Study of the influence of experimental conditions applied to the indirect tensile test versus type of bituminous mixture

摘要

The reference modulus of bituminous mixes, used for road design in France, is determined by the complex modulus measurement, carried out in the frequency domain at 15℃, 10 Hz or by the secant modulus in direct tension at 15℃, 0.02 s. However, there is strong interest to access this modulus using the indirect tensile (IT) test carried out in the time domain. Actually, this test appears to be easier to implement due to the sample manufacturing and numerous laboratories are already equipped. The present study proposes to determine the experimental condition to be applied to the IT test in order to get the reference modulus. A theoretical approach, based on the Maxwell and Huet viscoelastic linear models, is used to find the testing conditions at which the IT test has to be performed to give as precisely as possible the reference modulus. This procedure is applied on a large database of materials for which the viscoelastic spectrum has been provided. The influence of the loading waveform, which cannot be systematically controlled, is studied. For a force increasing linearly with time, the temperature at which the IT test has to be performed is close to 10℃, whatever the bituminous mix type. Moreover, the error that would have been committed by applying the equivalent temperature T_(eq) = 10℃ during the indirect tensile test is evaluated. This error depends on the loading waveform but always remains, theoretically, under 1000 MPa. This study has been carried out in the framework of collaboration between LCPC and USIRF (Union des Syndicats de l'Industrie Routiere francaise).