DETERMINATION OF RECYCLED ASPHALT PAVEMENT (RAP) CONTENT IN ASPHALT MIXES BASED ON EXPECTED MIXTURE DURABILITY

Abstract

Decreasing supplies of locally available quality aggregate in some areas, growing concern over waste disposal, and the rising cost of asphalt binder have resulted in greater use of recycled asphalt pavement (RAP) for new road construction. Unfortunately, the incorporation of RAP introduces one more variable to consider when predicting the durability of the newly constructed asphalt concrete pavement. Traditional determination of the RAP quantity allowed for addition to the virgin asphalt concrete mix has an empirical nature and is based on viscosity measurement of a blended binder. The primary objective of this study was to develop an implementable testing procedure that will effectively determine recycled asphalt pavement (RAP) content limits based on mix durability loss. The research approach involved laboratory examination of twenty intermediate course bituminous concrete mixes, to evaluate changes in asphalt binder properties and mix durability resulting from the addition of various levels of RAP. Specimens of virgin asphalt binder and blended virgin/RAP binder were tested (both non-aged and oven-aged) by Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) to evaluate stiffness properties at various temperatures. Bituminous mix specimens compacted at optimum binder contents were tested (both non-conditioned and moisture-conditioned) for indirect tensile strength and absorbed energy characteristics. Non-conditioned specimens were also tested for unconfined compressive strength. The BBR test results indicate that creep stiffness of blended asphalt binder increases with increasing RAP content. The moisture damage test results indicate that RAP addition has an effect on the durability performance of bituminous concrete. A procedure based on the Absorbed Energy concept is suggested for use by the Ohio Department of Transportation for determining optimum RAP content when designing a bituminous concrete mix. Recommended values of Indirect Tensile Strength and Absorbed Energy (prior to aging and after aging) are provided for use in classifying potential durability performance of bituminous mixes containing RAP.