Impact of alkaline exposure and curing environment on mechanical properties of FRCM systems

Fibre Reinforced Cementitious Matrix (FRCM) systems are widely used retrofitting solutions for strengthening existing structures, offering a high strength-to-weight ratio and excellent compatibility with traditional substrates like masonry. However, the durability of these systems under aggressive environmental conditions remains an open research topic. In particular, the alkaline environment produced by lime-based mortars, used as matrices in FRCM composite materials, might negatively affect the embedded fibres, potentially compromising their long-term performance. This study investigated the durability of two FRCM systems, one incorporating glass fibres and the other basalt fibres, when exposed to alkaline conditions. Textile specimens were immersed in an alkaline solution at two temperatures (23 °C and 40 °C) for a total duration of 1000 h to evaluate fibre degradation. In addition, FRCM coupons were tested to assess the influence of curing conditions and temperature on the tensile performance of the composite system, while mortar prisms cured under identical conditions were tested to characterise the matrix behaviour. To explore the feasibility of accelerated aging protocols, FRCM coupons manufactured using conditioned textiles were also tested. Complementary Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses were performed on both the fibres and their coatings, providing microstructural insights that support the mechanical findings in the tensile tests on textiles.