Lorina Popescu

Analytically Based Approach to Rutting Prediction

An analytically based (mechanistic-empirical) procedure was conducted to estimate the development of rutting in asphalt pavements as a function of both traffic loading and environment as defined by pavement temperatures. The procedure uses permanent strain determined for a representative asphalt concrete mix as a function of load repetitions, shear stress, and elastic shear strain. It combines multilayer elastic analysis for determining key shear stresses and strains in the asphalt concrete resulting from traffic loading to be used in the permanent strain expression with a time-hardening procedure for the accumulation of permanent strain as a function of both traffic loading and environment. The WesTrack test sections were used to calibrate the methodology, with results of rutting predictions evaluated for four different test sections from that experiment. Based on the results of the regression analyses, an expression can be used to determine coefficients for use in the permanent strain expression that reflect the permanent deformation characteristics of a specific mix as measured in repeated simple shear test at constant height. In addition to the WesTrack examples, results illustrated the use of the approach to predict rutting development in a controlled loading condition at 50°C (122°F) using the heavy vehicle simulator.

ACCELERATED PAVEMENT TESTING OF RUTTING PERFORMANCE OF TWO CALTRANS OVERLAY STRATEGIES

Results of accelerated pavement tests (APT) at elevated temperatures on dense graded asphalt concrete and gap-graded asphalt rubber hot mix (ARHM-GG) are presented. APT testing was performed by use of a Caltrans heavy vehicle simulator. The overlays were placed on previously untrafficked sections of an existing flexible pavement. Variables included in the experiment were overlay type, ARHM-GG overlay thickness, tire/wheel type (dual/bias-ply; dual/radial, wide-base single, aircraft), and pavement temperature (40°C, 50°C, at 50 mm depth). Results presented include the rut development for the different variables, changes in layer thickness, and changes in air-void content. Analyses were performed for evaluating the relative contributions of shear deformation and densification to rut development.

Accelerated pavement testing of rutting and cracking performance of asphalt-rubber and conventional asphalt concrete overlay strategies

ABSTRACT The California Department of Transportation (Caltrans) has two primary strategies for overlay of flexible pavements: overlay with dense graded asphalt concrete (DGAC), and overlay with asphalt rubber hot mix gap-graded (ARHM-GG). Caltrans ARHM-GG overlays are typically designed to be about half the thickness of DGAC overlays for a given set of conditions. This paper contains results of two accelerated pavement test (APT) experiments conducted using Caltrans Heavy Vehicle Simulators (HVS). One experiment was conducted at elevated temperatures to study the relative rutting performance of the mixes and the other one at moderate temperatures to study the relative cracking performance of the mixes. In the rutting experiment the effects of overlay type, ARHM-GG overlay thickness, tire/wheel type (dual/bias-ply; dual/radial, wide-base single, aircraft), and pavement temperature (40°C, 50°C at 50 mm depth) on pavement rutting, and the changes in layer thickness and air-void contents were analyzed to evaluate the relative contributions of shear deformation and densification to rut development. For the cracking experiment, deflection and crack length measurements indicate that the half thickness ARHM designs used by Caltrans are reasonable, and that the primary distress mechanism is reflection cracking. The results also indicate that continued hardening of the asphalt-bound and unbound layers occurs in the overlaid pavements.

PERFORMANCE OF DOWEL BAR RETROFITTED CONCRETE PAVEMENT UNDER HEAVY VEHICLE SIMULATOR LOADING

The California Department of Transportation uses dowel bar retrofit (DBR) as a rehabilitation strategy for concrete pavements. Two test sections were retrofitted with dowel bars and a third section was designated as a control on US-101 near Ukiah, California. All three sections were subjected to accelerated pavement testing by using the Heavy Vehicle Simulator (HVS). The results obtained with the HVS demonstrated a large improvement in load transfer efficiency (LTE) and decreases in maximum vertical deflections and vertical deflection differences from DBR. LTE was not damaged by trafficking on the sections with DBR and was less sensitive to temperature changes than the control section. Falling weight deflectometer testing showed damage to the interlock at the joint on the control section and no damage on the sections with DBR. Joint and crack deflections and deflection differences increased with trafficking. A total equivalent loading of approximately 11,000,000 equivalent single-axle loads was applied to each of the sections with DBR without failure occurring.