In this work, we seek to assess and optimise the performance of an integrated chloride detection sensor based on the DC electrical resistivity measurement. We specifically seek to evaluate the detection threshold of chlorides. The main problem of the resistivity measurements in concrete is the dispersion of results mainly linked to the material heterogeneity and electrical contact limitations. To take into account the uncertainty of the measurement, we used a measurement device and sensors based on Geoelectrical Imaging methods. It gives richer information than the one delivered by conventional resistivity measurement sensors. Thus, it allows the use of statistical analysis and quality assessment methods. Before performing tests in concrete, we worked in a medium of known and homogenous resistivity in order to assess and optimise the performances of the acquisition system. Then we performed tests on concrete specimens containing different contents of chloride ions. Performance assessment of the resistivity probe is based on an analysis of receiver operating characteristic curves and the detection threshold of chlorides is calculated using the αδ method.

This paper presents the Structural Health Monitoring (SHM) system developed for a port wharf of a freight terminal, in Saint-Nazaire, France. This concrete structure has been equipped with a multi-sensor system for the monitoring of concrete ageing. The measurement chain is designed to detect the penetration of chloride ions in order to quantify the risk of reinforcement bars corrosion. Modifications of the mechanical behavior of the structural elements of the wharf are also monitored. At first, the sensors embedded within the structure and the acquisition devices are described. The data from the monitoring performed during the first months of the structure service life are then presented. The concrete monitoring at early age providing data like temperature history, strain and resistivity is useful both for the wharf owner and the construction company since it indicates where concrete shrinkage is likely to cause cracking and gives an indicator of material hardening. These data were compared to the results of material tests carried out on concrete. The study shows that a measurement chain dedicated to the SHM could be a useful tool for validating the quality of the construction of a reinforced concrete structure before being used in the framework of long-term monitoring.

Optical fiber strain sensing cables are widely used in structural health monitoring; however, the impact of a harsh environment on them is not assessed despite the huge importance of the stable performances of the monitoring systems. This paper analyzes (i) the impact of the different constituent layers on the behavior of a strain sensing cable whose constitutive materials are metal and polyamide, (ii) the radiation influence on the optical fiber strain sensing cable response (500 kGy of $\gamma$ -rays), and (iii) the behavior of the cable under high axial strain (up to 1%, 10,000 $\mathsf{\mu }\mathsf{\epsilon }$ ). Radiation impact on strain sensitivity is negligible for practical application, i.e., the coefficient changes by 4% at the max. The influence of the composition of the cable is also assessed: the sensitivity differences remain under 15%, a standard variation range when different cable compositions and structures are considered. The elasto-plastic behavior is at the end evaluated, highlighting the residual strain (about 1600 $\mathsf{\mu }\mathsf{\epsilon }$ after imposing 10,000 $\mathsf{\mu }\mathsf{\epsilon }$ ) of the cable (especially for metallic parts).

Underground radioactive waste disposal facilities must be monitored to guarantee their correct and safe exploitation during the early stage of their service life. This will be the case in Cigéo, the french industrial geological disposal facility for high-level and intermediate-level long-lived waste, which must be monitored for the first a hundred years at least. For this purpose optical fiber strain sensing cables can be chosen for their low intrusivity and resistance to harsh radiation environment. In this paper, a monitoring method able to follow shape evolution of the structure’s section, based on distributed strain sensing is tested on a high-level waste disposal cell mock-up, a steel lined micro-tunnel of 762 mm of outer diameter. The cell demonstrator is built in Meuse/Haute-Marne Underground Research Laboratory, in the same geological environment as the one envisaged for Cigéo but it is empty of waste. After 7 months of loading of the rock around the mock-up, a maximum of 2 mm of diameter reduction is observed with Rayleigh-scattering based strain sensing technique and 10 mm of spatial resolution around the circumference. This validation under realistic test conditions opens up to the use of the method in-situ for tunnel monitoring in harsh environment.

Concrete shrinkage monitoring is performed using simplified 2-axes version of the Eshelby-type 3D sensor [1] embedded in the center of a cylindrical specimen. The sensor measurements yielded during shrinkage are compared with external LVDT's measurements. The accuracy and repeatability of the embedded sensor is validated thanks to three loading and unloading cycles during compression testing by comparing the internal strains with external strain gages measurements and numerical simulations results. The concrete was formulated in order to generate significant autogenous deformation. The shrinkage was monitored in setting concrete in sealed and drying conditions. The results are in agreement with existing knowledge of early-age cracking phenomena and the temperature influences on the evolution of the strain during shrinkage. This study shows the ability of the proposed embedded sensor to monitor shrinkage within concrete