Critical methods of geopolymer feedstocks activation for suitable industrial applications.

As health and safety issues emanating from human activities on terrestrial environment is becoming ever challenging, the production of Ordinary Portland Cement is identified as a key contributor. This technology threatens environmental quality by emitting significant quantity of carbon dioxide (CO) that threatens Net Zero delivery. Consequently, the development of cement alternatives with substantial CO reduction/sequestration during production has become imperative. Geopolymers obtained from industrial residues are poised as promising alternatives in managing environmental systems but selection of appropriate method of activation has limited their wider industrial applications. This article discusses four key activation methods and their combinations used in four main feedstocks to advise on their energy requirements, product compressive strength and environmental/industrial applications. Reviewing and characterising 302 published literatures with focus on most relevant and recent advances in the field, this review found that hybrid techniques combining mechanical activation method produces geopolymers with the highest compressive strength and thus the best method. Geopolymer made by mechano-chemical activation method of slag achieved the highest compressive strength while geopolymer produced by microwave assisted activation of clay and ultrasonic activation of fly ash cum slag are most economical in curing energy demand. Hybrid activation is the current development in the field and integration of this method with mechanical activation is poised as the future geopolymer activation technology as it demonstrates greatest efficiency potential.