Pozzolana used as an admixture in concrete has the following advantages: 
1) It improves workability with lesser amount of water. 
2) It increases the heat of hydration and so lets the concrete set quickly. 
3) It increases the resistance of concrete to attack by salts and sulphates. 
4) Leaching of calcium hydroxide is avoided as Ca(OH)2 is converted to cementitious product by pozzolanic action 
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