Flexible Pavements

M.N.Nagabhushana, Senior Principal Scientist, Co-ordinator (PD&R), Pavement Engineering Area, CSIR-CRRI, New Delhi

Introduction

Layers of a Flexible Pavement
The heavy wheel loads and fast traffic on modern highways require adequate cover called the pavement on the natural soil to provide a hard wearing surface and to distribute the loads within the bearing capacity of the soil without getting overstressed itself.

Characteristics of Pavement Layers
  • Wearing course or surface course takes the stresses at top to protect the lower layers and hence shall be superior- Bituminous and/or cement concrete layer/s used
  • Base course must possess high resistance to deformation in order to withstand high pressure imposed upon it by providing added stiffness and resistance to fatigue
  • Sub-base is normally used as a drainage layer to keep the structure free of excessive moisture.
  • The purpose of the lower layers is to even provide a working platform and regulate the surface on which upper layers are built.
Based on the composition, pavement structure is categorized as either flexible or rigid or composite. Flexible pavements are those which have very small or negligible flexural strength to offer, but transfer the load stresses through the structure from a grain-to-grain contact. The initial installation cost of a flexible pavement is quite low, can be opened early to traffic and can be planned with a stage construction, which is why this type of pavement is more commonly seen universally. However, the flexible pavement requires maintenance and routine repairs every few years. In addition flexible pavement deteriorates rapidly; cracks and potholes are likely to appear due to poor drainage and heavy vehicular traffic.

Though, flexible pavements can mean just granular layers, the present demands are for those with a bituminous surfacing, whether thick or thin. Hence, it is pertinent to review the bituminous technologies particularly, since the otherwise lower granular layers have relatively lesser options and thereby have only specific roles.

NBM&CW March 2016