Damage Effects of Overload Axes on Pavement Structures

This paper established the axle load distribution model of overload axes by practical axle-meter investigations. To study the effects of overload axes on pavement distress, deflection and deflection basin tests with axle load from 60kN to 190kN were conducted on different pavement structures. The relationship between axle load and its deflection as well as its deflection basin curvature was obtained by statistical analyses. A methodology for deriving the equivalent conversion factors of overload axes to equivalent standard axle loads (ESAL) of 100kN is developed, obtaining the relationship between the equivalent conversion factors and the axle loads. Comparing the calculated defiections with the measured deflections, that elastic layered system theory is suitable for analyzing overload vehicles was verified. Consequently, the stresses and strains caused by overload axes were calculated by elastic layered system theory. The results showed that overload axes led to greater stresses and strains causing premature pavement fatigue distress. To guarantee the expected performance in overload axes pavement, the structure thickness needed increasing was obtained. The results are of referential values in the control of semi-rigid pavement overloadings.

Application of viscoelastic continuum damage approach to predict fatigue performance of Binzhou perpetual pavements

For this study, the Binzhou perpetual pavement test sections constructed in Shandong Province, China, were simulated for long-term fatigue performance using the layered viscoelastic pavement analysis for critical distresses （LVECD） finite element software package. In this framework, asphalt concrete was treated in the context of linear visco- elastic continuum damage theory. A recently developed unified fatigue failure criterion that defined the boundaries of the applicable region of the theory was also incorporated. The mechanistic modeling of the fatigue mechanisms was able to accommodate the complex temperature variations and loading conditions of the field pavements in a rigorous manner. All of the material models were conveniently characterized by dynamic modulus tests and direct tension cyclic fatigue tests in the laboratory using cylindrical specimens. By comparing the obtained damage characteristic curves and failure criteria, it is found that mixtures with small aggregate particle sizes, a dense gradation, and modified asphalt binder tended to exhibit the best fatigue resistance at the material level. The 15 year finite element structural simulation results for all the test sections indicate that fa- tigue performance has a strong dependence on the thickness of the asphalt pavements. Based on the predicted location and severity of the fatigue damage, it is recommended that Sections 1 and 3 of the Binzhou test sections be emoloved for perpetual pavement design.

Influence of shock absorber condition on pavement fatigue using relative damage concept

Considering the importance of the road transportation nowadays, concerns related to pavement deterioration and maintenance have become relevant subjects. Especially for commercial vehicles, the vertical dynamic load （characterized by the tire-road interaction） is directly related to wear on the road surface. Given this, the main objective of this paper is to analyse effects of vertical loads applied on the flexible pavement, considering the variation of the condition of shock absorbers from a truck＇s front suspension. The mea- surements were performed on a rigid truck, with 2 steering front axles, in a durability test track located in Brazil. With a constant load of 6 tons on the front suspension （the maximum allowed load on front axles according to Brazilian legislation）, 3 different shock absorber conditions were evaluated： new, used and failed. By applying the relative damage concept, it is possible to conclude that the variation of the shock absorber conditions will significantly affect the vertical load applied on the pavement. Although the results clearly point to a dependent relationship between the load and the condition of the shock ab- sorbers, it is recommended to repeat the same methodology, in future to analyse the influence of other quarter car model variants （such as spring rate, mass and tire spring stiffness）.