Cracking and Aging of Asphalt Mixtures Using the Illinois Flexibility Index Test

Abstract

Cracking is a serious asphalt pavement distress that can affect ride quality and impact road safety. The increased use of reclaimed asphalt pavement (RAP), recycled asphalt shingles (RAS), and modified asphalt binders has led to the production of asphalt mixtures that are prone to cracking issues. In addition, asphalt aging, which occurs during mix production and construction as well as during pavement service life, is a significant factor that can exacerbate issues related to all modes of cracking. Consequently, the volumetric mix design method alone can no longer secure acceptable long-term pavement performance, and several transportation agencies in Canada currently are integrating performance tests into mix design procedures to increase longevity and durability of asphalt mixtures. This study investigated the influence of common mix design properties on cracking and aging resistance and developed preliminary cracking performance–based specifications for balanced mix design implementation. Six loose plant-produced mixtures consisting of a range of mix design properties were compacted in the laboratory to produce short-term- and long-term-aged specimens. The Illinois flexibility index test (I-FIT) was used to evaluate cracking performance of both short-term- and long-term-aged specimens. The results showed that mixtures with higher nominal maximum aggregate size (NMAS), limestone aggregates, and RAS reduced cracking performance. Conversely, incorporating RAP and RAS and using stiffer binders improved aging resistance, whereas use of limestone aggregates contributed to lower aging resistance.