Quantitative Strain Measurements of Kevlar Fibers in Composite Concrete Using Raman Spectroscopy

This study presents a Raman-spectroscopy-based quantitative analysis technique for measuring strain in Kevlar single fibers embedded in concrete. By irradiating the fibers with a laser, the researchers established a linear relationship between Raman scattering intensity and the fibers’ cross-sectional area, linking spectral parameters (e.g., peak position, half-width, intensity, and area) to mechanical strain. Experiments on DuPont Kevlar 49 fibers involved axial tensile loading using a micro-loading device, with Raman spectra (785 nm laser) captured at each displacement step. The results showed that the G’ peak position (1610 cm−1) shifted linearly with strain, while the peak area provided the most reliable correlation. Scanning electron microscopy (SEM) validation confirmed the method’s accuracy for early-stage strain measurements (maximum deviation: 7.31%), although excessive loading caused surface damage and signal distortion. The study demonstrates the feasibility of Raman spectroscopy for micro-scale strain analysis in fiber-reinforced concrete, despite sensitivity to experimental conditions (e.g., laser intensity, optical alignment).