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Concrete In Australia : September 2013
36 Concrete in Australia Vol 39 No 3 CONFERENCE TECHNICAL PAPER types of slag concrete were used in the construction of the retaining walls. It appears that the cores from the mid panel of downstream wall (taken in February 2010) comprised geopolymer concrete, whereas that from other panels and upstream walls consisted of either blended slag cement concrete or partially activated slag cement. e latter concretes had lower slag contents than geopolymer concrete. 1.3 Corrosion monitoring Information supplied by VicRoads showed that reference MnO2 electrodes were installed at the time of construction, as shown in Figure 6. e reference electrode monitoring boxes, which were installed separately for the downstream and upstream walls, contained three pairs of wires, labelled Top, Mid and Bottom to indicate the locations of the electrodes in the retaining wall. e wire to the reinforcing steel is white and that to the Mn/MnO2 reference electrode is blue. e half-cell potentials between reinforcing steel and reference electrode were measured at the different locations using a multimeter (internal impedance > 10 MΩ). 1.4 Concrete mix composition e appearance of the cores indicated that two types of concrete were present in cores from different areas. e exact concrete mix designs used in the retaining walls are not Figure 1. Location of cores on downstream retaining wall. Figure 2. Location of cores on upstream retaining wall. Core 2 Core 1 Core 3 Downstream wall monitoring box Core2259- 1 Core2259- 2 Upstream wall monitoring box Core 4 Core 5 Core 6 Core 2259-4 Core 2259-3 Figure 3. Locations of Cores 2259-3 and 2259-4 on the upstream wall. Note that Cores 4-6, drilled in 2010, were taken from the part of the wall facing left. Figure 4. View of drilled cores, exhibiting dark greenish colour due to high slag content. Cores on the left are from downstream wall and those on the right from upstream wall. Figure 5. View of Cores 2259-1 to 2259-4 (from left to right). Cores 2259-1 and 2259-2 are from the downstream wall; Cores 2259-3 and 2259-4 from upstream wall. available, but the concrete would have had to comply with the requirement of VicRoads Specification Section 610, which requires a concrete grade of VR400/40, i.e. 400 kg/m3 binder content and 40 MPa strength grade. e approximate mix ingredients are given in Table 3. 2.0 RESULTS AND DISCUSSION 2.1 Half-Cell Potentials of Reinforcing Steel Bars e type of reference electrode used was a manganese dioxide electrode in alkaline gel, which was installed adjacent to steel bars at nominated locations (Figure 6). Originally, calibration values were produced by the manufacture for the potential of each electrode, which was measured against saturated calomel electrode (SCE). e calibration data were used for converting the measured values to CSE potentials, so that the measured