Experimental assessment of flexible pavement behaviour under freezing conditions and winter weight premiums

As it is well documented, structural behaviour of flexibles pavements in cold regions is significantly affected by environmental factors and traffic loads. When it comes to pavement damage, the action of freeze and thaw is one of the most important inputs to consider. During thaw, the loss of bearing capacity is addressed by the seasonal load restriction policies enforced in many countries. On the other hand, during winter, frost action induces an important increase in the bearing capacity of flexible pavements due to the viscoelastic response of asphalt concrete and to the freezing of pore water in granular materials and soils. The pavement strengthening with frost penetration has led some transportation agencies to allow winter weight premiums (WWP). Currently, the main issue related to WWP programs is the variety of legislation for both among and within jurisdictions. This variety is caused, in part, by the lack of a rational decision criterion for the application of an axle load limit increase based on the mechanical behavior of frozen pavements. The objective of this project was to document the mechanical behavior of freezing pavements and to develop a rational criterion for the onset of winter load premiums. An experimental approach with the use of Laval University full-scale heavy vehicle simulator was considered to monitor the response of two different flexible pavements built in a 24 m3 indoor test pit over a low plasticity clay and a silty sand subgrade soils, respectively. They were instrumented to monitor temperature profiles, surface deflection, as well as stress, strain and moisture content in each layer. The simulator was used to apply the air freezing temperature (-10 °C) and to periodically load the pavement surface using a standard dual-wheel set (half axle) varying in the range of 4500 to 6250 kg. The results collected allowed documenting how the response of different pavement structures changes with respect to frost penetration and temperature, and allowed quantifying the effect of the load magnitude on the change of the pavement response and damage.