A REVIEW ON PERFORMANCE OF CONCRETE MIXES CONTAINING FLY ASH

The particle sizes in fly ash vary from less than 1 μm (micrometer) to more than 100μm with the typical particle size measuring under 20 μm. Only 10% to 30% of the particles by mass are larger than 45μm.The surface area is typically 300 to 500 m2/kg, although some fly ashes can have surface areas as low as 200 m2/kg and as high as700 m2/kg. For fly ash without close compaction, the bulk density(mass per unit volume including air between particles) can vary from 540 to 860 kg/m3 (34 to 54 lb/ft3), whereas with close packed storage or vibration, the range can be 1120 to1500 kg/m3(70 to 94 lb/ft3).Fly ash is primarily silicate glass containing silica, alumina, iron, and calcium. Minor constituents are magnesium, sulfur, sodium, potassium, and carbon. Crystalline compounds are present in small amounts. The relative density (specific gravity) of fly ash generally ranges between 1.9 and 2.8 and the color is generally gray or tan. And there are two types of fly ash namely Class C fly ash and Class F fly ash. The incorporation of coal fly ash can enhance the ability to place, consolidate, and finish fresh concrete; to control the temperature and cracking tendency of recently cast concrete; and to reduce the porosity and penetrability of hardened concrete. These factors result in increased durability that promotes a longer service life and increased sustainability for national infrastructure. If coal fly ash use in concrete decreases, there are no viable alternatives in sufficient volume to meet the demand for concrete with all the benefits as described.