Jorge Barbosa Soares

Characterization and thermal behavior of polymer-modified asphalt

A styrene-butadiene-styrene modified asphalt cement was characterized by infrared, differential scanning calorimetry, thermogravimetric analysis and empirical tests such as ring and ball softening point, penetration and elastic recovery. After aging in the rolling thin-film oven, the polymer-modified asphalt presented structural changes relating to oxidation of the material. The infrared spectra showed an increase in hydroxyl groups and the formation of carbonyl compounds and sulphoxides. The percentage of crystallized fraction calculated from differential scanning calorimetry was 0.41%. Thermogravimetric analyses in inert and oxidative atmospheres revealed distinct events during thermal decomposition; the initial activation energies were similar, but changed as the process evolved.

CONSIDERING MATERIAL HETEROGENEITY IN CRACK MODELING OF ASPHALTIC MIXTURES

Cracking in the asphaltic layer of pavement has been shown to be a major source of distress in roadways. Previous studies in asphaltic mixture cracking have typically not considered the material heterogeneity. A numerical method of analysis is presented that is based on the theory of fracture mechanics, in which the binder and the aggregates are treated as distinct materials. The simulations performed are verified and calibrated from simple and conventional laboratory tests. The study investigates crack evolution under monotonic loading, even though the method outlined can be further developed for the investigation of asphalt mixture fatigue. The approach discussed is part of a multiscale framework for pavement analysis, in which the damage due to cracking at the local scale can be considered in a global analysis at the actual pavement scale.

MODEL FOR PREDICTING DAMAGE EVOLUTION IN HETEROGENEOUS VISCOELASTIC ASPHALTIC MIXTURES

Cracking in the asphaltic layer of pavements has been shown to be a major source of distress in roadways. Previous studies in asphaltic mixture cracking typically have not considered the material heterogeneity. The sequel of a study in which the binder and the aggregates were treated as distinct materials is presented. Besides consideration of the viscoelastic behavior of the bulk asphalt binder, a micromechanical viscoelastic cohesive zone model introducing ductility at the crack tip has been considered. The simulations performed are verified and calibrated from simple and conventional laboratory tests. The study investigates crack evolution under monotonic loading, even though the method outlined can be further developed for the investigation of asphalt mixture fatigue.

Aggregate Shape Properties and Their Influence on the Behavior of Hot-Mix Asphalt

Aggregate shape properties, such as form, angularity, and surface texture, highly influence the performance of hot-mix asphalt (HMA). Rutting is related to aggregate angularity and form, which affects the interlock among particles. Fatigue cracking can be decreased by an aggregate rough surface texture, which improves the aggregate-binder interaction. Several researchers have been studying new automated and more precise techniques, such as the aggregate image measurement system (AIMS), to improve the determination of aggregate shape parameters. This paper presents an analysis of aggregates from three different mineralogical sources, investigating the influence of shape properties on HMA design and mechanical properties. The results indicated that the aggregates had similar shape properties, despite differences in the mineralogical composition. This might be a direct effect of similar quarrying procedures. Surface texture resulted in different values, which can be explained by results from the petrographic analyses. In general, the aggregates’ shape properties resulted in HMA samples with similar mechanical behavior. The HMA specimens were also analyzed in terms of their internal structure, which included the investigation of a number of contact points, and aggregate particles’ segregation and orientation characteristics.

Asphalt binders modified by SBS and SBS/nanoclays: effect on rheological properties

In this work, it was investigated the effect of organically modified vermiculite and montmorillonite (OVMT and OMMT, respectively) in asphalt binders (AB) modified by SBS (styrene-butadiene-styrene). The physical and rheological properties were performed for AB, 4.0% SBS MB and nanocomposite AB modified by 2.5% SBS with 2.5% of organoclays. The modified binders (MB) result in the enhancement of complex modulus (G*) and reduction of phase angle (d), which means greater resistance to permanent deformation. The viscosity, penetration and thermal susceptibility were appropriate. The black diagrams show that the effect of nanoclays OVMT and OMMT was similar to the effect of Cloisite®. The rheological properties of the nanocomposite were comparable to the 4.0% SBS MB, identifying a cost reduction due to the potential of replacing polymer with clay. The presence of OVMT improved the storage stability of SBS MB, an important result, as the phase separation is a major obstacle to the use of SBS in paving.

Multiscale Modeling to Predict Mechanical Behavior of Asphalt Mixtures

This study presents a multiscale computational model for predicting the mechanical behavior of asphalt mixtures. The model can account for mixture heterogeneities by considering individual mixture constituents through the scale-linking technique: a local scale in a form of the heterogeneous representative volume element and a global scale that has been homogenized from local scale responses. The model is implemented with a finite element formulation, so that geometric complexities, material inelasticity, and the growth of time-dependent damage can be properly handled. Damage is in the form of cracks modeled with nonlinear viscoelastic cohesive zones. The primary purpose of this paper is to present the multiscale modeling framework developed and to evaluate the applicability of the multiscale modeling technique to determine the performance of asphalt mixtures and structures when damaged. This is accomplished by employing only material properties at the constituent level (local scale) as model inputs. The indirect tensile test of fine-aggregate matrix mixture is simulated as an example, and the simulation results are compared with experimental results to evaluate the applicability of the model. Predictive power of the model and the benefits related to the reduction of computational efforts and laboratory tests are further discussed.

