Backfill coal mining is a promising approach to mitigate the movement of the overburden. Industrial waste such as fly ash has been added to improve its economic viability, but the strength of the paste backfill diminishes.  This study then aims at enhancing the strength of the backfill material using silicate additive and CO₂. The backfill material is formulated with 90% fly ash and 10% cement. The results show that the strength of the paste backfill is more pronounced by the co-activation of silicate additive and CO₂, where the strength is doubled after 28 days of curing. Furthermore, the setting time is also accelerated that shortens waiting sequence in backfill operation. Silicate additive and CO₂ reaction induce a denser paste backfill by higher C-S-A-H and silica gels and carbonate product. These findings could lower the material cost in backfill mining.

Cemented paste backfill; fly ash; Silicate additive; CO2; Strength