Fundamental Properties of Asphalts and Modified Asphalts, III

SUBTASK 2-2. AGING
SUBTASK 2-2.1. IMPACT OF WATER ON AGING
Statement of Problem
The presence of moisture has been shown to increase the rate at which aging progresses in
paving asphalts. Since aging ultimately leads to embrittlement and pavement failure,
determining and modeling the influence of moisture is important to the prediction of pavement
performance.
Approach
The sensitivity of asphalts to environmental factors is being determined using laboratory PAV
aging tests on unmodified asphalts with and without moisture in the oven. Analytical tests
applied include spectroscopic (FTIR) and rheologic (DSR) of the aged materials. Master curve
and shift factors are used to quantify changes.
Goal
Develop relationships that predict the long-term aging of asphalts in the presence of moisture.
Support of FHWA Strategic Goals
The ability to reliably reproduce in the laboratory the aging that occurs in-sevice is vital to the
highway community. With the development of a correlation between laboratory aging data and
field pavement performance, an agency may be able to predict the advent of distresses in the
field, therefore, improving the cost effectiveness of the preventative maintenance and/or
rehabilitation measures that are commonly used. This subtask supports the FHWA Strategic
Goal of Optimizing Pavement Performance.
Work Conducted This Quarter
To evaluate the impact of moisture on the aging characteristics of asphalt binders in terms of
physical chemical relationships, previously collected data including the rheological and chemical
properties of eight RTFO- and RTFO/PAV-aged SHRP asphalts were analyzed extensively. The
RTFO-aged asphalts were PAV aged for different lengths of time in the absence and presence of
water. To further develop an understanding of the relationship between rheological properties
and chemical properties mathematically, the complex modulus was plotted against carbonyl
content for different aging times, 140, 240, and 480 hours for eight asphalts. The detailed results
were presented in previous quarterly reports (December 31, 2007 and March 31, 2008). It was
reported that both the complex modulus and carbonyl content increase with increasing aging
time and that different asphalts have different sensitivities to aging. The complex modulus
increases more sharply with increasing carbonyl content for some asphalts than for others. A
statistical model, logistic with two parameters, was applied to describe the relationship. This
equation is shown as follows:
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