Pavement Damage Due to Different Tire and Loading Configurations on Secondary Roads
Due to the large percentage of goods moved by commercial trucks and its ever-growing freight industry, the U.S. needs innovative technologies to improve the efficiency of trucking operations and ensure continuous growth of the economy. One example of such a technology is the introduction of wide-base single tires to replace conventional dual tire systems. After more than two decades of research powered mainly by the tire industry, a new generation of wide-base tire was recently introduced. Compared to the first generation of wide-base tires, these new tires offer safety and cost-savings characteristics. Despite the significant advancements achieved through previous research projects on the impact of wide-base tires on pavements, past investigations have not evaluated the damage wide-base tires cause to low-volume secondary roads. This pavement class is widely encountered in many trucking applications, although for short distances, but the impact of the new generation of wide-base tires on these pavement structures is unclear. In addition, the static uniform loading assumption used in conventional flexible pavement design methods is inconsistent with realistic tire loading conditions and may result in erroneous pavement response and damage predictions. To address these shortcomings, this research project uses a developed three-dimensional (3-D) finite element model to predict pavement responses to loading applied by various tire configurations on secondary road pavements. This model incorporates the measured 3-D tire-pavement contact stresses, hot-mix asphalt (HMA) linear viscoelasticity, continuous moving load, and utilizes implicit dynamic analysis. The impact of wide-base tires on secondary road pavement damage was analyzed using available damage models, and the results were compared to the damage from conventional dual-tire assemblies. Findings of the study suggest that due to the different contact stress distributions at tire-pavement interface, the impact of the new generation of wide-base tire (455/55R22.5) on secondary road pavements varies when compared to the impact of the conventional dual-tire assembly.
Effects of tire configurations on pavement damage
In response to the introduction of new generations of wide-base tires, pavement responses to different tire configurations were measured at the Virginia Smart Road. The investigated new generations of wide-base tires have wider treads and greater loadcarrying capacities than conventional wide-base tires. Results of the experimental program indicated that the steering axle was the most damaging of all the tested axles. A finite element (FE) parametric study was then conducted to evaluate different failure mechanisms that were not quantified in the field. The developed FE models were calibrated and properly validated against stress and strain measurements obtained from the experimental program. Four failure mechanisms were considered in the pavement damage evaluation: fatigue cracking, primary rutting, secondary rutting, and top-down cracking. Results indicated that the new generations of single wide-base tires, 445/50R22.5 and 455/55R22.5, would cause the same or relatively greater pavement damage than conventional dual tires. Based on the calculated combined damage ratios, equivalent loads were determined to balance the damage induced by the new generations of wide-base tires with that of the dual-tire assembly. Given that the overall truck weight is reduced by approximately 450kg when wide-base tires are used, it is reasonable to implement the load limits currently applied to the dual-tire assembly to the second new generation of wide-base tire, 455/55R22.5.
FATIGUE PERFORMANCE EVALUATION OF WESTRACK ASPHALT MIXTURES USING VISCOELASTIC CONTINUUM DAMAGE APPROACH
The primary objective of this project is to develop laboratory test methods and a fundamentally sound fatigue model that accurately predict or rank the fatigue performance of asphalt mixtures in the field. For the validation of the model, eight WesTrack mixtures with varying gradations, asphalt contents, and air void contents were used. Both direct tension and indirect tension tests were conducted. This report presents the findings from direct tension and indirect tension tests. From the direct tension testing, a methodology was developed by which the material response under any uniaxial tensile testing condition (type of loading and temperature) can be predicted from the material response obtained from a single testing condition. The methodology makes use of a uniaxial constitutive model for asphalt concrete that is based upon the elastic-viscoelastic correspondence principle and work potential theory, a continuum damage theory based on thermodynamics of irreversible process. Uniaxial tensile testing is performed under controlled crosshead mode for both cyclic and constant rate to failure tests. Various strain amplitudes, frequencies, and rates are applied at several test temperatures. A single characteristic curve can be found that describes the reduction in material integrity as damage grows in the specimen regardless of the applied loading conditions (cyclic versus monotonic, amplitude/rate, frequency). The characteristic curve at any temperature can be found by utilizing the time-temperature superposition principle and the concept of reduced time. Eight WesTrack mixtures are tested and the methodology is used to successfully predict the fatigue damage at different testing conditions from a single condition. A test and analysis procedure for the fatigue characterization of asphalt mixtures based on this methodology is proposed and potential applications are discussed. In this report, also presented are the viscoelastic characterization of asphalt concrete in indirect tensile testing and the development of a simple performance test for fatigue cracking. The analytical solutions to calculate creep compliance and center strain from displacements measured on the specimen surface were developed based upon the theory of viscoelasticity. These developments were verified by 3-D finite element viscoelastic analysis and tests. A simple performance test was developed based on these solutions and work potential theory. To evaluate its validity, the indirect tensile tests were performed on WesTrack asphalt mixtures varying aggregate gradations, asphalt contents, and air void contents. Fracture energy obtained from indirect tensile strength testing and creep testing was highly correlated with field performance of these mixtures at WesTrack. A combination of indirect tensile creep and strength testing was proposed as a simple performance test for fatigue cracking.