Fly Ash Concrete
Chemical Composition of Fly Ash
The table below shows typical compound analyses for two fly ashes and a natural pozzolana (Class F fly ash, Class C fly ash and Class N – Natural) and ordinary portland cement.
A glance at the table reveals:
2. The major difference between fly ash and portland cement is the relative quantity of each of the different compounds. Portland cement is rich in lime (CaO) while fly ash is low. Fly ash is high in reactive silicates while Portland cement has smaller amounts.
IS 3812 (Part 1): 2003 (Pulverized Fuel Ash — Specification for use as Pozzolana in Cement, Cement Mortar and Concrete) specifies Chemical requirements for Fly ash as tabulated below:
|S.No||Characteristics||Requirements for Siliceous Pulverized Fuel Ash||Requirements for Calcareous Pulverized Fuel Ash|
|1||Silicon dioxide (SiO2 ), plus aluminium oxide (Al2O3), plus iron oxide (Fe2O3) percent by mass, min||70||50|
|2||Silicon dioxide (SiO2 ), percent by mass, min||35||25|
|3||Reactive silica in percent by mass, min||20||20|
|4||Magnesium oxide (MgO), percent by mass, max||5||5|
|5||Total Sulphur as Sulphur tri oxide (SO3), percent by mass, max||3||3|
|6||Available alkalis as sodium oxide (Na2O), percent by mass, Max||1.5||1.5|
|7||Total chlorides in percent by mass, Max||0.05||0.05|
|8||Loss on ignition, percent by mass, Max||5||5|
Concrete-Techgroup thanks Headwaters Resources , USA for granting them permission to use their resources in developing this article.