Peter E. Sebaaly

Precision of ASTM D 5821 Standard Test Method for Determining the Percentage of Fractured Particles in Coarse Aggregate

An interlaboratory study was conducted to develop a precision statement for ASTM D 5821-95, Standard Test Method for Determining the Percentage of Fractured Particles in Coarse Aggregate. The experimental design included ten laboratories, four materials, and three replicates per material per laboratory, resulting in 54 degrees of freedom. Outlier detection was given careful con sideration due to the subjective nature of the method, and resulted in exclusion of one laboratorys data, reducing the degrees of freedom to 48. The materials included three partially crushed gravel blends and one quarry stone blend. As expected, multilaboratory variability was greater than singleoperator variability. There was also a greater level of variability associated with two or more fractured face determinations than with one or more fractured face determinations. Surprisingly, the greatest variability was observed for the quarry stone rather than for the crushed gravels. The results of the analysis were compared with other available data. The level of variability associated with this study was less than that observed in other studies, due most likely to the highly fractured nature of the materials used in the study.

Laboratory Evaluation of Mixes Containing Recycled Asphalt Pavement (RAP)

ABSTRACT This paper presents the findings of a laboratory-based research project that evaluated the impact of three RAP sources at three levels of RAP content (0, 15, and 30%) on the mechanical properties of the final mix. Two asphalt binder grades were targeted for the final mix. The binder grade for the new asphalt binder was selected using appropriate blending charts for high and low temperatures. Overall the addition of RAP to a mixture resulted in an acceptable moisture resistance, however a reduction in the unconditioned and conditioned tensile strength was observed. In most of the cases, the addition of RAP to a mixture resulted in an equivalent or better rutting resistance than the virgin mix (0% RAP). Depending on the RAP source and content, the addition of RAP to a mixture with an unmodified target asphalt binder resulted in either a better or worse fatigue resistance. On the other hand the addition of RAP to a mixture with a polymer modified target asphalt binder resulted in a worse fatigue resistance regardless of the RAP source and content. Finally, the addition of RAP to a mix resulted in a similar or better resistance to thermal cracking than the virgin mix and reasons for that were proposed.

Oxidative Aging of Asphalt Binders in Hot-Mix Asphalt Mixtures

This study evaluated the effect of different aggregate sources along with their Corresponding change in mixture characteristics to determine the influence of both on binder oxidation rates and changes in mixture stiffness when compacted mixtures were exposed to laboratory aging conditions. The two aggregate sources, Colorado and Nevada, had different gradations and different water absorption rates, which led to differences in the calculated asphalt binder apparent film thicknesses (AFT) for each mixture. Two asphalt binders, an unmodified PG 64-22 and a styrene–butadiene–styrene–modified PG 64-28, were used. The overall findings of the study indicated that both the aggregate and mixture characteristics influenced the oxidation rates of the binder, with the two binders oxidizing by similar amounts when aged in mixtures with the same characteristics (AFT and mixture air voids). The oxidation changes in the binder had differing effects on the stiffness of the mixture as a function of age. Not only were the aggregate and mixture characteristics important to the mixture stiffness and aging relationship, but the binder characteristics themselves, in particular polymer modification, influenced the aging and stiffness relationships of mixtures with age.

Validation of a Pavement Response Model Using Full-scale Field Tests

This paper provides details on a field verification program undertaken to validate the applicability of a finite-layer mechanistic model that has been selected to perform pavement response calculations. The proposed pavement response model is more realistic since it can handle moving traffic loading conditions, and it takes into consideration important factors such as vehicle speed and the non-uniform stress distributions (normal and shear) at the tire-pavement interface. Typically in pavement studies, the strain responses are required only at a few selected locations and for such problems the proposed approach is ideally suited. The applicability of the finite-layer approach and the ensuing computer program 3D-Moving Load Analysis (3D-MOVE) has been verified using two well-documented full-scale field tests (Penn State University test track and Minnesota road tests). As many as thirty eight measured strain responses were compared with those computed by 3D-MOVE and the comparison is very good. The computed impact of vehicle speed on the tensile strain at the bottom of the AC layer is consistent with those measured in both the field tests. Many mechanistic pavement response models are deficient since they do not incorporate the influence of vehicle speed and the complex tire-pavement contact stress distribution.

Impact of Lime and Liquid Antistrip Agents on Properties of Idaho Hot-Mix Asphalt Mixture

In 2005, the Idaho Transportation Department constructed a field project on State Highway 67 (SH-67) to evaluate the impact of hydrated lime and a liquid antistrip agent on the mechanical properties of an Idaho hot-mix asphalt (HMA) mixture. This paper documents the results of a laboratory evaluation on field-produced HMA mixtures sampled from lime and liquid antistrip test sections on SH-67. As the two mixtures were subjected to multiple freeze-thaw (F-T) cycles, the mixture treated with hydrated lime (lime mixture) maintained good resilient-modulus properties over the entire 21 F-T cycles. The mixture treated with the liquid antistrip agent (liquid mixture) fully disintegrated after 22 F-T cycles. The results of a mechanistic analysis showed that, as a result of multiple F-T cycling, the liquid mixture will incur a 220% increase in potential rutting compared with the lime mixture, which will incur only a 65% potential increase in rutting. The dynamic moduli in compression demonstrated that both dry and moisture-conditioned lime mixtures can be considered less susceptible to rutting compared with liquid mixtures. Furthermore, the lime mixtures demonstrated better resistance to moisture damage than the liquid mixtures on the basis of the ratio of dynamic modulus in tension of moisture-conditioned to dry mixtures. The additional stiffness of the lime mixtures did not contribute to premature fatigue cracking when mixtures were subjected to dynamic creep testing in the tensile mode of loading.

