Reaction kinetics, microstructure and strength behavior of alkali activated silico-manganese (SiMn) slag - Fly ash blends

- Industrial waste materials have been used for alkali activated cement development.
- SiMn slag and fly ash blended to overcome limitations for alkaline cement production.
- Co-existence of geopolymer gel with C-(A)-S-H gel improves the binder properties.
- Slag addition altered the reactivity and developed compact microstructures.
- Fly ash addition slowed down the reaction rate and formed uniform, compact matrix.

Two industrial waste namely air cooled silico-manganese (SiMn) slag and fly ash has been used synergistically to develop alkali activated cement at ambient temperature. Isothermal conduction calorimetric studies (ICC) revealed that addition of SiMn slag resulted in an increase in reactivity. A new hump in ICC after 1.4 h of reaction is appeared in blends rich with SiMn slag, which is due to the formation of primary C-(A)-S-H gel. The shift in band corresponding to Si-O-Si/Al at ∼1000 cm−1 towards lower frequency in Fourier transform infrared spectrum with slag inclusion suggest the structural reorganizations and formation of a new calcium rich gel. The main reaction product is detected as (N)-A-S-H and C-(A)-S-H (where, N = Na2O, A = Al2O3, C = CaO, S = SiO2, H = H2O) based heterogeneous hydrated gel with varying Si/Al, and Na/Ca ratios. Both Si/Al ratio (obtained in EDX analysis) of gel phases and compressive strength increases with slag introduction. The improvement of mechanical strength with increasing slag is associated with more reactive CaO content of the slag, and co-existence of C-A-S-H and N-(C)-A-S-H type gel in the reacted matrix.