Pavement Materials

1. PAVEMENT MATERIALS

2. Introduction
Pavement subjected to various conditions
Weather changes
Impact loads
Imposed loadsetc.
Should not undergo excessive deformation and settlement
Differential settlement – failure of pavement
Hence, high compressibility and plastic properties are not
desirable for pavement construction
Good quality soil isrequired

3. Pavement Cross section
Consists of different layers
Embankment
Subgrade
Subbase
Base
Wearing course
Different types of materials are used depending on the layer
requirement.

4. Soil is the main constituent in Subgrade andembankment
Aggregates are used in the Sub base and base layer
Aggregates and binding material in the top layer
 Sub grade and embankment provides support forthe
pavement
Different types of failures such as rutting and shoving in the
flexible pavements, cracking in the rigid (concrete)
pavements are due to poor subgrade soil.

5. Soil
Accumulation or deposit of earth material formed by the
disintegration of rocks
Desirable Properties:
Stability
Incompressibility
Permanency of strength
Minimum change involume
Good drainage
Ease ofcompaction

6. Index Properties of Soil
 The soil properties based on which identificationand
classification are done are known as index properties.
Grain SizeDistribution
Liquid limit
Plasticity Index
Grain size distribution is determined by mechanical analysis
Liquid limit by Casagrande apparatus

7. Grain Size distribution
Coarse grained soilsby
Sieve analysis (for non-cohesive soils) – sievingmaterial
successively through smaller sieves.
 for cohesive soils – wet sieveanalysis
Soil finesby
Sedimentation analysis – hydrometer method, pipette method.
Gradation characteristics can be obtained
i.e., proportion of different soils i.e., sand, gravel, silt, clayetc
can be found out.

8. Aggregates
Objectives
Role ofaggregates
Source ofaggregates
Properties ofaggregates
Tests onaggregates

9. Introduction
Combination or group of particle masses
Used with bindingmedium
92-96 percent of bituminousconcrete
 7 0 -80 percent of cement concrete

10. Sources
Natural
Obtained from large rock formation by quarrying
Excavated rock is crushed to obtain aggregates of different sizes
Manufactured
 B y product of industries
Brick ballast

11. Classification on Natural Aggregates
Igneous
Cooling ofmagma
Crystalline in structure
Grain size classification, composition based classification
Sedimentary
Formed by variousdeposits
Classified based on predominantmineral
Metamorphic
Formed from igneous orsedimentary

12. Desirable properties
Clean and free of clay and organicmatter
 B e angular and not flaky

13. Desirable properties
Clean and free from clay and organic matter
Strength
Hardness
Toughness
Shape
Adhesion with bitumen
Durability
 B e non- absorptive
 B e resistant to abrasion on exposure to traffic
Freedom from deleteriousparticles

14. Chemical Properties of aggregates
Important for bituminous and cement concrete mixes
Surface chemistry decides how well bitumen adheres t
o
aggregate
Poor adhesion results in stripping causing the failureo
f
pavements
 I n PCC pavements, if reactive silica is present in aggregates i
t
reacts expansively with cement paste. Causing expansion,
which leads to cracking and other types of failures.

15. Stripping of aggregates
 One of the main failure modes in bituminouspavements
 Due to loss ofadhesion
Water affinity ( hydrophilic orhydrophobic)

16. Alkali-aggregate reaction
This is main mode offailure
Chemical reaction between aggregates and hydroxyl ions a
associated alkalis in the cement
Concrete deterioration is slow but progressive
Depending on the type of minerals present in the minerals
these reactions and resultant decay varies

17. Physical properties of aggregates
Gradation and size
Toughness and abrasion resistance
Durability and soundness
Particle shape and surface texture
Specific gravity
cleanliness

18. Gradation and Size
Effect of gradation and size in bituminous mixes
Workability
Layer thickness
Thickness of lift
Stability
Stiffness
Resistance to deformation
Fatigue strength
durability
Permeability
Surface texture and frictionalresistance

19. Physical properties – gradation and
size
Effect of gradation and size in bituminous mixes
Strength
Dimensions of structural element
 w/c ratio
Stability
Durability
Workability
Fatigue strength
shrinkage

20. Strength, Hardness, Toughness
Subjected to
Stress action due to wheelload
Wear andtear
Crushing
Hardness
Constant rubbing andabrasion
Hard enough to resist the abrasive action caused bytraffic
Toughness
Resistance to impact
 Ex: jumping of steelwheels

21. Shape, Adhesion, Durability
Rounded, cubical, angular, flaky or elongatedshape
Flaky and elongated particles will have less strength
Should have less affinity withwater
Other wise stripping willoccur
Withstand adverse weather action
Also called assoundness
Should be clean and free from organicmatter

