Testing Principle：In the condition of equal spacing, The sound speed of cracked concrete will be longer than complete one. The depth of sound is calculated from the sound propagation time and the distance between the probes
1.The quality of concrete around the crack is basically the same
2. The sound speeds in concrete and cracked concrete are the same
3. The first wave of the cross-slot can be detected by transducer after bypasses the end of crack.
Standard of China Engineering Construction Standardization Association: Technical Specification for Ultrasonic Detection of Defects in Concrete (CECS21:2000)
The Parameters of Crack
No water, slugg inside the crack; The depth of crack is within 50mm; The connection of T,R transducer is not parallel to the rebar axis
1. Measuring the complete concrete: Measured without cross-stitching: Measure 3-5 points t with different spacing L (internal edge spacing of the transducer), and obtain 3 - 5 groups (L, t)
Do linear regression: L，= a + b · t
Use a to correct L: L= L， + |a|
Calculate the speed of sound :b
2.Measuring the cracked concrete:(L;t1)
Transducer measure speed time in crack ; Distance=L; Correspendance speend time=t1
Calculate the depth of crack
1.Three-point average method: if the first wave is found to be inverted, then the depth h is averaged at this point and the distance between adjacent two points.
2. If no first-phase anti-phase is found, the depth of the seam is calculated from the depth of each distance calculation h ; Remove data after L<h or L>3h and then average