Transport-controlled durability enhancement of sustainable lightweight alkali-activated composites with calcined clinoptilolite and basalt fiber

This study investigates the influence of calcined clinoptilolite (CCZ) and basalt fiber (BF) on the mechanical, thermal, and durability properties of lightweight alkali-activated expanded perlite-based composites. Ground granulated blast furnace slag (GBFS) was used as the primary precursor, while CCZ (0-15%) partially replaced GBFS and BF (0–1.2%) was incorporated to improve crack resistance. All mixtures were thermally cured at 80 °C for 8 h. The mixture containing 10% CCZ and 1.2% BF achieved the highest compressive strength of 4.70 MPa, representing an increase of approximately 175% compared with the reference mixture. Incorporation of 5-10% CCZ together with BF refined the pore structure, reducing porosity to 20.86%, water absorption by up to 36%, and sorptivity by up to 67.8%. Thermal conductivity ranged from 0.206 to 0.271 W/m·K, indicating good thermal insulation performance. After 120 days of sulfate exposure, the optimum mixture exhibited only 2.49% compressive strength loss, whereas 15% CCZ caused pronounced deterioration. Following 100 freeze-thaw cycles, the 12F5C mixture showed the lowest strength loss (8.48%). Exposure to 200 °C slightly enhanced compressive strength, while 600 °C resulted in substantial degradation. SEM–EDS and XRD analyses revealed a denser reaction matrix with improved gel continuity, supporting the observed improvements in mechanical performance and durability.