Analysis of the linear viscoelatic behaviour of bitumen with high quantities of filler

The performances of asphalt concretes are influenced by the quantity and quality of fines (filler). Large amounts of filler change the rheological behavior and limit the possibility of movement for the bitumen, that is blocked by the fine particles. In this study the Authors evaluated the behaviour of mastics (bitumen and fines) in the linear viscoelatic (LVE) field, mixing various types of binder with different fillers. To this purpose, bitumen produced in Italy with penetration grade 50/70 and 70/100 mm/10 were used. The fillers used were: cement, coal ash, steel slag and limestone. The amount of filler added in the bitumen varied from 0% to 100% by volume. Tests were performed using a dynamic shear rheometer with two geometries (PP20 and PP08) and a gap of 2 mm, in amplitude and in frequency sweep, with temperature scales between 15°C and 70°C. The results of the tests allowed to verify that with a high content of filler (in particular, with the 100%) the behaviour of mastic undergoes a radical change, due to the reduction of mobility induced by the fines. It was also verified that the model of Christensen-Anderson, which well describes the behaviour of mastics with a low percentage of filler, is not suitable for mastics with a high content of fines. This aspect has an important effect on the bituminous mixture which, with a high content of filler, presents more problems of fatigue cracking due to the friction between the particles of filler and bitumen