Piezoresistivity in continuous carbon fiber cement-matrix composite

Piezoresistivity was observed in cement-matrix composites with 2.6-7.4 vol% unidirectional continuous carbon fibers. The direct-current electrical resistance in the fiber direction increased upon tensile loading in the same direction, such that the effect was mostly reversible when the stress was below that for the tensile modulus to decrease. The gage factor was up to 60. The resistance increase was due to fiber-matrix interface degradation, which was mostly reversible. Above the stress at which the modulus started to decrease, the resistance increased with stress/strain abruptly, due to fiber breakage. The tensile strength and modulus of the composites were 88% and 84%, respectively, of the calculated values based on the rule of mixtures.