POSITIVE AND NEGATIVE PRESSURE SENSITIVITIES OF CARBON FIBER-REINFORCEDCEMENT-MATRIX COMPOSITES AND THEIR MECHANISM

The pressure sensitive behaviors of carbon fiber-reinforced cement-mat rix composites with differentmoisture content s were studied. The result s show that the relative change in resistanceΔR/ R0 varies with the moisture content of the composites. With higher moisture content , the relative change in resistanceΔR/ R0 increases withthe increase of compressive st ress , and decreases during unloading , demonst rating the positive pressure sensitivity.However , when the moisture content is reduced af ter specimens’being oven-dried , the relative change in resistanceΔR/ R0 decreases monotonically with the increase of compressive st ress , and increases monotonically during unloading , showing the negative pressure sensitivity. The mechanism for these phenomena is discussed.