Fracture experiments of three-point bending notched granite beams were performed under cyclic loading using digital image correlation (DIC) and acoustic emission (AE) techniques. The damage evolution process of the specimen under cyclic loading was analysed on the basis of AE ring count and b value. The strain and displacement fields and the fracture process zone (FPZ) ahead of the crack tip were revealed by DIC. The results showed that the AE characteristics of rock fracture indicated a noticeable Kaiser effect in the stage of cyclic loading and unloading. Moreover, when the loading force reached 70% of its peak value, the AE characteristics showed the Felicity effect. The damage produced during the loading-unloading process contributed to the development of the cracks leading to the catastrophic fracture. Besides, a relatively high loading rate was found to help to suppress the development of the FPZ at the crack tip.
K E Y W O R D Sacoustic emission, cyclic loading, digital image correlation, fracture damage, rock
In rock engineering, cyclic loading may occur before and after the loading forces reach the load‐carrying capacities of rocks. This investigation aims to comprehensively present the fracture behavior of cracked rocks subjected to prepeak and postpeak cyclic loads. In the experiments, fracture mechanisms of notched granite beams were analyzed in‐depth through digital image correlation (DIC) and acoustic emission (AE) technologies. The experiments showed that the specimen deformation gradually developed from elastic to elastic–plastic in the prepeak loading–unloading cycles, and microcracking was dominated by tension. In the postpeak cycles, the horizontal strain, horizontal displacement, and effective crack length generally increased cumulatively with the cycle number but locally decreased with unloading. Interestingly, many microcracks were still produced and the proportion of shear‐type AE signals increased during the unloading processes in the postpeak cycles.
In order to investigate the effect of temperature and pH on the early hydration rate of alkali-activated slag (AAS), NaOH was used as alkali activator, and the nonevaporable water (NEW) content of the slag paste at different temperatures (5, 20 and 35°C) and pH (12.10, 12.55, 13.02, and 13.58) was measured. On the basis of the Arrhenius formula, the hydration rate of slag was characterized by the content of nonevaporative water, and the apparent activation energy of slag hydration at different pH was also obtained. e early hydration rate of slag was significantly affected by temperature and pH of activator solution. e apparent activation energy E a of slag decreased with the increase of pH, and there was a good linear relationship between them. When pH was less than 13.02, increasing the temperature can accelerate the hydration rate of slag. However, under the condition of high pH (pH � 13.58), the hydration rate of slag was negatively correlated with temperature, which was related to the "shell forming" phenomenon of slag hydration.
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