Impact of fiber hydrophilicity on the performance of porous alkali-activated fly ash materials

Abstract

Porous alkali-activated fly ash (PAA-FA) is a sustainable building material, but its low compressive strength limits application. This study demonstrates that incorporating polyvinyl alcohol (PVA) fibers effectively enhances mechanical properties, with a 55% increase in compressive strength (from 1.1 MPa to 1.7 MPa) at an optimal 2.0 wt.% and 3 mm length. Crucially, fiber-matrix interfacial adhesion, governed by surface hydrophilicity, was identified as the key reinforcement mechanism. Hydrophilic PVA fibers formed strong bonds with the matrix, while hydrophobic polypropylene (PP) fibers reduced strength. Surface modification to increase PP fiber hydrophilicity successfully improved composite strength to 1.5 MPa, confirming this mechanism. Furthermore, fiber characteristics directly tailored the porous structure: hydrophilic fibers increased slurry viscosity, yielding finer pores and a 77% higher specific surface area, whereas hydrophobic fibers created interconnected pores, enhancing sound absorption. This work quantifies the critical role of fiber type, dosage, length, and surface chemistry, providing a strategic approach to mechanically strengthen PAA-FA and tailor its functional properties for specific structural and acoustic applications.