Oxidation of bitumen

Kinetics and Energetics of Oxidation of Bitumen in Relation to In Situ Combustion Processes... 

We propose that the complicated dry oxidation of bitumen can be represented as the sum of contributions from two classes of oxidation reaction. One class of reactions is the partial oxidation that leads to deposition of coke and formation of "oxygenated bitumen", with very little production of carbon oxides and water. This class of reactions is concisely summarized by... 

The mass balance for carbon during dry oxidation of bitumen in our calorimeter can be calculated from the above results in combination with some of our chemical results for oxidized samples reported elsewhere ( 2). This mass balance is summarized in Table IV, where the following relationships have been used ... 

Both of the above chemical studies point towards the increased importance of the burning process at 285°C in determining the initial rate of heat production. The role of water as yet remains undefined other than at the higher temperature of 285°C it appears to have the opposite effect on the bitumen sample compared to the process at 225°C i.e., it appears that water vapor encourages pathways by which the various components of bitumen react with oxygen. Preliminary calculations of the total heats evolved during the wet oxidation of bitumen sands indicate that they are independent of the partial pressure of oxygen in the system at... 

Table 4-98 Onset temperature and maximum temperature of the 1st peak Tj of the oxidation of bitumen in 7 bar air (/3 = 10 K/min)...

Fig. 4-78 Low Temperature Oxidation of Bitumens (First DSC Peak) Half Life Time tjyj versus Temperature (Mean Values)...

During the oxidation process long-life radicals are formed, which are mesomerically stabilized. These radicals can induce the oxidation of bitumen binder in the road surface or roofing felt, even at low temperatures under the influence of UV radiation. Moreover temperatures up to 60 °C or 80 °C may be reached at the surfaces of roads or roofing felts as a result of the IR radiation in sunlight. However, the energetic UV rays can only penetrate the surface for a few micrometers due to the dark color of the bitumen. 

Table 4-210 Half life time t 2 of the oxidation of bitumen B80.

Paving bitumens are bitumens produced from the residue distillation of crude oil, whereas oxidised bitumens are produced from bitumen subjected to a blowing process during which oxidation of bitumen occurs. 

Oxidation and, consequently, ageing of bitumen after construction are affected by climatic conditions (ambient temperatures and periods of sunshine) and voids in the bituminous mixture. Greater oxidation of bitumen is expected in geographical locations where ambient temperatures are high and sunshine periods are longer in a year. A similar result is expected between open and dense graded bituminous mixtures. 

Another function of the fibres is to increase the relative surface area of the mixture so as to incorporate higher percentages of bitumen and thus reduce the rate of oxidation of bitumen. Reduction of the rate of oxidation increases the pavement s service life (improves fatigue life and slows appearance of ravelling). From all fibre types, cellulose fibres have been found to allow the higher increase of bitumen content in the mixture (Peltonen 1989). 

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