Research On Concrete Damage Detection By Using Acoustic Emission Technology

Acoustic emission technique is a dynamic nondestructive examination method developed in recent years, and has been extensively used in materials performance measurement and damage detection of structures because it has simple principle, high sensitivity and convenient operation and can realize real-time monitoring on line, and would have great potential in the future. In this paper the damage law and fracture mechanism of concrete materials are researched on the basis of the analysis of AE characteristics of concrete materials, and then the failure process of reinforced concrete beams and concrete structures strengthened by CFRP are monitored and researched to give some theoretical and practical reference for the application of AE technique in the damage examination and health monitoring of concrete structures. The main contents are as follows:Firstly,24concrete specimens of4different groups are made and uniaxial compression test, splitting tensile test and simple shearing test are conducted to research the AE characteristics and damage mechanism of concrete materials. The results reveal that AE characteristics have a high correlation with compressive strength, stress type and stress level. AE activities show great difference under different stress level and different stress type, and the frequency distribution characteristics are also different under different stress.Secondly, the fracture mechanism and characteristic of concrete material are researched through three point bending test of notched concrete beams. The fracture process zone is measured through AE location method and the strain field is analyzed by digital speckle metrology. Results show that the catastrophe of AE parameters can be used to determine the initial cracking load and unstable cracking load, and the localization of fracture process zone is in accord with the real failure graph. Therefore, it is feasible to study on concrete fracture process by applying AE technology.Thirdly, the damage characteristics of concrete corroded by acid solution and low temperature sea water are researched by AE rate process theory and a calculation method for damage factors and constitutive equations of corroded concrete is put forward taking into account of the initial damage. The results show that this method has high precision and reliability.Further, the damage monitoring and damage localization of reinforced concrete beams are researched by AE technique and a function of AE sources position concentration degree (PCD) is presented for the evaluation of damage degree. Results show that AE parameters and PCD are highly correlated with the strains of steel bars and concrete and beam deflection.Finally, compression tests of CFRP reinforced concrete columns are carried out and a modified formula for the compressive strength is presented based on the AE test results. On the other hand, the failure process of concrete filled CFRP-steel tube under bending is monitored and recorded by AE technique and AE signals are analyzed by wavelet analysis method, and the whole process is simulated by finite element analysis. The results show that AE parameters and waveforms change with the breakdown of concrete filled CFRP-steel tube and can distinct different damage mode.