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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.

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.

Workability of Concrete
Fig. 1: Workability of Concrete

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.

Concrete Setting
Fig. 1: Concrete Setting

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

?What are 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.

?Why are natural pozzolans added to concrete mix?

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.

?How do natural pozzolans influence concrete 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.

?Do natural pozzolans make concrete stronger?

The use of natural pozzolans declines the early strength of concrete. However, a lower percentage would not influence the strength.

?Do natural pozzolans improve concrete durability?

The natural pozzolans can improve concrete durability.

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Madeh Izat Hamakareem

Madeh Izat Hamakareem

EDITOR
Madeh is a Structural Engineer who works as Assistant Lecturer in Koya University. He is the author, editor and partner at theconstructor.org.

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