PSI - Issue 44

Giuseppe Bramato et al. / Procedia Structural Integrity 44 (2023) 2302–2309 Author name / Structural Integrity Procedia 00 (2022) 000–000

2306

5

4. Experimental results 4.1. Direct tensile test on FRCM samples

The tensile test results on FRCM coupons are illustrated in Fig. 6 in terms of stress-strain relationship. In detail, the stress refers to the cross-section of the fabric and the strain is related to the GL zone. The specimens made with lime-based mortar exhibited a quasi bi-linear behavior, while in case of cementitious matrix the evolution of the cracks within the matrix is more evident.

1200

1200

1000

1000

800

800

σ [ MPa ]

σ [ MPa ]

600

600

400

400

200

200

0

0

0,000 0,005 0,010 0,015 0,020 0,025 0,030 0,035

0,000 0,005 0,010 0,015 0,020 0,025 0,030 0,035

ε [-]

ε [-]

(a)

(b)

Fig. 6. FRCM samples stress-strain curves: (a) lime-based mortar, (b) cementitious mortar In Table 1 the test results were reported in terms of cracking strength, ultimate strength and deformation and slope of the un-cracked phase. In detail cracking strength, graphically defined at the slope change point, represents the tension at which the first crack is opened, while the slope ( E I FRCM ) was computed as the secant modulus passing through two characteristics point: the origin (0,0) and the transition point where the first crack appears. Table 1. Direct tensile test on FRCMs results: lime-based mortar. Label s cr,FRCM [ MPa ] s u,FRCM [ MPa ] e u,FRCM [ - ] E I FRCM [ GPa ] Label s cr,FRCM [ MPa ] s u,FRCM [ MPa ] e u,FRCM [ - ] E I FRMC [ GPa ]

FRCM_B_R_1 FRCM_B_R_2 FRCM_B_R_3 FRCM_B_R_4 FRCM_B_R_5 FRCM_B_R_6 FRCM_B_R_7 FRCM_B_R_8

330.95 300.53 250.21 325.11 232.53 266.42 363.04 282.05 293.86 15.08%

749.46 631.46 661.11 801.29 632.40 783.38 846.58 569.44 709.39 13.92%

0.024 0.023 0.023 0.023 0.022 0.024 0.025 0.019 0.023

554.06 584.25 502.59 637.58 454.38 529.92 793.83 470.07 565.84 19.42%

FRCM_B_M_1 FRCM_B_M_2 FRCM_B_M_3 FRCM_B_M_4 FRCM_B_M_5 FRCM_B_M_6 FRCM_B_M_7 FRCM_B_M_8

600.03 351.47 672.61 582.46 628.02 754.91 520.12 666.25 596.98 20.30%

873.36 817.79 1061.99 1147.81 1031.63 1114.56 1107.78 917.73 1009.08 12.24%

0.028 0.018 0.025 0.025 0.021 0.027 0.029 0.026 0.025

1332.08 661.87 914.56 1096.03 1325.87 1031.46 1112.49 1397.91 1109.03 22.20%

Mean

Mean

7.90 %

14.80%

Cov

Cov

It was observed that the CoV of ultimate tensile stress s u,FRCM and strain e u,FRCM are lower than cracking stress and un-cracked slope ones. This difference is probably due to the brittle behaviour of the mortars and their mechanical properties. In fact, as well known, the first stage of the curve is probably strongly influenced by the mechanical properties of the mortar, while the last phase is more linked to the mechanical performance of dry fibre. It was observed that the mechanical properties of mortar influenced the results in terms un-cracked slope, cracking and ultimate stress and ultimate strain with an increment of 96.00%, 103.15%, 42.25%, 8.70% respectively. As expected, the influence of mechanical properties of the mortar was lower in the second phase. However, the obtained data need to be strengthened with a large experimental campaign. In order to evaluate the influence of the kind of mortar the results were elaborated as reported in Fig. 7. The experimental curves were grouped for evaluating the average curve the scatter area was defined. In both case the expected trilinear behavior could not always be found. It seemed that the shape of the curves wasn’t influenced by the kind of mortar. The ratio between the average FRCM coupons ultimate tensile strength and the experimental dry fiber