A study at the DPG Institute of Technology and Management in Gurugram investigated the effects of blending different concentrations of silica fumes with ground granulated blast furnace slag-based (GGBFS) geopolymer concrete. Findings reported in Nature concluded that the addition of 10% silica fumes ‘significantly’ enhanced the durability and strength of the resulting concrete
Chemical Composition of GBFS
Spectroscopic analyses indicate that GBFS contains the following main components:
- Silicon dioxide (SiO₂): 30-40% – contributes to the formation of the amorphous phase necessary for pozzolanic reactions.
- Calcium oxide (CaO): 35-45% – essential for the formation of C-S-H (calcium-silicate-hydrate) gel, which provides strength to concrete.
- Aluminum oxide (Al₂O₃): 7-15% – influences reactivity and setting time.
- Magnesium oxide (MgO): 5-10% – may contribute to delayed expansion if not well controlled.
The fineness and amorphous structure of GBFS determine its degree of reactivity in an alkaline environment. Alkaline activation tests show that in the presence of sodium hydroxide (NaOH) or sodium silicate (Na₂SiO₃) solutions, slag rapidly forms hydrated gels, improving the mechanical properties of concrete.
