pavement materials:aggregates

1. Pavement Materials: Aggregates
M.E. 1ST SEM
SUB:H.M.C

2. Sources of Aggregates
• Natural aggregate mainly from
• Igneous rock
• Metamorphic rock
• Sedimentary rock

3. Types of Aggregates
• Fine Aggregate :
Aggregate particles mainly between the 4.75 mm
size and the 75µm sieve.
• Coarse Aggregate:
Aggregate particles mainly larger than 4.75 mm.
• Pit Run :
Aggregate from a sand or gravel pit with no
processing.

4. Types of Aggregates
• Crushed Gravel
• Pit gravel (or sand) that has been put through a
crusher either to break the rounded gravel particles
into smaller sizes or to produce rougher surfaces
• Crushed Rock
• Aggregate from the crushing of bedrock. All particles
are angular and not rounded as in gravel
• Screenings
• Chips, dust, powder that are produced from
crushing

5. Types of Aggregates
• Concrete Sand
• Sand that has been washed to remove dust and
fines
• Fines
• Silt, clay, or dust particles smaller than 75um
usually the undesirable impurities in
aggregates

6. • Uniformly graded
- Few points of contact
- Poor interlock (shape dependent)
- High permeability
• Well graded
- Good interlock
- Low permeability
• Gap graded
- Only limited sizes
- Good interlock
- Low permeability
Types of Gradations

7. Desirable properties
1. Strength
2. Hardness
3. Toughness
4. Shape of aggregates
5. Adhesion with bitumen
6. Durability
7. Freedom from deleterious particles

8. 1. Strength of Aggregate
• The aggregates used in top layers are
subjected to
(i) Stress action due to traffic wheel load,
(ii) Wear and tear,
(iii) Crushing.

9. 2. Hardness of Aggregate
• The aggregates used in the surface course are
subjected to constant rubbing or abrasion due
to moving traffic.
• The aggregates should be hard enough to
resist the abrasive action caused by the
movements of traffic.
• The abrasive action is severe when steel tired
vehicles moves over the aggregates exposed
at the top surface.

10. 3. Toughness
• Resistance of the aggregates to impact is
termed as toughness.
• Aggregates used in the pavement should be
able to resist the effect caused by the jumping
of the steel tired wheels from one particle to
another at different levels causes severe
impact on the aggregates.

11. 4. Shape of aggregates
• Particular shape range may have rounded,
cubical, angular, flaky or elongated particles.
• Flaky and elongated particles will have less
strength and durability ( Compared to cubical, angular
or rounded particles of the same aggregate.)
• Hence too flaky and too much elongated
aggregates should be avoided as far as
possible.

12. 5. Adhesion with Bitumen
• The aggregates should have least effect of
water absorption.
• If there is affinity by water , bituminous
coating will strip off from the aggregate in
presence of water.
• Means all aggregates will be separated out
from the bitumen in presence of water.

13. 6. Durability
• The property of aggregates to withstand
adverse action of weather is called soundness.
• The aggregates are subjected to the physical
and chemical action of rain and bottom water,
impurities there-in and that of atmosphere.
• Hence it is desirable that the road aggregates
used in the construction should be sound
enough to withstand the weathering action.

14. 7. Freedom from deleterious particles
• Aggregates should be clean, tough and
durable.
• It should be free from at or elongated pieces,
dust, clay balls and other objectionable
material.

15. Aggregate tests
1. Crushing test
2. Abrasion test
3. Impact test
4. Soundness test
5. Shape test
6. Specific gravity and water absorption test
7. Bitumen adhesion test

16. 1. Crushing Test
• Test is standardized by IS:2386 part-IV
• Aim: to determine the crushing strength of
aggregates.
• Material: Dry aggregates passing through 12.5
mm sieves and retained in 10 mm sieves.

17. 1. Crushing Test
Apparatus:
• A steel cylinder (both side open ends) of internal
dia. 15.2 cm.
• A square base plate.
• Plunger having piston dia. 15 cm.
• A cylindrical measure of Internal Dia 11.5 cm and
height 18 cm.
• Steel tamping rod : dia. 1.6 cm and length 45 -60
cm.
• Balance of capacity 3 kg / accuracy up to 1 gm.
• Compression testing machine capable of applying
load of 40 tonnes ,Rate of loading 4 tonnes/ min.

