Bridging the gap between the physical and virtual - a focus on large scale inspection during the recycling of wind turbine blades

Project Challenges

Chloride induced corrosion or chloride corrosion is particularly prevalent in steel and reinforced concrete structures and is a destructive process leading to damage of internal structures. It occurs when chloride ions, typically found in sodium chloride and calcium chloride, penetrate the protective oxide layer on the metal surface and react with the underlying metal. This reaction leads to the formation of metal chlorides, which are highly soluble and can wash away, exposing more of the metal to corrosion. Reinforced concrete structures, where steel reinforcement bars (rebar) are embedded, are particularly susceptible. Marine and coastal environments are most problematic due to high levels of salt in the air and water, but issues also occur in areas where de-icing salts are used on roads to make them safer during the winter.

Regular inspection and maintenance are crucial to detect and address corrosion early. Remediation may involve removing corroded material, applying corrosion inhibitors, or installing additional protective measures. It is important to conduct regular inspections and maintenance, as chloride induced corrosion can compromise the structural integrity of buildings, bridges and other infrastructure, leading to safety concerns and costly repairs or replacements.

Bridges are integral components of the highway network, and extensive deterioration poses significant concerns, affecting both public safety and imposing economic strains. Currently, bridge deck inspections involve closing sections of highways, removing the road surface layer, and manually conducting tests such as tactile hammer testing and half-cell potential scanning on the exposed concrete deck. Subsequently, the deck is resurfaced before the highway can be reopened. This manual process is time-consuming, expensive, and disrupts road users. The efficacy of a vehicle-mounted Ground Penetrating Radar (GPR) system for Non-Destructive Testing (NDT) inspections of bridge decks, offers an alternative to the labour-intensive manual inspections.

The Outcome

• A detailed literature review of the state-of-the-art processing models for chloride detection and evaluation;
• Vehicle mounted inspection of three bridges for subsurface features including asphalt, rebars and concrete layers. This included assessment of depth and thicknesses of these layers;
• Mapping of subsurface features outlined the benefits of vehicle mounted GPR inspection using optimised scan parameters providing high density subsurface information;
• The mapped features were inline with expected locations and depths according to bridge drawings;
• The inspection has shown that it is possible to incorporate a chloride detection methodology within an inspection workflow. Further work is required to fully assess the attenuation-based methodology due to unknown variation of chloride over the inspected bridge;
• Vehicle mounted inspection using GPR has shown that significant cost savings can be achieved, while providing improvements to maintenance activities such as repair via more accurate estimates of required work, materials and extent of repair required;
• Chloride detection could provide early warning of rebar corrosion and concrete delamination, pre-empting and optimising maintenance operations which could lead to less costly repairs and reduced/optimised repair times;
• Future challenges have been identified, including importance of GPR parameter calibration, response signal interpretation, bridge design complexity, and material core sampling requirements.