Xicheng Qi

Assessment of Aging at FHWA’s Pavement Testing Facility

Field cores were taken in 1995 and 2002 from eight asphalt pavements constructed in 1993 at FHWAs pavement testing facility to evaluate in situ pavement aging. Dynamic mechanical properties of these cores were evaluated by using the Superpave® shear tester. The moduli of aged pavements were also predicted from binder, aggregate, and mixture properties with available prediction models, and the aging severity levels of all pavements were compared between the lab-measured and model-predicted. Eight pavements with two polymer-modified and six unmodified binders were evaluated in this study. Polymer-modified asphalt pavements showed comparatively lower aging than unmodified asphalt pavements. For unmodified asphalt pavements, stiffer asphalts tended to have higher aging indices. The binder aging index was found to be inversely proportional to the loading frequency, and differences between the aging indices for different binders were higher at lower frequency. Comparison of lab-measured and model-predicted bin...

Mechanistic Analyses of FHWA's Accelerated Loading Facility Pavements: Primary Response

In-depth details are provided for mechanistic analyses conducted for the asphalt pavements of the FHWA accelerated loading facility (ALF) by using available programs, including KENPAVE, WINLEA, EVERSTRS, EVERFLEX, and VESYS 5W. These pavements were constructed by using highly modified and unmodified asphalt binders. The described analyses focused on primary response under the ALF pavements. This study included multilayer elastic theory (MLET) solutions, finite element analysis, and analysis using the VESYS 5W program. Predictions of the primary response for the fatigue mode included the horizontal tensile stress and strain at the bottom of the hot-mix asphalt (HMA) layer and for the rutting mode included the vertical compressive stress and strain on top of each pavement layer. The impact of loading frequency and stress sensitivity (nonlinearity) on fatigue primary response, rutting primary response, and principal stresses was investigated. The frequency did affect the fatigue tensile stress and strain, primarily at the bottom of the HMA layer. It also affected the major and minor principal stresses, particularly at the bottom of the HMA layer. The frequency effect on the rutting compressive stress was insignificant, whereas it was considerable for the compressive strain within the HMA layer. The MLET solutions that used a linear elastic base provided reasonable predictions for the measured tensile strains for highly modified and unmodified asphalt pavements with an absolute percentage error in the range of 0% to 15% percent in most cases. The solutions of the MLET and VESYS 5W programs were capable of providing good predictions of the vertical deformation within the HMA layer that correlated well with the measured permanent deformation values.

Pavement Responses from the Full-Scale Accelerated Performance Testing for Superpave and Structural Validation

In the summer of 2002, under a new transportation pooled fund study TPF-5(019), 12 full-scale lanes of pavements with various modified asphalts were constructed at the Federal Highway Administrations (FHWA) Pavement Testing Facility (PTF) in Virginia. The primary goal of the study is to use FHWAs two Accelerated Loading Facility (ALF) machines to validate and refine changes being proposed in the Superpave binder specification to properly grade modified asphalt binders. The study will also provide valuable data to test new features of NCHRP 1-37A Pavement Design Guide Methodology as well as other pavement technologies. During the construction, all 12 lanes were instrumented with strain gauges and survey plates. Multiple-depth deflectometers (MDDs) were installed in selected lanes. Pavement responses from both strain gauges and MDDs were measured after the construction and during the course of ALF loading in the pavement rutting and fatigue tests. This paper presents an overview of the pooled fund study, instrumentation, measured pavement responses and comparisons to the predicted responses from elastic layered solutions.

ULTRA-THIN WHITETOPPING REHABILITATION TECHNOLOGY AND ITS BONDING EVALUATION

A comprehensive bonding evaluation was conducted on an Ultra-Thin Whitetopping (UTW) experiment with eight full-scale pavement sections constructed with various design features. Strain responses were measured to monitor the bonding condition change during the accelerated loading. After the completion of loading, laboratory Iowa shear tests and field pull-off tests were performed to quantify the bond strength of the UTW-asphalt interface. Additional factors such as asphalt binder type, shearing direction, and the variability of the tests were also included in the evaluation.