18. Observation table

19. 2. Abrasion Test
• Abrasion tests on aggregates are generally
carried out by any on of the following
methods:
1. Los Angeles abrasion test.
2. Deval abrasion test.
3. Dorry Abrasion test.

20. 2. Abrasion Test
• Aim: to test the hardness property of
aggregates and to decide whether they are
suitable for different pavement construction
works.
• The principle of Los Angeles abrasion test is to
find the percentage wear due to relative
rubbing action between the aggregate and
steel balls used as abrasive charge.

21. Los Angeles abrasion test setup

23. Observation Table

24. 3. Impact Test

25. Observation Table: Impact Test

26. 4. Soundness Test
• IS:2386 part-V.
• Aim: To study the resistance of aggregates to
weathering action, by conducting accelerated
weathering test cycles.
• The Porous aggregates subjected to freezing
and thawing are likely to disintegrate
prematurely.

27. • 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 –
110 C to a constant weight.
• After five cycles, the loss in weight of aggregates
is determined by sieving out all undersized
particles and weighing.
• And the loss in weight should not exceed 12
percent when tested with sodium sulphate and
18 percent with magnesium sulphate solution.
4. Soundness Test

28. Soundness Test
Sample submerged in magnesium or
sodium sulfate—causes salt crystals to form
in the aggregate pores

29. 5. Shape Test
• FLAKINESS INDEX: The flakiness index of
aggregates is the percentage by particles whose
least dimension (Thickness) is less then 3/5th (0.6)
of their mean dimension.
• The Elongation Index of an aggregate is the
percentage by weight of particles whose greatest
dimension (length) is greater then 1 and 4/5th
times (1.8times) their mean dimension.
• The test is not applicable to size smaller then 6.3.
mm.

30. 5. Shape Test
• ANGULARITY NUMBER: the angularity
number of an aggregate is the amount by
which the percentage voids exceeds 33 after
being compacted in a prescribed manner.
• The minimum allowable combined index of
aggregates used in surface course in different
types of pavement is 30 %.

31. Flakiness Index Test Instrument

32. Flakiness Index Test In Progress

33. Elongation Test Instrument Diagram

34. Elongation Test In Progress

35. Observation table: Flakiness Index

36. Observation Table: Elongation Index

37. Angularity Number

38. 6. Specific Gravity
• The specific gravity of a solid is the ratio of its
mass to that of an equal volume of distilled
water at a specified temperature.
• Apparent Specific Gravity: Gapp, is computed
on the basis of the net volume of aggregates
i.e the volume excluding water-permeable
voids. Thus

39. Cont…
• where, MD is the dry mass of the aggregate, VN is
the net volume of the aggregates excluding the
volume of the absorbed matter, W is the density
of water.
• Bulk Specific Gravity: Gbulk, is computed on the
basis of the total volume of aggregates including
water permeable voids. Thus
• where, VB is the total volume of the aggregates
including the volume of absorbed water.

40. Water absorption:
• We can measure the volume of voids by
weighing the aggregates dry and in a
saturated, surface dry condition, with all
permeable voids filled with water.
• The difference of the above two is MW.
• MW is the weight of dry aggregates minus
weight of aggregates saturated surface dry
condition. MD is the dry mass of the
aggregate, Thus
7. Water Absorption Test

41. Cont…
• The specific gravity of aggregates normally used
in road construction ranges from about 2.5 to
2.9.
• Water absorption values ranges from 0.1 to
about 2.0 percent for aggregates normally used
in road surfacing.

42. 8.Bitumen Adhesion Test
• Bitumen adheres well to all normal types of
road aggregates provided they are dry and
free from dust.
• In the absence of water there is practically no
adhesion problem of bituminous construction.
• Adhesion problem occurs when the aggregate
is wet and cold.

43. • Static immersion test is one specified by IRC
and is quite simple.
• 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%.
8.Bitumen Adhesion Test