Precision Estimates for AASHTO Test Method T308 and the Test Methods for Performance-Graded Asphalt Binder in AASHTO Specification M320 (2005)

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18 CHAPTER 4: CONCLUSIONS AND RECOMMENDATIONS 4.1 GENERAL This study was conducted to prepare precision estimates for AASHTO standards found in AASHTO Standard Specification M320, “Performance-Graded Asphalt Binder”, and for AASHTO Standard Test Method T308, “Determining the Asphalt Binder Content of Hot-Mix Asphalt (HMA) by the Ignition Method”. The study conclusions and recommendations are as follows: 4.2 CONCLUSIONS AND RECOMMENDATIONS RELATED TO SPECIFIC STANDARDS 4.2.1 AASHTO T308-04, Determining the Asphalt Binder Content of Hot-Mix Asphalt (HMA) by the Ignition Method Commentary: The current precision estimates for T308 are based on the results of four aggregate types, four replicates, and twelve participating laboratories using Method A only. This is a small number of laboratories compared to the number of labs in the AMRL proficiency sample program. The small number of laboratories may not capture all of the variability inherent in the test method. The precision and bias statement in Section 4.4 is based on testing by over 350 laboratories on three different paired aggregate samples and applies to both Method A and Method B. Conclusion: The precision statement derived from analyzing the AMRL PSP data comes from much larger data sets than the current estimates. These estimates reflect variability that is reflective of what is occurring in the laboratory setting. Recommendation: It is recommended that the precision and bias statement in Section 4.4 be adopted for T308. 4.2.2 AASHTO T48-04, Flash and Fire Points by Cleveland Open Cup Commentary: The precision estimates for flash point currently published in T48-04 are based on testing over ten years ago by eleven laboratories. Though seven oils were used in the study, only one asphalt (AC 10) was used. The precision and bias statement in Section 4.5 is based on testing by over 98 laboratories on eight different paired binder samples and four binder grades. Over time, the results of AMRL proficiency sample testing indicate that the degree of precision given in the current precision statement cannot be obtained. Two possible sources of variation are the

19 difficulty in achieving the required rate of temperature rise and improper application of barometric correction. Conclusion: The precision estimates for flash point should be revised. Recommendation: It is recommended that the precision and bias statement for “flash point” in Section 4.5 be adopted for T48. 4.2.3 AASHTO T228-04, Specific Gravity of Semi-Solid Bituminous Materials Commentary: The study showed that single-operator precision is slightly better than currently indicated in the test method and that the multilaboratory precision is significantly better than currently indicated. Information regarding testing of soft pitch tar or testing of asphalt at 15.6 °C was not available from AMRL data, therefore the precision estimates for those tests were not considered for revision by this study. Conclusions: The precision estimates currently published in T228-04 for specific gravity of asphalt determined at 25 °C should be revised. Recommendations: (1) It is recommended that the precision and bias statement in Section 4.6 for determining the specific gravity of asphalt at 25 °C replace the precision and bias statement stated in section 14 of ASTM D70. (2) It is recommended that the precision estimates for “pooled values” for testing soft tar pitch and asphalt at 25 °C given in the current precision and bias statement of T228-04 be disregarded. 4.2.4 AASHTO T240-03, Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test) Commentary: The precision statement currently published in T240-03 does not include a precision estimate for the loss of mass determination. Test method T240-03 does not contain a statement regarding bias.

20 A review of the data showed that the standard deviation changed for different values of mass loss. Coefficient of variation also was not appropriate since standard deviation was not proportional to mass loss. However, the review indicated that the standard deviation can be expressed as a function of the mass change (x) by using an equation. Conclusions: The high coefficient of determination for the derived equation indicates it is the most informative form of precision for this method. Since this approach has not been commonly used in precision statements, a table with stratified estimates was included to assist the user. Recommendations: (1) It is recommended that the precision and bias statement in Section 4.7 be adopted for T240. (2) The materials included in this study did not gain mass during testing. It is recommended that a study be conducted to develop precision estimates for materials that gain mass. 4.2.5 AASHTO T313-04, Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR) Commentary: The AMRL proficiency data analyzed in this study is more up to date than the AMRL data used for the current estimate of precision and reflect recent changes to the test method. The results of the study show that testing precision is better than indicated by the precision estimates currently provided in the test method. Conclusion: The precision and bias statement currently published in T313-04 should be revised. Recommendation: It is recommended that the revised precision and bias statement in Section 4.8 be adopted for T313. 4.2.6 AASHTO T314-04, Determining the Fracture Properties of Asphalt Binder in Direct Tension (DT) Commentary: A precision and bias statement is not provided in T314-04.

