Explanation:

Rapid hardening cement is a type of cement that has a higher rate of strength development compared to ordinary Portland cement. It achieves its early strength due to a combination of factors, one of which is finer grinding.

Finer Grinding:
The main reason for the early attainment of strength in rapid hardening cement is its finer grinding. The cement clinker is ground to a much finer particle size than ordinary Portland cement. Finer grinding increases the surface area of the cement particles, allowing for a faster reaction with water. This leads to the formation of hydration products at an accelerated rate, resulting in early strength development.

Increased Surface Area:
The finer grinding of rapid hardening cement increases the surface area of the cement particles. This increased surface area promotes a higher rate of chemical reactions between the cement and water. The hydration process, which is responsible for the hardening of cement, occurs when water reacts with the cement particles to form hydration products. By increasing the surface area, more cement particles come into contact with water, leading to a faster reaction and the formation of hydration products.

Accelerated Hydration:
The accelerated hydration of rapid hardening cement is another factor that contributes to its early strength attainment. Hydration is the chemical reaction that occurs between water and cement, resulting in the formation of hydration products such as calcium silicate hydrate (C-S-H) and calcium hydroxide (CH). These hydration products contribute to the strength development of the cement paste.

Conclusion:
In conclusion, the early attainment of strength in rapid hardening cement is mainly due to its finer grinding. Finer grinding increases the surface area of the cement particles, allowing for a faster reaction with water and accelerated hydration. This results in the formation of hydration products at a higher rate and leads to the early development of strength in rapid hardening cement.