Measurement of crack length sensitivity and strain gage factor of carbon fiber reinforced cement matrix composites

•Novel measurement methods and results for carbon fiber cement based composites.•Novel measurement of strain–electrical resistance in split tensile test.•Novel measurement of crack length–electrical resistance in bending test.•Mechanisms enlightened for strain sensitivity–fiber volume %.•Mechanisms enlightened for crack sensitivity–fiber volume %.

Five different carbon fiber reinforced cement matrix composites with fiber length of 13 mm were designed having different fiber volume fractions. From each mix, six samples of 5 cm cubes and three 4 × 4 × 16 cm prism samples were cast. Compression, split tensile and notched bending tests were applied to three samples from each mix with simultaneous electrical resistance measurements. Strong correlations between strain and electrical resistance change were reported. At percolation threshold, the strain caused shift of the system from post percolation to pre-percolation, changing the electrical resistance dramatically; causing highest gage factor. The microstructure controlled mechanisms were enlightened. The split tensile test and notched bending test with simultaneous electrical resistance, strain and crack length measurements have been applied as novel methods.

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