Distributed fiber optic sensing for internal strain monitoring in full life cycle of concrete slabs with BOFDA technology

Effective health monitoring of concrete structures is vital in structural and geotechnical engineering, especially for internal monitoring in harsh environments. This article presents and validates a solution for distributed fiber optic sensing (DFOS) using Brillouin optical frequency-domain analysis (BOFDA) technology for monitoring the internal strain throughout the life cycle of common concrete slabs. The principle and sensing mechanism of BOFDA are briefly introduced and analyzed. A well-designed and deployed fiber under test (FUT) layout is utilized to accurately capture the internal strain distribution of a concrete slab. Besides, fiber Bragg grating (FBG) sensors and a thermocouple probe are incorporated for point strain reference and global temperature compensation. This paper presents a comprehensive monitoring method of concrete slabs throughout their entire life cycle. The monitoring process covers the preparation, pouring, curing, corrosion, and loading stages. Our experimental results demonstrate the feasibility of holistically monitoring strain distribution in concrete slabs over their lifetime. Additionally, post-processing of the data enables tracking of strain evolution at specific sensor nodes of interest. Furthermore, our study includes an extreme loading scenario, allowing examination of the strain variation process at rebars and key nodes. The strain distribution patterns observed in the experiment align with the finite element simulation results. These findings provide valuable guidance for crack prediction and structural health monitoring (SHM) of concrete slabs. The proposed scheme offers a unique and highly precise solution for full life-cycle SHM capable of functioning effectively in harsh environments such as energization and saltwater corrosion, thereby expanding its potential applications.