Study On The Propertise Of The Carbon-nanotube Cement-based Composite

Health monitoring of the structure is a kind of nondestructive sensing technology which using the scene. Used to study the internal system features of the structure and detect structure degradation and damage. Carbon Nanotube-Cement Composite(MWNT/CC) has good conductivity and piezoresistivity as a new conductive composite material. It is a kind of ideal piezoelectric materials, suitable for structural health monitoring of engineering. However, in the practical engineering, temperature and water content have a great influence on the resistivity and piezoresistivity of the composite material in practical engineering. Thus, analysis on the smart character variation of the composite materials under different environmental factors according to the conductive theory and further applying these rules to the real-time monitoring of concrete structure, has important significance. In view of the MWNT/CC, this subject has been studied as follows:Study on the dispersion and mechanical properties of the carbon nanotubes(CNTs). We studied the CNTs dispersion under different types of surfactants and different concentrations, analyzed the influence of the addition of CNTs on the mechanical properties and conductive properties of the cement-based composites. The experimental results showed that when sodium dodecyl benzene sulfonate (SDBS) behaved as a surfactant and SDBS: MWNTs= 4:1, the dispersion of CNTs was up to 91%; when mixing amount of MWNT increased from 0 to 0.1%, the corresponding compressive strength of composites increased by 3.26%(from 58.2MPa to 60.1MPa), the flexural strength increased by 20%(from 10.2MPato 12.3MPa).Study on the conductivity and smart character of the MWNT/CC. We researched the variation of conductivity and smart character of the MWNT/CC under different environmental effect and different freeze-thaw conditions. By laboratory test we also analyzed the variation of composite resistivity and smart character at different temperatures and humidity conditions and observed the piezoresistivity and reversibility. The results showed that the electrical resistivity of cement-based material was 8.8×104Ω·cm, while that of the composite which added CNTs dropped to 3.2×103Ω·cm; when the mixing amount of MWNT was 0.1%, the maximum resistance change rate of the composite was 8.2%; there was a strong negative linear relationship between the sensitivity and water content, with a R2 of 0.915 under the environmental coupling effect; the resistance change rate first increased and then decreased with the number of fatigue effect and always increased with the number of freeze-thaw action.Resistivity-stress mathematical model of MWNT/CC. Based on the conducting percolation theory, the general effective media(GEM) equation proposed by Mclachlan et al and the general tunneling equation proposed by Simmons et al,, we established mathematical model of the composite between resistivity and stress with the corrections concerning temperature and humidity to master resistivity changes of the composite under different environmental conditions.