Christopher Abadie

Permanent Deformation Analysis of Hot-Mix Asphalt Mixtures with Simple Performance Tests and 2002 Mechanistic-Empirical Pavement Design Software

A complex laboratory study in characterization of permanent deformation resistance of hot-mix asphalt (HMA) mixtures is presented. Six plant-produced HMA mixtures were selected for this study. The main objective was to characterize the permanent deformation characteristics of HMA mixtures based on four laboratory tests, namely, the dynamic modulus |E*|, flow number, frequency sweep at constant height (FSCH), and Hamburg-type loaded wheel-tracking tests. The secondary objective was to evaluate the sensitivity of the dynamic modulus |E*|-test results in pavement rutting performance prediction with the 2002 mechanistic-empirical (M-E) pavement design software. Test results indicate that the |E*|-test was sensitive to the nominal maximum aggregate size in an HMA mixture. Larger aggregates combined with aged materials tend to have high |E*|-values at high temperatures. However, both the |E*|- and FSCH tests could not correctly rank the permanent deformation characteristics for the six HMA mixtures considered i...

Relationship between Molecular Compositions and Rheological Properties of Neat Asphalt Binder at Low and Intermediate Temperatures

The main objective of this study was to establish the relationship between asphalt binder deformation properties at intermediate and low temperatures, its molecular compositions, and mix performance. To achieve this objective, nine straight binders obtained from two asphalt suppliers were tested using the ductility and the direct tensile tests. To assess the results of these tests, selected asphalt binders were evaluated using high pressure gel permeation chromatography (HP-GPC), differential scanning calorimetry (DSC), and dynamic mechanical analysis. Measurements showed that an inverse correlation exists between binder ductility at intermediate temperatures and failure strain at low temperatures. In other words, a binder that provides high ductility at intermediate temperatures would be characterized by poor elongation properties at low temperatures. This trend was related to the binder molecular compositions as characterized by HP-GPC. An increase in the binder content of low molecular weight results in an increase in its ductility at intermediate temperatures. However, an increase in paraffinic maltene content results in the binder tending to crystallize at higher temperatures as it approaches the glassy region. This was confirmed through DSC measurements, which showed that an increase in crystalline fractions may have a negative impact on the binder stiffness at low temperatures. In general, physical properties of the binder can be strongly linked to its molecular constituents. In addition, there was a positive correlation between the binder ductility and the measured tensile strength of the mixture as well as its strain at failure. Using a binder with a high ductility resulted in a mixture with greater indirect tensile strength and a stronger ability to resist cracking at intermediate temperatures.

Use of Sweep Test for Emulsion and Hot Asphalt Chip Seals: Laboratory and Field Evaluation

In 2011 ‘Manual for Emulsion-Based Chip Seals for Pavement Preservation’, sweep test is recommended as one of the laboratory test methods for chip seal design and construction. Currently, sweep test is considered to be a promising test for emulsion-based chip seals. To this end, the objective of this study is to evaluate the sensitivity of sweep test for both emulsions and hot asphalts with respect to aggregate mineralogical types, aggregate precoating, aggregate moisture content, asphaltic materials type and application rates of asphaltic materials. For field evaluation, fifteen chip seal test sections were prepared with three asphaltic materials and five aggregates in a 9-acre parking lot. After two years of construction, each of the fifteen sections was visually inspected primarily for aggregate loss and bleeding and was given a distress rating. The percent aggregate loss from sweep test was compared with the field distress rating. The results indicate that shale lightweight is better than any crushed stone while clay lightweight performed worst among the six aggregates tested using sweep test. Precoated aggregates performed better with hot asphalt than emulsion. Between the two hot asphalts, PAC-15 performed better than AC20-5TR. In case of hot asphalt, percent aggregate loss increases as moisture content increases in oven dry, air dry and saturated surface dry aggregate. However, for emulsion, air dry aggregates performed the best. For both emulsion and hot asphalt, an increase in asphaltic materials application rate reduces the percent aggregate loss significantly. In field evaluation, distress survey ranking matched with sweep test results except for one CRS-2P section and one PAC-15 section. Finally, three replicates were used in this study and overall, the results indicate that sweep test using both emulsions and hot asphalts can be an effective tool for evaluation of performance of chip seals with respect to aggregate mineralogy, precoating, aggregate moisture content, types of asphaltic materials, application rates of asphaltic materials, and later field distresses.

