Durability‑aimed performance of glass FRCM‑confined concrete cylinders: experimental insights into alkali environmental effects

This study explores the structural performance of concrete cylinders confined with glassbased fabric-reinforced cementitious matrix (FRCM) systems, emphasizing the effects of prolonged exposure to alkali-rich environments. FRCM confinement has gained attention for its ability to enhance compressive strength and ductility in concrete elements, but its long-term durability under chemically aggressive conditions remains a critical concern. In practical applications, exposure to alkaline environments— such as those found in concrete pore solutions— can significantly impact the mechanical integrity of the composite system, particularly the bond between the glass fibers and the cementitious matrix, which is essential for effective confinement. To assess these effects, an experimental program was conducted involving glass-FRCM coupons, dry fabrics, and concrete cylinders externally wrapped with glass-FRCM. These specimens were immersed in a simulated alkaline solution for durations of 1000, 2000, and 3000 h. Both confined and unconfined cylinders were subjected to axial compression tests to evaluate changes in compressive strength, axial strain capacity, and failure mechanisms. Additionally, digital microscopy was used to examine microstructural deterioration and chemical alterations in the glass fibers and matrix, providing insight into the degradation processes at the fiber-matrix interface. The results indicate that alkali exposure progressively weakens the interfacial bond between the glass fibers and the cementitious matrix, with the extent of degradation closely linked to the exposed surface area. This deterioration leads to a measurable decline in confinement effectiveness over time.