Cleaner geopolymer prepared by co-activation of gasification coal fly ash and steel slag: durability properties and economic assessment

Geopolymer is a material with high early strength. However, the insufficient durability properties, such as long-term strength, acid-base resistance, freeze–thaw resistance, leaching toxicity, thermal stability, sulfate resistance and carbonation resistance, restrain its practical application. Herein, a long-term stable geopolymer composite with high final strength (ASK1) was synthesized from shell coal gasification fly ash (SFA) and steel slag (SS). Additionally, a geopolymer composite with high early strength (ASK2) was also synthesized for comparison. The results showed that ASK1 exhibited better performance on freezing-thawing resistance, carbonization resistance and heavy metals stabilization compared to the ASK2 at long-term curing. Raising the curing temperature could accelerate the unconfined compressive strength (UCS) development at initial curing ages of 3 to 7 d. Both ASK1 and ASK2 exhibited excellent acid-base and sulfate corrosion resistance. An increase for UCS was seen under KOH solution and MgSO 4 solution corrosion for ASK1. All leaching concentrations of heavy metals out of the two geopolymers were below the standard threshold, even after 50 freezing-thawing cycles. Both ASK1 and ASK2 geopolymer concrete exhibited higher sustainability and economic efficiency than Portland cement concrete. The result of this study not only provides a suitable way for the utilization of industrial solid waste in civil and environmental engineering, but also opens a new approach to improve the long-term stabilities of the geopolymers.