Dynamic Viscoelastic Analysis of Asphalt Pavements using a Finite Element Formulation

ABSTRACT This paper studies the effect of time and load rate on the structural response of asphalt pavements when the surface layer is a linear viscoelastic material. A finite element incremental algorithm for dynamic analysis of viscoelastic solids is presented, where the stresses are computed using a hereditary integral in which the relaxation modulus is described by a Prony-Dirichlet series. The stresses are integrated in a semi-analytical form, whereas the dynamic equilibrium equations are integrated by the Trapezoidal Rule. Different pulse loads are considered and the viscoelastic responses of different asphalt layer thicknesses are compared. Several performance indicators typically utilized in pavement design are studied, particularly those at the surface layer, i.e., tensile stress and strain, shear strain, and surface deflection.

Evaluation of polishing and degradation resistance of natural aggregates and steel slag using the aggregate image measurement system

Aggregate resistance to polishing and degradation can be related to the change in some of those aggregates particles’ characteristics. Polishing resistance can be related to the loss of surface texture, and it can affect asphalt pavements’ microtexture, influencing its skid resistance. Degradation resistance is related to the loss of angularity and to the aggregates’ breakage. It affects pavement distresses’ resistance and aggregate gradation. The methodologies used to evaluate these characteristics produce results that are mostly not representative. This paper aims to present a digital image processing (DIP) technique to evaluate aggregates’ resistance to polishing and degradation, along with the use of the Los Angeles abrasion equipment. The aggregate image measurement system was used to analyse the aggregates mainly not only with respect to angularity and surface texture, but also with respect to sphericity and flatness/elongation particle percentage, before and after the polishing and the degradation processes. Three natural aggregates (granite, gneiss and phonolite) collected from Brazilian quarries, and one by-product (steel slag) were evaluated. The findings from this study can be used to rank aggregates with respect to their shape properties. With the results obtained for the steel slag, it can be concluded that this material was the most resistant to polishing when compared with the natural aggregates.

Characterisation of ageing processes on the asphalt mixture surface

Ageing of asphalt binders leads to evolution of pavements mechanical performances, due to changes in their rheological behaviour and in the binder composition. Ageing leads to a hardening of asphalt, mainly due to the oxidation of the asphalt binder itself. Oxidation rate is influenced by several parameters, namely outside temperature, ultraviolet (UV) radiation and intrinsic characteristics of the mixture constituents. In order to assess physical and chemical characteristics of the binders in aged pavements, mixture samples of several centimetres in thickness are usually cored from the field. Binders are extracted from these asphalt samples. This process of extraction is typical but it does not allow differentiating bulk and surface characteristics. Indeed, only the surface binder is exposed to UV rays and weathering. In order to assess the ageing of only the surface layer, to verify, for instance the influence of ageing on adhesion characteristics, it is necessary to extract and recover only the surface asphalt binder. A new test protocol, presented in this paper, has been developed to fulfil this purpose. This protocol consists in sampling only small particles at the surface layer, extracting the binder from the particles and performing Fourier transform infrared spectroscopy (FTIR) tests to assess the ageing of the binder. As the quantity of binder is very small, a specific FTIR test method is used. This method consists in keeping the binder diluted in the solvent and placing the solution in the ray of the spectrometer to perform the measurement. This new method has been compared to a more typical one, which consists in applying the binder on a transparent plate after having extracted the binder from the solvent. Once it has been checked that the two methods provide the same results for three kinds of binders, surface ageing tests have been performed. Two different ageing processes were considered: an ageing on site and an accelerated ageing protocol using a climate chamber named Weatherometer (SUNTERTXXL+). In this chamber, temperature, humidity and rain are controlled. The comparison between the ageing in the laboratory and the field allowed correlating both processes to establish an accelerator factor with respect to the increase in carboxyl group.

Polycyclic aromatic hydrocarbons from asphalt binder: extraction and characterization

The asphalt binder, derived from petroleum, commonly employed in road paving contains PAHs (Polycyclic Aromatic Hydrocarbons) and a variety of other aliphatic and aromatic compounds. PAHs are pollutants that can induce health problems. This work aims to extract and characterize the PAHs in samples of asphalt binder and its concentration. Matrix solid phase dispersion was used as a technique for extraction of the PAHs. Characterization was performed employing gas chromatography and scanning tunneling microscopy. Fifteen of the priority PAHs listed by USEPA (United States Environmental Protection Agency), as well as coronene, were found in the binder samples.