Cement concrete is the main and essential constituent in the building construction mainly used in Columns, beams, slab, taxi tracks, run ways, foot path and floor etc. The strength and stability of the building is mainly related with the strength of cement concrete used in the building. There are four ingredients used in the cement concrete mix i.e. cement, fine aggregate, coarse aggregate and water but some time we add supplementary cementing materials (SCMs), and chemical admixtures and these last two components are optional. When water is added a chemical reaction called hydration occurs between water and Portland cement. In case when we add SCMs, then a second chemical reaction occur between some of the hydration products and the SCMs. These two reactions bind the aggregate particles to produce a very hard building material that is concrete.
Supplementary cementing materials have properties to make concrete hard when these are mixed with Portland cement. These materials react with the cement through hydraulic or pozzolanic activity or both. Some supplementary cementing materials are fly ash, ground granulated blast-furnace slag and silica fume etc.
Where as chemical admixtures are those elements if used in concrete they provide certain properties in concrete more effectively than by other means such as Air-entraining admixtures, Water-reducing admixtures, Retarding admixtures and other miscellaneous admixtures.
Fly ash is a by-product and the main source of fly ash is coal-fired electricity generating power plants. The fly-ash is obtained from combustion of coal through the high-temperature zone in the furnace leaving the molten ash. The molten ash is entrained in the flue gas and cools rapidly, when leaving the combustion zone it is called as fly ash. The fly ash is then collected in bag houses. Huge quantity of fly ash about 100 million tones approximately are produced in India annually and this is increasing rapidly and currently. There is waste disposal problem to dispose of fly ash. Generally large part of the fly ash is currently disposed of in landfills. It is more beneficial if we utilize the fly ash in useful applications such as housing, agriculture and industry and minimize the problem of disposal of fly ash.
Use of Fly Ash in the concrete:-
Fly ash with ordinary Portland cement (OPC) when used in concrete mix can save the quantity of cement. Fly ash can be used in concrete in two ways, one is direct use and other is in the factory. In the direct use the fly ash is used as a separate ingredient at the concrete batch plant or, can be blended with the OPC to produce blended cement which is called Portland-Pozzolana cement (PPC) in India. Fly ash blended cements are produced by several cement companies in India. In general, the use of fly ash in the concrete industry with OPC cement is normally ranges from 15 to 25%. If concrete is properly designed, the use of fly ash in concrete will improve some aspects of the performance of the concrete. The use of fly ash can increase long-term strength of the concrete and enhance the durability. The use of fly ash also helps to creates significant benefits to the environment. The use of fly ash in concrete reduces green house gas emission without negative impacts on the economy.
Use of crushed waste glass:-
The use of waste glass in concrete mix is also studied to reduce land fill problem and to reduce green house gas emission without negative impact on the economy. For this purpose effect of use of fine waste glass and coarse waste glass as aggregate in the Portland cement concrete mix with recycled glass on the fresh and hardened properties of Portland cement concrete at ambient and elevated temperatures is studied. Percentages of replacement from 0–100% of aggregates with fine waste glass and coarse waste glass considered.
In general, concretes made with 10% aggregates replacement with fine waste glass and coarse waste glass had better properties in the fresh and hardened states at ambient and high temperatures than those with larger replacement. Concretes made with FWG aggregates had higher compressive strengths than those made with CWG and FCWG at ambient and elevated temperatures. Extensive field and laboratory testing finds that if waste glass crushed and screened is used as sand substitute in concrete is strong and safe. The use of crushed glass in concrete can save the land fill cost, saving on unit cost of concrete and environmental benefits.