PSI - Issue 84

Anna Bontempi et al. / Procedia Structural Integrity 84 (2026) 1039–1046

1043

The CFRP bars were then positioned and instrumented with strain gauges (Figure 5a). Temporary wooden reference guides were installed at 1.5 m intervals to control the thickness of the sprayed mortar layer (Figure 5b). Prior to casting, the substrate was pre-wetted to a saturated-surface-dry condition. As mentioned before, the strengthening mortar was applied mainly by spraying, with local manual application in the areas where the temporary formwork guides were removed, after the target thickness had been achieved (Figure 5c).

(a)

(b)

(c)

Figure 5: CFRP strengthening bars (a); wooden temporary reference guide for the thickness of the overlay (b).

Sprayed specimens were cast to characterize the mechanical properties of the strengthening material under conditions representative of on-site application. Table 2 presents the FRM-PP main properties. With regard to the CFRP bars, experimental testing is particularly difficult to carry out. The bars employed in the present experimental program have not yet been tested, whereas additional bars with the same diameter were tested at an external laboratory. Therefore, the material properties adopted at this stage are based on both the results of the external laboratory tests and the values provided in the manufacturer’s technical datasheet, as reported in Table 3. Table 2: Strengthening mortar's properties. Table 3: CFRP bars properties.

CFRP bars

FRM-PP

Φ [mm] fu [MPa] E [GPa]

12

f c [MPa]

41

2540 168

Fibers’ shape

straight

Fibers’ length [mm] Class [UNI EN 14651]

24 4e

After curing of the mortar, the girder was instrumented with 45 devices to measure the applied load, deflections at midspan and at the loading points, support displacement, shear and flexural cracks width and strains in both the existing reinforcement and the strengthening bars. In addition, the slip between the existing concrete and the mortar overlay was monitored using four displacement transducers, positioned, as shown in Figure 6a, near the supports. The beam was tested under four-point loading (Figure 6b) up to collapse, which occurred due to rupture of the CFRP bars.

(a)

(b)

Figure 6: potentiometric transducer for the measurement of the slip between the existing section and the overlay (a); load scheme on 4 points (b).