Influence of design parameters on engineering properties of angular shaped fly ash aggregates

Abstract

Fly ash of thermal power plants substitute’s construction materials and can help to preserve non-renewable resources. In the construction industry, more particularly in concrete and road construction, a huge quantity of aggregate is being used. Fly ash aggregate is a unique alternative for the construction industry at present. However, the properties of fly ash aggregate are mostly controlled by the type and dosage of additive used besides the characteristics of ash and curing method adopted. In the present study, specimens from various combinations of fly ash with hydrated lime, ground granulated blast furnace slag, and cement were prepared at maximum dry unit weight with optimum moisture content and cured by hot water curing method. The cured specimens were crushed to prepared angular shaped fly ash aggregates. The influence of the binding additives on the unconfined compressive strength of mixes and aggregate impact value was studied. Measured engineering properties were also analyzed through a micro-level study. The addition of lime enhanced the unconfined compressive strength of mixes and impact value of aggregates, whereas, replacement of lime with the ground granulated blast furnace slag and cement reduced the strength of the mixes. Unconfined compressive strength value of mixes shows the inverse relationship with impact value of aggregate prepared from that mixes and a correlation between unconfined compressive strength and aggregate impact value has been proposed. Moreover, the effect of moisture content and pressing force on compressive strength and aggregate impact value was also investigated on optimum mixes. From these experimentations, the optimum combinations of fly ash-additive mixes, the optimum value for moisture content, and pressing force were chosen; and angular shaped fly ash aggregates were produced by hot water curing method. Furthermore, the various physical properties, mechanical properties and durability index of these fly ash aggregates are discussed and compared with the Indian standard specifications. The leaching behavior of these aggregates was also examined in this study. The addition of lime gives better results compared to cement and ground granulated blast furnace slag and use of lime seems to be more cost-effective. Thus, these cold bonded fly ash aggregates with significant strength may find prospective use in civil engineering construction sector.