Preparation and Properties of Alkali Activated Coarse Aggregates Using Fly Ash and Slag

Coarse aggregate is an essential component of concrete which influences the properties of concrete. Generally, natural crushed stones are being used for the concrete production. The increased demand of aggregates for concrete production can be countered by using alternate aggregates. Production of artificial aggregates from industrial wastes appear as a promising and sustainable alternative to natural aggregates as it helps in utilizing large amount of industrial byproducts in concrete, reduces environmental pollution and also relieves the issues involved in their waste disposal. Hence, this study aims at the utilization of industrial wastes (fly ash and slag) for the manufacture of synthetic aggregates which could be a potential sustainable alternative for the coarse aggregates. Cold bonded pelletized aggregates were prepared by using alkali-activated Class F fly ash and ground granulated blast furnace slag. Alkali mixture of sodium silicate (Na2SiO3) and 10M sodium hydroxide (NaOH) solution were used for the chemical activation of fly ash and slag. Two types of synthetic aggregates were prepared using the fabricated disc pelletizer; mix containing only slag and another mix with equal proportion of fly ash and slag, and the aggregates were heat cured for 24 hours. Tests were done to determine properties such as aggregate surface texture and shape, particle size distribution, bulk density and specific gravity, and the results were compared with the properties of normal aggregates (natural crushed stones). The results indicate that synthetic aggregates made by alkali activation of fly ash and slag could be a potential alternative to the crushed stones.