❱ ❱ Bridge inspections systems take to the air with the use of drones loaded with sensors

❱ ❱ Large amounts of data from the drone sensors are stored in the cloud for engineering analysis

❱ ❱ Images from IR thermography can be mapped to visual bridge deck images to gain insight into potential deck delamination

sensing devices to replace the need for labour-intensive coring operations, which require extended road closures. There are two main issues that are investigated at the time of

inspection – delamination and reinforcing bar (rebar) corrosion. Ground Penetrating Radar (GPR): Radar antennas fixed to a vehicle are driven along the bridge driving lanes to transmit electromagnetic energy pulses into the bridge deck. Several passes are often required with different energy frequencies to gain the optimum combination of penetration depth and resolution. The return signal is analysed to provide insight into the bridge deck layer thicknesses and properties and is of particular benefit in detecting rebar problems, which often occur deep inside the deck. Infrared Thermography: IR Thermography is also a vehicle based technique and can be performed in a single pass of each driving lane at normal speeds. The thermal properties are evaluated and mapped onto an image of the bridge deck to visualise the temperature profile and identify areas of delamination or debonding of the road surface. The benefit of the vehicle based approached is that heavier cooled cameras can be used, which provide greater resolution and clarity at high speed. The alternative microbolometer IR cameras are lighter and cheaper but don’t provide as much detail.


Recognising the more widespread use of drones for aerial visual inspections, Infrasense has moved into the use of UAV technology for making IR inspections of bridge decks. Due to

weight considerations, microbolometer IR cameras are used. The company recently completed internal research to assess the feasibility and accuracy of aerial imaging for mapping bridge deck conditions. The results of this study provided support for implementation on future projects. The primary advantage of the aerial method is its efficiency. Data can be collected for hundreds of bridge decks in a single day, and, using Infrasense’s processing and analysis methods, defects can be quantified and mapped very quickly. The two methods used for aerial surveys of bridge decks are infrared thermography (IR) and high-resolution visual (HRV). The infrared technology was able to detect delaminations just under the surface of the bridge deck, which were then plotted onto an infrared map, where delaminated boundaries could be delineated. HRV was coupled with this method to rule out any thermal anomalies on the deck such as debris, shadows, wet spots or staining. Keen to adopt the technology, Infrasense believes that aerial imaging will open the door to comprehensive routine bridge deck evaluations at a relatively low cost. This fills a real need in the inspection market as accurate,

network-level data is required to facilitate asset management decisions, according to an Infrasense spokesperson.

A COMBINATION OF APPROACHES Creating a map of potential problems is only the first part of making bridge maintenance plans and more data is always needed from the ground. The main advantage of the use of drones is the speed with which initial assessments can be made. Once this has been done, highways agencies can prioritise

the next phase of work to make detailed assessments based on coring and physical inspections, from which a maintenance plan can be made. By only focusing on assets identified as needing attention, time and money is saved. To obtain the greatest benefit from the use of drones, there needs to be a combination of technologies and skills. With Intel’s expertise in drones and data management, the structural engineering expertise of companies such as Collins Engineering and the sensing and imaging expertise of Infrasense, a detailed and structured approach can be taken to the way different highways agencies can manage the hundreds of thousands of assets that are under their care. n

DAQ, Sensors & Instrumentation Vol 2 No. 1 /// 3

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