HIGHWAY ENGG.HIGHWAY ENGG.

Er. Varun Dogra Er. Varun Dogra

TOPIC:-TOPIC:-

ROAD MATERIALROAD MATERIAL

INTRODUCTIONINTRODUCTIONThe various materials used for constructing the road The various materials used for constructing the road

pavement are termed as pavement are termed as “Road Materials”.“Road Materials”. The The different road materials in use such as soil, different road materials in use such as soil, aggregate and binders must be tested as per IRC aggregate and binders must be tested as per IRC specifications before using them in road specifications before using them in road construction. The soil is considered as one of the construction. The soil is considered as one of the principal highway materials used in road principal highway materials used in road construction as they from the major portion of the construction as they from the major portion of the pavement structure. They should be sufficiently pavement structure. They should be sufficiently strong to withstand the stresses due to traffic wheel strong to withstand the stresses due to traffic wheel loads. The bituminous materials like bitumen and loads. The bituminous materials like bitumen and tar or cements are principally used as binder for tar or cements are principally used as binder for road aggregates and as water proofing materials.road aggregates and as water proofing materials.

Different Types of Road MaterialsDifferent Types of Road MaterialsThe different types of road materials used The different types of road materials used

as highway construction can be broadly as highway construction can be broadly classified into following categories:classified into following categories:

SoilSoil AggregatesAggregates BindersBinders

Soil refers to all types of soils used as highway Soil refers to all types of soils used as highway subgrade such as clay, silt, sand, loam, shale etc. subgrade such as clay, silt, sand, loam, shale etc. The common road aggregate used for road The common road aggregate used for road construction are:construction are:

Crushed rock aggregate (Natural stone)Crushed rock aggregate (Natural stone) GravelGravel Sand Sand Moorum Moorum Brick batsBrick bats Kankar Kankar Laterite Blast furnace slagBlast furnace slag Fly ash etc.Fly ash etc.

The principal binders used for making are: Cement Bitumen Tar etc.Cement is used as a binding material for

constructing cement concrete roads whereas bitumen and tar used as binders for construction of bituminous roads or black topped roads.

Some of the miscellaneous materials like brick, wood, rubber, metal, glass etc. may also be used for road construction.

SOILSA soil may be defined as “the top layer of ground consisting of a mixture of earthy materials with particles varying in size, shape, structure and chemical composition.” All road structure are supported by soils.

“The science about soils dealing origin and formation of soils, soil properties, soil classification and identification, soil tests and soil surveys etc. required for road construction is termed as Road Soil Engineering”.

““Highway Engineering soil studies is now a days Highway Engineering soil studies is now a days picking up pace because total failure of the picking up pace because total failure of the roads in majority of the cases have revealed roads in majority of the cases have revealed after investigation that the failure was mainly after investigation that the failure was mainly due to the faulty subgrade rather than the due to the faulty subgrade rather than the pavement.pavement.

The common most soils used in highway The common most soils used in highway construction are:construction are:

ClayClay SiltSilt SandSand Loam ( Mixture of Sand, Silt and Clay)Loam ( Mixture of Sand, Silt and Clay) Marl (Earthy mixture of minerals like quartz, Marl (Earthy mixture of minerals like quartz,

calcite etc.)calcite etc.) Shale (Compressed and laminated clay) etcShale (Compressed and laminated clay) etc.

Soils of poor bearing capacity like Black cotton Soils of poor bearing capacity like Black cotton soils, peat etc. may also be used after soil soils, peat etc. may also be used after soil stabilization. The ideals surface of an earth stabilization. The ideals surface of an earth road should consists of following:road should consists of following:

a)a) Clay, 10 – 20 %Clay, 10 – 20 %b)b) Silt, 5 – 15 %Silt, 5 – 15 %c)c) Sand, 65 – 75 %Sand, 65 – 75 %

Subgrade SoilSubgrade Soil

““The well compacted soil which acts as a base to The well compacted soil which acts as a base to support the road pavement from beneath and support the road pavement from beneath and forms one integral part of the road structure is forms one integral part of the road structure is termed as Subgrade soil.” The design of a termed as Subgrade soil.” The design of a successful road pavement depends upon the successful road pavement depends upon the subgrade upon which it is to rest. No base course subgrade upon which it is to rest. No base course or wearing course can last long unless it is or wearing course can last long unless it is supported by a well prepared subgrade. This is so supported by a well prepared subgrade. This is so because soil is a highly variable material and as because soil is a highly variable material and as such subgrade will vary considerably. The mostsuch subgrade will vary considerably. The most

desirable properties which an ideal subgrade desirable properties which an ideal subgrade should possess are:should possess are:

i.i. Strength and stabilityStrength and stabilityii.ii. Drainage andDrainage andiii.iii. Ease of compaction. Furthermore it should be Ease of compaction. Furthermore it should be

incompressible and resistant to weathering incompressible and resistant to weathering action and shall possess non swelling action and shall possess non swelling characteristics.characteristics.