21 Conclusion: A precision and bias statement is needed. Recommendation: It is recommended that the precision and bias statement in Section 4.9 be adopted for T314. 4.2.7 AASHTO T315-04, Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) Commentary: The AMRL proficiency data analyzed in this study is more up to date than the AMRL data used for the current estimate of precision and reflect recent changes to the test method. The results of the study show that testing precision is better than indicated by the precision estimates currently provided in the test method. During the analysis of DSR data on “original” binder, the study observed that the “phase angle” and the testing variation for the determination of the “phase angle”, δ, appeared to be different for the modified binder analyzed in this study when compared to the unmodified binders (See Appendix C). The difference between modified binders and unmodified binders was not apparent for determinations of G*, G*/sinδ, or G*·sinδ. It should be noted that only one modified binder was included in the study and that precision estimates for the determination of “phase angle” are not included in the proposed precision and bias statement contained within this report. Conclusion: The precision and bias statement currently published in T315-04 should be revised. Recommendations: (1) It is recommended that the precision and bias statement in Section 4.10 be adopted for T315. (2) It is recommended that an additional study be conducted using modified binders if precision estimates are desired for the phase angle. 4.2.8 AASHTO T316-04, Viscosity Determination of Asphalt Binder Using a Rotational Viscometer Commentary: The AMRL proficiency data analyzed in this study is more up to date than the AMRL data used for the current estimate of precision and reflect recent changes to the test method. The results of the study show that testing precision is better than indicated by the precision estimates currently provided in the test method.

22 Conclusion: The precision and bias statement currently published in T316-04 should be revised. Recommendation: It is recommended that the precision and bias statement in Section 4.11 be adopted for T316. 4.3 GENERAL CONCLUSIONS AND RECOMMENDATIONS The analysis technique described in this study can be used effectively to analyze paired proficiency sample test data sets to obtain robust single operator and multilaboratory precision estimates for a variety of test methods. A comparison of the 95% difference by count and the calculated d2s limits in Appendix D shows there is no real difference between the two numbers. Even when the values are not the same, there does not appear to be a large enough deviation that would require reporting the various d2s or d2s% limits reported in this report in a manner other than described in ASTM E 177 [16].

23 4.4 PRECISION STATEMENT FOR AASHTO T308 Determining the Asphalt Binder Content of Hot-Mix Asphalt (HMA) by the Ignition Method X. Precision and Bias X.1 Precision Criteria for judging the acceptability of ignition burn results for asphalt content obtained by Method A or Method B are given in Table X. X.1.1 Single-Operator Precision (Repeatability) – The figures in Column 2 of Table X are the standard deviations that have been found to be appropriate for the conditions of test described in Column 1. Two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should not be considered suspect unless the difference in the two results exceeds the values given in Table X, Column 3. X.1.2 Multilaboratory Precision (Reproducibility) – The figures in Column 2 of Table X are the standard deviations that have been found to be appropriate for the conditions of test described in Column 1. Two results submitted by two different operators testing the same material in different laboratories shall not be considered suspect unless the difference in the two results exceeds the values given in Table X, Column 3. Table X – Precision Estimates (1s)a Single Operator Precision: Asphalt Content (%) 0.069 0.196 Multilaboratory Precision: Asphalt Content (%) 0.117 0.330 a These values represent the 1s and d2s limits described in ASTM Practice C670. Condition Acceptable Range of Two Test Results (d2s)a Standard Deviation Note – The precision estimates given in Table X are based on the analysis of test results from three pairs of AMRL proficiency samples. The data analyzed consisted of results from 353 to 461 laboratories for each of the three pairs of samples. The analysis included two binder grades: PG 52-34 and PG 64-22. Average results for asphalt content ranged from 4.049% to 5.098%. The details of this analysis are in NCHRP Final Report, NCHRP Project No. 9-26, Phase 3. X.2 Bias – Any biases inherent to the ignition oven process used for test methods A and B, when testing for asphalt content and aggregate gradation, are accounted for by the determination and application of appropriate correction factors.

