Evaluation of the coarse aggregate influence in the fatigue damage using fine aggregate matrices with different maximum nominal sizes

Abstract

Fatigue cracking is one of the most common distresses in flexible pavements in Brazil and in the world. Fatigue damage in asphalt mixtures originates as a small scale phenomenon. Recently, some authors have used the fine portion of the asphalt mixtures, called Fine Aggregates Matrix (FAM), as an intermediate step to estimate the hot mix asphalt (HMA) behavior. By definition, the FAM is composed of fine aggregates, mineral filler and asphalt binder. There are many volumetric issues of these kind of mixtures. In Brazil, the developed research regarding FAM uses sieve #10 (2.00mm) in the FAM sample preparation, since the #16 sieve (most used in the literature) does not belong to the set of national standardized sieves. Recently, some authors have used the concept of continuum damage mechanics in viscoelastic media in order to quantify the damage during the fatigue testing. In this theory the cracks are considered homogeneous dispersed in the medium, and are represented from internal state variables, determined experimentally. The objective of this study is to evaluate the influence of the variation of one of the FAM constituents, the aggregates, by varying its Maximum Nominal Size (MNS), on damage resistance of these asphalt mixtures. To achieve the objective, Linear Amplitude Sweep (LAS) and time sweep (TS) tests at controlled stress and controlled strain modes of loading were performed on the mixtures and the results were analyzed using the simplified viscoelastic continuum damage (S-VECD) methodology creating C vs S curves. Through the results and a failure criterion based on energy, cyclic tests can be simulated at different loading conditions for Wöhler’s curves construction. The FAM dynamic moduli obtained are very similar to the frequency used to induce damage. However, for lower frequency, the intermediate FAM presented lower stiffness value. It was concluded that FAM with different MNS present very distinct damage performance, and the decrease in the MNS results in an increase in the mixture damage performance for low strain amplitudes. Also, the LAS testing protocol does not allow failure prediction due to the absence of failure in this type of test for FAM.