Pozzolanic Index and lime requirement of low calcium fly ashes in high volume fly ash mortar

- HVFA concrete require more lime than the lime released by hydration reaction.
- Pozzolanic Index (PI) linearly varies with fineness of fly ash.
- The lime needed or excess is calculated for replacements levels of 20-80%.
- HVFAC with up to 80% fly ash can be developed without compromising the properties.

The major drawback for High Volume Fly Ash Concrete (HVFAC) is low strength development. It is because of the production of less lime by the hydration due to less cement present. However, the exact amount of the lime required for HVFAC system is an unsolved problem so far due to the complexity of hydration and pozzolanic reactions. This paper presents the application of the theory of a logical Pozzolanic Index proposed by Dunstan R Edwin in 2006 for three fly ashes of different chemical and physical properties. Based on the procedure used to find the Strength Activity Index proposed by ASTM C 618, an experimental analysis is conducted on mortar compressive strength, whose results are used to determine the Pozzolanic Index. Thereby calculates the required lime for each replacement of cement with fly ash ranging from 0 to 80% for the three fly ashes. It also concludes that the finer the fly ash the more reactive and consumes more lime at certain age of concrete.