Performance of geopolymer composites reinforced with treated date palm and polypropylene fibers

This study investigates the synergistic mechanical and durability performance of slag-based geopolymer composites reinforced with alkali-treated date palm fibers (TDPF) and polypropylene fibers (PPF), with particular emphasis on interfacial behavior, pore structure evolution, and acid resistance. The novelty of this research lies in the combined microstructural-mechanical-durability assessment of treated agro-waste fibers directly compared with synthetic fibers under identical geopolymer conditions, including exposure to sulfuric acid. Fibers were incorporated at volume fractions of 0.15%, 0.30%, and 0.50%, with lengths of 6 mm and 12 mm. The optimal composition (0.50% TDPF, 12 mm) achieved a 22.8% increase in compressive strength at 28 days and a 19.1% increase at 90 days. Flexural strength improved by up to 29.9% at early age and remained enhanced (approximately 18-19%) at later ages. SEM-EDS and FTIR analyses confirmed improved fiber-matrix interaction and enhanced integration within the aluminosilicate network in TDPF composites. Water absorption and open porosity were influenced by fiber type and dosage; however, optimized long-fiber mixtures reduced pore connectivity despite the hydrophilic nature of natural fibers. After 15 days of exposure to 3.5% H₂SO₄ solution, fiber-reinforced composites maintained structural integrity, with strength degradation limited to approximately 9-10%, demonstrating stable chemical resistance. Overall, the results indicate that alkali-treated date palm fibers provide competitive mechanical performance while offering a sustainable alternative to synthetic reinforcement in geopolymer composites, thereby supporting low-carbon and circular construction strategies.