Ageing of bitumen has been long-recognized as one of the major reasons responsible for the gradual deterioration of asphalt pavements. Age-hardening of the binder leads to the embrittlement of the overall asphalt mixture, which entails its increased susceptibility to traffic and environmental induced damage. As a result, high maintenance efforts as well as increased expenses are required to allow for an asphalt pavement to reach its expected service-life.
Past research efforts have established a solid background with respect to the implications of bitumen ageing on the overall response of an asphalt mixture as well as on the binder’s physico-chemical properties. In the same framework, studies have demonstrated that the ageing process of bitumen in the field is not solely a function of the bitumen type itself, but rather, added effects have been identified attributed to the mineral matter and the asphalt mixture design parameters.
This thesis attempts to provide a deeper understanding of the effect of mineral aggregates on the ageing of bitumen, and more specifically, the effect of a special fraction of the solid phase in asphalt mixtures, the mineral fillers. Six different mineral fillers were employed in this research, covering a wide range of physical and composition-related (i.e. elemental/mineralogical) properties. Bitumen-mineral filler blends were prepared, according to a single design protocol, and the resulting mastics along with neat bitumen were subjected to accelerated laboratory ageing by means of the Pressure Ageing Vessel.
The rheological (i.e. Dynamic Shear Rheometer) evaluation of the resulting materials and the derivation of ageing indices revealed the overall ability of the mineral fillers, regardless of their individual properties, to mitigate the ageing of bitumen incorporated in the mastics. The chemical (i.e. Fourier Transform-Infrared Spectroscopy) investigation of the materials showed that, in fact, the chemically active mineral fillers catalysed the oxidation of bitumen incorporated in the mastics. These results allowed for the identification of two mechanisms through which the effect of the mineral fillers on the ageing of bitumen occurs. The first one is related to the physical presence of the mineral matter in the mastics, whereas the second one to the developed physico-chemical interactions between the mineral fillers’ particles and the bitumen. Basic mineral fillers were found to be more efficient in reducing the age-hardening of mastics, compared to acidic ones, by allowing for more intensive interactions between the mastics’ constituent materials. Moreover, there are indications that the mineral fillers’ specific surface area also has a primary role to the developed interactions, and, by extension, to the ageing behavior of the mastics.
Finally, in addition to the aforementioned main findings, binders were extracted and recovered from the aged mastics, in an effort to derive further information on the effect of mineral fillers on ageing of bituminous mixtures by investigating the aged mastics’ constituent materials on their individual level. The rheological and chemical examination of the recovered materials did not lead to any further insight regarding the research questions of this study. Instead, features were revealed which manifest that the extraction and recovery of bitumen may not be a suitable approach for the investigation of the research problem addressed in this thesis.
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Research has been conducted into the diagenesis of the Luxembourg Sandstone. Literature studies were followed by a visit to the outcrop, after which thin sections were studied. The Luxembourg Sandstone Formation has been deposited in the Hettangian and Sinemurian, both lower Jurassic ages.
A sea strait connecting the Northern German Basin and the Paris Basin was located in present day Luxembourg. A tidal dominated delta deposited the weathering products form a part of the Rhenohercynian Zone, the Ardennes, into the transgressive sea strait to create sandstone deposits. The outcrop near the village of Echternach is characterised by two rock types visible as horizontal beds
and lenses: one well cemented and a less cemented sandstone. The less cemented zones tend to be better resistant to weathering and this causes the less cemented rock to overhang the cemented rock. The cemented zones have been cemented with calcite crystals and minor amounts of quartz cement. The sandstone consist of fine grained, moderately sorted, angular quartz grains with minor amounts of feldspars, opaque minerals, muscovite and zircon crystals. Detrital mudstone grains and ferroan cement were also present. The cemented rocks are classified as Lithic Arenites whilst the less cemented zones are classified as Sublithic Arenite, both have a recycled orogenic provenance. Three
parameters have influenced the cementation. Firstly permeability differences caused by deposition of clay and deposition of coarser material. Paths of permeability have formed through the sediments and this favoured cementation. Secondly, heterogeneous deposition of carbonate holding content provided
extra nucleation sites, again encouraging cementation. Lastly, carbonate redistribution took place in later stages causing carbonates to move from less cemented zones to cemented zones, causing even more cement to precipitate. Since calcite crystals dissolve more easily than quartz in the meteoric realm, the cemented rocks have been dissolved more, creating the appearance of the formation. ... Read more