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Investigation of the Current Levels of Dust-to-Binder Ratio on Durability of Asphalt Mixtures
AuthorHierholzer, Forrest Joseph
AdvisorHand, Adam J. T.
Civil and Environmental Engineering
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Durability refers to the resistance of Asphalt Concrete (AC) to several forms of cracking. It is the goal of State Highway Agencies (SHAs) and local authorities alike, to maintaining adequate durability and ensure good pavement performance. Since the early 2000s, escalating asphalt binder costs have significantly increased the use of reclaimed asphalt pavement (RAP) within AC mixtures. This increase, although cost effective and environmentally conscious, has detrimentally affected AC durability. Optimization of RAP and the regulation of AC durability is currently being addressed during the design and construction of AC pavements through Quality Control (QC) and Quality Assurance (QA) testing. With that being said, AC mixtures produced in the field commonly experience a loss of durability compared to laboratory designed AC mixtures. This loss of durability is frequently thought to be attributed to mixture adjustments and material inconsistencies caused during production and can occur within agencies whose specifications do not include multiple production volumetric requirements. One volumetric requirement that is thought to significantly affect AC durability is Dust Proportion (DP). Mixture DP is notable due to its ability to effectively regulate detrimental AC mixture fines compared to current practices.The purpose of this study was to investigate current DP levels and their impact on mixture performance. AC mixture durability, as well as stability, were evaluated using the Indirect Tensile Cracking (Ideal-CT), Texas Overlay (OT), Indirect Tensile Strength (IDT), and Hamburg Wheel Track (HWTT) tests. Comparisons between field mix lab compacted (FMLC), lab mix lab compacted (LMLC), and a modified DP lab mix lab compacted (1.6 LMLC) AC mixture were analyzed. Results from this study showed that the relationship between the number of cycles till failure determined from the OT test and the CTindex determined from the Ideal-CT test were highly correlated. Mixture properties including the DP, effective binder, total binder, absorbed binder, and film thickness were also determined to significantly affect the IDT and Ideal-CT testing results. Results from this study allowed the researchers to better understand how mixture fluctuations during AC production and deviations from the mixture design affected AC performance. A DP specification and specification language regarding other volumetric properties and performance tests were recommended based on the findings of this study. This research shall serve as a guide to help other local and state regulatory agencies with AC durability concerns.