In France, mechanical tests are used essentially for characterizing the performance of bituminous concretes for mix design purposes, production control requiring retroaction times that are much too short. Compacting characteristics are studied with an imposed angle gyratory shear compacting press; an indication of the results obtained on the job site is obtained by correlation with a pilot compactor. A number of plate samples are prepared with a laboratory-tired compactor. Resources of increasing complexity are used for the study of permanent deformation characteristics. The repeated compression test with a lateral load is used for research purposes, and the wheel-tracking rutting test is used for mix design studies. Because the concern here was fatigue. performance, the bending test was used to study the influence of composition factors. More recently, a shear fatigue test, which is more representative of the loads to which the thin surface courses are subjected, has been employed. However, fatigue tests are too costly and time consuming to be used for mix design studies, so a new test has been developed to measure stiffness moduli and to estimate fatigue properties. Secant moduli at different temperatures, linearity loss, and strength at 0 C are determined by a full tensile test on each sample. An estimate of the bending fatigue curve at 10 C is obtained by two regressions. For the mix design, the diversity of functions to be provided and the cost of testing make it necessary to rank the problems according to importance and to define a methodology that can be adapted to different cases.

The various mechanical tests used in France for the practical mix design of bituminous materials may be classified according to the type of property concerned and the quality of evaluation of this property. The focus of this paper is the essential elements defining current French mix design technology: