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Bitumen & Asphalt

- Nilanjan Mitra

A black or dark brown nonA black or dark brown non--crystalline solid or viscous material, crystalline solid or viscous material, composed principally of high molecular weight hydrocarbons, composed principally of high molecular weight hydrocarbons, having adhesive properties, derived from petroleum either having adhesive properties, derived from petroleum either by natural by natural or refinery processes and substantially soluble in carbon or refinery processes and substantially soluble in carbon disulphide.disulphide.

Basic Refining ProcessBasic Refining ProcessAsphalt is simply the residue left over from petroleum Asphalt is simply the residue left over from petroleum refining.refining.Crude oil is heated in a large furnace to about 340Crude oil is heated in a large furnace to about 340°° C (650C (650°° F) F) and partially vaporized.and partially vaporized. It is then fed into a distillation tower It is then fed into a distillation tower where the lighter components vaporize and are drawn off for where the lighter components vaporize and are drawn off for further processing.further processing.The residue from this process (the asphalt) is usually fed into The residue from this process (the asphalt) is usually fed into a vacuum distillation unit a vacuum distillation unit where heavier gas oils are drawn heavier gas oils are drawn off.off. Bitumen grade is controlled by the amount of heavy gas Bitumen grade is controlled by the amount of heavy gas oil remaining.oil remaining. Other techniques can then extract additional Other techniques can then extract additional oils from the asphalt.oils from the asphalt.

••Depending upon the exact process and the crude oil source, Depending upon the exact process and the crude oil source, different different bitumensbitumens of different properties can be produced.of different properties can be produced.Additional desirable properties can be obtained by blending crudAdditional desirable properties can be obtained by blending crude oils before e oils before distillation or bitumen after distillation.distillation or bitumen after distillation.

REFINERY OPERATIONREFINERY OPERATION

•• Bitumen used in road Bitumen used in road pavementspavements

Bitumen as roofing agentBitumen as roofing agent

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Bitumen constituents and general properties

Carbon : 82Carbon : 82--88 %88 %Hydrogen : 8Hydrogen : 8--11 %11 %SulphurSulphur : 0: 0--6 %6 %Oxygen : 0Oxygen : 0--1.5 %1.5 %Nitrogen : 0Nitrogen : 0--1 %1 % Colloidal,

no specific melting, boiling or freezing point, insoluble in water, hydrophobic,chemically inert, oxidise slowly

BITUMEN• Bitumen is a black, oily,

viscous material that is a naturally-occurring organic byproduct of decomposed organic materials.

• It is sticky,thick,Tar like form of petroleum derived from polycyclic aeromatichydrocarbonGeneral uses of Bitumen:

•Constructions of roads, runways and platforms.•Water proofing to prevent water seepage.•Mastic floorings for factories and go‐downs.•Canal lining to prevent erosion.•Dump‐proof courses for masonry.

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Bitumen plays a vital role in road construction typically as binder.

Application condition requires bitumen to behave as mobile liquid.There are three ways to reduce its viscosity:•Heat it•Dissolve it in solvents•Emulsify it.In heating it involves some: •Energetic •Environmental and •Health problemsAs process is inefficient and involvesLoss of heat and even fumes causing air pollution

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In case using solvents:We make use of volatile dilatants like kerosene petroleum which adds to its cost     

although viscosity get reduced as it is uneconomical.

Test: penetration test for the Test: penetration test for the grade of bitumengrade of bitumen

80/100, 100/120, or 60/7080/100, 100/120, or 60/70

Grades > 40 used in roadconstruction

Test : ring and ball softening Test : ring and ball softening point testpoint test

It is the temperature at which It is the temperature at which bitumen changes its state from bitumen changes its state from semi solid to semi liquidsemi solid to semi liquid

Suitability of its applicability in different areas

Ductility : It is the distance at which the film formed when a standard sampIt is the distance at which the film formed when a standard sample of le of bitumen in a briquette mould trenched at the constant rate of pubitumen in a briquette mould trenched at the constant rate of pulling, breaks.lling, breaks.

Viscosity : resistance to flow or inverse of fluidityresistance to flow or inverse of fluidity

Flash point : Temp at which bitumen catches fire momentarilyTemp at which bitumen catches fire momentarily

Fire point : Temp at which bitumen completely burnsTemp at which bitumen completely burns

Durability : refers to longrefers to long--term resistance to oxidative hardening of material in fieldterm resistance to oxidative hardening of material in field

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Bitumen Classifications

Native Bitumen : distillation of crude oil, produced in different viscosity grades

Cutback Bitumen : bitumen whose viscosity has been reduced with suitable volatile dilutant usually a petroleum distillate like gasoline, kerosene, etc.

Fluid binder which can be handled at air temp.Can be mixed with aggregate in cold conditionRapid curing – naptha/gasoline; high volatility; tack coats/surface treatmentMedium curing – kerosene; moderate; stockpile patching mixSlow curing – diesel fuel; low; prime coat, dust control.

