A SEMINAR REPORT ON
AGEING OF BITUMEN
Bitumen is a common binder and has gradually replaced road tar for construction purposes mainly because of the cancer risk. It is a mixture of organic liquids that are highly viscous, black, sticky and entirely soluble in carbon disulfide. The ageing of bitumen is a complex process based on the chemical composition of the bitumen, the pavement structure and climate. It leads to deterioration of pavements and leads to loss of adhesive, cohesive, self healing and water proofing properties of bitumen. There are mainly two types of ageing that is short term and long term ageing. There are two basic mechanisms involved in binder ageing; these include an irreversible process like chemical changes of the bitumen, consisting of oxidation of bitumen molecules, and loss of volatile components which subsequently has an impact on the rheological properties of the binders. The reversible process is the second mechanism termed as physical hardening; this involves the reorganization of the binder molecular structure, under specific conditions.
2. AGEING OF BITUMEN
3. THERMAL AND UV AGEING
4. REJUVENATION TREATMENTS
5. EFFECT OF FILLER
Bitumen is a complex mixture of chemical compounds. It can be characterised by fractionation into groups based on polarity. The ageing of bitumen is one of the principal factors causing the deterioration of asphalt concrete pavements. The ageing modes of failures includes fatigue, thermal induce cracks, and raveling. In practice the actual time for short-term ageing in construction sites varies and depends on hauling distances or paving delays. Bitumen ageing occurs during the mixing and construction process as well as during long-term service in the road. The circumstances at different ageing stages vary considerably. The factors affecting bitumen ageing include characteristics of the bitumen and its content in the mix, nature of aggregates and particle size distribution, void content of the mix, production related factors, temperature and time. All these factors operate at the same time, making the process of bitumen ageing very complex. There are two basic mechanisms involved in binder ageing; these include an irreversible process like chemical changes of the bitumen, consisting of oxidation of bitumen molecules, and loss of volatile components which subsequently has an impact on the rheological properties of the binders. The reversible process is the second mechanism termed as physical hardening; this involves the reorganization of the binder molecular structure, under specific conditions. The main mechanisms of ageing of bitumen are oxidation and the loss of volatiles. When bitumen ages it becomes higher in viscosity (stiffer) and the composition changes noticeably. These changes can lead to brittleness and loss of adhesion, especially in the presence of water. Like many substances, bitumen is slowly oxidized in contact with atmospheric oxygen. The degree of oxidation is highly dependent on the temperature, time and the thickness of bitumen film. Hardening due to oxidation has long been held to be the main cause of ageing. It depends on chemical composition and origin of bitumen. Ageing produces polar species that can form singles or multiple structures. Volatility is caused due to the evaporation of volatile component which depends mainly upon temperature and exposure conditions. Penetration grade bitumen is relatively non volatile and therefore the amount of hardening resulting from loss of volatile is fairly small. These mechanisms can have different effects on bitumen and roads.
UV and thermal ageing are two quite different types of ageing. However, the current bitumen performance evaluation system gives little consideration to UV and thermal ageing. The intense UV and thermal radiation causes serious ageing of...
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