Synthesis of geopolymers derived from fly ash with an addition of perlite

The study summarizes the results of fly ash-based geopolymer testing. Geopolymer samples were synthesized in a process involving two cycles. In the first cycle the activating agent was sodium hydroxide. The second method used the liquid residue from the synthesis of zeolites with the hydrothermal method. These processes were investigated to find out how the addition of perlite affects the mechanical properties of geopolymers (compressive strength, Young?s modulus, shear modulus, Poisson?s ratio) and their thermal expansion behaviour. It was shown that the addition of perlite enables the control of geopolymer elasticity, whilst only affecting the compressive strength to a minor degree. The conducted analysis showed that the 10% addition of perlite during the synthesis of geopolymers from fly ash causes an increase in the material elasticity, whilst reducing its compressive strength by 40%. It was also established that the application of the residual solution from the hydrothermal synthesis of zeolites produces geopolymer materials with improved heat-insulating properties, though with lower compressive strength than specimens obtained using NaOH. The proposed experiment confirms the possibility that fly ash can be effectively utilized to produce two useful materials (zeolites and geopolymers) without generating waste. This approach is fully in line with the principles of circular economy. ? 2021 Elsevier Ltd. All rights reserved.