Difference between Clinker and Fly ash
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) whereas fly ash is reach in reactive silicates.
The same oxides and compounds exist in fly ash and Portland cement. Fly ash compounds are amorphous (glassy) in nature due to rapid cooling and the cement compounds are crystalline in nature due to slower cooling.
The table shows the basic chemical difference. Portland cement is manufactured with CaO, some of which is released in a free state during hydration. As much as 20% of free lime is released during hydration. This liberated lime forms the necessary ingredient for reaction with fly ash silicates to form strong and durable cementing compounds no different from those formed during hydration ofordinary Portland cement.
A review of the chemistry of both materials makes it apparent that a blend of the two will enhance the concrete product and efficiently utilize the properties of both.
Through pozzolanic activity, fly ash combines with free lime to produce the same cementious compounds formed by the hydration of Portland cement.
