Interlaboratory Study of the Standard Test Method for Evaluating Bond of Seven-wire Steel Prestressing Strand

July 15, 2020
Publication: Precast/Prestressed Concrete Institute Journal
Author(s): Ashwin Poudel Rémy D. Lequesne William N. Collins Enrico Lucon David Darwin

An interlaboratory study involving 19 laboratories was conducted to quantify the precision of ASTM A1061-16, Standard Test Methods for Testing Multi-Wire Steel Prestressing Strand, which describes methods for measuring yield strength, elastic modulus, elongation, breaking strength, and relaxation. Relaxation measurements were outside the project scope. Yield strength, elastic modulus, and breaking strength results showed low variability, with reproducibility limits less than 4%, 10%, and 3% of the mean reported values, respectively. Elongation results exhibited high variability, resulting in a reproducibility limit close to 50% of the mean reported value. Compliance with the requirements of the standard was an issue, with 74%, 82%, 32%, and 100% of laboratories submitting valid results for yield strength, elastic modulus, elongation, and breaking strength, respectively. Strand fracture location was sensitive to the type of grips used for testing. Several changes to ASTM A1061 are proposed to improve clarity and precision.

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