Lect 14-testing procedures for road aggregates

transportation engineering book

1. TESTING PROCEDURES
FOR ROAD AGGREGATES
Lecture 14
Prof. P. K. Bhuyan
Dept. of Civil Engg.
NIT Rourkela

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Importance of Testing
Aggregates form major part of pavement
structure (88-96% by weight, 80% by volume)
Load transfer by grain to grain contact
Are used in construction of pavements using
cement concrete, bituminous material and in
WBM / WMM
Have to bear load stresses and resist wear
Are also subjected to impact due to moving
loads and adverse weather conditions

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Contd….
The desirable characteristics
1.Gradation and appropriate size
2.Strength and toughness
3.Cubical shape
4.Low porosity
5.Proper surface texture
6.Hydrophobic characteristics
7.Durability
8.Specific gravity

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Factors
The required properties depend on:
1. type of pavement construction
2. traffic and
3. climatic conditions
All the properties need not be present for
aggregates for a particular construction

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Test Types
1.Sieve Analysis
2.Aggregate Crushing Value Test
3.Aggregate Impact Test
4.Abrasion Test
5.Soundness Test
6.Specific Gravity and Water Absorption Tests
7.Shape Tests
8.Polished Stone Value Test and
9.Stripping Value of Road Aggregate Test

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1. Sieve Analysis

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Significance of Test
Each type of aggregate test
requires a specified aggregate
size (E.g. 10-12.5 mm for
crushing test)
Each bituminous mix type has a
recommended aggregate
gradation(% passing 26.5 mm
in 55-90 for GSB1)
So aggregate is passed through
a set of sieves to get material of
various sizes

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Sieves and Sieve-shaker

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Procedure
Bring the sample to an air dry condition either by drying
at room temperature or in oven at a temperature of 100
o
C
to 110
o
C.Take the weight of the sample.
Clean all the sieves and sieve the sample successively
on the appropriate sieves starting with the largest.
Shake each sieve separately over a clean tray.
On completion of sieving note down the weight of
material retained on each sieve.
Report the results as cumulative percentage by weight of
sample passing each of the sieves

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Observation Sheet
IS:2386 Part I; IS: 383
I.S. Sieve
designation
Weight of
sample
retained (gm)
weight retained
Percent of
(%)
Cumulative
percent of weight
retained (%)
Percentage
passing
(%)
63 mm
40 mm
20 mm
12.5 mm
10 mm
4.75 mm

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Observation Sheet
IS Seive
Designation
(mm)
Weight of
sample
retained
(gm)
Weight
retained
(%)
Cumulative
weight
retained
(%)
Passing
(%)
63 100 6.25 6.25 93.75
40 200 12.5 18.75 81.25
20 400 25 43.75 56.25
12.5 400 25 68.75 31.25
10 300 18.75 87.5 12.5
4.75 200 12.5 100 0
1600 100

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Gradation chart0
20
40
60
80
100
120
4.75 10 12.5 20 40 63 63
Gradation

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2. Aggregate Crushing Test

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Significance
Aggregate crushing value provides a relative
measure of resistance to crushing under a
gradually applied compressive load
Aggregates subjected to high stresses during
rolling and severe abrasion under traffic
Also in India very severe stresses come on
pavements due to rigid tyre rims of heavily loaded
animal drawn vehicles

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Test Set-up

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Procedure
Surface dry aggregates passing 12.5 mm and
retained on 10 mm selected
3.25 kg aggregate required for one test sample
Cylindrical measure filled with aggregates in 3
layers, tamping each layer 25 times
After leveling the aggregates at the top surface the
test sample is weighed
The cylinder is now placed on the base plate

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Contd….
The cylinder with the test sample and plunger in
position is placed on compression machine
Load is applied at a rate of 4 tonnes per minute upto
40 tonnes
The crushed aggregate is taken out, sieved through
2.36 mm IS sieve and weighed to get material
passing
Aggregate crushing value = W2*100/W1
W2= Weight of crushed material
W1=Total weight of sample

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Load Application
Sample being loaded
in the compression
machine at 4 T per
minute for 10 minutes
(upto 40 T)

