Repair and corrosion management of reinforced concrete structures

The durability of concrete structures is affected by a number of factors such as environmental exposure, electrochemical reactions, mechanical loading, impact damage and others. Of all of these, corrosion of the reinforcement is probably the main cause for the deterioration of steel reinforced concrete (RC) structures. Corrosion management is becoming increasingly necessary as a result of the growing number of ageing infrastructure assets (e.g. bridges, tunnels etc.) and the increased requirement for unplanned maintenance in order to keep these structures operational throughout their design life (and commonly, beyond). The main RC repair, refurbishment and rehabilitation approaches generally employed can be broadly categorised under a) conventional, b) surface treatments, c) electrochemical treatments and d) design solutions. The overarching aim of this research was to identify the key corrosion management techniques and undertake empirical investigations focused on full-scale RC structures to investigate their long-term performance. To achieve this, individual research packages were identified from the above broad five approaches for repair, replacement and rehabilitation. These were 1) Patch repairs and incipient anodes, 2) Impressed Current Cathodic Protection, 3) Galvanic Cathodic Protection and 4) Hydrophobic treatments. The selection of the above research packages was based on past and present use by the construction industry to repair, refurbish and rehabilitate RC structures. Their contributions may be broadly categorised as i) Investigations on how specific treatments and materials perform, ii) Investigations on the effectiveness of existing methods of measurements and developing alternatives, iii) Changes to the existing theory of corrosion initiation and arrest and iv) Changes to management framework strategies. The key findings from each research package can be summarised as follows: Macrocell activity appears to be a consequence rather than a cause of incipient anode formation in repaired concrete structures, as has previously been presented; ICCP has persistent protective effects even after interruption of the protective current; Discrete galvanic anodes installed in the parent concrete surrounding the patch repair are a feasible alternative to galvanic anodes embedded within the patch repairs of RC structures; Silanes may have a residual hydrophobic effect even after 20 years of service

Electrochemical treatments of corroded reinforcement in concrete

Electrochemical treatment methods have been used to arrest corrosion and protect the serviceable life of a structure. This paper analyses the corrosion initiation mechanisms, the chemical reactions taking place at the steel interface and the transportation process. The available options are briefly discussed and their advantages and disadvantages examined. The conclusions drawn, focus on the current practice and how the discussed electrochemical treatments can be used to optimize performance

Design and specification so that 21st century reinforced concrete structures won't corrode so soon

Design and specification so that 21st century reinforced concrete structures won't corrode so soo

The world's first hybrid corrosion protection systems for prestressed concrete bridges

The Kyle of Tongue Bridge in Sutherland, Northern Scotland opened in 1970, has an overall span of 184m consisting of 18 approximately equal spans and carries a single lane dual carriageway. Prestressed concrete beams form the deck, with reinforced concrete pilecaps supported on steel piles. The bridge was patch repaired in 1989 due to chloride induced corrosion. However, inspections from 1999 onwards reported on-going corrosion and structural deterioration. A refurbishment contract was let in 2011 to extend the service life of the structure for a 30 year period by providing corrosion arrest and prevention. The Tiwai Point Bridge in Invercargill, Southland, New Zealand opened in 1969, has an overall span of 486m consisting of 27 approximately equal spans and carries a single lane dual carriageway. It is comprised of prestressed and post-tensioned concrete beams forming the deck, with reinforced concrete pilecaps supported on prestressed concrete piles. The superstructure was replaced in 2009-2010 due to severe corrosion to the reinforcement. Hybrid cathodic protection systems were developed and implemented for both structures. For Kyle of Tongue, hybrid cathodic protection was used to arrest existing corrosion activity to the prestressed concrete beams of the superstructure and extend their service life for a 30 year period by providing corrosion arrest and prevention. For Tiwai Point Bridge, a trial hybrid cathodic protection system was developed to provide corrosion prevention to the prestressed concrete piles within the tidal zone with a targeted service life of 50 years. Hybrid electrochemical treatment provides an attractive alternative to other corrosion protection treatments as it combines the power to arrest the corrosion activity with the simplicity and low maintenance requirements of galvanic technologies. It offers a temporary energising phase to arrest corrosion followed by a permanent galvanic mode phase which is particularly beneficial for prestressed concrete structures in order to reduce hydrogen embrittlement risk. This paper provides a summary of the performance of such hybrid electrochemical systems and how they can be advantageously utilised on prestressed concrete structures to extend their service life

Underslung cable structures – a feasible alternative?

