Issue 46

J. Liu et alii, Frattura ed Integrità Strutturale, 46 (2018) 352-360; DOI: 10.3221/IGF-ESIS.46.32 355 There are 6 stages of scanning on concrete test specimens, included the initial stage, as shown in Tab. 2. CT scan times Loading(kN) Percent of the peak strength 1 st scan 0 0% 2 nd scan 30 22.3% 3 rd scan 60 44.8% 4 th scan 90 67.2% 5 th scan 120 89.6% 6 th scan 134 100% Table 2: The load corresponding to the six scanning time of the concrete specimen. There are 499 CT scanning images in every test specimen, 5 CT scanning images are chosen to conduct the analysis due to the limited space, as shown in Fig. 3. Figure 3: Concrete sections map of CT scan. CT scanning test and acoustic emission test were conducted in 4 groups concrete test specimens under uniaxial compression, then the load-time curve, CT images and acoustic emission parameters were collected during the loading process. The concrete test specimens with initial 9.2% porosity are chosen to analyze in this thesis as the limited space. The CT scanning images of initial state, 30kN, 60kN, 90kN, 120kN, and 134kN when destroyed are listed in Fig. 4. Figure 4: CT scanning images of concrete in different loading. As shown in Fig. 4, there is no obvious cracks during the early loading stages in test specimens with 9.2% initial porosity, and the early loading stages can be considered as a compaction process for the pores for the reason of its relative large porosity. The internal micro cracks connect with micro pore and eventually the main visible cracks generate until the test specimens are destroyed.