Investigation of the Recycling of Geopolymer Cement wastes as Fine Aggregates in Mortar Mixes

Fly ash-slag based Geopolymer cement (GPC) is presenting mechanical properties and environmental advantages that make it the predominant “green” alternative to Portland cement (PC). Although numerous life-cycle analyses praising its’ environmental advantages have been published, disposal after the end of its life remains an issue that has barely been explored. The present study is investigating the recyclability of fly ash-slag GPC as aggregate in mortars. The purpose of the study was to evaluate the effect of GPC fine recycled aggregates (RA), at replacement levels of 25% and 50%, on the main mechanical properties of PC and GPC mortar mixes. The results were compared with those obtained by corresponding mixes incorporating natural and PC RA. The main physical properties of GPC RA were examined and proven to be comparable to those of PC RA and slightly inferior to those of natural sand. A negligible effect was observed at 28-day compressive and flexural strength of PC mortars with GPC aggregates having a milder effect than PC. As far as GPC mortars are concerned the influence of GPC aggregates was enhancing for the investigated mechanical properties. Additionally, a screening test showed that recycled Geopolymer aggregates are not prone of inducing alkali silica reaction