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Concrete In Australia : September 2013
Concrete in Australia Vol 39 No 3 35 purposes entails stringent requirements which need to be met. Duxson, et al. (2007a, b) and van Deventer et al. (2012) have highlighted barriers to commercial application of geopolymer concrete as a construction material. is includes lack of long- term performance data and need for willingness of relevant agencies to allow the material to be used in field structures. Vic Roads recently allowed geopolymer materials to be used in non-structural components of bridge structures as detailed by Andrews-Phaedonos (2011, 2012). Corrosion monitoring reference electrodes were installed to check the corrosion of the reinforcing steel in geopolymer concrete. e author also discussed current barriers in the application of geopolymer concrete to structural elements of VicRoads bridges. For this to eventuate, the geopolymer concrete must meet all the requirements of VicRoads Specification Section 610 for Structural Concrete. One example of field application of geopolymer concrete is its use in landscaping retaining walls at the west abutment of the Swan Street Bridge, Melbourne in 2009, as described by Sklepic (2011). Shortly after the construction of the reinforced geopolymer concrete retaining walls, VicRoads commissioned ARRB Group to undertake in-situ and laboratory diagnostic investigations on the condition of the retaining walls at this bridge. e results of this work (Shayan and Xu, 2010, 2012) have shown that the concrete in the retaining walls contained either a blended slag cement or a slag-based geopolymer binder. e latter had a very low chloride diffusion coefficient, but the volume of permeable voids (VPV) was larger than that required by VicRoads Specification Section 610. is paper presents the results of the investigation conducted and discusses the performance of the materials in the retaining walls. 1.1 Scope of the investigation e investigation included in-situ corrosion monitoring of reinforcement steel in the retaining walls, using reference electrodes which were embedded in the concrete at the time of construction of the walls, as well as extraction of concrete cores for strength testing, micro-structural examination of concrete, using scanning electron microscopy (SEM) combined with energy-dispersive X-ray (EDX) analysis, petrographic examination, determination of volume of permeable voids (VPV), soluble alkali content, chloride ingress in laboratory testing, and chloride diffusion coefficient. e monitoring of half-cell potentials included several measurements conducted since construction of the retaining walls late in 2009. 1.2 Site investigation and concrete core sampling e west abutment of the Swan Street Bridge is located at Alexandra Avenue at the Botanical Gardens side of the Yarra River in Melbourne, and consists of downstream and upstream retaining walls. Early in 2010, three cores were drilled from each of the downstream and upstream retaining walls, including one 94 mm diameter core and five 76 mm diameter cores. Table 1 presents details of the six cores and their allocation to various tests. e locations of the core holes, after being filled and repainted, and the locations of reference electrode monitoring boxes are shown in Figure 1 and Figure 2. In 2011 four additional cores were taken for further examinations, two from each of the downstream and upstream retaining walls. Table 2 lists the locations of the four cores and allocated tests. e locations of Cores 2259-1 and 2259-2 are also presented in Figure 1, which shows that Core 2259-2 came from the same panel as Cores 1-3, which were taken in 2010. e locations of Cores 2259-3 and 2259-4 are presented in Figure 3. e appearance of the cores taken in 2010 and 2011 are shown in Figures 4 and 5, respectively. e cores from 2010 and Core 2259-2 exhibited typical dark greenish colour in the interior indicating that the binder was rich in blast furnace slag, which in turn indicted that the geopolymer concrete was based on blast furnace slag as the binder. e newly exposed concrete exhibited a light colour in the exterior zone of the core, due to oxidation in air. e cores obtained in this investigation showed that two Table 2. List of the four cores and allocated tests. Table 1. Details of drilled cores. Wall Core # Core ID Diameter (mm) Length (mm) Tests Downstream Core 1 C10/2036-1 94.2 154-162 ASTM C1202, NT Build443 Core 2 C10/2036-2 76.5 160-165 AVPV, petrography Core 3 C10/2036-3 76.6 150-160 SEM/EDX, Compressive strength Upstream Core 4 C10/2036-4 76.6 151-155 SEM/EDX, Compressive strength Core 5 C10/2036-5 76.6 155-156 AVPV, petrography Core 6 C10/2036-6 76.6 154-156 Compressive strength Core ID Wall location Tests C11/2259-1 Downstream Density, VPV, SEM C11/2259-2 Downstream Density, VPV, SEM, Soluble alkali C11/2259-3 Upstream Density, VPV, SEM C11/2259-4 Upstream Density, VPV, SEM, Soluble alkali