SUPERPAVE Gyratory Shear Compactor. The study has been structured in different levels through which the influence of individual parameters on HMA compaction has been evaluated. This has been done by considering different mixture structures (i.e. different composition of the mixtures) and by taking into account the effects caused by variations of temperature and binder type. Part of the research has focused on the development of a rheological model for the simulation of the laboratory compaction process of HMA. This has lead to the detailed analysis of the effects caused by the various parameters on compaction. When considering final results. It can be pointed out that the workability factor k was observed to be independent from temperature and binder type. On the contrary, it proved to be sensitive to variations of the bitumen content and of the percentages of the fine aggregate fractions. In particular, workability was directly influenced by variations of filler content and of the quantities of aggregate material associated to sieves with an opening of 0.400, 0.180 and 0.075 mm. By increasing the filler content, workability increases; by increasing the quantities of fine material associated to the abovementioned sieves, workability is reduced.. This is due to the fact that more dense structures are obtained with the consequence of encountering a greater difficulty in reorganising and redistributing aggregates in the bulk of the mixture. Variations of the autocompaction parameter C1 were also analysed. It was thus observed that such a parameter depends only upon the coarser aggregate fractions, and more specifically upon the maximum aggregate size. Only minor effects caused by variation of the binder content were noted. In the rheological modelling of the compaction process it was observed that the employed parameters are dependent upon a series of factors which are linked to the composition of the mixtures, to test conditions (especially to temperature) and to the level of compaction (number of gyrations and compaction pressure).