Influence of Fly Ash and Ground Granulated Blast Furnace Slag on the Mechanical Properties and Reduction Behavior of Cold-Agglomerated Blast Furnace Briquettes

The utilization of fly ash and ground granulated blast furnace slag (GGBFS) as supplementary cementing materials in cold-agglomerated blast furnace briquetting was investigated. Sample analysis included chemical and mineralogical composition, particle size, and scanning electron microscopy and the produced briquettes were evaluated for mechanical durability (2, 7, and 28 day tumble strength), mineralogy, thermal decomposition (DSC–TG–MS), and disintegration under reducing conditions at 800°C (LTD). Based on the data, only the use of GGBFS with or without fly ash led to satisfactory 28 day mechanical durability compared to the 28 day reference mean value. The most promising series, where 20% of Portland cement was replaced by a three-fold amount of GGBFS, attested to a 30% strength increase at 28 day compared to the respective reference mean value. However, the 48 hour durability values proved inferior to respective references due to the comparatively larger particle size (one fly ash sample) and slower strength development provided by the supplements. The LTD (800°C) values determined by isothermal reduction at 800°C were strongly correlated (R2 = 0.694) with briquette mechanical durability governed by the dehydration of the C–S–H phase at approximately 320–360°C established by DSC–TG–MS. Subsequent to the dehydration of C–S–H, briquette durability was possibly maintained by the formation of an intermediate carbonated phase prior to final breakdown under the conditions of the LTD (800°C) test. Briquette moisture optimization was encouraged by the variation in detected levels, prospectively emphasized by the ability of industrial-scale briquetting plants to operate on comparatively lower moisture levels.