Synthesis and evaluation of engineering property of geopolymer from nickel-laterite mine silt and coal fly ash

The management of wastes have become a challenge especially for big industries since a large amount of wastes are being generated. These industries such as the nickellaterite mining are generating huge amount of nickel-laterite mine silt (NLMS) which are washed during rainy season contaminating nearby bodies of water. Similarly, coal power plants are generating enormous amount of coal fly ash (CFA) wastes which are usually disposed in landfills contributing to air and water pollution. Hence, upcycling such wastes to high-value products will not only solve environmental problems but can also provide additional revenue. In this study, the utilization of NLMS and CFA as geopolymer precursors and sodium hydroxide (SH) and sodium silicate (SS) as alkali activators were investigated as a sustainable material for built environment. It has been an attractive alternative to Portland cement-based binder because of its simple process, large-scale utilization and lower carbon footprint. Geopolymer can be synthesized from the reaction of aluminosilicate solids and alkali activator such as aqueous solution of alkali hydroxides and alkali silicates. Optimal mix formulation of 50% NMLS/50% CFA, SH-to-SS ratio of 1:2, and an activator-to-precursor ratio of 30:70 yielded a 28- day unconfined compressive strength (UCS) of 22.1±5.4 MPa. Furthermore, using an optimized formulation of 50.12% NLMS/49.88% CFA, SH-to-SS ratio of 0.516, and an activator-to-precursor ratio of 0.428 yielded an actual UCS value of 36.26±3.6 MPa. 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.