Microstructure-based identification of bitumen performance

Abstract

Motivated by recent progress in both experimentation and the micromechanical description of the behavior of multi-composed materials, a multiscale model for asphalt is currently developed at the Christian Doppler laboratory for "Performance-Based Optimization of Flexible Pavements" at Vienna University of Technology. This model allows us to relate macroscopically observable asphalt properties to finer-scale information. Since the mechanical properties of asphalt and the influence of environmental conditions (temperature, aging) originate from the binder properties, a proper characterization of bitumen is essential for the predictive capability of the anticipated multiscale model. In this paper, the characterization of bitumen, comprising the bitumen chemistry, its microstructure, and its viscoelastic properties, is presented for two types of bitumen (standard and polymermodified bitumen) considering the unaged and aged state. The obtained results provide new insight into the durability behavior of binders, explained by changes of the chemical composition, the microstructure, and the micromechanical properties of bitumen.

Towards a microstructural model of bitumen ageing behaviour

“…While a sample is scanned by a focused electron beam, the signal arising from the interactions between the surfaces of the constituents of the sample and the electrons can be intensified by a gas within the testing chamber and, thus, the microstructure is made visible. When bitumen is tested by ESEM, results suggest a string-like structure embedded in a matrix (Stangl et al 2006) (see Figure 4), while the top film of the matrix is removed by the electron beam. Taking a closer look at the strings, spherical centres can be identified, which are connected by strings.…”

“…Thereby, SARA fractionation separating bitumen into saturates, aromatics, resins and asphaltenes (Corbett 1969, Lesueur 2009) is the most common way to identify the constituents of bitumen. Imaging methods such as atomic force microscopy (AFM) or environmental scanning electron microscopy (ESEM) enable to visualise the (micro)structures built up by these constituents (Bodan 1982, Yen 1992, Espinat et al 1998, Forbes et al 2001, Pauli et al 2003, Bearsley et al 2004, Jäger 2004, Masson et al 2006, Stangl et al 2006, Lesueur 2009, Schmets et al 2010, Nahar et al 2013a, 2013b and, hence, allow for the development of models predicting the mechanical behaviour.…”

Micromechanical Description of Bitumen Aging Behavior

“…4 The original bitumen with an asphaltene content of 8.73 wt% (left, AFM topography scan of the maltene phase (center), and an artificially composed binder with an asphaltene content of 8.73 wt% (right) (Hofko et al 2015) wrinkling along the long axis are dispersed over a contiguous matrix (perpetua phase). Both phases are often mentioned as typical characteristics for the bitumen microstructure (Stangl et al 2006;Masson et al 2006;Nahar et al 2013aNahar et al , b, 2014Schmets et al 2010;Pauli et al 2001). While terraced patterns form a third phase adjacent to the catana phase, the spherical inclusions in the matrix (fourth phase) is not commonly observed within the bitumen microstructure indicating an incompatibility in interaction between different molecular classes, which suggests that the bitumen is a blend of petroleum products of different crude oil origins to exhibit a desired penetration index (Hofko et al 2015).…”

“…By using the AFM experimental setup, the surface of the sample is scanned and a contiguous matrix with embedded "bee"-like inclusions can be observed (Jäger et al 2004). Since the top film of the matrix is removed by an electron beam, ESEM images give an insight into the material and suggest a string-link structure within a matrix (Stangl et al 2006) showing spherical centers connected by the strings. As all these inclusions, fluorescent centers and spherical structures exhibit similar dimensions (size range between 1 and 10 μm), they are assumed to represent the same structures.…”

“…Thereby, SARA fractionation separating bitumen into saturates, aromatics, resins and asphaltenes (Lesueur 2009;Corbett 1969) is the most common way to identify the constituents of bitumen. Imaging methods like Atomic Force Microscopy (AFM) or Environmental Scanning Electron Microscopy (ESEM) enable to visualize the (micro)structures built up by these constituents (Stangl et al 2006;Jäger et al 2004;Masson et al 2006;Nahar et al 2013aNahar et al , b, 2014Schmets et al 2010;Pauli et al2001;Forbes et al 2001;Bearsley et al 2004;Lesueur 2009;Espinat et al1998;Bodan 1982) and, hence, allow for the development of models predicting the mechanical behavior.…”