The reactivity of fly ash is generally difficult to determine because neither a single physical nor chemical property nor any combination of these can be used characterize a particular sample completely. A direct reflection of this is the range of pozzolanicity tests proposed by standards worldwide and the applicability and relevance of such tests is currently being debated.
In many countries, codes of practice and standards relating to fly ashes are currently under review. Some work has been carried out in countries including Australia, United Kingdom, and the United States on commercial fly ashes with a view to possible classification and implementation into standards [1-2]. It is generally recognized that current standards on fly ash do have some inadequacies with regard to performance prediction when included in concrete. Fineness requirements for fly ash for use in structural concrete (BS3892: Part 1) in the United Kingdom are currently being debated  with many workers suggesting that it would be possible to produce durable concrete with ashes which would not comply with the requirements of the standard .