24 4.5 PRECISION STATEMENT FOR AASHTO T48 Flash and Fire Points by Cleveland Cup X. Precision and Bias X.1 Precision – Criteria for judging the acceptability of test results for flash point of asphalt binder obtained by this method are given in Table X. Criteria for judging the acceptability of fire point test results can be found in ASTM D92. X.1.1 Single-Operator Precision (Repeatability) – The figures in Column 2 of Table X are the standard deviations that have been found to be appropriate for the conditions of test described in Column 1. Two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should not be considered suspect unless the difference in the two results exceeds the values given in Table X, Column 3. X.1.2 Multilaboratory Precision (Reproducibility) – The figures in Column 2 of Table X are the standard deviations that have been found to be appropriate for the conditions of test described in Column 1. Two results submitted by two different operators testing the same material in different laboratories shall not be considered suspect unless the difference in the two results exceeds the values given in Table X, Column 3. Table X – Precision Estimates (1s)a (d2s)a Single Operator Precision: Flash Point (°C) 3 8 Multilaboratory Precision: Flash Point (°C) 10 28 a These values represent the 1s and d2s limits described in ASTM Practice C670. Condition Standard Deviation Acceptable Range of Two Results Note 1 – The precision estimates for Flash Point given in Table X are based on the analysis of test results from eight pairs of AMRL proficiency samples. The data analyzed consisted of results from 98 to 148 laboratories for each of the eight pairs of samples. The analysis included four binder grades: PG 52-34, PG 64-16, PG 64-22, and PG 70-22. Average flash points ranged from 268.5 °C to 353.5 °C. The details of the analysis are in NCHRP Final Report, NCHRP Project No. 9-26, Phase 3. X.2 Bias – The procedure of this test method has no bias because flash point and fire point can only be defined in terms of this test method.

25 4.6 PRECISION STATEMENT FOR AASHTO T228 Specific Gravity of Semi-Solid Bituminous Materials X. Precision and Bias X.1 Precision – Criteria for judging the acceptability of the relative density results obtained by this method are given in Table X. X.1.1 Single-Operator Precision (Repeatability) – The figures in Column 2 of Table X are the standard deviations that have been found to be appropriate for the conditions of test described in Column 1. Two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should not be considered suspect unless the difference in the two results exceeds the values given in Table X, Column 3. X.1.2 Multilaboratory Precision (Reproducibility) – The figures in Column 4 of Table X are the standard deviations that have been found to be appropriate for the conditions of test described in Column 1. Two results submitted by two different operators testing the same material in different laboratories shall not be considered suspect unless the difference in the two results exceeds the values given in Table X, Column 5. Table X – Precision Estimates (1s)a (d2s)a (1s)a (d2s)a Asphalt: Specific Gravity (15.6 °C) 0.0011 0.0032 0.0018 0.0051 Specific Gravity (25 °C) 0.0008b 0.0021b 0.0013b 0.0035b Soft Tar Pitch: Specific Gravity (15.6 °C) 0.0013 0.0038 0.0029 0.0083 Specific Gravity (25 °C) 0.00083 0.0023 0.0017 0.0048 a These values represent the 1s and d2s limits described in ASTM Practice C670. b The precision estimates denoted by the superscript "b" are based on the analysis of test results from eight pairs of AMRL proficiency samples. The data analyzed consisted of results from 104 to 121 laboratories for each of the eight pairs of samples. The analysis included four binder grades: PG 52-34, PG 64-16, PG 64-22, and PG 70-22. Average specific gravities in the analysis ranged from 1.0058 to 1.0428. The details of this analysis are in NCHRP Final Report, NCHRP Project No. 9-26, Phase 3. Multilaboratory Standard Deviation Acceptable Range of Two Results Condition Standard Deviation Acceptable Range of Two Results Single-Operator Note – Values in Table X not marked with a superscript “b” are precision estimates retained from ASTM D70-03 Section 14, Table 1. These values were not part of the scope of the AMRL research activities described with the superscript “b”. X.2 Bias – No information can be presented on the bias of the procedure because no material having an accepted reference value is available.

