翻 译 原 文Low-temperature failure behavior of bituminous binders and mixesABSTRACTA research including a large experimental campaign on the thermo-mechanical behavior of different bituminous materials in the large strain amplitude domain is proposed. The primary goal of this paper is to identify and determine the links between the failure properties of bituminous binders and those of mixes at low temperatures.The thermo-mechanical behavior of bituminous binders was evaluated with the tensile strength at a constant strain rate and constant temperatures. The thermo-mechanical behavior of bituminous mixes has been studied byperforming measurements of the coefficient of thermal dilatation and contraction, tensile tests at constant temperatures and strain rates, and Thermal Stress Restrained Specimen Tests. Some pertinent links between fundamental properties of binders and mixes are established. Some characteristics which appear as pertinent and discriminating enough with regard to the low-temperature failure properties of bituminous mixes are presented.Keywords : bitumens, bituminous mixes, rheological behavior, thermo-mechanical properties, failure properties, tensile strength, TSRST, low temperature, brittle, ductile, brittle/ductile transition temperature.INTRODUCTIONThe different domains of bitumen behavior can be illustrated according to the strain amplitude (_) and the temperature (T), at a given strain rate. FIGURE 1 (drawn from (1) and (2) points out : the brittle and ductile domains, where the tensile strength p can be measured, the brittle failure, which could be characterized by the fracture toughness Kc (Linear Elastic FractureMechanics), the linear elastic behavior, characterized by the moduli E and G, the linear viscoelastic domain, characterized by the complex moduli E* and G*, the purely viscous (Newtonian) behavior, characterized by the viscosity , for strains of a few percent, the domain where the behavior is highly non-linear.A bituminous mix has also a complex temperature-sensitive behavior. Its response to a given loading is strongly dependent on temperature and loading path. In addition, at a given temperature and a given strain rate, four main typical behaviors can be identified according to the strain amplitude () and the number of applied cyclic loadings (N) (see FIGURE 2, from (3).This paper is aimed at providing an assessment of the work conducted to date within the framework of a partnership between the “Dpartement Gnie Civil et Btiment” of the Ecole Nationale des TPE, Appia and Eurovia. This study focused on the thermo-mechanical behavior of different bituminous materials in both the small strain domain and the large strain domain, at low and mid temperatures, when considering only a small number of loadings This paper only deals with the characterization of the failure properties (i.e. in the large strain amplitude domain) of bituminous materials, at low and mid temperatures. It may be underlined that this paper completes two previous papers which focused on the linear viscoelastic behavior of bituminous materials (i.e. in the small strain domain) at low and intermediate temperatures (2) and (4).MATERIALSFour very different bitumens have been tested : two pure bitumens (10/20 and 50/70 penetration grade), and two polymer modified bitumens with a high content of polymer, one with plastomer and one with elastomer. The polymer modified binders are named hereafter PMB1 and PMB2. TABLE 1 presents the results of the conventional tests (the Fraass brittle point, the Penetration at 25C and the Softening Point Ring and Ball) initially performed on the different binders.Four different bituminous mixes, made from the 10/20, 50/70, PMB1 and PMB2 bitumens with one type of aggregate and grading, have been tested. The mixture samples had a continuous 0/10mm diorite grading, a 31% void content and a binder content of 6% by dry weight of aggregate.TESTS ON BINDERSSHRP Direct Tensile Tests (DTT)As described in AASHTO TP3 and (5), the SHRP Direct Tensile Test consists in elongating 27mm high bitumen samples at 1mm/min and at constant temperatures. The corresponding strain rate () equals 2.22m/m/h. At least six repeats at each temperature were realized on unaged samples. Apart from the determination of the conventional temperature leading to failure at 1% strain, T=1%, our analysis also consists in characterizing a threshold temperature separating the brittle behavior and the ductile one. Moreover, the tensile strength (maximum tensile stress) and thecorresponding strain for each temperature are considered and represented in FIGURE 3.In our opinion, the ranking of binders in function of their strain tolerance using the parameter T=1% does not seem to be really pertinent in the sense that this approach is rather empirical. This parameter will be hereafter compared with a new concept of brittle/ductile transition temperatur