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.
One of the most important safety requirements of a road is its capability of preventing skidding of vehicles. However, this requirement so called "skid resistance" evolves during the whole pavement life. Phenomena that are identified to be responsible of this evolution are binder removal, aggregate polishing and seasonnal variations. In addition, ageing of bitumen is also identified to play a significant role on skid resistance evolution. One of the main results of previous works about skid resistance evolution was a model that takes into account two of the above listed phenomena such as bitumen scrouring and aggregates polishing. This present work is a continuation of the previous ones. It tries to include the effect of ageing in the above model. An updated model of evolution of skid resistance including this latter effect is proposed. This model is composed by a set of elementery functions in which some of them can be easily identified. The model can predict the evolution of skid resistance by combining effects of ageing, polishing and binder removal.
This study deals with the development of a new test method simulating the effect of ageing on skid resistance. This test is applied to bituminous mixes in this study, but can also be applied to concrete. This test relies on two machines, the Wehner–Schulze machine, to measure the friction, and the Weatherometer sunset machine, to simulate weather effects (rain, wind, sunlight, etc.). The relevance of this test is evaluated from comparisons between changes in friction and a chemical function linked to bitumen ageing: the carbonyl index. Validation is performed on bituminous mixture samples exposed to natural and accelerated ageing modes. Three very thin asphalt concrete (VTAC) slabs are manufactured in the laboratory with three different types of bitumens. Two specimens are extracted from each slab: one for natural ageing and the other for accelerated ageing. The evolutions of friction and carbonyl index measured on these samples submitted to the two ageing modes exhibit similar tendencies for all three bitumen types, thus confirming the relevance of the test. A conversion factor describing the correspondence between the durations of accelerated ageing and those of natural ageing is proposed for each type of bitume
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