Cross-section of road showing soil subgrade in Cross-section of road showing soil subgrade in cutting (a) and embankment (b)cutting (a) and embankment (b)

Function of Soil as a Highway SubgradeFunction of Soil as a Highway Subgrade1.1. To provide adequate support to the road To provide adequate support to the road

pavement.pavement.2.2. To distribute all the wheel loads coming on to the To distribute all the wheel loads coming on to the

road pavements to a larger area beneath the soil.road pavements to a larger area beneath the soil.3.3. To prevent the sub soil water from entering the To prevent the sub soil water from entering the

road pavement by capillary action i.e. the road pavement by capillary action i.e. the subgrade should consist of self draining material.subgrade should consist of self draining material.

4.4. To prevent formation of waves, corrugation, ruts, To prevent formation of waves, corrugation, ruts, pot-holes, cracks etc. in black top pavements by pot-holes, cracks etc. in black top pavements by remaining intact and stable under adverse climatic remaining intact and stable under adverse climatic and loading conditions.and loading conditions.

ROAD AGGREGATESROAD AGGREGATESThe materials, natural or artificial used for the The materials, natural or artificial used for the

construction of road pavement above the construction of road pavement above the prepared subgrade are termed as road prepared subgrade are termed as road aggregates.aggregates.

The main functions of road aggregates are:i. To bear stresses due to wheel loads.ii. To resist the abrasive action of traffic.

The road aggregate can be classified into:The road aggregate can be classified into: 1) Natural aggregates2) Artificial aggregatesThe aggregates obtained from the natural rocks

are termed as natural aggregates. The common natural aggregates used for road construction are:

a. Crushed rock aggregateb. Gravel andc. Sand

The aggregates artificially prepared or various by products of industrial plants used for road construction are termed as artificial aggregates. The important artificial aggregates used for road construction are:

a) Brick aggregates (crushed bricks)b) Blast furnace slag (byproduct of steel

plant)c) Fly ash (residue of thermal plant)

Requirements of a Good Road Aggregate (As Per IRC Specification)As per IRC specifications a good road aggregate

should have following properties:1. It should be sufficiently hard to resist rubbing

action (Abrasion) due to moving wheel loads.2. It should be quiet tough to resist any type of

fracture against hammering impact of moving vehicles.

3. It should be sufficiently strong to ensure safety against crushing i.e. it should be able to withstand high stresses due to wheel loads.

4.4. It should be sound and durable to resist It should be sound and durable to resist disintegration due to weathering agencies.disintegration due to weathering agencies.

5.5. It should have good cementatious property It should have good cementatious property i.e. good binding ability to grip together i.e. good binding ability to grip together rough broken stones by forming own rough broken stones by forming own binding material and thus imparting binding material and thus imparting resistance to displacement.resistance to displacement.

6.6. It should have good adhesive property also It should have good adhesive property also i.e. binding ability with common binders i.e. binding ability with common binders like bitumen and tar.like bitumen and tar.

7.7. It should have poor affinity with water i.e. It should have poor affinity with water i.e. it should absorb less water.it should absorb less water.

8.8. It should have high specific gravity. The It should have high specific gravity. The specific gravity of rocks generally vary specific gravity of rocks generally vary from 2.6 to 2.9.from 2.6 to 2.9.

