Tech.slote TAJ -1 7^7 



fdbtQZfa 



N-1747 



February 1986 

 By A.P Smith 

 Sponsored By Naval Facilities 

 Technical Note Engineering Command 



NCEL 



UNDERWATER NONDESTRUCTIVE 

 TESTING OF CONCRETE: AN 

 EVALUATION OF TECHNIQUES 



ABSTRACT Three commericially available instruments for testing concrete 

 above water were successfully modified for underwater use and evaluated in 

 laboratory and field tests. One instrument 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 

 evaluates the surface hardness of the concrete and obtains a general/condition 

 assessment. The third instrument 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 operation 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 underwater 

 use. The modifications did no t affect th e data from the other two instruments, 

 and all of the instrumep*s^/vere easily opeTateckbv a diver. 



DOCUMENT - 

 LIBRARY 



Woods Hole Oceanographic 

 Institution 



NAVAL CIVIL ENGINEERING LABORATORY PORT HUENEME CALIFORNIA 93043 



I /X Approved for public release; distribution unlimited. 



