have been increased to 1,000 frames/sec, if desired. However, after 

 several tests and no coverage of failure, the film speed was reduced to 

 100 frames/sec to increase the film time to 80 seconds. The camera was 

 installed in eight specimens but failure coverage was not obtained in 

 any test. The techniques used to try to predict imminence of failure 

 are discussed in the Test Procedure section. 



TEST PROCEDURE 



The pressure vessel used in the tests had an inside diameter of 72 

 inches (1830 mm) and an operational pressure of 5,500 psi (37.9 MPa). 

 The pressure load was created by pumping additional water into the 

 vessel and thereby compressing the fluid. Freshwater was used in the 

 tests. 



The temperature of the water typically varied between 3° and 10°C 

 for different tests; however, the temperature inside the specimens 

 typically varied between 10° and 13°C . The higher temperature inside 

 the specimens was due to warmer room temperature and Hghts for the 

 television . 



All specimens were placed in the pressure vessel on the evening 

 before testing and allowed to soak in order that the degree of water 

 saturation of the concrete for the different specimens would be the 

 same. It was hoped that soaking overnight partially saturated the 

 concrete to equal levels . 



The rate of pressure application was 10 psi/min (0.069 MPa/min) 

 between hold periods where data were recorded. Hold periods occurred 

 at 25 psi (0.172 MPa) increments and typically lasted for 2.5 minutes. 

 From the beginning to the end of the test, the overall pressuri2ation 

 rate was about 5 psi/min (0.034 MPa/min). 



The television monitor was operated throughout the test. Its use 

 was invaluable in operating the deflectometer system, detecting leaks, 

 and recording implosion on videotape. 



48 



