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1 CHAPTER 1- INTRODUCTION AND RESEARCH APPROACH 1.1 Background Under the National Cooperative Highway Research Program (NCHRP) Project 09-26A, the AASHTO Materials Reference Laboratory (AMRL) is conducting a multi- phase research project to determine or update estimates of precision of selected AASHTO test methods. The AASHTO T180 standard test method, âMoisture-Density Relations of Soils Using a 4.54-kg (10-lb) Rammer and a 457-mm (18-in.) Dropâ [1] is among the test methods that lack precision estimates. The test method is used to determine the required degree of compaction and a method to obtain the required compaction of soil-aggregate mixtures. An interlaboratory study (ILS) was designed to develop the precision estimates for AASHTO T180. The precision statistics from analysis of AMRL soil proficiency sample data [2] were also incorporated in the development of the AASHTO T180 precision statement provided in this report. 1.2 Problem Statement The design and control of compaction of soils is an important aspect of a pavement construction process. The level of accuracy in which a degree of compaction of soil-aggregate mixture is specified has a significant effect on the performance of a pavement as a whole. Currently, there are no precision estimates that would define the accuracy requirements for laboratory measurement of maximum density and optimum water content as specified in AASHTO T 180. Therefore, this study aims to determine repeatability and reproducibility precision of maximum density and optimum moisture content measured according AASHTO T 180 test method. 1.3 Research Objectives The overall objective of this study is to determine precision estimates for the AASHTO T 180, âMoisture-Density Relations of Soils Using a 4.54-kg (10-lb) Rammer and a 457-mm (18-in.) Dropâ test method. The change in precision estimates of maximum density and optimum water content with the change in soil-aggregate type and gradation is also being investigated. 1.4 Scope of Study The scope of the project involves the following major activities: I. Design and conduct an interlaboratory study (ILS): a. Select four soil-aggregate mixtures using two different grading (coarse and fine) and two types of filler (silt and clay) that satisfy the grading requirements of pavement base and subbase (Chapter 2). b. Conduct preliminary testing on the selected materials (Chapter 2). c. Produce 420 specimens to send to 35 participating laboratories for the ILS
2 (Chapter 2). d. Prepare instructions for testing the specimens. e. Analyze ILS results and develop precision estimates for maximum dry density and optimum moisture content (Chapter 3). II. Analyze AMRL Soil Classification and Compaction Proficiency Sample Program (PSP) data to develop precision estimates for maximum density and optimum moisture content. The data used were obtained according to AASHTO T180 or ASTM D1557 [3] test methods in the past three years (Chapter 4). III. Recommend a precision statement for AASHTO T180 based on the precision estimates developed from ILS and PSP data (Chapter 5). IV. Make conclusions and recommendations based on the findings of the study (Chapter 6).
