A recent joint study by Arizona State University and the Arizona Department of Transportation (ADOT) was conducted to evaluate certain Warm Mix Asphalt (WMA) properties in the laboratory. WMA material was taken from an actual ADOT project that involved two WMA sections. The first section used a foamed-based WMA admixture, and the second section used a chemical-based WMA admixture. The rest of the project included control hot mix asphalt (HMA) mixture. The evaluation included testing of field-core specimens and laboratory compacted specimens. The laboratory specimens were compacted at two different temperatures; 270 °F (132 °C) and 310 °F (154 °C). The experimental plan included four laboratory tests: the dynamic modulus (E*), indirect tensile strength (IDT), moisture damage evaluation using AASHTO T-283 test, and the Hamburg Wheel-track Test. The dynamic modulus E* results of the field cores at 70 °F showed similar E* values for control HMA and foaming-based WMA mixtures; the E* values of the chemical-based WMA mixture were relatively higher. IDT test results of the field cores had comparable finding as the E* results. For the laboratory compacted specimens, both E* and IDT results indicated that decreasing the compaction temperatures from 310 °F to 270 °F did not have any negative effect on the material strength for both WMA mixtures; while the control HMA strength was affected to some extent. It was noticed that E* and IDT results of the chemical-based WMA field cores were high; however, the laboratory compacted specimens results didn't show the same tendency. The moisture sensitivity findings from TSR test disagreed with those of Hamburg test; while TSR results indicated relatively low values of about 60% for all three mixtures, Hamburg test results were quite excellent. In general, the results of this study indicated that both WMA mixes can be best evaluated through field compacted mixes/cores; the results of the laboratory compacted specimens were helpful to a certain extent. The dynamic moduli for the field-core specimens were higher than for those compacted in the laboratory. The moisture damage findings indicated that more investigations are needed to evaluate moisture damage susceptibility in field.
Asphalt concrete is the most recycled material in the United States and its reclamation allows the positive reuse of the constituent aggregates and asphalt binder, contributing to the long-term sustainability of the transportation infrastructure; decreasing costs, and the total energy and greenhouse emissions embodied into new materials and infrastructure. Although the national trends in Reclaimed Asphalt Pavements (RAP) usage are encouraging, the environmental conditions in Phoenix, Arizona are extreme and needs further consideration.
The objective of this research study was to evaluate the viability of using RAP in future pavement maintenance and rehabilitation projects for the City. Agencies in the State of Arizona have been slow adopting the use of RAP as a regular practice. While the potential benefits are great, there is some concern on the impact to long-term pavement performance.
RAP millings were sampled from the city’s stockpiles; processed RAP and virgin materials were provided by a local plant. Two asphalt binders were used: PG 70-10 and PG 64-16. RAP variability was evaluated by aggregate gradations; extracted and recovered binder was tested for properties and grading.
A mixture design procedure based on the City’s specifications was defined to establish trial blends. RAP incorporation was based on national and local practices. Four different RAP contents were studied 10%, 15%, 25%, and 25% content with a softer binder, in addition to a control mix (0% RAP).
Performance tests included: dynamic modulus to evaluate stiffness; Flow Number, to assess susceptibility for permanent deformation (rutting); and Tensile Strength Ratio as a measure of susceptibility to moisture damage.
Binder testing showed very stiff recovered asphalts and variable contents with a reasonable variability on aggregate gradations. Performance test results showed slightly higher modulus as RAP content increases, showing a slight improvement related to rutting as well. For moisture damage potential, all mixtures performed well showing improvement for RAP mixtures in most cases.
Statistical analysis showed that 0%, 10%, 15% and 25% with softer binder do not present significant statistical difference among mixtures, indicating that moderate RAP contents are feasible to use within the City paving operations and will not affect greatly nor negatively the pavement performance.
