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Final Report Summary - DOSECOPS (Development of sustainable electrochemical corrosion protection systems for reinforced concrete structures)

Reinforced concrete (RC) has formed a major part of the infrastructure, particularly in developed countries. Structures made from RC can be subjected to a number of deterioration processes, the most important of which are associated with corrosion of embedded steel, which can dangerously affect the service life of the structures. Two major causes that are connected to corrosion of reinforcing steel in concrete structures are carbonation and chloride attack. Carbonation is the reaction between atmospheric CO2 and alkaline components of concrete, producing a carbonated surface layer in which the pore solution pH value is depressed to near-neutral levels. A secondary effect of carbonation, also significant in terms of its influence on corrosion, is that it can cause the release of bound chlorides into the pore solution phase of concrete that contains a modest level of chloride salts as a contaminant, thus exacerbating the corrosive nature of the electrolyte. In addition, carbonation can also influence the diffusion of chloride ions in concrete as it can alter the physical and chemical characteristics of pore structure and thus the transport properties of concrete. Chloride attack is mostly found in highways and marine or coastal structures, in which chloride ions, originating from deicing salts or seawater, are the primary cause of reinforcing steel corrosion. The chlorides that are transported through the concrete pore network and micro-cracks not only can change the pH value of concrete pore solution but also depassivate the oxide film covering the reinforcing steel and accelerate the reaction of corrosion. The worst situation is when a concrete structure is subjected to both carbonation and chloride attack.

This PIRSES project is to bring together an international team of researchers, with a wide variety of skills in electrochemistry, materials science, civil and structure engineering, nanotechnology, electromechanical engineering, chemical engineering, and computer modelling, to develop new electrochemical treatment methods for both new and old reinforced concrete structures to minimise both repairing and monitoring costs, and improve the structures’ long-term safety. The scientific objectives of the project are:

• To investigate the ingress behaviour of nanoparticles in concrete materials and the mechanism that they react with cement paste to produce a cementing reaction in the pore space to form a new composite.
• To investigate the influence of the magnitude and duration of the externally applied electric field and the size and concentration of nanoparticles in the external electrolyte solution on the improvement of concrete mechanical properties, pH values and other ionic concentrations, as functions of position within the treated concrete affected by carbonation using experimental methods.
• To investigate the influence of the magnitude and duration of the externally applied electric field and the size and concentration of nanoparticles in the external electrolyte solution on the improvement of concrete mechanical properties, pH values, chloride and other ionic concentrations, as functions of position within the treated concrete affected by chloride attack using experimental methods.
• To develop performance-based novel, smart cathodic prevention systems for new marine RC structures using modern solar power equipment, in which the power source of the cathodic prevention system will be supplied by solar power and the system will be operated and controlled by the system itself.
• To develop finite element analysis models to simulate the transport of various ionic and molecular species in the pore electrolyte of concrete under the influence of electrochemical treatment with internal reinforcing steel cathodes of varied configurations and external surface anodes placed in electrolytes containing positively charged nanoparticles, and apply the model to simulate the electrochemical chloride removal, electrochemical realkalization, and electrochemical nanoparticle injection processes for carbonated concrete, chloride contaminated concrete and the cathodic prevention systems to examine the effectiveness of the processes.
• To evaluate the effectiveness of the proposed electrochemical processing methods in the laboratory and field with the goal of making them commercially viable and to provide corresponding user guidelines.

During the period of the project the consortium has made 156 secondment months of researcher exchange, in which 69.59 secondment months are the EU researchers to TC partners and 86.41 secondment months are the TC researchers to EU partners. The project involves 52 researchers (32 ESR and 20 ER), in which 23 researchers are from TC partners and 29 researchers are from EU partners. Through the collaborated research work between individual partners, the consortium has produced a total of 67 technical papers (45 journal papers and 22 conference papers). During the period of the project the consortium has organised 10 workshops, nine of which were original planned in the related work packages, one of which was a supplementary. The outcomes of the research have made a great impact on our understanding on how the electrochemical process can improve the concrete performance and properties, particularly the behaviour of cement and concrete materials at a nano-scale level. The research provides vital information on how to repair the deteriorated concrete more effectively and how to engineer cement on a nano-scale to tailor the properties of concrete. In addition to the joint research activities taking place in each individual partner, the project as a whole has provided young researchers, who are involved directly or indirectly in the project, various intensive training-through-research programmes and complementary skills training, which has greatly improved their career perspectives.

Effective maintenance of buildings and structures made from concrete materials is critical and, in Europe, it is estimated that over half of the annual construction budget is currently spent on the rehabilitation and renovation of existing structures. This figure is expected to increase as the infrastructure is getting older. The proposed project has made significant contribution to our society by developing innovative, sustainable and robust repairing methods which use modern electrochemical methods and nanotechnology and not only can improve the durability of the treated concrete but also increase the bond and tensile strength of the material while reducing the shrinkage and cracking tendency. This makes concrete repair easy, fast, reliable and last longer. The project has a direct benefit to public since a structure requiring less repairing in its service life implies that there is less disruption to the public. The findings of this project not only attract a wide range of interests in the scientific arena, both in the public and private sector, but also bring about economic advantages for both Europe and China since most of the existing RC building stock in Europe were constructed before 1970, with current difficult decisions to be made as to whether refurbishment can be justified as an alternative to replacement. While in China a large number of new RC structures were built in the last three decades, some of which have shown some corrosion problems and need to have remediation. This requires careful estimation of the extensions of working lives that can be brought about by whatever remedial measures are chosen. The project also demonstrated how urgent the existing design codes need be changed in order to follow the new requirement for developing sustainable infrastructures to meet the challenge of climate change.

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UNIVERSITY OF PLYMOUTH
United Kingdom
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