Effect of Spray Dryer Absorbers as Mix Enhancer on HMA Performance

Abstract

For many years Coal Combustion Products (CCPs), and, especially fly ash, have been effectively used as a partial replacement of portland cement in different types of concrete, as well as in flowable fills, embankments and soil stabilization. On the other hand, the use of CCPs in asphalt pavements has been very limited. Only few researchers have reported on the benefits of CCPs in asphalt. This research investigates the effect of Spray Dryer Absorber (SDA) CCP on HMA performance with respect to laboratory measured performance indicators at both the mastic and mixture level using a PG58-28 unmodified binder. In this study, two SDA materials and a reference limestone filler was introduced to an asphalt mastic at 0, 5, 15, and 25% by volume. After mastic evaluation, only one of the SDA materials was introduced to an asphalt mix at 10% replacement of the binder by mass and compared to a standard 3 million ESAL control mix. With respect to performance, all mastics and mixtures were tested for aging index, fatigue, and low-temperature thermal cracking resistance. The HMA mix with SDA had the higher resistance to aging where the aging index was significantly lower/reduced than that of the control mix. The same trend was observed for repeated fatigue loading. Overall, the SDA mix outperformed the control HMA. The reported study proves that replacing 10% by mass of the asphalt binder with SDA does not hinder workability, and improves aging resistance, moisture damage resistance, and fatigue life. This implies a significant impact associated with CCPs utilization in flexible pavements rather than landfilling.