Caracterização avançada de ligantes e misturas asfálticas brasileiras

Abstract

The linear viscoelastic (LVE) and damage characterization of bituminous mixtures is imperative to analyse and design pavements. Bituminous mixtures inherit the viscoelastic behavior of bitumen. The bitumens used in paving change their properties and chemical constitution because they come from different petroleum or mixtures of petroleums and from different production routes. In order to develop the knowledge of the influence of the bitumens on the properties of the bituminous mixtures it is essential to know the stiffness of the bituminous mixture when subjected to different loads, temperatures and loading frequencies and their resistance to permanent deformation and fatigue. This research suggests that these properties of mixtures could be predicted from testing at other scales, such the chemical and rheological scales of bitumen. The general objective of this research is to define chemical and rheological markers of bitumens that affect the behavior of the mixture and to understand the multiscale correlations of laboratory results for conventional and modified Brazilian bitumens. The bitumens chosen for the development of this research were collected in most refineries in the country, seeking to represent the Brazilian production of bitumens at certain time. This study contemplates the characterization of twelve bitumens, emphasizing the conventional bitumens produced in seven refineries. Nine Bitumens 50/70, one 30/45 and two modified bitumens with rubber and SBS polymer were selected. Twelve mixtures were made with the same aggregate grading (19mm maximum nominal size and designed by the Superpave methodology) varying only the bitumen. To reach the objective, several chemical, rheological and damage tests in bitumen and mixtures were performed. An extensive experimental campaing to find the main chemical components in bitumen was carried out: Elemental analysis by X-ray fluorescence analysing Ni, V and S. Speciation of sulfur compounds by the methods of Green and Payzant. Saturates, Aromatics, Resins and Asphaltenes (SARA) fractionation, size distribution of molecules and linear chains, as well as determination of N, C and H content. Complex modulus tests were performed in bitumens using the Dynamic Shear Rheometer (DSR) and the compression complex modulus test was carried out to measure the LVE behaviour of the materials. The DSR was used to perform the Multi‐Stress Creep and Recovery Test (MSCR) to calculate the behavior of bitumen regarding permanent deformations and Flow Number (FN) and Hamburg tests were performed on the mixture scale. In the fatigue domain, Linear Amplitude Sweep (LAS) tests were performed on the bitumen scale and the direct tension cyclic fatigue test for mixtures. For the LVE results, the 2D 2S2P1D (2 Springs, 2 Parabolic Elements, 1 Dashpot) modelling was used and it was verified that all the mixtures had similar values of the constants E0 (glassy modulus) and E00 (static modulus), however, they were not identical as expected, reinforcing the influence of the bitumens. The Shift-Homothety-Shift in time-Shift (SHStS) transformation was applied to verify the correspondence of LVE behaviours of related bitumens and mixtures and presented successful predictions of mixtures LVE behaviour from bitumens LVE behaviour for nine of the twelve materials. The LVE tests results in bitumens shows that the same specification bitumens have different LVE behaviour. Some chemical markers results show good relation with the LVE behavior of bitumens: the % of high size molecules, % of Sulfur and Ni. The results of the permanent deformation of bituminous mixtures were coherent with the MSCR results, showing that it is possible to predict the damage by permanent deformation in mixtures from the bitumen scale. The high % of Sulfur and Nickel seems to improve the bitumens permanent deformation behaviour. The LAS results (failure criterion used was Gr or pseudo-energy PSE) showed that most of the 50/70 bitumens are in the same fatigue class when comparing the bitumen fatigue factors (FFBpse 19ºC). The simplified viscoelastic continuum damage (S-VECD) was used to calculate the fatigue factor of the mixtures (FFM), which had a good relationship with the FFB results for the conventional bitumens. The average size of the linear chains is a factor that correlates well with fatigue, as is the percentage of Saturates and Thiophenes. The greater the quantity of these components, the more resistant to fatigue is the bitumen. In general, it is concluded that the properties of the mixtures can be predicted from the results of the bitumen. Furthermore, the characteristics of bitumens can be partially explained by some chemical properties.