In the asphalt materials community, the most critical research need is centered around a paradigm shift in mixture design from the volumetric process of the previous 20-plus years to an optimization procedure based on laboratory-measured mechanical properties that should lead to an increase in long-term pavement performance. This study is focused on advancing the state of understanding with respect to the value of intermediate temperature cracking tests, which may be included in a balanced mix design. The materials included are plant-mixed, laboratory-compacted specimens reheated from the 2013 Federal Highway Administration’s (FHWA’s) Accelerated Loading Facility (ALF) study on reclaimed asphalt pavement/reclaimed asphalt shingle (RAP/RAS) materials. Six commonly discussed intermediate temperature (cracking and durability) performance testing (i.e., Asphalt Mixture Performance Tester [AMPT] Cyclic Fatigue, Cantabro, Illinois Flexibility Index Test [I-FIT], Indirect Tensile Cracking [ITC, also known as IDEAL-CT], Indirect Tensile Nflex, and Texas Overlay Test) were selected for use in this study based on input from stakeholders. Test results were analyzed to compare differences between the cracking tests. In addition, statistical analyses were conducted to assess the separation among materials (lanes) for each performance test. Cyclic fatigue and IDEAL-CT tests showed the most promising results. The ranking from these two tests’ index parameters matched closely with ALF field performance. Furthermore, both showed reasonable variability of test data and they were successful in differentiating between different materials.
Asphalt binder, as one of the load-carrying components of the pavement, is a viscoelastic, thermoplastic material characterized by a certain level of rigidity of an elastic solid body, but, at the same time, flows and dissipates energy by frictional losses as a viscous fluid. Due to its complexity and importance, many studies were conducted to understand and alleviate its performance. Creep tests have been used to characterize asphalt materials at different service temperatures. Permanent strain or rutting is one of the most important pavement distresses. It is believed that the accumulated strain in asphalt binder, as a consequence of traffic, is mainly responsible for the rutting of asphalt pavements. Repeated creep tests were developed to identify non-viscous flow that contributes to the permanent deformation from the total dissipated energy. The low-temperature cracking of asphalt pavements is a major pavement distress mechanism in cold regions. Since asphalt is a viscoelastic material, part of said stresses is dissipated through relaxation, but, eventually, they build up until they reach the strength of the material, leading to the formation of cracks to relieve these stresses. Conducting creep test at low temperatures is a common test method to characterize thermal cracking behavior of asphalt binders.
As balanced mixture designs move forward, obtaining index properties quickly will become critical to routine application. This paper details a study into streamlining performance tests so that users may make decisions on as-designed and as-built material in a shorter period. This study is unique to asphalt materials research through its use of the Scrum methodology. Scrum is a form of the Agile project management technique often used in software development to manage complex projects. This process can also address the intricacies of applied research, with a focus on delivering high-value products through an iterative procedure. This paper is focused on optimizing temperature–frequency combinations in dynamic modulus (| E*|) tests to generate an equivalent master curve more rapidly. Three different versions of | E*| tests were conducted on four mixtures using combinations of five temperatures and seven frequencies in an asphalt mixture performance tester (AMPT). Cyclic fatigue testing was also conducted, which allowed for computation of the apparent damage capacity ( Sapp). The results for Sapp show that there is no statistical difference between the three versions. Also, analysis showed that the total testing time for | E*| can be reduced by half without significant changes to master curves and values of Sapp generated under the testing sweep prescribed in the test standards. A streamlined testing version is provided based on a predefined evaluation approach to ensure adequate equivalency of critical parameters from the full testing suite.
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