chapter 1 pozzolanas in concrete

chapter 1 pozzolanas in concrete - Utilization of...

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Unformatted text preview: Utilization of Industrial wastes in the Production of Blended Concrete FLY ASH INTRODUCTION FLY ASH Concrete is almost mandatory part of building these days, especially in seismically active regions. Unfortunately concrete production causes some problems for our environment. The production of Portland cement, the glue that usually binds concrete together, puts about one ton of carbon dioxide into the atmosphere for every ton of cement produced.(half from the fuel used to cook the raw limestone and half from the chemical reaction that calcifies the limestone.) Worldwide, the production of portland cement alone accounts for 6-8% of the human-generated carbon dioxide. Fly ash is a waste product generated by coal burning power plants. It is generally either landfilled or, where lack of regulations permit, it is just blowing out of smoke state into the atmosphere. Fly ash can pollute groundwater with heavy metals and in the air becomes particulate pollution or smog. Fortunately fly ash can be used as a replacement for Portland cement in concrete and according to many experts, makes for better concrete. It is generally considered inert and safe once bound up in concrete. Fly ash is comprised of the non-combustible mineral portion of coal. When coal is consumed in a power plant, it is first ground to the fineness of powder. Blown into the power plants boiler, the carbon is consumed leaving molten particles rich in silica, alumina and calcium. These particles solidify as microscopic, glassy spheres that are collected from the power plants exhaust before they can fly away hence the products name: Fly Ash. Flyash is defined in Cement and Concrete Terminology (ACI Committee 116) as the finely divided residue resulting from the combustion of ground or powdered coal, which is transported from the firebox through the boiler by flue gases. Flyash is a by-product of coal-fired electric generating plants. Chemically, fly ash is a pozzolan. When mixed with lime (calcium hydroxide), pozzolans combine to form cementitious compounds. Concrete containing fly ash becomes stronger, more durable, and more resistant to chemical attack. Mechanically, fly ash also pays dividends for concrete production. Because fly ash particles are small, they effectively fill voids. Because fly ash particles are hard and round, they have a ball bearing effect that allows concrete to be produced using less water. Both characteristics contribute to enhanced concrete workability and durability. Finally, fly ash use creates significant benefits for our environment. Fly ash use conserves natural resources and avoids landfill disposal of ash products. By making concrete more durable, life cycle costs of roads and structures are reduced. Furthermore, fly ash use partially displaces production of other concrete ingredients, resulting in significant energy savings and reductions in greenhouse gas emissions. Utilization of Industrial wastes in the Production of Blended Concrete...
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chapter 1 pozzolanas in concrete - Utilization of...

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