Study On Key Parameters Of RC Acoustic Emission Damage Detection

Reinforced concrete structure is the most widely used structure types in the construction field. However, due to various factors, resulting in internal reinforced concrete structure with varying degrees of damage, which is a serious threat to security and stability of structure. So for reinforced concrete structures damage detection, structural damage to understand the situation, given in advance to prevent reinforcement measures without delay. Acoustic emission testing technology because of its advantages of dynamic real-time detection, become the topic research in the field of nondestructive detection. In this paper, take the key parameters（amplitude attenuation and velocity） which influence the acoustic emission test results as the research objects, Focus on the influence rule of parameters of materials and structures of reinforced concrete slabs, as well as cracks produced by the force to acoustic emission wave propagation characteristics. The main contents and results are as follows:By means of Pencil Lead Breaks（PLB）, to determine the acoustic emission detection parameters（threshold, velocity, peak identification time, identification of the impact time, impact locking time） which are applicable to reinforced concrete slabs, provide technical support for the subsequent loading test.Considering four parameters of material and structure, including thickness, concrete strength, coarse aggregate maximum particle size and reinforcement, design nine reinforced concrete members（B₁-B₉）. By conducting with the Pencil Lead Breaks, established the relationship between the ages of RC and amplitude attenuation and velocity, determine the influence of these four parameters to acoustic emission amplitude attenuation and wave velocity. The results showed that thickness and concrete strength are important factors affecting acoustic emission amplitude attenuation and wave velocity. The greater the thickness, the greater the amplitude attenuation; the higher the concrete strength, the smaller the amplitude attenuation; Acoustic emission wave velocity decreases with the increase of thickness of the concrete, as it increases with the increase of concrete strength grade. In addition, the maximum aggregate size and reinforcement ratio affect acoustic emission amplitude attenuation and wave propagation velocity, but to a lesser extent.These research results for the detection and recognition of reinforced concrete board material and structure parameters by acoustic emission provide reference.Design and make three members(B₁₀-B₁₂) with different thickness of concrete cover. By means of Pencil Lead Breaks（PLB）,determine the effect of the thickness of the protective layer of concrete on amplitude attenuation and velocity, the greater the thickness of concrete cover, the smaller the amplitude attenuation and the velocity. By setting different thresholds to determine the impact on velocity, the lower the threshold, the closer the calculated velocity to the true value of stress wave propagation in reinforced concrete. By static loading test to study the impact of the law of crack depth, width, number to acoustic emission amplitude attenuation and velocity, and to explore the effectiveness of Felicity in damage evaluation. Test and analysis results show that the crack depth is the main factor affecting the amplitude attenuation and wave velocity, the larger the crack depth, the greater the amplitude attenuation, the smaller the wave velocity, crack width and the number has no effect on amplitude attenuation and velocity. In addition, through regression analysis, obtain formulae expressing the relasionship between maximum depth of cracks and amplitude attenuation or velocity. Finally, study the impact of velocity fixed and variable velocity on damage localization results, results show that the variable velocity has a higher accuracy on damage locating in reinforced concrete structures.