Fatigue performance and stiffness properties of Stone Mastic Asphalts with steel slag and coal ash

This paper describes the results of an experimental investigation and a theoretical study on the fatigue behaviour of Stone Mastic Asphalt (SMA) mixes, determined by the four-point bending test, according to the EN 12697-24 Annex D standard. The testing was performed on SMA mixes with Electric Arc Furnace (EAF) steel slag and Coal Bottom Ash, used at different proportions, in partial substitution for natural limestone and filler. The mix design method was based on the volumetric properties, as well as on the moisture resistance of the asphalt concretes. Both the Bailey’s method and a conventional approach were used in order to identify the design grading curves of the mixes. Fatigue life was evaluated by means of the empirical approach, related to a 50% reduction in the initial stiffness modulus, as well as using more rational concepts, related to the macro-structural damage condition of the mixtures, in terms of dissipated energy and damage accumulation. With respect to the control SMA with limestone aggregates, the asphalt concretes with EAF slag and Coal Ash presented improved fatigue properties and delayed macro-crack initiation.