Asphalt Concrete Mixture Long-Term Aging Protocol Representative of Arizona’s Climatic

📨 Contact: Hasan Ozer
🔖 Researchers: Awais Zahid, Nafiur Rahman
🤝 Sponsor:  Southwest Pavement Technology
📅 Timeline: 2023 – Ongoing

Loose Mixture Long-Term Aging

Field aging of asphalt concrete (AC) mixtures is a complex phenomenon resulting in significant changes in the rheological properties and chemistry of binders and impacting key performance characteristics of asphalt mixtures. Laboratory simulation of the field aging characteristics of asphalt concrete (AC) mixes is essential in characterizing its long-term performance. Hence, long-term aging protocols have become a key part of the Balanced Mix Design (BMD) framework adopted by many state and local agencies.

Arizona Climatic Condition

The thermal profile of Arizona during a typical summer month shows that the air temperature reaches as high as 120°F in the summer season in the valley area (Phoenix). This indicates Arizona’s extreme and diverse climatic conditions and found that the Phoenix metropolitan area experiences air temperatures above 100°F for around 110 days during the summer, with maximum temperatures reaching 120°F. Incorporating any of the existing LTA protocols into a BMD protocol implemented in extreme climatic conditions, such as in Arizona, remains a challenge. The long-term aging protocol is developed for Arizona’s diverse climatic condition.

Accelerated Loose Mix Long Term Aging

A practical and accelerated long-term aging protocol is developed for regions under extreme climatic conditions in which heavily polymer-modified binders are predominantly used. According to the protocol, temperature and aging duration are adjusted to simulate eight years of field aging on the pavement surface based on the oxidative kinetics model developed in the NCHRP 09-54 study. The developed accelerated LTA protocols are validated using representative rheology, chemical and mixture-level cracking test. The developed LTA protocol can be integrated into a BMD framework employing index-based and more advanced fracture testing protocols. The NCHRP 9-54 aging protocol recommended temperature (95°C) and the accelerated aging protocol (135°C) have comparable rheological, chemical and mixture cracking testing results after long-term aging at two different temperatures but different durations.  Aging at 135°C for 30 hours does not cause any evident damage to binders’ rheology and chemical makeup.

Validation And Verification of Developed LTA Protocol

The Southwest Pavement Technology Consortium’s first test section is constructed on April 10, 2024, for the long-term aging study. The test section is located on S 74th St, Mesa, AZ 85208, between E Drummer Ave and E Dewberry Ave. The construction involves milling and 2-inch overlay of the asphalt concrete. Aerial view of the test section for the long-term aging study immediately after construction, showcasing the two lanes with different compaction densities (96% and 93%). This test section has aims to explore how pavement density influences aging by comparing the penetration of aging effects in each lane when exposed to environment. This Field aging study will show how density affects pavement durability and performance over time. A thermal drone captures the thermal images of the test section after compaction. These thermal images highlight temperature variations across the section, showing the uniformity and potential compaction quality of the pavement. The new surface is constructed using multiple variables, and the section is instrumented to collect data that will aid the consortium’s core projects. The collected data will achieve the following objectives:

The cores obtained from the section are mainly used to investigate aging in the binder. The asphalt binder is extracted and recovered from the top and bottom disk of two cores obtained from each subsection. The rheological and chemical properties of the extracted binder are determined using a dynamic shear rheometer (DSR) and Fourier Transform Infrared Spectroscopy (FTIR). The additional cores obtained from control section having no coating are collected from both low- and high-density lane of test section to determine the fracture energy and the creep compliance of the mixture.

Application of surface coating to the test section

Field core collection from the test section