Distributed Corrosion Detection using Dedicated Optical Fiber Sensor (OFS) based Steel Rebar within Reinforced Concrete Structures by Optical Frequency-Domain Reflectometry (OFDR)

Détection répartie de la corrosion par capteur à fibre optique et OFDR sur les armatures de renforcement en acier des structures en béton armé

Sylvain Magne (1) , Shamyr Ali Alvarez (2) , Stéphane Rougeault (1)

1 LCFO (CEA, LIST) - Laboratoire Capteurs Fibres Optiques (CEA, LIST)
2 CNAM - Conservatoire National des Arts et Métiers [CNAM]

Corrosion is a major pathology for Civil Engineering structures, affecting long-term reliability. Huge direct costs (maintenance, rehabilitation) and indirect costs (lost productivity, litigation, outages, delays, downtimes) justify strategies to minimize the impact of corrosion. Regarding civil engineering (CE) infrastructures constructed of reinforced concrete, steel reinforcing bars (rebars) are naturally corrosion-protected when embedded into concrete (pH ~ 13). Concrete carbonation (“generalized” corrosion) and chloride ion penetration (“pitting” corrosion) both accelerate their corrosion rate. Corrosion products grow in volume and the increase in pressure at the steel-concrete interface leads to cracks of the concrete layer and acceleration of degradation. They may escape as well through cracks, thus leading to a reduction in rebar diameter and global structure weakening. Until now, inspections are carried out periodically and involve indirect measurement techniques (e.g. chemical-, impedance-, potential-based) that are time-consuming, costly and probabilistic in nature. Imaging techniques (e.g. ultrasonics) provide information about internal damage or voids within concrete but are of limited range of investigation (limited to accessible surfaces). Since it is impossible to predict where corrosion would start in large infrastructures, distributed monitoring techniques are desirable in order to early detect its onset, particularly in hidden or inaccessible areas. We investigated the OFDR technique in the perspective of a Condition-Based Maintenance (CBM), identified as a future challenge in order to provide safe operating conditions and cost savings. The use of telecom-grade fibers as sensors is motivated by their cost-effectiveness, electrochemical passivity, electromagnetic immunity and networking/multiplexing capability. We report on an original fiber-based corrosion sensor design employing usual steel rebars in order to avoid galvanic corrosion to occur. Since the sensor is a rebar, it also behaves as an extensometer and a dedicated design is proposed to discriminate between global thermomechanical loadings and local corrosion mechanical effects. Changes in OFDR signals with respect to reference signals provide localization, identification and direct measurement of corrosion. The sensing device was successfully tested under accelerated pitting corrosion as a proof-of-concept.

Mots clés: instrumentation; corrosion; structural health monitoring; long-term reliability; civil engineering; reinforced concrete; steel reinforcing bars; Concrete carbonation; chloride ion penetration; steel-concrete interface; degradation; inspection; Imaging technique; distributed monitoring technique; Condition-Based Maintenance; sensor; telecom-grade fiber; electrochemical passivity; electromagnetic immunity; networking capability; multiplexing capability; fiber-based corrosion sensor; sensor design; extensometer; thermomechanical loading; local corrosion mechanical effects; signal processing; reference signal; localization; identification; proof-of-concept; rebar; Optical Fiber Sensor; concrete structures; OFDR

Domaines: Instrumentations et Détecteurs [physics.ins-det]; Mécanique des solides [physics.class-ph]

Sylvain Magne, Shamyr Ali Alvarez, Stéphane Rougeault. Distributed Corrosion Detection using Dedicated Optical Fiber Sensor (OFS) based Steel Rebar within Reinforced Concrete Structures by Optical Frequency-Domain Reflectometry (OFDR). European Workshop on Structural Health Monitoring (EWSHM), BINDT, Jul 2018, Manchester, United Kingdom. 23306 (12 p.). ⟨hal-04559121⟩