Efficient road construction materials for longer life of roads

1. HIGHWAY ENGG.HIGHWAY ENGG.
Er. Varun DograEr. Varun Dogra

2. TOPIC:-TOPIC:-
ROAD MATERIALROAD MATERIAL

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

4. Different Types of Road MaterialsDifferent Types of Road Materials
The different types of road materials usedThe different types of road materials used
as highway construction can be broadlyas highway construction can be broadly
classified into following categories:classified into following categories:
 SoilSoil
 AggregatesAggregates
 BindersBinders

5. Soil refers to all types of soils used as highwaySoil 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 roadThe common road aggregate used for road
construction are:construction are:
 Crushed rock aggregate (Natural stone)Crushed rock aggregate (Natural stone)
 GravelGravel
 SandSand
 MoorumMoorum
 Brick batsBrick bats
 KankarKankar
 Laterite
 Blast furnace slagBlast furnace slag
 Fly ash etc.Fly ash etc.

6. 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.

7.  SOILS
A 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”.

8. ““Highway Engineering soil studies is now a daysHighway Engineering soil studies is now a days
picking up pace because total failure of thepicking up pace because total failure of the
roads in majority of the cases have revealedroads in majority of the cases have revealed
after investigation that the failure was mainlyafter investigation that the failure was mainly
due to the faulty subgrade rather than thedue to the faulty subgrade rather than the
pavement.pavement.
The common most soils used in highwayThe 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.

9. Soils of poor bearing capacity like Black cottonSoils of poor bearing capacity like Black cotton
soils, peat etc. may also be used after soilsoils, peat etc. may also be used after soil
stabilization. The ideals surface of an earthstabilization. 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 %

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

11. desirable properties which an ideal subgradedesirable properties which an ideal subgrade
should possess are:should possess are:
i.i. Strength and stabilityStrength and stability
ii.ii. Drainage andDrainage and
iii.iii. Ease of compaction. Furthermore it should beEase of compaction. Furthermore it should be
incompressible and resistant to weatheringincompressible and resistant to weathering
action and shall possess non swellingaction and shall possess non swelling
characteristics.characteristics.

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

13. Function of Soil as a Highway SubgradeFunction of Soil as a Highway Subgrade
1.1. To provide adequate support to the roadTo provide adequate support to the road
pavement.pavement.
2.2. To distribute all the wheel loads coming on to theTo 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 theTo prevent the sub soil water from entering the
road pavement by capillary action i.e. theroad 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 bypot-holes, cracks etc. in black top pavements by
remaining intact and stable under adverse climaticremaining intact and stable under adverse climatic
and loading conditions.and loading conditions.

14.  ROAD AGGREGATESROAD AGGREGATES
The materials, natural or artificial used for theThe materials, natural or artificial used for the
construction of road pavement above theconstruction of road pavement above the
prepared subgrade are termed as roadprepared 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.

15. The road aggregate can be classified into:The road aggregate can be classified into:
1) Natural aggregates
2) Artificial aggregates
The aggregates obtained from the natural rocks
are termed as natural aggregates. The
common natural aggregates used for road
construction are:
a. Crushed rock aggregate
b. Gravel and
c. Sand

16. 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)

17. 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.

18. 4.4. It should be sound and durable to resistIt should be sound and durable to resist
disintegration due to weathering agencies.disintegration due to weathering agencies.
5.5. It should have good cementatious propertyIt should have good cementatious property
i.e. good binding ability to grip togetheri.e. good binding ability to grip together
rough broken stones by forming ownrough broken stones by forming own
binding material and thus impartingbinding material and thus imparting
resistance to displacement.resistance to displacement.

19. 6.6. It should have good adhesive property alsoIt should have good adhesive property also
i.e. binding ability with common bindersi.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. TheIt should have high specific gravity. The
specific gravity of rocks generally varyspecific gravity of rocks generally vary
from 2.6 to 2.9.from 2.6 to 2.9.

20. Shape of AggregatesShape of Aggregates
Road aggregates may be of different shapesRoad aggregates may be of different shapes
such as rounded, semi rounded, cubical,such as rounded, semi rounded, cubical,
angular, flaky or elongated. Shape of anangular, flaky or elongated. Shape of an
aggregate plays an important role in itsaggregate plays an important role in its
selection as a good road aggregate in roadselection as a good road aggregate in road
construction. Flaky and elongatedconstruction. Flaky and elongated
particles have generally less strength andparticles have generally less strength and
durability as compared to rounded anddurability as compared to rounded and
cubical particles of same stone. Suchcubical particles of same stone. Such
particles or stones should be avoided asparticles or stones should be avoided as
far as possible.far as possible. Rounded aggregates are

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

22.  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

23. 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.

