Recommended Practice on Strand Bond-Recommended Practice on Strand Bond

Video Transcription

Video Summary

This PCI webinar, presented by Clay Naito of Lehigh University, focuses on the Recommended Practice (RP) for Strand Bond in prestressed concrete applications, particularly the updates in the 2020 and 2025 PCI RPs. Strand bond—critical for transferring stress and ensuring structural integrity—relies on four mechanisms: adhesion, mechanical interlock, friction, and wedging action (Hoyer’s effect). Good strand bond is essential for transfer length, development length, flexural and shear strength, and overall durability in pretensioned concrete products.<br /><br />Historically, various tests have measured strand bond quality, culminating in the ASTM A1081 test, developed from extensive research, to evaluate strand surface bond capacity in a standardized mortar matrix. PCI's 2020 RP sets acceptance criteria for this test, requiring a six-quarter running average bond strength of 14,000 lbs-force, with no quarterly average below 12,000 lbs-force.<br /><br />The 2025 RP maintains the ASTM A1081 criteria but adds practical quality assurance (QA) and quality control (QC) measures at precast plants to better evaluate bond performance in real concrete mixes under plant-specific conditions. Two approved QC tests are the strand block pullout and strand drawing tests, which assess bond performance with actual plant materials and processes. If strand test results fall below acceptance levels, these plant-level tests can demonstrate "fitness for service," providing acceptance pathways without compromising code development lengths.<br /><br />The updated RP clarifies strand types (standard vs. high bond), includes more strand sizes, and supports application in bridge design, noting AASHTO LRFD’s 2027 inclusion of these practices. PCI emphasizes ongoing research and risk-based QA/QC approaches to adapt to evolving materials and plant practices. The webinar concludes with Q&A, addressing applications to emerging strand types like 300ksi steel strands.

Keywords

PCI webinar

Strand Bond

prestressed concrete

Recommended Practice 2020

Recommended Practice 2025

ASTM A1081 test

quality assurance

quality control

strand block pullout test

AASHTO LRFD 2027