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 MgSO4 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. [graphic not available: see fulltext]