Short- and Mid-Term Loose Mix Conditioning Protocols for Asphalt Overlay Balanced Mix Design and Quality Control and Quality Acceptance

Abstract

Many aspects of balanced mix design (BMD) and performance-related quality control and quality acceptance (QC/QA) testing depend heavily on how the asphalt mixes are conditioned. There is, therefore, a critical need for practical loose mix conditioning protocols. The main objective of this study was to establish practical loose mix condition protocols for both the BMD and QC/QA phases. To develop these protocols, this paper reviewed the field performance and pavement lives of more than 200 test sections around the United States and found most of these test sections were 50-mm thick asphalt overlays where cracking is evident in 1 to 4 years. Based on this finding, the paper developed two conditioning protocols for asphalt overlays: short-term and mid-term. The short-term conditioning is intended for volumetric design, BMD rutting performance test, and QC/QA testing at asphalt plants, while the mid-term conditioning is mainly for BMD cracking performance test. A series of IDEAL cracking tests were then conducted with 13 mixes and the test results confirmed the validity of the mid-term conditioning protocol. It was also found that conditioning time affected mix cracking resistance significantly. The longer the conditioning time, the poorer the cracking resistance. When conditioned too long, the normalized cracking resistance difference among various mixes diminished. For asphalt mix composition, binder source (or quality) and asphalt absorption are two significant factors affecting the normalized cracking resistance of asphalt mixes; in contrast, mix type, asphalt binder content, and the use of rejuvenator had insignificant influence.

Study of Measures to Design Asphalt Mixes Including High Percentages of Recycled Asphalt Pavement and Recycled Asphalt Shingles

“…The CT index was introduced based on the ideal cracking (IDEAL-CT) test method ( 12 ). Several studies have also reported that fracture energy, fracture work density, flexibility index values, and CT index values show high correlation with field results ( 13 – 16 ). However, the simplicity, practicality, and repeatability of the IDEAL-CT have increased the popularity of this test over the past years ( 17 , 18 ).…”

“…Cracking test (CT) index values on load–displacement curve obtained from indirect tension/IDEAL-CT test method ( 15 ).…”

“…Generally, the use of RAP or RAS, a low binder content, and a stiff binder grade will improve the rutting resistance of asphalt mixes ( 10 , 22 ). Zhou ( 15 ) evaluated the CT index used in the IDEAL-CT method for laboratory mixes that contained different amounts of recycled materials and different binder grades, binder contents, and aging conditions. That study reported higher CT index values for mixes with less recycled material, a softer virgin binder, a higher binder content, and less aging.…”