Paratibha Aggarwal, Assoc. Professor, Civil Engg. Deptt., N.I.T. Kurukshetra
IntroductionSelf-Compacting Concrete (SCC), which flows under its own weight and does not require any external vibration for compaction, has revolutionized concrete placement. Use of Self-Compacting Concrete (SCC) in the construction industry has grown significantly due to its technical advantages . Generally, SCC is achieved using new generation superplasticizers to reduce the water-binder ratio. In addition, supplementary cementitious or inert materials such as limestone powder, natural pozzolana, fly ash and bottom ash are also used to increase the viscosity and reduce the cost of SCC.
The consumption of all types of aggregates has been increasing in recent years in most of the countries at a rate far exceeding that suggested by the growth rate of their economy or of their construction industries. Artificially manufactured aggregates are more expensive to produce and the available source of natural aggregate may be at a considerable distance from the point of use, in which case the cost of transportation is a disadvantage. The other factors to be considered are the continued and expanding extraction of natural aggregates accompanied by serious environmental problems. Often it leads to irremediable deterioration of the countryside. Quarrying of aggregates leads to disturbed surface area, but the aggregate from industrial wastes are not only adding extra aggregate sources to the natural aggregate but also prevent environmental pollution. Worldwide, coal-fired power generation presently accounts for roughly 38% of total electricity production. While coal use in some of the developed countries remains static or is in decline, significant increases in coal-fired generation capacity are taking place in many of the developing nations and large capacity increases are planned. However, coal burning electric power plants cause several environmental problems, such as air and land pollution. One of the main by-product of power plant i.e. bottom ash appear to possess the potential to partially replace regular sand as fine aggregate in normal concrete mixtures, providing a recycling opportunity for them. One of the primary impediments to beneficial reuse of bottom ash is the lack of engineering data designers can use to evaluate the efficacy and economy of using the by-product in place of natural sand. The engineering properties and behavior of sands can be readily estimated from the literature for use in preliminary design. In contrast, there is a dearth of information of engineering properties and behavior for bottom ash and there are insufficient data to confirm that industrial by-products, which appear similar to sands, also have comparable engineering properties, more so in a different type of concrete like Self-compacting concretes.
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