Development of quality standards for inclusion of high recycled asphalt pavement content in asphalt mixtures - phase II.
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2015-03-01
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Abstract:To conserve natural resources and energy, the amount of recycled asphalt pavement has been steadily increasing in the construction
of asphalt pavements. The objective of this study is to develop quality standards for inclusion of high RAP content. To determine if
the higher percentage of RAP materials can be used on Iowa’s state highways, three test sections with target amounts of RAP
materials of 30%, 35% and 40% by weight were constructed on Highway 6 in Iowa City. To meet Superpave mix design
requirements for mixtures with high RAP contents, it was necessary to fractionate the RAP materials. Three test sections with actual
RAP materials of 30.0%, 35.5% and 39.2% by weight were constructed and the average field densities from the cores were
measured as 95.3%, 94.0%, and 94.3%, respectively. Field mixtures were compacted in the laboratory to evaluate moisture
sensitivity using a Hamburg Wheel Tracking Device. After 20,000 passes, rut depths were less than 3mm for mixtures obtained
from three test sections. The binder was extracted from the field mixtures from each test section and tested to identify the effects of
RAP materials on the performance grade of the virgin binder. Based on Dynamic Shear Rheometer and Bending Beam Rheometer
tests, the virgin binders (PG 64-28) from test sections with 30.0%, 35.5% and 39.2% RAP materials were stiffened to PG 76-22, PG
76-16, and PG 82-16, respectively. The Semi-Circular Bending (SCB) test was performed on laboratory compacted field mixtures
with RAP amounts of 30.0%, 35.5% and 39.2% at two different temperatures of -18 and -30 °C. As the test temperature decreased,
the fracture energy decreased and the stiffness increased. As the RAP amount increased, the stiffness increased and the fracture
energy decreased. Finally, a condition survey of the test sections was conducted to evaluate their short-term pavement performance
and the reflective transverse cracking did not increase as RAP amount was increased from 30.0% to 39.2%.
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