Concrete and Overview

Distinguishing between three states of concrete

Plastic State : When the concrete is first mixed it is like 'bread dough'.It is soft and can be worked or moulded into different shapes. In this state concrete is called PLASTIC. Concrete is plastic during placing and compaction. The most important properties of plastic concrete are workability and cohesiveness. A worker will sink into plastic concrete. Setting State: Concrete then begins to stiffen. The stiffening of concrete, when it is no longer soft, is called SETTING.Setting takes place after compaction and during finishing. Concrete that is sloppy or wet may be easy to place but will be more difficult to finishing.

Concrete that is sloppy or wet may be easy to place but will be more difficult to finish. A worker leaves footprints in setting concrete. Hardening State: After concrete has set it begins to gain strength and harden. The properties of hardened concrete are strength and durability. Hardened concrete will have no footprints on it if walked on.

Workability of Concrete

Workability means how easy it is to:

• PLACE
• HANDLE
• COMPACT
• FINISH a concrete mix.

Concrete that is stiff or dry may be difficult to Handle, Place, Compact, and Finish and, if not constructed properly, will not be as strong or durable when finally hardened.

Major Factor affecting the workability of concrete

Workability is affected by the amount of cement paste, which is the soft or liquid part of the concrete mix. The more paste mixed with the coarse and fine aggregates, the more workable a mix.

Aggregate grading

Graded Aggregate means that there is a range of size of aggregates, from large rocks to smallsands. Well-graded aggregates give a more cohesive mix, too much coarse aggregate gives a boney mix.