Development of a non-destructive test for viscoelastic characterization of asphalt mixtures

Abstract

Traditionally, the complex modulus of asphalt mixtures is obtained by a cyclic and quasi-static test, which demands more time and requires specialized personnel. This justifies the importance of developing alternative methods that are more economical, simple and applicable in the field. This is particularly important considering the emergence of increasingly mechanistic pavement design methods and field control. The objective of this research was to develop a nondestructive test, based on the principle of wave propagation and impact resonance for determining the stiffness of asphalt mixtures. For this purpose, the first version of the (Impact Resonance Testing - IRT), pioneer in Brazil, equipment was developed and validated with elastic materials. The results indicated that the proposed IRT produces adequate resonance responses similar to classical tests (quasi-static, static and ultrasonic). After this step and with the second version of the IRT equipment, the test was performed with the Frequency Response Function (FRF) measurement on an asphalt mixture specimen at 3 temperatures (-10, 4 and 20°C) with 2 IRT equipment, one developed at the Federal University of Ceará (UFC) and another already existing at the École de Technologie Supérieure (ÉTS) of the University of Quebec. The results of the experimental FRF obtained with the two tests for the same specimen of asphalt mixture presented less than 1% difference between the peaks of the resonant frequencies. Finally, to analyze the IRT test results and obtain the master curve, an inverse analysis was proposed, based on simulation with a Finite Element Software and divided into 4 main steps. This methodology showed to be adequate, and when comparing the global master curves obtained with the traditional cyclic test and the dynamic ones (IRT UFC and IRT ÉTS), they presented a very close correlation. The existing differences are due to experimental dispersions and nonlinearity effects of the viscoelastic material (possible effect of load level on impact). Therefore, this master's thesis brought up the development in Brazil of an IRT test with FRF measurement and proposed an inverse analysis to obtain asphalt mixture master curves. It also contributed directly to the approximation between research laboratories of UFC-Brazil and ÉTS-Canada, in addition to the Ecole Nationale des Travaux Publics de l'Etat (ENTPE) of the University of Lyon-France, where equipment of the same nature had been pioneered.