Evaluation of the concept of equivalent temperature for pavement design

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 0eq. 0eq is defined as the mean temperature leading to the same fatigue damage of the pavement as the real temperature variations. The calculation of 0eq 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 0eq, 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 0eq, with climate and material properties. The effect of these variations on pavement design is discussed.