Table of Content

1. Introduction
2. What are Fine aggregates
3. What are Coarse aggregates
4. What are aggregates used for

Introduction

Aggregates are granular substances that form 70 to 80 percent of the total volume of the concrete. They are hard and inert substances that are free from any kind of chemicals or adhesive of clay. Aggregates include sand, gravel and crushed aggregates like stone chippings or crushed stone. These are available naturally in the form of a homogeneous bulk product. Sieve analysis is done to classify and grade the aggregates into different categories.

Aggregates are classified into two broad categories, namely

1. Fine aggregates
2. Coarse aggregates 

What are Fine aggregates?

Fine aggregates are relatively smaller filler materials less than 4.75 mm in diameter used in construction to fill the voids. These are spherical in shape when compared to coarse aggregates. Fine aggregates are made using natural sand, stone screenings, burnt clay, surki, fly ash, cinders. It is divided into three categories based on the source, uncrushed gravel, crushed gravel and partially crushed gravel. They fill the voids between the larger particles, contributing to the workability of concrete. They also improve the cohesion and reduce the water demand in the mixture. Fine Aggregates are used in mortar, concrete, plaster, filling the voids in coarse aggregates, and filling of layers in roads.

What are Coarse aggregates?

Coarse aggregates are large filler materials used in construction.  These are larger than 4.75mm and their diameter generally ranges from 9.55-37.5 mm. Coarse aggregates are cubical or flaky in shape. It is made using broken bricks, gravel, pebbles, broken stones, clinkers, and cinders among others. It is divided into three categories, namely natural rock disintegration, crushed gravel or stone and dolomite aggregates. Coarse aggregates provide the main structural component of concrete and contribute to the overall strength and stability of the mixture. They are also primarily responsible for the load-bearing capacity of the concrete. Coarse aggregates are used in concrete and railway track ballast. These are also used for the construction of roads, and for that, the aggregate must possess the following qualities.

• Strength
• Hardness
• Toughness
• Durability
• Adhesion with bitumen
• Shape

What are aggregates used for?

Given below are the uses of aggregates.

1. Aggregates are used as a base or sub base in the construction of roads.
2. These provide dimensional stability to the structure.
3. These are used to reduce the load and assist in removing the groundwater from the road during the construction of roads and railway ballast. 
4. Aggregates help in increasing the volume of the concrete and also reducing the cost. They account for 70-80% of the weight of concrete and 75-85% of the weight of plain cement concrete.
5. These boost the hardness, elasticity and abrasion resistance of the concrete, and make it more durable and stronger.
6. Other than these, its usage includes fills, backfills, drainage and filtration 

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