Tuesday, October 6, 2009

Re: [papercreters] Fly ash & coal ash the same thing?



There is a distinction between fly ash and coal ash.   There are four distinct and extremely different byproducts that result from the combustion of coal.   The finest of coal ash particles is called "fly" ash because it is transported from the combustion chamber by exhaust gases.  It is a the fine powder formed from the mineral matter in coal, consisting of the noncombustible matter in coal plus a small amount of carbon that remains from incomplete combustion.  Fly ash is generally light tan in color and consists mostly of silt-sized and clay-sized glassy spheres. This gives fly ash a consistency somewhat like talcum powder. Properties of fly ash vary significantly with coal composition and plant-operating conditions.

 

Fly ash can be referred to as either cementitious or pozzolanic. A cementitious material is one that hardens when mixed with water. A pozzolanic material will also harden with water but only after activation with an alkaline substance such as lime. These cementitious and pozzolanic properties are what make some fly ashes useful for cement replacement in concrete and many other building applications.  There are two classes of fly ash.

 

Class F fly ash

The burning of harder, older anthracite and bituminous coal yields Class F fly ash, which requires a cementing agent, such as Portland cement, quicklime, or hydrated lime, with the presence of water in order to react and produce cementitious compounds.

 

Class C fly ash

Fly ash produced from the burning of younger lignite or subbituminous coal is the more commonly available and best for building applications.  It has pozzolanic properties and also some self-cementing properties.  In the presence of water, Class C fly ash will harden and gain strength over time. 

 

Neal


----- Original Message -----
From: "ClarkG" <cgetty@ci.azusa.ca.us>
To: papercreters@yahoogroups.com
Sent: Monday, October 5, 2009 2:32:35 PM GMT -07:00 Chihuahua / La Paz / Mazatlan
Subject: [papercreters] Fly ash & coal ash the same thing?

 

Hi all

I was watching 60 Minutes last night.

One segment was talking about coal ash. It it the same a fly ash?

Clark



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