Bond Strength of Reinforcing Bars with Varying Encapsulation Qualities

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Title: Bond Strength of Reinforcing Bars with Varying Encapsulation Qualities

Author(s): Pasquale Basso Trujillo, Marc Jolin, Bruno Massicotte, and Benoît Bissonnette

Publication: Structural Journal

Volume: 115

Issue: 6

Appears on pages(s): 1707-1717

Keywords: artificial voids; beam end; bond strength; encapsulation; hypothesis testing; shotcrete; sprayed concrete; voids

Date: 11/1/2018

Abstract:
The encapsulation quality of reinforcing bars represents a common concern among structural engineers when shotcrete structures are designed. Because little scientific information is available regarding the potential bond strength reduction of bars with adjacent defects along their length, ASTM A944-10 “beam-end” specimens with different encasement qualities were tested. To limit the size variability of voids when spraying, voids were created using silicone inserts, which also made it possible to control their exact size and position. Artificial voids were encased with a placed shotcrete mixture and transversal lengths of up to 30% of the bars’ perimeter were investigated. A low water-binder ratio (w/b) was employed to guarantee an insignificant bleeding capacity of the mixture as is commonly observed in shotcrete. The results support previous investigations by showing that transversal void lengths beyond 20% induce a considerable change in the slope of the stress-slip curve and an important reduction of the ultimate bond stress.