Study On Fiber Dispersion Detection And Durability Of Modified Polyester Fiber Concrete

Modified polyester fiber-reinforced concrete is widely used in construction industry because of its excellent properties.However,the rapid and effective evaluation of the dispersivity of polyester fibers in concrete and its influence on the mechanical properties,crack resistance and durability of the material have to be studied urgently.Therefore,this thesis studied comprehensively the physical and chemical properties of modified polyester fibers,mixing technology of fiber-reinforced concrete,and durability of modified polyester fiber-reinforced concrete in marine environment.Based on the results obtained,the characterization method and testing method of fiber dispersion are established.The influence mechanism of the firbers on durability of concrete in marine environment has been studied.A systematic evaluation method has been proposed.This study provides technical basis and experimental method for improving the construction and engineering design of polyester fiber-reinforced concrete.The specific research contents are as follows:1)The compositions of concrete matrix was determined.Modified polyester fiber-reinforced concrete with different addition of fibers has been prepared to study the influence of its crack resistance level,fracture energy and compressive strength.The results indicate that with the increase of fiber content,the crack resistance level of concrete increases and the fracture energy increases accordingly.When the fiber content increased to 1.3 kg/m3,the fracture energy of fiber-reinforced concrete could be increased up to 233 N/mm,which was 180.7%and 36.3%higher than normal concrete and fiber-reinforced concrete with fiber addition of 1.1 kg./m3.In addition,the addition of proper amount of modified polyester fibers can effectively improve the compressive strength of concrete.2)In order to explore the influence of modified polyester fibers on concrete strength and failure process,the combination of uniaxial compression test and acoustic emission test was used to analyze the variation law of acoustic emission characteristic parameters such as the ringing rate,energy count rate and peak frequency in the mechanical failure process of concrete mixed with different addition of modified polyester fiber.It is found that with the increase of polyester fiber content,the low-frequency acoustic emission ringing count and energy counting rate are gradually reduced,the trend characteristics disappear and the dispersion is strengthened;and the acoustic emission appears to be shorter in the stage of plastic failure.The addition of modified polyester fibers changes the internal structure and the generation and expansion of cracks,which in turn changes the acoustic emission characteristics.3)The paper systematically reveals the influence mechanism of different dosage of modified polyester fibers on the crack resistance,chloride resistance,freeze-thaw resistance and carbonation resistance of concrete.The results indicate that modified polyester fibers can effectively improve concrete against chlorine penetration.The carbonation resistance is also significantly promoted.In addition,the fibers decreases the formation of micro-cracks and capillary pores inside the concrete.The compactness of concrete was thereby improved The mutual cross-linking tensile properties of the fibers can absorb the energy generated by the temperature stress.When the frost resistance grade reaches F225,and the fiber content is 1.3kg/m3,the crack resistance level is grade I.4)A new quantitative method to characterize the dispersibility of polyester fibers in concrete by means of fractal dimension method was proposed.The fiber dispersion influence coefficient was introduced into the chloride ion diffusion coefficient of concrete.Considering the carbonation of concrete,chloride ion binding ability and the influence of pore structure,the durability evaluation model of fiber-reinforced concrete has been establish with consideration of fiber dispersion coefficient,carbonation and chloride coupling.5)Based on the image processing technology and the microscopic image recognition system,the obtained image of modified polyester fiber-reinforced concrete has been analyzed.Thereby the dispersion model of fibers in concrete and its evaluation method has been established.The system of fiber image recognition and analysis method based on the image processing method is developed,and the reliability of the image processing results has been also verified.