Development of a Monitoring System for Concrete Structures

With a newly developed, energy-efficient data logger, the FHNW – together with DuraMon AG – enables the continuous monitoring of corrosion in reinforced concrete structures. This innovative solution provides precise real-time data, helping to detect damage early and significantly reduce maintenance costs.

Corrosion is one of the main causes of damage to bridges, tunnels, and other concrete structures. Traditional inspection methods typically provide only momentary snapshots and are associated with considerable uncertainties. In collaboration with DuraMon AG, the Institute of Sensors and Electronics at FHNW has developed an innovative wireless monitoring system that enables continuous condition assessment of reinforced concrete – making an important contribution to the safety and longevity of critical infrastructure.

Conventional inspection procedures often rely on visual checks or destructive and non-destructive testing. However, these methods offer limited insights into the temporal progression of corrosion processes. DuraMon AG therefore provides a new monitoring solution capable of simultaneously capturing all parameters relevant to corrosion in reinforced concrete structures – such as pH value, chloride concentration, and the electrical impedance of concrete.

Reliable and long-term monitoring requires autonomous, energy-efficient, and communication-robust measurement systems. The key challenge lies in wirelessly transmitting measurement data even in environments such as tunnels or parking garages.

The joint project between FHNW and DuraMon AG pursued the following goals:

• Development of an energy-efficient data logger with an autonomous operating time of more than 10 years.

• Integration of a LoRa/LoRaWAN communication system that operates reliably in complex building structures.

• Implementation of highly sensitive corrosion measurement methods, including the precise detection of very small corrosion currents.

• Design of a wireless firmware update system (FUOTA) to enable maintenance without on-site interventions.

• Development of a modular test environment for automated quality and functionality testing before customer deployment.

• Analysis of LoRa signal propagation in real environments such as parking garages and tunnels to derive general installation guidelines.

Over the course of the project, an optimized data logger was developed to collect measurements from sensors embedded in concrete and transmit them via a dedicated LoRaWAN network. Key results include:

• New corrosion current measurement: Precise measurement in the range of ±25 µA with a resolution below 0.01 µA and an input impedance under 20 Ω.

• FUOTA-enabled firmware: A specially developed bootloader ensures secure wireless firmware updates despite the limited bandwidth of LoRa communication.

• Communication analysis in real environments: Extensive field tests in tunnels and parking garages provided valuable insights into signal strength, range, and optimal gateway placement.

• Modular test environment: A flexible testing platform allows the simulation of voltages, resistances, and currents, as well as the verification of power consumption and LoRa connectivity. A graphical user interface facilitates automated test sequences and documentation.

• Deployment in real applications: The developed data loggers are increasingly used by customers, contributing to improved structural monitoring.

The continuous corrosion monitoring system forms the basis for more advanced maintenance strategies in civil engineering. The insights gained regarding LoRa communication in complex environments enable more reliable planning for future installations. In the long term, the technology helps to:

• Plan maintenance measures more precisely,

• Reduce the cost of maintaining reinforced concrete structures,

• And significantly extend the service life of critical infrastructure.