26 4.7 PRECISION STATEMENT FOR AASHTO T240 Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test) X. Precision and Bias X.1 ...copy Section X.1 as it appears in T240-03 and renumber the section as necessary. X.2 Precision for Loss of Mass – Criteria for judging the acceptability of change in mass results obtained by this method are given in Tables 1 and 2. Table 1 should be consulted as the final qualifier for precision purposes. Table 2 has been added for the convenience of the user. X.2.1 Single-Operator Precision (Repeatability) – The equation in Column 2 of Table 1 indicates that the standard deviation of the test results (1s) can be expressed as a function of the mass change (X) for the conditions of test described in Column 1. Two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should not be considered suspect unless the difference in the two results exceeds the value determined by multiplying the 1s estimate determined in Column 2 for the average value of the two results by a factor of 2.83. This is shown in Table 1, Column 3. X.2.2 Multilaboratory Precision (Reproducibility) – The equation in Column 2 of Table 1 indicates that the standard deviation of the test results (1s) can be expressed as a function of the mass change (X) for the conditions of test described in Column 1. Two results submitted by two different operators testing the same material in different laboratories shall not be considered suspect unless the difference in the two results exceeds the value determined by multiplying the 1s estimate determined in Column 2 for the average value of the two results by a factor of 2.83. This is shown in Table 1, Column 3. Table 1 – Precision Estimates Single Operator Precision: Mass Loss (%) 1s = 0.0061 + 0.0363(X) d2s = (0.0061 + 0.0363(Xavg)) х (2.83) Multilaboratory Precision: Mass Loss (%) 1s = 0.00153 + 0.1365(X) d2s = (0.00153 + 0.1365(Xavg)) х (2.83) a These values represent the 1s and d2s limits described in ASTM Practice C670. b X and Xavg should be entered into equations as positive numbers. c The value Xavg represents the average value of two test results. Condition Standard Deviationa,b (1s) Acceptable Range of Two Test Resultsa,b,c (d2s) Note – The precision estimates given in Table 1 are based on the analysis of test results from eight pairs of AMRL proficiency samples. The data analyzed consisted of results from 166 to 191 laboratories for each of the eight pairs of samples. The analysis included five binder grades: PG 52-34, PG 64-16, PG 64-22, PG 70-22 and PG 76-22 (SBS modified). The samples used in the analysis had an average loss of mass ranging from -0.05% to -0.51%. The equations for precision estimates are reliable only in situations when the change in mass is negative. The details of this analysis are in NCHRP Final Report, NCHRP Project No. 9-26, Phase 3.

27 Table 2 – Stratified Estimates of Precision Single Operator Precision: Mass Loss (%) 0.0 to 0.1% 0.0079 0.0224 0.1 to 0.2% 0.0115 0.0327 0.2 to 0.3% 0.0152 0.0429 0.3 to 0.4% 0.0188 0.0532 0.4 to 0.5% 0.0224 0.0635 Multilaboratory Precision: Mass Loss (%) 0.0 to 0.1% 0.0084 0.0236 0.1 to 0.2% 0.0220 0.0623 0.2 to 0.3% 0.0357 0.1009 0.3 to 0.4% 0.0493 0.1395 0.4 to 0.5% 0.0630 0.1781 Standard Deviationa (1s) Acceptable Range of Two Test Resultsa (d2s) a The values represented in this table are the 1s and d2s limits described as stratified values. Table 1 of this standard should be consulted as the final qualifier for precision purposes. Condition