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Observation Sheet
Observations
Test No.
Average
1 2 3
Wt. of Aggregate Sample
Filling in The Cylinder=
W1(gms)
362 354 343
Wt. of Aggregate Sample
Passing 2.36 mm Sieve
After the Test= W2 (gms)
116 102 84
Aggregate Crushing
Value =
W2 / W1x 100
32% 28.8 %24.5 %28.5 %
Note: Value recorded up to first decimal place

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Specifications
45 %
Max for
Other Surfaces
30 %
Max for Surface
Course
As per IRC:15 1970
And
IS: 2386:Part IV
Aggregate Crushing Value for
Cement Concrete Pavements
Specified By

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Discussion
Indirect measure of crushing strength
Low value indicate strong aggregates
Surface course need more strength than base course
Should not exceed 30% for cement concrete surface ,
and 45% for others

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3. Aggregate Impact Test

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Significance
This test assesses the suitability of aggregate as
regards the toughness for use in pavement
construction
Road aggregates subjected to pounding action
due to traffic loads-so possibility of breaking
Should be tough enough-so proper aggregates to
be used
Suitability to be checked by laboratory tests

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Test Set-up

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Procedure
1.Aggregate passing through 12.5mm IS sieve and retained on
10mm sieve is filled in the cylindrical measure in 3layers by
tamping each layer by 25blows. Determine the net weight of
aggregate in the measure (W1)
2.Sample is transferred from the measure to the cup of
aggregate impact testing machine and compacted by tamping
25 times
3. The hammer is raised to height of 38cm above the upper
surface of the aggregates in the cup and is allowed to fall freely
on the specimen

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Test In progress

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Contd….
After subjecting the test specimen to 15
blows, the crushed aggregate is sieved
through IS 2.36mm sieve
Weigh the fraction passing through IS 2.36
mm sieve(W2)
Aggregate impact value = W2 / W1 x100
w2 = Weight of fines passing 2.36 mm
w1 = Weight of sample
Mean of the two values reported

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Observation Sheet
Observations
Test No.
Avg
1 2 3
Wt. of Aggregate Sample
Filling in The Cylinder=
W1(gms)
319 323
Wt. of Aggregate Sample
Passing 2.36 mm Sieve
After the Test= W2 (gms)
65 68
Aggregate Impact Value=
W2 / W1 x100
20.37 21.05 21
Note: Value Recorded to the Nearest Whole Number

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Specifications
30Bituminous Wearing Surfaces
IS: 2386: Part IV and IRC:15 1970; MORTH: 2001
30WBM Surface course
35
Bituminous Macadam, Base
course
45Cement Concrete Base course
50WBM Sub-base course
Aggregate Impact
Value, Max, %
Type of Pavement
Material/Layer

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4. Los Angeles Abrasion Test

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Significance
It is resistance to wear or hardness of
aggregates
Road aggregates at the top subjected to
wearing action
Under traffic loads abrasion/attrition action
within the layers as well
To determine suitability, tests have to be
carried out

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Test Set-up

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Procedure
1.Aggregates dried in oven at 105 -110 °C. to constant
weight conforming to any one of the gradings
E.g. 1250 gm of 40-25 mm, 1250 gm of 25-20 mm,
1250 gm of 20-12.5 mm, 1250 gm of 12.5-10 mm, with
12 steel balls
2. Aggregate weighing 5 kg or 10 kg is placed in cylinder
of the machine ( W1gms)
3. Machine is rotated at 30-33 rpm for 500 revolutions
4.Machine is stopped and complete material is taken out
including dust

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Grading Requirement
GradingWt. in gms of each Sample in the Size Range, mm
Abrasive
Charge
80
-
63
63
-
50
50
-
40
40
-
25
25
-
20
20
-
12.5
12.5
-
10
10
-
6.3
6.3
-
4.75
4.75
-
2.36
Wt. ofCharge, gNo. ofSpheres
A - - -1250125012501250 - - - 12 5000±25
B - - - - -25002500 - - - 11 4584±25
C - - - - - - -25002500 - 8 3330±25
D - - - - - - - - -5000 6 2500±25
E250025005000 - - - - - - - 12 5000±25
F - -50005000NA - - - - - 12 5000±25
G
- - -50005000 - - - - - 12 5000±25

