Distributed optical fibre sensors in concrete structures: Performance of bonding adhesives and influence of spatial resolution

Abstract

Summary In this paper, the authors conducted an experiment where a reinforced concrete beam was instrumented with a 5‐m long polyimide single distributed optical fibre sensors (DOFS) performing four equal segments externally bonded to the bottom surface of the element, using for each segment a different type of adhesive. Three strain gauges were also used for comparison purposes. This beam was then loaded, producing expected equal levels of strain in each of the fibre segments for a more direct comparison of the different adhesives performance. The effect of alternating the spatial resolution is also analysed. In this exercise, additionally to the comparison with the other instrumented sensors, it is also important the consideration and analysis of the associated spectral shift quality (SSQ) values of the DOFS measurements.

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

“…Additionally, further studying should also be dedicated to assessing the effect of bending-induced-compression. This is in line with other researchers’ results [ 11 , 16 ] that suggest a certain “strain relaxing” and ”strain redistributing” influence of the silicone when it is used as a DOFS protecting material. Unfortunately, this phenomenon strongly influences the recommendability of the present bonding technique for this particular use.…”

“…The importance of this issue has only lately been recognized as all the produced publications date back to last decade [ 12 , 13 , 14 , 15 ]. Worthy of mention, are two extensive studies analyzing the influence of different bonding adhesives on the strain output of polyamide cladded DOFS attached to bare rebars [ 11 ] and concrete surfaces [ 16 ]. Yet, no definitive comparative study has been developed for the case of DOFS bonded to rebars when embedded inside RC structures.…”

Crack monitoring in reinforced concrete beams by distributed optical fiber sensors

“…Loss of information after cracking, however, may occur if the strains in the fiber exceed its measuring range when uncoated fibers are used in combination with stiff adhesives, which highlights the importance of choosing and correctly applying the right adhesive so that stresses are properly transferred from the substrate material to the fiber core, cf. (Barrias, Casas, & Villalba, 2019a). Attaching the fiber to the reinforcement, on the other hand, may not only be used to assess the cracking state of the structures but it can also provide valuable information about the loading state.…”

Experimental and Numerical Investigation on the Strain Response of Distributed Optical Fiber Sensors Bonded to Concrete: Influence of the Adhesive Stiffness on Crack Monitoring Performance

“…The dependence of the strain transfer process on the adhesive stiffness, as previously highlighted by theoretical approaches, suggests that it might be beneficial to use a soft polymer adhesive in the framework of crack monitoring applications. Indeed, crack opening generates a strain peak in the host material [ 7 , 29 ], which could be distributed over a broader length of the fiber core when a soft adhesive is used to bond the DOFS to the concrete surface. This solution may reduce the risk of DOFS breakage due to crack development, hence ensuring better durability of the SHM instrumentation under service condition.…”

“…Under both static and fatigue loads, epoxy showed the best performance and strain values obtained matched perfectly with those from the strain gauges. However, after the elastic regime (when the beam was cracked and loaded up to failure), only DOFS bonded using silicone, the adhesive with the lowest shear modulus, provided realistic results [ 29 ].…”