Pore Structure Characterization and Environmental Assessment of Ground Volcanic Pumice-Based Alkali-Activated Concrete

The impact of pore structure and its connectivity in ground volcanic pumice (GVP) and nano-silica (nSi)-based AAB on the chloride diffusion leading to corrosion of reinforcing steel for a period of up to 2.5 years was investigated in this study. ¹H proton NMR relaxometry was employed as an innovative method to examine the pore structure and connectivity in alkali-activated concrete (AAC), in conjunction with the assessment of bulk chloride diffusion. Alkali-activated GVP with marginal quantities of nSi outperformed similar grade conventional OPC concrete when exposed to bulk diffusion in accordance with ASTM C1556. There was nearly 80–90% reduction in chloride diffusivity in 5.0% and 7.5% nSi mixes and 60% increase in compressive strength. The contour maps showed that nSi incorporation greater than or equal to 5.0% significantly lowered porosity, enabled poor pore connectivity and minimized chloride diffusion, resulting in enhanced protection against chloride-induced corrosion of steel rebar in the AAC. It was revealed that the remarkable resistance of nSi-modified GVP-AAC to the aggressive environment was attributed to the better polymerization and physical influence enhanced the binder structure. The environmental assessment results showed that GVP-based alkali-activated mixes reduced CO₂ emissions by 53% to 60% compared to the OPC-based mix, demonstrating their strong potential for lowering the carbon footprint of concrete.