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After 500 –1000 revolutions

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Contd….
6.Sieved through 1.7 mm sieve
7. Weight passing is determined by washing the
portion retained, oven drying and weighing (W2
gms)
8. Aggregate abrasion value is determined
LAAV = W2 / W1 x100
W2 = Weight of fines passing 1.7 mm
W1 = Weight of the sample

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Specifications
60WBM Sub-base course
IS: 2386: Part IV; IRC:15 1970; IS: 383
30
Bituminous/Cement concrete
Wearing course
35
Bituminous Carpet, SD, Cement
Concrete surface course
40
WBM Surface course, BM binder
course
50
WBM Base course with bit.
Surfacing, BM Base course
L. A. Abrasion
Value, Max, %
Type of Pavement Layer

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Discussion
Select a grading close to the project for
testing
Simulate both abrasion and impact due to
wheel loads
It determines the hardness of the stone

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5.Soundness test

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Significance of Test
Toassesstheresistanceoftheaggregatesto
weathering
Almostallroadpavementsgetsubjectedtoalternate
wet-dryconditions
Freeze-thawsituationismainproblemincoldregions
Teststheresistancetodisintegration
Forthataggregatessubjectedtoacceleratedwet-dry
andfreeze-thawconditions

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Required Material
Magnesium Sulphate

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1.PreparationofSolutions
(a)PreparationofSodiumSulphatesolution
About420gmofanhydroussalt(Na
2
SO
4
)or1300gmofthecrystallinedecahydrate
(Na
2
SO
4
10H
2
O)isdissolvedperlitreofwater.
Thesolutionismaintainedat27±2°C,stirredfrequently,andataspecificgravityof
1.151to1.71
(b)PreparationofMagnesiumSulphateSolution:(Alternative)
About400gmofanhydroussalt(MgSO
4
)or1600gmofthecrystallinehydrate
(MgSO
4
7H
2
O)isdissolvedperlitreofwater.
Thesolutionismaintainedat27±2°C,stirredfrequently,andataspecificgravityof
1.295and1.308
Procedure

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Contd…
2.Cleanthecourseaggregateanddrytoaconstantweightat
105-110°Candseparatetodifferentsizeranges
(4.75-10mm=300gm,10-12.5mm=330gm,12.5-20mm=670gm,20-25
mm=500gm,25-40mm=1000gm,….,>80mm=300gm)
3.Weigheachfractionandplaceinseparatecontainersforthetest
4.ImmersethesampleinthepreparedsolutionofSodiumSulphate
ormagnesiumsulphatefor16to18hourssothatsolutioncovers
themtoadepthofatleast15mm

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Contd…
5. Use the cover of the container during the period of
immersion and maintain the temperature of solution at 27
o
C+/-
1
o
C
6. After immersion period, remove the aggregate from solution,
drain for about 15 minutes and place in the drying oven
maintained at a temperature of 105
o
C -110
o
C until it comes to
constant weight (4-18 hrs)
7. Again immerse in prepared solution for the next cycle of
immersion and drying
8. After completion of five cycles, cool the sample and wash off
sulphate. Check the wash water with barium chloride to see any
sulphate precipitate

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Immersion and Drying

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Contd…..
9. Each fraction of sample is then dried at a constant
temperature of 105
o
C -110
o
C, weighed and sieved
through specified IS sievesSize of Aggregate Sieve size used to determine loss
4 mm
8 mm
63-40 mm
40-20 mm
20-10 mm
31.5 mm
16 mm
10-4.75mm

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Contd….
10. Visual inspection for splitting, crumbling,
disintegration.
11. Report the weighted average from the
percentage loss for each fraction.

