Experimental Investigation of Prestressing Strand Bond on Behavior of Concrete Members

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Title: Experimental Investigation of Prestressing Strand Bond on Behavior of Concrete Members

Author(s): Jan Laco and Viktor Borzovic

Publication: Structural Journal

Volume: 114

Issue: 1

Appears on pages(s): 15-24

Keywords: bond; oil-based corrosion protection agents; post-tensioned structures; prestressing units; pullout tests

Date: 1/1/2017

Abstract:
This paper deals with experiences and results from experimental research focused on the bond of post-tensioned prestressing strands coated with oil-based corrosion protection and injected with grout to bond the tendons. The experimental research was split into two stages. The first stage was dedicated to testing the bond of sevenwire strands through single-strand pullout tests. The main objective of this stage was to compare the different specimens depending on their construction, where different bond situations were intentionally created. The main variables included the use of different types of coatings, time impact on the degradation of the corrosion protection, and the presence of the corrugated duct. The results from the pullout tests demonstrated significant bond loss in relation to the different types of corrosion protection. Where emulsifiable oil was used, the decrease of bond was approximately 67%, and where another protection material was used (which can be described as a thixotropic gel compound), a bond decrease of approximately 17% was observed. These results raise the question whether strands coated with oil-based corrosion protection can be assumed to be either fully bonded or mostly unbonded, which affects the design approach. In the second stage, the assumptions based on the previous pullout tests were tested with full-scale beam tests. This consisted of bending tests of two-span continuous girders, post-tensioned with seven-wire strands with various degrees of bond. The various bond conditions led to different behaviors of the beams under the applied loads. Based on the results from the beams, it was possible to establish whether the assumptions obtained from the pullout tests are pertinent to the real structural behavior.