PSI - Issue 44

Hasan Borke Birgin et al. / Procedia Structural Integrity 44 (2023) 1624–1631 Hasan Borke Birgin et al. / Structural Integrity Procedia 00 (2022) 000–000

1626

3

Fig. 1. Preparation procedure for concrete samples tested in this research.

Fig. 2. Preparation of smart beams: (a) placement of the small samples and pouring of concrete; (b) beams after curing, instrumented for the electrical tests.

3.1. Components

The smart full-scale beam and the small samples had a matrix material made of concrete (cement, sand, gravel, water) where was added a carbon-based filler. The cement was Portland type 42.5R, the sand and the gravel were from quarry, fillers were constituted by carbon microfibers type Sigrafil, provided by Sgl Carbon (diameter 5 µ m, length 6 mm). The sand had dimensions of 0 - 3 mm, while the gravel had maximum dimensions of 6 mm and 22.4 mm, for small cubes and full-scale beams, respectively. This difference was due to the small dimensions of the cubes (i.e. 40 mm of side) which were not suitable with great coarse aggregates. The cubes were produced in the Laboratory of Testing Materials of the Department of Civil and Environmental Engineering of Perugia, while the full-scale beams were produced by a construction company, under the control of the authors. 3.2. Preparation of samples The smart concrete with carbon microfibers was adopted for casting small cubes with a side of 40 mm and a bulk beam 150 x 250 x 3200 mm 3 . In both cases, the carbon microfibers were added mechanically at the percentage of 0.05%, in weight with respect to the cement. The cubes were instrumented with two 0.8-mm copper wires placed at a distance of 20 mm, and by two strain gauges applied at the lateral sides. After their curing at laboratory conditions, the cubes were isolated with insulating tape, and then embedded at the intradox of the reinforced concrete beam and fixed to the longitudinal rebars (Fig. 2(a)). The cables connected to the electrodes, and to the strain gauges were carefully protected during the preparation of the beam, and taken outside the beam. For the preparation of the full-scale beams, a steel reinforcement composed of three rebars with a diameter of 10 mm were placed at the bottom side of the beam, at a distance of approximately 3.5 cm from the external side. Stirrups with a diameter of 8 mm were placed at a distance of 170 mm in the central zone, and of 100 mm at the ultimate parts. The beams were simply supported by two steel plates partially embedded, at a mutual distance of 3000 mm. The bulk beam was instrumented with copper wires with a diameter of 0.8 mm, placed at a mutual distance of 400 mm throughout the structural element.