Enhancing structural performance of hybrid fiber-reinforced geopolymer composites with AFRP confinement: Experimental, theoretical, and finite element analysis

Geopolymer concrete (GC) is an eco-friendly alternative to ordinary Portland cement concrete, offering superior early mechanical properties, enhanced durability, and reduced environmental impact. However, its relatively low long-term compressive strength (CS) necessitates further enhancement for structural applications. While extensive research exists on unwrapped GC, limited studies have focused on the structural performance of aramid fiber reinforced polymer (AFRP)-wrapped GC. This study addresses this gap by investigating the axial performance of hybrid fiber-reinforced geopolymer concrete (HFRC) confined with AFRP. Eighteen cylindrical HFRC specimens, incorporating steel and polypropylene fibers and produced using NaOH concentrations of 6 M and 12 M to achieve CS values of 20 MPa and 35 MPa, were subjected to axial loading. Specimens were wrapped with one or two layers of AFRP, and their compressive strength, axial strain, elastic modulus, stiffness, failure modes, and stress-strain behavior were analyzed. A modified theoretical model was developed for axial strength predictions based on a database of 725 specimens. Finite element models (FEM) were also proposed to predict the structural performance of AFRP-confined HFRC and conduct detailed parametric analyses. One-way ANOVA was performed to examine the statistical significance of experimental results. The results revealed that AFRP confinement significantly enhanced the axial performance of HFRC. For 20 MPa HFRC, one and two AFRP sheets increased CS by 86.4 % and 129.4 %, respectively, while for 35 MPa HFRC, the improvements were 46 % and 68.9 %. AFRP confinement proved particularly effective for lower-strength HFRC. The proposed FEM accurately captured the axial behavior of specimens using a concrete damage plasticity model, with average discrepancies of 5.62 % for CS and 5.81 % for equivalent axial strain. The parametric analysis demonstrated a marked improvement in confined concrete strength with increasing AFRP thickness and elastic modulus, showing a 576 % increase in CS as AFRP thickness enhanced from 0.15 mm to 1.05 mm, and a 329 % rise as Young's modulus increased from 110 GPa to 245 GPa. These findings highlight the potential of AFRP confinement for optimizing the structural performance of HFRC.