Performance of metakaolin/slag-based geopolymer concrete made with recycled fine and coarse aggregates

In this paper, the potential use of both fine and coarse recycled demolition aggregates (RA) in geopolymer concrete (GC) manufacturing was investigated. The geopolymer binder adopted was a mix of metakaolin (MK) and granulated blast furnace slag (GBFS), activated by an alkaline solution (SiO2/Na2O=1.8) with a water to solid ratio of 0.5. A control GC (0% RA) with C35/45 class of compressive strength and S4 class of workability, and three GC mixtures with 10, 30 and 50% of RA were manufactured. It was found that the introduction of pre-saturated RA in GC mixtures does not affect the class of workability, but the slump loss over time decreased proportionally to the RA percentage. With 10% of RA, a slight decrease was recorded in both water porosity and mechanical performances. Moreover, a drop of 18 and 27% in compressive strengths was recorded with 30 and 50% of RA incorporation, respectively. Based on the obtained results and an extensive number of experimental data from the literature, the validity of empirical relationships between the mechanical performances of GC was assessed, and more adequate predictive equations were proposed.