Abstract:
Flexible pavements are typically designed to provide a good ride quality and to resist rutting and fatigue cracking. The two types of distresses are mainly caused by wheel loads and are accelerated by environmental factors. Although all the pavement layers (base, subbase and roadbed soil) contribute towards rutting and fatigue cracking, the contribution of the asphaltic concrete (AC) layer alone could be very significant.
The pavement network in Pakistan is experiencing premature rutting problem. The objective of this study is to identify the causes of failure of Islamabad Highway (G.T.Road Interchange – Airport Chowk) and suggest remedial measures.
Based on the objectives, selected road was divided into various good and bad sections. Rutting and fatigue cracking of each section was measured. Based on the severity of rutting, 11 sites were selected for coring. Two sites were selected for investigation of base and subgrade. The cores and samples of base and subgrade were subjected to various field and laboratory tests and material properties of each pavement layer were determined.
Statistical analysis was performed to find out the most significant material/ mix properties affecting the rutting. Test results and analysis revealed that apart from excessive load and environmental conditions, non standard and non uniform construction practices mainly of the top layer have resulted in pavement failure. Subgrade, though weak, is adequately protected by a very strong base course. Asphalt mix design followed was found to contain excessive sand and low coarse aggregate percentages. Vast variation in asphalt content and material properties indicate, poor quality control and bad construction practices. Good natural drainage and good quality base course have ensured structural adequacy of the pavement despite top layer failure.
