To produce a high class fly ash product, like our DP grades, the right run-off-station ash has to be selected. We have selected for our DP grades a raw ash meeting the American ASTM class F standard.
The various fly ash criteria are based on the type of fuel used in the boiler. Class F is based on bituminous hard coal which has a lime content of max. 8%, whereas class C fly ash predominantly based on lignite coal as a fuel shows a lime content between 8 % and 20 %. This rough guidance for selecting the right raw ash can be underpinned by establishing the glassy phase of the ash.
Class F fly ash is predominantly pozzolanic and needs the presence of lime for kicking off the pozzolan reaction (generated by the hydration of the cement in concrete).
Class C is roughly 50 % hydraulic (the hydraulic phase reacts with water) and 50 % pozzolanic.
Why did DIRK PHOENIX opt for class F ash?
The DP products are designed for construction projects in the Middle East, Africa and Asia, all countries with hot ambient climate. For such projects, additional heat generated by the 50 % hydraulic phase in class C ash is not desired. The malus of delayed strength when using class F fly ash can be overcome by mix design for which Dirk Phoenix have ready solutions.