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All three concrete mixes were prepared with a 0.45 water/cement or water/(cement plus silica fume) weight ratio with mixes 2 and 3 having 10 and 20 per cent weight replacement of the cement by silica fume. A well rounded, predominantly quartz river gravel (-1/2 to +1/4 mesh) was used as the aggregate for all mixes in a 1:1 proportion by weight to the cement.
A Hobart paddle mixer was used to blend the components with the cement being added to the water, mixing to wet, and then adding the aggregate. When silica fume was added to the mix (mixes 2 and 3), the silica fume was added to the water and mixed, then the cement was added, and then finally the aggregate. Mixing proceeded for three minutes, was halted for three minutes while the bowl walls were scraped with a plastic spatula, and resumed with a second mixing for three minutes. The concrete was cast in 25 mm (one inch) steel molds and was vibrated on a shaker table for 10 seconds to aid in consolidation. All cubes were demolded after 24 hours and placed in saturated lime (CH) water and cured until sampling at 28 days.