Synthesis of low temperature cured alkaline activated silicomanganese fume mortar

Silicomanganese (SiMn) fume is an industrial waste whose potency in the synthesis of alkaline activated mortar is yet to be explored. The major constituents of SiMn fume are SiO₂, MnO₂ and K₂O. SiMn fume based mortar cured at room temperature (23 ± 2 °C) was synthesized with NaOH (NH) of varied molarity (4, 8 and 12) and Na₂SiO₃ (NS) as alkaline activators with different ratios of NS/NH (2, 2.5 and 3). The maximum 28-day compressive strength of room temperature cured mortar of 36 MPa was achieved with combined NH-12M and NS/NH of 2.5. Utilization of only NH activator produced a low strength (6.8 MPa) mortar compared to using the combined activators due to inability of pure alkali to form condensed oligomers required for gelation. The combination of NS and NH was more workable and produced significant strength that increased with molarity of NH_aq due to proliferation of silica in the base material. SEM and XRD characterizations revealed that mortar of high molarity is more crystalline and denser with well compacted matrix compared to that of mild alkali (4 M). The crystalline phase in XRD was observed at 29.5° 2θ due to the formation of Nchwaningite (Mn²⁺ ₂SiO₃(OH)₂·(H₂O)). The strength development was due to high reactivity of MnO₂ with NS, especially when the ratio of NS/NH was 2.5.