PSI - Issue 36

Olena Stankevych et al. / Procedia Structural Integrity 36 (2022) 114–121 Olena Stankevych, Valentyn Skalskyi, Bogdan Klym et al. / StructuralIntegrity Procedia 00 (2021) 000 – 000

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Fig. 1. Distribution of maximum shear stresses at the points of the middle section of the reinforced concrete sample (the plane is delineated by a dashed line) for the mutual orientation of the reinforcement: (a) at an angle of 0  ; (b) 45  ; (c) 90  . 4. Influence of steel fibers on mechanical and acoustic properties of SFRC The detailed information on the mean and standard deviation values of the peak load and peak deflection are summarized in Table 3. SFRC with the fiber volume fraction of 2.5% shows the highest peak load, and SFRC with the fiber volume fraction of 1.5% shows the highest peak deflection.

Table 3. Means and standard deviation values of the peak load and peak deflection in the SFRC samples. Type of reinforced concrete Peak load, kN Peak deflection, mm Plain concrete 2.02±0.12 0.16±0.09 SFRC with 1.5% of fibers 2.24±0.23 0.64±0.1 SFRC with 2% of fibers 3.02±0.45 0.6±0.05 SFRC with 2.5% of fibers 3.99±0.47 0.59±0.08

During the three-point tests SFRC behaves better than the plain concrete, in which the load drops sharply when the initial macrocrack is formed in the sample. At the same time, in the reinforced concrete, the load-deflection curves consist of a relatively short branch of rigid deflection and a much longer branch of soft (pliable) deflection. The maximum load, deflection, and area under the curve increase with the increase of the fiber volume fraction in the concrete. Fig. 2 shows the typical time dependences of load and AE events for SFRC samples with different fiber volume fraction. It can be seen that initially AE activity in all samples is insignificant. In plain concrete, the number and amplitude of AE signals increase with approach to the maximum load, and in SFRC AE activity increases in the range of 40…50 s from the beginning of the experiment, which indicates the active development of microcracking at this time in the material. Considering the results of numerical simulations of stress distribution in the fiber composite, microcracks are first formed in the interfacial bond between the fiber and the matrix, and then propagate into the matrix. Due to the further increase of the load, the microcracks merge, forming macrocracks, which is accompanied by an increase in the generation of AE signals until the maximum load is reached. Further, the growth in the number of events slows down, entering the stationary mode. At this stage, a main crack has been already formed, and AE signals are generated due to microcracking, which accompanies its propagation.