Application of Impact Imaging Method on Nondestructive Detection of Void Defects in Sandwich-Structured Immersed Tunnel

Table 1

Comparison of nondestructive testing methods for void defects in steel-concrete composite structures.

Detection methods	Technical principle	Void type		Applicability
		Steel plate-concrete debonding	Steel plate-concrete filling defect
Ultrasonic method	Wave speed and reflected wave energy	Only identify the small defect area and cannot identify void height		△/×
Impact-echo method	Wave characteristics	Can identify thin steel plates, large voids, and cannot identify void height		△/×
Impact acoustic method	Sound pressure response	Can determine the location and area of the void and cannot describe the void height		△
Infrared method	Thermal conductivity difference	Can determine the location and size of the void		△
Neutron method	Neutron moderation principle	Can distinguish void area and average void height		○/△
Impact imaging method	Elastic wave theory	Can distinguish void area and void height		○/△

Note. ○: applicable; △: applicable under certain conditions; ×: not applicable.