Development of angular-shaped lightweight coarse aggregate with low calcium fly ash using autoclave curing - Experimental and microstructural study

Abstract

Synthesizing coarse aggregate using fly ash is a sustainable way to simultaneously solve the problems of its disposal and scarcity of natural aggregates. A novel technique is proposed in the present study to manufacture angular shaped fly ash aggregate from low calcium fly ash which involves a compaction-extrusion for agglomeration and autoclave or water bath curing for hardening. Cylindrical specimens with different fly ash-lime-cement mix proportions and curing combinations were prepared. Angular shaped fly ash aggregate was obtained by crushing the cured cylindrical specimens. The influence of curing on the unconfined compressive strength of cylindrical specimens and the aggregate impact value of the developed coarse aggregate in a hot water bath and autoclave were investigated. X-ray diffraction patterns, field emission scanning electron microscopy images and thermo-gravimetric analysis were carried out to study the effect of binder content, curing technique, steam pressure, and curing period on strength of aggregate. The autoclave curing method was found to be more effective in hardening the fly ash-binder mix compared to water bath curing for low calcium fly ash. The present work proposes a quick, cost-effective procedure (mixing, compaction-extrusion, curing, and crushing) for producing angular-shaped coarse aggregate from low-calcium fly ash. The developed lightweight fly ash aggregates have suitable angularity with rough surfaces for better interlocking and excellent mechanical properties (toughness, hardness, abrasion and soundness), meeting the criteria of aggregate for structural concrete and pavements.