Mechanical processing of wet stored fly ash for use as a cement component in concrete

Abstract

Wet storage effects on fly ash, mean processing may be necessary to achieve physical properties required for use in concrete. This paper considers drying, de-agglomeration and milling of various wet stored fly ashes at laboratory and pilot/benchtop scales, towards meeting these. In the laboratory, different batch quantities and milling times with as received/pre-screened materials were examined using a ball mill. Greater particle size reductions were obtained with increased milling time but at gradually reducing rates. Pre-screening and batch quantity had relatively minor effects on particle size reductions, with little difference found between these materials and dry stored fly ash. Extended milling time resulted in: a darkening of colour; slight increases in loss-on-ignition, the main oxides content, and crystalline components; reductions in water requirement (to a point); and greater reactivity. Similar effects were generally noted in concrete for the superplasticizing admixture dose to achieve a target slump and compressive (cube) strength. At pilot/benchtop scale, a dryer-pulverizer and jet mill were used, which gave general agreement with the behaviour noted in the laboratory, but with the effects tending to be less. Fineness levels in Standards were achievable, with subsequent performance appearing to depend on the milling process used.