An evaluation of the tensile strength of asphalt binder and mortar with recycled asphalt additives at low temperatures

Abstract

A standard grading system is used to evaluate the properties and expected performance of an asphalt binder. The most common grading system used in the US today is the performance grading (PG) system. This system prescribes an operational temperature range within which the binder is expected to perform satisfactorily without resulting in rutting, fatigue cracking or thermal cracking as a distress. On the low-temperature and thermal cracking end, this system uses both a metric related to stiffness and rate of relaxation (m-value) to establish a low temperature grade for a given asphalt binder. Although these parameters provide some information on the rate of relaxation and overall rigidity of the asphalt binder they don’t include an evaluation of the tensile strength of the asphalt binder. The tensile strength of the binder can furnish critical information about its resistance to cracking including thermal cracking. The asphalt industry has become particularly interested in the impact of recycled asphalt pavement (RAP) and additives such as rejuvenators on the behavior and performance of the material. The goal of this study was to evaluate the tensile strength characteristics of asphalt binders and composites in addition to their stiffness characteristics. The study was conducted in three parts: (1) the evaluation of tensile strength of asphalt binders with similar performance grades, (2) the evaluation of tensile strength of asphalt binders as a function of the amount of recycled asphalt binder added to the virgin binder, and (3) the influence of recycled asphalt and rejuvenators on the stiffness and tensile strength of asphalt mortars. In addition to these three objectives, this study also developed simplified methods to prepare and evaluate the tensile strength of asphalt binders and mortars as a material characterization tool to screen or evaluate the efficacy of RAP, rejuvenators, and other additives. Results show that similarly graded binders have a significant variability both in terms of their stiffness and strength and that rejuvenators can be used with RAP to achieve a balance of stiffness and strength.