Advancing FAA Asphalt Mix Design: Evaluation of Rutting Mechanical Tests for Balanced Mix Design
Loading...
Authors
Elias, Nicole George
Issue Date
2024
Type
Dissertation
Language
en_US
Keywords
Airfield Pavements , Asphalt Pavements , Balanced Mix Deisgn , Permanent Deformation
Alternative Title
Abstract
Asphalt concrete (AC) mix design methods have been progressing throughout the last century with the aim of reaching AC mixtures at a superior field performance level. The balanced mix design (BMD) is the latest advancement in mix design focusing on laboratory mechanical tests correlated to field performance, rather than relying fully on mixture volumetric properties. BMD provides better insights than conventional volumetric methods on how AC mixtures perform in the field. Following the implementation of BMD by various highway agencies at the local, state, and federal levels, the Federal Aviation Administration (FAA) is considering incorporating a BMD framework in their next specifications update for flexible airfield pavements as part of advisory circular 150/5370- 10H. This dissertation specifically focuses on the rutting aspect of the FAA BMD framework at the mix design stage as well as during control strip and final production. With the aim of developing rutting test specifications for airfield AC mixtures, the tasks of the dissertation involve setting preliminary rutting test criteria (based on thorough review of literature and developed mechanistic approach), selecting representative test protocols for airfield pavements, deriving initial rutting test criteria (based on laboratory experimental plan), refining test protocols (in particular specimen conditions) for final specifications, and recommending final refinement for the set test criteria. At the beginning, the rationale for current FAA rutting tests criteria was reviewed and additional preliminary criteria that are tailored to airfield mixture conditions were investigated in Chapter 3. This included reviewing Asphalt Pavement Analyzer (APA) thresholds developed in previous research studies based on airfield traffic level by means of Equivalent Highway ESALs (EHEs). Furthermore, the High Temperature Indirect Tensile highway test criteria for particular airfield conditions as function of traffic were refined based on the rutting resistivity model and EHE. Correlating results of laboratory rutting tests with field performance is a necessary step prior to the implementation of test specifications. Field performance and laboratory rutting test data from the FAA full scale accelerated test facilities along with in-place airfield pavements were evaluated against the recommended preliminary tests criteria. One of the key elements towards implementing BMD is setting adequate conditions for laboratory mechanical testing that best simulate actual field conditions. Accordingly, representative air void (AV) levels were identified in Chapter 4 for laboratory mechanical testing by analyzing quality control (QC) data of plant-mixed laboratorycompacted (PMLC) samples along with in-place density measurements for multiple existing airfield pavements. The laboratory compaction effort in the Superpave Gyratory Compactor (SGC) required to reach the recommended AV levels were evaluated for different specimen heights. The specimen height and AV level were then experimentally verified with the Ideal Rutting test (ASTM D8360-22) for these airfield mixtures. Based on analysis of field density, laboratory compaction effort, and mechanical test data, it was recommended in Chapter 5 to test 62 mm thick gyratory specimens at 7±0.5% AV (directly molded) or at 5±0.5% AV (after cutting), which should help capture the different aspects of the asphalt mixture's resistance to rutting in terms of aggregate skeleton and binder properties. The dissertation presented the experimental plan data in Chapter 6 including laboratory and plant produced samples of several airfield mixtures at two AV levels. Robust trends were found amongst different rutting tests, whereas for the Hamburg Wheel Track Test (HWTT), the data were significantly influenced by the variability of the rut depth with stripping failure, especially in the case of cut specimens. Thus, additional parameters from the HWTT that could isolate the stripping failure from the mixture rutting characterization were investigated. Based on the developed regression models and statistical analyses, initial test criteria were derived for the explored rutting tests based on the current FAA specification of maximum 10 mm APA 250 psi/250 lab rut depth after 4,000 cycles.