Asphalt mixture cracking has become the dominant type of asphalt pavement distress in Indiana. In recent years, efforts have shifted away from the standard Superpave mixture design method in search of methods to improve the resistance of asphalt pavements to cracking-related distress. This paper presents a review of the applicability of the Illinois Flexibility Index Test (I-FIT) to evaluate the cracking potential of Indiana asphalt mixtures. In this study, two cracking indices were compared: the flexibility index (FI) and the cracking resistance index (CRI), both derived from the load-displacement curve. The applicability of quality assurance (QA) tests of laboratory-compacted and field-compacted samples was also explored to evaluate the cracking potential, and I-FIT was investigated for its applicability as a performance-related quality control (QC)/QA test. The results show that the FI values obtained from field-compacted samples were consistently higher than those of the lab-compacted samples. Both the FI and CRI values were significantly affected by variations in specimen thickness and air void content, with higher FI values observed with an increase in the air void content and a decrease in specimen thickness. The CRI values were less sensitive to I-FIT variability and more repeatable compared to the FI values. Finally, as an illustrative example, the cumulative distribution function of the FI values for a population of asphalt concrete (AC) mixtures was used to establish the different ranges for the quality thresholds of the materials.
This study presents the determination of rutting and fatigue-based load equivalency factors (LEFs) for the bus rapid transit (BRT) buses operating in northern and southern Nevada. The methodology presented in this study was based on performance models calibrated to local material, traffic, and environmental conditions. The objectives of this study were accomplished by obtaining pavement responses corresponding to all cases of bus loading and climatic conditions by using the three-dimensional Move software, Version 2.1. The critical pavement responses were then used to estimate the LEFs for the various BRT vehicles. In the assessment of pavement damage, simplified and extended methodologies were developed. The interaction between pavement temperature and axle loading for both northern and southern Nevada BRT buses was considered in the extended method, which considered seasonal distributions of pavement temperature and bus passenger ridership to determine LEFs. In the simplified method, pavement responses from a single combination of the analysis temperature with either the average ridership loading or gross axle weight rating were considered. Results showed that pavement damage from BRT buses in Nevada was significantly influenced by variability in climatic conditions and passenger ridership. Of the two distress types evaluated in this case study, fatigue-based LEFs occurred at a significantly higher rate than rutting-based LEFs. Thus, for a given pavement structure, more fatigue damage is anticipated under the passage of a BRT bus.
This paper investigates the applicability of the Hamburg wheel-tracking test (HWTT) for asphalt mixture quality acceptance using laboratory-compacted specimens and field-compacted specimens. Density distribution functions for rut depths, stripping inflection points, and rutting resistance index (RRI) values used in the HWTT were obtained for mixtures with different nominal maximum aggregate size (NMAS) values and binder performance grades. Clear distinctions among the rut depth distributions for the high-temperature performance grade mixtures were observed in the laboratory-compacted specimens. The RRI values for both the laboratory and field-compacted specimens increased with an increase in the binder performance grade. In addition, the RRI values showed clear differences for different binder grades among the mixtures with the same NMAS. The range of the RRI distributions for the laboratory-compacted specimens was narrower than that of the field-compacted specimens. The stripping inflection points of the field-compacted specimens increased as the binder grade was increased, indicating better moisture damage resistance for stiffer mixtures. HWTT results were significantly influenced by the air voids content of specimens. The relationship between air voids content and RRI can be used for understanding the critical effect of in-place density in pavement performance. The laboratory-compacted and field-compacted specimens offer advantages and disadvantages. The laboratory-compacted specimens were much easier to fabricate to standard dimensions, and the field-compacted specimens present inherent variability in relation to air voids content, diameter, and thickness.
After the implementation of the Mechanistic-Empirical Pavement Design Guide (MEPDG) in Indiana, an overall evaluation of the stiffness characteristics of local AC mixtures and the ability of level III MEPDG predictive equations to estimate dynamic modulus (E*) with local mixtures was required. Therefore, the primary objectives of this study were to identify significant differences among Indiana asphalt mixtures, to evaluate the performance of commonly used E* predictive models, and to assess the influence of level III E* input on the pavement design life of typical pavement structures. It was found that Indiana mixtures do not show extensive variability among mixtures having the same nominal maximum aggregate size. When conducting a statistical analysis to group asphalt mixtures having similar characteristics, few mixtures were left out of the groups. In general, it was observed that mixtures having Ndes equal to 75, showed the lowest E* values along the entire frequency range. The Witczak 1-37A showed the most accurate and less biased E* predictions for Indiana mixtures. It showed the highest R2, and the least deviation from the measured E* values. However, predicted E* input values produced higher levels of pavement distress compared with measured E* values, indicating general overprediction. Besides, using level III (predictive) rather than level I (measured) E* input values can influence the pavement thickness design due to the functional performance (i.e., the International Roughness Index (IRI)). When a structural performance (i.e., bottom-up cracking) was taken into consideration, no influence of the E* input type on the design AC layer thickness was observed.
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