28 4.8 PRECISION STATEMENT FOR AASHTO T313 Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR) X. Precision and Bias X.1 Precision – Criteria for judging the acceptability of creep stiffness and slope results obtained by this method are given in Table X. X.1.1 Single-Operator Precision (Repeatability) – The figures in Column 2 of Table X are the coefficients of variation that have been found to be appropriate for the conditions of test described in Column 1. Two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should not be considered suspect unless the difference in the two results, expressed as a percent of their mean, exceeds the values given in Table X, Column 3. X.1.2 Multilaboratory Precision (Reproducibility) – The figures in Column 2 of Table X are the coefficients of variation that have been found to be appropriate for the conditions of test described in Column 1. Two results submitted by two different operators testing the same material in different laboratories shall not be considered suspect unless the difference in the two results, expressed as a percent of their mean, exceeds the values given in Table X, Column 3. Table X – Precision Estimates Single Operator Precision: Creep Stiffness (MPa) 2.5 7.2 Slope (m-value) 1.0 2.9 Multilaboratory Precision: Creep Stiffness (MPa) 6.3 17.8 Slope (m-value) 2.4 6.8 a These values represent the 1s% and d2s% limits described in ASTM Practice C670. Condition Coefficient of Variation (1s%)a Acceptable Range of Two Test Results (d2s%)a Note – The precision estimates given in Table X are based on the analysis of test results from eight pairs of AMRL proficiency samples. The data analyzed consisted of results from 174 to 196 laboratories for each of the eight pairs of samples. The analysis included five binder grades: PG 52-34, PG 64-16, PG 64-22, PG 70-22 and PG 76-22 (SBS modified). Average creep stiffness results ranged from 125.4 MPa to 236.8 MPa. Average slope results ranged from an m-value of 0.308 to 0.374. The details of this analysis are in NCHRP Final Report, NCHRP Project No. 9-26, Phase 3. Note – As an example, two tests conducted on the same material yield creep stiffness results of 190.3 MPa and 200.7 MPa, respectively. The average of these two measurements is 195.5 MPa. The acceptable range of results is then 7.2 percent of 195.5 MPa or 14.1 MPa. As the difference between 190.3 MPa and 200.7 MPa is < 14.1 MPa the results are within the acceptable range. X.2 Bias – No information can be presented on the bias of the procedure because no material having an accepted reference value is available.

29 4.9 PRECISION STATEMENT FOR AASHTO T314 Determining the Fracture Properties of Asphalt Binder in Direct Tension (DT) X. Precision and Bias X.1 Precision – Criteria for judging the acceptability of failure stress and strain results obtained by this method are given in Table X. X.1.1 Single-Operator Precision (Repeatability) – The figures in Column 2 of Table X are the coefficients of variation that have been found to be appropriate for the conditions of test described in Column 1. Two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should not be considered suspect unless the difference in the two results, expressed as a percent of their mean, exceeds the values given in Table X, Column 3. X.1.2 Multilaboratory Precision (Reproducibility) – The figures in Column 2 of Table X are the coefficients of variation that have been found to be appropriate for the conditions of test described in Column 1. Two results submitted by two different operators testing the same material in different laboratories shall not be considered suspect unless the difference in the two results, expressed as a percent of their mean, exceeds the values given in Table X, Column 3. Table X – Precision Estimates Single Operator Precision: Stress (MPa) 7.4 20.8 Strain (%) 11.4 32.2 Multilaboratory Precision: Stress (MPa) 18.6 52.5 Strain (%) 31.5 89.1 a These values represent the 1s%, and d2s% limits described in ASTM Practice C670. Condition Coefficient of Variation (1s%)a Acceptable Range of Two Test Results (d2s%)a Note – The precision estimates given in Table X are based on the analysis of test results from eight pairs of AMRL proficiency samples. The data analyzed consisted of results from 34 to 61 laboratories for each of the eight pairs of samples. The analysis included five binder grades: PG 52-34, PG 64-16, PG 64-22, PG 70-22 and PG 76-22 (SBS modified). Average stress results ranged from 2.79 MPa to 4.22 MPa. Average strain results ranged from 0.91% to 3.00%. The details of this analysis are in NCHRP Final Report, NCHRP Project No. 9-26, Phase 3. Note – As an example, two tests conducted on the same material yield stress results of 2.95 MPa and 3.15 MPa, respectively. The average of these two measurements is 3.05 MPa. The acceptable range of results is then 20.8 percent of 3.05 or 0.63 MPa. As the difference between 2.95 MPa and 3.15 MPa is < 0.63 MPa, the results are within the acceptable range. X.2 Bias – No information can be presented on the bias of the procedure because no material having an accepted reference value is available.