24. Function of BindersFunction of Binders
The various objectives achieved by binders inThe 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.

25. 3.3. It acts as a binding agent i.e. it binds theIt acts as a binding agent i.e. it binds the
surface particles together, thus checkingsurface particles together, thus checking
any loss of particles from the surface byany 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. itIt makes the road pavement durable i.e. it
resists the action of weathering agenciesresists the action of weathering agencies
like Wind and Sun. In short, it ensureslike Wind and Sun. In short, it ensures
long life for the road pavement.long life for the road pavement.

26. BITUMENBITUMEN
A non-crystalline hydrocarbon compound in a solidA non-crystalline hydrocarbon compound in a solid
or viscous state having adhesive properties andor viscous state having adhesive properties and
derived from crude petroleum either by naturalderived from crude petroleum either by natural
or artificial distillation is termed as Bitumen. Itor artificial distillation is termed as Bitumen. It
is completely soluble in carbon disulphideis 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 areImportant properties of Bitumen: Following are
some of the most important properties ofsome of the most important properties of
Bitumen:Bitumen:
1.1. It is a mixture of hydrocarbons and is black orIt is a mixture of hydrocarbons and is black or
brown in colour.brown in colour.

27. 2.2. It is an important byproduct of fractionalIt is an important byproduct of fractional
distillation of cube petroleum.distillation of cube petroleum.
3.3. It is a viscous fluid or semisolid and meltsIt is a viscous fluid or semisolid and melts
when heated.when heated.
4.4. It is an important binder used for binding roadIt is an important binder used for binding road
aggregates due to its adhesive nature andaggregates due to its adhesive nature and
water proofing properties.water proofing properties.
5.5. It can be produced in a variety of grades withIt can be produced in a variety of grades with
varying softness and volatility to suitvarying softness and volatility to suit
particular requirement of various types ofparticular requirement of various types of
roads.roads.
6.6. It is completely soluble in carbon disulphideIt is completely soluble in carbon disulphide
(CS(CS22) and carbon tetra chloride.) and carbon tetra chloride.

28. Chart showing fractional distillation inChart showing fractional distillation in
manufacturing bitumen or asphaltmanufacturing bitumen or asphalt

29. 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 constructionPaving grades (used for road construction
work).work).
2.2. Industrial grades (used for water proofingIndustrial grades (used for water proofing
work).work).
The paving grades available in India for highwayThe paving grades available in India for highway
construction are two types:construction are two types:
1.1. ‘‘A’A’ – type– type
2.2. ‘‘S’S’ – type– type

30. Cross-section of petroleum deposits showingCross-section of petroleum deposits showing
oil tappingoil tapping
(Bitumen is obtained from this crude petroleum)(Bitumen is obtained from this crude petroleum)

31. ‘‘A’A’ type denotes paving bitumen obtained from Assamtype denotes paving bitumen obtained from Assam
petroleum. These grades of bitumen are generallypetroleum. 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 othertype denotes paving bitumen obtained from other
sources. These grades of bitumen are designatedsources. 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.

32. TARTAR
Tar 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.

33. 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 productTar is a temperature susceptible product
resulting in great variation in viscosity withresulting in great variation in viscosity with
change in temperature.change in temperature.
2.2. It is not soluble in carbon disulphide andIt is not soluble in carbon disulphide and
carbon tetra chlohide but is soluble only incarbon tetra chlohide but is soluble only in
toluene.toluene.
3.3. It has a great content of free carbon and isIt has a great content of free carbon and is
readily distinguished by its typical odourreadily distinguished by its typical odour
(smell).(smell).

34. 4.4. It is more resistant to disintegrating action ofIt is more resistant to disintegrating action of
water. So it is more suitable to be used belowwater. 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 whenIt is more volatile and hardens rapidly when
exposed to air.exposed to air.

35. 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.

36. 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.

