Evaluation of internal void related defects in reinforced concrete slab using electromagnetic wave properties

This study aims to develop a damage-detection algorithm based on the electromagnetic wave properties inside a reinforced concrete structure.The proposed method involves employing two algorithms based on data measured using ground-penetrating radar—a common electromagnetic wave method in civil engineering.The possible defect area was identified based on the energy dissipated by the damage in the frequency-wavenumber domain,with the damage localized using the calculated relative permittivity of the measurements.The proposed method was verified through a finite difference time-domain-based numerical analysis and a testing slab with artificial damage.As a result of verification,the proposed method quickly identified the presence of damage inside the concrete,especially for honeycomb-like defects located at the top of the rebar.This study has practical significance in scanning structures over a large area more quickly than other non-destructive testing methods,such as ultrasonic methods.

Research on the imaging of concrete defect based on the pulse compression technique

When the synthetic aperture focusing technology （SAFT） is used for the detection of the concrete, the signal-to-noise ratio （SNR） and detection depth are not satisfactory. Therefore, the application of SAFT is usually limited. In this paper, we propose an improved SAFT technique for the detection of concrete based on the pulse compression technique used in the Radar domain. The proposed method first transmits a linear frequency modulation （LFM） signal, and then compresses the echo signal using the matched filtering method, after which a compressed signal with a narrower main lobe and higher SNR is obtained. With our improved SAFT, the compressed signals are manipulated in the imaging process and the image contrast is improved. Results show that the SNR is improved and the imaging resolution is guaranteed compared with the conventional short-pulse method. From theoretical and experimental results, we show that the proposed method can suppress noise and improve imaging contrast, and can also be used to detect multiple defects in concrete.

Experimental and numerical study on structural performance of reinforced concrete box sewer with localized extreme defect

An experimental and numerical investigation into the structural performance of reinforced concrete box sewers with typical corrosion-related extreme defects localized at the ceiling was conducted.Firstly,during the large-scale laboratory test,some key struc-tural responses were captured and evaluated,including the crack width development process(via digital image correlation measurement),ceiling deflection,and material strains of both complete and typical defective boxes.The failure modes and load-carrying mechanism throughout the specimen loading phases were analyzed.Furthermore,the specimen failure process was simulated using a damage-basedfinite element method,and a related parameter sensitivity analysis was performed.The results indicate that the defective ceiling cracked at mid-span under a low load value,but the bending capacity loss can be substituted by two shoulders and carry three tofive times more load before completely collapsing.The simulation matched the lab test qualitatively,and with the suggested set strategy of material parameters,the load-deflection feature curve could provide a practical prediction of the ultimate bearing capacity of the defec-tive sewers,with a 10–15%error on the safe side.