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Observation Sheet
Type of reagent used:
Type of course aggregate sample: Number of cycles:
Sieve size, mm
Grading of
original
sample
%
Weight of
test
fraction
before test
g
% passing
finer
sieve after test
Weighted
Average
PassingRetained
60 40 20 3000 4.8 0.96*
40 20 45 1500 8.0 3.6
20 10 23 1000 9.6 2.2
10 4.75 12 300 11.2 1.34
100 5800 8.10
IS: 2386: Part V and IS: 383; IRC: 17, 20, 27 (*4.8 x 20 /100 = 0.96 )

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Specifications
Course type
Loss of Weight, %Max
10 cycles
5 cycles
(IRC)
Sodium Sul.Magnesium Sul.Sodium Sul.
General Guide 12 18 #
Bituminous Surface Drs # # 12
Penetration Macadam # # 12
Bituminous Macadam # # 12

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Discussion
Useful to assess the resistance of the aggregate to
weathering
Average loss of weight after 10 cycles should not exceed
12% for Na
2SO
4and 18% for Mg
2SO
4
IRC specification: 12% max after 5 cycles of Na
2SO
4for
bituminous constructions

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6. Specific Gravity
and
Water Absorption
Tests

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Significance
Specific Gravity
1. Considered to be a measure of
strength of aggregate
2. Helps in stone identification
3. Very important input data for asphalt
mix-design

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Significance
WaWeight of the specimen in air
Ws Weight of the saturated surface dry
specimen in air
Ww Weight of the specimen in water

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Specific gravity
Apparent specific gravity (Gsa)
Ratio of the dry weight of the specimen in air (Wa)
to the weight of an equal volume water
Excludes the permeable voidsvoidsexcludingVolume
airinWeight
WwWa
Wa
Gsa 

 voidsexcludingVolume
airinWeight
WwWa
Wa
Gsa 

 voidsexcludingVolume
airinWeight
WwWa
Wa
Gsa 



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Specific gravity
Dry bulk specific gravity (Gsb)
Ratio of the dry weight of the specimen in air (Wa)
to the weight of an equal volume of water
Includes the permeable voids voidsexcludingVolume
airinWeight
WwWa
Wa
Gsa 

 voidsexcludingVolume
airinWeight
WwWa
Wa
Gsa 

 voidsincludingVolume
airinWeight
WwWs
Wa
Gsb 



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Specific gravity
Saturated surface dry (SSD) Bulk specific gravity
(Gsb-ssd)
The ratio of the weight of the saturated surface dry specimen
in air to the weight of an equal volume of water
Includes the weight of the water in the poresvoidsincludingVolume
waterincludingairinWeight
WwWs
Ws
ssdGsb 



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Contd….
Water Absorption
1. A measure of porosity/resistance to frost action of aggregate and
gives idea of strength
2. Higher values considered unsuitable for both bituminous as well
as concrete works. %
100
%
100)(
solidofWeight
absorbedwaterofWeight
Wa
WaWs
WA





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Example
Wa = 2031g Weight of the specimen in air
Ws = 2045 g Weight of the SSD specimen in air
Ww = 1304 g Weight of the specimen in water794.2
13042031
2031





WwWa
Wa
Gsa 741.2
13042045
2031





WwWs
Wa
Gsb 760.2
13042045
2045





WwWs
Ws
SSDGsb %689.0
2031
100)20312045(100)(





Wa
WaWs
WA

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Test Set-up
Container with
water
Basket with aggregate
Balance

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Procedure
About 2000 gm of aggregates are washed to remove
dust, drained and placed in the wire basket.
The basket is immersed in water at a temperature of
22
O
C to 32
O
C with at least 5 cm cover of water above
the top of the basket.
Immediately after immersion, the entrapped air is
removed from sample by lifting the basket 25 mm above
the base of the tank and allow it to drop 25 times, at the
rate of one drop per second.
The basket along with aggregates is kept completely
immersed in water for 24 ±0.5 hours and then weighed
in water at a temperature of 22
O
C to 32
O
C (W
1
g).

