EXECUTIVE SUMMARY 



Three commercially available instruments for testing concrete above 

 water were successfully modified for underwater use and evaluated in 

 laboratory and field tests. Each instrument represents a different tech- 

 nique for evaluating concrete structures. Instruments for the following 

 methods were tested: 



a. A magnetic rebar locator that can be used to locate rebar in 

 concrete structures and measure the amount of concrete cover over the 

 rebar. 



b. A Schmidt hammer that can be used to evaluate the surface hard- 

 ness of the concrete and obtain a general condition assessment. 



c. Ultrasonic test equipment that can be used to estimate compressive 

 strength, detect cracks, and provide 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. Only the Schmidt hammer showed 

 a shift in output data (23%) as a result of the modifications. This 

 shift can be eliminated by modifying the design. Modification for under- 

 water operation did not affect data from the other two instruments, and 

 all instruments were easily operated by a diver. 



A prototype concrete inspection system consisting of an R-Meter, 

 Schmidt hammer, ultrasonic test equipment, and a common data acquisition 

 system is recommended for development. 