37. ASPHALTASPHALT
The termsThe terms ‘Bitumen’‘Bitumen’ andand ‘Asphalt’‘Asphalt’ are oftenare often
confused. The actually refer to the sameconfused. The actually refer to the same
material. The word ‘Bitumen’ covers both tarmaterial. The word ‘Bitumen’ covers both tar
and asphalt, but conventionally, bitumen standsand asphalt, but conventionally, bitumen stands
for asphalt. Asphalt is more used in roadfor asphalt. Asphalt is more used in road
construction than the tar.construction than the tar.
Definition:Definition: Bitumen containing some inertBitumen containing some inert
material or mineral substances is referred to asmaterial or mineral substances is referred to as
‘Asphalt’.‘Asphalt’.
It is of two types:It is of two types:
1.1. Rock AsphaltRock Asphalt
2.2. Natural or lake AsphaltNatural or lake Asphalt

38. Rock asphaltRock asphalt is a bituminous lime stone usedis a bituminous lime stone used
for road pavements. It contains 70% tofor road pavements. It contains 70% to
90% of limestone and 10 to 20% of90% of limestone and 10 to 20% of
bitumen.bitumen.
The natural asphaltThe natural asphalt found in lakes andfound in lakes and
containing 40% to 70% of bitumen andcontaining 40% to 70% of bitumen and
about 30% of water, lime, clay and sand isabout 30% of water, lime, clay and sand is
termed as lake asphalt. Refined laketermed as lake asphalt. Refined lake
asphalt separated by application of heat isasphalt separated by application of heat is
the best material used for road making.the best material used for road making.

39. CUTBACK AND EMULSIONSCUTBACK AND EMULSIONS
Cutbacks:Cutbacks: The solution of bitumen or asphaltThe 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 iscreosote 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). Abitumen 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’ isTo prepare a ‘cutback’, the distilled ‘cut’ is
put ‘back’ into its residue and hence theput ‘back’ into its residue and hence the
name ‘cutback’ is used.name ‘cutback’ is used.

40. Function of cutbackFunction of cutback: A cutback has: A cutback has
following functions:following functions:
1.1. To soften the heavy or solid bituminousTo 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 aggregatesTo apply it easily over road aggregates
without heating or using minimumwithout heating or using minimum
heating.heating.
3.3. It can be used for all types of bituminousIt can be used for all types of bituminous
roads.roads.
4.4. It modifies and improves the properties ofIt modifies and improves the properties of
residual product in refineries which hasresidual product in refineries which has
otherwise little commercial value.otherwise little commercial value.

41. Emulsions:Emulsions: A liquid material in which aA liquid material in which a
substantial amount of bitumen (or tar orsubstantial amount of bitumen (or tar or
asphalt) is suspended in a finely divided stateasphalt) is suspended in a finely divided state
in an aqueous medium and stabilized byin an aqueous medium and stabilized by
means of suitable emulsifier or stabilizer ismeans of suitable emulsifier or stabilizer is
termed as bitumen emulsion or roadtermed as bitumen emulsion or road
emulsion.emulsion.
It may also be defined as “A two phase system orIt may also be defined as “A two phase system or
a mixture consisting of two immisciblea mixture consisting of two immiscible
liquids, the one dispersed in the other in theliquids, the one dispersed in the other in the
form of fine globules or droplets.”form of fine globules or droplets.”

42. Initially, bitumen or asphalt is broken up into fineInitially, bitumen or asphalt is broken up into fine
globules (of size about 3 microns i.e. 0.003globules (of size about 3 microns i.e. 0.003
mm) and dispersed in water. A small amountmm) and dispersed in water. A small amount
of emulsifier or emulsifying agent is addedof 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 ofa stable emulsion and to keep the globules of
dispersed bitumen in suspension. The commondispersed bitumen in suspension. The common
emulsifiers used are soaps, resinousemulsifiers used are soaps, resinous
substances, colloidal powders etc. Emulsionsubstances, colloidal powders etc. Emulsion
contains 50 to 60% of bitumen by weight andcontains 50 to 60% of bitumen by weight and
the remaining portion is water. When emulsionthe remaining portion is water. When emulsion
is applied on the road, it breaks down and theis applied on the road, it breaks down and the
binder globules start binding the roadbinder globules start binding the road
aggregates but full binding power developsaggregates but full binding power develops
only after evaporation of water.only after evaporation of water.

43. Function of Emulsion:Function of Emulsion:
Following are the important function, which anFollowing are the important function, which an
emulsion performs:emulsion performs:
1.1. It can be applied easily at normalIt can be applied easily at normal
temperature without heating.temperature without heating.
2.2. It is very suitable for coating over dampIt 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 patchIt 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.

44. References:-References:-
 Highway Engg. by Jagroop Singh.Highway Engg. by Jagroop Singh.
 Internet.Internet.