2. 8/16/2019 Aggregate Testing 2
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
3. 8/16/2019 Aggregate Testing 3
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
4. 8/16/2019 Aggregate Testing 4
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
5. 8/16/2019 Aggregate Testing 5
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
7. 8/16/2019 Aggregate Testing 7
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
9. 8/16/2019 Aggregate Testing 9
Procedure
Bring the sample to an air dry condition either by drying
at room temperature or in oven at a temperature of 100oC
to 110oC.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
10. 8/16/2019 Aggregate Testing 10
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
14. 8/16/2019 Aggregate Testing 14
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
16. 8/16/2019 Aggregate Testing 16
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
17. 8/16/2019 Aggregate Testing 17
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
18. 8/16/2019 Aggregate Testing 18
Load Application
Sample being loaded
in the compression
machine at 4 T per
minute for 10 minutes
(upto 40 T)
19. 8/16/2019 Aggregate Testing 19
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
20. 8/16/2019 Aggregate Testing 20
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
21. 8/16/2019 Aggregate Testing 21
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
23. 8/16/2019 Aggregate Testing 23
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
25. 8/16/2019 Aggregate Testing 25
Procedure
1. Aggregate passing through 12.5 mm IS sieve and retained on
10 mm sieve is filled in the cylindrical measure in 3 layers by
tamping each layer by 25 blows. 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 38 cm above the upper
surface of the aggregates in the cup and is allowed to fall freely
on the specimen
27. 8/16/2019 Aggregate Testing 27
Contd….
After subjecting the test specimen to 15
blows, the crushed aggregate is sieved
through IS 2.36 mm 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
28. 8/16/2019 Aggregate Testing 28
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
29. 8/16/2019 Aggregate Testing 29
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
31. 8/16/2019 Aggregate Testing 31
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
33. 8/16/2019 Aggregate Testing 33
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 ( W1 gms)
3. Machine is rotated at 30-33 rpm for 500 revolutions
4. Machine is stopped and complete material is taken out
including dust
34. 8/16/2019 Aggregate Testing 34
Grading RequirementGrading
Wt. 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.of
Charge,g
No.of
Spheres
A - - - 1250 1250 1250 1250 - - - 12 5000±25
B - - - - - 2500 2500 - - - 11 4584±25
C - - - - - - - 2500 2500 - 8 3330±25
D - - - - - - - - - 5000 6 2500±25
E 2500 2500 5000 - - - - - - - 12 5000±25
F - - 5000 5000 NA - - - - - 12 5000±25
G - - - 5000 5000 - - - - - 12 5000±25
36. 8/16/2019 Aggregate Testing 36
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
37. 8/16/2019 Aggregate Testing 37
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
38. 8/16/2019 Aggregate Testing 38
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
40. 8/16/2019 Aggregate Testing 40
Significance of Test
To assess the resistance of the aggregates to
weathering
Almost all road pavements get subjected to alternate
wet-dry conditions
Freeze-thaw situation is main problem in cold regions
Tests the resistance to disintegration
For that aggregates subjected to accelerated wet-dry
and freeze-thaw conditions
42. 8/16/2019 Aggregate Testing 42
1. Preparation of Solutions
(a) Preparation of Sodium Sulphate solution
About 420 gm of anhydrous salt (Na2SO4) or 1300 gm of the crystalline deca hydrate
(Na2SO4 10H2O) is dissolved per litre of water.
The solution is maintained at 27 ± 2°C, stirred frequently, and at a specific gravity of
1.151 to 1.71
(b) Preparation of Magnesium Sulphate Solution: (Alternative)
About 400 gm of anhydrous salt (MgSO4) or 1600 gm of the crystalline hydrate
(MgSO4 7H2O) is dissolved per litre of water.
The solution is maintained at 27 ± 2°C, stirred frequently, and at a specific gravity of
1.295 and 1.308
Procedure
43. 8/16/2019 Aggregate Testing 43
Contd…
2. Clean the course aggregate and dry to a constant weight at
105 - 110° C and separate to different size ranges
(4.75-10 mm=300gm, 10-12.5 mm=330gm, 12.5-20 mm=670 gm, 20-25
mm=500 gm, 25-40mm =1000gm,….,>80 mm=300 gm)
3. Weigh each fraction and place in separate containers for the test
4. Immerse the sample in the prepared solution of Sodium Sulphate
or magnesium sulphate for 16 to 18 hours so that solution covers
them to a depth of at least 15 mm
44. 8/16/2019 Aggregate Testing 44
Contd…
5. Use the cover of the container during the period of
immersion and maintain the temperature of solution at 27oC+/-
1oC
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 105oC - 110oC 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
46. 8/16/2019 Aggregate Testing 46
Contd…..
9. Each fraction of sample is then dried at a constant
temperature of 105oC - 110oC, weighed and sieved
through specified IS sieves
Size 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
47. 8/16/2019 Aggregate Testing 47
Contd….
10. Visual inspection for splitting, crumbling,
disintegration.
