MECHANICAL PERFORMANCE OF ALKALI-ACTIVATED CONCRETE INCORPORATING RECYCLED AGGREGATES AND STEEL FIBERS

This study evaluates the mechanical performance of alkali-activated concrete cured at ambient conditions and made with recycled aggregates (RA) and steel fibers. The precursor binder was either ground granulated blast furnace slag or a blend of slag and fly ash (3:1 and 1:1). The alkaline activator solution was a blend of sodium hydroxide and sodium silicate. Coarse aggregates were either natural aggregates (NA) or RA, while fine aggregates comprised desert dune sand. Steel fibers were incorporated, in 2%, by volume, in RA-based concrete mixes. Results showed that replacing NA by 100% RA in plain alkali-activated slag concrete led to decreases of 21, 23, and 51% in compressive, tensile splitting, and flexural strengths, respectively. Meanwhile, alkali-activated slag-fly ash blended (3:1 and 1:1) mixes experienced respective losses of up to 65, 50, and 57%. The corresponding properties of alkali-activated counterparts made with 100% RA increased by up to 172, 273, and 167% upon the addition of 2% steel fibers, by volume. Yet, the impacts of RA and steel fiber incorporation on the mechanical properties were more pronounced in concrete mixes having higher fly ash replacement. Alkali-activated slag and slag-fly ash blended concrete mixes incorporating 2% steel fibers, by volume, and 100% RA exhibited equivalent compressive strength and superior tensile splitting and flexural strengths to those of NA-based counterparts.