TYPES OF AGGREGATES

Aggregates

Aggregates is a broad category of coarse to medium grained particulate material used in construction, including granual material such as sand, gravel, crushed rock, slag and synthetic aggregates.Aggregates are used with a hydraulic cementing medium to produce concrete or motor.Aggregates occupy 60 to 80% of total volume of concrete.

Aggregates are called binding materials when it is mixed with cement and unbound material when used without cement or binding materials.

There are two types of aggregates:

• Fine Aggregates
• Coarse Aggregates

Fine Aggregates

Fine aggregate are usually sand or crushed stone that are less than 9.55 mm in diameter.When the aggregates are sieved through 4.75 mm sieve, the aggregate passed through it.Natural sand is generally used as fine aggregate while silt, dust, clay and stone are comes under this category.The purpose of the fine aggregate is to fill the voids in the coarse aggregate.In fine aggregates, the grain size lies between 4.75 mm and 0.15mm.In other words these pass through sieve size of 4.75 mm and retained on a sieve of 0.15 mm.

The size of various fine aggregates are as fallows:

• Stone Dust: 0.5 mm -5 mm
• Coarse Sand: 0.5 mm - 2 mm
• Medium Sand: 0.25 mm - 0.5 mm
• Fine Sand: 0.06 mm - 0.25 mm
• Silt: 0.002 mm - 0.06 mm

Coarse Aggregates

Coarse aggregate are greater than 9.55 mm in diameter.The usual sizes are in between 9.5 mm to 37.5 mm in diameter.When the aggregate is sieved through 4.75 mm sieve, the aggregate retained is called coarse aggregate.Gravel, cobble and boulders comes under this category.

The coarse aggregate acts as an inert filler material for concrete.The surface area of coarse aggregate is less than fine aggregate.

The size of various coarse aggregates are as fallows:

• Fine gravel: 4 mm -8 mm
• Medium gravel: 8 mm -16 mm
• Coarse gravel: 16 mm -64 mm
• Cobbles: 64 mm - 256 mm
• Boulders: 
• > 256 mm

Types of Aggregates

1. Gravel

Gravel or Graded stone is another coarse aggregate suitable for concrete mixes.Gravel is a loose aggregation of rock fragments.The most common type of rock used in gravel are sandstone, limestone, and basalt.

2. Sand

Sand is a granular materials composed of finely divided rock and minerals particles.It is a finest aggregate.It comes in different gradation such as builder sand, sharp sand and kiln dried sand which vary from coarsest to finest, respectively.Finer sand are good aggregate for mortor and grouts.

3.Granite

Granite is an igneous rock made up of primarily quartz, mica, feldspar, amphiboles and a mixture of additional trace minerals.It is an intrusive rock, meaning that it crystallized from magma that cooled far below earth surface.Granite is composed mostly of two minerals quartz and orthoclase feldspar. Quartz must make up at least 20%  of the rock and orthoclase at least 35%.

4. Crushed Stone

Crushed stone is a form of construction aggregate typically produced by mining a suitable rock deposit and breaking the removed rock deposit and breaking the removed rock to the desired size using crushers.Limestone and dolomite account for 71% of crushed stone.

5. Vermiculite Aggregate

Vermiculite aggregate is used to create a lightweight and insulating concrete that can be used on various forms of bases suitable to a variety of engineering design.This concrete aggregate is often used for roof deck systems and works with most concrete,woodand metal stracture decks.

6. Recycle Concrete

Recycle concrete is created by breaking, removing and crushing existing concrete to a preferred size.It is commonly used as a base layer for other construction materials.Recycled concrete as aggregate will typically have higher absorption and lower specific gravity than natural aggregate and will produce concrete with slightly higher drying shrinkage and creep.