This paper examines the behaviour and feasibility of under-slung cable structures. Consideration is given to their structural behaviour, their dynamics, their cost-effectiveness and the practicality of adopting such structures. The parameters that govern the behaviour and response of these structures are investigated and structural arrangements and details are proposed, which it is suggested would make the construction of such structures feasible. The aim of the paper is to generate discussion of this novel form of construction and to identify opportunities for the exploitation and development of such a concept. This paper discusses how underslung structures, when combined with a radical trussed stiffening girder, can provide an innovative but more sympathetic structure, which is stiff, stable and economically viable for both medium and long-span structures. It is shown that when there is a need to minimise the number or limit the location of the foundations required, such structures provide a means of adopting relatively large spans, while restricting the height of the cable supports and hence minimising the impact of the structure. The paper concludes by summarising the benefits that can be obtained from such structures both during construction and in use, and seeks to identify the opportunities and challenges that must still be met to facilitate the exploitation and development of such a concept

Towards rendering steel reinforced concrete immune to corrosion

This work reviews developments in the understanding of chloride induced corrosion of steel in concrete from both a kinetic and thermodynamic perspective. Corrosion damage is at least in part attributed to the production of acid at sites of corrosion initiation. Solid phase inhibitors provide a reservoir of hydroxyl ions to inhibit damage. Pit re-alkalisation is identified as an important protective effect in electrochemical treatments used to arrest corrosion. A process like pit re-alkalisation is achieved more easily by impressing current off sacrificial anodes using a power supply and may then be followed by low maintenance galvanic protection to prevent local acidification. Methods of monitoring the steel corrosion rate in electrochemically treated concrete have been developed and used to assess corrosion risk. Some of these concepts have been adopted in the recent international standard on cathodic protection, ISO 12696:2012. This work also considers some of the amendments to this standard

Site performance of galvanic anodes in concrete repairs

Galvanic anodes can be used to limit the extent of concrete replacement and extend the service life of patch repairs to reinforced concrete (RC) structures. They respond to changes in environmental conditions and this attribute has been employed to extend their use. Traditionally, galvanic anodes are installed within the repair area itself. Although simple to install, this has certain limitations however, due primarily to the resistivity of the repair material. A recent alternative has been to install galvanic anodes in pre-drilled cavities in the parent concrete around the perimeter of the patch repair. This paper reviews and compares the performance of discrete galvanic anodes installed both within the repair area and parent concrete in full-scale RC structures. Results indicate that galvanic anodes installed within the parent concrete had a more profound effect on the polarisation of the steel around the perimeter of the patch repair. This provides the empirical basis for alternative designs incorporating galvanic anodes that will enable increased corrosion protection to the steel reinforcement around the patch repair, which is generally considered to be at the highest risk

Long-term performance of hybrid anodes for cathodic protection of reinforced concrete

© 2018 The Authors, published by EDP Sciences. The long-term performance of hybrid anode corrosion protection systems (UK invention disclosed in Patent GB2426008B) was investigated on six bridge structures as part of a holistic approach to corrosion risk management, using the performance criteria in ISO BS EN 12696:2016. The aim of the study was to review the effectiveness of current design approaches to meet the residual service life when the anodes are operating in the galvanic phase. This was achieved by analysing data on the general condition of the structures, the ongoing performance of the installed hybrid anodes, and assessing the subsequent corrosion risk. It was found that the six structures were generally in good condition, 1 to 8 years after refurbishment works, with low associated corrosion risk in areas protected by the hybrid anode systems. This is a positive finding for the wider implementation of hybrid anode systems as an alternative corrosion management technique. The reinforcement in the protected areas remained predominately in a passive condition, with calculated corrosion rates below the ISO 12696:2016 recommended threshold of 2mA/m

Monitoring the passivity of steel subject to galvanic protection

This work investigates the assessment of the passivity of steel in concrete subject to galvanic protection. Under atmospherically exposed conditions the kinetics of the cathodic reaction often exhibit activation controlled behaviour. It is shown that in these conditions the corrosion rates estimated from a large negative potential shift are very similar to those determined using the more widely accepted polarisation resistance method. The results are considered in the light of the potential decay cathodic protection criterion, and show how criteria based on potential shift may be improved to monitor steel passivity induced in a galvanic cathodic protection system. This provides the basis for an improved reinforced concrete acceptance criterion that is focussed on the condition of the structure and is included within the ISO standard cathodic protection when applied to galvanic systems

Protection of steel in concrete using galvanic and hybrid electrochemical treatments

In this study, data from galvanic and hybrid electrochemical treatments applied to structures is analysed. It is shown that the protection of steel in concrete using galvanic anodes finds theoretical support from a basis of improving the environment or maintaining a benign environment at the steel. Protection current output responds to the aggressive nature of the environment and, as a result, galvanic anodes have substantially longer lives than originally predicted. Monitoring is preferably focused on monitoring the effect of the protection on the condition of the structure and may be achieved by monitoring either steel corrosion rate and/or steel corrosion potential. Monitoring is preferably combined with a risk management option such as a facility to apply a temporary impressed current treatment to arrest active corrosion if a risk is identified. An allowance for new galvanic protection criteria has been made in the latest European standard on Cathodic Protection of Steel in Concrete