Piezoresistivity Of Carbon Nanotubes-cement Composite

The structure function, safety and durability of ordinary portland cement concrete structures can not be guaranteed due to external natural environment and vehicle load and other factors, leading to a decline of the service life of concrete structures. In order to carry out a better structural damage detection, to make judgment of the interior damage of cement-based materials and timely diagnosis, to reduce and avoid catastrophic damage and significant casualties caused by major structural economic losses, and to improve the road service period, researchers have been trying to study how to recede the structural failure caused by cement materials by adding ceitain materials. In recent decades, to add some micron or even nanoscale conductive materials in the cement has attracted wide attention. Since carbon nanotubes were discovered in1991, it has been widely used in various fields of concern because of its variety of excellent physical and mechanical properties, and it is a new domestic smart material in the recent years. To add this kind of smart materials into cement-based materials and a variety of cement-based concrete structures in the rapid development is also a trend. In this paper, the carbon nanotubes materials with excellent mechanical properties and good electrical conductivity were added into the ordinary cement matrix, a new kind of cement-based composite materials was prepare by indoor tests, and the mechanical and electrical-sensitivity and other basic properties were studied.Since the existence of a strong carbon intermolecular forces within nanotube itself, the carbon nanotubes are easily intertwined and reunion, leading to a poor dispersion of carbon nanotubes in the cement matrix, so the dispersion of carbon nanotubes is need to study firstly. This paper attempts to use a variety of surface-active agents (sodium dodecyl sulfate SDS, sodium dodecyl benzene sulfonate SDBS, carbon nanotubes water powder TNWDIS, ethanol, etc.) to disperse carbon nanotubes (CNTS) for ultrasonic dispersion, when the CNTS was dispersed in water, it can be evenly distributed in the cement matrix.Experiment showed that different surfactants had different dispersibility on CNTS, and the different surfactant concentrations would directly affect the dispersing effect of CNTS in an aqueous system. Therefore, the optimal effectiveness of CNTS can be reach by selecting the appropriate surfactants and surfactant proportional relationship between the carbon nanotubes. Based on test results, TNWDIS has a significant effect for CNTS dispersion in water, followed by the SDS, SDBS and ethanol in a variety of surfactants.The macroscopic mechanical properties (flexural, compressive strength) of CNTS cement-based composite specimens is significantly improved due to the excellent mechanical properties and uniform dispersion of c CNTS. In this paper, the mechanical properties of specimen made of cement-based material mixed with a certain carbon nanotubes was studied. The results show that the mechanical properties of the specimen made by cement-based material mixed with carbon nanotubes are significantly improved compared with the specimen made by cement paste, especially for the flexural strength. However, since the carbon nanotube composite can increase the amount of water, so the strength of the composite is reduced to some extent when the mixing amount of CNTS is too much.CNTS have a certain impact on the conductive properties of cement-based composite, and the conductivity is significantly improved after a certain amounts of CNTS material was added. There are certain conductive polarization for ordinary cement paste and carbon nanotubes cement conductive material, the polarization specimens of ordinary cement paste is the longest and the polarization degree is the greatest. At the meantime, there is a certain relationship between the resistance change rate and the stress of cement-based composite nanotube specimen, and this phenomenon reflects a good pressure-sensitive properties. This effect is mainly due to the tunneling effect and interaction contact conductive effect. And the good pressure-sensitive properties can be applied to real-time health monitoring of concrete structures.