Concrete reinforced with up to 0.2 vol% of short carbon fibres

The use of short pitch-based carbon fibres (0.5% by weight of cement, 0.189 volume % (vol%) of concrete), together with a dispersant, chemical agents and silica fume, in concrete with fine and coarse aggregates resulted in a flexural strength increase of 85%, a flexural toughness increase of 205%, a compressive strength increase of 22%, and a material price increase of 39%. The slump was 102 mm (4 in) at the optimum water/cement ratio of 0.50. The air content was 6%, so the freeze-thaw durability was increased, even in the absence of an air entrainer. The aggregate size had little effect on the above properties. The minimum carbon fibre content for flexural strength increase was 0.1 vol%, although the flexural toughness was still increased below this fibre volume fraction. The optimum fibre length was such that the mean fibre length decreased from 12 mm before mixing to 7 mm after mixing, which used a Hobart mixer. The drying shrinkage was decreased by up to 90%. The electrical resistivity was decreased by up to 83%.