PSI - Issue 39

Andrea Pranno et al. / Procedia Structural Integrity 39 (2022) 688–699 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 7. Load versus mid-span deflection curves of plain steel bar-reinforced RC beams and of steel bar-reinforced UHPFRC beams enhanced with different content of GNPs (0%, 0.05%, and 0.1%).

Secondly, the mechanical behavior of the steel bar-reinforced UHPFRC beams without (black curve) and with the addition of graphene nanoplatelets (red and blue curves related to 0.05% and 0.1% of GNP volume fraction, respectively). As expected, the nano reinforced beams show greater load-carrying capacities compared with the standard reinforce concrete beams with increasing performance for increasing content of GNP. The numerical results highlighted that that the combination of reinforcements at the microscopic and nanoscopic scales considerably improves the flexural behavior of UHPFRC beams, in terms of load-carrying capacity and energy absorption. In detail, concerning the UHPFRC case, an increase of 11% and 20% in the absorbed energy, as well as increments of 4.8% and 11% in the first yielding load level are reached with the content of graphene nanoplatelets equal to 0.05% and 0.1% volume fraction, respectively. Figure 8 shows the deformed configurations and the color maps for all the investigated UHPFRC beams at a load level equal to 65kN and has been highlighted a substantial reduction in the crack pattern development for the beam with the highest GNP volume fraction (0.1%) compared to the other investigated cases. To investigate more deeply the fracture processes developed during the four-point bending test the crack width spacing, the average crack width, and the beam deflection have been measured and reported in Table 2.

Table 2. Average crack width, crack spacing and beam deflection at a load level of 65 kN.

Average Crack Width [mm]

Crack Spacing [mm]

Beam Deflection [mm]

UHPFRC

0.093 0.080 0.064

91 84 84

3.80 3.30 2.75

UHPFRC GNP 0.05% UHPFRC GNP 0.1%

The obtained results highlighted an increase of the bending stiffness and a reduction of the average crack width and crack spacing demonstrating an overall improvement of the mechanical performance of the UHPFRC with the addition of graphene nanoplatelets as reinforcement.