Properties And Modification Mechanism Of Nano-Silicon Oxide And Carbon Fiber Filled Cement Mortar

Previous researches have proved that nano-silicon oxide filled cement composites have excellent mechanical properties such as high toughness, high strength, high anti-fatigue and creep property and high fracture safety. Carbon fiber filled cement composites own advantages of good tensile strength and flexural strength, good electrostatic shielding, and electrically conductivity and pressure-sensitivity. In order to develop cement composites with superior mechanical and electrical properties, hybrid nano-silica and carbon fiber are used to enhance carbon fiber dispersion in the matrix and carbon fiber-matrix interface through nano/micro multi-scale effects. Based on research on the preparation and properties of doped single nano-silica or carbon fiber filled cement mortar, the performances of hybrid nano-silica and carbon fiber filled cement mortar are investigated. Main contents of this dissertation are as follows:(1) Nano-silicon oxide is difficult to disperse in cement composites. In addition, current research mainly focused on effects of nano-silica on the mechanical properties of cement composites, while study of the electrical properties is quiet little. Mechanical mixing, ultrasonic dispersion and water reducing agent are used to enhance the dispersion of nano-silicon oxide in cement mortar. The effect and mechanism of concentration of nano-silicon oxide on mechanical and electrical properties of cement mortar are studied. The optimum concentration of nano-silicon oxide in cement mortar was determined. Research results indicate that it is feasible to improve the nano-silica dispersion in cement through combination of physics dispersion and chemical dispersion. Flexural strength, compressive strength and electrical resistivity of nano-silicon oxide filled cement mortar increase with the concentration of nano-silicon oxide.(2) Mechanical properties and electrical properties of cement mortars with different lengths and contents of carbon fibre are tested. The enhancement mechanism of carbon fiber to cement mortar is analyzed through calculating number per unit volume of different lengths of carbon fiber in cement matrix, the average separation of carbon fiber and critical length of carbon fiber under external loads. Research results indicate that with the increase of the carbon fiber concentration, the amount in perunit volume of carbon fiber in cement mortar increases and the average separation decreases. Per unit volume of carbon fiber bears bigger loads and fiber critical length gradually increases. As a result, flexural and compressive strengthes of carbon fiber filled cement mortar gradually increase. In addition, the carbon fibers in mortar overlap with each other and conductive network is formed, which leads to decrease the electrically resistivity of carbon fiber filled cement mortar.(3) The mechanical properties and electrical properties of cement mortar with different contents of nano-silicon oxide, and different contents and lengths of carbon fiber are investigated. Research results indicate that nano-silicon oxide can promote the dispersion of carbon fiber in cement matrix and enhance interface structure and performance between carbon fiber and cement matrix, which contributes to improve the mechanical properties and electrically conductivity performance of cement mortar. When the nano-silicon oxide concentration is constant, flexural strength and compressive strength of cement mortar increase with the increase of carbon fiber content. However, the electrical resistivity decreases with the increase of carbon fiber content. When the carbon fiber content is constant, the flexural strength, compressive strength and electrical resistivity gradually increase with the increase of nano-silicon oxide content.6mm carbon fiber in length is more effective for improving flexural strength, compressive strength and electrically conductivity of cement mortar compared 3mm carbon fiber in length.