Clay-based geopolymer ceramic incorporated with electric arc furnace (EAF) steel slag waste

EAF slag generates vigorous fluxing action (due to high iron oxide content from 25.00 to 42.40 wt. %) when a high sintering temperature of up to 1180 °C is applied for sintering ceramic. This phenomenon is difficult to control and causes physical defects especially blistering and warpage of the ceramic. Hence, the geopolymerisation process is a more suitable alternative to replace the conventional firing process where alkaline activation is used, involving Na+ or K+ of functional groups and low temperature to produce EAF slag-based geopolymer ceramic. EAF slag (from one of Malaysia’s steel manufacturers) and China clay is characterised with X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) to identify its composition, crystalline phases present, and functional groups respectively. In this study, the EAF slag was prepared and characterised prior to incorporation in geopolymer ceramic. Next, the effect of body formulation and sintering temperature on properties of clay-based geopolymer ceramic incorporated with EAF slag were investigated. The EAF slag was crushed and ground before mixing with the sodium hydroxide (NaOH) solution (after being diluted with distilled water to 1 M), in which the solid to liquid ratio depends on raw materials' composition. The paste formed then was moulded and underwent pre-curing at 25 °C for 24 hours followed by curing temperature at 80 °C for another 24 hours. Then, the cured geopolymer powder was compacted at 20 MPa using a hydraulic press before sintering at 400 °C, 500 °C, and 600 °C. The final products were characterised by firing shrinkage, water absorption, apparent porosity, bulk density, crystalline phases, functional groups, and Raman analysis. The results show that EAF slag is suitable for the fabrication of geopolymer ceramic. Moreover, the incorporation of EAF slag into geopolymer ceramic decreases its percentage of water absorption and apparent porosity while increasing the bulk density. The compressive strength was also increased as the EAF slag was increased. Therefore, the mechanism of geopolymerisation of EAF slag incorporated clay-based geopolymer ceramic is thoroughly studied. The mechanism consists of two stages in which the first stage involves pre-activation by alkaline solution while the second stage involves low-temperature sintering. The chemical reaction of the two stages found that the dissolution reaction was able to pre-activate the raw materials before sintering. Overall, based on the study, the EAF slag is proven to be suitable for the fabrication of clay-based geopolymer ceramic.