WMA Pavements in Oklahoma: Moisture Damage and Performance Issues
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2013-08-01
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Abstract:This study explored the potential effects of using different Warm Mix Asphalt (WMA) technologies on the rut, fatigue and moisture-induced damage potential of WMA pavements. This task was pursued in two levels: (i) performance evaluation of WMA and control Hot Mix Asphalt (HMA) mixes in laboratory; and (ii) mechanistic evaluation of the moisture-induced damage potential of asphalt binders with different types of WMA additives and aggregates. For performance evaluation of asphalt mixes, a total of six Superpave mixes (three WMA plant mixes and three control HMA mixes produced in laboratory) were tested. WMA mixes consisted of one Advera® and one Evotherm® surface course mixes each and one Evotherm® base course mix. WMA mixes were collected from different projects in Texas. HMA control mixes corresponding to the collected WMAs were produced in the laboratory. The performance characteristics of mixes were evaluated by conducting Hamburg Wheel Tracking (HWT), retained indirect Tensile Strength Ratio (TSR) and Four-Point Bending Beam Fatigue (FTG) tests. Furthermore, in order to mechanistically evaluate the moisture-induced damage potential of different WMA additives combined with aggregates, Surface Free Energy (SFE) approach was applied. The SFE components of a PG 64-22 OK asphalt binder mixed with different percentages of Sasobit®, Advera®, Evotherm® and Permatac Plus® were measured using a Wilhelmy Pate (WP) and a Sessile Drop (SD) device. Moreover, the SFE components of a Dolese limestone and Snyder granite from Oklahoma were evaluated using a Universal Sorption Device (USD) and a SD device. The HWT test results showed that all of the tested WMA and HMA control mixes, except the Evotherm® mix with lime as anti-stripping agent, performed almost equally well against rutting and moisture-induced damage with no detectable stripping inflection point. The TSR test results provided no correlation between TSR values and the results from HWT test. However, indirect tensile strength values of mixes tested under dry condition in a TSR test were found to be well correlated with the inverse rutting rate obtained from a HWT test. The FTG test results revealed that all of the HMA control mixes showed a higher number of cycles to fatigue failure, compared to those of WMA mixes. The SFE test results showed that Sasobit® and Advera® do not significantly increase or decrease the moisture-induced damage potential of the asphalt binder, over different aggregates. However, use of Advera®-modified asphalt binder with basalt resulted in a measurable decrease in moisture-induced damage potential of the mix. Evotherm® was observed to have the maximum effect on the reduction of moisture-induced damage potential over different aggregates. Also it was observed that Perma-tac® Plus increased the resistance to the moisture-induced damage in almost all cases. Furthermore, through this study it was shown that the SD device, besides WP and USD, is capable of performing direct contact angle measurements on flat surfaces such as aggregate and asphalt binder. Findings of this study are expected to be useful to pavement professionals in understanding the moisture-induced damage mechanisms and designing WMA mixes.
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