Discrimination of the role of silica fume and nano-silica in alkali-activated slag paste

Silica fume and nano-silica have been widely investigated to hold the significant potential in enhancing the properties of alkali-activated slag (AAS) systems, however, discrimination of the respective role in such systems requires a clear elucidation. Multiple combinations of silica fume and nano-silica were incorporated into the AAS paste samples in an attempt to discriminate the respective influence of silica fume and nano-silica on the properties of AAS paste samples. The samples with nano-silica showed higher initial heat evolution compared to silica fume, yet no secondary acceleration heat evolution peak was observed. This feature resulted in the lower strength development at the early stages in the samples with nano-silica compared to those containing silica fume. The incorporation of nano-silica led to a lower pore size distribution than silica fume at 28 d of curing, contributing to the development of higher strength at later curing stages. Both the degree of Si polymerization and Al crosslinking in calcium aluminosilicate hydrate (C-A-S-H) increased by the incorporation of siliceous materials, with the incorporation of nano-silica further intensifying this effect. This work provided insights into the effects of incorporating silica fume and nano-silica into AAS systems from a microstructural perspective in which its novelty lies in offering visions into property modifications of AAS, shedding light on how each additive influences the properties.