EVALUATION SYSTEMS FOR CRUMB RUBBER MODIFIED BINDERS AND MIXTURES

The use of crumb rubber modified (CRM) asphalt mixtures has been increasing steadily. The reasons for this increase in use are twofold: the Intermodal Surface Transportation Efficiency Act of 1991 mandate and the potential of better performance. The technology of testing, design, and evaluation of CRM binders and mixtures has not yet caught up. Therefore, there is a need for establishing standard procedures for the design and evaluation of CRM mixtures. The outcome of a recent research project sponsored by the Nevada Department of Transportation (NDOT) is presented. The binder testing system concentrated on the newly developed Strategic Highway Research Program (SHRP) performance grading system and its applicability to CRM binders. It was concluded that the standard SHRP system will not work for CRM binders containing coarse rubber particles. The plate and cup system will have to be used for such CRM binders. However, the plate and cup system cannot adequately replace the bending beam rheometer for low-temperature testing. In the case of CRM mixtures, a modified Hveem mix design procedure was developed and validated on an actual NDOT project. Temperature susceptibility, moisture sensitivity, rutting resistance, and low-temperature cracking of CRM mixtures also are presented.

Long-Term Performance of Reflective Cracking Mitigation Techniques in Nevada

Hot-mix asphalt (HMA) overlay is one of the commonly used methods for rehabilitating deteriorated pavements. The Nevada Department of Transportation (DOT) uses HMA overlays as a rehabilitation technique for the majority of the states flexible pavements. One major type of distress influencing the life of an overlay is reflective cracking. In the past, Nevada DOT has experimented with a number of techniques— such as cold in-place recycling, reinforced fabrics, stress relief courses, and mill and overlay—to reduce the impact of reflective cracking on HMA overlays. Several projects were constructed under each category. The long-term field performance of various Nevada DOT reflective cracking mitigation techniques was evaluated; the techniques were used on flexible pavements at 33 field projects. Performances of the various projects were analyzed by fatigue, transverse, and block cracking measurements from Nevada DOTs pavement management system data. In addition, the statistical approach called principal component analysis was used to asses the effectiveness of each of the reflective cracking techniques. The study indicated that cold in-place recycling and mill and overlay were the most effective treatments for reflective cracking of HMA overlays over HMA pavements under Nevadas conditions, except when the existing pavement experiences severe alligator cracking. In such situations, it is recommended that HMA pavement be subjected to reconstruction or full-depth reclamation.

Evaluation of selected warm mix asphalt technologies

The overall objective of this study was to assess the performance of warm mix asphalt (WMA) mixtures in South Dakota based on laboratory and field evaluations. The study included three WMA technologies (Advera, Evotherm, and foaming) and three aggregate types (limestone, quartzite, and natural gravel). A comprehensive laboratory programme was conducted to assess the impact of WMA in terms of stiffness and mixtures’ resistance to moisture damage, rutting, fatigue cracking, and thermal cracking. Overall, the WMA mixtures performed comparatively similar to the hot mix asphalt (HMA) mixtures. The impact of the WMA technology was found to be aggregate dependent. WMA test sections were constructed on four Highways in South Dakota to validate the laboratory findings. During construction, percent compaction, roughness measurements were collected. Field observations indicated that WMA mixtures can be successfully produced and constructed using South Dakotas materials.

Evaluation of the Use of Reclaimed Asphalt Pavement in Airfield HMA Pavements

This paper summarizes the literature review as well as the documented use and performance of airfield pavements that used reclaimed asphalt pavement (RAP) in hot-mix asphalt (HMA). A review of in-service airfield pavements with RAP-containing HMA mixes was conducted as part of this study. Two civilian airports and one military airport were identified as currently using RAP in the HMA surface course. The three airports are Logan International Airport (BOS), Griffin-Spalding County Airport (6A2), and Oceana Naval Air Station (NTU). Furthermore, the impact of RAP on the performance life of HMA airfield pavements on a large hub, small hub, and general aviation was evaluated using actual airport traffic mixes. The performance life analysis used the characteristics and mechanical properties of HMA mixes in the linear elastic airfield pavement design software (LEDFAA1.3) to compare the estimated performance life of HMA pavements with and without RAP materials. The documented research effort has recently been conducted as part of the Airfield Asphalt Pavement Technology Program, Project 05-06.

Optimum Time for Application of Slurry Seal to Asphalt Concrete Pavements

This study evaluated the field performance of asphalt pavements with and without slurry seal applications, developed performance models for asphalt pavements without slurry seals and asphalt pavements receiving slurry seals at various times following construction, and identified the optimum time for applying slurry seals on asphalt pavements in the Washoe County, Nevada, region. This determination was achieved by evaluating the long-term pavement performance data collected with the MicroPAVER system for the past 15 years and the cost-effectiveness of slurry seals applied to new and existing flexible pavements at Years 0, 1, 3, 5, 7, and 9 after construction. This study found that applying slurry seal immediately after or 1 year after construction of the asphalt layer is not effective in regard to the benefit to users and the benefit–cost ratio for the agency. The optimum time of applying slurry seal depended on the type of construction activity. For newly constructed pavements, the optimum time to apply slurry seal was 3 years after construction. For pavements subjected to overlays, the optimum time to apply slurry seal was between 3 and 5 years after construction. However, for uniformity purposes, it was recommended that the agency apply slurry seal 3 years after construction of the asphalt layer for both new and overlay constructions.