Leni Figueiredo Mathias Leite

High temperature AFM study of CAP 30/45 pen grade bitumen

Bitumen is a complex mixture of hydrocarbons for which microstructural understanding is incomplete. In an effort to detail this microstructure, a asphalt cement sample (CAP 30/45) was analysed by thermal phase detection atomic force microscopy. Phase contrast and topography images showed that sample morphology is highly dependent on temperature. The ‘bee structure’ changed considerably at temperatures between 50°C and 56°C. A decrease of the oscillation amplitude was observed upon heating and the ‘bees’ completely disappeared at temperatures above 57°C. When the temperature was decreased after melting at 170°C, the ‘bees’ began to nucleate gradually at temperatures of 57°C and its evolution with time was followed. Changes in morphology were compared to thermal analysis results and a model for the ‘bee’ structure was proposed.

Mechanical properties of asphalt binders evaluated by atomic force microscopy.

Atomic Force Microscopy was employed in order to relate the features observed on the surface of a 50/70 asphalt binder according to its local stiffness and elastic recovery. Indentations were performed in different points of the surface and a significant variation of elasticity was observed between the points on the so‐called bee structure and the matrix. Also, indentations varying the maximum force were performed on similar white spots in the bee structure and the recovery was followed up to 1 h after indentation. It was observed that the elastic recovery is very much dependent on the colloidal structure of the bee. The final surface state of the binder, close to the bee for usual bees is not the same as the initial one indicating severe plastic deformation. Also, permanent phase change could be observed for bright spots presented in not well‐structured bee arrangements. A surface hardening was observed in the bee region.

Rheological evaluation of polymer-modified asphalt binders

)) using two oil shale contents (2 and 4%) and petroleum aromatic oil to evaluate comparatively the effect of the compatibilizer agent on the SBS PMB properties. The rheological characteristics of the SBS PMBs were analyzed in a dynamic shear rheometer (DSR) and the morphology accessed by fluorescence optical microscopy. The viscoelastic behavior of the samples corroborated the results for the classical properties and varied according to the sample morphology and composition. The results indicate that the aromatic and shale oils have similar effects on the microstructure, storage stability and viscoelastic behavior of the PMBs. Thus, shale oil could be successfully used as a compatibilizer agent without loss of properties or could even replace the aromatic oil. Following the Superpave methodology it was observed that the linear- and radial-SBS PMBs and linear-SBS PMB with 2% of shale oil can be used up to 70 °C, and the linear-SBS PMBs with 4% of shale oil or 2% of aromatic oil can be used only up to 64 °C.

RHEOLOGICAL STUDIES OF ASPHALT WITH GROUND TIRE RUBBER

ABSTRACT Laboratory studies about the interaction of asphalt cement with three different ground tire rubber (GTR) samples from different gradations were made using rheological and aging tests, and also chemical characterization tests. Rubber particle size, curing time, temperature and mixing rate were found to be important factors that affect the rubber depolymerization rate. It is possible to obtain homogeneous asphalt-rubber binders with non-detrimental viscosity at hot-mix temperatures, while still being elastic at rutting temperatures and less stiff at colder temperatures than base asphalt. The higher the rubber content in asphalt rubber, the better the cold stiffness properties and fatigue resistance, the lower the aging index. The proper combination of curing variables and asphalt composition is essential to assure good rheological properties. The high molecular size, the high asphaltenes content and high acidity in the asphalt cements resulted in blends more easily compatible and with good rheological properties.

A liquid chromatographyatmospheric pressure photoionization tandem mass spectrometric method for the determination of organosulfur compounds in petroleum asphalt cements

We present a sensitive liquid chromatography-atmospheric pressure photoionization tandem mass spectrometric (UHPLC-APPI-MS/MS) method for the determination of selected organosulfur compounds in Brazilian asphalt cements. It was possible to detect 14 organosulfur compounds of different classes where sulfoxides and sulfones presented higher sensibility in ionization than thiophenes and aromatic sulfides. A dopant-assisted APPI method was also tested, however, when chromatographic flow rate was optimized a decrease in signal was observed for all compounds. PAHs were tested and ruled out as possible interfering compounds and the matrix effect of asphalt cements was within an acceptable range for the quantification of organosulfur compounds. The proposed method was found to have satisfactory linearity and accuracy with recoveries between 83.85 and 110.28% for thianaphthene and 3-methylbenzothiophene, respectively. Therefore, the method allowed the characterization of organosulfur compounds in Brazilian asphalt cements and demonstrated changes in the amount quantified in asphaltenic and maltenic fractions after the RTFOT+SUNTEST aging process.

