Concrete and Process of Concreting

Concrete Defined as a building material obtained by mixing cement, aggregates and water in suitable proportions. Which when allowed to cure becomes hard like a stone. Three ingredients of concrete

1. Cement 2. Aggregates 3. Water

OPC conforming to Indian Standard specification is used Aggregates are inert or chemically inactive materials which form the bulk of cement concrete.

Two types of aggregates: Coarse and Fine.

Coarse form the main matrix and Fine forms the filler matrix Aggregates should be clean, free from organic matter and other impurities It must be sound and resistant to weathering action. Aggregates should be well graded for obtaining good quality concrete The quality of water used is very much important. Impurities present in it may interfere with the setting of cement, affect the strength, staining of its surface, corrosion of reinforcement etc. The quality of concrete depends on amount of water used. Presence of various salts in sea water adversely affect the qualities of concrete and it is not preferred.

Process of Concreting Batching: it is the process of measuring relative proportions of cement, aggregates and water in order to obtain desired quality of concrete. Two types batching: volume batching and weigh batching. Batching based on the volume of materials called volume batching and batching based on weight is called weigh batching. Mixing: It is the process of making a homogeneous mixture of cement, aggregates and water. Two types, hand mixing and machine mixing.

Transporting and Placing: concrete is conveyed in pans by head load or human ladder. In large and important works, various mechanical devices such as wheel barrow (hand cart) truck mixtures and dumpers, belt conveyers, chute, pumps and pipe lines etc are used for transporting.

Compacting: it is the process for expelling out the entrapped air and forcing the particles into a closer configuration to achieve maximum density of concrete.

Compaction: it can be done manually or mechanically. Hand compaction using hand tools ( Rodding, Ramming and Tamping) Mechanical compaction (internal vibrators, external vibrators, surface vibrators)

Curing: It is the process of keeping the set concrete damp for some days in order to ensure complete hydration of cement and to obtain properly hardened strong concrete. For OPC curing period is 7-14 days. Curing period depends on thickness of sections and type of cement.