Issue 78

S. A. Mustafa et alii, Fracture and Structural Integrity, 78 (2026) 298-314; DOI: 10.3221/IGF-ESIS.78.18

P ULL - OUT TESTS

T

wo principal failure modes were identified during testing: Concrete Cone Failure, characterized by concrete breakout around the anchored bar, and Combined Bond–Concrete Failure, involving both adhesive bond degradation and concrete breakout. The first part of the study set out to understand how well the implanted reinforcement could bond with the existing concrete. By focusing on pull-out behavior, this allowed us to choose the best bond material type in a simple way, without the complexity of wall behavior. Tab. 2 summarizes the results of the tested 23 specimens. Two failure modes were reported; Concrete Cone Failure (most common) and bond failure. Concrete cone failure was observed in most CMB-bonded specimens, indicating that adhesive-steel bond strength exceeded concrete tensile capacity. This is the desired failure mode for implanted bars, as reported by other researchers [6,21]. The second failure mode was Combined Bond-Concrete Failure. This was Noted primarily in SIKA-bonded specimens and mostly in larger-hole configurations, suggesting interfacial weakness and slip initiation preceding concrete breakout.

Bar Diameter ϕ (mm)

Bonding Material

Pull-out force (kN)

Bond stress (Mpa)

Specimen

Hole Diameter

Failure mode

P-1 P-2 P-3 P-4 P-5 P-6 P-7 P-8 P-9

16 16 16 16 16 16 16 16 16 16 16 16 16 16 18 18 18 18 18 18 18 18 18

CMB CMB CMB SIKA SIKA CMB CMB CMB SIKA SIKA CMB CMB SIKA SIKA CMB CMB CMB CMB CMB CMB CMB CMB CMB

109.7

1.941 1.663 2.088 1.923 1.592 1.611 1.982 1.752 1.938 1.537 1.657 1.798 1.783 1.552 1.881 1.576 1.774 1.926 1.626 1.603 1.799 1.538 1.73

Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure

1.125 ϕ (18 mm) 1.125 ϕ (18 mm) 1.125 ϕ (18 mm) 1.125 ϕ (18 mm) 1.125 ϕ (18 mm) 1.25 ϕ (20 mm) 1.25 ϕ (20 mm) 1.25 ϕ (20 mm) 1.25 ϕ (20 mm) 1.25 ϕ (20 mm) 1.375 ϕ (22 mm) 1.375 ϕ (22 mm) 1.375 ϕ (22 mm) 1.375 ϕ (22 mm) 1.125 ϕ (20.25mm) 1.125 ϕ (20.25mm) 1.125 ϕ (20.25mm) 1.25 ϕ (22.5 mm) 1.25 ϕ (22.5 mm) 1.25 ϕ (22.5 mm) 1.375 ϕ (24.75mm) 1.375 ϕ (24.75mm) 1.375 ϕ (24.75mm)

94

118

108.7

90

101.2 124.5

110

121.7

Combined Bond–Concrete Failure

P-10 P-11 P-12 P-13 P-14 P-15 P-16 P-17 P-18 P-19 P-20 P-21 P-22 P-23

96.5

Concrete Cone Failure

114.5 124.2 123.2 107.2 119.6 100.2 125.3 136.1 114.9 124.6 139.8 119.5 110

Combined Bond–Concrete Failure

Concrete Cone Failure

Combined Bond–Concrete Failure

Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure Concrete Cone Failure

Combined Bond–Concrete Failure

Concrete Cone Failure

Table 2: Pull-out test results.

In the beginning, 16 pull-out specimens (with steel bars of diameter 16 mm) were tested with the studied three different hole diameters using the two bonding materials (CMB and SIKA). It should be noted that two specimens bonded with the Sika adhesive experienced premature loss of adhesion shortly after loading commenced and were therefore excluded from the analysis. Consequently, the number of valid Sika test repetitions was lower than that of the corresponding CMB specimens. The results of the remaining tested 14 pull-out specimens showed that (CMB) consistently outperformed (SIKA) across all hole diameters, as can be seen in Fig. 9. In addition, (CMB) bonding material showed fewer bond-related failures. This performance of (CMB) may be attributed to higher adhesive shear strength, or better chemical interaction

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