Enhancing the chemical foaming process using superplasticizer in aerated geopolymer concrete

• Effect of superplasticizer on the expansion behaviour of GFC was studied. • Expansion behaviour was corrected to yield stress of fresh geopolymer. • Density of GFC has reduced from 940 kg/m 3 to 566 kg/m 3 with superplasticizer. • Porosity and pore size distribution has been affected by superplasticizer content. This study investigates a method of enhancing the foaming behaviour using a superplasticizer in geopolymer foam concrete (GFC) produced by the chemical foaming method. The GFC was synthesized using Aluminium powder as a gas-forming agent and a polycarboxylate based superplasticizer (SP) was introduced at varying dosages. The expansion behaviour of GFC was correlated with the SP dosage and the corresponding yield stress evolution at early age. The results demonstrated that, despite the same Aluminium dosage, the expansion of GFC has largely varied with the SP dosage in the mix. The high SP dosage attributes to a high and stable expansion rate, whereas the control mix (without SP) showed unstable expansion with intermediate collapse. The stability and distribution of air voids are attributed to the variation in the gas bubbles migration ability through the geopolymer media. The control mix has shown high yield stress that exerts high drag force onto the bubbles, resulting in bubble instability and collapse leading to a high density. In contrast, the mixes containing high SP dosage showed low yield stress that allows the migration of gas bubbles and result in low density. Although the setting time has slightly increased with the SP content, the expansion was completed well ahead of the initial setting time, indicating the impact of setting behaviour on the expansion is not significant. Furthermore, the variation of expansion behaviour was well reflected on the porosity and pore size distribution at the hardened state.