Waste bleaching clays as fillers in hot bituminous mixtures

Today, it is a well known fact that mineral fillers have a key role in controlling the mechanical characteristics of hot mix asphalts. The cohesion properties of bituminous mastics depend upon the fillers used, and, therefore, so do the effective strength of asphalt concrete and the durability of the pavement layer. In this study, waste bleaching clays from the food industry are proposed as an alternative to common limestone mineral filler for the production of Hot Mix Asphalts (HMA). The bleaching clays used here come from two consecutive stages in the industrial process for decolouring vegetable oils and producing biogas from waste clay, where the former is richer in residual organic fats (20–25% in weight against less than 1%). The aim of this research was to assess the performance of a common binder course asphalt mixture, in terms of physical and mechanical characteristics, when waste bleaching clays are used as an alternative. For this purpose, data obtained from a control hot mix asphalt produced with traditional limestone filler were compared to those recorded for bituminous samples containing waste bleaching clay from either the first or the second stage above, in place of the limestone filler. Results show a significant difference between the effects produced by the bleaching clays from the two stages on the performance of the asphalt concrete, where the second stage shows more positive effects both on indirect tensile strength and stiffness and on the bituminous mixture’s resistance to permanent deformations.