Use of expanded clay for the mix design of high-grip bituminous wearing courses

The required increasing needs for both safety and comfort for the road users, obliges the Road infrastructures Researchers to look for innovative material which could be successfully used for bituminous wearing courses. More precisely, the use of non-conventional aggregates, as for the case of expanded clay (EC), involves a significant improvement in the performances of a bituminous concrete from the standpoint of grip as well as of both micro and macro texture and noise reduction, the mechanical characteristics being comparable or, in case, even better than an ordinary conglomerate made of natural aggregates. Generally speaking, there are some previous studies in literature on the aggregates substitution, from the standpoint of weight, with different percentages of expanded clay . In order to save the particle size of the blend coming from the mix design procedure, the writers suggest the change of aggregates with expanded clay from the point of view of volume, so as to consider the large difference of the values of the apparent absolute gravity between expanded clay itself and natural aggregates. As a matter of fact, this study proposes the results of an experimental investigation on the performances of both a traditional bituminous concrete with silica aggregates and a SMA (Splittmastix Asphalt) made of calcareous and basaltic aggregates, 10 and 30% of the volume percentages of aggregates having been changed with structural expanded clay. The results are significant from the viewpoint of the failure domains tested by means of the UNIBAS M.P.T (UNIBAS Triaxial Test Apparatus) procedure and of the increase of superficial grip or micro and macro-texture. Furthermore, the study highlights the positive environmental aspects deriving from both the use of artificial aggregates and the reduced need of bitumen when expanded clay is used.