Optimization of the Mix Formulation of Geopolymer using Nickel-laterite Mine Waste and Coal Fly Ash

Geopolymer cement has been popularly studied nowadays compared to ordinary Portland cement but has demonstrated superior environmental advantages due to its lower carbon emissions and waste material utilization. Several studies on geopolymers have utilized various wastes like fly ash, blast furnace slag, silica fume, rice husk, or a combination of these wastes. This paper presents a mix formulation design experiment to produce a geopolymer from nickel-laterite mine waste (NMW) and coal fly ash (CFA) as a geopolymer precursor, and sodium hydroxide (SH) and sodium silicate (SS) as alkali activators. An I-optimal design experiment is used to predict the compressive strength for all the mixture's possible formulations and identify optimal proportions to minimize the average variance of prediction. A mixed formulation run of 50% NMW, SH-to-SS ratio of 0.5, and an activator-to-precursor ratio of 0.4286 yielded the highest 28-day unconfined compressive strength (UCS) of 22.1±5.4 MPa. Furthermore, using an optimized formulation of 50.12% NMW, SH-to-SS ratio of 0.516, and an activator-to-precursor ratio of 0.428, an actual UCS value of 36.26±3.6 MPa was obtained. The result implies that the synthesized geopolymer material can be potentially used for pedestrian pavers, light traffic pavers, plain concrete for leveling, building bricks, ceramic glazed facing brick, and fired clay bricks.