PSI - Issue 64

Maria Antonietta Aiello et al. / Procedia Structural Integrity 64 (2024) 1549–1556 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1554

6

1c, for both universities. These measurements must be pre-adjusted to account for the elastic elongation of the bar between the top side of the concrete cube and the anchor system of the LDTs.

Table 3. Main data and test results

Concrete type

Age of test [days]

R cm [MPa]

F max [kN] 32.4 27.6 34.8 38.6 42.5 26.2 30.0 35.5 42.0 44.9 38.5 43.5 35.0 20.5 37.2 33.0 33.9 44.9 41.6

F max,av [kN]

τ max [MPa]

τ max,av [MPa]

s max [mm]

s max,av [mm]

F u,80% [kN]

s u,80% [mm]

s u,80%,av [mm]

Lab

ID Specimen

GC_S_1 GC_S_2 GC_S_3 GC_S_1 GC_S_2 OC1_S_1 OC1_S_2 OC1_S_3 OC4_S_4 OC4_S_5 OC1_S_1 OC1_S_2

GC GC GC GC GC

28 28 50

43.7 43.7 48.2

14.3 12.2 15.4 17.1 18.8 11.6 13.2 15.7 18.6 19.8 17.0 19.2 14.6 15.6 13.7 14.2 18.8 17.4 8.5

0.54 0.50 0.80 0.55 0.46 0.96 0.79 0.37 0.88 1.18 1.00 0.82 2.43 1.46 2.24 1.63 1.77 2.58 2.53

25.9 22.1 27.8 30.7 20.9 24.0 28.4 33.6 35.9 34.8 28.0 16.4 29.8 26.4 27.1 36.0 33.3 34

1.87 2.29 2.33 2.29 2.31 1.96 2.36 1.96 2.58 3.02 3.02 2.31 4.17 2.42 4.16 3.55 3.33 4.30

29.99 (11.46%)

0.52 (5.06%)

2.08 (14.28%)

13.3

UniSa

-

-

-

-

130 130

50.0* 50.0* 47.1 47.1 47.1 50.9 50.9 52.0 52.0 52.0 52.4 52.4 51.4 51.4 50.6 * 50.6 *

40.6 (6.80%)

0.51 (12.60%)

2.30 (0.61%)

UniSal

17.9

OC1 OC1 OC1 OC4 OC4 OC1 OC1

50 50 50 28 28 50 50 50 32 32

30.55 (15.44%)

0.70 (42.82%)

2.06 (12.84%)

13.5

UniSa

43.43 (4.72%)

1.03 (20.60%)

2.8 (11.11%)

19.2

135 135

30.83

41.0 (8.62%)

0.91 (13.99%)

2.67 (18.84%)

UniSal

18.1

OC2_G1_1 OC2 OC2_G1_2 OC2 OC2_G1_3 OC2 OC3_G1_4 OC3 OC3_G1_5 OC3 OC2_G1_1 OC2 OC2_G1_2 OC2

36.11 (4.35%)

2.34 (5.75%)

4.17 (0.17%)

15.1

UniSa

33.43 (1.93%)

1.70 (5.82%)

3.44 (4.52%)

14.0

132 132

43.3 (5.40%)

2.56 (1.38%)

4.33 (0.82%)

Unisal

18.1

4.35 * Analytically estimated according to EC2 (2005); values in bold are not included in the average of results for the corresponding set All the specimens exhibited a pull-out failure since the bar was pulled out from the cube without any visible damage on concrete cover. Fig. 2 shows comparisons in terms of bond stress versus free-end slip (  -s) curves for identical tests performed in the two involved universities. In particular, Fig. 2a and 2b show the comparison between the bond performances exhibited by ordinary concrete and green concrete when the reinforcing bar is made of steel; Fig. 2 (c) and (d), instead, show, in the case of OC, the comparison in terms of bond performance between steel and GFRP bars. In the case of GC and OC with steel bar (Fig. 2a and 2b), the experimental behaviors of identical samples performed in the two laboratories are quite comparable. The (  -s) curves are characterized by an initial ascending branch in which the first part is governed by the chemical adhesion while for the remaining one the mechanical interlocking governs the bond behavior. In the first stage, when the steel-concrete stresses transfer mechanism is given by the chemical adhesion, the relative slips are almost zero. Once the chemical adhesion is overcome, a diffuse micro-cracking in the steel-concrete happens in the interfacial transition zone and the slip increases. In this second stage, the transfer mechanism is driven by the mechanical interlocking. After the attainment of the peak bond stress and the subsequent stress decay, a horizontal residual stress plateau is observed. In this case, similar bond strength values have been obtained for GC and OC1 with steel bars, despite a slightly difference in s max values. A barely significant difference between the two kinds of concrete was observed in the final branch of the bond stress – slip curves, in which it has been observed a slightly higher residual bond strength shown by green concrete; probably, this is due to the higher porosity of GC that can improve bond performances (Romanazzi et al. 2022). Conversely, the differences between traditional steel bars and FRP bars are more significant than those already seen in the comparison between conventional and unconventional concrete (Fig. 2c and 2d). In this case, indeed, the