PLAIN AND REINFORCED CONCRETE

Plain concrete: 

It is a mixture of sand , gravel,cement , and water which results in a solid mass .

Concrete is strong in compression but weak in tension. its tensile strength aprox , one tenth of compressive strength plain concrete is mostly used in mass concrete work. ( As in dams) 

Rainforced concrete : 

• It is a concrete with reinforcement embedded in it . The embedded reinforcement makes it capable of resisting tension also.
• Steel bars embedded in the tension zone of concrete, relieves concrete of any tension and takes all tension without separating from concrete 
• The bond between steel and surrounding concrete ensures strain compatibility i.e. the strain at any points in the steel is equal to that in the adjoining concrete.
• Reinforcing steel imparts ductility to concrete which is otherwise brittle material
• Here ductility means large deflection owing to yielding of steel , thereby giving ample warning of impending collapse 
• Tensile stress in concrete arises on account of direct tension, flexural tension , diagonal tension , temperature and shrinkage effect , restraint to deformation 
• Under these conditions, reinforcement must be provided across potential tensile crack .