Abstract
Bitumen aging is the major factor contributing to the deterioration of the road pavement. Oxidation and volatilization are generally considered as the most important phenomena affecting aging in asphalt paving mixtures. The present study was carried out to investigate whether various antioxidants provided by natural resources such as phospholipids, ascorbic acid as well as lignin from rice husk, could be used to reduce age hardening in asphalt binders. A selected bituminous material was modified by adding 2% w/w of the anti-aging natural additives and subjected to accelerated oxidative aging regimes according to the Rolling Thin Film Oven Test (RTFOT) method. The effects of aging were evaluated based on changes in sol-gel transition temperature of modified bitumens measured through Dynamic Shear Rheology (DSR). Moreover, changes of Electron Paramagnetic Resonance (EPR) spectra were monitored on the bituminous fractions asphaltene and maltene separated by solvent extraction upon oxidative aging. The phospholipids-treated binder exhibited the highest resistance to oxidation and the lowest age-hardening effect compared to the other tested anti-oxidants. The combination of EPR and DSR techniques represents a promising method for elucidating the changes in associated complex properties of bitumen fractions promoted by addition of free radical scavengers borrowed by green resources.
Highlights
In asphalt industry, the term aging identifies the process of deterioration of bitumen due to the occurrence of oxidation mechanisms and progressive loss of volatile components
Two important parameters are obtained from Dynamic Shear Rheology (DSR) tests on bitumen: the complex modulus, G*, and the phase angle, δ
Addition of phospholipids turned out to be beneficial in minimizing the shift of viscoelastic-sol transition temperature towards higher values in temperature sweep rheological tests, which is a typical fingerprint of bitumen hardening in response to oxidative phenomena
Summary
The term aging identifies the process of deterioration of bitumen due to the occurrence of oxidation mechanisms and progressive loss of volatile components. This alteration occurs over time and causes a change in the chemical, physical, colloidal and rheological properties of the bitumen itself, affecting the useful life of the road pavement as aging tends to make the binder more fragile and the conglomerate more prone to cracking [1]. Despite the impossibility of isolating the single oxidized components, the main functional groups have been identified. These include predominantly ketones and sulfoxides, accompanied by dicarboxylic anhydrides and dicarboxylic acids in much smaller concentrations [2]
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