In RCC slabs only iron rods are used but not of any other metal because

Options

A. it has more ultimate strength
B. they are cheap
C. elasticity is more
D. the coefficient of expansions of concrete and iron are equal.

Answer

To answer the question of why only iron rods are used in RCC (Reinforced Cement Concrete) slabs and not other metals, we can break down the reasoning into clear steps:

### Step-by-Step Solution:

1. **Understanding RCC Slabs**:
RCC slabs are composite materials made of concrete and reinforcing steel (iron rods). The concrete provides compressive strength, while the iron rods provide tensile strength.

2. **Thermal Expansion**:
When materials are heated, they expand. This property is quantified by the coefficient of thermal expansion, which indicates how much a material will expand per degree of temperature increase.

3. **Coefficient of Thermal Expansion**:
The coefficient of thermal expansion for concrete is approximately equal to that of iron. This means that when both materials are subjected to temperature changes, they will expand at similar rates.

4. **Importance of Matching Expansion Rates**:
If the iron rods and the concrete expand at the same rate, the bond between them remains intact. For example, if both materials experience a temperature increase (ΔT), they will both expand proportionally, maintaining their structural integrity.

5. **Consequences of Mismatched Expansion**:
If a different metal with a significantly different coefficient of thermal expansion were used, it could lead to problems. For instance, if the new metal expands more than the concrete, it could cause the concrete to crack due to the stress of the unequal expansion. Conversely, if the metal expands less, it could pull away from the concrete, leading to a loss of structural support.

6. **Conclusion**:
Therefore, the primary reason for using iron rods in RCC slabs is that their thermal expansion properties closely match those of concrete, ensuring that both materials can work together effectively under varying temperature conditions without causing structural failure.