Experimental study on time-dependent fracture under long time constant loading

Time-dependent fracture in mass concrete, which happens under long-time constant loading due to creep in the bulk of the specimen and time-dependent crack growth, is closely associated with the safety and durability of concrete structures in service. The standard three-point bending beams are tested under constant loads representing 70%, 75%, 80%, 85% and 95% of the peak loads of the specimens for monotonic short-time loading. Time-dependent crack mouth opening displacement CMOD(t) in concrete under different long-time constant loading is obtained. Experimental results show that CMOD(t) increases with increasing loading time t. The time curve of crack mouth opening displacement CMOD(t)-t displays the features of three stages. CMOD(t) increases rapidly in the primary stage, but the crack mouth opening rate CMOR(t) slows down. In the secondary stage, CMOD(t) increases and CMOR(t) is almost constant. In the tertiary stage, CMOD(t) and CMOR(t) all increase rapidly until the rupture of the specimen. For the test of time-dependent fracture, the critical crack mouth opening displacement CMOD(t) is relatively higher compared to the monotonic static loading test. The CMOD(tc) decreases with the increasing percentage of the peak load and approaches critical crack mouth opening displacement CMODc of monotonic static loading test. For the specimens loaded to the different percentage of the peak load, the lifetime decreases with increasing long-term constant load. The lifetime as well as the percentage of the peak load are exponential. © 2020, China Water Power Press. All right reserved.