11. Report the weighted average from the
percentage loss for each fraction.
48. 8/16/2019 Aggregate Testing 48
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
Passing Retained
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 )
50. 8/16/2019 Aggregate Testing 50
Discussion
Useful to assess the resistance of the aggregate to
weathering
Average loss of weight after 10 cycles should not exceed
12% for Na2SO4 and 18% for Mg2SO4
IRC specification: 12% max after 5 cycles of Na2SO4 for
bituminous constructions
52. 8/16/2019 Aggregate Testing 52
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
53. 8/16/2019 Aggregate Testing 53
Significance
Wa Weight of the specimen in air
Ws Weight of the saturated surface dry
specimen in air
Ww Weight of the specimen in water
54. 8/16/2019 Aggregate Testing 54
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 voids
voidsexcludingVolume
airinWeight
WwWa
Wa
Gsa
voidsexcludingVolume
airinWeight
WwWa
Wa
Gsa
voidsexcludingVolume
airinWeight
WwWa
Wa
Gsa
55. 8/16/2019 Aggregate Testing 55
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
56. 8/16/2019 Aggregate Testing 56
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 pores
voidsincludingVolume
waterincludingairinWeight
WwWs
Ws
ssdGsb
57. 8/16/2019 Aggregate Testing 57
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
58. 8/16/2019 Aggregate Testing 58
Example
Wa = 2031 g Weight of the specimen in air
Ws = 2045 g Weight of the SSD specimen in air
Ww = 1304 g Weight of the specimen in water
794.2
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
60. 8/16/2019 Aggregate Testing 60
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
22OC to 32OC 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 22OC to 32OC (W1 g ).
62. 8/16/2019 Aggregate Testing 62
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 (W2 g).
The surface dried (10-60 mts) aggregate is then
weighed (W3 g)
64. 8/16/2019 Aggregate Testing 64
Contd….
The aggregate is placed in an oven at a
temperature of 100oC TO 110oC for 24
± 0.5 hours.
It is then removed from the oven,
cooled and weighed (W4 g).
12
65. 8/16/2019 Aggregate Testing 65
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)
66. 8/16/2019 Aggregate Testing 66
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 =
67. 8/16/2019 Aggregate Testing 67
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
68. 8/16/2019 Aggregate Testing 68
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
69. 8/16/2019 Aggregate Testing 69
7. Shape Tests
Determination of:
a.Flakiness Index
b.Elongation Index
c.Angularity Number
70. 8/16/2019 Aggregate Testing 70
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
71. 8/16/2019 Aggregate Testing 71
Test Set-up
Length Gauge for Elongation Index
Thickness Gauge for Flakiness Index
72. 8/16/2019 Aggregate Testing 72
Procedure (Flakiness)
(a). Flakiness Index: The flakiness index of aggregates is the
percentage by weight of particles whose least dimension is less than
three-fifths (0.6) of their mean dimension. Applicable to sizes>= 6.3
mm
1.The sample is sieved through IS sieve sizes 63, 50, 40, 31.5, 25,
20, 16, 12.5, 10 and 6.3 mm
2. Minimum 200 pieces of each fraction to be tested are taken and
weighed (W1 gm)
3. Separate the flaky material by using the standard thickness gauge
74. 8/16/2019 Aggregate Testing 74
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
75. 8/16/2019 Aggregate Testing 75
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)
76. 8/16/2019 Aggregate Testing 76
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. Separate the elongated material by using the standard
length gauge
78. 8/16/2019 Aggregate Testing 78
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
79. 8/16/2019 Aggregate Testing 79
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)
80. 8/16/2019 Aggregate Testing 80
Specifications
Type of pavement construction Limit 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
81. 8/16/2019 Aggregate Testing 81
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 27oC 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
83. 8/16/2019 Aggregate Testing 83
Contd….
4. The sample of single-size aggregate is dried in an oven at 100o
to 110oC 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
84. 8/16/2019 Aggregate Testing 84
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, g 4185 4195 4190
Mean weight of aggregate filling the cylinder, Wt =2870
Angularity Number = 67 – { (4190/2.71x100)/C } = 13
85. 8/16/2019 Aggregate Testing 85
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
87. 8/16/2019 Aggregate Testing 87
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
88. 8/16/2019 Aggregate Testing 88
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 120oC
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.
90. 8/16/2019 Aggregate Testing 90
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
91. 8/16/2019 Aggregate Testing 91
Test in Progress
Sample taken out from
water bath
Observing the aggregate
Stripping
92. 8/16/2019 Aggregate Testing 92
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
93. 8/16/2019 Aggregate Testing 93
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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Significance
1. The Polished Stone Value of 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 emery for
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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Contd….
3. The degree of polish of the specimens is then measured
by means of the portable skid resistance tester under
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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Observation Sheet
No. of trials
Mean ValueProperty
1 2 3
Polished
stone
value (Recommended Min 55)
MORTH
PSV =
BS: 812 Part 114: 1989