Abstract
This paper gives insight in the research and investigations which were undertaken on a post tensioned light-weight concrete box girder bridge in the Netherlands. This project started in the first half of 2013 and measurements are still executed regularly. Due to long-term leakage of a longitudinal joint between 2 parts of the bridge, chlorides had penetrated into the concrete up to the level of the reinforcement and beyond, causing severe corrosion of the steel, spalling of the concrete cover and eventually causing danger for the shipping underneath the bridge due to falling lumps of concrete. To solve this problem, Galvanic Cathodic Protection (GCP) was applied in 2 stages. Firstly, in 2013, zinc based anode strips were applied on the soffit of 2 post tensioned lightweight bridge segments for the purpose of testing and monitoring. After obtaining good results from the test, in 2014/2015 the remaining 29 bridge segments were repaired and protected with the same GCP system as well. This paper reviews subsequent potential decay and current densities measurements, which have provided valuable information on GCP performance and throwing power. The results of anode performance at different locations and depths are reviewed. Concrete resistivity has shown a major influence on the effectiveness of the installed GCP system.
Highlights
1.1 The bridge The bridge in question is the Neerbossche Bridge which spans a canal at Nijmegen, The Netherlands (Figure 1). 1.2 The projectThe damage in the bridge was extensively investigated and reported [1] in a preliminary phase and it was concluded that the damage was limited to the concrete surface at the soffit of the northern cantilever of the span of the southern bridge
In view of the good results that were obtained in this test, the suitability of this Galvanic Cathodic Protection (GCP) system was proven, the full scale project on the remaining 29 bridge segments was executed in the winter of 2014/2015
Since 2013 potential decay values, current outputs and resistances were measured during a period of almost 6 years on 2 selected bridge segments in which a large amount of RE’s were installed and on the surface narrow zinc strip anodes
Summary
The damage in the bridge was extensively investigated and reported [1] in a preliminary phase and it was concluded that the damage was limited to the concrete surface at the soffit of the northern cantilever of the span of the southern bridge (see Figure 2). The anode material used for the protection of the steel reinforcement was a surface mounted zinc anode. A large number of reference electrodes (titanium decay probes, referred to as RE’s) were embedded in the concrete of these 2 segments in order to monitor the effectiveness of the CP system, within the protected area and outside the protected area. With these ‘remote’ RE’s the so-called throwing power of this CP system could be established. In view of the good results that were obtained in this test, the suitability of this GCP system was proven, the full scale project on the remaining 29 bridge segments was executed in the winter of 2014/2015
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