Ageing infrastructure is becoming a growing concern for developed economies, as vital structures such as bridges have been built for 40 years or more. It is common knowledge that over time structures degrade, and the addition of heavy impact from vehicles and harsh weather conditions makes these structures even more unsuitable for use. BBC news reported that the average age of a bridge in the US is 43 years old, whilst in the UK it was found that over 2000 bridges were not suitable to carry the heaviest vehicles which are permitted on public highways. This is a widespread problem that can ultimately lead to loss of life, demonstrated by the Genoa bridge collapse in 2018.
Efforts are being made to rectify this issue with the US promising $110bn to go towards the repairs for roads and bridges in poor condition as part of a huge Infrastructure Bill. The role that corrosion plays, however, is not highlighted enough as the steel and concrete are heavily impacted in many ways. These include:
• Deterioration of concrete in harsh environments (such as chloride ions and frost) which leads to moisture ingress and corrosion of steel
• Concrete carbonation which causes embedded steel reinforcements to corrode, with the resulting expansion cracking and weakening the concrete
The issue of corrosion is evident, with 70% of all infrastructure damage stemming from corrosion problems. C-Probe Systems offer protection to new and existing transport and marine infrastructure through Impressed Current Cathodic Protection (ICCP) and monitoring, providing sustainable resilience for this vital fabric of society. Structural health monitoring is vitally important for these structures, to ensure whole life performance.
The restoration of the Bervie Jubilee Bridge in Scotland is an example of protecting an older structure through ICCP. Cracks had begun appearing in its concrete cover and water leakage from the deck through half-joints that carried de-icing salts from the road above. In 2008, following extensive deck joint replacement, deck repairs and waterproofing replacement occurred in 2003.
Restoration of the support beams and half-joints using traditional structural concrete repairs were then needed, partnered with ICCP methods to protect this structure from immediate corrosion issues and control in the long term. The final installation saw over 8500 anodes drilled in with ICCP operation in 20 zones with separate control of the beams and the half-joints. These zones are networked together along the length of the bridge to minimise the amount of cable to the project and managed from a single communication point to the north of the bridge.
For the time, this project would have been ahead of its time compared to others, as it was ESG compliant for low carbon and sustainable outcomes. C-Probe collaborated with the client to take careful steps to repair and protect bridge, choosing to retain the structure and use controllable long-term technology that was respectful to the environment, securing the embodied carbon, while also taking control of the degradation risk to futureproof the asset.
In contrast, C-Probe were called to provide elements of an ICCP protection system to be cast into the Rambler Channel Bridge (Hong Kong), along the newly constructed airport route between Lantau and the airport. The cathodic protection was to increase the service life of the structure by at least 60 years, and specific monitoring was to keep an eye on other bridge elements to detect the future ingress of chloride ions into the concrete.
The Achilles CP management system allowed the client to control and monitor the cathodic protection system for individual zones, but also allowed expansion into other bridge management networks. The result was implementation of cost-effective systems that not only provided whole life protection, but valuable data that allowed future planning of remedial measures to be made more effectively.
Both projects demonstrate how corrosion can affect both new and existing structures, showing how it can impact safety and the increase the cost of repairs. Mitigation is vital, before it can get too troublesome; The Rambler Channel Bridge is a busy shipping route, for example, so it was essential to implement a non-disruptive but effective control system.
For existing assets, it is important to recognise that they were built to comply with less stringent safety standards than we expect today, but this can be forgotten due to their fundamental role in society. Bringing those assets up to date is a growing priority, and controlling corrosion is at the heart of this. C-Probe demonstrates how this can be done through low carbon, non-invasive methods that not only retain vital embodied carbon and increase resilience, but also protect the heritage of the structure.