Drones are well known for their roles in military applications. However, more recently, drones as tools for potential civilian applications have gained significant attention.
Equipped with cameras, sensors, and other intelligent devices, drones are being used in domains such as agriculture, forestry, archaeology, architecture, and construction, and in different applications, including photography, package deliveries, logistics, safety surveillance, mapping, search and rescue operations, visual inspection of hard-to-reach locations.
The use of drones in constructions, especially for monitoring large-scale civil infrastructures under maintenance or construction (such as high mast luminaires, dams, photovoltaics, facades, building roofs, industrial and historical buildings, bridges), is catching on.
Inspections in these structures are complex, hampered by access issues, and involving high costs and relatively long intervals between assessments. In addition, conventional inspection practices are inadequate since they rely on human-based visual inspection via scaffolding, rope, elevating platforms, or a unique vehicle and often require specially trained climbers for data acquisition.
According to studies, the construction site is one of the most dangerous workplaces. Drones are a great potential tool for reducing injuries on construction worksites and are turning out to be a speedy and cost-saving solution.
Here are some of the critical thermal measurements executed by drones at construction sites.
- Crack thickness and length
- Sizes of elements
- Long term deflections
- Concrete delamination
- Type of material of structures (masonry, concrete)
- Presence of steel rebars
- Water leakages or humidity
- Performance of conducts and pipelines
- Determination and location of voids in concrete
- Determination of fresh and hardenest concrete stages
Practical issues of drones in construction
Similar to any technology, drones have their own issues. The most commonly mentioned issue is accuracy. The accuracy of the drone measurements dramatically depends on the sensor type and characteristics of the platform the drone is built on. Position accuracy can be affected by the thermal sensor characteristics, such as the sensor resolution and the color depth. Temperature accuracy is determined by the color depth as well as by the accuracy of the calibration. Therefore, proper calibration of the thermal imager is necessary to extract scientifically relevant data in all the applications.
Another issue is the limited flight time and the need to change batteries. The flight time of a typical drone battery is approximately 25 minutes, and it could be lower in the case of a windy day. For inspections of small structures, the need to change batteries may not be necessary, but for bigger ones, it represents a problem. It means to stop the fly and more time to finish the inspection. Moreover, a mechanical malfunction or loss of power can cause the drone to rapidly fall to the ground and crush.
Environmental factors, typically weather conditions or path obstructions, are some pivotal factors influencing drone performance in construction sites. For example, weather conditions such as high-speed wind, rain, high temperature, shadows, and glare from the reflective surface can not only affect the quality of the visual data but can render the drone inoperable.
Gusts of wind can highly impact drone stability, resulting in turbulence and compromised data quality, especially in small and lightweight drones. Extreme windy conditions and overexposure of visual cameras to sun or snow are also factors affecting drone performance. This can result in the acquisition of unclear or fuzzy data leading to difficulties in damage detection. Appropriate ambient temperature during image acquisition is vital, as extreme cold can affect the battery performance, reducing flight duration.
If not properly operated, drones present potential safety hazards to construction workers, especially indoors. In the enclosed indoor construction environment, the sound of a drone can distract a worker, resulting in injury or property damage. Workers are also at risk if they come into physical contact with them or other objects in the site, such as building materials, concrete columns, or cables hanging from the ceiling, causing damage to the worker, object, and/or itself.
Here are the key practical issues on the use of drones in construction:
- Equipment constraints such as battery life and payload limitations
- Path obstructions and unfavorable weather conditions, including gusts of wind and precipitation
- Network instability or GPS-denied conditions.
- Line of sight constraints
- Injuries and property damages
- Labor and work distraction
- Regulatory restrictions and privacy concerns
- Communication loss/interference/low-quality images
- Analysis of extensive database of visual assets