Hybrid BOTDA-DIC sensing for flexural behavior characterization of eco-concrete reinforced beams under four-point loading

This study investigates the performance of Brillouin Optical Time Domain Analysis (BOTDA) and Digital Image Correlation (DIC) for monitoring the flexural behavior of two reinforced concrete (RC) beams constructed using eco-concrete containing Palm Oil Boiler Ash (POBA) and nano-silica as partial cement replacement. Two simply supported beams (300 cm × 15 cm × 25 cm) with different concrete compressive strengths were tested under four-point bending until failure to evaluate the sensing performance under varying structural responses. Distributed strain from BOTDA and full-field displacement from DIC were compared with mid-span deflection measured by Linear Variable Differential Transformers (LVDTs). Both sensing systems successfully captured strain development and stiffness degradation. BOTDA recorded the progressive increase of tensile strain at the bottom fiber, reaching 10,000-18,000 µε, as cracking advanced, while DIC identified multiple flexural cracks with openings ranging from 0.05 to 3.28 mm. BOTDA-derived deflection showed good agreement with LVDT and DIC, with differences less than 7%. The findings highlight the complementary advantages of both systems: BOTDA provides distributed and continuous strain monitoring for global behavior, while DIC captures localized deformation and crack development with high precision. Together, these techniques offer a complementary and reliable approach for detailed structural assessment of reinforced concrete beams.