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21 and modified behavior may be caused by ambient humidity depressions on the surface. Based on metallographic studies, and temperature differences. Such variations are typically a strong correlation between surface roughness and bond accommodated by modifying line speed. strength was not apparent, but only a very limited number of No QC testing is conducted on lubricants used in strand strand cross-sections were evaluated because of the labor- production. intensive nature of this technique. However, EIS studies were Until recently, the post-production strand QC testing at used to measure the capacitance per nominal unit area, a prop- strand production facilities generally consisted of periodic erty controlled by the surface area of the strand on a micro- relaxation strength and modulus of elasticity testing, with scopic scale. This microscopic surface area is linked to the no specific tests performed to verify bond performance. microstructural roughness. A strong correlation between bond However, in 2007, a 2-year quarterly program of NASPA strength and a parameter equal to the ratio of the lubricant bond tests (pull-out tests from mortar) was initiated, and concentration and this capacitance per nominal unit area was initially included the participation of 10 NASPA members found. Since the lubricant concentration is also based on the supplying strand to the domestic U.S. market. One pro- nominal surface area, this parameter is a measure of the rela- ducer has since stopped supplying to the domestic market tive concentration of lubricant residue per actual microscopic and has dropped out. Currently, this program consists of surface area. tests conducted on lengths of strand randomly sampled Petrographic studies have shown that there is a difference from the first 500 ft. of a 1500-ft. pack of strand supplied in cement hydration at the interface of strand compared to for testing. This testing is performed under the supervision the surrounding concrete that appears to be a direct result of of Bruce Russell of OSU, who has been contracted to per- the presence of residual lubricant. Cement hydration studies form this work. Three NASPA bond tests, consisting of six comparing the interfacial features of as-received strand with strands each are performed. Only 0.5-in. diameter strands strand that had been cleaned and stripped of its residual lubri- have been included in this effort. cant demonstrate that the cement particles at the strand in- Strand producers demonstrated interest in the chemistry- terface of the as-received strand appears to be less hydrated based surface characterization methods and expressed than the surrounding cement, while the interface of the a willingness to use such methods in their plants, if their cleaned strand is similar to the bulk cement. This reduction efficacy can be proven. in cement hydration at the interface was also seen in studies of the transfer zone of a concrete sample containing strand that exhibited poor bond. The residue on the strand appears Findings of Supplemental to have the ability to affect hydration of the cement immedi- Investigations ately adjacent to the strand. Detailed results of supplemental investigations are presented These supplemental investigations, although not directly in Appendix D. The significant findings are summarized here. involved in formulating the QC tests, provided a greater un- The supplemental investigations focused on the strand and derstanding of concrete, lubricant, and strand interaction. strand/concrete interface, in an attempt to gain a greater un- The presence of residual lubricant on the surface of the strand derstanding of some factors that may influence bond. Studies is a result of the amount of lubricant used, heating proce- of surface roughness and the relationship between surface dures, washing procedures, and the microscopic surface roughness and lubricant residue were carried out using met- roughness. Residues of chemical surface treatments and/or allographic methods, scanning electron microscopy with lubricants appear to have an impact on cement hydration energy dispersive X-ray spectrometry, and electrochemical adjacent to the strand, possibly also reducing the strength of impedance spectroscopy (EIS). The effect of lubricant residue the bond. on cement hydration was evaluated with petrographic and chemical investigations of the concrete immediately adjacent Findings of Evaluation to the strand. of Test Methods Possible relationships between surface-roughness charac- teristics (together with the concentration of residual lubricant Detailed results of the testing program are presented in on the strand) and bond strengths were assessed. The relation- Appendix B. The conclusions of the testing program are ship between surface roughness and bond strength is compli- summarized here. cated by the presence of residual lubricant, as demonstrated by scanning electron microscopy/energy dispersive X-ray Mechanical Testing spectroscopy (SEM/EDS) analysis; higher concentrations of residual lubricant appear to be associated with greater surface As mentioned, the transfer length test is considered the roughness, with the lubricant occurring predominately within most realistic measure of bond performance and was used as