Structural health monitoring is a key factor in life cycle management of infrastructures. Truly distributed fiber optic sensors are able to provide relevant information on large structures, such as nuclear power plants or nuclear waste disposal facilities. The sensing chain includes an optoelectronic unit and a sensing cable made of one or more optical fibers. A new instrument based on Optical Frequency Domain Reflectometry (OFDR), enables to perform temperature and strain measurements with a centimeter scale spatial resolution over hundred of meters and with a level of precision equal to 1 μ strain and 0.1 °C. Several sensing cables are designed with different materials targeting to last for decades, either embedded in the concrete or attached to the surface of the structure. They must ensure an optimal transfer of temperature and strain from the concrete matrix to the optical fiber. Based on the European guide FD CEN/TR 14748 “Non-destructive testing – Methodology for qualification of non-destructive tests”, a qualification method was developed. Tests were carried out using various sensing cables embedded in the volume or fixed to the surface of plain concrete specimens and representative-scale reinforced concrete structural elements. Measurements were performed with an OFDR instrument, while mechanical solicitations were imposed to the concrete element. Preliminary experiments seem very promising since measurements performed with distributed sensing systems are found comparable to values obtained with conventional sensors used in civil engineering and with the Strength of Materials Modelling. Moreover, the distributed sensing system makes it possible to detect and localize cracks appearing in concrete during the mechanical loading.

Over the last 30 years, structural reinforcement and retrofitting with externally bonded composite materials have proven to be efficient and cost-effective solutions to increase both the safety and the lifespan of civil engineering structures, including nuclear power plants. The effectiveness of the strengthening system highly depends on the level of adhesion between the fiber-reinforced polymer (FRP) composite material and the concrete surface. Therefore, on-site evaluation of the bond quality is critical to assess the performance and predict the durability of the system in place. The direct tension pull-off test is most commonly used to quantify the adhesion level, but this standardized method has many drawbacks. In the present study, it is proposed to evaluate the bond properties by using a nondestructive test (NDT) derived from the standard pull-off test. This innovative test enables the measurement of an interfacial “stiffness” which may be used as a bond quality criterion. This paper gives an insight into the performance of the proposed NDT method, when applied in laboratory conditions to concrete slabs reinforced with bonded pultruded carbon FRP plates (CFRP). Three different epoxy adhesive systems with a broad range of Young’s moduli were used for the specimens’ preparation, in order to vary the stiffness of the concrete/CFRP interface. The purpose was to simulate different levels of interfacial adhesion that could be observed for a single adhesive system. It was shown that the test method was able to detect differences in the interface stiffness beyond experimental uncertainties, and it should therefore enable the detection of differences in the bond quality for a given adhesive system as well. The sensitivity of the NDT was then discussed, and its detection capabilities were predicted for standard field conditions. In the last part, strain measurements were collected during the NDT, thanks to distributed optical fiber sensors (DOFS) embedded in the adhesive joints of the strengthened specimens. An analysis of the strain profiles was found to provide complementary information on the quality of the adhesive bond.

The maintenance and evaluation of concrete nuclear containment walls is a major concern as they must, in case of an accident, ensure the confinement of the nuclear radiations and resist to the loads. A homemade multi-receiver multi-source dry contact linear probe to record ultrasonic surface waves on concrete in the frequency range [60 kHz – 200 kHz] has been used in this context. The measurement protocol includes the summation of up to 50 spatially distributed seismograms and the determination of the surface waves phase velocity dispersion curve. The probe has been tested against several concrete states under no loading (water saturation level, temperature damage). Then, the same measurements have been performed on sound and fire damaged slabs submitted to uniaxial loading (stress up to 30 % of the concrete compression resistance). It is shown that the robustness and precision of the surface waves measurement protocol make it possible to follow the stress level. In March 2017 a first experiment with this surface wave probe has been conducted on a reduced 1:3 scale nuclear containment plant (EDF VeRCoRs mock-up) under loading conditions that replicates that of decennial inspection. The surface wave phase velocity dispersion curves of each state are compared and cross-validated with other NDT results.

Tall and complex vertical structures, especially reinforced concrete chimney stacks and bridge piers, present challenges for non-destructive testing (NDT) professionals, particularly where internal or subsurface imaging is required and visual inspection is not sufficient. Traditional approaches such as rope access or scaffolding pose logistical, financial, and safety burdens, often limiting the feasibility of thorough inspections. In this paper, we present a collaborative project between HausBots (developers of climbing robotic platforms), ACS (creators of the MIRA ultrasonic tomography system), and EDF (end user and asset owner), which demonstrates the viability of advanced robotic-assisted ultrasonic inspection on vertical concrete infrastructure. A field trial on a large concrete chimney stack at an EDF facility validated the successful integration of ultrasonic tomography with a wall-climbing robot using HausBots’ proprietary AEROGRIPTM adhesion system. The project highlights how robotic inspection platforms can deliver safe, high-resolution, subsurface data from hard-to-access areas without manual intervention or elevated work platforms. This paper offers a detailed review of the methodology, technical integration, field results, and broader implications for the future of infrastructure assessment.