Different pavement materials used in the road construction. Importance of soil, aggregate pavement materials. Tests on Soil for pavement construction. Tests on aggregate for pavement construction.
Requirements of soil and aggregates in pavement.
2. Introduction
Pavement subjected to various conditions
Weather changes
Impact loads
Imposed loads etc.
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 is required
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 and embankment
Aggregates are used in the Sub base and base layer
Aggregates and binding material in the top layer
Sub grade and embankment provides support for the
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 in volume
Good drainage
Ease of compaction
6. Index Properties of Soil
The soil properties based on which identification and
classification are done are known as index properties.
Grain Size Distribution
Liquid limit
Plasticity Index
Grain size distribution is determined by mechanical analysis
Liquid limit by Casagrande apparatus
7. Grain Size distribution
Coarse grained soils by
Sieve analysis (for non-cohesive soils) – sieving material
successively through smaller sieves.
for cohesive soils – wet sieve analysis
Soil fines by
Sedimentation analysis – hydrometer method, pipette method.
Gradation characteristics can be obtained
i.e., proportion of different soils i.e., sand, gravel, silt, clay etc
can be found out.
9. Consistency Limits and Indices
•Atterberg limits are the limits of water content used to define
soil behavior.
10. Soil types
Based on the particle size and properties
Different types are there
Classification is primarily based upon
Grain Size distribution
Index Properties
Based on the grain size, soils are classified as below.
Gravel
Sand
Silt
Clay
11. Different Systems of Classification
USGS
Textural Soil Classification
Burmister Method
Casagrande Soil Classification
Unified Soil Classification System
BIS
HRB
And a lot more… But all classifications do not have a
common sizes for defining soil class.
12. Unified Soil Classification
Developed By Casagrande in 1948
Airfield construction - world war II
Modified to suit the reqt of other constructions
According to USCS
Coarse grained soils –> (grain size distribution): More than
50% retained on 75micron
Fine grained soils –> (plasticity characteristics): More than
50% passes through 75micron
13. USC System
Gravel – More than 50% on sieve no: 4 (4.75mm)
Sand - More than 50% passes sieve no: 4 (4.75mm)
Coarse grained contains <5% fines – well graded (GW, SW)
Poorly graded – GP, SP
For more than 12% fines – GM, GC, SM etc.
For Fine grained soils
LL is 50% or less – ML, SL etc (soils of low compressibility)
MH, SH etc., - LL more than 50% ( soils of high
compressibility)
Highly organic soils are termed as peat
15. Indian Standard Soil Classification
Similar to USCS
Difference is w.r.t fine grained soils
Sub divided into 3 categories – low, medium and high
compressibility
Total 18 types of soils
Symbols used are same as USCS
18. Tests on Soil
For evaluating the properties of soil
Strength, Stiffness etc are studied
Shear tests
Bearing Tests
Penetration tests
19. Shear Tests
Carried out on the small samples
Performed in the laboratory
Direct Shear tests
Tri-axial compression test
Un-confined compression test
20. Bearing Tests
Carried out on the subgrade soils
Insitu tests
Load bearing area
Results vary with the properties of the soil under the test
Penetration test is a small scale bearing test
Size of loaded area is small
Ratio of penetration to size of loaded area is large
Can be insitu or laboratory
21. California Bearing Ratio Test (CBR)
Developed by the California Division of Highway
For classifying and evaluating the Soil sub grade and base
course materials for flexible pavements
It is an empirical test
Cannot be related directly with the fundamental properties of
the soil
Used to determine material properties for pavement design
22. CBR denotes the measure of resistance to penetration of
pavement material or soil, of standard plunger under
controlled conditions.
Conducted in laboratory on re-moulded specimens.
(undisturbed samples can also be used)
Procedure for determining CBR value is standardized by
various agencies including BIS.
23.
24. Plunger of 50mm
1.25mm/minute penetration
Load reqd. for penetration of 2.5mm and 5.0mm are
recorded.
CBR value is expressed as the percentage of the standard
load value in standard material.
For 2.5mm penetration
Standard load = 1370kg, unit standard load = 70kg/cm2
For 5.0mm penetration
Standard load = 2055mm, unit standard load = 105kg/cm2
25. CBR Test
Specimen in mould is compacted to maximum dry density
(OMM)
IS heavy compaction as per IS: 2720 part VII for heavy traffic
roads
IS light compaction for low traffic roads
The specimen subjected to soaking for 4 days
Swelling and water absorption are noted
Then weight is placed on the top of specimen in the mould.
Assembly is placed under the plunger of the loading frame.
26.
27. Reasons for Initial Concavity of shape
Top layer of the soaked soil is too soft after soaking
Top surface of soil not even
Plunger is not vertical
Plunger arrangement is wrong
Normally penetration value at 2.5mm is higher than 5.0mm.
And higher value is recorded as CBR.
Average of 3 test specimens have to taken as the value.
Presence of coarse grained particles result in poor
reproducibility of results
Material passing through 20mm sieve is only used in the test.
29. Plate Bearing Test – Apparatus
Bearing Plates – 750, 600, 450 and 300mm dia and 15 to
25mm thickness
A loading device consisting of hydraulic jack and proving ring
arrangement or pressure gauge
Reaction frame for giving thrust to plates.
Datum frame and dial gauges are used to measure settlement
of loaded plate.
30. Plate Bearing Test - Procedure
Test site is levelled and plate is seated properly on the
surface
For modulus of subgrade reaction of natural ground – top
soil upto 20cm is removed.
