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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. CONTENTS 1. INTRODUCTION 2. AGEING OF BITUMEN 3. THERMAL AND UV AGEING 4. REJUVENATION TREATMENTS 5. EFFECT OF FILLER 6. CONCLUSION 7. REFERENCES 1. INTRODUCTION

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 bitumen, which influences its performance. As a result, the durability of the pavement decreases. The comparison of physical and rheological properties of UV aged, thermal aged and original bitumen shows that the physical properties like penetration and ductility decrease and softening point increases with age and rheological properties deteriorates with age as loss modulus and phase angle decreases.

Rejuvenation in principle is the replacement of oils lost and rebalances the bitumen composition so it is no longer brittle . There are different rejuvenation techniques like chip sealing, sand sealing and fog sealing. Fog seal involve emulsion with or without sand cover, Sand seal involves emulsion followed by clean sand or fine aggregate cover and Chip seal involves emulsion followed by an aggregate cover and is the most common surface treatment. Addition of fillers also helps in reduction of ageing of bitumen. 2. AGEING OF BITUMEN The properties possessed by bitumen such as physical and rheological properties changes gradually.

This change is due to Ageing of Bitumen. The change in composition with time is Ageing of Bitumen. This leads to several problems like deterioration of pavements, loss of properties of bitumen like adhesion , cohesion, and self healing capability. It also reduces the ability of water proofinf and resistance to abrasion. There can be short term and long term ageing. 2. 1TYPES OF AGEING There are two types of ageing mainly 2. 1. 1Short term ageing It can be mainly due to high temperature and exposure to air and working and mixing conditions. It leads to loss of volatiles. In labs it can be attained by Rolling Thin Film Oven Test (RTFOT). . 1. 2Long term ageing It can be mainly due to mix type and prolonged exposure to heat, oxygen and UV Rays. It can lead to oxidation and loss of volatiles. 2. 2 AGEING MECHANISM 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. 2. 2. 1OXIDATION 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. As bitumens age, they incorporate oxygen at reactive sites of one or two different types: ? Heteroatoms ? Benzylic carbon groups Polar groups containing oxygen are formed and these tend to associate into micelles of higher micellar weight thereby increasing the viscosity of bitumen. Polar hydroxyl, carbonyl and carboxylic groups are formed, resulting in larger and more complex molecules which make the bitumen harder. 2. 2. 2VOLATILITY 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. Lower molecular weight oils fractions- part of they dispersing phase may sometimes be lost by evaporation. This mostly occurs in handling but, depending on the bitumen, occur over time in the surface of the road. Such loss changes the bitumen compositional balance. These mechanisms can have different effects on bitumen and roads. 2. 2. 3 EFFECT OF AGEING MECHANISMS ON BITUMEN AND ROAD On bitumen the increase in polar groups will increase associations hence stiffening. This process is not reversible.

This can also create a relative depletion of oils and a more brittle binder is formed. Decreases in oils will result in the same brittleness. This makes a compositionally unstable product with high levels of hydrolysable groups. Hence cohesion and adhesion is compromised. The rate at which this occurs will depend on the bitumen composition and the conditions of handling and service. On roads brittle binder is less able to resist cracking and ravelling and this effect is exacerbated at low temperatures and high rates of traffic loading and this can lead to traffic congestions, increased rate of accidents etc. . THERMAL AND UV AGEING 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 . Due to the differences in air composition and the length of the solar radiation path between plateaus and low-altitude plains, plateaus have unique climatic and environmental features due to their more intense radiation, longer daylight hours, and especially their much higher UV percentage, which ranges from 20% to 25% of the total solar light. This is five times more than that on plains.

Such intense UV and thermal radiation causes serious ageing of bitumen, which influences its performance. As a result, the durability of the pavement decreases. The tests conducted and comparison of physical and rheological properties of UV aged, thermal aged and original bitumen is given below. 3. 1EXPERIMENT PROCEDURE, RESULTS AND DISCUSSIONS 3. 1. 1SAMPLE TAKEN In order to study the influence of UV and thermal radiation on bitumen properties and to compare differently aged samples, three types of base bitumen (denoted as A, B, and C) from different sources but with the same penetration grade.

