2.3. Sample preparation
Fly ash samples containing 0 wt.% and 10 wt.% additions of each of the dried and ground metal finishing wastes were prepared. These were thoroughly mixed to ensure a uniform distribution of metal finishing waste in the fly ash. A small amount of water (∼7 wt.%) was added during mixing to act as a binder and cylindrical green pellets, 20 mm in diameter were formed by uniaxially pressing 5 g mixed powder samples at 38 MPa in a stainless steel pressing die. The ‘green’ samples formed were then dried at 105 ◦C for 12 h prior to sintering. Sintered samples were produced by firing at temperatures between 1000 ◦C and 1250 ◦C using a Lenton electric furnace. Samples were rapidly heated at a ramp rate of 20 ◦C/min with a 60 min dwell at the maximum firing temperature. The furnace was then cooled at approximately 20 ◦C/min to room temperature.