The Effect of Mechanochemical Activation of Coal Fly Ash on the Mechanical Properties of Cementitious Composites

The low reactivity of untreated coal fly ash limits its effective utilization as a supplementary cementitious material. This study examined high-alumina, low-calcium Class F fly ash from the Ekibastuz thermal power plant and compared mechanical activation, NaOH activation, and their combined use in cementitious composites. For the principal mechanical-activation series, 15% of the binder was replaced with fly ash and milling time was varied from 0 to 30 min. Under the documented BMU-100 conditions (400 rpm; grinding-media-to-fly-ash mass ratio 10:1), the highest measured 28-day compressive strength was 34.0 ± 0.3 MPa after 15 min; longer milling increased specific surface area but did not further increase strength. In the separate alkaline-activation series, 4% NaOH produced 34.5 MPa, while the combined treatment also produced 34.5 MPa and therefore did not establish a synergistic interaction. Conclusions concerning fly-ash replacement level are restricted because replacement-level screening and strength testing were conducted in separate sequential series. The findings are specific to the investigated ash, mixture design, and laboratory conditions.