Their basic physical and chemical properties are summarised in Table 1. Table 1. Physico-chemical properties of original bitumen Bitumen variety | A-Original| B-Original | C-Original | Penetration | 79 | 82 | 81 | Ductility | 52. 7 | 74. 3 | 45. 3 | Softening points| 46. 3 | 42. 6 | 45. 9 | 3. 1. 2ARTIFICIAL AGEING PROCEDURES UV AGEING : The ultraviolet radiation equipment mentioned by Tan is used. The bitumen was exposed to UV at a temperature of 73oC for 9 hours, so that the radiation energy was equivalent to the total energy received over a period of 5 months in Tibet.

THERMAL AGEING : A rolling thin-film oven (RTFO) was used in this study for thermal ageing. This method is used for measuring the combined effects of heat and air on a thin moving film of bitumen. The test simulates the hardening that binder undergoes during mixing in an asphalt plant. A moving film of bituminous binder is heated in an oven to a specified temperature under Standardised conditions, i. e. 163 oC and 75 min for a given period of time with a constant supply of air. The RTFOT also provides a quantitative measure of the volatiles lost during the ageing process. 3. 1. 3TESTS FOR DETERMINATION OF PHYSICAL PROPERTIES

PENETRATION TEST It is to find the consistency of the bitumen and bituminous binders. Penetration expressed as the distance in the tenths of a millimetre that a standard needle will penetrate vertically into a sample of the material under specified conditions of temperature, load and loading duration. The operating parameters of the test shall be a test temperature of 25°C, an applied load of 100 g (needle, needle holder and the extra weight) and a loading duration of 5 seconds. SOFTENING POINT TEST It is a method for the determination of the softening point of bitumen and bituminous binders in the range of 28° C to 150° C.

Softening point temperature is a temperature at which material under standardized test conditions attains a specific consistency. Two horizontal discs of bituminous binder, cast in brass rings shall be heated at a controlled rate in a water bath while each supports a steel ball. The softening point shall be reported as the mean of the temperatures at which the two discs soften enough to allow each ball, enveloped in bituminous binder to fall a distance of 25 mm. DUCTILITY TEST The “ductility test” gives a measure of the sdhesive property of bitumen and its ability to stretch.

Ductility of a bituminous material is measured by the distance in centimeters to which it will elongate before breaking when two ends of standard briduette specimen of the material are pulled apart at a specified speed and at a specified temperature. 3. 1. 4TEST FOR DETERMINATION OF RHEOLOGICAL PROPERTIES DSR(DYNAMIC SHEAR RHEOMETER)TEST It is used for the determination of the equiviscous characteristics on bitumen. The complex modulus is the sample total resistance to deformation when repeatedly sheared and the phase angle (? ) which is the lag between the applied shear stress and the resulting shear strain.

DSR test uses a thin asphalt binder sample sandwiched between two circular plates. The lower plate is fixed while the upper plate oscillates at 10 rad/sec (1. 6 Hz) to create a shearing action. Alternatively, a known oscillatory shear stress is applied to the test specimen and resulting shear strain is measured. A computer attached to the rheometer , controls the conditions under which the measurements are made. 3. 1. 5COMPARITIVE RESULTS PHYSICAL AND RHEOLOGICAL PROPERTIES Table 2:Comparison of physical properties BITUMEN VARIETY| A| B| C|

PENETRATION(intenths of mm)| ORIGINAL BITUMEN| 79| 82| 81| | THERMAL AGEING| 60| 74| 54| | UV AGEING| 46| 51| 49| DUCTILITY(cm)| ORIGINAL BITUMEN| 52. 7| 74. 6| 45. 3| | THERMAL AGEING| 36| 36. 2| 29. 8| | UV AGEING| 11. 8| 30| 23. 1| SOFTENING POINT(OC)| ORIGINAL BITUMEN| 46. 3| 42. 6| 45. 9| | THERMAL AGEING| 48. 1| 47. 3| 50| | UV AGEING| 56. 7| 48| 54. 2| Table 3:Comparison of chemical properties BITUMEN VARIETY| A| B| C| LOSS MODULUS| ORIGINAL BITUMEN| 1. 19| 0. 97| 0. 96| | THERMAL AGEING| 1. 03| 0. 99| 0. 85| | UV AGEING| 0. 80| 0. 92| 0. 74| PHASE ANGLE| ORIGINAL BITUMEN| 20. | 13. 1| 13. 2| | THERMAL AGEING| 18. 9| 12. 7| 11. 2| | UV AGEING| 13. 8| 12| 10| 4. REJUVENATION TREATMENT The ageing of bitumen is a complex process based on the chemical composition of the bitumen, the pavement structure and climate. As bitumen ages it becomes more brittle and surface cracking and ravelling may occur. Reseal or overlay treatments do not change the underlying binder characteristics and reflective cracking can occur. Rejuvenation systems have as an aim the modification of this underlying bituminous material to create a rejuvenated binder that is more flexible.