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Aggregate-filled Basket Immersed
Trapped air being
driven out

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Contd….
The basket and aggregates are removed from water
and allowed to drain for few minutes.
The aggregates are emptied from basket onto the dry
absorbent cloth and surface dried, without directly
exposing to sunlight
Empty basket is returned to the water tank, Jolted 25
times and weighed in water (W
2
g).
The surface dried (10-60 mts) aggregate is then
weighed (W
3
g)

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Surface Drying of Aggregate

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Contd….
The aggregate is placed in an oven at a
temperature of 100
o
C TO 110
o
C for 24
±0.5 hours.
It is then removed from the oven,
cooled and weighed (W
4
g).
12

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Calculations
Specific gravity
= dry wt of aggregate(W4)
wt of equal vol of water(W3-(W1-W2))
Apparent specific gravity
= dry wt of aggregate(W4)
wt of equal volume of water excluding air voids(W4-(W1-W2))
Water absorption
= wt of water absorbed (W3-W4)
oven dried wt of aggregates (W4)

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Observation Sheet
Size of the aggregates = Aggregate Type =
Details
Test number
Mean
Value1 2
1. Weight of saturated aggregate and basket in water
= W1 g
2. Weight of basket in water = W2 g
3. Weight of saturated surface dry aggregates in air =
W3 g
4. Weight of oven dried aggregates in air = W4 g
5. Specific gravity = W4/W3-(W1-W2)
6. Apparent specific gravity = W4/W4-(W1-W2)
7. Water absorption = (W3-W4)*100/W4 %
(i) Mean value of specific gravity =
(ii) Mean value of apparent specific gravity =
(iii) Mean value of water absorption =

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Specifications
Property
Range for road
construction
Specific Gravity 2.5-3.0 (average 2.68)
Water Absorption
0.1-2.0 percent
IS: 2386; IRC: 17, 23 & 48; IRC: 47

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Discussion
Separate procedure for size less than 10 mm, 10-40 mm, and
more than 40 mm
High specific gravity indicates high strength
Water absorption is a measure of porosity, and resistance to
frost action
These are absolute material properties
Gradation assumes aggregate have approximately same
specific gravity

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7. Shape Tests
Determination of:
a.Flakiness Index
b.Elongation Index
c.Angularity Number

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Significance
Shape of crushed aggregates determined by the percentage of
flaky and elongated particles
Shape of gravel determined by its angularity number
Flaky and elongated aggregate particles tend to break under
heavy traffic loads
Rounded aggregates preferred in cement concrete pavements as
more workability at less water cement ratio
Angular shape preferred for granular courses/flexible pavement
layers due to better interlocking and hence more stability

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Test Set-up
Length Gauge for Elongation Index
Thickness Gauge for Flakiness Index

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Procedure (Flakiness)
(a).FlakinessIndex:Theflakinessindexofaggregatesisthe
percentagebyweightofparticleswhoseleastdimensionislessthan
three-fifths(0.6)oftheirmeandimension.Applicabletosizes>=6.3
mm
1.ThesampleissievedthroughISsievesizes63,50,40,31.5,25,
20,16,12.5,10and6.3mm
2.Minimum200piecesofeachfractiontobetestedaretakenand
weighed(W1gm)
3.Separatetheflakymaterialbyusingthestandardthicknessgauge

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Flakiness Index Test in Progress

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4.The amount of flaky material is weighed to an accuracy of
0.1 percent of the test sample
5. If W1,W2,W3,…. are the total weights of each size of
aggregates taken and w1,w2,w3,….. are the weights of
material passing the different thickness gauges then:
Flakiness Index
= (w1+w2+w3+….)*100
(W1+W2+W3+….)
FI =w x100 %
W
Where,
W = Total wt of material taken in gms
w = Total wt of material passing in gms
Flakiness

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Observation sheet (Flakiness Index)
Passing
through
I.S. Seive,
(mm)
Retained
on I.S.
Seive,
(mm)
63 50 W1 23.9 w1=
50 40 W2= 27 w2=
40 31.5 W3= 19.5 w3=
31.5 25 W4= 16.95 w4=
25 20 W5= 13.5 w5=
20 16 W6= 10.8 w6=
16 12.5 W7= 8.55 w7=
12.5 10 W8= 6.75 w8=
10 6.3 W9= 4.89 w9=
Total W= w=
Size of aggregate
Wt. Of the
fraction
consisting of at
least 200
pieces (gm)
Thickness
gauge size,
(0.6 times the
mean sieve)
(mm)
Weight of
aggregate in each
fraction passing
thickness gauge
(gms)

