INTRODUCTION TO REINFORCED CEMENT CONCRETE (R.C.C)

WHAT IS REINFORCED CEMENT CONCRETE?

REINFORCED CEMENT CONCRETE IS A COMPOSITE MATERIAL WHICH COMPRISES OF CONCRETE AND STEEL.

THE PLAIN CEMENT CONCRETE HAS HIGH COMPRESSIVE STRENGTH BUT ITS TENSILE STRENGTH IS VERY LOW. THE TENSILE STRENGTH OF P.C.C (PLAIN CEMENT CONCRETE) IS ABOUT 10% OF ITS COMPRESSIVE STRENGTH. THUS TO INCREASE ITS TENSILE STRENGTH THE PLAIN CEMENT CONCRETE IS REINFORCED WITH STEEL BARS IN THE TENSILE ZONE OF CONCRETE.

*SINCE THE FAILURE OF CONCRETE IS BRITTLE IN NATURE WHICH TAKES PLACE WITHOUT GIVING ANY WARNING, INTRODUCTION OF STEEL IN CONCRETE MAKES IT A DUCTILE MATERIAL WHICH GIVES SUFFICIENT WARNING BEFORE FAILURE OF STRUCTURE/MEMBER.

WHY STEEL IS USED AS REINFORCING MATERIAL IN CONCRETE?

1. IT IS EASILY AVAILABLE

2. IT POSSESS HIGH TENSILE STRENGTH.

3. IT DEVELOPS GOOD BOND WITH CONCRETE

4. THE COEFFICIENT OF EXPANSION OF STEEL AND CONCRETE IS NEARLY SAME.

5. STEEL HAS HIGH  ELASTICITY.

CHARACTERISTIC STRENGTH OF CONCRETE (Fck)

CHARACTERISTIC STRENGTH OF CONCRETE MAY BE DEFINED AS THE STRENGTH BELOW WHICH NOT MORE THAN 5% OF THE TEST RESULTS ARE EXPECTED TO FALL.

GRADE OF CONCRETE

IT IS EXPRESSED IN TERMS OF ITS CHARACTERISTIC COMPRESSIVE STRENGTH ( 150mm CONCRETE CUBE AT 28 DAYS) EXPRESSED IN N/mm² OR MPa.

GRADE OF CONCRETE	TYPE OF CONCRETE
M 10
M 15	ORDINARY GRADE CONCRETE
M 20
M 25 – M 55	STANDARD GRADE CONCRETE
M 60 – M 100	HIGH GRADE CONCRETE

                                          DURABILITY CONDITIONS

EXPOSURE CONDITION	DESCRIPTION	MINIMUM GRADE OF CONCRETE	MINIMUM NOMINAL COVER
MILD	PROTECTED FROM RAINFALL	M 20	*20 mm
MODERATE	SUBJECTED TO RAINFALL, SUBMERGED IN NORMAL WATER, FOUNDATION IN NON-AGGRESSIVE SOIL	M 25	30 mm
SEVERE	COASTAL AREA, ALTERNATE DRYING & WETTING IN NORMAL WATER, SUBJECTED TO HEAVY RAINFALL, SUBMERGED IN SEA WATER	M 30	**45 mm
VERY SEVERE	ALTERNATE DRYING & WETTING IN SEA WATER, SUBJECTED TO SEA SPRAY, FOUNDATION IN AGGRESSIVE SOIL	M 35	50 mm
EXTREME	TIDAL ZONE, SUBJECTED TO AGGRESSIVE CHEMICALS	M 40	75 mm

NOTE - (* =THIS CAN BE REDUCED TO 15 MM FOR REINFORCING BAR OF DIAMETER 12 mm OR LESS)

(** = THIS CAN BE REDUCED TO 40 mm IF GRADE OF CONCRETE IS M 35  OR HIGHER)