USE OF FLY ASH IN RECYCLED AGGREGATE CONCRETE

Abstract

Nowadays, environmentally friendly building is becoming a crucial issue in construction industry. The course towards sustainable concrete involves minimizing the environmental impact of concrete production and as well as reducing the global CO2 emissions. Globally, the concrete industry consumes large quantities of natural resources, which are becoming insufficient to meet the increasing demands. At the same time, large number of old buildings and other structures have reached the end of their service life and are being demolished, resulting in generation of demolished concrete. Some of this concrete waste is used as backfill material and much being sent to landfills. Recycling concrete by using it as replacement to new aggregate in concrete could reduce concrete waste and conserve natural resources of aggregate. In the last two decades, varieties of recycling methods for construction and demolition wastes have been explored and are in well-developed stages. Fly ash is known to be a good pozzolanic material and has been used to increase the ultimate compressive strength and workability of fresh concrete. The approach adopted here includes a 30% substitution of natural aggregates by recycled concrete aggregates as well as the use of (0%,5%,10%,15%) by mass of fly ash as a partial substitute of Portland cement. This paper discusses the strength characteristics of natural and recycled aggregate concrete using fly ash. The most important benefit is reduced permeability to water and aggressive chemicals. This increases strength and reduces permeability.