Laboratory study of lime kiln dust as a moisture damage reducing agent in dense graded asphalt concrete mixture

Road authorities are experiencing a considerable degree of moisture associated distresses such as ravelling and stripping, on flexible pavements. Therefore, it is required to modify asphalt concrete (AC) mixtures to have higher moisture damage resistance. Previous studies have shown that hydrated lime (HL) increases the resistance to the adverse effect of water in the AC mixture. But it has limited usage as it is expensive. The first part of this research project confirmed that lime kiln dust (LKD) is a good substitute for HL as an effective mineral filler in AC mixture and 50% LKD of bitumen binder mass gives the optimum performance. This paper addresses the use of LKD as moisture damage reducing agent in Dense Graded Asphalt (DGA). Stripping potential of LKD was investigated to ensure sustained adhesion between bitumen and aggregates in instances where pavement saturation is evident. Tensile strength ratio (TSR) and resilient modulus ratio (MrR) were used to predict the moisture resistance of DGA mixture and studied the long-term aging effect on those parameters. TSR test was conducted according to the modified Lottman test method and MrR test was performed using the indirect tensile method on mixtures with LKD, HL, and control mix. The test specimens were prepared with an air void ratio of 8±1%. Mixtures with LKD and HL have satisfied Austroads and super-pave mix design specifications which is TSR> 80% and MrR>70% for low moisture susceptibility. LKD and HL mixtures have shown more than 100% for both TSR and HL because the presence of these filler materials cause to enhance adhesion and cohesion bonds within the mixture when water exists. LKD behaves almost the same as HL and provides well resistance for moisture associated fatigue cracking and wheel path rutting deteriorations regardless of the aging conditions. Overall, LKD is excellent moisture damage reducing agent