Bitumen Emulsions : liquid product in which a substantial amount of bitumen is dispersed as finely divided droplets in an aqueous medium containing an emulsifier and a stabilizer.

Cationic Emulsion – +ive charge, adhere to –ive charge particles like silica, acid nature, used with wet aggregates and in cold weather.

Anionic Emulsion – -ive charge, adhere to +ive charge particles like limestone, alkaline nature

Modified Binder : Bituminous product which are more stable under heavy loads, braking,accelerating loads, shows increased resistance to permanent deformation in hot weather, resistsfatigue load and shows better adhesion between aggregate and binders

Types of Modifiers :SulphurNatural RubberCrumb Rubber from discarded tyresStyrene-butadiene-Styrene (SBS)Ethylene vinyl acetate (EVA), polypropylene,etc

Advantages of modified bitumen:

Lower susceptibility to daily seasonal temperature variationsHigher resistance to deformation at elevated pavement temperatureBetter ageing resistance propertiesHigher fatigue life of mixesBetter adhesion between aggregates and binder, especially under exposure to waterPreventing cracking and reflective crackingOverall improved performance in extreme climatic conditions and under heavy traffic conditions.

Some other types of Bitumen:Blown Bitumen, Warm Asphalt, Foamed bitumen …..

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What are emulsions?

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Types of emulsions:

(a) O/W emulsion, (b) W/O emulsion, (c) multiple W/O/W.

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Bitumen Emulsion is a 2‐phase system consisting of •Bitumen•Water•Other Additives  

•The bitumen is dispersed throughout the water phase in form of discrete globules, heldin suspension by electrostatic charges stabilized by emulsifier

•The Emulsion contains 40-75% of bitumen,.1-2.5%emulsifier,25-60%water and other ingredients•Typically of .1 – 50 µm in diameter.•It is mainly dark brown in color after breaking changes to black.

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Primary objective is to use for road surfacing without much heating.• As main advantages this improves the handling of bitumen at room

temperature.• Promotes surface interactions .• Its mixture with the aggregate attains full strength.• Economical and saves energy .• Reduced atmosphere pollution. • Water can also added before use to dilute as per requirement.• Rains can not effect it at the time of use and after use.

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WHY BITUMEN EMULSIONS ?

Types:Bitumen emulsions can be divided into four

classes:1)Cationic emulsions.2)Anionic emulsions.3)Non-ionic emulsions.4)Clay-stabilized emulsions.

The first two are most widely used 23

Cationic emulsions• If an electric potential is supplied between

two electrodes immersed in an emulsion containing positively charged particles of bitumen, they will migrate to the cathode.

• This emulsion is said to be cationic.

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Anionic emulsions• If an electric potential is supplied between

two electrodes immersed in an emulsion containing negatively charged particles of bitumen, they will migrate to the anode.

• This emulsion is said to be anionic.

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Non-ionic emulsions• If the bitumen particles in the emulsion are

neutral, then they will not migrate to any of the pole.

• These type of emulsions are NON-IONIC.• Mainly used in road ways.

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Clay-stabilized emulsions• These are mainly used for industrial

applications.• In these materials, emulsifiers are fine

powders, often natural or processed clays and bentonites.

• Particle size is very much less when compared with the bitumen particles in emulsions.

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Manufacture of Bitumen emulsions• Bitumen emulsions can be manufactured

using batch process or continuous process.

• Bitumen emulsions are made in continuous inline processes involving dispersing technologies like rotor stators, colloidal mills and static mixers.

• High shearing forces are required for producing emulsions.

• Colloidal mills contain high speed rotors. 29

Manufacturing conditions• The speed of rotors is in the range of

1000-6000 revs/min.

• Bitumen is generally heated to temperature of 100-140 degree celsius.

• The viscosity of the bitumen is kept less than 2 poise.

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Figure 2. Schematic diagram of a bitumen emulsion plant

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• As an alternative to colloid mill, a static mixer can be used.

• This contains no moving parts.

• The high shear necessary to produce an emulsion is generated by pumping the input materials at high speed.

Role of Emulsifiers in Bitumen Emulsion• An emulsifier is a substance which stabilizes an emulsion by

increasing its kinetic stability.

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In order to be effective, it must be water soluble and have a balance between hydrophilic & litho phobic properties.In emulsion, the ionic portion of emulsifier is located at surface of the bitumen droplet   by hydrocarbon chain.The ionic portion of the emulsifier imparts a charge to the droplets themselves and counter‐ions diffuse into the water.As the concentration of the emulsifier increases, the particle size of the emulsion is reduced.

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•In Simple emulsifier(                 ) ‘R’ represents the Hydrophobic (Lithophilic)portion of emulsifier•Usually long chain hydrocarbon consisting of 8 to 22 carbon atoms.•The Hydrophilic can consist of amines , sulphonates , ether, alcohols.

−+− ClNHR 3

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• It performs various functions within bitumen emulsion.1. Makes emulsification easier by reducing the interfacial tension

between bitumen and water.2. Stabilize the emulsion by preventing coalescence of droplets.3. Dictates its performance characteristics such as setting and

adhesion .4. Emulsifier also decreases rate of flocullation.

