Tensile stress–strain behavior and microstructure of PVA fiber‐reinforced geopolymer composites modified by nano‐ SiO ₂

Abstract

With the rapid development of green and low‐carbon construction materials, engineering geopolymer composites (EGCs), characterized by high strength, superior toughness, and excellent durability, have attracted increasing attention. However, achieving a synergistic enhancement of both strength and ductility in EGCs remains a critical challenge. To address this issue, this study systematically investigated the effects of nano‐silica (nano‐SiO ₂ ) on the tensile stress–strain behavior and microstructural evolution of polyvinyl alcohol (PVA) fiber‐reinforced EGCs. EGC specimens containing different nano‐SiO ₂ dosages (0%, 0.5%, 1.0%, 1.5%, and 2.0%) were prepared and evaluated through compressive, flexural, and uniaxial tensile tests. Furthermore, the underlying strengthening mechanisms were analyzed using scanning electron microscopy, x‐ray diffraction, and mercury intrusion porosimetry. The results demonstrated that the appropriate incorporation of nano‐SiO ₂ significantly improved the overall performance of EGCs, with the NS‐1.0% mixture exhibiting the optimal performance. Compared with the control specimen without nano‐SiO ₂ (control‐0%), the compressive, flexural, and tensile strengths of the NS‐1.0% group increased by 13.47%, 5.52%, and 39.84%, respectively. In addition, the incorporation of 0.5%–1.0% nano‐SiO ₂ markedly enhanced the initial stiffness and strain‐hardening capacity of the EGCs, while also promoting a more stable post‐peak strain‐softening response. Microstructural analyses revealed that nano‐SiO ₂ facilitated geopolymerization through both filler and pozzolanic effects, thereby refining the pore structure, improving matrix densification, and strengthening the fiber‐matrix interfacial bonding. However, excessive nano‐SiO ₂ content (>1.0%) resulted in particle agglomeration and the formation of additional pore defects, which adversely affected the mechanical performance and tensile toughness of the composites. Overall, this study provides valuable insights into the strengthening and toughening mechanisms of nano‐SiO ₂ ‐modified EGCs and offers a theoretical basis for developing high‐performance geopolymer composites with enhanced strength and ductility.