Shape of AggregatesShape of AggregatesRoad aggregates may be of different shapes Road aggregates may be of different shapes

such as rounded, semi rounded, cubical, such as rounded, semi rounded, cubical, angular, flaky or elongated. Shape of an angular, flaky or elongated. Shape of an aggregate plays an important role in its aggregate plays an important role in its selection as a good road aggregate in road selection as a good road aggregate in road construction. Flaky and elongated construction. Flaky and elongated particles have generally less strength and particles have generally less strength and durability as compared to rounded and durability as compared to rounded and cubical particles of same stone. Such cubical particles of same stone. Such particles or stones should be avoided as particles or stones should be avoided as far as possible.far as possible. Rounded aggregates are

preferred in cement concrete roads as they preferred in cement concrete roads as they possess low specific surface area (requiring possess low specific surface area (requiring less cement) and higher workability. less cement) and higher workability. However in WBM roads and bituminous However in WBM roads and bituminous construction, angular aggregates are construction, angular aggregates are preferred to rounded aggregates due to high preferred to rounded aggregates due to high degree of inter locking with each other. The degree of inter locking with each other. The particle shape is determined by the particle shape is determined by the percentages of flaky and elongated particles percentages of flaky and elongated particles contained in it and by determining its contained in it and by determining its angularity. The evaluation of shape of road angularity. The evaluation of shape of road aggregates is made in terms of flakiness aggregates is made in terms of flakiness index and angularity number.index and angularity number.

BINDERS The materials used in road construction for

binding together the road aggregates and providing a smooth and impermeable surface for movement of vehicular traffic is called Binders.

The common binders used in road construction are:

Cement Bitumen Tar

Cement mortar or cement slurry is used as a binder in cement bound macadam roads. However cement is used as a main ingredient in construction of cement concrete roads.

Bitumen and Tar are the most commonly used bituminous binders in road pavement construction. Such roads are also termed as black top roads or bituminous roads. In road engineering, the term ‘binder’ significantly refers to bituminous materials only.

Function of BindersFunction of BindersThe various objectives achieved by binders in The various objectives achieved by binders in

road construction are:road construction are:

1. It acts as a cushion for the road surface and absorbs the kneading and abrasive action of wheel loads.

2. It makes the road surface impermeable i.e. it seals the surface against ingress of water.

3.3. It acts as a binding agent i.e. it binds the It acts as a binding agent i.e. it binds the surface particles together, thus checking surface particles together, thus checking any loss of particles from the surface by any loss of particles from the surface by suction under the action of moving loads.suction under the action of moving loads.

4.4. It makes the road pavement durable i.e. it It makes the road pavement durable i.e. it resists the action of weathering agencies resists the action of weathering agencies like Wind and Sun. In short, it ensures like Wind and Sun. In short, it ensures long life for the road pavement.long life for the road pavement.

BITUMENBITUMENA non-crystalline hydrocarbon compound in a solid A non-crystalline hydrocarbon compound in a solid

or viscous state having adhesive properties and or viscous state having adhesive properties and derived from crude petroleum either by natural derived from crude petroleum either by natural or artificial distillation is termed as Bitumen. It or artificial distillation is termed as Bitumen. It is completely soluble in carbon disulphide is completely soluble in carbon disulphide (CS(CS22). The properties of bitumen depend upon ). The properties of bitumen depend upon its source and the method of preparation.its source and the method of preparation.

Important properties of Bitumen: Following are Important properties of Bitumen: Following are some of the most important properties of some of the most important properties of Bitumen:Bitumen:

1.1. It is a mixture of hydrocarbons and is black or It is a mixture of hydrocarbons and is black or brown in colour.brown in colour.

2.2. It is an important byproduct of fractional It is an important byproduct of fractional distillation of cube petroleum.distillation of cube petroleum.

3.3. It is a viscous fluid or semisolid and melts It is a viscous fluid or semisolid and melts when heated.when heated.

4.4. It is an important binder used for binding road It is an important binder used for binding road aggregates due to its adhesive nature and aggregates due to its adhesive nature and water proofing properties.water proofing properties.

5.5. It can be produced in a variety of grades with It can be produced in a variety of grades with varying softness and volatility to suit varying softness and volatility to suit particular requirement of various types of particular requirement of various types of roads.roads.

6.6. It is completely soluble in carbon disulphide It is completely soluble in carbon disulphide (CS(CS22) and carbon tetra chloride.) and carbon tetra chloride.

Chart showing fractional distillation in Chart showing fractional distillation in manufacturing bitumen or asphaltmanufacturing bitumen or asphalt

Grades of Bitumen: Grades of Bitumen: There are generally two grades of Bitumen:There are generally two grades of Bitumen:1.1. Paving grades (used for road construction Paving grades (used for road construction

work).work).2.2. Industrial grades (used for water proofing Industrial grades (used for water proofing

work).work).

