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Sources and Types

Bitumen Guide

Definitions

Sources

Properties

Types of Bitumen Bitumen Handling

Definitions

Bitumen is a non-crystalline viscous material, black or dark brown, which is substantially

soluble in carbon disulphide (CS2), possessing adhesive and water-proofing qualities.It consists essentially of hydrocarbons and would typically comprise at least 80% carbon and15% hydrogen, the remainder being oxygen, sulphur, nitrogen and traces of various metals.

Asphalt is a word with different meanings. In American usage asphalt, or, in full, asphaltcement, is used to mean bitumen (or bitumen binder). In the term 'rock asphalt' it defines amineral substance that may be impregnated with bitumen or pitch. Outside America the word

asphalt means a mixture of bitumen and mineral aggregates laid as a road surface.

Sources

Bitumen does occur naturally, but for all intents and purposes itis petroleum on which theworld relies for its supplies of bitumen today. The bitumen content of crude can vary between

15% and 80%, but the more normal range is 25% to 40%. In fact the three broad

classifications for crude oils are:

bitumen based

paraffin based

bitumen and paraffin based

Depending on the type of crude, bitumen is present either in the form of colloidally dispersed

particles or in a true solution. During the refining process, as petroleum oils are taken away bydistillation, the proportion of oil to bitumen particles changes. Instead of being dispersed andrelatively few in number, the particles become closer to one another and the size of the

particles increases. At the point when the distillation process is usually stopped, thepetroleum bitumen is a colloidial dispersion of black solids (hydrocarbons), known asasphaltenes, in a dispersion medium, which is an oily brown yellow liquid known as malthene

fraction. Also present to act as a stabilizing agent to keep the asphaltenes in suspension areanother group of hydrocarbons known as resins.Bitumen is found in nature in several forms, from the hard, easily crumbled bitumen in rock

asphalt to the softer, more viscous material found in tar sands and asphalt 'lakes'. It iscommonly mixed with varying proportions of mineral or vegetable impurities that need to beextracted before it can be used effectively as an engineering material. However it may be

found as an asphaltite, a natural bitumen without impurities that varies in the extent to which itis soluble in carbon disulphide. Natural bitumen occurs, as does petroleum, as the result ofthe special decomposition of marine debris. It will have been moved over many thousands of

years through porous rocks such as limestone or sandstone, often by volcanic action. In someareas notable for their petroleum resources, for example the Middle East, semi-fluid bitumencan be found oozing out of fissures near hot springs or seeping out of the ground.

Rock asphalt, with its variable and relatively low content of bitumen, tends to be found away

from the places where bitumen is needed. It is costly to move around and to process.

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It is important to draw the distinction between bitumen and coal tar. The latter is obtained fromthe carbonisation of coal and, although it is black and viscous in appearance, it has very

different chemical properties.Engineering projects in every part of the world, from the construction of transcontinentalhighways to the waterproofing of flat roof surfaces, rely on the particular properties of

bitumen. Crude oil processed by the petroleum industry provides all but a small percentage of

this vital material.

Properties

Bitumen's main property is that of a very strong and durable adhesive that binds together a

very wide variety of other materials without affecting their properties. Its durability is essentialto major engineering projects such as roads and waterways where it must do its job for 20years or more.

Bitumen is insoluble in water but is soluble in numerous organic solvents. As it is highlywaterproof, it can act as an effective sealant. It also resists action by most acids, alkalis andsalts. It does not contaminate water so it can be used to line watercourses.

It is a thermoplastic material: it softens and becomes liquid with the application of heat andhardens as it cools.Bitumen can be spread relatively easily in the areas where it is required because it can readily

be liquefied by one of three methods:

applying beat

dissolving it in petroleum solvents dispersing with water (emulsification).

Bitumen gives controlled flexibility to mixtures of mineral aggregates which is why so much ofthe total annual production is used in road building. It is available at an economic cost virtually

all over the world.

