Latex-modified cement mortar reinforced by short carbon fibres

The addition to cement mortar of 0.37 volume% (vol%) of short, pitch-based carbon fibres, together with latex (styrene-butadiene) and antifoam, increased the flexural strength by 54% and the compressive strength by 30% at 28 days of curing; relative to mortar containing latex and antifoam, the fibres increased the flexural strength by 33%, had little effect on the compressive strength and increased the price by 17%. In addition, the fibres increased the flexural toughness and decreased the electrical resistivity. Fibre contents > 1.1 vol% resulted in substantial degradation of the compressive strength and slight degradation of the flexural strength at 7 days of curing, relative to the strengths at a fibre content of 0.37 vol%. The optimum latex/cement ratio was 0.2. The latex served to disperse the fibres and increase the bonding between the fibres and the matrix. Partial replacement of cement by silica fume in mortar containing latex, antifoam and fibres did not increase the flexural strength.