Effect of Lower Working Temperatures on Physical and Mechanical Properties of Warm Mix Asphalt Mixtures

Abstract

This thesis document present details on methodology, results, and conclusions of the research performed on warm mix asphalt (WMA) mixtures. The prime objective of this research was to evaluate mix design, workability and mechanical properties of dense-graded asphalt mixtures modified with non-foaming WMA additives at lower working (mixing and compaction) temperatures. Further, to provide wider margin between mixing and compaction temperatures that can ensure WMA mixtures for longer hauling time and better performance. Asphalt mix design properties were evaluated by the Superpave method for various design gyrations (Ndes) and the workability properties were evaluated in terms of Superpave gyratory compactor (SGC) densification indices, using Bahia and Locking point method. Mechanical properties such as, resistance to moisture-induced damage was evaluated by the tensile strength ratio (TSR) approach, rutting resistance was evaluated by laboratory wheel tracking test using the wheel rut tester (WRT), and flexural fatigue characteristics was evaluated by four point bending using a repeated load testing machine. The effect of nominal maximum aggregate size (NMAS), working temperature, and type of mixture on properties of WMA mixtures were investigated. The experimental results were statistically analyzed to identify the major influencing factors and their significance using one way ANOVA test. Mix design properties were found statistically significant with respect to NMAS, Ndes, working temperature, and type of mixture. WMA mixtures compacted at lower working temperature were suitable for higher traffic levels and the design asphalt content of WMA mixtures were found lower than that of control mixtures. Sasobit modified WMA mixtures (WS) compacted at 90 0C and 70 0C are more workable and resistant to traffic. These mixtures exhibited higher resistance to moisture-induced damage, rutting and fatigue than those of control mixtures (CM), Rediset modified WMA mixtures (W-R) and Zycotherm modified WMA mixtures (W-Z). However, WMA mixtures compacted at 90 0C and 70 0C showed lower moisture-induced damage, rutting and fatigue resistance than control mixtures compacted at 130 0C. In addition, workability and mechanical properties of NMAS26.5 mixtures was significantly higher than NMAS19 mixtures. WMA mixtures prepared with saturated surface dry aggregates were more prone to moisture-induced damage compared to that of WMA mixtures made withoven dry aggregates. In addition, WMA mixtures prepared with surface saturated dry aggregates and compacted at 90 0C and 70 0C marginally fulfilled the minimum TSR requirement.