22. Aggregate tests
Crushing test
Abrasion test
Impact test
Soundness test
Shape test
Specific gravity and water absorption test
Bitumen adhesion test

23. Crushing Test
Testing aggregate against compressive stress
IS:2386 Part –IV
Provides a relative measure of resistance to crushing
Specimen in the mould is subjected to gradual load
 Dry aggregates passing through 12.5mm sieve andretained
on 10mm sieve
Filled in cylindrical mould of 11.5 mm dia and 18cm heigh
 3 layers tampered each 25 times

24. Crushing Test
Test sample is weighed (w1) and placed incylinder
Compressive load of 40 tonnes applied at a rate of 4 tonnes
per minute
Crushed aggregates are sieved through 2.36mm sieve
Weight of material passing the sieve is measured(w2)
Aggregate crushing value = (w1/w2)x100
 < 10 indicates strong aggregate
Above 35 meansweak

25. Abrasion test
 To test the hardness property of aggregates
 Los Angeles abrasion test isused
Standardized by BIS, IS:2386 Part IV
Principle is to find the percentage wear due to relative
rubbing action between aggregate and steel balls
Consists of a steel drum (dia 700mm, length520mm)
Abrasive charge – steel balls of dia 48mm and weight 350 t
o
450 gms are placed inside the cylinder
 N o of spheres to be used depends on the grading of sample

26. Abrasion test
Quantity depends on gradation ( 5 to 10kg)
Cylinder rotated at around 33-35 rpm for 500 to 1000
rotations
Material is sieved through 1.7mm sieve
Passed amount is expressed as percentage of total aggregate
weight
This is called los angeles abrasion value. Max valuesare,
 For WBM –40
Bituminous concrete - 35

27. Impact test
Resistance to impact of aggregates
Aggregates passing 12.5 mm sieve and retained on 10 mm sieve
Filled in a cylindrical steel cup of internal dia 10.2 mm and depth
5 cm
Material filled in 3 layers
Metal hammer of weight 13.5 to 14 kgs is arranged to dropwith
afree fall of 38cm in vertical direction
Total blows are15
Crushed aggregate is passed through 2.36mm IS sieve
Aggregate Impact value = Expressed as ratio of total weight
 Ma x value for:WBM is 40, Bituminous concrete is 35

28. Soundness test
 T o evaluate resistance to weathering action
Accelerated weathering test cycles
Aggregates of specified size are subjected to cycles of
alternate wetting in a saturated solution of either sodium
sulphate or magnesium sulphate for 16 - 18 hours and then
dried in oven at 105 − 110C.
 5 cycles
Loss in weight is determined bysieving
Loss in weight should not exceed 12 percent when tested
with sodium sulphate and 18% when tested with magnesium
sulphate solution.

29. Shape tests
 The particle shape of the aggregate mass is determined bythe
percentage of flaky and elongated particles in it.
 The flakiness index is defined as the percentage by weight of
aggregate particles whose least dimension is less than 0.6 times
their mean size.
 The elongation index of an aggregate is defined as the
percentage by weight of particles whose greatest dimension
(length) is 1.8 times their mean dimension. (applicable only to
aggregates larger than 6.3mm)

30. Specific gravity and water absorption
Specific gravity of an aggregate is considered to be a measure
of strength or quality of the material
Absorption properties also indicate the strength.More
porous rocks are weak in nature.
Test Procedure:
 2 kg sample of aggregate is washed and drained, kept in wire
basket.
Immersed in distilled water at temperature 22 to 32 C with
water cover atleast 50mm.
Trapped air is removed by dropping the basket for 25 times
at a height of 25mm from the bottom.

31.  And weight of basket and aggregates is noted inimmersed
condition. (W1).
Then they are removed from water and allowed to drain forfew
minutes.
Aggregates kept in a dry water absorbentcloth
Empty basket moved back to water, jolted 25 times, weight i
s
W2.
Then aggregates moved to another dry cloth and again driedfor
10 to 60 minutes.
Weight of surface dried aggregate =W3
Aggregate kept in oven at 110 C for 24 hours.
Cooled and weighed.(W4)

34. Bitumen adhesion test
Bitumen adheres well to all normal types of road aggregates
provided they are dry and free from dust
Adhesion problem occurs when the aggregate is wet and cold
 the presence of water causes stripping of binder fromthe
coated aggregates
Static immersiontest
 The principle of the test is by immersing aggregate fully
coated with binder in water maintained at 400C temperature
for 24 hours.
 IRC has specified maximum stripping value ofaggregates
should not exceed 5%.