A Data Processing Method for the Grouting Quality Evaluation of the Pre-stressed Pipeline by GPR

The grouting quality of pre-stressed pipeline is of crucial to the safety of the concrete bridge, which has been a great concern to the people.When the pre-stressed pipeline is not grouting full, its effective stress and the operational performance will be greatly reduced due to the steel strand corrosion, so does the durability and safety of the bridge. Ground penetrating radar (GPR) has been widely used in the field of non-destructive quality detecting for its advantages such as high efficiency, and intuitively results. However, When GPR is used for concrete detection on bridges, the imaging result will be greatly influenced by the rebar in the concrete because of strong reflection and interference of electromagnetic signal from it. It effects the result in two ways, On one hand, it makes most of the electromagnetic signal that emitted by the antenna can’t spread through the steel mesh deep in the concrete structure; on the other hand, the electromagnetic signals reflected from the quality defects in the pre-stressed pipelines is much weaker than the reflection signal from the steel mesh, so that the information of grouting defects will be over shadowed and almost can not be recognized. The most popular idea which has also been applied in practice is to suppress the interference of the rebar when using the conventional GPR data processing method. For ordinary concrete structure, suppression the interference of the rebar can improve the quality of signals to a certain degree, but it works ineffectively in the pre-stressed concrete structure of bridge because the arrangement of the rebar is more complexly in that case. In the concrete structure of bridge, the rebar is almost equally spaced in depth direction. According to this character of distribution, this paper proposed a new method for reducing the interference of rebar on basis of the traditional processing method. We verified this method using simulation data, indoor sandpit experimental data, cast-in-place beam experimental data and field data. Results show that the interference of the rebar is basically excluded and the characteristics of the defect in the pre-stressed pipeline have been significantly strengthened. Through drilling on the abnormal position, the grouting defect in the pre-stressed pipeline was accurately verified, which shows a promising future of our method for practical applications.