Intelligent corrosion sensors for armour at the Canal construction site
Within the framework of the project to underground the railway tracks of the access channel of Valencia, Rover Infrastructures has participated in a pioneering and innovative initiative of structural monitoring using intelligent corrosion sensors. This work is a good location since its structural elements are exposed to humid environments or more aggressive conditions and were in the process of execution to be able to undertake their installation.
This collaboration has been developed within the framework of the State R&D&I Program Oriented to the Challenges of Society, in the project “Intelligent monitoring to reduce uncertainty in the useful life: potentiostatic corrosion sensors, PID2020-119744RB-C21 and C22”, funded by the State Research Agency and in which the Universitat Politècnica de València (UPV), specifically the SMART group (IDM-Department of Architectural Constructions), together with the Eduardo Torroja Institute of Construction Sciences (IETcc-CSIC) have participated.
The main objective of the project has been to implement advanced technologies that allow real-time assessment of the state of reinforced concrete structures. Thus anticipating deterioration processes and improving maintenance management throughout the life cycle of the infrastructure.
Technology for infrastructure sustainability
The sensors developed by UPV’s SMART Group allow for monitoring key parameters related to corrosion of armatures in concrete structures. These sensors are divided into two major groups:
- Triggering sensors: detect the presence of chlorides, changes in pH, oxygen availability, temperature and resistivity of concrete.
- Corrosion rate sensors: measure the steel section loss, providing quantitative information on the evolution of the corrosive process.
All sensors are designed to operate continuously and remotely, sending data to a web server accessible from any computer. Its robustness ensures high durability, even in harsh environmental conditions.
Installation on site: interference-free integration
The location of the different control points was agreed with Rover Infrastructures and Dragados to avoid interference with work. Also, the different building elements, their environmental exposure and the arrangement of construction joints or cold joints were taken into account as “critical” points in this type of infrastructure. The installation of sensors has been carried out at four strategically selected control points (PCs) in the underground structure:
- PC1: Lower face of the slab, underground area with high humidity.
PC2: Cold joint between screen wall and slab, critical point for possible leaks.
PC3: Side face of the crowning beam, in contact with ground fill.
PC4: Upper face of the slab, under urbanizable area.
The installation was carried out in two phases, using 3D printed auxiliary parts to ensure correct positioning of the sensors during the concreting. Subsequently, they were connected to a central unit equipped with a mini PC and an RS485 communication system, powered by solar energy that allows the autonomous monitoring in real time of the corrosion of the armatures at multiple control points (CP). Measurement data is stored and processed on the server being remotely accessible via an online interface.
What parameters do these sensors monitor in the infrastructure?
The sensors allow a wide range of parameters to be recorded, including:
- Corrosion potential (Ecorr): indicates the risk of corrosion of the armatures.
- Density and corrosion rate (icorr, vcorr): evaluate the propagation stage.
- Corrosion penetration (Px): quantifies the steel thickness loss.
- Concrete resistivity (ρ): related to durability and the presence of moisture.
- Temperature: directly affects corrosion kinetics.
- Chloride activity and pH variations: key triggers.
- Oxygen availability: influences the corrosion rate.
The positive results obtained after 10 months of monitoring
Over a period of 300 days, the installed sensors have been continuously monitored. The results have been very positive:
- Progressive reduction of icorr: initial values above 1 μA/cm2 dropped to levels below 0.1 μA/cm 2, indicating effective armor passivation.
- Stability in corrosion potential: evolution towards more electropositive values, consistent with the low risk of corrosion.
- Increasing resistivity: associated with the reduction of internal humidity and the evolution of concrete.
Very low cumulative corrosion penetration: in most sensors, less than 1 μm.
The variable corrosion density (icorr), expressed as μA/cm 2, is commonly used as a quantitative indicator of the level of corrosion in armatures. The graph in Figure 4 represents the evolution of corrosion current (icorr) recorded at different control points (PC) of the structure throughout the monitoring period. Initially, icorr values above 1 μA/cm2 are recorded (which is interpreted as high corrosion) which is consistent with the transition period in which the concrete has not yet fully developed the alkaline conditions necessary for the passivation of the armatures.
As the days go by and the cement hydration process progresses, a decrease in icorr values is observed, which indicates the passivation of the armatures where the values tend to stabilize towards low or even negligible levels over time. Only at control point PC2, corresponding to the cold joint between the screen wall and the plate, slightly higher values were observed. Although they were equally low, which reinforces the system’s usefulness in identifying critical areas.
Figure 5 shows the evolution of the corrosion potential (V vs SCE) that allows to establish the risk of corrosion according to the standard UNE 112083. An upward trend is observed, that is, an evolution towards values of more electropositive potential or low corrosion risk and which is consistent with the corrosion density (icorr) values obtained; therefore, the passivation of the armatures is clearly evident.
Advanced analysis with multivariate techniques
In addition to the classical parameters, voltammetric sensors such as “electronic language” have been used to assess the corrosion initiation stage. These sensors make it possible to analyze the availability of oxygen and the presence of aggressive ions using cyclic voltammetry techniques and multivariate analysis.
This approach enables early detection of possible carbonation or chloride entry processes, even before visible damage to the structure is evident.
Rover committed to innovation to incorporate advanced solutions into the world of construction
The results obtained confirm that the installed monitoring system is functioning correctly and, in addition, we can certify that it is not affected by environmental conditions. The information collected thus allows to anticipate deterioration processes, optimize maintenance and improve infrastructure management.
At Rover Infrastructures, we reaffirm our commitment to applied research, technological innovation and sustainability in all our projects. This project is a clear example of how technology can transform the way we design, build and maintain our infrastructure, adding value and ensuring long-term functionality.