In-Fiber Optic Salinity Sensing: A Potential Application for Offshore Concrete Structure Protection.

Dong Luo,Yanchao Yue,Jianxun Ma,Hangzhou Yang,Peng Li

doi:10.3390/s17050962

Abstract

The protection of concrete structures against corrosion in marine environments has always been a challenge due to the presence of a saline solution—A natural corrosive agent to the concrete paste and steel reinforcements. The concentration of salt is a key parameter influencing the rate of corrosion. In this paper, we propose an optical fiber-based salinity sensor based on bundled multimode plastic optical fiber (POF) as a sensor probe and a concave mirror as a reflector in conjunction with an intensity modulation technique. A refractive index (RI) sensing approach is analytically investigated and the findings are in agreement with the experimental results. A maximum sensitivity of 14,847.486/RIU can be achieved at RI = 1.3525. The proposed technique is suitable for in situ measurement and monitoring of salinity in liquid.

Highlights

Salinity is a significant property of natural water and industrial wastewaters
Portland cement plays a key function in maintaining the health of the structure, it is an alkaline material
It is the preferred choice to place the concrete structure at, or near, an alkaline environment to preserve and maintain the integrity of the concrete structure; it is challenging in the scenario where concrete structures are built in a marine environment

Summary

Introduction

Salinity detection and measurement has widespread applications and a great realistic significance in the protection of the marine environment, oceanic, mariculture, water source quality, and concrete structures [1]. Due to the pores and micro-cracks in the concrete, the saline solution can infiltrate into the concrete structures. The infiltrated saline solution is a mild acid that lowers the pH of the concrete and compromises the adhesive ability of the cement that holds the concrete structures together. The saline solution attacks the concrete paste and increases the pore size, which allows more infiltration of the saline solution and other chemical substances into the deeper parts of the concrete structures, exacerbating the freeze/thaw cycle damage. When the salt reaches the steel reinforcement, the thin protective layer of iron oxide surrounding the reinforcement has limited ability against the corrosive attack. Considering the connection between the solution salinity, the pH of the solution, and the strength of the concrete paste, the salinity concentration can serve as a good indicator for diagnosis and structural monitoring of the concrete under corrosion

Results

Discussion

Conclusion