Effect of Composition on Characteristics of Powder Coating Sludge (PCS)-Metakaolin-Based Geopolymer

Abstract

The aim of this research is to experimentally study the application of powder coating sludge (PCS) and metakaolin as geopolymer. The PCS is a lot of waste which is released after the powder coating production process. While metakaolin comprises SiO2 and Al2O3 which can be used to produce geopolymer. Therefore, this study aimed to determine a suitable geopolymer mix ratio, using PCS as part of the mixture. This research also investigated the effect of metakaolin/PCS ratio, sodium hydroxide (NaOH)/sodium silicate (Na2SiO3) ratio, curing time, NaOH concentration and solid/liquid ratio on compressive strength of geopolymer. The coefficient of thermal conductivity was tested by using a suitable composition. Kaolin in this experiment was calcined at 700 °C for 2 h. Alkaline activators for molding were NaOH and Na2SiO3. Samples were hardened in an electric oven at 80 °C for 4 h before being removed from the moulds and cured at room temperature within 7, 14 and 28 days. Metakaolin/PCS ratios of 90:10, 80:20, 70:30 and 60:40, and solid/liquid ratios of 0.8 and 0.6 were performed. Concentration of NaOH were 6, 8, 10, 12 and 14 molars and NaOH/Na2SiO3 ratios were 1:1.5, 1:2 and 1:2.5, respectively. The experiments were conducted in triplicate. Results of 3 PCS tests showed that the highest composition of Al2O3 and SiO2 were 3.37 and 1.99 % w/w, respectively. The sample which is based on 60 % metakaolin and 40 % PCS, 10 molars NaOH, NaOH/ Na2SiO3 of 1:1.25, solid/liquid of 0.6 and curing time of 28 days had a maximum compressive strength of 81 kg/cm2, while the coefficient of thermal conductivity was 0.1766 W/(mŸk). Therefore, it can be concluded that the PCS has the potential to partially replace metakaolin as geopolymers material.
 HIGHLIGHTS
 
 Geopolymer comprises alumina (Al2O3) and silica (SiO2) and the advantages of geopolymer production are environmentally friendly and reduce energy consumption 
 
 
 The appropriate metakaolin/PCS ratio and concentration of activators provide the highest compressive strength
 
 
 The geopolymer of this study has low thermal conductivity coefficient therefore it is a good insulation material