Evaluation of the concept of equivalent temperature for pavement design

Resumé

Because of the thermal susceptibility of bituminous materials, the levels of
stress, strain, and damage in bituminous pavements are strongly dependent on temperature.
As taking into account temperature variations in design of bituminous pavements is difficult,
design is performed, in France, for a constant temperature, called the equivalent temperature
θeq.
θeq is defined as the mean temperature leading to the same fatigue damage of the pavement as
the real temperature variations. The calculation of θeq requires knowing the variation of
modulus and fatigue properties of bituminous materials with temperature. If such results are
generally available for the modulus, it is seldom the case for fatigue properties. For this
reason, in practice, a constant equivalent temperature of 15 °C is assumed for design.
This paper presents a study carried out to determine real values of θeq, for different pavements
and climatic conditions, using real measurements of temperature and traffic on experimental
pavements, and experimental values of fatigue properties at different temperatures. The
results indicate significant variations of θeq with climate and material properties. The effect of
these variations on pavement design is discussed.