Louisiana's Experience with Open-Graded Friction Course Mixtures

The Louisiana Department of Transportation and Development (DOTD) began developing open-graded friction course (OGFC) mixtures in the late 1960s and early 1970s. Then, in the late 1980s, a moratorium was imposed on their use because of some early failure issues. However, OGFC mixture performance and service life have improved significantly since a new generation of OGFC mixture was promoted in the United States in the late 1990s. Inspired by the success of other state agencies, the Louisiana DOTD modified the earlier mix design and constructed four new OGFC sections during the past decade to evaluate pavement performance and safety benefits. This paper includes a comprehensive evaluation of Louisiana OGFC mixtures based on their laboratory and field performance. Laboratory work entailed material and mixture design in addition to numerous laboratory tests, namely permeability, draindown, tensile strength ratio, and loaded wheel test. Field evaluation involved visual inspection, pavement condition survey, skid resistance, and traffic safety. With few exceptions in the laboratory, the selected OGFC mixtures showed the potential to meet current Louisiana DOTD specifications, as well as various performance standards established by previous studies. The field analysis indicated that the OGFC test sections showed improved rutting, cracking, and skid performance when compared with typical Superpave® roadway sections. This performance evaluation will likely support the ongoing use of OGFC mixtures in the state of Louisiana. Additionally, the evaluation provides an opportunity to continually improve the current OGFC specification and mix design procedures adopted by the Louisiana DOTD.

Performance of Louisiana's Chip Seal and Microsurfacing Program, 2002

A 5-year field performance study was conducted of the 1995–1996 Chip Seal and Microsurfacing projects with a summary of data generated by the Louisiana Department of Transportation and Development’s pavement management group. The pavement management data set includes performance indicators such as the international roughness index, crack analysis, rut depth, and ground-penetrating radar thickness. A subjective survey designed for maintenance surfacing was developed and used on this same set of projects. The pavement condition rating was examined from the point of pretreatment and annually until spring of 2001. The survey suggests that treatments will improve a pavement’s initial condition, but no conclusion can be drawn on the effect on pavement condition index (PCI) over time compared with untreated pavements, as all pavements’ PCI curves are similar and are independent of PCI before treatment. General observations for chip seal projects are as follows: the median PCI was 75 after 52 months with a significant reduction in cracking; 20% of the projects showed moderate to heavy bleeding; rutting was not evident; and measurement for skid resistance was very good. For a life expectancy of 5 years, the equivalent annual cost (EAC) of a chip seal is approximately 27 cents a year. For micro-surfacing projects, the median PCI of microsurface sections is approximately 85 after 60 months of service with significantly fewer cracks detected after treatment. Projects with 0.5-in. initial rut showed substantial reduction after treatment. The friction numbers (FN) for smooth tire are in the low teens to low thirties on 50% of the projects. The lower numbers are attributed to a combination of the use of limestone and high asphalt content. Sandstone sections exhibited FNs in the 50s. For a life expectancy of 6 years, the EAC is about 49 cents a year.

Performance of Superpave Projects in Louisiana

The Louisiana Department of Transportation and Development (Louisiana DOTD) initiated the implementation of the Superpave® system by the end of the past decade. This study evaluated 8 to 10 years of field performance of 21 Louisiana Superpave projects, which included five Interstates, four U.S. routes, and 12 Louisiana routes. The evaluation was limited to the field performance of projects relative to age and did not consider factors associated with materials or construction. The criteria used to evaluate performance were confined to rutting, the international roughness index (IRI), alligator cracking, and random cracking. Superpave distress data were collected and stored in the pavement management system database of the Louisiana DOTD every 2 years. The collected data sets were analyzed and compared with Louisiana performance prediction models. These models were developed in the late 1990s by an expert panel from the Louisiana DOTD to predict the deterioration of pavement near the end of its design life. The original performance prediction models were reevaluated in 2002, and roughness models were implemented in 2003. The analysis indicated that after 8 to 10 years of service, most of the projects on Interstate and state highways were in good condition relative to the distress factors evaluated. Superpave seemed to control the early rutting and cracking in hot-mix construction while maintaining good IRI over the years. Points of concern, however, were the few issues of rutting on U.S. highways and cracking on Louisiana routes. In general, the rate of deterioration for rutting and IRI was lower than the prediction from the performance models.

