Reinforced Concrete Slab Thickness and Maximum Size of Reinforcement Bar


To determine the maximum size of reinforcement bar that can be used in a reinforced concrete slab, we need to consider the slab thickness and the requirements for proper reinforcement placement.

1. Requirements for Reinforcement Placement

Reinforcement bars are typically placed in the tension zone of a concrete slab to enhance its structural capacity. To ensure effective reinforcement placement, certain requirements need to be met:

- Sufficient concrete cover: The reinforcement bars must have adequate concrete cover to protect them from corrosion and provide fire resistance.

- Proper spacing: The reinforcement bars should be spaced at regular intervals to ensure effective load transfer and prevent cracking.

2. Concrete Slab Thickness

In this case, the concrete slab is 75 mm thick. This thickness is considered relatively thin for a reinforced concrete slab.

3. Maximum Size of Reinforcement Bar

The maximum size of reinforcement bar that can be used in a concrete slab depends on the concrete cover requirement. As per standard design practices, the minimum concrete cover for a reinforced concrete slab is typically specified as a multiple of the maximum aggregate size.

- For 75 mm thick concrete slabs, the maximum aggregate size is usually limited to 20 mm. This means that the concrete cover requirement is approximately 20 mm.

- The maximum size of the reinforcement bar that can be used is determined by subtracting the concrete cover requirement from the slab thickness. In this case, the maximum size of the reinforcement bar is 75 mm - 20 mm = 55 mm.

4. Available Options

a) 12 mm diameter: This option is greater than the calculated maximum size of 55 mm, so it cannot be used.

b) 10 mm diameter: This option is also greater than the calculated maximum size of 55 mm, so it cannot be used.

c) 8 mm diameter: This option is less than the calculated maximum size of 55 mm, so it can be used.

d) 6 mm diameter: This option is less than the calculated maximum size of 55 mm, so it can be used.

Conclusion

From the given options, the maximum size of reinforcement bar that can be used in a 75 mm thick reinforced concrete slab is 8 mm in diameter (option C).