Range of Fineness Modulus for Sand and its Effect on Concrete Strength

Fineness modulus is a measure of the size of particles in aggregates such as sand, gravel, and crushed stone. It is defined as the sum of the cumulative percentages of the aggregate retained on each of a specified series of sieves, divided by 100. A higher fineness modulus indicates that the aggregate particles are coarser, while a lower fineness modulus means that the particles are finer.

The fineness modulus of sand used in concrete is an important parameter that affects the strength and durability of the concrete. A suitable range of fineness modulus is required for making good quality concrete. Generally, the range of fineness modulus for sand used in concrete is between 2.2 and 3.2. However, if the fineness modulus of sand is outside this range, it can affect the concrete strength negatively.

Least Suitable Range of Fineness Modulus for Making Good Concrete

The range of fineness modulus of sand which is least suitable for making good concrete is 3.5 - 4.5. Sand with a fineness modulus within this range is considered too coarse and will result in a weak and porous concrete. The reasons why this range of fineness modulus is least suitable for making good concrete are as follows:

1. Poor Workability: Sand with a fineness modulus of 3.5-4.5 has a high percentage of coarse particles, which makes it difficult to mix and place in the concrete mix. This results in poor workability of the concrete, making it hard to achieve proper compaction and consolidation.

2. Low Strength: The high percentage of coarse particles in the sand with a fineness modulus of 3.5-4.5 reduces the surface area available for bonding with cement paste. This results in weak and porous concrete, which has low compressive strength and durability.

3. High Porosity: Sand with a fineness modulus of 3.5-4.5 has a high percentage of voids between the coarse particles. This increases the porosity of the concrete, making it susceptible to water penetration and freeze-thaw damage.

Conclusion

The range of fineness modulus of sand is an important parameter that affects the quality and strength of concrete. Sand with a fineness modulus of 3.5-4.5 is least suitable for making good concrete, as it results in poor workability, low strength, and high porosity. A suitable range of fineness modulus for sand used in concrete is between 2.2 and 3.2.