Mechanical Evaluation of Na-Based Strain-Hardening Geopolymer Composites (SHGC) Reinforced with PVA, UHMWPE, and PBO Fibers

Abstract

Strain-hardening geopolymer composites (SHGC) show increased deformation capacity due to a multiple cracking tolerance under tensile loading. To evaluate their mechanical performance, a common metakaolin-based mixture was produced. Three types of short fibers were evaluated as disperse reinforcement: polyvinyl alcohol (PVA), ultra-high molecular weight polyethylene (UHMWPE), and poly(p-phenylen-2,6-benzobisoxazole) (PBO). The composites’ mechanical features were analyzed in compression, three-point-bending, and tension tests with subsequent Environmental Scanning Electron Microscopy (ESEM) analysis of the fracture surfaces. Digital Image Correlation (DIC) was used to evaluate the extent of multiple cracking and crack widths under uniaxial tension. Additionally, single-fiber pullout tests were performed. PBO-based composites yielded the highest mechanical properties, reaching a 4.8 MPa peak stress in tension at a strain level of 2.3%, with a larger number of cracks. PVA and UHMWPE-based materials, however, demonstrated a lower mechanical performance, because of their larger diameter, lower mechanical properties and fiber-matrix adhesion.