Aggregates

Aggregates

Aggregates are the very important constituent in concrete. They give body to the concrete, reduced shrinkage, increase durability, strength and effect economy. Aggregates occupy 70–80 per cent of the volume of concrete. Aggregates such as sand, gravel and crushed stone used with a binding material such as water, bitumen, Portland cement, lime, etc to form asphalt concrete and Portland cement concrete.

 Earlier, aggregates were considered as chemically inert materials but now it has been recognized that some of the aggregates are chemically active and also that certain aggregates make chemical bond at the interface of aggregate and paste.

Classification

Aggregates can also be classified on the basis of the shape, weight, Source and size.

Aggregates can be classified by weight  as (I) Normal weight aggregates, (ii) Light weight aggregates and (iii) Heavy weight aggregates. 

There will only discussing the normal weight aggregates.

Normal weight aggregates can be further classified as natural aggregates and artificial aggregates.

Natural	Artificial
Sand, Gravel, Crushed	Broken Brick,
Rock such as Granite,	Air-cooled Slag.
Quartzite, Basalt,	Sintered fly ash
Sandstone	Bloated clay

Classification of Aggregates on the bases of shape

·         Rounded Aggregates

·         Irregular or partially rounded aggregates

·         Angular aggregates

·         Flaky aggregates

·         Elongated aggregates

·         Flaky and elongated aggregates

Classification of Aggregates on the bases of Size

Aggregates are divided into two categories to respect of size

(I) Coarse aggregate  

(ii) Fine aggregate.

The size of aggregate bigger than 4.75 mm is considered as coarse aggregate and aggregate whose size is 4.75 mm and less is considered as Fine Aggregate.

Classification of Aggregates of the basses of Source.

There are three kind of Aggregates by the 
 

Source Igneous rock Aggregates,

Sedimentary rock Aggregates,

Metamorphic rock Aggregates,