Strength development of fly ash based composite material

Abstract

The term „fly ash‟ is often used to describe any fine particulate material precipitated from the stack gases of industrial furnaces burning solid fuels. The amount of fly ash collected from furnaces on a single site can vary from less than one ton per day to several tons per minute. The characteristics and properties of different fly ashes depend on the nature of the fuel and the size of furnace used. Pulverization of solid fuels for the large furnaces used in power stations creates an immediate, urgent problem; dry fly ash has to be collected from the stack gases and disposed of quickly and safely. Fly ashes generally fall into one of two categories, depending on their origin and their chemical and mineralogical composition. Combustion of anthracite or bituminous coal generally produces low-calcium fly ashes; high-calcium fly ashes result from burning lignite or sub-bituminous coal. Both types contain a preponderance of amorphous glass. Composite material made of fly ash is used in many ways and is subject to a variety of different loading conditions, and so different types of stress develop. The compressive strength of concrete, one of its most important and useful properties and one of the most easily determined, is indicated by the unit stress required to cause failure of a specimen. In addition to being a significant indicator of load-carrying ability, strength is also indicative of other elements of quality concrete in a direct or indirect manner. In general, strong concrete will be more impermeable, better able to withstand severe exposure, and more resistant to wear. On the other hand, strong concrete may have greater shrinkage and susceptibility to cracking than a weaker material. Finally, the concrete-making properties of the various ingredients of the mix are usually measured in terms of the compressive strength.