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.
Rut Depth Estimation for Mechanistic-Empirical Pavement Design Using Simple Shear Test Results
This paper presents a methodology for estimating rut depths in asphalt concrete pavement structures for use in mechanistic-empirical pavement design and analysis. The procedure utilizes stiffness and plastic strain versus repetitions data obtained from the SHRP-developed repeated load simple shear test conducted at constant height (RSST-CH). To use this methodology, the pavement is assumed to behave as a multilayer elastic system for determination of key stresses and strains to permit rutting estimates to be made at the pavement surface for specific mix types. Influences of temperature and time of loading on the asphalt concrete stiffness are considered in an ad-hoc manner. The paper includes a discussion of the approach used as well as calibrations of the methodology for selected WesTrack pavement sections (those with rutting but no visible fatigue cracking). Specific performance models for three California dense-graded asphalt concrete mixes obtained from calibrations obtained from Heavy Vehicle Simulator tests under controlled temperature conditions are also presented. Results of the use of two of these models to estimate rutting in an in-service pavement near Sacramento, California for which condition data were available are also presented. The methodology is then used to evaluate 17 different pavement sections designed according to the current Caltrans procedure for a range in traffic loadings and checked to ensure that the asphalt concrete thicknesses were adequate to resist fatigue cracking. Results of these analyses performed for three climate regions reflect current Caltrans experience with performance of the mixes used. Appendices to the paper include the description of the development of the performance model from RSST-CH tests on WesTrack mixes and the step by step procedure used to calculate rut depth for a specific pavement structure.
Fascism in Britain: A History, 1918-1985
Tracing its origins from shortly after the World War I, this book presents a portrait of fascism in the 1930s. It reassesses Mosley's career, describes the reasons for internment in 1940 and the effect it had on leading fascists, exposes the famous Britons who subscribed to fascism, reveals the ominous re-emergence of the tradition after 1945, and explains its remarkable persistence into the l980s.