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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 asphalt binder and hot-mix asphalt (HMA). 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]. This report includes the results of Phase 3 of NCHRP 9-26 where data from the AMRL Proficiency Sample Program (PSP) are used to create or update precision estimates for a variety of test methods. This includes those specified in AASHTO Standard Specification M320, âPerformance-Graded Asphalt Binderâ, and AASHTO Standard Test Method T308, âDetermining the Asphalt Binder Content of Hot-Mix Asphalt (HMA) by the Ignition Methodâ [3,4]. Laboratories participating in the AMRL Proficiency Program receive annual or biannual shipments of paired proficiency samples which are tested according to specified AASHTO test methods [5,6]. The results of the testing are returned to AMRL for analysis, summarization, and reporting back to the laboratories. AMRL has an extensive database of test results for the broad range of construction materials included in its proficiency sample program. Data used in this study are for HMA ignition samples (T308), and for test methods for performance-graded asphalt binder and viscosity graded asphalt (M320). The proficiency samples included in these programs cover a range of test values and grades of materials. This report includes a robust technique developed by AMRL for analyzing proficiency sample data. This technique is a four step methodology for shaving off extraneous results and analyzing the core data of a paired data set. The results of the analysis of the âcore dataâ can then be used to obtain reliable single-operator and multilaboratory estimates of precision. In this study, over 91 paired data sets comprised of over 28,000 test results were analyzed using the analysis technique developed. The analysis resulted in precision statements for eight separate test methods. In order to account for changes in test precision resulting from recent improvements in the test methods, only the most recent proficiency samples were used.
2 1.1.1 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. Others need to be expanded to take into account a wider range of materials while some newer test methods may not have precision estimates of any kind. This study addresses specific tests having these deficiencies. 1.1.2 RESEARCH OBJECTIVES The objective of Phase 3 of NCHRP Project 9-26, herein referred to as the Phase 3 study, is to develop or update single-operator and multilaboratory precision estimates for the following test methods: 1. AASHTO T308 Determining the Asphalt Binder Content of Hot-Mix Asphalt (HMA) by the Ignition Method 2. AASHTO T48 Flash and Fire Points by Cleveland Open Cup 3. AASHTO T228 Specific Gravity of Semi-Solid Bituminous Materials 4. AASHTO T240 Effect of Heat and Air on a Moving Film of Asphalt (Rolling Thin-Film Oven Test) 5. AASHTO T313 Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR) 6. AASHTO T314 Determining the Fracture Properties of Asphalt Binder in Direct Tension (DT) 7. AASHTO T315 Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR) 8. AASHTO T316 Viscosity Determination of Asphalt Binder Using a Rotational Viscometer 1.2 SCOPE OF STUDY This work is limited to an evaluation of data collected from laboratories participating in the Performance Graded Asphalt Binder, Viscosity Graded Asphalt Cement, and Hot-Mix Asphalt Ignition Oven portions of the AMRL Proficiency Sample Program. There are 91 data sets analyzed and included in this report.
3 1.3 PROFICIENCY SAMPLES USED IN STUDY Included in the study are the most recent AMRL proficiency samples that include the test methods covered in the Research Objectives (Section 1.1.2). These samples include multiple grades of material when it was possible to do so. The following tables describe the pertinent information for the samples used. Performance Viscosity Modified Grade Grade Binder IGN 3 & 4 PG 64-22 AC 20 March 2002 No IGN 5 & 6 PG 64-22 AC 20 March 2003 No IGN 7 & 8 PG 52-34 AC 10 March 2004 No Sample Date of Designation Final Report Table 1 â Proficiency Samples Used in Analysis of T308 The hot-mix asphalt ignition oven (IGN) samples listed in Table 1 are used in the analysis of T308. Performance Viscosity Modified Grade Grade Binder PGB 181 & 182 PG 64-16 AC 10 January 2001 No PGB 183 & 184 PG 70-22 -- June 2001 No PGB 185 & 186 PG 64-22 AC 20 January 2002 No PGB 187 & 188 PG 76-22 -- May 2002 Yes PGB 189 & 190 PG 64-22 AC 30 December 2002 No PGB 191 & 192 PG 52-34 AC 10 May 2003 No PGB 193 & 194 PG 64-22 AC 20 December 2003 No PGB 195 & 196 PG 70-22 -- May 2004 No Date of Final ReportDesignation Sample Table 2 â Proficiency Samples Used in the Analysis of T240, T313, T314, T315, and T316 The performance graded asphalt binder (PGB) samples listed in Table 2 are used in the analysis of T240, T313, T314, T315, and T316. (The PG 76-22 is an SBS modified binder.) Performance Viscosity Modified Grade Grade Binder BAC 181 & 182 PG 64-16 AC 10 January 2001 No BAC 183 & 184 PG 70-22 -- June 2001 No BAC 185 & 186 PG 64-22 AC 20 January 2002 No BAC 187 & 188 PG 64-22 AC 30 May 2002 No BAC 189 & 190 PG 64-22 AC 30 December 2002 No BAC 191 & 192 PG 52-34 AC 10 May 2003 No BAC 193 & 194 PG 64-22 AC 20 December 2003 No PGB 195 & 196 PG 70-22 -- May 2004 No Sample Date of Designation Final Report Table 3 â Proficiency Samples Used in the Analysis of T48 and T228 The viscosity graded asphalt cement (BAC) samples and one PGB sample listed in Table 3 are used in the analysis of T48 and T228.
