Natural pozzolans affect several concrete properties in both fresh and hardened state. It improves the workability of concrete and increases its setting time. The reduction of concrete bleeding and segregation is one of the crucial benefits of natural pozzolans. It enhances concrete durability, but reduces early strength and ultimate strength when the mix contains a high percentage of natural pozzolans.
The natural pozzolans are “a siliceous or siliceous and aluminous material, which in itself possesses little or no cementitious value, but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties.”, as per ASTM C125.
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How does Natural Pozzolan affect Concrete Properties?
1. Concrete Workability
Fine-grain size of natural pozzolans create lubricant effects on concrete. As a result, the consistency and workability of concrete are improved. The improvement of concrete workability means lesser concrete mix water demand, which is advantageous from an economic point of view.
2. Setting Time
The use of natural pozzolans increases the setting time of concrete. The higher the amount of natural pozzolans in concrete, the longer the setting time. The increase in setting time is beneficial for hot weather concreting.
3. Bleeding and Segregation
The natural pozzolans increase the volume of paste in concrete and reduce water demand. As a result, it reduces the bleeding and segregation of concrete.
4. Concrete Durability
Natural pozzolans fill the micropores in the cement matrix and increase the durability of concrete considerably. Test results at 28 days and 56 days showed that there is a mild improvement in concrete durability by the use of ground natural pozzolans.
5. Concrete Strength
The use of natural pozzolans declines the early strength of concrete. The addition of a high percentage of natural pozzolans (greater than 15%) reduces the ultimate strength of concrete. However, a lower percentage would not influence the strength.
FAQs on the effect of natural pozzolans on the properties of concrete
The natural pozzolans are “a siliceous or siliceous and aluminous material, which in itself possesses little or no cementitious value, but will, in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties.”, as per ASTM C125.
Natural pozzolans affect several concrete properties in both fresh and hardened state. It improves the workability of concrete and increases its setting time.
The reduction of concrete bleeding and segregation possibility is one of the crucial benefits of the natural pozzolans.
It enhances concrete durability but reduces early strength and ultimate strength when the mix contains a high percentage of natural pozzolans.
The use of natural pozzolans increases the setting time of concrete. The higher the amount of natural pozzolans in concrete, the longer the setting time. The increase in setting time is beneficial for hot weather concreting.
The use of natural pozzolans declines the early strength of concrete. However, a lower percentage would not influence the strength.
The natural pozzolans can improve concrete durability.