A laboratory and field investigation of the pullout performance of GFRP bars in gypsum

The growing demand for permanent reinforcement systems for unstable rock masses, ensuring high reliability in terms of mechanical performance and long-term durability, is a widely discussed topic in the geotechnical field. Galvanized or steel bars are the most commonly used materials for anchors in these applications; however, they are prone to corrosion. In aggressive environments characterized by high humidity or continuous water seepage, stainless steel bars are often used, despite their significantly higher cost. In this context, Glass Fiber Reinforced Polymer (GFRP) bars offer an attractive alternative due to their inherent corrosion resistance, high tensile strength, and lightweight properties. This study investigates the tensile behaviour of GFRP bar nails embedded in gypsum rock, a material often prone to instability and mechanical degradation. Extensive pull-out tests were conducted under both laboratory and field conditions to evaluate the mechanical performance and bond strength between the GFRP bars, the grout material, and the gypsum matrix. Particular attention was given to the development and optimization of test instrumentation, ensuring perfect axial force transmission, high-quality data acquisition, and enhanced reliability of experimental outcomes. The results of the experimental campaign are presented and discussed in detail, with a focus on the performance of GFRP nails using two different grout materials: resin and cement. The findings highlight the potential of GFRP nails as a cost-effective and durable solution for reinforcement systems, particularly in highly aggressive environments where traditional materials are prone to premature failure.