Impact self-assembly of low-binder-content geopolymer parts

In the current study, we produce low-binder-content geopolymer parts through impact self-assembly. After sand (the filler) and a small amount of fly ash-alkaline activator mixture (the binder) are premixed, they are impacted by a hammer in a drop tower. The hammer mass is around 2∼5 kg and the drop distance is 0.2∼0.8 m. The flexural strength of the cured material is ∼5 MPa, comparable to typical portland cement. The key processing parameter is the impact momentum of the hammer. Repeated impact improves the microstructural uniformity. The low binder content helps minimize the materials cost, reduce the carbon emission, and lower the demand of class F fly ash. [Display omitted] •A geopolymer-binder composite is developed, as an advanced green cement.•The material uses only ∼15% class-F fly ash, which helps mitigate the worldwide fast declination of fly ash supply (due to the closure of coal plants).•The material is stronger than structural concrete.•The process is fast and simple, mainly involving hammer impact on premixed sand and binder.•The fabrication has almost no carbon emission, and consumes little energy.