Research On Compression Sensitivity Of Carbon Fiber Rein-forced Cement-based Composites Based On Interfacial Effect

The mechanism of compression sensitivity of carbon fiber reinforced cement-based composites (CFRCC) is complicated. Serving as a bridge which transfers stress and other information between carbon fiber and concrete matrix, the interface of the composites plays an important role on the compression sensitivity of the composites. The interface properties influence the general properties of the composites directly.This dissertation was supported by the Key Project of National Science Foundation under grants No.10672128. On the basis of predecessors' researches, the influence of surface treatment of carbon fiber is systematically presented in progress. The effect of interface properties on the compression sensitivity of the CFRCC and the mechanism is studied.The researches and the conclusions as follows:(1) The influence and mechanism of surface treat of the carbon fiber on functional response of the CFRCC was studied by experiments. As-received carbon fiber is deficient in the chemical groups on the surface. The surface of the fiber is inactive. Surface treat of the carbon fiber improves both the interfacial bonding strength and the interfacial ductility. The interfacial stability and fatigue properties are improved through surface treat of the carbon fiber. With interfacial bonding strength and interfacial ductility increasing, the interfacial debonding is not easy and repeatability and reliability of the sensing ability increase. The change in resistance is more smoothly. But the gage factor decrease at some extent.(2) Single fiber pull-out testing was conducted to study the origin of the functional response to loading of CFRCC. The resistance increases with tensile displacement increasing. When the interfacial bonding force reaches its maximum, the bond between fiber and matrix is broken completely, and the resistance increases abruptly. The change in resistance is mainly due to the change in interface. This electromechanical behavior can be explained by tunneling effect.(3) The variation of resistance of single fiber pull-out under cyclic loading was studied. The irreversibility of the resistance change is associated with the irreversibility of interfacial debonding. The deformation of interfacial structure in elastic region is reversible, and the resistance change caused by this part of interfacial structure in elastic deformation is also reversible. The change in resistance is in accord with the change in interface.(4) A simple formula was proposed to explain the mechanism of compression sensitivity of carbon fiber reinforced cement-based composites based on interface effect. The compression sensitivity of carbon fiber concrete is analyzed based on shear-lag theory and single fiber pull-out testing on the basis of predecessors' researches. The results showed that the content of water, content of carbon fiber and interface strain can change the sensitivity of CFRCC to the loading.