Stress-strain characteristics and brittleness index of alkali-activated slag and class C fly ash mortars

An experimental study on the stress-strain characteristics of alkali-activated slag (AAS) and alkali-activated class C fly ash (FAC) mortars subjected to axial compression is presented. The effect of activator concentration (Na2O % and silica modulus (Ms)) on compressive strength, elastic modulus, ultimate stress, and ultimate strain of AAS and FAC mortars is evaluated. Further, the stress-strain behavior is studied and the brittleness index (BI) values of AAS and FAC mortars are determined as a function of strain. The brittleness indices obtained for AAS and FAC mortars are 52% and 48% respectively. The compressive strength of mortars is related to the BI. Higher concentrations (>= 4% Na2O and >= 1.25 M) of activator led to improved ultimate stress, strain, elastic modulus, and increased brittleness. The influence of shrinkage mitigation methods such as internal curing using light weight aggregate (LWA), the addition of polypropylene fibers, and shrinkage reducing admixtures (SRA) on stress-strain characteristics and brittleness of alkali -activated mortars are also determined. Alkali-activated mortar mixtures containing LWA (10-30%), fibers (1-2%) and, SRA (2.5-7.5%) exhibited a lower BI.