Chloride Durability and Microstructural Analysis of Alkali Activated Slag Mortars Containing Nanosilica

Traditional ordinary Portland cement (OPC) concrete has been the main choice for construction purposes for a long time. However, environmental impacts of OPC clincker production and the enormous amount of by-products generated through various industrial activities, have posed the research society to introduce novel materials to replace OPC paste. In the past few decades, alkali activated materials (AAMs) have been proven to be a suitable replacement for conventional OPC mixtures. In this study, mechanical and durability properties of alkali activated slag (AAS) mortars is evaluated. Nanosilica at dosages of 2% and 4% and silica fume at dosages of 5%, 7.5% and 10%, were incorporated into mortar mixtures as ground granulated blast furnace slag (GGBFS) replacement. In addition, solution-to-pozzolan ratio and alkaline activator type were selected as variables. Compressive strength test is performed for mechanical properties evaluation, also bulk diffusion test was used to investigate the durability properties of mortar samples. 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. A microstructural analysis is performed through scanning electron microscope (SEM) micrographs and energy dispersive X-Ray (EDX) analysis, results showed proof on filler effect of nanosilica particles, also the presence of calcium was observed which indicates the presence of CSH gel in structure of AAS samples which is a determination on differences between AAMs and geopolymers.

Keywords:

alkali activated slag , mortar , durability , chloride diffusion , microstructure