Study And Engineering Application Of Sensitive Properties Of Nano-carbon Fiber Polyurethane Matrix Composites

This paper takes the engineering practice of polyurethane cement(PUC)to reinforce bridges as the background.By adding conductive fillers such as nano-carbon fiber(CNF)to the PUC,it is made into nano-carbon fiber polyurethane cement(CPUC)composites.According to the preparation and mechanical properties of the CPUC,a systematic study on the sensitivity characteristics of CPUC is carried out,and a simple and easy method is proposed to evaluate the CNF dispersion effect.The variation regulation of CPUC resistivity under fatigue load is studied,and the fatigue cumulative damage is quantitatively evaluated by CPUC resistivity change.At the same time,the relationship model between resistance change rate and external load is established,and the bearing capacity condition of beam body is evaluated in real time.Moreover,the double effect of beam body health monitoring is realized.While strengthening the concrete column by CPUC to improve the bearing capacity of the column,the longitudinal strain of the steel bar is evaluated by the change rate of the longitudinal resistance in the CPUC,and the damage degree of the column is quantitatively characterized to form an outer CPUC concrete column with the function of self-diagnosis of damage.Finally,a reinforced solid bridge is used as an example to monitor the strain of the key section of the main beam before and after tensioning the prestressed steel bundle outside the main beam and under the static load test by using the integrated CPUC intelligent sensor,which verifies its feasibility in engineering application.And this research provides theoretical basis and direction for CPUC engineering application in the direction of intelligent monitoring.The main findings are as follows:1.Using two-component polyurethane(PU)as cementitious material,cement as the main fine aggregate and CNF as the main conductive filler,CPUC composites were prepared by one-step method of mechanical high-speed blending by surface chemical modification of CNF particles.The average compressive strength and flexural strength of CPUC are 53.7 MPa and 30.75 respectively MPa.When the temperature is between-40??40?,the direct tensile strength range is between 24.13MPa and 18.13MPa,the ultimate strain is less than 5500 ??,and the average value of the bond stress between CPUC and concrete is 3.47MPa,which is greater than the bond strength of concrete material itself.The bond shear strength could reach 3.08MPa,which is 8%higher than that of PUC without carbon fiber.2.Using sensitivity 500 as the reference index of pressure-sensitive characteristics,the relationship between the concentration CNFs conductive filler of CPUC composites and its corresponding positive hexahedron resistance variation coefficient is established,which can evaluate the dispersion effect of CNFs in the composites,and then distinguish the sensitivity characteristics of the CPUC,and provide a simple and feasible new method for the sensitivity discrimination of CPUC mixtures.3.Under fatigue load,CPUC fatigue life accords with the weibull distribution of two parameters,and the resistivity increases with the raise of fatigue stress amplitude and cycle times CPUC bending-pull state.Under different ambient temperature fatigue load,the bending-pull resistivity increases gradually with the increase of temperature.CPUC resistivity change can be used to predict the cumulative damage of flexural and tensile fatigue.The threshold resistivity or ultimate resistivity could be used as the measure of initial damage or failure,which may provide theoretical basis for practical engineering application.4.The yield load and ultimate load of the beam can be significantly increased by using CPUC material to reinforce the concrete beam When as the reinforcement material,CPUC the ultimate load and ductility index of the beam are increased greatly compared with the PUC.The change rate of resistance in CPUC bending process can reflect the whole procedure of strain state in the process of steel bar stress,and the sudden change rate of CPUC resistance can be used to monitor the yield of steel bar,and then safety warning can be carried out.According to the constitutive relation between the initial resistance change rate and the tensile strain of the CPUC material,a model of the relationship between the resistance change rate and the external load can be established to evaluate the bearing capacity of the beam body in real time,and the double effect of health monitoring of the beam body can be realized while strengthening.5.Reinforcement of concrete columns by CPUC can improve the bearing capacity,ductility and energy dissipation capacity of columns to varying degrees,and raise significantly with the increase of CF content The longitudinal strain of steel bar or concrete can be estimated by the CPUC longitudinal resistance change rate,and the damage degree of the column can be quantitatively characterized to form an outer CPUC concrete column with the function of self-diagnosis of damage,which provides a new way for the health monitoring and early warning of the structure.6.Using integrated CPUC intelligent sensor,the strain of the key section of the main beam in static load test before and after tension of a real bridge box girder is measured,which indicates that the CPUC intelligent sensor can monitor the concrete surface strain in real time,then quantitatively evaluate the damage degree of the components,and have a certain safety reserve,which verifies its feasibility and reliability in engineering application.