Uniaxial compressive behaviors of fly ash/slag-based geopolymeric concrete with recycled aggregates

The uniaxial compressive stress-strain behaviors of fly ash/ground granulated blast furnace slag (GGBFS) geopolymeric concrete containing recycled aggregate were investigated in this study. Geopolymeric concretes with the variations of three recycled aggregate replacement ratios (i.e., 0%, 50% and 100%) and four contents of slag (i.e., 0%, 10%, 20% and 30% of the mass of total binder) were tested under uniaxial compression. Special attention was devoted to the failure behaviors and patterns, stress-strain characteristics (such as the peak stress, the elastic modulus, the peak strain, and the ultimate strain) and energy absorption capacity. The results showed that the peak stress, elastic modulus and energy absorption (toughness) decreased with the increase of the replacement ratio of recycled aggregate, while these mechanical properties increased when the content of slag increased. The reverse trend was observed with respect to the ductility. Moreover, the inclusion of slag could alleviate the negative effects of the recycled aggregate replacement on the stress-strain characteristics of geopolymeric concrete. Additionally, a stress-strain model was developed in this study by modifying the parameters of the existing stress-strain model with the best prediction. This new proposed model can satisfactorily describe the stress-strain behaviors for both geopolymeric natural aggregate concrete and geopolymeric recycled aggregate concrete.