Study On The Dispersion Of Short Carbon Fibers And Compression Sensibility Of CFRC

Carbon fiber reinforced cement-based composites (CFRC), as a kind of functional and structural material, have their advantages: excellent material properties and self-diagnosing functions. One of key factors to ensure the compression-sensibility stableness of CFRC is the dispersion of short carbon fiber (CF) in cement paste uniformly. Firstly, the effect of carboxy methylcellulose (CMC) on the dispersion of CF is investigated and evaluated in this thesis. The variation coefficients of the mass of CF in 16 mixtures with different proportion CMC and silica fume are calculated. Using this method, the optimum components of CFRC are proposed. Such as CMC surface lubricating, silica fume filling effect, viscosity of mixture and mixing process are analyzed to explore the mechanism of CF dispersed in the cement matrix. The present of CF dispersed one by one is examined by a scanning electron microscope (SEM). At the same time the length distribution of CF in CFRC is obtained. Secondly, the influence of the dispersion of CF on conductivity and flexural strength of CFRC are discussed. Lastly, the compression sensibility of CFRC is tested. The main conclusions are drawn as following:1. For the sake of CF dispersed uniformly in the cement paste, the formulation of CMC and silica fume are used in the amount of 0.8% and 15% respectively. And in the meantime, the special mixing mode is suggested.2. The dispersion of CF in CFRC is a complex physical, chemical and mechanical process. Two phases are included: the dispersion of CF in dispersant solution and that in cement. Such factors as the CMC surface lubricating, silica fume filling effect, viscosity of mixture and mixing process play important roles in these two phases. The former three factors affect the dispersion of CF in dispersant solution; otherwise the last two affect the dispersion in cement.3. The conductivity and flexural strength are influenced directly by the dispersion of CF. The better the dispersion is, the lower the electrical resistivities of specimens are, the higher flexural strength and toughness is.4. The tamping procedure and uniform dispersion of short CF in cement paste lead to the excellent compression-sensibility stability ofCFRC. A tamping procedure is adopted because it proved to more effective at reducing air void in the specimens; the reason that CFRC is capable of sensing stress and strain is the insert-in and pull-out effect of short CF within the cement matrix under load.