Mechanical and durability properties of alkali activated slag coating mortars containing nanosilica and silica fume

Mechanical and durability performances of alkali activated slag (AAS) mortars are evaluated. Nanosilica at the dosages of 2% and 4% and silica fume at the dosages of 5%, 7.5% and 10% were incorporated into mortar mixtures as ground granulated blast furnace slag (GGBFS) replacement. Mixtures of sodium hydroxide (NaOH) or potassium hydroxide (KOH) and sodium silicate (Na2SiO3) were used to activate the GGBFS. Flowability, compressive strength, sorptivity, chloride permeability, and bond strength tests were applied to single, binary, and ternary blended AAS mortars in order to assess the effect of the variables on mechanical, durability, and bond strength performances of the AAS mortars. Results indicated that nanosilica incorporation significantly improved the performance of AAS mortars, while silica fume addition more than 5% didn't contribute in performance improvement. Migration and diffusion coefficients obtained from chloride durability tests revealed the high influence of nanosilica on microstructural development also NaOH activated mortars showed better performance against chloride penetration. A microstructural analysis was performed through scanning electron microscope (SEM) micrographs and energy dispersive X-ray (EDX) analysis. Results showed proof on filler effect of nanosilica particles, silica fume agglomeration and disintegration of AAS system as a result of thermal exposure during sorptivity test.