Use of recycled aggregates in pressed fly ash geopolymer concrete

In this study, the physical, mechanical, and thermal properties of pressed geopolymer concrete (PRGC) mixed with recycled concrete aggregate (RC) and recycled concrete block aggregate (RB) were investigated. Lignite coal fly ash, sodium hydroxide solution (NaOH), and sodium silicate solution were used as source materials to make geopolymer paste. The effect of fly ash to aggregate ratios and concentrations of NaOH on PRGC properties were tested. Test results were also compared to those of PRGCs mixed with conventional aggregate (limestone dust, SD). The test results showed that PRGCs containing RC and RB exhibited lower dry density, thermal conductivity, and compressive strength than those of PRGCs containing SD. Nevertheless, the compressive strength of PRGCs mixed with recycled aggregates was close to the compressive strength for moderate strength lightweight concrete as per ACI 213. Moreover, the lower thermal conductivity and dry density indicated better insulating properties than that of PRGCs containing SD. The developed PRGCs containing RC and RB in the study can be used for the manufacturing of hollow geopolymer-based concrete block which are green material with improved insulating properties.