Cellular geopolymer is produced by aerating Alkali-activated Fly ash (AAF) binder paste using Aluminum powder. The cellular structure created in the geopolymer depends on the AAF binder paste rheology and the surface tension of the activating solution. The constant strain rate rheological behavior of AAF binder paste varies between Maxwell flow and yield type depending on the activating solution content. Aeration with a stable bubble structure is achieved in an AAF binder paste with a yield-type constant strain-rate response. AAF binder pastes which exhibit a Maxwell-flow type constant strain rate response cannot retain bubbles in suspension. Addition of clay transforms the constant strain rate rheological behavior of the AAF binder paste from Maxwell-flow to yield type response producing a stable aerated paste. Increasing the clay content in the AAF binder paste increases its yield stress. The total porosity in the cellular geopolymer is controlled by the size and quantity of aluminum powder. Equivalent total porosity is achieved with a lower dosage of finer aluminum powder. Yield stress and surface tension have opposing influences on the pore size without influencing the total porosity. Increasing the yield stress of the AAF binder paste by adding clay produces an increase in the mean pore diameter. Adding surfactant to the AAF binder paste decreases the mean pore diameter in the cellular geopolymer. The porosity and the mean pore diameter in the cellular geopolymer can be controlled with the use of clay, and surfactant and by regulating the content and fineness of the aluminum powder. © 2022 Elsevier Ltd