Cement is a binder, a substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete.

Cements used in construction are usually inorganic, often lime or calcium silicate based, and can be characterized as either hydraulic or non-hydraulic, depending on the ability of the cement to set in the presence of water (see hydraulic and non-hydraulic lime plaster).
 
Different grades of cement are specified by IS 1489-1991. Cements are mainly classified on the basis of compressive strength of particular cement.For example if cement has compressive strength of 33 N/mm2 then it is classified under grade 33.

Mainly 3 grades of cements are used:
GRADE 33 ORDINARY PORTLAND CEMENT:
Fineness=300 m2/kg
Compressive strength after 3 days=16 N/mm2
Compressive strength after 7 days=22 N/mm2
Compressive strength after 28 days=33N/mm2
Grade 33 cement has high workability and is mainly used for mortar in masonry work and for plastering.
 
 
IS 269(1989) COVERS THE SPECIFICATION OF GRADE 33 ORDINARY PORTLAND CEMENT.
GRADE 43 ORDINARY PORTLAND CEMENT:
Fineness=225 m2/kg
Compressive strength after 3 days=23 N/mm2
Compressive strength after 7 days=33 N/mm2
Compressive strength after 28 days=43 N/mm2

Grade 43 cement is moderately sulphate resisting and has good workability. Grade 43 cement has low chloride content and thus resists corrosion on R.C.C. Grade 43 cement has smooth and better finish.
Grade 43 cement is mainly used in:
Ready mix concrete.(R.M.C)
Reinforced cement concrete work (R.C.C)
Pre-cast concrete. (Example in Delhi Metro pillars)
Silos and chimneys.
IS 8112(1989) COVERS THE SPECIFICATION OF GRADE 43 ORDINARY PORTLAND CEMENT.

GRADE 53 ORDINARY PORTLAND CEMENT:
Fineness=225 m2/kg
Compressive strength after 3 days=27 N/mm2
Compressive strength after 7 days=37 N/mm2
Compressive strength after 28 days=53 N/mm2
Grade 53 cement has low chloride content and is moderately sulphate resisting. Volume of cement required is less due to high strength and surface area which saves the cost of construction.
Grade 53 cement is used in:
Industrial buildings, roads and subways.
Pre-cast concrete.
R.C.C Bridges.
Concrete sleeper for railways.
 
IS 12269(1987) COVERS THE SPECIFICATION OF GRADE 53 ORDINARY PORTLAND CEMENT.