Concrete has high compressive strength but poor tensile strength. It is prone to crack when open for tension to provide sufficient tensile strength, reinforcements in the form of steel bars are provided. The combination of co ncrete and steel reinforcement results in a material known as Reinforced Cement Concrete (RCC).
It contains favourable properties of both the concrete and the steel. Steel is used as reinforcing material due to its high tensile strength and elasticity, and its thermal coefficient is nearly same as that of concrete.
Ingredients of Reinforced Cement Concrete:
1. Cement
2. Fine aggregate (or coarse sand)
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3. Coarse aggregate
4. Water
5. Reinforcement
Cement used should be as per the specifications of BIS (Bureau of Indian Standard). Generally sand is used as find aggregate. Sand should be coarse with fines modulus 2.90 to 3.20. Coarse aggregate may stone grit, gravel or some other inert material. It should be hard, durable and free from other injurious materials such as saltpetre, salts etc.
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Generally crushed stone grit, granite tips, stone ballast is used for this purpose. For RCC work, the size of coarse aggregate varies from 2cm to 3cm. Potable water which is free from impurities like sulphates, chlorides etc. is better use for RCC.
Grades and Strength of Reinforced Cement Concrete:
Concrete mix in RCC works is classified into the following categories:
The mix 1:3:6 indicates proportions of cement, aggregate and sand respectively.
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M10 and M20 grade of concrete is used in mass concrete work. M15 is generally used for all purpose of general nature such as RCC slabs, and flooring. M20 and M25 is used for thin RCC members such as precast members, shed roofs, thin shell etc. M35 and M40 are used in pre-stressed concrete structures i.e. for post-tensioned and pre-tensioned concrete members respectively. Strength of cement depends on the water cement ratio.
i. Mild steel bars (Plain bars)
ii. High yield strength deformed (HYSD) bars
iii. Twisted bars
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iv. Steel wires (or Tendons)
i. Mild Steel Bars (Plain Bars):
The main drawback of these bars is their poor bond stress.
ii. Deformed Bars (HYSD Bars):
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These bars are more suitable in comparison to plain bars.
iii. Twisted Bars:
Cold worked twisted bars are used to improve the bond between concrete and reinforcing materials. These bars increase the yield stress by about 50% and thus save reinforcing material by 33%. These bars have greater bond strength and hence are very useful for water retaining structures such as retaining walls, dams etc. The size of bars varies from 5 mm to 50 mm.
iv. Steel Wires:
Steel wires with high elasticity are used in pre-stressed concrete members. They have a diameter of about 6mm and are known as tendons. They are also used in the form of wire mats.
RCC has many advantages. It can be moulded into any desired shape due to its plastic properties. It is fire resistant, damp proof, rigid, durable and impermeable to moisture. Its structures can bear the shocks of earthquake effectively. Maintenance of RCC work is less while its appearance is good.