Detection Of Impact Echo Of Tendon Ducts Grouting Quality Based On Signal Phase Analysis

In the process of grouting,the post tensioned prestressed bridge is prone to the situation of insufficient grouting and cavity.After the bridge is completed and put into service,the water in the air will gradually infiltrate into the duct,leading to the corrosion of prestressed steel strands,which will reduce the bearing capacity of the bridge.The prestressed grouting is a concealed project,no matter in the construction or in the use process,it can not be intuitive to get the situation of grouting inside the duct.As a non-destructive testing method,the impact echo method can quickly detect the internal condition of prestressed duct.But in the actual detection,the phenomenon of misjudgment and missed judgment still exists,and the reliability of detection is often questioned.How to improve the reliability of the impact echo method is one of the most important problems to be solved.According to the current research situation,and combined with the latest research results at home and abroad,this paper carried out the following research:Firstly,the phase analysis method of impact echo is introduced.The function of traditional amplitude frequency domain analysis is to judge the reflection interface and determine the depth of the interface.The function of phase analysis is to judge whether these reflections come from the steel beam interface or the free interface,which greatly improves the reliability of impact echo detection.Phase analysis can effectively distinguish plain concrete and full grouting duct,which makes it possible to use impact echo method to detect the location of steel beam.Combined with the model test,it is concluded that the reflection phase of the slab bottom of plain concrete is smaller than that of the slab bottom of full grouting hole.Secondly,in the research object from the simple top and bottom plate,web research to the box girder chamfering,the analysis of unequal thickness plate,chamfering single-layer channel,double-layer channel and other working conditions,expand the scope of application of the impact echo method.Some results and conclusions are obtained:(1)the impact echo method is also applicable to plates with different thickness;(2)the single-layer channel at the chamfer has a high accuracy of judgment;(3)for the double-layer channel,only the defect condition of the first layer channel closest to the test surface can be judged,and the condition of the second layer channel cannot be judged;(4)in the dense channel arrangement,the condition of the adjacent channel is also applicable to the test hole The channel has no interference.Finally,the location of the defect in the hole,the impact duration and the position of the steel beam are analyzed.The conclusion is as follows:(1)the defect in the hole is not always detected.When the defect is parallel to the test surface,the effect is the best.When the defect is perpendicular to the test surface,it is difficult to detect.Conclusion it can be verified by model test;(2)impact duration has no effect on frequency response,only affects the phase value of defect.(3)The impact echo method is also applicable to the scattered steel bundles near the anchorage end.