Influência da umidade e do envelhecimento térmico em misturas asfálticas à quente.

Abstract

The aging process, mainly inherent to the asphalt binder, occurs more intensely in short-term aging, but this phenomenon persists throughout the pavement's service life. In this sense, the oxidative effect on the asphalt mix causes its premature cracking and a more realistic compression of this phenomenon is necessary for the elaboration of future projects. The simulation of aging in the laboratory aims to represent the situations to which the materials will be submitted in the field and, therefore, to evaluate the chemical, rheological and mechanical behavior. Therefore, temperature and humidity are important variables in the analysis of the aging process of asphalt mixtures. Therefore, this research evaluated the mechanical, rheological, chemical and physical performance of asphalt mixtures composed of Asphalt Binder (AB) 50/70 and Polymer Modified Asphalt (PMA) 55/75 under four different aging conditions: without aging (i); short-term thermal aging (ii); long-term thermal aging (iii) and long-term thermal aging including humidity (iv). The study was divided into two stages: rheological, chemical and physical evaluation of the binders; and mechanical investigation of asphalt mixtures. In the first stage, the rheological tests were carried out: Degree of Performance (PG); Asphalt binder creep and recovery determined under multiple stresses (MSCR) and Linear Amplitude Sweeping (LAS) for the three initial aging conditions. In the second stage, the mechanical tests of Tensile Strength by Diametral Compression (TS), Damage by Induced Moisture (LT), Modulus of Resilience (MR), Dynamic Modulus (MD) and Resistance to Permanent Deformation (Flow Number) and the chemical analysis using Fourier Transform Infrared Spectroscopy (FTIR) for the four aging conditions. The rheological results indicate, for both binders, an increase in viscosity, an increase in the number of fatigue cycles at low strains; elevation of PG and reduction of non-recoverable compliance (MSCR). Furthermore, AB 50/70 was more susceptible to long-term aging. For asphalt mixtures, TS and MR increased after thermal aging and moisture addition. The resistance to permanent deformation increased after thermal aging, but reduced later with increasing humidity. The thermal impact is insignificant when analyzing the LT, however, the insertion of moisture in aging caused susceptibility to adhesion failure in AB 50/70 mixture; being negligible at PMA 55/75. The MD increased after thermal aging for both binder and moisture acted as an oxidative effect in the mixture with AB 50/70. Finally, the protocol analyzed considering the joint effect of humidity and regional temperature proved to be essential for an effective long-term evaluation of the chemical, rheological and mechanical behavior of asphalt mixtures, since it has a more reliable simulation range compared to current methods of aging.