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Concrete In Australia : September 2013
46 Concrete in Australia Vol 39 No 3 CONFERENCE TECHNICAL PAPER Bridge as part of major rehabilitation works undertaken at these bridges in 2010 and 2011 respectively. ese bridges are located in the inner metropolitan area and were both suffering from corrosion induced deterioration due to carbonation effects of the low-quality concrete and further exacerbated by moisture ingress from the deck above (7, 8). A galvanic anode cathodic protection (CP) system was installed in the piers of Queen Street Bridge in 2011 as part of major concrete jacketing of the piers to mitigate the chloride induced corrosion of the steel reinforcement. e new galvanic anodes were connected onto the steel reinforcement and encased with self compacting concrete (SCC) to form the new reinforced concrete jacketing for the deteriorated concrete piers. e effectiveness of the galvanic anode CP system has been monitored by testing the potentials of the steel relative to reference electrodes embedded in Pier 1 of the bridge (9). In 2009 a number of half-cell reference electrodes were also installed adjacent to the steel reinforcement in two landscape retaining walls at a bridge over the Yarra River to monitor the ability of geopolymer concrete to provide long-term protection for the steel reinforcement (10, 11). It is important that seasonal temperature variations are taken into account and allowed for when monitoring and assessing corrosion monitoring sensors, when cast in, to monitor the corrosion state of the steel in concrete structures or the performance of concrete repair works. Temperature variations may result in seasonal fluctuations of corrosion rates and electrode potentials of the steel reinforcement. 2.0 MONITORING OF PATCH REPAIRS AND COATING SYSTEMS AT SAWTELLS INLET BRIDGE -- MARINE EXPOSURE Sawtells Inlet Bridge at Tooradin on the South Gippsland Highway was constructed in 1968 and underwent major remediation work in 1991 and 1992 due to chloride induced corrosion related deterioration of the reinforced concrete elements (1, 2, 3). e repairs to the columns and crossheads included patch repairs (Figure 1) and the application of a polymer modified cementitious coating to Pier 1 (on the Melbourne side), and a three part epoxy coating to Pier 2 (on the Tooradin side) in both atmospheric and tidal/splash zone microclimates. e repair work also included the installation of a permanent corrosion monitoring system comprising eight permanently embedded Ag/AgCl reference electrodes (Figure 1) and thirty sets of four stainless steel pins embedded in the concrete surface to allow measurement of the concrete resistivity. is was to enable the ongoing monitoring of the effectiveness of the various concrete repair methods and protective coatings in limiting chloride induced corrosion of concrete coastal bridges. An area of 0.4 m × 0.9 m was left untreated as a control area immediately below the crosshead on each downstream column for subsequent comparison. A dual silane impregnation plus acrylic anti-carbonation coating system was applied to the superstructure elements. ree reference electrodes were embedded within the major patch repairs on each pier with similar locations on both piers (Figure 1). Monitoring of all electrodes was done initially on a monthly basis and progressively at regular time intervals (Figure 2) at junction boxes which are attached to the side of crossheads to eliminate the possibility of vandalism. A high impedance voltmeter has been used for the monitoring. All electropotential measurements were considered relative to the original readings of the reference electrodes. One reference electrode was installed close to the steel reinforcement in the major patch repairs of the Repair patch Repair patch Control area Control area Dandenong Pier Downstram End (Not to scale) Tooradin Pier Downstram End (Not to scale) 900mm D2 600mm T2 T3 D1 D3 Figure 1. Location of Ag/AgCl reference electrodes and patch repairs (1). Figure 2. Half-cell potential of the internal sensors. "D" = Melbourne Pier (Pier 1); "T"= Tooradin Pier (Pier 2). -600 -480 -360 -240 -120 0 120 Jul-91 Nov-92 Mar-94 Aug-95 Dec-96 May-98 Sep-99 Jan-01 Jun-02 Oct-03 D1 D2 D3 T1 T2 T3 Half-cell Potential (mV, Ag/AgCl)