Field and Laboratory Evaluation of Environmental Effects on Chip Seal Performance: Freeze-thaw and Asphalt Aging

Chip seals generally deteriorate as a result of asphalt oxidation, wear and polishing of aggregate, bleeding, and raveling (loss of aggregates). In this study, two major environmental effects on chip seal performance, freeze-thaw and asphalt aging were investigated based on laboratory tests and field distress survey. For freeze-thaw evaluation, laboratory chip seal samples were prepared for 18 combinations (6 aggregates X 3 asphaltic materials). A simple freeze-thaw protocol was developed. It was observed that freeze-thaw loss is much higher than post freeze-thaw sweep test and control (dry) sweep test. Evaluation of freeze-thaw effect on aggregate types reveals that both the precoated and uncoated expanded shale lightweight performs comparatively very well against freeze-thaw plus sweep test. Evaluation of freeze-thaw effect on asphaltic materials types reveals that CRS-2P performs better than PAC-15 and AC20-5TR. For aging evaluation, asphaltic materials were extracted from 15 (5 aggregates X 3 asphaltic materials) field test sections and increase in stiffness due to aging were determined using a dynamic shear rheometer. For each of the five aggregates, CRS-2P shows the lowest G*/sina indicating minimum field aging susceptibility among the three asphaltic materials. For each of the aggregates, AC20-5TR shows slightly higher G*/sina than PAC-15 indicating maximum field aging susceptibility among the three asphaltic materials used in this study. It is evident from this study that precoating of aggregates increased the aging indices. For the field evaluation, fifteen chip seal test sections were prepared with three asphaltic materials and five aggregates in a 9-acre parking lot. Overall field distress ratings of the CRS-2P sections are better than those of PAC-15 sections and overall distress ratings of PAC-15 (sum of distress ratings of all the PAC-15 sections) sections are better than overall distress ratings of AC20-5TR sections which closely reflect the observations in freeze-thaw evaluation and asphalt aging evaluation.

Multiple shear step approach to determine the rotational viscosity of asphalt emulsions and its correlation with water content of original and diluted emulsions

Abstract Viscosity determination of thixotropic emulsions with good repeatability has always been a major challenge. Currently, Saybolt Furol viscometer (SFV) is used to determine the viscosity of the emulsion, but the main drawback of the SFV is that it cannot simulate the behaviour of emulsion under different shear rate. Rotational viscometer (RV) can measure viscosity at different shear rates. Due to the thixotropic behaviour of the emulsions, getting repeatable results by following the hot binder specification is a problematic task. In this study, a new multiple shear step approach is used to determine the viscosity of the emulsified asphalt using RV. Three low viscous (SS-1, SS-1H and SS-1L) and two high viscous (CRS-2 and CRS-2P) emulsions were used in this study. Shear stress is gradually stepped up to different levels after certain time interval to determine the viscosity. In this manner, emulsion undergoes a known shear state and each reading is preceded by a certain repeatable shear history. It was observed that with the progression of time and simultaneous increase in shear rate, the viscosity results are much more stable and repeatable with less than 5% coefficient of variance. The final specifications proposed are 220–730 and 5–90 cP at 50 rpm and 30 °C for high and low viscous emulsions, respectively, which are based on 98% probability. Viscosity measured by this approach also showed strong correlation with water content (R2 > 0.94). The correlation between viscosity and water content is even stronger after dilution. With different dilution water content, viscosity of CRS-2 and CRS-2P exhibited R2 values of 0.97 and 0.98, respectively.