30 4.10 PRECISION STATEMENT FOR AASHTO T315 Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) X. Precision and Bias X.1 Precision – Criteria for judging the acceptability of dynamic shear results obtained by this method are given in Table X. X.1.1 Single-Operator Precision (Repeatability) – The figures in Column 2 of Table X are the coefficients of variation that have been found to be appropriate for the conditions of test described in Column 1. Two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should not be considered suspect unless the difference in the two results, expressed as a percent of their mean, exceeds the values given in Table X, Column 3. X.1.2 Multilaboratory Precision (Reproducibility) – The figures in Column 2 of Table X are the coefficients of variation that have been found to be appropriate for the conditions of test described in Column 1. Two results submitted by two different operators testing the same material in different laboratories shall not be considered suspect unless the difference in the two results, expressed as a percent of their mean, exceeds the values given in Table X, Column 3. Table X – Precision Estimates Single Operator Precision: Original Binder: G*/sinδ (kPa) 2.3 6.4 RTFO Residue: G*/sinδ (kPa) 3.2 9.0 PAV Residue: G*·sinδ (kPa) 4.9 13.8 Multilaboratory Precision: Original Binder: G*/sinδ (kPa) 6.0 17.0 RTFO Residue: G*/sinδ (kPa) 7.8 22.2 PAV Residue: G*·sinδ (kPa) 14.2 40.2 a These values represent the 1s% and d2s% limits described in ASTM Practice C670. Condition Coefficient of Variation (1s%)a Acceptable Range of Two Test Results (d2s%)a Note – The precision estimates given in Table X are based on the analysis of test results from eight pairs of AMRL proficiency samples. The data analyzed consisted of results from 185 to 208 laboratories for each of the eight pairs of samples. The analysis included five binder grades: PG 52-34, PG 64-16, PG 64-22, PG 70-22 and PG 76-22 (SBS modified). Average original binder results for G*/sinδ ranged from 1.067 kPa to 2.342 kPa. Average RTFO residue results for G*/sinδ ranged from 2.274 kPa to 7.733 kPa. Average PAV residue results for G*·sinδ averaged from 1100 kPa to 4557 kPa. The details of this analysis are in NCHRP Final Report, NCHRP Project No. 9-26, Phase 3. Note – As an example, two tests conducted on the same PAV residue yield results of 1200 kPa and 1300 kPa, respectively. The average of these two measurements is 1250 kPa. The acceptable range of results is then 13.8 percent of 1250 kPa or 173 kPa. As the difference between 1200 and 1300 is < 173 kPa, the results are within the acceptable range. X.2 Bias – No information can be presented on the bias of the procedure because no material having an accepted reference value is available.

31 4.11 PRECISION STATEMENT FOR AASHTO T316 Viscosity Determination of Asphalt Binder Using a Rotational Viscometer X. Precision and Bias X.1 Precision – Criteria for judging the acceptability of viscosity results obtained by this method are given in Table X. X.1.1 Single-Operator Precision (Repeatability) – The figures in Column 2 of Table X are the coefficients of variation that have been found to be appropriate for the conditions of test described in Column 1. Two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should not be considered suspect unless the difference in the two results, expressed as a percent of their mean, exceeds the values given in Table X, Column 3. X.1.2 Multilaboratory Precision (Reproducibility) – The figures in Column 2 of Table X are the coefficients of variation that have been found to be appropriate for the conditions of test described in Column 1. Two results submitted by two different operators testing the same material in different laboratories shall not be considered suspect unless the difference in the two results, expressed as a percent of their mean, exceeds the values given in Table X, Column 3. Table X – Precision Estimates Single Operator Precision: Average Viscosity (Pa·s) 1.2 3.5 Multilaboratory Precision: Average Viscosity (Pa·s) 4.3 12.1 a These values represent the 1s% and d2s% limits described in ASTM Practice C670. Condition Coefficient of Variation (1s%)a Acceptable Range of Two Test Results (d2s%)a Note – The precision estimates given in Table X are based on the analysis of test results from eight pairs of AMRL proficiency samples. The data analyzed consisted of results from 142 to 202 laboratories for each of the eight pairs of samples. The analysis included five binder grades: PG 52-34, PG 64-16, PG 64-22, PG 70-22 and PG 76-22 (SBS modified). Unmodified average viscosity results ranged from 0.272 Pa·s to 0.719 Pa·s. The modified binder average viscosity ranged from 1.621 Pa·s to 1.638 Pa·s. The details of this analysis are in NCHRP Final Report, NCHRP Project No. 9-26, Phase 3. Note – As an example, two tests conducted on the same material yield viscosity results of 0.500 Pa·s and 0.510 Pa·s, respectively. The average of these two measurements is 0.505 Pa·s. The acceptable range of results is then 3.5 percent of 0.505 Pa·s or 0.018 Pa·s. As the difference between 0.500 Pa·s and 0.510 Pa·s is < 0.018 Pa·s, the results are within the acceptable range. X.2 Bias – No information can be presented on the bias of the procedure because no material having an accepted reference value is available.