High-volume fly ash Self Consolidating Concrete with coal bottom ash and recycled concrete aggregates: Fresh, mechanical and microstructural properties

The study focuses on the use of coal bottom ash (CBA) and recycled concrete aggregates (RCA) as partial replacements for natural fine aggregates (NFA) and natural coarse aggregates (NCA) in high-volume fly-ash self-consolidating concrete (HVFA-SCC). The CBA and RCA were replaced in combination from 0 to 30% and 0-50%, respectively. Experimental results showed that the com-bined use of CBA (20%) and RCA (25%) in HVFA-SCC significantly enhanced compressive, split-ting tensile, flexural and direct shear strength at 120 days. Additionally, it was discovered that 25% of RCA and 20% of NFA substitution with NCA and CBA, respectively, were noted as opti-mum replacement levels considering the effects on designed HVFA-SCC mixes up to later-age strength. Microstructural investigations such as scanning electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopic proved that micro level properties of HVFA-SCC improved with higher curing periods as Fly Ash (FA) and CBA exhibited the poz-zolanic reactions. Such reactions lead to additional calcium-silicate-hydrates and dense mi-crostructure formation consequently enhancing the mechanical properties.