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Elongation Index
Elongation Index: The percentage by weight of
particles whose greatest dimension is greater than one and
four fifth times (1.8 times) their mean dimension. Applicable to
sizes >=6.3 mm
1. The sample is sieved through sieve sizes, 50, 40, 25, 20,
16, 12.5, 10 and 6.3
2. Minimum 200 pieces of each fraction to be tested are
taken and weighed (W1 gm)
3.Separatetheelongatedmaterialbyusingthestandard
lengthgauge

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Elongation Index Test in Progress

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4. The amount of elongated material is weighed to an accuracy of
0.1 percent of the test sample
5. If W1,W2,W3,…. are the total weights of each size of
aggregates taken and w1,w2,w3,….. are the weights of
material retained on the different length gauge slots then:
Elongation Index
= (w1+w2+w3+….)*100
(W1+W2+W3+….)
EI = w x 100 %
W
Where,
W = Total wt of material taken in gms
w = Total wt of material retained in gms
Elongation Index

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Observation sheet (Elongation Index)
Passing
through
I.S.
Seive,
(mm)
Retained
on I.S.
Seive,
(mm)
50 40 W1= 81 w1=
40 25 W2= 58 w2=
25 20 W3= 40.5 w3=
20 16 W4= 32.4 w4=
16 12.5 W5= 25.5 w5=
12.5 10 W6= 20.2 w6=
10 6.3 W7= 14.7 w7=
Total W= w=
Size of aggregate
Wt. Of the
fraction
consisting of
at least 200
pieces (gm)
Length
gauge size,
(1.8 times
the mean
sieve) (mm)
Weight of
aggregate in
each fraction
retained on
length gauge
(gms)

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Specifications
Type of pavement constructionLimit of Flakiness Index(%)
Bituminous carpet 30(Combined FI and EI)
Asphaltic concrete
Penetration macadam
Bit. Surface dressing
25(do)
Bit. Macadam, WBM base
& surfacing course
15(do)
Cement Concrete 35
IS: 2386, Part I; IRC: 14-48 ; MORTH: 2001

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Angularity number
The angularity number measures the percent
voids in excess of 33 percent which is obtained
in the case of the most rounded gravel particles.
Ranges from 0-11 (rounded gravel-crushed
angular)
1. The cylinder is calibrated by determining the
weight of water at 27
o
C required to fill it
2. Aggregate is sieved through 20, 16, 12.5, 10,
6.3 and 4.75 mm IS sieves
3. About 10 kg of the predominant size should
be available

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Test in Progress

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Contd….
4.The sample of single-size aggregate is dried in an oven at 100
o
to 110
o
C for 24 hours and then cooled
5. The scoop is filled with aggregate which is allowed to slide
gently into the cylinder from the lowest possible height
6. The aggregate is filled in three layers, tamping each layer
evenly 100 times with a tamping rod
7. After the third layer is tamped, the aggregates are struck off
level with the help of tamping rod and surface finished
8. The aggregate with cylinder is now weighed to the nearest 5 g.
The mean weight of aggregate is found

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Calculations and Observation Sheet
Angularity number = 67 -W x 100
G x C
where, W = mean weight of aggregates in the cylinder,g
C = Weight of water required to fill the cylinder,g
G = Specific gravity of aggregate (2.71)
Weight of water filling the cylinder = C g =
Specific gravity of the aggregate = G =
Particulars
Trial number
Mean
1 2 3
Weight of aggregate filling the
cylinder to the nearest five grams, g41854195 4190
Mean weight of aggregate filling the cylinder, Wt =2870
Angularity Number = 67 –{ (4190/2.71x100)/C } = 13

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Discussion
Elongated, flaky and angular materials decreases the
workability of the mix, and not preferred in cement concrete
Angular aggregates are preferred in flexible pavement at WBM
/ WMM
Angularity number ranges from zero for perfectly rounded
aggregate (rounded pebbles) to about 11 percent for freshly
crushed aggregates
But for DBM & BC mix design may be modified to incorporate
high angularity number

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8. Stripping Value
of
Road Aggregates

