Compressive Strength and Leaching Characteristic of Geopolymer Composite from Coal Fly Ash and Nickel Laterite Mine Spoils

Abstract

Geopolymer, also referred to as “alkali-activated material” or “zeocement”, is an emerging sustainable material to replace Portland cement-based binder. It requires a straightforward process and has the potential for large-scale waste valorisation and utilisation and a lower carbon footprint. Several aluminosilicate materials as geopolymer precursors have been explored, such as coal fly ash and metakaolin, among others. However, the characteristics of raw materials vary depending on the source. Hence, this study aims to synthesise geopolymer composite from raw materials that are available locally. Coal fly ash and nickel laterite mine spoils were explored as a potential geopolymer precursor. Optimal mix formulation of 50 % nickel laterite mine spoils / 50 % coal fly ash, sodium hydroxide to sodium silicate ratio of 1:2, and activator to precursor ratio of 0.44:1 yielded a 28 d compressive strength of 22.1 ± 4.4 MPa and a 180 d compressive strength of 32.3 ± 7.4 MPa. The result implies that this eco-friendly geopolymer material can be potentially used for pedestrian pavers, light traffic pavers, and plain concrete for levelling and structural applications. Before any field-scale application, investigating the leachability of material is imperative. Hence, the toxicity characteristic leaching procedure (TCLP) was employed to evaluate the leachability behaviour of both the raw materials and developed geopolymer composite in this study. The results revealed that the concentration of the trace metals released pose no significant environmental and leaching hazard into the soil, surface, and groundwater sources based on the threshold limit as defined by USEPA.