Types of Bitumen

There are five major classifications of petroleum bitumen produced by the refining andmanufacturing process:

Paving grade bitumen (or asphalt cement in American usage) is refined and blended tomeet road engineering and industrial specifications that take into account different climaticconditions. As a product it is the most widely used bitumen. It may also be considered as the

parent bitumen from which the other types, listed below, are produced.Cutback bitumensconsist basically of bitumen that has been diluted in order to make it morefluid for application, mainly in road making. Their fluidity depends on the degree of hardness

of the bitumen base and the proportion of diluent (or flux) to bitumen. They are classifiedaccording to the time it takes them to become solid, as rapid curing (RC), medium curing(MC) or slow curing (SC) cutbacks. The cutback varies according to the flux, white spirit

commonly being used for RC grades, kerosene for MC and diesel for SC. They set as the fluxevaporates. This evaporation is currently regarded as a potentially undesirable characteristicfrom the point of view of the environment and health and safety, so cutback bitumens are

looked upon less favourably than the more modem bitumen emulsions.Inbitumen emulsionsthe basic bitumen has also been diluted in order to facilitateapplication. Hot bitumen, water and emulsifier are processed in a high-speed colloid mill that

disperses the bitumen in the water in the form of globules that are normally in the 5-10micrometre size range but may be even smaller. The emulsifier produces a system in whichfine droplets of bitumen, of between 30% and 80% of the volume, are held in suspension. if

they separate in storage, the emulsion can easily be restored by agitation.

Bitumen emulsions have a low viscosity and can be workable at ambient temperatures, whichmakes them ideal for use in roadbuilding. This application requires controlled breaking and

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setting. The emulsion must not break before it is laid on the road surface but, once in place, itshould break quickly so that the road can be in service again without delay.

Particles of bitumenare dispersed inwater to make

bitumen emulsions

are usually between 5and 10 micrometres

in size. This diagramgives an indication ofrelative size

The mechanical performance of bitumen emulsions can be tailored like that of otherconstruction materials.Bitumen emulsions are divided into three categories:

Anionic with negatively charged globules

Cationic with positively charged globules Non-ionic with neutral globules.

The main grades for bitumen emulsions are classified as follows:

Anionic Cationic

ARS CRS Rapid setting

AMS CMS Medium setting

ASS CSS Slow setting

The development of bitumen emulsions is an area where technological progress is still being

made to meet engineering demands. The first emulsions were the anionics. They arecurrently less favoured than the cationics because the positively charged globules of bitumencoat the aggregates more thoroughly and have greater adhesion. Use of cationic emulsions is

therefore increasing.Industrial bitumen(or oxidized bitumens) are made by blowing air through hot paving gradebitumen. The result is a product that softens at a higher temperature than that at which paving

grade bitumen softens. It also has more rubberlike properties and its viscosity is much lessaffected by changes in temperature than is the case with paving grade bitumen.Modified bitumensare formulated with additives to improve their service performance by

changing such properties as their durability, resistance to ageing, elasticity and/or plasticity.As well as natural rubbers, polymers such as styrene butadiene styrene (SBS), thermoplasticrubbers and ethylene vinyl acetate (EVA) are commonly used to modify bitumen and some

companies, including BP, have their own proprietary technology using special polymers orpolymer blends.This is an exciting development of growing importance due to the ability of modem technology

to satisfy the demands of the bitumen market internationally. For example, polymers thatextend the range of temperatures at which bitumen is worked will enable roadbuilders to workeffectively for more months of the year. A modified bitumen that increases the extent to which

a road 'bounces back' after being subjected to heavy traffic, in terms of weight and volume,

will contribute towards a longer road life and lower maintenance costs.

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Bitumen Handling

The four major factors involved in handling bitumen are:

the high handling temperatures and the need forpurpose-designed vessels

the flammable nature of certain grades

the need to safeguard the health and safety ofpersonnel the training of personnel

Owing to their high viscosity, most bitumens have to be heated to make them sufficiently fluidfor bulk distribution and for application. Contact with bitumen or the equipment involved intransporting, storing or applying it can cause severe skin burns at the recommended handling

temperatures. For example, even a fleeting touch at 80C can be expected to burnunprotected skin.