Comparison of Uni and Bi-directional Load Induced Rutting in Flexible Pavement with Accelerated Pavement Testing Facility (APTF)

The Indian Road Network is the second largest in the world after U.S. and flexible pavement is the most sought pavement in India. In fact, majority of roads in India (more then 90%) are flexible pavement due to ease of construction and initial cost of construction. The design of flexible pavement in India mainly consider rutting and fatigue life as per Indian Road Congress (IRC:37-2001). There are many factors that affects the rutting of the flexible pavements namely speed, contact pressure, temperature, quality of construction, wandering of the vehicle and layer thickness etc. The present paper focuses on rutting itself which is governed by direction of traffic, while keeping other parameters nearly same. The effect of movement of heavy traffic in a channelized as well non channelized way on pavement resulting in rutting has been studied with the state of art equipment, Accelerated Pavement Testing Facility (APTF), by CSIR-CRRI, with the aim of finding the performance through evaluation for uni and bi-directional rutting characteristic of pavement. Rutting is the longitudinal depression in the wheel path of the pavement. It can either be instability or structural rutting. Rutting can cause hydroplaning, increase in vehicle operating cost and psychological problems while driving. The amount of rutting under unidirectional loading was compared with the bidirectional loading case with almost the same number of passes. The change in air voids were also calculated from the rutted as well as non rutted portion. The magnitude of rutting under unidirectional loading was more as compared to the one under bi-directional loading. The comparative study has clearly demonstrated that the damage to flexible pavement by rutting with unidirectional load is more critical and nearly twice as compared to the damage by bi-directional loading. This aspect stresses the need for accounting the directional movements in our pavement design guidelines and depending on whether testing uni-directional or bi-directional, a different “transfer function” or relationship to real in service loading is required.