New testing method for assessing the cracking sensibility of stressed tendon rods in aggressive environments

• Testing method for assessing the cracking sensibility of stressed tendon rods
• The test arrangement allows the simultaneous acquirement of load, CMOD and COD.
• SCC test for assessing the environment-assisted stress intensity factor of bars.

The paper presents a new testing method for assessing the cracking sensibility in aggressive environments of tendon rods for prestressed concrete structures, on the basis of Fracture Mechanics concepts. First, it approaches the fundamentals of the designed test in the context of existing fracture specimens, regarding the geometrical limitations introduced by the environmental assisted cracking of the rods, perpendicularly to the load direction. The analysis showed that fatigue precracked chevron-notched short bar specimen (SBS) is providing the largest measurement range of stress intensity factor to be explored in stress-corrosion cracking (SCC) tests. Then, the equation relating the elastic stiffness of SBSs to crack size was experimentally validated for specimens with true cracks produced by fatigue. SCC verification tests were made with an innovative horizontal loading device and the crack mouth opening displacement (CMOD) was acquired and numerically analyzed with a video digital image correlation system. The tests showed that SCC is fully governed by the small scale-yielding regime at the crack tip. Hence, the main process parameters as crack extension and environment-assisted stress intensity factor were empirically obtained for each time sequence of the SCC tests. To simplify further SCC tests instrumentation, an empirical correlation was stated between CMOD and crack opening displacement (COD) as measured by a conventional extensometer mounted on the loading grips of the specimen. This correlation was also validated in the SCC tests.