INFLUENCE OF FILLERS ON PERFORMANCE PROPERTIES AND AGEING SUSCEPTIBILITY OF ASPHALT MIX CONTAINING RAP

Abstract

The availability of natural aggregate is limited by high prices, scarcity, longer hauling distances, and environmental restrictions. To address these issues, the use of Reclaimed Asphalt Pavement (RAP) and alternative filler materials is being considered. RAP is often used with Warm Mix Asphalt (WMA) additive to reduce production temperature and limit emissions at the asphalt plant and worksite. However, the long-term performance of recycled mixes is a concern due to the ageing of the mix, which can result in higher moisture susceptibility, lower fatigue, and cracking resistance properties. This ageing can be caused by intrinsic and extrinsic variables during production and service life. While extensive research has been conducted on the topic, the potential of fillers, especially alternate fillers, on ageing resistance of recycled asphalt mixes has not been thoroughly studied. Since fillers are in contact with asphalt binder in the mix, their physical and chemical interactions can affect the rate of asphalt binder ageing due to oxidation. This study on recycled asphalt mix aims to address these research gaps through three tasks: (1) examining the individual and combined effect of hydrated lime and WMA additive; (2) evaluating the ageing resistance potential of waste fillers; and (3) promoting the sustainable utilization of widely produced fine-grained industrial wastes. The study employs a new approach that investigates the effects of both hydrated lime filler and Sasobit warm mix additive on the long-term performance of asphalt mixes containing 50% RAP. Short-term and long-term ageing simulations were conducted based on standard AASTHO R30 ageing protocols to evaluate the properties of the recycled mixtures. Tests were carried out on the Marshall stability, indirect tensile strength, moisture susceptibility, rutting, ravelling resistance, stiffness modulus, and fatigue cracking. The results indicated that the recycled control mix was significantly affected by long-term ageing, as evidenced by its reduced moisture susceptibility, fatigue, and cracking resistance properties. However, the presence of the Sasobit additive limited the extent of ageing, with hydrated lime acting as a multifunctional additive. The warm mix additive decreased the moisture and rutting resistance of the mix in long-term ageing. Notably, the use of both additives resulted in a considerable improvement in performance by reducing ageing and enhancing fatigue and cracking resistance. The positive outcome was attributed to the modification of oxidation kinetics by hydrated lime and warm mix additive, which react with oxidation products, preventing harmful effects on the mix. The study aimed to investigate the potential of waste fillers in improving the ageing resistance of recycled asphalt mix and was divided into two stages. Firstly, the effect of the type of filler on ageing susceptibility was evaluated by incorporating jarosite, hydrated lime mud, fly ash, and sugarcane ash filler into the asphalt mix with 50% RAP. The performance properties of the unaged and long-term aged recycled asphalt mix, including cracking resistance, moisture susceptibility, resilient modulus, rutting, and fatigue resistance, were analyzed. The results showed that the type of filler had a significant impact on the ageing resistance of the recycled mix. Secondly, the quantity of filler on ageing susceptibility was evaluated, and the results indicated that the ageing resistance potential of the hydrated lime mud filler was the highest among the studied waste fillers for all the properties. This was attributed to its fine particle size, higher porosity, presence of calcite, and increased asphalt film thickness in the mix. Overall, the study concluded that hydrated lime mud filler has excellent potential for improving the ageing resistance of recycled asphalt mixtures. To evaluate the effect of filler quantity, various proportions of the studied fillers were added to the recycled asphalt mixtures (2%, 4%, and 6%). The asphalt mixes were then subjected to both unaged and long-term ageing conditions, and their performance was evaluated using various measures, including MS, ITS, TSR, MQ, CAL, and RM, with ageing indices. The data were analyzed using two-way ANOVA, and the results indicated that both the type and quantity of filler had a statistically significant effect on the ageing susceptibility of the recycled asphalt mixes in terms of MS, ITS, TSR, and RM. However, only the type of filler, not the quantity, had a substantial impact on the ageing susceptibility of the mix with respect to its rutting resistance (MQ). On the other hand, neither the type nor quantity of filler had a statistically significant effect on the ageing susceptibility of the recycled asphalt mixes in terms of their ravelling resistance (CAL). Notably, the apparent film thicknesses of recycled mixes were found to significantly affect their ageing susceptibility. To promote sustainable use of commonly produced fine-grained industrial waste, along with reclaimed asphalt pavement (RAP), in warm mix asphalt (WMA) production, varying quantities (2-6% by weight of aggregates) of ground granulated blast furnace slag (GS), dried limestone sludge (LS), and fly ash (FA) were used as fillers. The extensive testing showed that the recycled WMA exhibited satisfactory engineering performance and superior environmental suitability. Mixes containing LS and GS demonstrated superior performance against common pavement distresses such as rutting and cracking, due to their high porosity, fine particle size, specific surface area, and abundance of calcareous minerals. Additionally, a design was created for a one-kilometer stretch of two-lane asphalt pavement using optimally produced mixes based on mechanistic-empirical guidelines. The design showed that using these mixes could save up to 52 tonnes of conventional filler material, reduce costs by 36%, and cut greenhouse gas emissions by 35%. The study's outcomes are expected to address critical issues such as scarcity of natural aggregates, eco-friendly and cost-effective waste disposal, and reduction of greenhouse gas emissions in pavement construction practices, while improving the engineering performance of the mixes against moisture damage, temperature, and aging susceptibility.