Study On Long-term Mechanical Properties And Pressure-sensitivity Of Concrete Containing Nano-sized Carbon Black Or Carbon Fibers

The long-term mechanical and pressure sensitive behavior of concrete containing nano-sized carbon black or carbon fibers are studied in this experimental research. Results show that when the addition of nano-sized carbon black is appropriate, the compressive strength of concrete is improved when the age of the concrete is 28 days. However, when the age is 90 days or 180 days, the compressive strength of nano-sized carbon black concrete is not as high as normal concrete. When an appropriate amount of carbon fibers are put into normal concrete, the flexural strength at the age of 28 days, 90 days and 180 days are all improved. By using the method of nitrogen- absorption, the porosity analysis reveals that nano-sized carbon black can act as a the nano-filler of pores and voids in concrete in order to improve its mechanical properties.Meanwhile, nano-sized carbon black/carbon fiber concretes have high pressure-sensing ability. Results show that when the addition of nano-sized carbon black or carbon fibers is 0.5% and 0.75%, the sensitivity of the concretes are higher than normal ones. Results also show that the relative change in resistance ( ( R-R₀ )/R₀) is influenced by the way of electrical conduction, the moisture content of concrete and the age of concrete.The electrical conduction modes are proposed in the paper in order to explain the mechanism of pressure sensitivity.