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20. Continued 



condition assessment. The third instrument evaluated was ultrasonic test equipment that 

 estimates compressive strength, detects cracks, and provides a general condition rating of 

 the concrete based on sound velocity measurements. 



Laboratory and field tests did not reveal any problems with the fundamental opera- 

 tion of each instrument after they were modified. There was a 23% shift in the output 

 data for the Schmidt hammer as a result of the modifications, but this shift can be elimina- 

 ted by designing it for underwater use. The modifications did not affect the data from the 

 other two instruments, and all of the instruments were easily operated by a diver. 



Library Card 



Naval Civil Engineering Laboratory 



UNDERWATER NONDESTRUCTIVE TESTING OF CONCRETE: AN 

 EVALUATION OF TECHNIQUES, by A. P. Smith 

 TN-1747 64ppillus February 1986 Unclassified 

 1. Underwater inspection 2. Nondestructive testing I. YO995-01-004-310A 



Three commercially available instruments for testing concrete above water were successfully 

 modified for underwater use and evaluated in laboratory and field tests. One of the three instru- 

 ments was a magnetic rebar locator that locates rebar in concrete structures and measures the 

 amount of concrete cover over the rebar. Another instrument was a Schmidt hammer that evalu- 

 ates the surface hardness of the concrete and obtains a general condition assessment. The third 

 instrument evaluated was ultrasonic test equipment that estimates compressive strength, detects 

 cracks, and provides a general condition rating of the concrete based on sound velocity measure- 

 ments. Laboratory and field tests did not reveal any problems with the fundamental operations of 

 each instrument after they were modified. There was a 23% shift in the output data for the Schmidt! 

 hammer as a result of the modifications, but this shift can be eliminated by designing it for under- 

 water use. The modifications did not affect the data from the other two instruments, and all of 

 the instruments were easily operated by a diver. 



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SECURITY CLASSIFICATION OF THIS I 



