Bitumen Durability-Measurement by Oxygen Absorption

Abstract

The absorption of oxygen by bitumens in the light and in the dark was measured at ambient temperature with stirred solutions in an indifferent solvent to avoid problems owing to diffusion effects. The rate of absorption was considerably increased by light (fluorescent lighting) and by traces of certain metals. All chemicaltype fractions prepared from bitumens by chromatographic separation oxidized in the light, but only the asphaltenes and resins absorbed oxygen in the dark, this reaction being probably initiated by the stable free radicals present in bitumens. The concentration of reactive components in dark-colored bitumens is higher than in light-colored ones, but in practice the dark color acts as a protection against excessive oxidation in the light. Few of the compounds known to inhibit oxidation reactions appeared to affect bitumen oxidation. Those that were active accelerated oxygen absorption in the light but had hardly any effect in the dark. The effects found with these substances in the light experiments were checked with Weather-O-meter experiments.A study of bitumen oxidation is of importance for several reasons.

A Review of the Fundamentals of Asphalt Oxidation: Chemical, Physicochemical, Physical Property, and Durability Relationships

“…Studies by King and Corbett (5), using thin films at 150ºC, and by Knotnerus (6), using dilute toluene solutions at ambient temperature, showed that the saturates fraction was relatively inert to reaction with oxygen as measured by oxygen uptake. The naphthene aromatics (5) and aromatics (6) fractions showed slight and no reactivity, respectively. However, the Corbett polar aromatics fraction and the Knotnerus resins and asphaltenes fractions were highly reactive with oxygen.…”

The oxidation of bitumen witnessed in-situ by infrared spectroscopy

“…However, in the high pH range, a path leading to sulfinic (RSO 2 H) and sulfonic acids (RSO 3 H) is predominantly observed [44]. Thus in the presence of basic AC fillers, such as hydrated lime [45], at this stage of reaction a different path should be observed.…”

“…The conclusion drawn from this analysis is that the peroxide species must form in the initial stage of oxidation in the system upon exposure to oxygen. Knotnerus [44] proposed that the analogue for the oxidation reaction in bitumen should be sought in 9,10-dihydroanthracene, which upon uptake of oxygen would form anthracene and hydrogenperoxide or 9-hydroxyperoxide-10-hydroanthracene [6]. The conclusion was drawn based on the similar molar uptake of oxygen per assumed mol of average bitumen used in that study, that 9,10-dihydroanthracene is a correct analogue.…”

“…However, there were one decade differences in the oxygen uptake between the bitumens e.g. Middle East and Venezuelan one [44]. The later was more in line with oxygen uptake in analogous n/a [32] Italics was used to distinguish that the signal in that region is not due to assignment typical for bitumen, i.e.…”

Effect of Inter-Molecular Association on Bitumen Oxidation

“…(Branthaver, 1993b;Ball and Herrington, 1996;Lau et ai, 1992;Petersen et al, 1993a), or thin films (Dickinson et al, 1958;Petersen, 1989), or for bitumens in solution (Knotnerus, 1972;Ronvaux-Van Keerbergen and Thyrion, 1989). The rate of oxidation can be described in terms of two concurrent first order reactions, one rapid and one slow (effectively constant), giving rise to equation (I) (Herrington, 1998;Huh and Robertson, 1996):…”