1. On the basic of geological origin
(a) Naturat aggregate
(a) Naturat aggregate
- Natural aggregate are obtained by crushing form quarries of igneous , sedimentary or metamorphic rocks
- Most widely used aggregate are from igneous origin
- Aggregates obtained from pites or dredged from river most ofter are not clean enough or well graded to suit the quality requirement . They therefore requird sieving and washing before they can be used in concrete
(B) Artifical aggregates
- Broken bricks , blast furnace slag and synthetic aggregates are artificial aggregates
- Broken bricks called as brick bats are suitable for mass concreting, for example, in foundation bases. They are not used for reinforced concrete works.
- Blast furnace slag aggregate is obtained from slow cooling of the slog followed by crushing .
- These dense and strong aggregates as obtained are used for making precast concrete products .
- The blast furnace slag aggregate has good fire resistant properties but are responsible for corrosion of reinforcement due to sulphur content of slag
- Synthetic aggregates are obtained by thermally processed material such as expanded clay and shale used for making light weight contact .
2. On the Basis of size
(a) coarse Aggregate
- Aggregate ranging form 80 mm - 4.75 mm are identified as coarse aggregates.
- These are obtained form natural disintegration or artificial crushing of rocks.
(b) Fine Aggregate
- Aggregate passing through 4.75 mm sieve are defined as fine
- They may be natural sand - deposited by rivers , crushed stone sand - obtained by crushing stones and crushing gravel sand .
- Smallest size of fine aggregate ( sand ) is 0.06 mm
- Depending upon the partical size , fine aggregate are described as fine , medium and coarse sands
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