High Volume Fly Ash RCC for Dams/Mixture Optimization and Mechanical Properties

A series of roller-compacted concrete mixtures were developed for the Norwegian Skjerka hydropower project. The mixture optimization was based on the medium paste concept of the international Committee on Large Dams (ICOLD) using crushed aggregate from the dam site. The mixture optimization consists of a two-step procedure minimizing the paste content, keeping the compacted density about 97.5% of the theoretical air-free density, and giving an optimal loaded Vebe time of 10 - 20 seconds. Nine mixtures were produced using low calcium fly ash and portland cement with various fly ash-cement proportions. The water-binder ratio was kept constant at 0.53 according to the Norwegian code for mass concrete for dams. The laboratory test results showed that 8 of 9 binder combinations produced RCC within the design criteria. The compressive strength development of the water-cured specimens was impressive despite the rather low cement contents, giving 1 year strengths of 2 times the 28-day strengths. The use of high-volume fly ash concrete for RCC dams is one example of concrete in harmony with lower environmental impact and less use of resources.