Manufacturing and utilization of Fly Ash Angular Aggregate for Sustainable Construction

Abstract

This study deals with preparation of fly ash aggregate and various tests performed on the fly ash aggregate. These aggregate are manufactured by using fly ash of class F, 25% of bentonite and 40% of water content by weight of fly ash. Disc pelletizer was used for mixing fly ash, bentonite and water homogeneously until most of the sample turned into small balls. After pelletization process, sample was compressed into briquettes to reduce the pores. Briquettes are allowed for surface drying and then heated at a temperature of 1250°C for 10 hours. Sintered briquettes are then crushed into angular aggregates by an aggregate crusher.

Various tests like specific gravity, water absorption, crushing value and impact value, bulk density tests were conducted on fly ash aggregate for characterization of fly ash angular aggregate. Crushing value and impact values satisfies the requirements of aggregate used for concrete
constructions and pavement works. Crushing value of fly ash aggregate is 26%, which is below 45% thus satisfying minimum requirement for crushing strength. Impact value is 18%, which is less than 45% thus satisfying minimum requirement for impact resistance. Crushing value of fly ash aggregate is 42% smaller than the normal aggregate. Impact value of fly ash angular aggregate is only 20% smaller than the normal aggregate. The water absorption of fly ash aggregate is 7.49% more compared to normal aggregate due to the presence of pores. Concrete mixture design for M20 grade was done as per IS 10262: 2009. Concrete cubes with conventional concrete and concrete with 10%, 20%, 30% and 100% replacement of natural aggregates with fly ash angular aggregate respectively. The compressive strength of concrete cubes at 7 days, 14 day and 28 days were found and compared the strength variation between conventional and fly ash aggregate concrete after curing.Incorporating fly ash angular aggregate in concrete reduces the strength of concrete for 10% to 20% replacement, but the compressive strength has increased for 30% and 100% replacements. The conventional concrete compressive strength is 11.5% more than the concrete with 100% replacement of natural aggregate by fly ash angular aggregate. Fly ash aggregate concrete is 12.5% lighter than the conventional concrete.

Concrete beams with concrete of grade M20 was casted. Conventional concrete beam and concrete beam with 100% replacement of natural aggregate by fly ash angular aggregate were compared for flexural strength. The flexural strength of concrete beam with 100% replacement of natural aggregate by fly ash angular aggregate (FAAC100)is less than conventional concrete beam by only 3KN.The deflection of conventional concrete beam under L/2 distance at 50KN load is 12.5% less than the concrete beam with 100% replacement of natural aggregate by fly ash angular aggregate (FAAC100).The fly ash aggregates may be suitably used in concrete construction.