coal fly ash % used in cement?

Answer 1

Portland Flyash Cement contains up to 30% fly ash. The flyash is pozzolanic, so that ultimate strength is maintained. Because flyash addition allows a lower concrete water content, early strength can also be maintained. Where good quality cheap flyash is available, this can be an economic alternative to ordinary Portland cement.

Answer 2

You can specify any amout of fly ash you want. The fly ash is cheeper that other compounds so it makes the mix cheeper. Too much will hurt the strength.

Answer 3

If you are specifying a very smooth finish you should limit it to 10% because the finishers will have difficulty because the concrete will tend to stick to the trowel.