The paving grades available in India for highway The paving grades available in India for highway construction are two types:construction are two types:

1.1. ‘‘A’A’ – type – type2.2. ‘‘S’S’ – type – type

Cross-section of petroleum deposits showing Cross-section of petroleum deposits showing oil tapping oil tapping

(Bitumen is obtained from this crude petroleum)(Bitumen is obtained from this crude petroleum)

‘‘A’A’ type denotes paving bitumen obtained from Assam type denotes paving bitumen obtained from Assam petroleum. These grades of bitumen are generally petroleum. These grades of bitumen are generally designated as A35, A65, A90, A 200 etc.designated as A35, A65, A90, A 200 etc.

‘‘S’S’ type denotes paving bitumen obtained from other type denotes paving bitumen obtained from other sources. These grades of bitumen are designated sources. These grades of bitumen are designated as S35, S65, S90, S200 etc.as S35, S65, S90, S200 etc.

Desirable properties of Bitumen for road construction

1. Adequate viscosity and fluidity for easy and efficient spraying.

2. Unsusceptible to temperature variations.3. Durability.4. Adequate affinity and adhesion with road

aggregates.

TARTARTar is a viscousTar is a viscous liquid, jet black in colour obtained

as a residual product after destructive distillation of coal or wood in the absence of air.

Based on the natural organic matter from which tar is obtained as a by product, it is referred to as wood tar or coal tar accordingly.

Coal tar is more popular and widely used for making roads and is also referred as ‘road tar’. The other important types of tar are wood tar, peat tar, bone tar and water gas tar. Except water gas tar, other types are not considered suitable for road paving.

Properties of Road Tar:Properties of Road Tar:Following are the properties of Road Tar:Following are the properties of Road Tar:1.1. Tar is a temperature susceptible product Tar is a temperature susceptible product

resulting in great variation in viscosity with resulting in great variation in viscosity with change in temperature.change in temperature.

2.2. It is not soluble in carbon disulphide and It is not soluble in carbon disulphide and carbon tetra chlohide but is soluble only in carbon tetra chlohide but is soluble only in toluene.toluene.

3.3. It has a great content of free carbon and is It has a great content of free carbon and is readily distinguished by its typical odour readily distinguished by its typical odour (smell).(smell).

4.4. It is more resistant to disintegrating action of It is more resistant to disintegrating action of

water. So it is more suitable to be used below water. So it is more suitable to be used below ground level as a water proofing material.ground level as a water proofing material.

5.5. Its weather resistant ability is inferior. Its weather resistant ability is inferior.

6.6. It is more volatile and hardens rapidly when It is more volatile and hardens rapidly when exposed to air.exposed to air.

Comparison between Bitumen and Tar

Bitumen Tar

1. It is black or brown in colour obtained by distillation of cube petroleum.

2. It is soluble in carbon disulphide and in carbon tetrachloride.

1. It is also black or brown in colour but produced by destructive distillation of coal or wood.

2. It is soluble in only toluene.

Bitumen Tar

3. It has good weather resisting property.

4. It is less temperature susceptible.

5. The free carbon content is less as compared to tar.

6. Due to high viscosity, it cannot be tested is orifice viscometer.

3. Its weather resisting ability is inferior to bitumen.

4. It is more temperature susceptible resulting in great variation in viscosity of product with temperature.

5. The free carbon content is more and is detected by solubility test.

6. Tars and cutbacks are generally tested in orifice viscometers for viscosity test.

ASPHALTASPHALTThe terms The terms ‘Bitumen’‘Bitumen’ and and ‘Asphalt’‘Asphalt’ are often are often

confused. The actually refer to the same confused. The actually refer to the same material. The word ‘Bitumen’ covers both tar material. The word ‘Bitumen’ covers both tar and asphalt, but conventionally, bitumen stands and asphalt, but conventionally, bitumen stands for asphalt. Asphalt is more used in road for asphalt. Asphalt is more used in road construction than the tar.construction than the tar.

Definition:Definition: Bitumen containing some inert Bitumen containing some inert material or mineral substances is referred to as material or mineral substances is referred to as ‘Asphalt’.‘Asphalt’.

It is of two types:It is of two types:1.1. Rock AsphaltRock Asphalt2.2. Natural or lake AsphaltNatural or lake Asphalt

Rock asphaltRock asphalt is a bituminous lime stone used is a bituminous lime stone used for road pavements. It contains 70% to for road pavements. It contains 70% to 90% of limestone and 10 to 20% of 90% of limestone and 10 to 20% of bitumen.bitumen.