A thin coat consisting of bituminous binder and aggregates is typically spread over the entire carriageway width of mid-aged low-volume flexible pavements, to keep such pavements in motorable condition, consequently deferring the need for major preventive maintenance or resurfacing. Such seal coating treatments are known to heal surface cracks and ravelled surfaces and waterproof the underlying pavement layers and are therefore expected to ultimately have an impact on pavement surface condition and ride quality, pavement deterioration rate, or both.

Emulsion is the best way to deliver such a system; it can be in a number of forms including a rejuvenation sealer, an enrichment emulsion or a chip sealing emulsion. 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. For this reason an averageing process is more practical. This involves the use of a bituminous oils/resin fraction.

In general many formerly used aromatic oils that were the mainstay of rejuvenation systems are no longer easy to access and many have health questions associated with them. The main aim was to soften the aged binder and create a broad-spectrum rejuvenation that replenished volatiles and dispersing oils while promoting adhesion. In aged systems acidic species for example can compromise adhesion in the presence of water, these obviously cannot be removed from the bitumen so needs to be counteracted in some way. This may be done chemically with alkaline additives.

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. Emulsion requirements are to be effective the rejuvenation needs to be in contact with the aged binder and have the ability to penetrate this binder. The emulsion needs thus to be stable, however in sealing systems the emulsion must also coat wet and adhere to stone quickly. For this reason careful formulation and emulsifier choice is needed. Emulsion general requirements thus are no different to the application specific requirements of any emulsion.

In this rejuvenation approach different applications can be accommodated and the emulsion is developed to act largely independently of the rejuvenator by balancing formulation parameters. 4. 1TYPES OF REJUVENATION TREATMENTS 4. 1. 1FOG SEAL Fog seal is an inexpensive treatment to surface seal a pavement and protect it from elements. A light spray  of asphalt emulsion is applied to the pavement to seal the voids and prevent further deterioration due to oxidation and moisture. A timely fog seal can effectively stop raveling and moisture damage and improve and extend service life of a pavement.

Fog seals can also be used  to enhance colour and reduce dust in new chip seal pavements. Fog seals are best suited for pavements displaying low-to-moderate distress. Fog seals are used on both low and high volume roads. 4. 1. 2CHIP SEAL Chipseal is a pavement surface treatment that combines one or more layer(s) of asphalt with one or more layer(s) of fine aggregate. In the United States, chip seals are typically used on rural roads carrying lower traffic volumes, and the process is often referred to as “asphaltic surface treatment”.

Chip seals are constructed by evenly distributing a thin base of hot bitumen or asphalt onto an existing pavement and then embedding finely graded aggregate into it. The aggregate is evenly distributed over the seal spray, then rolled into a smooth pavement surface. A chip-seal-surfaced pavement can optionally be sealed with a top layer, which is referred to as a fog seal or enrichment. 4. 1. 3SAND SEAL Sand seal is a pavement surface treatment that combines one or more layer(s) of asphalt with one or more layer(s) of sand. Here emulsion followed by clean sand or fine aggregate cover. . EFFECT OF FILLER Filler is a fine material passing through 0. 63mm sieve which is obtained from aggregates. The increase in the amount of filler greatly affects the bitumen age that is greater filler is less the ageing of bitumen . The addition of ? ller to the mixture can improve adhesion and cohesion substantially. The bitumen–filler system (mastic), which is thicker and tougher than bitumen alone, improves the adhesive qualities and, in providing a covering ? lm of greater thickness, also can slow down the ageing processes. The effects of the addition of ? ler are directly related to their characteristics and the degree of concentration of the ? ller in the bitumen–? ller system. The advantages that ? ller offers for the durability of the bituminous mixtures in the case of water action are due, in principle, to its physical characteristics, which reduce the porosity of the granular structure and thereby make access by water and air difficult. Moreover, the chemical nature of ? ller may mean greater affinity with the asphalt binder, which can improve resistance to the displacement that water causes the bitumen. . CONCLUSION Ageing influences bitumen chemistry and rheology significantly. Chemical changes include the formation of carbonyl compounds and sulfoxides, transformation of generic fractions, and increases in amount of large molecules or molecular association. , molecular weight and poly dispersity . As a result of the chemical changes, the mechanical properties of aged bitumens become more solid-like, as indicated by increased complex modulus and decreased phase angle. However, the chemical and rheological changes are generally not consistent.

