Residual Flexural Performance of Large-Scale Ferronickel Slag Alkali-Activated Concrete Slabs After Fire Exposure

This paper investigates the flexural behavior of unfired and fired one-way slabs constructed from reinforced ferronickel slag-based alkali-activated concrete. The study aims to expand the limited knowledge of large-scale testing of alkali-activated concrete structural elements, with a particular emphasis on their post-fire performance. Four slabs, each measuring 2.1 × 0.9 × 0.18 m³, were produced—two made of alkali-activated concrete and two of conventional concrete incorporating ordinary Portland cement. Both types of concrete exhibited similar compressive strengths. In each group, one slab served as a reference (control specimen—tested under monotonic four-point bending in its original state), while the other was subjected to a standard fire curve on the tensioned side before mechanical testing. The fired slabs were then tested in a cooled condition under ambient conditions. The effect of fire on the alkali-activated concrete was further examined using mercury intrusion porosity and scanning electron microscopy. The results reveal that the load capacity of structural members cast with alkali-activated concrete is only slightly lower than that of their conventional concrete counterparts (6% lower). However, the alkaliactivated slabs retain more of their stiffness and ductility after fire exposure.