Environmental factors such as temperature, air, and water can have a profound
effect on the durability of asphalt concrete mixtures. In mild climates where good
quality aggregates and asphalt cement are available, the major contribution to
deterioration may be due to traffic loading and the resultant distress is manifested
in the form of fatigue cracking, rutting, and raveling. But, when more severe
climates are coupled with poor materials and traffic, premature failure may result.
The objectives of this research are twofold and includes: (1) development of a test
system to evaluate the most important factors influencing the water sensitivity of
asphalt concrete mixtures; and (2) development of laboratory testing procedures that
will predict field performance. This research also addresses the hypothesis that much
of the water damage in pavements is due to water in the asphalt concrete void
system. It is proposed that most of the water problems occur when voids are in the
range of about 5% to 12%. Thus, the term "pessimum" voids is used to indicate that
range (opposite of optimum).
In order to evaluate the hypothesis and the numerous variables, the Environmental
Conditioning System (ECS) was designed and fabricated. The ECS consists of three
subsystems: (1) fluid conditioning, where the specimen is subjected to predetermined
levels of water, air, or vapor and permeability is measured; (2) an environmental
cabinet that controls the temperature and humidity and encloses the entire load
frame; and (3) the loading system that determines resilient modulus (M[subscript n]) at various
times during environmental cycling and also provides continuous repeated loading
as needed.
The ECS has been used to evaluate four core materials and also to investigate the
relative importance of mixture variables thought to be significant. Many details
regarding specimen preparation and testing procedures were evaluated during a
"shakedown" of the ECS. As minor variables were resolved, a procedure emerged
which appears to be reasonable and suitable. An experiment design for the four core
mixtures was developed, and the overall experiment design included three ranges of
void ( <5% low; 5-12%, pessimum; > 12% high). Six-hour cycles of wet-hot (60° C)
and wet-freeze ( -18° C) are the principle conditioning variables, while monitoring
MR at 25° C before and between cycling. A conventional testing procedure
(AASHTO T-283) was also used on the core mixtures to provide a baseline for
comparison.
Results to date show that the ECS is capable of discerning the relative differences
in "performance" such as MR. Three hot cycles and one freeze cycle appear to be
sufficient to determine the projected relative performance when comparing different
aggregates, asphalts, void levels, loading, etc. Based on these results, a water
conditioning procedure has been recommended and also a procedure for water
conditioning specimens prior to testing in fatigue, rutting, and thermal cracking. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36536 |
| Date | 05 May 1992 |
| Creators | Al-Swailmi, Saleh H. |
| Contributors | Terrel, Ronald L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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