The short-term ageing of the bitumen in asphalt concrete mixtures is said to take place during production of the mixtures at the plant. Changes in the physical and rheological properties of bitumen due to thermal and UV ageing were investigated by experiments such as penetration, ductility, softening points, and DSR , and comparisons of sensitivities to thermal and ultraviolet radiation were made. The transformation of chemical components during ultraviolet ageing was also observed and the influence of UV ageing on bitumen performance was explained from this perspective.

Based on these investigations, some conclusions can be drawn as : Ultraviolet and thermal ageing have quite different influences on bitumen performance. The results of the experiments indicate that UV ageing has an obvious effect on the physical and rheological properties of bitumen. Most bitumen has different sensitivities to thermal and UV radiation. Evaluations based on thermally aged bitumen do not truly reflect the influences of ultraviolet ageing, and there are some limitations on the substitution of ultraviolet with thermal ageing.

The transformations that take place in the chemical components during UV ageing are related to the changes in properties. Rejuvenation systems have as an aim the modification of this underlying bituminous material to create a rejuvenated binder that is more flexible. Emulsion is the best way to deliver such a system; it can be in a number of forms including a rejuvenation sealer, an enrichment emulsion or a chip sealing emulsion. 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. Several modes of rejuvenating methods like fog seal, chip seal, sand seal were discussed . The mode of operation depends on the emulsion formulation and bringing the rejuvenator in contact with the aged pavement. This can optimise the diffusion into the age pavement. The effects of the addition of ? ller are directly related to their characteristics and the degree of concentration of the ? ller in the bitumen–? ller system. The advantages that ? ler offers for the durability of the bituminous mixtures in the case of water action are due, in principle, to its physical characteristics, which reduce the porosity of the granular structure and thereby make access by water and air difficult. 7. REFERENCES 1. Suleiman ArafatYero, Mohd Rosli Hainin ,The Influence of Short-Term Ageing on Bitumen Properties, ARPN Journal of Science and Technology . 2. Samuel Labi And Kumares C. Sinha, F. ASCE, Effectiveness Of Highway Pavement Seal Coating Treatments, Journal Of Transportation Engineering © Asce / January/February 2004. . Tejash Gandhi, Chandrakiran Akisetty, Serji Amirkhanian, Laboratory evaluation of warm asphalt binder ageing characteristics, International Journal of Pavement Engineering. 4. Glynn Holleran, Tom Wieringa, John Tailby, Rejuvenation Treatments for Aged Pavements. 5. Rodrigo Miro Recasens, Adriana Martinez, Felix Perez Jimenez, and Hugo Bianchetto, Effect of Filler on the Aging Potential of Asphalt Mixtures, Journal of the Transportation Research Board, No. 1901, Transportation Research Board of the National Academies, Washington, D.

C. , 2005, pp. 10–17. 6. Xiaohu Lu, Ulf Isacsson, Effect of ageing on bitumen chemistry and rheology, Received 15 October 2000; received in revised form 16 July 2001; accepted 25 October 2001,Science Direct. 7. Juntao Lin , Peida Guo , Li Wan, Shaopeng Wu, Laboratory investigation of rejuvenator seal materials on performances of asphalt mixtures, Science Direct. 8. Tan Yi-Qiu, Wang Jia-Ni, Feng Zhong-Liang and Zhou Xing-Ye, Influence and mechanism of ultraviolet ageing on bitumen performance.