Short Answer:

Aggregates in concrete are small pieces of stone, sand, gravel, or crushed materials that are mixed with cement and water to form concrete. They make up the major portion of concrete and help in giving strength and stability.

Aggregates are divided into two main types: fine aggregates (like sand) and coarse aggregates (like gravel or crushed stone). They reduce cost and improve the durability of concrete.

Detailed Explanation:

Aggregates in concrete

Aggregates are very important materials used in concrete. They are the inert (non-reactive) materials that are mixed with cement and water to form concrete. Aggregates occupy about 70 to 80 percent of the total volume of concrete, which means they are the main component of concrete.

The main function of aggregates is to provide strength, stability, and bulk to concrete. Without aggregates, concrete would be weak and expensive because only cement paste cannot provide enough strength. Aggregates also help in reducing shrinkage and cracking in concrete.

Aggregates are generally obtained from natural sources like riverbeds or from crushed rocks in quarries. They are selected carefully to ensure good quality construction.

Types of aggregates

Aggregates are mainly classified into two types based on their size.

Fine aggregates
Fine aggregates are small particles such as sand. Their size is usually less than 4.75 mm. They fill the gaps between coarse aggregates and help in making concrete dense and workable.

Fine aggregates improve the finish and smoothness of concrete surfaces. They also help in reducing voids and increasing strength.

Coarse aggregates
Coarse aggregates are larger particles such as gravel or crushed stones. Their size is usually more than 4.75 mm. They provide bulk and strength to concrete.

Coarse aggregates form the main framework of concrete and help it to bear heavy loads. They also reduce the amount of cement required, which lowers the cost.

Functions of aggregates in concrete
Aggregates perform several important functions in concrete. They increase the strength of concrete by providing a solid mass. They help in reducing the amount of cement required, which makes construction economical.

Aggregates also improve durability by making concrete resistant to wear and tear. They reduce shrinkage and cracking during drying. They also help in improving the workability of concrete, making it easier to mix and place.

Properties of good aggregates
Good aggregates should have certain properties to ensure quality construction. They should be strong, hard, and durable. They should not break easily under load.

They should be clean and free from dust, clay, or organic materials. Impurities can weaken the bond between cement and aggregates. Aggregates should have proper size and shape for better packing and strength.

They should also have good resistance to weather conditions and chemical attacks.

Shape and size of aggregates
The shape and size of aggregates affect the properties of concrete. Rounded aggregates provide better workability, while angular aggregates provide better strength.

Proper grading of aggregates (mix of different sizes) helps in reducing voids and improving density. Well-graded aggregates result in stronger and more durable concrete.

Importance of aggregates in concrete
Aggregates are essential for making strong and durable concrete. They form the main body of concrete and help in carrying loads. Without aggregates, concrete would not be suitable for construction.

They also make concrete economical by reducing the use of cement. Proper selection of aggregates ensures better performance and long life of structures.

Conclusion:

Aggregates are the main components of concrete that provide strength, stability, and durability. They are classified into fine and coarse aggregates and play an important role in construction. Proper quality and selection of aggregates are necessary for strong and long-lasting concrete structures.