Concrete is a composite material used for the construction purpose. Concrete consist of coarse material bounded with binder material cement. It is the widely used construction material. In concrete the cement and water mix which form a paste matrix which fills the voids between the coarse aggregate and hardens over time. Freshly mixed concrete before set is known as green concrete, whereas after hardens it is known as hardened concrete. Sufficient curing time is required for the hardening of concrete.The addition of admixture improves its strength and other properties, the mostly used admixture are silica, ground slag furnace, rice husk ash etc..
The water cement ratio is the ratio of water to the cement and it is one of the main factor for the composition of ingredients in the concrete.
The water cement ratio is the factor which determines the strength of the concrete. The optimum value of water cement ratio varies from 0.4 to 0.6.
Grades of concrete
The grades of concrete is the ratio by which ingredients is mixed. The ingredients that are used in concrete are cement, fine aggregate and coarse aggregate. The “M” denotes Mix design of concrete followed by the compressive strength number in N/mm2
“Mix” is the respective ingredient proportions which are
Cement: Sand: Aggregate Or Cement: Fine Aggregate: Coarse Aggregate.
Admixture are ingredients added to the concrete during the mixing time of concrete to improve its chemical and physical properties.It reduces the const of construction and also improves the properties of hardened concrete.
The main admixtures used for making of concrete are
- Set retarders
- Air entrainers
- Water reducers
- Fly ash
- Granulated blast furnace slag
- Silica fume
Classification based on the American concrete institute
- Water reducing admixtures
- Set controlling admixtures
- Air-entraining admixtures
- Miscellaneous admixtures
- Admixtures for flowing concrete