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29 Table 8. Regression coefficients for model based Corrosion Potential, and as Table 12, which was developed for on Contact Angle Measurement after Lime Dip & the model based on the combination of Contact Angle Mea- Change in Corrosion Potential. surement after Lime Dip & Organic Residue Extraction for those residues determined to be stearate only. Predictor Coefficient Constant 1.209 Using Table 11 as the example, the first row shows the re- Contact Angle after Lime Dip (°) -0.007 sults of these two individual QC tests obtained for Source 349. Change in Corrosion Potential after 6 h (V)--as Received 1.233 Based on the regression model, the predicted mortar pull-out Adjusted Coefficient of Determination (R2 adj.) 0.73 stress at 0.1-in. slip is 0.264 ksi. The lower bound on the pre- diction interval for that combination of the two test results Table 9. Regression coefficients for model based on must be calculated specifically using those values and is Contact Angle Measurement after Lime Dip & Organic 0.131 ksi. Since 0.131 ksi is less than the mortar pull-out Residue Extraction (stearate-based residues). threshold of 0.313 ksi, this source fails to meet the minimum Predictor Coefficient threshold for the combined Contact Angle Measurement Constant 0.864 after Lime Dip & Change in Corrosion Potential performance. Contact Angle after Lime Dip (°) -0.006 For Source 548, the lower bound on the prediction interval Extracted Organic Residue (mg/cm2) -1.093 calculated for the specific combination of test results measured Adjusted Coefficient of Determination (R2 adj.) 0.98 for that source is 0.420 ksi, and this source "passes" since this value exceeds the 0.313 ksi threshold. The last column shows Table 10. Regression coefficients for model based whether that strand would be expected to pass based on the on Weight Loss on Ignition (LOI), Contact Angle actual pull-out test result. The conclusions reached based on Measurement after Lime Dip & Change in Corrosion the prediction interval and the actual pull-out test results are Potential. consistent for Sources 349 and 548. However, this is not always Predictor Coefficient the case; the evaluation process based on the prediction inter- Constant 1.203 val is by definition conservative, and some sources will be Weight Loss on Ignition (mg/cm2) -0.846 judged as failing that may not fail in the actual pull-out test. Contact Angle after Lime Dip (°) -0.006 A similar example is shown in Table 10, which was developed Change in Corrosion Potential after 6 h (V)--as Received 1.178 Adjusted Coefficient of Determination (R2 adj.) 0.76 for the model based on the combination of Contact Angle after Lime Dip & Organic Residue Extraction (for stearate- based residues). lower bound on the prediction interval, and the comparison of the lower bound and the actual pull-out test result with the Interpretation of Elemental Analyses specified mortar pull-out threshold of 0.313 ksi, for two of the Relative to Manufacturing Processes three multiple regression models. These are shown as Table 11, which was developed for the model based on the combination The atomic absorption and colorimetric analyses of wash of Contact Angle Measurement after Lime Dip & Change in solutions from strands from various sources indicated varied Table 11. Evaluation of prediction interval for model based on Contact Angle Measurement after Lime Dip & Change in Corrosion Potential. Mortar Pull-Out 0.1-in Slip Stress (ksi) Contact Pass/Fail* Pass/Fail* Strand Angle Change in Value Based on Experimentally Lower Bound Based on Source after Corrosion Predicted by Prediction Determined in of Prediction Pull-Out Test ID Lime Potential (V) Regression for Interval from Pull-Out Test Interval Result Dip (°) QC Results QC Tests 349 87 -0.289 0.156 0.264 0.131 Fails Fails 548 79 -0.080 0.623 0.576 0.420 Passes Passes 697 68 -0.154 0.606 0.559 0.417 Passes Passes 717 94 -0.241 0.206 0.276 0.136 Fails Fails 478 73 -0.272 0.409 0.38 0.232 Fails Passes 960 76 -0.211 0.409 0.435 0.303 Fails Passes 102 87 -0.266 0.315 0.291 0.161 Fails Passes 103 79 -0.172 0.397 0.463 0.331 Passes Passes 151 98 -0.322 0.273 0.149 0.003 Fails Fails * Threshold for passing is 0.313 ksi.
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30 Table 12. Evaluation of prediction interval for model based on Contact Angle Measurement after Lime Dip & Organic Residue Extraction (100% stearate only). Mortar Pull-Out 0.1-in Slip Stress (ksi) Contact Pass/Fail* Extracted Pass/Fail* Strand Angle Value Based on Organic Experimentally Lower Bound Based on Source after Predicted by Prediction Residue Determined in of Prediction Pull-Out Test ID Lime Regression for Interval from (mg/cm2) Pull-Out Test Interval Result Dip (°) QC Results QC Tests 717 94 0.117 0.206 0.211 0.176 Fails Fails 478 73 0.033 0.409 0.420 0.388 Passes Passes 960 76 0.035 0.409 0.401 0.371 Passes Passes 102 87 0.069 0.315 0.303 0.274 Fails Passes 151 98 0.037 0.273 0.276 0.240 Fails Fails * Threshold for passing is 0.313 ksi. levels of sodium, calcium, potassium, zinc, boron, and phos- are zinc phosphate and sodium borate, also known as borax. phate on the strand samples. The presence and concentration Lubricants typically consist primarily of either sodium stearate, of these elements is largely governed by the specific pre- calcium stearate, or some other fatty acid blend. treatment process and wiredrawing lubricants used in the Tables 13 and 14 show each strand source ranked in ascend- manufacturing of strand from each specific source, although ing order of concrete or mortar pull-out bond performance other sources of some of these elements may also be involved. together with the prominent elements removed during the The pretreatments commonly used in strand production extraction process, and the presumed pretreatment and Table 13. Compounds likely used in manufacture of each source--historic and recently manufactured strands. Concrete Pull- Prominent Presumed Presumed Strand out Bond Elements Pretreatment Lubricants Stress (ksi) calcium salt of 153 Ca, Zn, P zinc phosphate - fatty acid KSU-H Na, K, B borax Na/K stearate 0.209 SC-F Ca, Zn zinc phosphate calcium stearate 0.223 101 Na, K, B borax Na/K stearate 0.241 KSU-F Na, K, B borax Na/K stearate 0.241 102 Na, Ca, B borax Na/Ca stearate 0.441 SC-H Na, K, Zn zinc phosphate sodium stearate 0.472 151 Na, B borax calcium stearate 0.541 sodium salt of SC-IS Na, Zn zinc phosphate 0.682 fatty acid sodium salt of 103 Na, Zn zinc phosphate 0.944 fatty acid Table 14. Compounds likely used in manufacture of each source--OSU strands. Mortar Pull- Prominent Presumed Presumed Strand Out Bond Elements Pretreatment Lubricants Stress (ksi) calcium salt of 349 Ca, Zn, P zinc phosphate fatty acid and 0.156 resin 717 Na, Ca, Zn, P zinc phosphate Na/Ca stearate 0.206 478 Na, K, Zn, P zinc phosphate Na/K stearate 0.409 960 Na, K, Zn, P zinc phosphate Na/K stearate 0.409 calcium salt of 697 Ca, Zn, P zinc phosphate fatty acid and 0.606 resin Na/K salt of fatty 548 Na, K, Zn, P zinc phosphate 0.623 acid