This is the geology

1. Road aggregate materials
BY:
ISMAIL
MOHAMOUD
ALI

2. Introduction
• Those types of rocks or mineral fragments that
can be used as an aggregate material in
combination with other natural or artificial
materials like cement and bitumen etc. for
preparing an ideally suitable road surface may
be termed as Road Materials.

3. • Importance. The greater part of the body of a
road is generally constituted by the
aggregates, which are supposed to bear the
main stress under all types of traffic without
undergoing much surface abrasion. Thus,
much importance is always attached to the
selection of the right type of aggregates for
ensuring stability and durability of a road.

4. • This requires a thorough understanding of the
properties that a good road aggregate should
always possess on the one hand and also a
comprehensive knowledge of important rock
types that are suitable for use as source of
these aggregates.

5. • Aggregates used in road construction should
have the following properties:
a. Strength:
• The aggregate to be used in road construction
should be sufficiently strong to withstand
crushing and several stresses due to traffic
wheel load.
Properties of Aggregates
Used in Roads

6. b. Hardness:
• The aggregates used in the surface course are
subjected to rubbing or abrasion. So, the
aggregate should be hard enough to resist
wear and tear due to the abrasive action of
traffic.

7. c. Toughness:
• Resistance to impact is termed as toughness.
• Aggregates used in the pavement are also
subjected to impact due to moving wheel
loads and hammering action due to jumping
of tires.
• Hence, toughness is another desirable
property of road aggregate.

8. d. Soundness/Durability:
• The property to withstand adverse action of
weather or the ability to remain strong over a
long period is called durability or soundness.
• Aggregates are subjected to the physical and
chemical action of rain and groundwater.

9. e. Shape of aggregate
• Aggregates may be of different shapes such as
cubical, rounded, flaky, elongated, etc.
• Flaky and Elongated aggregates have lower
strength.
• So, generally round and angular are preferred.

11. f. Adhesion with bitumen
• Adhesion simply means a binding property
with other materials.
• So, aggregate should have proper or good
binding properties with bitumen/asphalt.

12. g. Free from foreign particles
• Foreign materials like dust, chemicals, etc
reduce the binding property of aggregate i.e.
adhesion between aggregate and bitumen is
reduced.
• So, the material should be free from foreign
materials.

13. Common road aggregates
• The following are considered the common road
aggregates:
a) Basalts
• These are dark colored basic igneous rocks that
have been extensively used as road materials in
areas of their occurrence. The rock is generally
characterized with a crushing strength between
2000-3000 kg/cm² and also with great
toughness. Their specific gravity varies between
2.8-3.

14. Basalt aggregates

15. b) Granites
• All varieties of granites are eminently suitable
as building as well as road materials by good
quality of their properties. The darker
varieties are used more as road materials.

16. Granite aggregates

17. c) Sandstones
• These are sedimentary rocks covering large
parts of the globe. These form the most
commonly used type of road aggregates. Many
varieties are known to exist and almost all of
them are generally found suitable as road
stones. The crushing strength of sandstones
varies from 600kg/cm² for calcareous varieties
to as much as 2500 kg/cm for quartzitic types.

18. Quartzites are widely used as road stones because of
their very hard nature, high crushing strength, compact
character, and good weathering resistant properties.

19. d) Limestones
• They vary considerably in their strength
characteristics depending upon their texture
and structure. Hard and compact varieties
are sufficiently tough to withstand normal
traffic loads. Clayey varieties, however, may
be too soft.

21. e) Gravels
• Rounded and smooth pebbles and rock
fragments of any composition above 2 mm
diameter are collectively termed as gravels.
Their common size range is between 2-7 cm.
These are found as deposits and also along
river bed and sea beaches. Some common of
gravels are:

22. i. Stream bed gravels
ii. River terrace gravels
iii. Flood plain gravels
iv. Beach gravels
v. Glacial gravels
Gravel aggregates

23. Thank you