Issue 78

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

Prior to the application of the adhesive, each hole was cleaned out to remove drilling dust and debris since they can reduce the bond between materials. This procedure was conducted by brushing the inside of the hole using a steel brush, and then compressed air was blown into the hole until removing all the dust. Once assured of the hole cleanliness and dryness, the CMB adhesive was injected with a dual cartridge applicator. The adhesive was applied from the bottom of the hole upward to avoid any air entrapment along the whole depth. Bar insertion and alignment Once the hole was filled by the adhesive, the reinforcement bar was inserted immediately to avoid premature hardening of the adhesive. Each reinforcement bar was pushed accompanied by gentle rotation to ensure an even distribution of adhesive all over the bar surface. Care was taken to maintain the specified embedment length in each specimen, in addition to the alignment of the reinforcement bars to be consistent with the alignment of the vertical reinforcement configuration of the shear wall. Maintaining proper alignment at this step was very important to ensure that all bars would work together effectively during cyclic loading. To maintain the required reinforcement configuration during adhesive curing, the locations of all bars were established and verified before drilling based on the designed reinforcement layout. After insertion, the bars were manually adjusted to ensure the specified spacing, verticality, and embedment depth. The high viscosity of the adhesive system, together with careful inspection during the curing period, was sufficient to prevent bar movement and maintain the required alignment until complete adhesive hardening was achieved. Curing conditions All pull-out specimens and full-scale shear walls, the specimens were cured to ensure consistent strength prior to any kind of test being conducted. They were placed under moist curing conditions to ensure proper hydration process in the concrete and uniform strength gaining. Once the concrete was cured, the holes were drilled and the steel bars were implanted, following the process described above. Then the specimens were kept untouched until the adhesive was fully hardened before the commencement of the pull-out tests, and before the shear walls were cast. Prior to this, each implanted bar was checked manually and inspected visually to insure no shrinkage, cracks, movement in the bars or slippage. After casting the wall bodies of the shear wall specimens, they were cured to ensure that they reached the designed compressive strength. Pull-out test setup Pull-out tests were conducted using a standard testing machine following ASTM pull-out testing procedures. The concrete cylinder was restrained from upward movement, while the steel bar was gripped by the machine, as shown in Fig. 6. Tensile force was applied gradually until failure. The pull-out tests were performed under displacement-controlled loading using a universal testing machine. A constant displacement rate of 1 mm/min was maintained throughout the test until failure occurred. This allowed evaluating the bond between the steel, adhesive, and concrete without interference from other failure modes. During testing, the load was recorded continuously by the machine’s built-in sensors. Observations were made immediately after failure to document the characteristics of the failed interface. After each test, the failure mode was identified by examining the bar and the condition of the concrete around the hole. Failures were categorized as concrete failure, bond failure, or a combination of the two.

Figure 6: Pull-out Test Setup.

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