• Adding a slag-based geopolymer (LG) with 20% nano-metakaolin (NM) replacement increased soil strength by nearly 21 times and reduced the compression index by about 70%.
• NM accelerates hydration reactions and forms a densely packed fabric, substantially improving the hydromechanical properties of soft clayey soils.
• Raising the curing temperature approximately doubles the polymerization kinetics and soil solidification, but NM-containing composites may exhibit brittle behavior.
• Incorporating polypropylene fibers into LGNM mixtures boosts energy absorption capacity by ≥10 times and enhances residual strength, offering economic, technical, and environmental benefits over traditional binders.