Evaluation of Recycling Agent and Extender Dosage Selection Procedures to Restore the High-Temperature Climatic Performance Grade

Abstract

Dosage selection is important for effective use of recycling agents and extenders in asphalt pavements. A standardized protocol for extender and recycling agent dosage selection does not presently exist. NCHRP Project 09-58 established a recycling agent dosage selection procedure that aims to restore the desired high-temperature grade of a blend of recycled binder, virgin binder, and additive. Their simplified procedure relies on the existence of class-specific relationships between the blended system high-temperature grade and additive content. Further, the dosage selection procedure assumes complete recycled binder availability. There is general consensus that complete recycled binder availability is not achieved in practice, which may yield asphalt mixtures with poor rutting performance. This study seeks to evaluate the universality of the slopes proposed in NCHRP Project 09-58 to both extenders and recycling agents and evaluate the rutting resistance of asphalt mixtures prepared using additive dosages selected to restore the high-temperature grade of the blended binder system. This study encompasses one reclaimed asphalt pavement (RAP) and one recycled asphalt shingles (RAS) mixture. Two extender and two recycling agent products were evaluated. The results indicate that different additive types yield different slopes of the blended system high-temperature grade versus additive content. The results also show that uncertainty should be accounted for when establishing a dosage selection procedure to ensure that the blended binder grade does not fall below the desired value. The rutting resistance of mixtures prepared using additive dosages intended to restore the high-temperature grade all passed recommended Hamburg wheel-track criteria.

Benchmarking Recycled Binder Blends Using Statistical Analysis: A Case Study of Virginia and North Carolina

“…Figure 3, a and b , shows the distributions of | G *|/sin(δ) @64°C of NC’s PG 64-22 binders and the blends in the unaged (Original) and short-term-aged (rolling thin film oven, RTFO) conditions. The characterization of the recycled blends containing MRAS was avoided in the Original condition, as a non-uniform distribution of the MRAS was observed in this state ( 15 ).…”

“…B3 and a PG 64-22 virgin binder from NC, referred to here as B4, was used to constitute NC’s blends. The dosage level of the RA-modified systems representing the NCDOT mixtures was selected to restore the high-temperature PG (PGH) of the blended system to a target of 64°C, as detailed elsewhere ( 15 ). A maximum RA dosage limit of 10% was considered for both NC’s and VA’s materials as recommended in NCHRP Project 09-58 ( 3 ).…”

“…The component materials were blended using a power drill with a paddle attachment, and the RAs were incorporated using a syringe. The detailed procedure describing the binder blend preparation can be found elsewhere ( 15 ).…”

“…In general, the topics studied in recent years included, but are not limited to, the performance and evaluation of recycled asphalt binder blends and recycled asphalt mixtures ( 6 – 8 ), classification of RAs ( 4 , 9 ), and chemistry of RAs ( 10 , 11 ). Further, considerable attention has been placed on the development of dosage selection procedures based on the high-temperature (HT), intermediate-temperature (IT), and low-temperature (LT) performance of the blended binder system ( 12 – 15 ). However, limited studies have been conducted on comparing the rheological characteristics of RA-modified systems using different dosage selection procedures to typical virgin binders accepted for asphalt pavement construction.…”