Natural zeolite powder as a cement substitution in sustainable concrete: influence on engineering properties, durability, and microstructure characteristics

Abstract The high carbon footprint of Portland cement production has raised urgent concerns regarding the environmental sustainability of conventional concrete. To address this, there is growing interest in utilizing natural pozzolans as partial cement replacements in construction materials. Among these, natural zeolite offers promise due to its inherent silica-alumina structure and pozzolanic potential. However, most studies to date have focused on thermally activated or synthetic zeolites, with limited research on the performance of untreated natural zeolite in conventional curing conditions. This study explores the influence of natural zeolite type F, used as a cement replacement at 10%, 15%, 20%, and 25%, on the fresh, mechanical, durability, and microstructural properties of concrete. Experimental evaluations included slump, compressive strength, ultrasonic pulse velocity, water absorption, electrical surface resistivity (ESR), rapid chloride ion penetration (RCPT), and microstructure characterization via scanning electron microscopy (SEM), x-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analysis. Experimental results revealed that a 15% zeolite replacement level delivered optimal performance, achieving a 56-day compressive strength of 67.1 MPa, RCPT of 1719 Coulombs, and ESR of 15.08 Ω·cm. Water absorption decreased significantly over time, and SEM images showed a denser microstructure with fewer voids. XRD confirmed the consumption of portlandite and enhanced pozzolanic activity. FTIR spectra supported these findings by revealing stronger O–H and sharper Si–O–T bands in zeolite-blended mixes, particularly at 15% replacement, indicating effective hydration and secondary gel formation. A multi-criteria assessment integrating mechanical and durability metrics further confirmed that the 15% zeolite mix attained the highest overall performance score (OPS = 0.90), outperforming both control and higher replacement levels. This research demonstrates that natural zeolite can be effectively used without calcination to enhance both the sustainability and durability of concrete, offering a low-cost and eco-friendly alternative binder, particularly in regions with accessible zeolite resources.