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Concrete In Australia : June 2014
Concrete in Australia Vol 40 No 2 27 and 2.5m high. One side of the trial was stepped to simulate the downstream steps of the dam, and a transverse joint waterstop was installed on the opposite (upstream) side. The RCC mix used in the 400mm layer trial embankment was the same as that used in the majority of the 300mm layer trial and eventually the dam itself. While different compaction plant and patterns were investigated during the construction of both trials, generally the 13t twin drum roller was used with one static pass and three high frequency, low amplitude passes, on both the 300mm and 400mm layer trials. As with the first trial embankment, the second trial was cored with a 150mm single tube core barrel. Coring was undertaken to enable the RCC and GERCC within the trial to be visually assessed. Furthermore cores samples were located so that direct tensile testing could be undertaken on samples from lift joints. A placement methodology was developed; this reliably achieved the desired compaction for the RCC and GERCC facing at greater depth to expedite the placement process. The results of trials allowed a considerable proportion of the dam to be constructed using 400mm layers, until geometric constraints necessitated a return to 300mm layers for the upper portion. Pioneering precast units onsite The dam included inclined galleries that extend through approximately 60m vertical height up each abutment. To form the gallery penetrations in each RCC layer without impacting the RCC placement process, precast stairs and lintels were manufactured on site. These precast units could be stacked in place up to 1.2m high, allowing the inclined gallery construction to stay in front of the RCC placement instead of being a limitation to RCC production. After consultation with international contractors and RCC dam experts, there is no known instance of this process having been used on any previous RCC dam in the world. Use of aggregates from geologically altered source While most of the innovations and process improvements developed at the Cotter Dam project relate specifically to the construction of RCC dams, there is some relevance to the broader industry regarding improvement of standards in concrete construction. There is very little literature available regarding dimensionally unstable aggregates. Historically, questionable aggregate sources would be discarded in preference to reliable sources where aggregates could be produced to commonly accepted standards. However, the increasing demand on the industry to demonstrate sound, sustainable, cost efficient use of materials warrants greater investigation of aggregate sources, particularly for remote projects where alternative aggregate sources may be considerably limited and/or cost prohibitive. The experience from Cotter Dam, and the research produced, has been presented to the industry via the RCC 2012 Conference to enable future construction projects to potentially benefit from this research and learnings. While the investigations involved several recognised test procedures, some new test methods were also developed which provide a further potential benefit to industry for similar future testing campaigns. RCC batching production control While continuous mixers are often used for RCC dam construction, a batch plant was used at Cotter Dam to ensure The dam cross section comprises a vertical upstream face and stepped downstream face with a nominal slope of 0.75H:1V. 22-29 - cover story.indd 27 22-29 - cover story.indd 27 22/05/14 11:46 AM 22/05/14 11:46 AM