Influence of Fly Ash–Ground Granulated Blast Furnace Slag Blends and PVA Fibres on the Dimensional Stability, Durability and Microstructure of Foamed Concrete

Foamed concrete is susceptible to drying shrinkage and environmental deterioration because of its porous structure. This study evaluated the effects of fly ash–ground granulated blast-furnace slag blends and polyvinyl alcohol fibres on the dimensional stability and durability of FC. Sixteen mixtures with SCM replacement levels of 0–35% and PVA fibre contents of 0–0.3 vol.% were tested for accelerated drying shrinkage, freeze–thaw resistance, sulfate wet–dry resistance, chloride penetration, and visible pore structure. A normalised multi-criteria evaluation was used to compare the mixtures across five performance indicators, with sensitivity analysis performed for six weighting schemes. Increasing SCM replacement generally increased the drying shrinkage but reduced the chloride penetration depth by 26.7%, 33.3%, and 56.7% at 15%, 25%, and 35% replacement, respectively. At 25% SCM replacement, PVA fibres reduced freeze–thaw-induced compressive strength loss by 62.12–98.48% relative to the corresponding fibre-free mixture. Optical microscopy identified a local stratified region in one of three C0.3 specimens, which was not considered a systematic feature. C0.3 achieved the highest overall score under equal weighting and remained among the top three mixtures under all six weighting schemes. Within the investigated mixture range, C0.3 showed consistently high overall performance, although longer-term durability assessment is required.