Stiffening plates of decreasing dia are placed
Jack and proving ring assemble is fitted
3 to 4 dial guages are fixed on the periphery of plates
31. Plate Bearing Test – Procedure
A pressure of 0.07kg/cm2 (320 kg for 75cm dia plate) is applied
and removed after few seconds
Dial readings are noted corresponding to zero load
Load applied by means of jack, to cause a settlement of 0.25mm
When no increase in settlement or when the rate is less than
0.025mm/min the load dial reading and settlement readings are
noted down
Average values are considered
Next, load is increased so the settlement will be 0.25mm extra
This way experiment is repeated upto 1.75mm or more.
32.
33. Modulus of subgrade reaction is the reaction pressure
sustained by the soil sample under a rigid plate of standard
diameter per unit settlement measured at a specified
pressure or settlement.
IRC specifies that the K value be measured at 1.25 mm
settlement.
K = p/0.125 (kg/cm2/cm)
34. Allowance for Worst Subgrade Moisture
K value will be lowest at soaked condition
Moisture content during test may seldom represent worst
condition at site
K value obtained is modified by a factor to represent the
worst condition
2 consolidation test specimens are prepared
1 sample tested in un-soaked condition in lab – pressure –
deformation curve drawn (pressure for 0.125mm is noted)
2nd
specimen soaked
36. Correction for smaller plate
Some cases not possible to cause settlement of 0.175cm for
the 75 dia plate
Smaller dia plate will be used
Obtained K1 value is modified
Assuming subgrade as an elastic medium, where modulus of
elasticity is
∆ = 1.18pa/E
But , K = p/ ∆ = E/1.18a
If E is constant for a soil, Ka = K1a1 => K = K1a1/a
38. Introduction
Combination or group of particle masses
Used with binding medium
92-96 percent of bituminous concrete
70 -80 percent of cement concrete
39. Sources
Natural
Obtained from large rock formation by quarrying
Excavated rock is crushed to obtain aggregates of different sizes
Manufactured
By product of industries
Brick ballast
40. Classification on Natural Aggregates
Igneous
Cooling of magma
Crystalline in structure
Grain size classification, composition based classification
Sedimentary
Formed by various deposits
Classified based on predominant mineral
Metamorphic
Formed from igneous or sedimentary
42. Desirable properties
Clean and free from clay and organic matter
Strength
Hardness
Toughness
Shape
Adhesion with bitumen
Durability
Be non- absorptive
Be resistant to abrasion on exposure to traffic
Freedom from deleterious particles
43. Chemical Properties of aggregates
Important for bituminous and cement concrete mixes
Surface chemistry decides how well bitumen adheres to
aggregate
Poor adhesion results in stripping causing the failure of
pavements
In PCC pavements, if reactive silica is present in aggregates it
reacts expansively with cement paste. Causing expansion,
which leads to cracking and other types of failures.
44. Stripping of aggregates
One of the main failure modes in bituminous pavements
Due to loss of adhesion
Water affinity ( hydrophilic or hydrophobic)
45. Alkali-aggregate reaction
This is main mode of failure
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
46. Physical properties of aggregates
Gradation and size
Toughness and abrasion resistance
Durability and soundness
Particle shape and surface texture
Specific gravity
cleanliness
47. 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 frictional resistance
48. 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
49. Strength, Hardness, Toughness
Subjected to
Stress action due to wheel load
Wear and tear
Crushing
Hardness
Constant rubbing and abrasion
Hard enough to resist the abrasive action caused by traffic
Toughness
Resistance to impact
Ex: jumping of steel wheels
50. Shape, Adhesion, Durability
Rounded, cubical, angular, flaky or elongated shape
Flaky and elongated particles will have less strength
Should have less affinity with water
Other wise stripping will occur
Withstand adverse weather action
Also called as soundness
Should be clean and free from organic matter
52. 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 and retained
on 10mm sieve
Filled in cylindrical mould of 11.5 mm dia and 18cm heigh
3 layers tampered each 25 times
53. Crushing Test
Test sample is weighed (w1) and placed in cylinder
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 means weak
54. Abrasion test
To test the hardness property of aggregates
Los Angeles abrasion test is used
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, length 520mm)
Abrasive charge – steel balls of dia 48mm and weight 350 to
450 gms are placed inside the cylinder
No of spheres to be used depends on the grading of sample
55. 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 values are,
For WBM – 40
Bituminous concrete - 35
56. 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 drop with a
free fall of 38cm in vertical direction
Total blows are 15
Crushed aggregate is passed through 2.36mm IS sieve
Aggregate Impact value = Expressed as ratio of total weight
Max value for: WBM is 40, Bituminous concrete is 35
57. Soundness test
To 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 by sieving
Loss in weight should not exceed 12 percent when tested
with sodium sulphate and 18% when tested with magnesium
sulphate solution.
58. Shape tests
The particle shape of the aggregate mass is determined by the
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)
59. 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.
60. And weight of basket and aggregates is noted in immersed
condition. (W1).
Then they are removed from water and allowed to drain for few
minutes.
Aggregates kept in a dry water absorbent cloth
Empty basket moved back to water, jolted 25 times, weight is
W2.
Then aggregates moved to another dry cloth and again dried for
10 to 60 minutes.
Weight of surface dried aggregate = W3
Aggregate kept in oven at 110 C for 24 hours.
Cooled and weighed. (W4)
61.
62.
63. 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 from the
coated aggregates
Static immersion test
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 of aggregates
should not exceed 5%.