what is concrete and properties of concrete

WHAT IS CONCRETE :-

A composite material that consists essentially of a binding medium, such as a mixture of portland ce- ment and water, within which are embedded parti- clesorfragmentsofaggregate,usuallyacombination of fine and coarse aggregate. Concrete is by far the most versatile and most widely used construction material worldwide. It can beengineeredtosatisfyawiderangeofperformance specifications, unlike other building materials, such as natural stone or steel, which generally have to be used as they are. Because the tensile strength of con- crete is much lower than its compressive strength, it is typically reinforced with steel bars, in which case it is known as reinforced concrete. See REINFORCED CONCRETE.

Properties of Concret:-

Plain concrete is prepared by mixing cement, sand (also known as fine aggregate), gravel (also known as coarse aggregate) and water with specific proportions. Mineral admixtures may also be added to improve certain properties of concrete. Thus, the properties of concrete regarding its strength and deformations depend on the individual properties of cement, sand, gravel, water and admixtures. Clauses 5 and 6 of IS 456:2000 stipulate the standards and requirements of the individual material and concrete, respectively. Plain concrete after preparation and placement needs curing to attain strength. However, plain concrete is very good in compression but weak in tension. That is why steel is used as reinforcing material to make the composite sustainable in tension also. Plain concrete, thus when reinforced with steel bars in appropriate locations is known as reinforced concrete.  
The strength and deformation characteristics of concrete thus depend on the grade and type of cement, aggregates, admixtures, environmental conditions and curing. The increase of strength with its age during curing is considered to be marginal after 28 days. Blended cements (like fly ash Depending on several factors during its preparation, placement and curing, concrete has a wide range of compressive strength and the material is graded on the basis of its compressive strength on 28th day also known as "characteristic strength" as defined below while discussing various strength and deformation properties. cement) have slower rate of strength gain than ordinary Portland cement as recognized by code,