As we were about to start production of the prestressed members for a new job, an engineer from the testing lab inspected the steel strand. He rejected it because it was too rusty. Is there a way to determine whether rusting will have a harmful effect on strand performance?
Determining an acceptable amount of rust on prestressing steel strand is a difficult for the inspector and producer. ASTM A 416 states, "Slight rusting, provided it is not sufficient to cause pits visible to the unaided eye, shall not be cause for rejection." The real concern is with pitting. Pits are stress raisers, reducing the strand's ability to withstand repeated or fatigue loading. Inspection is based upon the visible estimate of pitting in the strand. The PCI Manual suggests removing rust with a pencil eraser to expose any pitting. A more practical method is to use a Scotch Brite Cleaning Pad No. 96, which cleans a larger area for observation. After the strands are cleaned, a set of visual standards can be used to help field inspectors make proper judgments of strand suitability.
Figure 1 & 2
Figure 1 and Figure 2 show two different strand surfaces before and after pad cleaning. Pitting is visible in the after photo for Figure 2, so the strand should be rejected. Reference A. S. Sason, "Evaluation of Degree of Rusting on Prestressed Concrete Strand", PCI Journal, V. 37, No. 3, May-June 1992, pp. 25-30.