Distributed Optical Fiber Sensing Bonding Techniques Performance for Embedment inside Reinforced Concrete Structures

Abstract

Distributed optical fiber sensors (DOFS) are modern-day cutting-edge monitoring tools that are quickly acquiring relevance in structural health monitoring engineering. Their most ambitious use is embedded inside plain or reinforced concrete (RC) structures with the scope of comprehending their inner-workings and the functioning of the concrete-reinforcement interaction. Yet, multiple studies have shown that the bonding technique with which the DOFS are bonded to the reinforcement bars has a significant role on the quality of the extracted strain data. Whilst this influence has been studied for externally bonded DOFS, it has not been done for embedded ones. The present article is set on performing such study by monitoring the strain measurement quality as sampled by DOFS bonded to multiple rebars with different techniques and adhesives. These instrumented rebars are used to produce differently sized RC ties later tested in tension. The discussion of the test outputs highlights the quasi-optimal performance of a DOFS/rebar bonding technique consisting of incising a groove in the rebar, positioning the DOFS inside it, bonding it with cyanoacrylate and later adding a protective layer of silicone. The resulting data is mostly noise-free and anomalies-free, yet still presents a newly diagnosed hitch that needs addressing in future research.

A Review of Recent Distributed Optical Fiber Sensors Applications for Civil Engineering Structural Health Monitoring

“… Strain profiles of a 15 × 15 × 210 mm Ø20 Reinforced Concrete (RC) tie test with the DOFS bonded with a combination of groove, cyanoacrylate and silicone [ 49 ]. …”

“… Influence of the rib pattern on the steel strain profiles during the double pull-out test of the RC tie 15 × 15 × 240 mm Ø20 (top five figures). Relative average reading noise (bottom) [ 49 ]. …”

“…This last conclusion was later demonstrated to be the main reason for the rise in SRAs in Bado et al [49]. The article was aimed at providing a contribution to the effort of establishing the best thin non-coated OFDR DOFS/rebar bonding technique whenever the instrumented bar is to be embedded inside of RC structures.…”

“…Alj et al [42] investigated the strain response of thick-coated DOFS sealed in a groove on the surface of a concrete structure using a polymer adhesive and aimed to identify optimal conditions for crack monitoring. Initially, a Finite Element Model was developed (see Figure 10) to understand the strain transfer process between the DOFS core and the host structure which showed that the softer the adhesive is, the lower the strain transferred to the DOFS glass core due to redistribution over a broader length of the sensor (similarly to what was observed in [48][49][50]). .…”

“…Additionally, as also visible in Figure 7, the oscillations of the profiles, easily confusable with signal noise, were stated to be the influence of the transversal rib on the tensile Figure 7. Strain profiles of a 15 × 15 × 210 mm Ø20 Reinforced Concrete (RC) tie test with the DOFS bonded with a combination of groove, cyanoacrylate and silicone [49].…”