The natural asphaltThe natural asphalt found in lakes and found in lakes and containing 40% to 70% of bitumen and containing 40% to 70% of bitumen and about 30% of water, lime, clay and sand is about 30% of water, lime, clay and sand is termed as lake asphalt. Refined lake termed as lake asphalt. Refined lake asphalt separated by application of heat is asphalt separated by application of heat is the best material used for road making.the best material used for road making.

CUTBACK AND EMULSIONSCUTBACK AND EMULSIONSCutbacks:Cutbacks: The solution of bitumen or asphalt The solution of bitumen or asphalt

in a volatile solvent like kerosene, spirit, in a volatile solvent like kerosene, spirit, creosote etc. to reduce the consistency is creosote etc. to reduce the consistency is termed as a Cutback. It contains 80% termed as a Cutback. It contains 80% bitumen and 20% solvent (or dilutant). A bitumen and 20% solvent (or dilutant). A ‘cut’ actually refers to a volatile liquid, ‘cut’ actually refers to a volatile liquid, which is distilled off in a oil refinery.which is distilled off in a oil refinery.

To prepare a ‘cutback’, the distilled ‘cut’ is To prepare a ‘cutback’, the distilled ‘cut’ is put ‘back’ into its residue and hence the put ‘back’ into its residue and hence the name ‘cutback’ is used.name ‘cutback’ is used.

Function of cutbackFunction of cutback: A cutback has : A cutback has following functions:following functions:

1.1. To soften the heavy or solid bituminous To soften the heavy or solid bituminous material and convert it into a liquid form.material and convert it into a liquid form.

2.2. To apply it easily over road aggregates To apply it easily over road aggregates without heating or using minimum without heating or using minimum heating.heating.

3.3. It can be used for all types of bituminous It can be used for all types of bituminous roads.roads.

4.4. It modifies and improves the properties of It modifies and improves the properties of residual product in refineries which has residual product in refineries which has otherwise little commercial value.otherwise little commercial value.

Emulsions:Emulsions: A liquid material in which a A liquid material in which a substantial amount of bitumen (or tar or substantial amount of bitumen (or tar or asphalt) is suspended in a finely divided state asphalt) is suspended in a finely divided state in an aqueous medium and stabilized by in an aqueous medium and stabilized by means of suitable emulsifier or stabilizer is means of suitable emulsifier or stabilizer is termed as bitumen emulsion or road termed as bitumen emulsion or road emulsion.emulsion.

It may also be defined as “A two phase system or It may also be defined as “A two phase system or a mixture consisting of two immiscible a mixture consisting of two immiscible liquids, the one dispersed in the other in the liquids, the one dispersed in the other in the form of fine globules or droplets.”form of fine globules or droplets.”

Initially, bitumen or asphalt is broken up into fine Initially, bitumen or asphalt is broken up into fine globules (of size about 3 microns i.e. 0.003 globules (of size about 3 microns i.e. 0.003 mm) and dispersed in water. A small amount mm) and dispersed in water. A small amount of emulsifier or emulsifying agent is added of emulsifier or emulsifying agent is added (nearly 1 percent) to facilitate the formation of (nearly 1 percent) to facilitate the formation of a stable emulsion and to keep the globules of a stable emulsion and to keep the globules of dispersed bitumen in suspension. The common dispersed bitumen in suspension. The common emulsifiers used are soaps, resinous emulsifiers used are soaps, resinous substances, colloidal powders etc. Emulsion substances, colloidal powders etc. Emulsion contains 50 to 60% of bitumen by weight and contains 50 to 60% of bitumen by weight and the remaining portion is water. When emulsion the remaining portion is water. When emulsion is applied on the road, it breaks down and the is applied on the road, it breaks down and the binder globules start binding the road binder globules start binding the road aggregates but full binding power develops aggregates but full binding power develops only after evaporation of water.only after evaporation of water.

Function of Emulsion:Function of Emulsion: Following are the important function, which an Following are the important function, which an

emulsion performs:emulsion performs:1.1. It can be applied easily at normal It can be applied easily at normal

temperature without heating.temperature without heating.2.2. It is very suitable for coating over damp It is very suitable for coating over damp

surfaces or in wet weather conditions.surfaces or in wet weather conditions.3.3. It is ideally used for maintenance and patch It is ideally used for maintenance and patch

repair work of bituminous roads.repair work of bituminous roads.4.4. It can also be used for stabilization of soils.It can also be used for stabilization of soils.

References:-References:-

Highway Engg. by Jagroop Singh.Highway Engg. by Jagroop Singh. Internet. Internet.