Page 7 - zana-training e book

2.2 What is an Aggregate?

Terms to describe the gravels, crushed
stones, recycled concrete and other
materials which are mixed with cement
and water to make concrete.

i. Constitute 60 - 75% of total concrete volume.
ii. Originally viewed as inert material dispersed for economic reasons.
iii. Give body to the concrete, reduce shrinkage and effect economically.

Aggregates are classified into 2 types according to size

i. Fine aggregate
ii. Coarse aggregate

Fine Aggregate

i. When the aggregate is sieved through 4.75mm sieve, the aggregate passed
through it called as fine aggregate.
ii. Natural sand is generally used as fine aggregate, silt and clay are also come
under this category. The soft deposit consisting of sand, silt and clay is termed
as loam.
iii. The purpose of the fine aggregate is to fill the voids in the coarse aggregate and
to act as a workability agent.

Table 1.1 : Size fine aggregate

Fine Aggregate Size Variation (mm)

Coarse Sand 2.0 – 0.5
Medium Sand 0.5 – 0.25
Fine Sand 0.25 – 0.06
Silt 0.06 – 0.002

Clay < 0.002