Dynamic Tensile Response of Basalt Fibre Grids for Textile-Reinforced Mortar (TRM) Strengthening Systems

The present work constitutes the initial experimental effort to characterise the dynamic tensile performance of basalt fibre grids employed in TRM systems. The tensile behaviour of a bi-directional basalt fibre grid was explored using a high-speed servo-hydraulic testing machine with specialised grips. Deformation and failure modes were captured using a high-speed camera. Tensile strain values were extracted from the recorded images using the MATLAB computer vision tool, 'vision.PointTracker'. The specimens, consisting of one and four rovings, were tested at intermediate (1-8/s) and quasi-static (10^-3/s) strain rates. After the tensile tests, scanning electron microscopy (SEM) analyses were performed to examine the microscopic failure of the material. Linear and non-linear stress-strain behaviours were observed in the range of 10^-3 to 1/s and 4 to 8/s, respectively. Tensile strength, ultimate strain, toughness, and elastic modulus increased at intermediate strain rates. Overall, the dynamic increase factors for these properties, except for the latter, were between 1.4 and 2.3. At the macroscopic level, the grid failed in a brittle manner. However, microscopic analyses revealed that the failure modes of the fibre and polymer coating were strain-rate sensitive. The enhanced tensile performance of the grid under dynamic loading conditions rendered it suitable for retrofitting structures prone to extreme loading conditions.