Stressed Failure Of Carbon Fiber Reinforced Concrete And Section Fractal Analysis

With low cost, reactants and simple process, good performance, concrete is the large building materials that be used most widely. But since the major, brittle, high tensile strength and low shortcomings seriously limits its application scope and engineering effect. Application of fiber material of high elastic modulus carbon can significantly improve the mechanical strength and physical properties. But for the enhancement, toughening, crack etc effect and its working principle understanding is still not get complete reunification.In view of the above engineering technical problems, this paper studies the carbon fiber geometry features especially the fiber length and concrete admixture on the mechanical strength and fracture characteristics of the influence law.Through the establishment of regression model, the influence of the length and content of carbon fiber on the resistivity, compressive strength, splitting tensile strength, fracture surface shape and fracture energy were investigated. In the meanwhile, some efforts were conducted to make use of the fractal theory to calculate the concrete fracture surface of the actual area, and to calculate the fracture energy of concrete more accurately. The main experiments and results are summaried as following:Firstly, by changing the length (3mm,5mm) and mixing amount (0-1%) of carbon fiber, the resistivity of specimen in different type of power supply was measured. Test results show that,in ac power supply circuit, carbon fiber incorporation can significantly reduce the resistivity of concrete, the carbon fiber mixing amount on the influence of concrete resistivity are obvious, The influence of carbon fiber length is not significant. But with dosage conditions, the resistivity of short carbon fiber concrete is lower than long carbon fiber concrete.Second, the contrast test of carbon fiber length and mixing amount on the influence for the concrete compressive strength, the effect of water-binder ratio and mixing amount for the7d and28d compressive strength is very significant, the influence of the length of the carbon fiber for the7d and28d compressive strength is not significant. Moderate carbon fiber to concrete compressive strength strengthening, after the increase of carbon fiber dosage can reduce the compressive strength of concrete. Carbon fiber in concretes easier to form a continuous network structure, and the improvement of concrete setting soil tensile strength is more obvious, But exist interface defect between carbon fiber and cement stone, when the mixing amount of carbon fiber too much will decrease the compressive strength of concrete.Thirdly, through the bending method of three point, to calculate the fracture toughness of carbon fiber in different water cement ratio, carbon fiber length (3mm,5mm) and mixing amount (0-1%), and draw the Load-CMOD curve.The effect of mixing amount and water-binder ratio for the fracture toughness of concrete is very significant. With the water-binder ratio conditions, with the increase of carbon fiber mixing amount, the fracture toughness of CFRC basically increase linearly,in the volume proportion of0.7%conditions, with the increase of fiber volume ratio, this increase of relationship for strengthen almost increase linearly, when the mixing amount of more than0.7%it will declines. All the Load-CMOD curve of CFRC and Load-CMOD of typical concrete curve present the same shape, with water-binder ratio of concrete smaller, the curve slope of rising Load-CMOD curve is smaller.Finally, calculate the work needed for fracture of specimen, make reconstruction of section and calculate fractal dimension, and then find out the area of the fracture surface, calculate the fracture energy of specimen. Using the digital image to measure fracture surface of concrete has the feasibility, and need equipment simple economy, does not cause damage to section, fractal theory can calculate the actual area of the surface of concrete fracture truly,then get more accurate calculation of the fracture energy of concrete. Carbon fiber can obviously enhance the fracture energy of concrete, at the same time increases the fractal dimension of fracture surface, namely carbon fiber can greatly increase the work of fracture. Through the establishment of regression model, carbon fiber length and mixing amount can performance the influence of fractal dimension for concrete fracture surface and fracture energy well.