Effect of moisture on piezoresistivity of carbon fiber-reinforced cement paste

Piezoresistivity, as exhibited by carbon fiber-reinforced cementbased material, allows a structural material to sense its strain or stress through electrical resistance measurement. This paper addresses the worst scenario associated with the effect of moisture on the piezoresistivity of carbon fiber-reinforced cement paste. This scenario is associated with both water saturation and a fiber content below the percolation threshold. For this scenario relative to the condition after drying at room temperature, the gauge factor (fractional change in resistance per unit strain) is decreased by at least 12% and the variability of the gauge factor with the strain amplitude and with the strain history is increased. These negative effects are attributed to the water at the fiber-matrix interface. The water interferes with the electronic conduction across the interface. Nevertheless, the piezoresistivity remains strong, the signal-to-noise ratio of the resistance remains high, and the relationship between resistivity and strain remains quite linear.