Micro/meso scale investigations on F-slag sand developed with synergistic use of fly ash and slag

The present study propounds development of an artificial sand, with a prime aim of exploring a potential substitute for natural river sand. The artificial sand, named F-Slag sand, within the particle size range of 4.75 − 0.075 mm, is developed with the combined use of fly ash (FA) and ground granulated blast furnace slag (GGBS) as binder solids (BS) blended in proportions of 90:10, 80:20, 70:30, 60:40, and 50:50. Pelletization, by employing a custom designed disc pelletizer equipment, and geopolymerization, a process of binding and bonding of FA and GGBS particles to form sand size fractions, techniques are adopted to synthesize F-slag sand. Pelletizer speed of 15 rpm, pelletization duration of 10 min, and alkali activator solution to BS ratio of 0.06 are found optimal to produce the sand. A comprehensive micro/meso-analysis, including 3D computed tomography scan, scanning electron microscopy, X-ray diffraction, Brunauer-Emmett-Teller analysis, and Fourier transform infrared spectroscopy are performed on F-slag sand and attempts are made to interpret macro-applications of it. Demonstrably, the synergistic use of GGBS and FA has completely alleviated the need for elevated curing of sand. The gradational analysis revealed that more than 90% of BS are converted into sand size fractions (4.75 − 0.075 mm). F-slag sand exhibited specific gravity of 2.1, water absorption of 17%, permeability 4.2 × 10− 3 cm/sec, angle of internal friction of 38°, and crushing value of 14.8%. In comparison, river sand showed 2.6, 4%, 3.6 × 10− 3 cm/sec, 39° and 6.3% respectively. The loose and compacted bulk densities of F-slag sand are measured at 698 and 991 kg/m3, which are significantly lower vis-à-vis of river sand (1546 and 1728 kg/m3). Micro-analysis confirms dense, well-bonded particles with meso–macroporous connectivity, indicating enhanced mechanical stability and durability. Moreover, leaching and environmental risk analysis affirms that F-Slag sand poses no ecological threat. The outcome of the study, proposition of a novel construction material, elucidates that F-slag sand could be a potential substitute for river sand in building (concrete, mortar, plastering, lightweight structures), mining (mine backfilling) and environmental (drainage & filter) applications.