CHARACTERISTICS OF GEOPOLYMER MORTAR PRODUCED USING NICKEL SLAG

Abstract

Nickel slag is a non-metallic mineral waste primarily composed of olivine, generated from the nickel mining industry. Indonesia holds a large quantity of this waste, but its utilization remains limited. Proper processing of nickel slag has the potential to enhance industrial productivity, contribute to economic growth, and mitigate environmental impacts. In North Maluku, the rapid development of the nickel industry has increased slag production, which, if unmanaged, poses a threat to environmental balance. This research aims to utilize nickel slag as the base material for producing geopolymer bricks, using fly ash from the Rum Steam Power Plant as the binder and an alkaline activator mixture of NaOH and Na₂SiO₃. The mixture consisted of 50% nickel slag and 50% binder, with the binder composed of 55% fly ash and 45% activator. Two concentrations of NaOH solution—8 M and 10 M—were used, with a 1:1 ratio of NaOH to Na₂SiO₃. Compressive strength and water absorption tests were conducted on 5×5×5 cm³ cube specimens. Results showed that compressive strength increased with curing temperature, from 40°C to 80°C. The highest compressive strength was recorded at 80°C: approximately 32 kg/cm² for the 8 M solution and 34 kg/cm² for the 10 M solution. Water absorption decreased with higher curing temperatures, with the lowest value of 23.88% at 80°C using the 10 M solution. According to SNI 03-2493 standards, the geopolymer mortar produced in this study is classified as quality grade IV.