AGING OF BITUMEN
Transportation facilities are required for the economic development of a country .
Population growth and economic development result extensive development of asphalt-paved roadways
Bitumen is used for coating in pavement construction .
Bitumen serves as a satisfactory binder in improvement of physical interlocking of aggregate bitumen mixes
Its properties changes as it ages in bulk storage , transport and storage on site.
The aging of bitumen then leads to deterioration of pavement
Complex process based on chemical composition pavement structure and climate.
Bitumen must be resistant to change in properties over time
Based on hardening or stiffening of asphalt material
1 short-term ageing.
2 long-term ageing.
Aging produces polar species that can form structures.
The main mechanisms of aging of bitumen are oxidation and loss of volatiles.
OXIDATION AND LOSS OF VOLATILES
Occurs due to loss of lower molecular weight volatiles. This loss rate depends on the concentrations, temperature, and environment.
As bitumen age they incorperate oxygen at reactive sites .
benzyclic carbonic groups
Hetero atoms in Unaged bitumen may be polar or nonpolar
Oxidation may be catalyzed by components in the bitumen and by some metal compounds in the aggregates.
The level of carbonyl or sulphoxide groups is not affected
This mechanism is free radical and is initiated by peroxide formation
The predominant materials formed in oxidation are oxygen polar functionalities
The amphoterics are the most reactive in terms of reactivity are capable of forming interlinked structures because they have more than one reactive site ( Fig). Mono functional materials with one oxidizable site, can act as chain terminators, limiting the degree of associations. The amphoterics have a large effect on the viscosity of the bitumen; the monofunctional polar molecules do not. .
EFFECT OF DIFFERENT TYPES OF AGEING ON BITUMEN PERFORMANCE
EFFECT OF THERMAL AND ULTRAVIOLET AGING
The study was done by Tan Yi-Qiu1, Wang Jia-Ni1
Three types of base bitumen from different sources with the same penetration grade are taken as A ,B ,C.
EFFECT OF STORAGE ON PROPERTIES
Ã‚Â The study was done by Emery and Collonell
Degradation rates of physical indices of aged bitumen
Figure shows the changes to physical indices of bitumen A and B caused by aging. 1 A is more UV radiation sensitive. Its penetration decreased by 42%.ductlity decreased by 77.6% and the softening points increased by 22.6%,showing poor anti â€œUV ability. 2 B is not very sensitive to UV but is more thermally sensitive .as only small changes caused by UV radiation but greater changes in ductility and softening points caused by thermal aging can be seen . 3 Variations in the physical indices indicate than bitumen has different sensitivities due to Thermal and UV aging.
Rejuvenation in principle is simple ,replace the oils lost and rebalance the bitumen composition so it is no longer brittle .
This is not generally possible, as it would require sophisticated extraction testing and remodelling of binder in the road.
The controlling factor in rejuvenation is diffusion, to ensure a positive result, the level of diffusion must be controlled by careful choice of rejuvenator and the delivery method .
EFFECT OF FILLER
Filler is a fine material which passes a 0.63 mm sieve, derived from aggregate or other granular material.
The greater the amount of filler added the less the bitumen ages.
Increasing the content indicates a smaller decrease in penetration a smaller increase in the softening point and smaller increase in the bitumen indicator that ,aging is less
The addition of filler to the mixture can improve adhesion and cohesion.
The effects of addition of filler are directly related to the characteristics and degree of concentration of filler in the bitumen filler system
Effect of aging on bitumen performance was studied .The conclusion drawn from the study are
Properties of bitumen ductility ,viscosity and penetration varies with age
For different types of aging ,the properties are different
For storage ,penetration decreases 90% for 26 days and viscosity increased 77% for 26 days
For different sources of aging For UV aging 30% penetration for 9 hours and 17% in thermal aging. ductility varies 14% for UV and 44% for thermal aging.
The aging can be prevented by rejuvenation methods like . emulsion treatment and addition of filler ,Thus rejuvenating the bitumen ensures longer life to pavement