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

Understanding the mechanical properties of the grid component of textile-reinforced mortars (TRM) is critical because they directly influence the behaviour and strengthening capabilities of the composite. This study explored the dynamic tensile behaviour of a bi-directional basalt fibre grid using a high-speed servo-hydraulic direct tensile testing machine with specialised grips. Failure mode and deformation were captured with a high-speed camera. Tensile strain values were extracted from the recorded images using a Matlab computer vision tool - 'vision.PointTracker'. Specimen sizes of one and four rovings were tested at intermediate (1-8/s) and quasi-static (10-3/s) strain rates for comparison. After the tensile tests, scanning electron microscopy (SEM) analyses were performed to examine the microscopic failure of the grid. Linear and non-linear stress-strain behaviours were observed in the range of 10-3 to 1/s and 4 to 8/s, respectively. Increased strain rate enhanced tensile strength, ultimate strain, toughness, and elastic modulus. Overall, the dynamic increase factors for these properties, except for the elastic modulus, were between 1.4 and 2.3. At the macroscopic level, the grid generally failed in a brittle manner. However, microscopic analysis revealed that the fibre and polymer coating were strain rate sensitive. The enhanced tensile performance of the grid under dynamic loading circumstances makes it suitable for retrofitting structures prone to extreme loading conditions.