ABSTRACT
Horizontal tensile strain at the bottom of the asphalt concrete in a flexible pavement is a primary design parameter, used to predict bottom-up fatigue cracking, in most modern mechanistic-empirical thickness design approaches. Designers typically simulate static loading events using layered elastic theory to make the strain prediction which represents peak tension relative to a zero baseline level. However, in reality, dynamic loading events usually cause the pavement to experience a compressive strain inflection point prior to tensile peak strain in the direction of travel. This type of response has been shown to contribute to the initiation and propagation of transverse cracks but has yet not been fully investigated. Furthermore, in some cases, the mode will shift from predominantly tensile to predominantly compressive strain. This research utilized four instrumented full-scale flexible pavement sections at the National Center for Asphalt Technology (NCAT) Pavement Test Track to study the inflection-peak relationship and the mode reversal phenomenon. The data were collected on a weekly basis over 17 months. Eight-axle trucks traveling at 72 kph were used to induce the strain events and, though complete strain histories were gathered, the analysis focused on the mode and magnitude of the inflection point and peak strain level as the axles passed over the strain gauges. Consistent trends were found in the ratio of peak to inflection point strain levels and layered elastic analysis confirmed these findings and demonstrated the impact of layer properties on whether the strain was tensile or compressive.
