Current Projects

Sponsor: Southern Plains Transportation Center (SPTC)

Completed: 2017

In order to sustain high traffic volume, coupled with heavier loads and extreme weather conditions in the Southern Plains Transportation Center (SPTC) region, asphalt industries introduce polymer-modified binders (PMBs) to enhance durability and strength of asphalt  pavements. For quality assurance and quality control (QA/QC) purposes, asphalt binder producers (refineries) and users (state agencies) follow the widely used dynamic shear rheometer (DSR) test method (AASHTO T 315) to capture viscoelastic properties of PMBs even though the AAHTO T 315 method is designed for unmodified asphalt binders. The recently balloted multi stress creep recovery (MSCR) test method (AASHTO TP 70) on short-term aged binders can potentially resolve this problem. The MSCR can better relate the predicted laboratory-based high temperature properties of PMBs and additive modified binders to actual rutting performance of in-service pavements. The main objective of this research was to develop simple and dynamic shear rheometer based test method that can be used as alternative to PG Plus tests (elastic recovery and force ductility) to accurately determine high temperature performance of asphalt materials. Toward meeting the objective of this study, materials (asphalt binders) from different sources in the SPTC region were collected for mechanistic evaluation. Further, Binders were also recovered from reclaimed asphalt pavement(RAP) and tested in the laboratory. In particular, multiple stress creep recovery (MSCR) tests were conducted on asphalt binder samples. The  MSCR results from this study can be used to develop guidelines for the Region 6 states and implementable specifications for commonly used  asphaltic materials under extreme temperature .

Sponsor: Southern Plains Transportation Center (SPTC)

With recent developments in testing equipment, test methods and studies focused on performance testing, asphalt mix design methods are moving increasingly from empirical to mechanistic. In spite of these developments, the moisture-induced damage (also called stripping) potential of asphalt mixes, is generally evaluated using the retained indirect tensile strength ratio (TSR) test or from the stripping inflection point (SIP) in the Hamburg wheel tracking (HWT) test. Although widely used as indicators of moisture-induced damage potential, neither of these tests directly addresses the mechanisms governing stripping of asphalt pavements. A mechanistic approach is needed for screening of asphalt mixes at the design stage to combat moisture-induced damages of pavements that cost millions of dollars annually. A particular area of weakness is screening of mixes containing reclaimed asphalt pavement (RAP) and warm-mix asphalt (WMA). According to recent studies, the Surface Free Energy (SFE) characteristics of asphalt mixes can be used effectively to quantify bond strength and debonding of aggregate and asphalt binder in presence of water, which cannot be achieved using either a TSR or a HWT test. In this collaborative study, two flagship universities in Oklahoma (OU and OSU) and two local companies are developing an interactive SFE database for commonly used aggregates and asphalt binders in Oklahoma. The database  include mixes containing RAP, WMA, polyphosphoric acid (PPA), polymer-modified binders, and liquid anti-stripping agent. 

Sponsor: Oklahoma Department of Transportation

In recent years, several pavement failures have been reported in Oklahoma due to insufficient or excessive tack coat application.  The primary causes of failure were insufficient or excessive tack coat application. In some cases, application of inadequate or excessive amount of tack coat was due to confusion or use of different units and calculation methods during construction. This is primarily due to lack of specific guidelines for the selection of tack coat type, application rate, placement, and evaluation.  It is also important to evaluate the effectiveness of the selected type and application rate of tack coat as a quality-control procedure, prior to construction. This study aims to evaluate the effectiveness of tack coats used by ODOT with respect to tack coat type and application rate, pavement surface conditions, moisture-induced damage and temperature. Laboratory-compacted samples and  field cores from selected projects are  being tested selectively to evaluate the tack coat performance. The result from this project is expected to improve the current practice used for the selection of tack coat type and application rate in Oklahoma. Also, results from this study will be used to develop recommendations and possible development of quality control measures for tack coats for enhanced performance.

Sponsor: Southern Plains Transportation Center (SPTC)

The WMA technology allows a reduction in mixing and placement temperatures of asphalt mix, leading to a major saving in fuel cost, cutting emissions, and achieving better mix workability at a lower temperature. Therefore, many Departments of Transportation (DOTs) and highway agencies are motivated to evaluate the performance of WMA mixes and develop relevant specifications. Among several WMA technologies, the plant foaming technique for producing WMA (called foamed-WMA in this proposal) widely used by the asphalt industry in Oklahoma using water for the foaming process.

Although the use of Reclaimed Asphalt Pavement (RAP) and foamed-WMA technique is increasing rapidly in Oklahoma and the other states in Region 6, a widely-accepted guideline/specification for mix design of WMA containing RAP is not available. In the absence of such guideline/specification, the pavement industry is designing the foamed-WMA mixes by using the specifications originally developed for the HMA mix design, which is produced at temperatures approximately 50°F higher than those used for production of WMA. Due to difference in HMA and foamed-WMA’s mixing and placing temperature, binder properties and possible presence of water in foamed-WMA, using HMA mix design for a foamed-WMA without making adjustment in JMF may not be a realistic approach.  Also, most asphalt mix design laboratories in Oklahoma do not own a laboratory foamer. Additionally, the compactability, moisture-induced damage potential, rutting resistance and fatigue resistance of WMA mixes may be significantly different than those of their HMA counterparts. To address the aforementioned concerns, the present study aims to develop a special provision for designing foamed-WMA mixes, specifically WMA mixes containing RAP.

Sponsor: Southern Plains Transportation Center

Use of poly-phosphoric acid (PPA) is known to be an effective way to increase the stiffness of asphalt binders. Therefore, toward improving the performance of a base binder, many suppliers (refineries) in the United States modify it with PPA. Many transportation agencies,however,  are concerned about the performance characteristics of PPA modification. This concern is mainly due to possible negative interaction of PPA-modified asphalt binders with other mix components, such as lime, liquid anti-striping agents (ASA), and emulsions. Since PPA is a hydrophilic material and it easily absorbs water, asphalt binders modified with higher percentages of PPA have a tendency to absorb water and loose strength, which is expected to result in increased moisture damage and increased rut. The present study aims to evaluate effect of PPA modification of selected performance grade (PG) binders on their viscosity and performance grade through Superpave binder testing protocols. Effects of selected ASA and WMA additives on PPA-modified binders on viscosity and PG data are also being evaluated. In addition, the rutting and moisture susceptibilities of selected PPA-modified mixes are evaluated by using Hamburg Wheel Tracking (HWT) and Tensile Strength Ratio (TSR) test data. The moisture damage potential of selected asphalt binder and aggregate systems is estimated through the surface free energy (SFE) technique. The chemical compositions of the base and PPA-modified binders are determined by using an Elemental Analyzer. This study is expected to help ODOT in formulating guidelines for PPA-modified asphalt binders.