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Abstract:
This paper presents concrete mix design as well as the results of testing of concrete during production of precast foundations for wind power turbines which are to be located in the Baltic Sea. From 2002 to 2010 approximately 120 000 m3of concrete was cast to form 210 foundation blocks. Concrete production and casting was performed in Poland and the manufactured concrete blocks were transported to wind farms in Denmarkand Sweden. Massive reinforced concrete blocks were designed to be laid at the sea bottom about 7.5-12.5 m below the water level. For concrete mix design the following exposition classes were assumed: XC4, XF4, XS3 and XM3 according to EN 206-1. Exposure to exceptionally severe environmental conditions was assumed: chemical aggression and mechanical wear by seawater, freezing and thawing in saltwater. Because of thelarge size of blocks the danger of thermally induced cracking of concrete was carefully considered and computer simulation of stress build-up was used to select the optimal solution. Concrete mix C45/55 was designed using cement CEM III/A 32.5N HSR NA (containing about 60%GGBFS), silica fume, crushed aggregates up to 32 mm and water-reducing and air-entraining additives. High durability of concrete in the aggressive environment was predicted on the basis of microscopic testing of cement hydration products and quantitative evaluation of microstructure. The challenging issue was to maintain a stable air void system in concrete during the whole production process: air void characteristic was regularly monitored in fresh concrete using AVA and in hardened concrete using computer image analysis.Heat of hydration data and monitoring of temperature during concrete hardening provided necessary proof of a non-cracked structure

Keywords:
durability of concrete, air void system in concrete, sustainable production, heat of hydration