Asphalt, also known as bitumen is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term asphaltum was also used. The word is derived from the Ancient Greek ἄσφαλτος ásphaltos. The Pitch Lake is the largest natural deposit of asphalt in the world, estimated to contain 10 million tons.
Petroleum asphalt is a sticky, black and highly viscous liquid or semi-solid that is present in most petroleum crude oils and in some natural deposits. Petroleum crude oil is a complex mixture of a great many different hydrocarbons. Petroleum asphalt is defined as that part of crude oil which is separated from the higher-boiling hydrocarbons in crude oil by precipitation upon the addition of lower-boiling hydrocarbon solvents such as propane, pentane, hexane or heptane. The precipitated material consists of asphaltenes which have an average molecular weight of about (800 – 2500 g/mole) and exist in the form of flat sheets of polyaromatic condensed rings with short aliphatic chains.
Over the years, petroleum asphalt has been referred to as bitumen, asphaltum or pitch. The terminology varies from country to country and from individual to individual. Asphalt is often confused with coal tar (or coal pitch) derived from the pyrolysis of coal and which has a different chemical structure than asphalt.
When petroleum asphalt is combined with construction aggregate (sand, gravel, crushed stone, etc.) for use in road construction or paving, it has often been referred to as asphaltic concrete, asphaltic cement, bituminous concrete, blacktop or road tar.
Technology of asphalt pavements by asphalt oil started 170 years ago, with an experiment involving natural rubber with bitumen in the 1840s, attempting to capture the flexible nature of rubber in a longer lasting paving surface. Now a day’s especially rubber process oil use instead of natural rubber for bitumen rubber blend as asphalt oil for pavement.
Nowadays the rubberized asphalt technology is being adopted in many other parts of the world: Taiwan is pioneer inasphalt mixtures for flexible pavement rehabilitation; furthermore, rubberised asphalt oil has been trialled in Beijing and for use in new and maintenance work as part of the preparation for the 2008 Olympics in China and it has also been used in EcoPark Project in Hong Kong.
Blending rubber oil with bitumen in asphalt
The principal objects of adding rubber to bitumen are to give the bitumen elasticity, to increase its ductility and to reduce its susceptibility to temperature changes. The effectiveness of rubber in bringing about these desirable changes depends on the extent to which the rubber dissolves in the bitumen. To dissolve read ily, the rubber must be unvulcanised and be in a finely divided state. Rubber exists in this condition in the form of latex, and it is known to add rubber in this form both to bitumen emulsions and to hot bitumen and to add rubber in the forms of vulcanized and unvulcanised rubber powder to hot bitumen and to asphalt paving mixtures during the process of mixing.