Structural Health Monitoring Against Coastal Erosion

Using litter for marine environmental protection. What sounds contradictory became a successful environmental, economic and technological approach with the ECO-SMART BREAKWATER project. 

The "ecological" aspect of this project is based on a recycling process. Aggregate from construction and demolition work and fiber, obtained from the litter of oceanic Posidonia, are transmuted into elements for a breakwater system. Thus, the very same ecosystem the elements arise from also benefits from it - the marine habitat.

The "smart" part of the solution is the instrumentation with HBK optical sensors, which ensure the monitoring of marine environmental and structural parameters. These signals are acquired and processed in real time by a remote station.

Why structural health monitoring? For monitoring, controlling, and managing structural risks in real time. The information on the tensile state of the breakwater elements is of fundamental importance, as tensile stresses within these elements may - in extreme conditions - induce fracturing. The consequence could be the compromise of the stability of the entire breakwater system.

Before installing the HBK optical fiber sensors on the full-scale breakwater element, they were validated by the Resilient and Sustainable Civil Engineering Unit team of the Brindisi-based CETMA Center, in collaboration with Skema srl. To ensure that the sensors work properly, they were first tested on a prototype in small physical laboratory tests.

To show if the results of the FBG sensor are coherent with conventional sensors, a comparison was made: 1. the response of the HBK FBG sensor, embedded in a concrete cylinder to a cyclic compression test with loads between 1 and 5 MPa, with: 2. the response of conventional electric elastic extensometers, fixed with adhesive on the surface of the cylinder itself.

The comparison showed that the FBG sensor responds in a way that congruently responded to stress. A difference between the values of the two sensors was due to the different positions in which the measurement was made.

Fig.1 shows the internal chain:

To distinguish a temperature signal from a deformation signal, 4 deformation sensors and 2 temperature sensors are connected in a single chain, embedded in the concrete during fabrication of the ECOSMART – BREAKWATER element.

Fig.2 illustrates the external chain:

2 accelerometers and 1 temperature sensor are connected in a chain, anchored to the exterior of the ECOSMART – BREAKWATER element.