United States Department of Transportation
i
Chemical Characterization of Asphalts Related to Their Performance
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2019-07-01
[PDF-4.17 MB]
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Edition:Final report, 12/1/2012-6/30/2015
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Abstract:In this project the researchers studied a correlation between molecular structure and corresponding compositional analysis of asphalt binders of conventional hot mix asphalt (HMA) mixtures as well as mixtures containing reclaimed asphalt pavement (RAP) and/or recycled asphalt shingles (RAS) with their cracking potential at intermediate temperature. The molecular size and structure of asphalt components of RAP and RAS undergo large changes during their exposure to environmental factors, which affects the physical properties imparted to their mixtures with conventional asphalt liquids. The composition of the mixtures prepared using a PG 70-22M binder was ascertained using thin layer chromatography/FID detection (Iatroscan), gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The distribution of species by molecular mass was determined by deconvoluting gel permeation chromatographs, emphasizing in particular, the amount of asphaltenes as they are related to the age hardening of asphalt materials. The extent of sample aging is apparent from the carbonyl oxygen content from FTIR measurements of the mixtures. Fracture resistance of laboratory produced mixtures was assessed using the Semi Circular Bend Test (SCB) test procedure; a minimal value of 0.5 kJ/m² was considered acceptable. Mixtures containing up to 5% RAS, 15% RAP and 15% RAP/5% RAS met the SCB standard. Molecular fractionation through GPC of mixtures containing RAS confirmed the presence of highly associated asphaltenes in greater concentrations than mixtures containing recycled asphalt pavement (RAP). High concentrations of high molecular weight associated asphaltenes (mol wt > 20K Daltons) which are present in RAS samples decrease the fracture resistance of the asphalt mixtures. The use of recycling agents, Cyclogen-L, Hydrogreen, Asphalt Flux and Re-refined engine oil bottoms (REOB), did not reduce the concentration of the highly associated asphaltenes; further they failed to improve the cracking resistance of the asphalt mixtures evaluated in this study. However, the recycling agents effected quantitative extraction of the RAS asphalt component.
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