ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC Lisbon Portugal 31 May - 1 June 2012 DURABLE STRUCTURES

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1 International Conference : from construction to rehabilitation CATHODIC PREVENTION OF REINFORCED CONCRETE STRUCTURE CAIS DO JARDIM DO TABACO - LISBON Henrique Alves, Zita Lourenço, António Martins, Cruz Ferreira Zetacorr, APL, Somague WHY DO WE NEED CATHODIC PROTECTION /PREVENTION?

2 International Conference : from construction to rehabilitation Cathodic Prevention is gaining acceptance in parts of the world where good quality concrete is available, but the importance of the structure, the difficulty of future maintenance or the harshness of the marine conditions leads to its adoption to minimize the total life cycle cost over the structures life. It has been used in: -bridges -wharfs and ports -seawater intake structures, caissons HOW CP WORKS CP is defined as the reduction or elimination of corrosion by making the potential of steel more negative, i.e. cathodic. This is achieved by passing a small dc current from an external anode trough the concrete to the rebar. Sacrificial anode system Impressed current system (ICCP) ICCP components: Cathode (reinforcement) Anode Power supply Sensors It is critical that all embedded components of the system provide long life, are easy to install and do not get damaged during construction: anode system, connections and cabling, reference electrodes/monitoring sensors.

3 International Conference : from construction to rehabilitation CAIS DO JARDIM DO TABACO 680 m long quay located between Doca da Marinha and Cais de Santa Apolónia New Lisbon cruise terminal. STRUCTURE The width of concrete deck varies along the quay. The structure consists of a reinforced concrete deck supported on concrete piles. Most concrete elements were pre-cast. CP was installed in the pile caps, beams and slabs.

4 International Conference : from construction to rehabilitation ANODE SYSTEM The most common anode systems used are based on Titanium, either mesh or ribbon type systems. For the ribbon anode, the type of ribbon used and the spacing is calculated based on: the required current density, life expectancy of anode and in order to obtain an adequately uniform polarization of the reinforcing steel. Can be designed for 100 years life Ribbons attached to the reinforcement before concreting ANODE INSTALLATION- Pile Cap

5 ICDS12 International Conference : from construction to rehabilitation DS ANODE INSTILLATION- PRECAsT BEAMS 12 LNEC Lisbon 31 May - 1June 2012 IC INSITU BEAM JUNCTION LNE C LNEC Lisbon 31 May - 1June 2012

6 International Conference : from construction to rehabilitation The Ti/MMO ribbon anodes, installed at approximately 400 mm centers Ribbons were attached to the reinforcement before concreting; Reference electrodes/sensors: In the pile cap- tidal zone- Ag/AgCl reference electrodes Beams- Mn/MnO2 Slabs- Mn/MnO2 and depolarization probes of Ti/MMO The electrodes were attached to the reinforcement cage at the designed locations before concrete placement. The cathodic connections were also installed before concrete placement

7 International Conference : from construction to rehabilitation ZONING The system was divided in independently controlled zones, considering the different structural elements and the different exposure conditions. The anode zones were divided in anode sub-zones, in order to allow for more control of the current to those areas if required. Each anode zone is powered by na independent output of the power supply. Manually controlled T/R, consisting of: -Power supplies, one output per zone -Output current and voltage meters -High input impedance voltmeters for potential measurements

8 International Conference : from construction to rehabilitation TESTING Electrical continuity testing of the reinforcing steel in each section. Electrical continuity of cathodic and testing connections, Electrical continuity of anodic connections in each zone. Reference electrodes testing. Short circuit testing between reinforcement and anode must be extensively performed before, during and after concrete pouring. This testing was continuously performed during concreting in the pre-cast yard and in situ. Total length of the Quay: 680 m Total concrete area with cathodic prevention: m2 Ribbon: 105 km Nº reference electrodes /sensors: 533 Nº zones - output of the T/R: 150

9 International Conference : from construction to rehabilitation MONITORING RESULTS Graph show the effect of the tide in the ON and OFF potential in the pile caps, beams and slabs RESULTS 1) i - Current density, ma/steel surface area 2) E Potential 3) ON potential 4) Instantaneous off potential

10 International Conference : from construction to rehabilitation CONCLUSIONS If well designed, installed and maintained the cathodic prevention systems can provide an economically viable solution to minimize the total life cycle cost of new structures in aggressive environments. The installation of these systems during the construction of the structures are much simpler and more economical than the retrofitting of CP to existing structures. The authors would like to thank the Port Administration, APL, for authorization to present this paper. Structural project: WW and STA CP project and supply: Zetacorr Contractor: Somague/SETH/OFM