Click for next page ( 37


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 36
36 Regular QC testing should decrease the likelihood that poor Future Work bonding strand would reach the market. Lots of strand exhibit- ing unacceptable behavior identified by these test methods Although a variety of researchers has made conclusions should then be tested further using the Level II organic residue about the most appropriate mechanical test methods for extraction test and mechanical pull-out testing. evaluating strand bond, the limited results of this research The determination of thresholds for two of the individual program suggested that concrete pull-out test results corre- QC tests (Contact Angle Measurement after Lime Dip and lated better with transfer length test results than with mortar Change in Corrosion Potential of Strand) was possible based pull-out test results. Although the mortar pull-out test demon- on the relationships between the QC test and the mortar pull- strated good correlation, it is not clear that this is the best out test results for this sample set; however, these thresholds test for measuring the strand bond quality. Further work is are conservative. The available data were not sufficient to allow needed to resolve the questions related to performance-based threshold determination for the other two individual methods (i.e., mechanical) tests of strand bond that were left unanswered with the same constraints. The threshold determination by the elimination of further development of mechanical tests process is governed by the prediction intervals, which are de- from this research program. It is recommended that a multi- termined by the uncertainty in the regression results. Sources laboratory test program be conducted following the concepts of uncertainty, which ideally would be minimized, include outlined by ASTM E1169-07 Standard Practice for Conduct- inability of the test methods to predict bond, scatter in both ing Ruggedness Tests (ASTM 2007) and conducted at qualified the QC and mortar pull-out test results, close grouping of laboratories that are not already involved in the historically sources in terms of bond performance, and a limited number contentious discussions regarding strand bond issues. of data points for the regression analysis. Although a small task if an effective test method can be de- Although a significant amount of work and scientific rigor fined, further work is also needed to ascertain the extent and has gone into the development of the thresholds, they should significance of local variations in the strand performance not be considered absolute. Additional data could possibly be within a single spool. During the program outlined in this used to reduce the uncertainty alluded to above and may allow document, the relationship between test results and proxim- a reduction in the thresholds. Specifically, if the QC tests were ity on the strand could not be tracked. Nevertheless, such a conducted on the samples included in the quarterly pull-out variation has direct impact on the evaluation of any test testing program currently being conducted by NASPA, this method, since such variation would become combined with information would be valuable to further refine the regression variations related to the test method itself. relationships. As stated, additional work is needed to refine the thresholds Another possible means for implementing these test meth- for bond acceptability that will be used to establish alert ods is the development of process-specific regression models (pass/fail) thresholds for the QC test results. The incorporation and thresholds. The dataset for this study included strand of additional data into the regression analysis would improve sources manufactured with a number of different pretreatment the confidence in the validity and usefulness of the QC test and lubricant processes. Limiting the data included in the re- methods and may also allow less restrictive thresholds to be gression analysis to a single production process, such as might defined. be done at an individual strand manufacturing facility, would The threshold on the mortar pull-out test result adopted by likely significantly improve the correlation of the QC test NASPA is based on development length testing of four strand methods, since the QC test results would be influenced mainly sources. For the sake of the QC threshold determination con- by variations in concentration of a specific lubricant and pre- ducted during this program, it has been assumed that this treatment and not the simultaneous variations of a variety of threshold is a well-defined absolute. However, although addi- lubricant and pretreatment chemistries and concentrations. tional work to refine this threshold would require a significant A better correlation would also allow the development of less effort, such an effort would be valuable and would provide restrictive thresholds. greater confidence in the performance of strand.