Study Of Impact Echo Response In Bridge Deck With Asphalt Overlays

With the continuous development of the entire transportation industry in China,the construction of bridge projects has also increased.However,during the entire life cycle of the bridge structure,due to design defects,substandard construction quality,load effect after the completion of the bridge and the aging of the structure itself,the bridge structure will inevitably produce different degrees of damage and defects.As a load-bearing structure that directly bears the pressure of the wheels,the bridge deck is more likely to be damaged under the load of the vehicle and environmental erosion.Therefore,quick and accurate inspection of the bridge deck can effectively reduce the maintenance cost of the bridge,improve the durability and reliability of the deck structure,and ensure the normal operation of the bridge.Because there are many asphalt pavement layers on the bridge deck,this paper conducts a theoretical study on the rapid detection of the internal damage of the asphalt pavement deck based on the impact echo based on the impact response characteristics of the traditional single-layer concrete slabs.Through theoretical analysis,numerical simulation,improvement of detection methods,etc.,a more comprehensive analysis of material properties,defect depth,excitation position,etc.was carried out.For the asphalt-concrete double-layer slab,combined with the impact echo response characteristics and surface wave dispersion characteristics,the asphalt surface and the concrete bottom are separately stimulated to comprehensively identify the internal defects of the asphalt-concrete.The study found:(1)In double-layer concrete slabs,impact echoes can identify defects in different concrete layers;(2)In the asphalt-concrete double-layer board,due to the large difference in wave impedance between asphalt and concrete,the impact echo can only identify the defects of the single-layer board,that is,the excitation is applied on the surface of the asphalt layer,and the impact echo can only identify the asphalt Layer defects,can not identify the defects of the concrete layer;and when the excitation is applied on the bottom of the concrete layer,the impact echo can only identify the defects of the concrete layer;(3)For shallow defects(depth <7cm),the impact echo frequency is very high,and the attenuation is fast.It is not dominant in the spectrum chart and is easily covered by low-frequency signals.At this time,the shallow echo cannot be used to identify shallow defects.Therefore,when the excitation is applied on the surface of the asphalt layer,the impact echo can only identify the defects of the asphalt layer with a depth ? 7 cm.Similarly,when the excitation is applied on the bottom of the concrete layer,the impact echo can only identify the defects of the concrete layer with a depth of ?7cm;(4)Simultaneous application of double excitation can accelerate the detection speed of single excitation,the arrangement distance of the two excitations will affect the accuracy of the detection results;(5)Based on the dispersion characteristics of the surface wave,when the thickness of the asphalt layer is between 20 mm and 50 mm,the ratio of the wavelength of the "inflection point" of the surface wave dispersion curve to the thickness of the asphalt layer is about 0.8This thesis has 77 pictures,34 tables,and 100 references.