Evaluation of moisture sensitivity properties of ADOT mixtures on US 93 : final report.
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2001-11-01
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Edition:Final report
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Abstract:In 1993, the Arizona Department of Transportation (ADOT) constructed pavement test sections as part of the Long
Term Pavement Performance (LTPP) Specific Pavement Studies (SPS). The test sections are located on US 93 north
of Kingman, Arizona, and consist of both SPS-1 and SPS-9 experiments constructed at the same location. As early as
1996 it was reported that fatigue cracking was occurring in the SPS-9 Superpave sections. A field visit in 1998 by
personnel from ADOT, LTPP, and the FHWA revealed that the SPS-9 Superpave test sections were experiencing
premature fatigue cracking while the SPS-1 test sections which used Marshall Mix designs had not experienced any
distress. The survey team concluded that moisture sensitivity may be the primary cause of the premature fatigue of
the Superpave designed HMA mixtures. An investigation into this premature failure was subsequently initiated.
This report describes the performance of the SPS-9 sections and documents the laboratory evaluation of mixtures
and cores from the three sections in an effort to assess the appropriateness of the Superpave moisture damage
requirements. The three evaluated sections included: a Superpave designed section with 1” nominal maximum size, a
Superpave designed section with 3/4” nominal maximum size, and an ADOT Marshall designed section with 3/4”
nominal maximum size. The two Superpave sections did not include anti-stripping additive based on the results of the
Superpave moisture sensitivity testing. The ADOT section included 2% Portland Cement (PC) based on the results of
the ADOT immersion compression test.
This research project evaluated the moisture sensitivity of the HMA mixtures used on all three sections using a
modified AASHTO T-283 procedure and a modified ADOT immersion compression test procedure. Laboratory
mixtures and field cores were tested by the modified AASHTO T-283 method using both the freeze/thaw and no
freeze/thaw conditioning methods. Three methods of compaction were used (gyratory 4- and 6-inch and Marshall 4-
inch).
The analysis of the data generated in this study led to the following conclusions: The moisture conditioning
(freeze/thaw and no freeze/thaw) did not significantly impact the retained strength ratios of HMA mixtures as measured
by the resilient modulus (Mr) and Indirect Tensile Strength (ITS) test procedures. The impact of compaction method
on retained strength of HMA mixtures is affected by other factors such as: type of mixture and the addition of PC.
The impact of adding PC to HMA mixtures showed mixed results depending on compaction method. The ability
of the modified AASHTO T-283 method in assessing moisture sensitivity of HMA mixtures, with either the gyratory
or the Marshall compaction methods, is questionable. Similarly, ADOT immersion compression test results provided
questionable value in discriminating between acceptable and unacceptable mixes.
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