1. AGGREGATES

2. DEFINITION:
Inert or chemically inactive materials which when bonded together with cement forms concrete

3. 70% to 80% of concrete is composed of aggregates
Properties of aggregates affect properties of concrete.
Avoids cracking and gives strength to concrete.
Eg: natural sand, gravel, crushed stone etc.

4. CLASSIFICATION According to nature of formation According to size
Natural aggregates
Artificial aggregates
According to size
Coarse aggregates
Fine aggregates
All-in aggregates
According to shape
Rounded aggregates
Irregular or partially rounded aggregates
Flaky aggregates
Angular aggregates
Elongated aggregates

5. According to nature of formation
Natural aggregates:
obtained from natural sources

6. Artificial aggregates:
Artificial aggregates: manufactured from raw materials by fusing in rotary kiln

7. According to size: Coarse aggregates: retained on 4.75mm sieve.
max. size for plain concrete – 150mm
max. size for reinforced concrete – 60mm or less

8. Single sized aggregates
Coarse aggregates:
Graded aggregates
Single sized aggregates

9. Fine aggregates:. passing through 4. 75mm seive and retained on 0
Fine aggregates: passing through 4.75mm seive and retained on 0.15mm sieve.

10. Fine aggregates: Natural sand Crushed stone sand
Broken brick fine aggregate

11. All – in aggregates Comes from pit or river bed
Used without seperating into different sizes.
Contains fine and coarse aggregates
Used for unimportant works

12. According to shape
Rounded aggregates: Surface area minimum Concrete requires lesser cement – low strength

13. Irregular aggregates: natural irregularity due to attrition with rounded edges

14. Flaky aggregates: usually angular – thickness is small relative to other dimensions

15. Angular aggregates: - well defined edges - concrete – more cement – high strength and durability

16. Elongated aggregates:
Elongated aggregates: length is considerably greater than other two dimensions concrete – poor quality and less durable.

17. Sources of aggregates:
Pit Sand
River Sand
Sea Sand

18. Pit Sand: pits dug at a depth of 1
Pit Sand: pits dug at a depth of 1.5m to 2m in soil sharp, angular porous and free from harmful chemicals for making mortar

19. River Sand: obtained from river beds and banks bright and clear – sharp or rounded for mortar and plastering

20. Sea Sand: seashores brown and rounded contains salts – not used for construction

21. Manufactured Sand: manufactured in stone crushers less impurities better control over size and quality

22. Requirements: Hard, strong, durable
Should not react with cement or steel
Angular and rough surface
Free from organic substances
Contains stone gravels and sand or in various combinations

23. Grading of aggregates
Representation of particle size in a sample of aggregates
Good grading – all standard sizes in required proportions
Sieve analysis – determination of proportions of particles in an aggregate by seperation on sieves

24. Sieve analysis 80 mm 40 mm 20 mm 10 mm 4.75 mm 2.36 mm 1.18 mm
600 microns
300 microns
150 microns
pan

25. Sieve analysis

26. Weight of residue on each sieve
% weight retained
Cummulative % weight retained
Fineness modulus =
WR – sum of cummulative % retained

27. type Fineness modulus Fine sand 2.2 to 2.6 Medium sand 2.6 to 2.9
Sands are classified as:
type
Fineness modulus
Fine sand
2.2 to 2.6
Medium sand
2.6 to 2.9
Coarse sand
2.9 to 3.2

28. Based on gradation well graded – good representation of all sizes

29. Poorly graded: excess of of certain sizes

30. Gap graded: one or intermediate sizes are missing