Frost damage evaluation of concrete irrigation structure by X-ray CT and AE energy release trend at the initial loading stage

Abstract

Deterioration of concrete infrastructures occurs for several reasons, leading to operational problems and further collapse. Freezing-thawing processes are one of the active damage mechanisms in cold regions causing defect accumulation in the inner structure of the material and reduction of the mechanical properties. The optimal way to evaluate the damage degree is by applying non-destructive testing (NDT) methods which allow detailed and integrated results. In this research, a relationship between Acoustic Emission (AE) release energy trend and X-ray Computed Tomography (CT) parameters was investigated for damage quantification. Visualization and extraction of the internal concrete components were conducted by X-ray CT. The ultrasonic pulse velocity (UPV) and resonant frequency methods were employed for the determination of the dynamic modulus of elasticity. After utilizing AE on the compression test, the damage characterization was evaluated. The extensive description of structural members in in-service structure was acquired using principal component analysis (PCA). The X-ray CT results show that all specimens have initial damage degrees in form of cracks and voids unevenly distributed within the concrete matrix. Regarding the irrigation structure, all concrete specimens have unique particle characteristics depending on which structural members they were drilled out from. Moreover, it is observed that the accumulated damage in the form of voids positively correlates with the initial AE energy release rate. In concrete specimens with low damage degrees, the AE energy release has an upward trend of low amplitude (≤50 dB) with a silent stage at the initial loading and sudden release only near the final failure. In contrast, heavily damaged concrete shows continuous AE energy release of high amplitude (≥60 dB) and with a high initial AE energy release rate corresponding to the uninterrupted crack propagation and coalescence in the early stage of fracture and throughout the loading due to the high weak zones ratio. These results indicate that frost damage can be evaluated by the comprehensive analysis of the fracture process of concrete based on X-ray CT and AE results to characterize the damage degree.