Performance of geopolymeric process for developing fly ash based sand and its validation for engineering applications

Scarcity and increased regulations on the mining of natural sand resources, besides constraints on the usage of recycled sand, necessitate a substitute for river sand. Synthesis of sand (artificial) from industrial wastes/by-products seems to be a doable, prospective, and sustainable solution to replenish ever depleting such a precious reserve. This study demonstrates the synthesis and development of artificial sand with fly ash alone as a precursor material. The novelty of the study lies in custom designing disc pelletizer equipment for pelletizer speed, tilt angle, auto spray of solution and feedstock, and exploring geopolymer technology with cold bonding technique to synthesize fly ash based sand (FAB Sand). Sand within the desirable gradation from 4.75 to 0.075 mm has been successfully developed by varying alkali activator solution (AAS) to binder solids (BS) ratio (0.32, 0.34, 0.36), pelletization duration, t_p, (20, 30, 40 min) and pelletizer speed, P_s, (10, 15, 20 rpm). It is established that the aggregation of particles by bonding and binding is the chief mechanism beyond sand formation. The results illustrate more than 90% conversion of fly ash into sand. The usability of FAB sand is validated with engineering applications such as concrete, mortar, plastering, and mine void filling. The compliance of developed sand in construction and geotechnical applications emphasizes the further necessity of synthesizing coarse, medium, and fine sand fractions exclusively. The findings prove the possibility of synthesizing (a) fine sand with AAS/BS ratio of 0.32 for any t_p, 0.34 for 20/40 minutes t_p and 0.36 for 40 min t_p, and (b) medium sand with AAS/BS ratio of 0.36 for 30 min t_p. The proposed novel solution for FAB sand not only alleviates the mining of sand from rivers but also provides sustainable solutions to the valorization of industrial wastes.