Analysis of asphaltic binders modified with PPA by surface techniques.

Samples of unmodified and modified asphalt binders containing 1% polyphosphoric acid were studied. Fourier‐transform infrared spectroscopy was used to evaluate the structural indices of the functional groups present in the samples and the results indicated there was a strong interaction between the polyphosphoric acid and oxygenated species. Contact angle measurements indicated that adhesion of the binder to the aggregate depended on the polyphosphoric acid content. Atomic force microscopy was used to relate features observed on the surface of the asphalt binder 50/70, with their local mechanical properties such as stiffness and elasticity. It was observed that the surface of the sample containing 1% polyphosphoric acid provides stiffness values lower than the unmodified asphalt binder.

Determination of oxygen and nitrogen derivatives of polycyclic aromatic hydrocarbons in fractions of asphalt mixtures using liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization.

Liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization was used for the determination of polycyclic aromatic hydrocarbon derivatives, the oxygenated polycyclic aromatic hydrocarbons and nitrated polycyclic aromatic hydrocarbons, formed in asphalt fractions. Two different methods have been developed for the determination of five oxygenated and seven nitrated polycyclic aromatic hydrocarbons that are characterized by having two or more condensed aromatic rings and present mutagenic and carcinogenic properties. The parameters of the atmospheric pressure chemical ionization interface were optimized to obtain the highest possible sensitivity for all compounds. The detection limits of the methods ranged from 0.1 to 57.3 μg/L for nitrated and from 0.1 to 6.6 μg/L for oxygenated derivatives. The limits of quantification were in the range of 4.6-191 μg/L for nitrated and 0.3-8.9 μg/L for oxygenated derivatives. The methods were validated against a diesel particulate extract standard reference material (National Institute of Standards and Technology SRM 1975), and the obtained concentrations (two nitrated derivatives) agreed with the certified values. The methods were applied in the analysis of asphalt samples after their fractionation into asphaltenes and maltenes, according to American Society for Testing and Material D4124, where the maltenic fraction was further separated into its basic, acidic, and neutral parts following the method of Green. Only two nitrated derivatives were found in the asphalt sample, quinoline and 2-nitrofluorene, with concentrations of 9.26 and 2146 mg/kg, respectively, whereas no oxygenated derivatives were detected.

Segregation and Crystallization of Waxes on the Surface of Asphalt Binders as Observed by Atomic Force Microscopy

In an effort to detail the thermal variation of the bitumen microstructure, one sample of asphalt cement (CAP 30/45) was analyzed by atomic force microscopy before and after thermal treatment. Phase contrast and topography images showed that sample morphology is highly dependent on the thermal history of the sample. It can be observed that thermal treatment can lead either to asphaltene flocculation or to wax crystallization. In situ measurements indicated that, after thermal cycles, “bees” appear to be immersed in a lamellar structure that resembles a surface crystallization process. Conditions for the crystallization of the waxes as well as the stability of the “bee” are discussed.

Fatigue Behavior of Asphalt-rubber Binders Modified With Shale-oil Residue

This work aims at evaluating the effects of the proportions of crumb rubber and shale-oil residue on the fatigue parameter G*sinδ. Eight asphalt binders were submitted to short- and long-term aging and then tests in the oscillatory-shear mode were performed. Based on regression models, response trace plots, and contour plots were made. Both rubber and oil reduce the G*sinδ parameter, increasing the controlled-mode fatigue resistance. As the test temperature decreases, the intensity of the effects of rubber and oil on G*sinδ increases and the number of mixtures that meet the Superpave limit of 5.0 MPa reduces.