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Significance
Some types of aggregates have lesser affinity with
bitumen in comparison with water and hence
displacement of bituminous binder occurs when the
mix comes in contact with water
Stripping test would be suitable to assess whether the
binder would keep the bond with aggregate in the
presence of water
The use or otherwise of a suitable anti-stripping agent
can be decided

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Procedure
About 200 gm aggregates passing 20 mm sieve and
retained on 12.5 mm sieve is washed with water,
rinsed in distilled water and dried in an oven at 120
o
C
for two hours.
About 5 % by weight bitumen is heated to 160°C and
aggregate to 100°C and mixed thoroughly.
3. Mixing is carried out by hand in a suitable mixing
pan using a spatula and mixing is continued for 5
minutes at approximately 60 turns per minute.

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Coated Aggregates

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Cont….
Coated aggregate is transferred to a glass jar of 500 ml and
allowed to cool to room temperature
Distilled water is added up to half of the jar
The jar is kept in 40°C oven for 24 hours
The stripping value is measured as the percentage exposed
aggregate visually

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Test in Progress
Sample taken out from
water bath
Observing the aggregate
Stripping

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Observation Sheet
Type of aggregate
Type of binder
Percenatage of binder used
Total weight of aggregate
Total weight of binder
Temp. of water bath
No. of observation Stripping (%)
1
2
3
Average value

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Specifications
As per IRC specifications:
Maximum stripping value for aggregates to be used in
bituminous construction, like, surface-dressing
penetration macadam
bituminous macadam
bituminous carpet
= 25%
Refer: IS: 6241; IRC : 17, 20, 23, 27 and 48

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Discussion
Visual assessment lead to poor reproducibility
New approaches are based on light reflection from the
aggregate before and after immersion in water
Anti-stripping agent reduces the stripping

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9. Polished Stone Value Test

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Significance
1.The Polished Stone Valueof aggregate gives a measure of
resistance to the polishing action of vehicle tyres under
conditions similar to those occurring on the surface of a road
2.The action of road vehicle tyres on road surfaces results in
polishing of the top, exposed aggregate surface, and its state of
polish is one of the main factors affecting the resistance to
skidding.
3.Resistance to this polishing action is determined principally by
the inherent qualities of the aggregate itself.
4.The PSV test is carried out in two stages -accelerated polishing
of test specimens followed by measurement of their state of
polish by a friction test

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Procedure
1.Four curved test specimens are prepared from each
sample undergoing test
2.Each consists of 35 to 50 representative chippings of
carefully controlled size supported in a rigid matrix.
3.Fourteen specimens are clamped around the
periphery of the 'road wheel' and subjected to two
phases of polishing by wheels with rubber tyres
4.The first phase is of abrasion by a corn emeryfor
three hours, followed by three hours of polishing with
an emery flour. Two of the fourteen samples are of
Control stone

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Test Set-up

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Contd….
3. The degree of polish of the specimens is then measured
by means of the portable skid resistance testerunder
carefully controlled conditions
4. Control specimens are used to condition and check the
slider before the test; also a pair of control specimens is
included in each test run of fourteen specimens to check
the entire procedure and to allow for adjustment of the
result to compensate for minor variations in the polishing
and or friction testing
5. Results are expressed as polished stone values (PSVs),
the mean of the four test specimens of each aggregate

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Skid resistance (friction) tester
Also called Skid tester or Friction test machine
The machine is based on the hod principle
It has a pendulum consisting of a tubular arm rotating about a
spindle attached to a vertical pillar
At the end of the tubular arm is a head of constant mass with a
spring loaded rubber slider
The pendulum is released from a horizontal position so that it
strikes the sample of aggregate with a constant velocity
The distance the head travels after striking the sample is
determined by the friction of the surface of the sample, which
has undergone preparation by the Accelerated Polishing
Machine
The results shown by the Skid-Tester as Polished-Stone Values
are the coefficient of friction multiplied by 100

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Skid resistance (friction) tester

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Skid resistance (friction) tester

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Observation Sheet
No. of trials
Mean Value
Property
1 2 3
Polished
stone
value (Recommended Min 55)
MORTH
PSV =
BS: 812 Part 114: 1989

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