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Precision Estimates of AASHTO T 242 (2009)

Chapter: CHAPTER 1- INTRODUCTION AND RESEARCH APPROACH

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Suggested Citation:"CHAPTER 1- INTRODUCTION AND RESEARCH APPROACH." National Academies of Sciences, Engineering, and Medicine. 2009. Precision Estimates of AASHTO T 242. Washington, DC: The National Academies Press. doi: 10.17226/23017.
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Suggested Citation:"CHAPTER 1- INTRODUCTION AND RESEARCH APPROACH." National Academies of Sciences, Engineering, and Medicine. 2009. Precision Estimates of AASHTO T 242. Washington, DC: The National Academies Press. doi: 10.17226/23017.
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Page 2
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Suggested Citation:"CHAPTER 1- INTRODUCTION AND RESEARCH APPROACH." National Academies of Sciences, Engineering, and Medicine. 2009. Precision Estimates of AASHTO T 242. Washington, DC: The National Academies Press. doi: 10.17226/23017.
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NCHRP Web-Only Document 142: Precision Estimates of AASHTO T 242 1 CHAPTER 1- INTRODUCTION AND RESEARCH APPROACH 1.1 INTRODUCTION Under National Cooperative Highway Research Programs (NCHRP) Project 9-26, the AASHTO Materials Reference Laboratory (AMRL) is conducting a multi-phase research project to improve estimates of precision in AASHTO test methods for various highway construction materials. The report from Phase 1 of Project 9-26 includes precision estimates of selected volumetric properties of HMA using non-absorptive aggregates [1]. The report from Phase 2 discusses the results of an investigation into the cause of variations in HMA bulk specific gravity test results using non-absorptive aggregates [2]. The report from Phase 3 includes a robust technique developed by AMRL for analyzing proficiency sample data for the purpose of obtaining reliable single-operator and multilaboratory estimates of precision [3]. The report from phase 4 includes two parts. Part one covers the precision estimates of selected volumetric properties of HMA using absorptive aggregates. Part two of the report investigates the effect of aging period on the volumetric properties of HMA with absorptive aggregates [4]. The report from Phase 5 includes update of precision estimates for AASHTO Standard Test Method T 269 [5]. This report includes the results of Task 7 of NCHRP 9-26A to prepare precision estimates for AASHTO Standard Test Method T 242, “Frictional Properties of Paved Surfaces Using a Full-Scale Tire.” [6] Included in this study are friction data from evaluation of state friction measurement systems that have been calibrated at Texas Transportation Institute (TTI) and Transportation Research Center (TRC) field test centers. Two sets of data were analyzed in this report: “Initial” and “Final” as referred by TTI or “Arrival” and “Departure” as referred by TRC. The Initial or Arrival set was collected by state systems as they arrived to the center for calibration. The Final or Departure set was collected after adjustments were made to the state systems to put them into compliance with ASTM E 274 [7], which is equivalent to AASHTO T 242. The precision statements for AASHTO T 242 standard method were determined based on the analysis of the friction data from the Final State Friction Systems at TTI and TRC. The analysis method suggested by ASTM E 691 was utilized for determining the single- operator and multilaboratory estimates of the precision. 1.2 PROBLEM STATEMENT AASHTO Standard Test Methods applicable to highway materials require periodic studies to determine estimates of precision. Some precision estimates become outdated as a result of improvements in the methods while other estimates need to be verified to see if they are still accurate. Some precision estimates need to be expanded to take into account a wider range of materials while other newer test methods may not have precision estimates of any kind. The AASHTO T 242-96 (2004) lacks a precision statement. There is only a report of an acceptable standard deviation, which needs to be verified and expended using the most recent friction data for variety of surfaces and speeds.

NCHRP Web-Only Document 142: Precision Estimates of AASHTO T 242 2 1.3 RESEARCH OBJECTIVE The objective of Task 7 of NCHRP 9-26A study is to prepare single-operator and multilaboratory precision estimates for the AASHTO T 242, “Frictional Properties of Paved Surfaces Using a Full-Scale Tire” using data collected based on the most recent version of the test method. The resulting precision estimates would reflect a variety of paved surfaces and vehicle speeds included in the evaluation of the state friction systems. 1.4 SCOPE OF STUDY This work is limited to an evaluation of data collected from state friction systems participating in the TTI and TRC field center calibration program. The precision estimates for measuring frictional properties of paved surfaces are determined based on analysis of the final state friction data of TTI and TRC test centers when data were collected after adjustments were made to the state systems to put them into compliance with AASHTO T 242. 1.5 DATA USED IN STUDY Included in the study are the most recent TTI and TRC friction data collected as part of evaluation of state friction measurement systems that are conducted annually. The reported friction numbers (FN) were determined from the forces required to slide the locked test tires on three paved surfaces at three different speeds. The following provide explanation of the data provided by the test centers for analysis in the study. 1.5.1 TTI Friction Data The TTI data analyzed in this study were collected at the TTI test center and are referred to as Initial and Final friction measurements. The Initial data set consisted of 288 friction numbers from 12 run repeats of 8 state systems as they arrive to the center. The data were collected at one speed on three surfaces. The final data set consisted of 1260 friction numbers from 12 repeats of 12 state friction systems after they have been calibrated at the center. The data were collected at three speeds and on three surfaces. The surfaces referred as Pad 1, Pad 2, and Pad 3 correspond to HMA with seal coat, HMA with seal coat and sand, and hydraulic cement concrete, respectively. The three speeds and the number of friction systems operated at each speed are provided in Table 1-1.

NCHRP Web-Only Document 142: Precision Estimates of AASHTO T 242 3 Table 1-1- Number of friction systems operated at different speeds on various surfaces of the TTI test field 1.5.2 TRC Friction Data The TRC data used in the study are referred as the Arrival (ARR) and Departure (DEP) friction measurements. The ARR data were collected as the state friction measuring systems arrived the center for calibration and the DEP data were collected after the systems were calibrated. The ARR data consisted of 1296 friction numbers from 12 run repeats of 12 state systems on three surfaces at three different speeds. The DEP data were received from either left (L), right (R), or both wheels of either ribbed (501), smooth (524), or both test tire types. A total of 5400 friction numbers from twelve skids of 50 different configurations of state friction systems were analyzed. The speeds at which each of the friction systems were run include 20, 40, and 60 mph (32.2, 64.4, and 96.6 km/h). The surfaces, which are referred to as Pad 4, Pad 5, and Pad 6, correspond to thick coating of coal-tar emulsion over asphalt, grade 5 aggregate (screened -1/4 + 10) set in epoxy over asphalt, and finish coat of Ohio DOT highway asphalt mix 404, respectively. Table 1-2 provides the number of ARR and DEP systems operated at the three speeds on the three pads. Table 1-2- Number of friction systems operated at different speeds on various surfaces of the TRC field test

Next: CHAPTER 2- RESULTS OF ANALYSIS AND ESTIMATES OF PRECISION »
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TRB’s National Cooperative Highway Research Program (NCHRP) Web-Only Document 142: Precision Estimates of AASHTO T 242 examines precision estimates for AASHTO (American Association of State Highway and Transportation Officials) T 242, “Frictional Properties of Paved Surfaces Using a Full-Scale Tire.”

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