Mechanical Performance of Fiber-Reinforced Geopolymer Mortars: Effect of Aggregate Replacement

Ordinary Portland cement (OPC) production is responsible for approximately ۵–۸% of global CO۲ emissions, driving urgent demand for low-carbon binder alternatives. Geopolymer mortars based on ground granulated blast-furnace slag (GGBFS) have emerged as a promising solution; however, their mechanical performance is highly sensitive to aggregate type and mix design. This study investigates the combined effect of aggregate type, natural sand, recycled concrete aggregate (RCA) at ۵۰% and ۱۰۰% replacement, and pumice, and polypropylene (PP) fiber content (۰, ۰.۵%, and ۱.۰%) on the compressive strength, flexural strength, and water absorption of GGBFS-based geopolymer mortars cured at ۶۰°C. Twelve mortar mixtures were prepared using alkaline activation and tested at ۷ and ۲۸ days. Results showed that the reference mixture (natural sand) achieved the highest ۲۸-day compressive strength (۲۵.۵۰ MPa). Among the RCA mixtures, it was observed that ۱۰۰% replacement of natural sand performed better than ۵۰% replacement, with compressive strength reaching ۱۳.۷۳ MPa. Pumice-based mixtures showed lower compressive strength reaching ۱۰.۲۰ MPa but showed potential for lightweight structural applications. Adding ۰.۵% PP fibers consistently improved flexural strength across all aggregate types, with GPM۰.۵PP achieving the highest value of ۱.۸۹ MPa; however, increasing fiber content to ۱.۰% caused strength reduction. Water absorption exhibited an inverse relationship with compressive strength, with pumice and high-fiber mixtures exhibiting the greatest absorption values. Aggregate type and fiber content strongly affected the mechanical performance of GGBFS-based geopolymer mortars. Among the tested dosages, ۰.۵% PP fibers gave the best flexural strength without reducing compressive strength.

کلیدواژه ها:

Geopolymer mortar ، Recycled Concrete Aggregate ، Pumice ، Polypropylene Fibers