Effect of yield stress development on the foam-stability of aerated geopolymer concrete

This study investigates the instability of fresh geopolymer foam concrete (GFC) synthesised through the pre-foaming technique, particularly at ultra-low densities (430–460 kg/m3). Initial setting time and the yield stress development with time were measured for the base mixes and correlated to the level of stability. We observed that the foam stability was established through the yield stress development at the start, well before the initial setting of the binder. The settlement was noticeably reduced when the initial yield stress satisfied the stability criterion to prevent drainage. The base mix with the highest initial yield stress and the fastest yield stress development rate displayed the highest level of stability in the fresh GFC. Apart from the direct measurement of settlement, foam stability was well reflected in the hardened properties of the GFC such as pore size distribution, pore homogeneity and mechanical strength. •Instability of fresh geopolymer foam concrete was studied at ultralow densities.•Settlement is well estimated by the stability criterion to prevent drainage.•Settlement was prevented in the mix with the fastest yield stress development rate.•Fresh state stability influenced the hardened properties.