Review and analysis of Hamburg Wheel Tracking device test data.
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2014-02-01
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Abstract:The Hamburg Wheel Tracking Device (HWTD) test (TEX-242-F) and the Kansas Test Method KT-56 (KT-56), or
modified Lottman test, have been used in Kansas for the last 10 years or so to predict rutting and moisture damage potential of
Superpave mixes, especially mixes containing Reclaimed Asphalt Pavement (RAP). Thermal Stress Restrained Specimen Test
(TSRST) was performed on selected mixes following AASHTO TP 10. All specimens tested were prepared with the Superpave
gyratory compacter.
Results showed that the number of wheel passes and rut depth from the HWTD test are significantly different for
Superpave mixes with various RAP content. Recycled Superpave mixtures with crushed gravel aggregates and sand significantly
improve overall rutting performance compared to crushed stone or crushed stone and gravel combinations in the mix. Aggregate
type also influences rutting performance of virgin Superpave mixtures. Rutting performance of Superpave mixes with or without
RAP is significantly affected by the binder source.
Statistical analysis proved that the total number of wheel passes, creep slope, and stripping slope of Superpave mixes with
RAP in HWTD tests are significantly affected by RAP content, binder grade, and asphalt sources at 90% confidence interval. RAP
percentage in the mix, aggregate type, and interaction between RAP content and aggregate type also affect the pure stripping
failure phase (stripping slope) and total wheel passes at the stripping inflection point. Analysis of variance (ANOVA) on Superpave
mixtures with RAP showed the number of wheel passes at stripping inflection point and stripping slope are significantly affected
by mix type and binder source. Rutting performance is highly influenced by voids in mineral aggregate (VMA) and RAP asphalt
content. Superpave mixtures with higher RAP content also tend to fracture at higher temperatures in the Thermal Stress Restrained
Specimen Test, indicating that these mixtures are more vulnerable to low-temperature cracking. Thus, low-temperature cracking
potential of high RAP mixture must be evaluated during the mixture design process.
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