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Emulsifier functions Types of Emulsifier:1. Anionic2. Cationic3. Non-ionic

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Defined on basis of polar bonds

• Cationic emulsifier-Electrovalent and Polar head group is positively charged & imparts positively charged to the surface of the bitumen droplets.

• It is prepared by dissolving hydrocarbon amines in acids

E.g.39

−

−+− ClNHR 3

• Anionic emulsifier-Electrovalent and Polar head group is negatively charged & imparts negatively charged to the surface of the bitumen droplets.

• It is produced by dissolving fatty acids in sodium hydroxides.

• E.g.40

+−− NaCOOR

HOCHCHCOOR X)( 22−

• Non ionic –The hydrophilic head group is covalent , polar and dissolves without ionization.

Note-There are products with amphoterichead group character which may adopt positive or negative charges depending on pH

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Properties of bitumen emulsionIt is stable under transportation ,storage &application

condition.

But it may break soon after application.It may have low viscosityIt may flow due to irregular spraying but not due to road

irregularities

Important properties of Bitumen emulsion:1. Stability2.Viscosity3. Breaking4. Adhesivity

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Emulsion stability

• This property indicates the resistance ability to change properties over time. As stability is very important in storage ,transport & use.

• Stable emulsion will change over time slowly.• Reason for instability can be physical or chemical

process.• As emulsion is a example of colloidal system in non

equilibrium state. If system reaches to equilibrium Emulsion will go through several process like flocculation, sedimentation, and coalescence leading to instability of emulsion

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Fig: Schematic view of some of destabilizing processes

Emulsion Viscosity

• The viscosity of the bitumen emulsion is important for pumping and transportation.

• In some applications, for example surface dressing, bitumen emulsion is sprayed on the road. In this case the viscosity is critical. As It should be low enough to permit even spraying but at the same time high enough to prevent run-off, once it is sprayed on the road.

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Emulsion breaking

Bituminous emulsions are designed to “break” deliberately in contact with moist aggregates, releasing a binder film on and between the mineral aggregates.

There can be two kind of breaking:1.Breaking of anionic bitumen emulsions2.Breaking of cationic bitumen emulsions

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Emulsion adhesivity

• The physical-chemical adsorption of bitumen and surfactant onto the mineral surface is governed by Vander Waals attraction forces, electrostatic forces or covalent and electrovalent bindings, and responsible for the film adhesion.

• To optimize the bitumen adsorption on substrate, surfactant concentration should be slightly lower than the critical micelle concentration (CMC), nevertheless surfactant concentration higher than CMC is necessary to increase the stability of the unstable thermodynamic emulsion. Ionic surfactant can adsorb on slightly charged substrates. Non-ionic surfactants adsorb on mineral surfaces mostly by hydrogen bonding or Vander Waalsattractive forces. The adsorption of surfactant changes the hydrophobic hydrophilic behaviour of the substrate, thus acting on the adhesion of the bitumen. 48

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1- Rapid Setting (RS-1) :

Provides rapid deposition - mainly used for Tack Coat.

2- Rapid Setting (RS-2) :

Provides rapid deposition – mainly used for Tack Coat and Surface Dressing.

3- Medium Setting (MS) :

A versatile grade, Provides Comparatively slower deposition, used for Repair work/surface dressing, Plant or road mixes with coarse aggregates and Penetration macadam.

4- Slow Setting-1 (SS-1) :

Consumes long time to form bituminous film with best penetration on a porous medium, used for Prime coat, Crack sealing and Fog Seal.

5- Slow Setting-2 (SS-2) :

Low in solvents, provides slow deposition of bituminous film, used for plant or road mixes like MSS, SDBC, Slurry Seal and for Prime coat applications.

As per Indian Standard (IS-8887:2004), five grades of Cationic Bitumen Emulsions are available:

The International Standard (ASTM D 2397-05) materials in four grades with sub-grades are available (which differ prominently in their chemicaland setting profiles) as:

1- Rapid Setting Sub-grade : CRS-1 & CRS-22- Medium Setting Sub-grade : CMS-2 & CMS-2h3- Slow Setting Sub-grade : CSS-1 & CSS-1h4- Quick Setting Sub-grade : CQS-1H

IS 7393:1974Uses of Bitumen emulsion

• Crack Filling: To stop entering water in structural layer of pavement Bitumen emulsions preferably containing rubber are used as they are inexpensive and effective.

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Grouting: It is the method of construction or stabilizing of road surfaces and footpath. Emulsion is applied to compacted dry aggregate and due its low viscosity it penetrates through void structure of the aggregate.

• Soil Stabilization: For agricultural land where fresh top soil is susceptible to surface erosion ,bitumen emulsion can be used as binding agent also helps in retaining soil moisture & improving thermal insulation

• Slip layer & concrete curing: Bitumen emulsions are used to create a membrane between layers of concrete to retain strength of upper layer by preventing water seepage into lower layers by avoiding rigid adhesion. Also it is sprayed on top surface to avoid evaporation of water.

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