Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
8 CHAPTER 2- DESIGN AND EXECUTION OF THE ILS To obtain a reliable measurement of organic content in soils, it is essential to develop precision estimates for the AASHTO T267 test method. In this respect, the AASHTO Subcommittee on Materials has requested the precision estimates of AASHTO T267 to be developed. An interlaboratory study was designed and conducted in which three different soil types, blended with three different percentages of organic material, were analyzed. The following sections will report the details of the design of the ILS. The approach used for the design of the ILS was based on ASTM E691-07, âStandard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Methodâ [2]. As specified in E691, the development of a precision statement required participation of a minimum of 6 laboratories. The precision estimates in this study were developed using the data collected from 27 laboratories. 2.1 Test Specimens The samples prepared for the ILS included 500 g of each of the three types of soils (silt, clay, and sand) that were blended with three different percentages (2%, 5%, 8%) of fine walnut shell grit as the organic material. Also, 100 g of each of the three soil types with no additional organic material were provided to the laboratories in order to determine the inherent level of organic material of each soil type. A total of 360 bottles were sent to 30 different laboratories, each receiving 12 bottles of samples. The instructions requested the operators to take three 20-g representative specimens from each bottle and heat them in the ignition oven as conforming to AASHTO T267 test method. 2.2 Test Apparatus The apparatus used for determining the organic content include drying oven, balance conforming to M231 class G1, muffle furnace capable of maintaining a continuous temperature of 455 ± 10°C, evaporating dishes, and desiccators as requested in Sections 3.1 to 3.7 of AASHTO T267. A turbula machine was used during the sample preparation for homogeneous blending of the soil and organic material. 2.3 Participating Laboratories The laboratories for participation in the AASHTO T267 ILS were selected based on their performance in soil proficiency sample testing. The laboratories were ranked by their scores earned through accreditation process. The laboratories with the highest ranking of 5 were contacted and thirty of those laboratories, which responded positively, were selected for the study. The results of testing T267 ILS samples were received from 27 laboratories. 2.4 Interlaboratory Sample Preparation and Shipping A total of 360 bottles were shipped to different laboratories in sets of four bottles from three types of soils. The four bottles of each soil type contained four different percentage of organic material of 0%, 2%, 5%, 8%. In each bottle, there was three times the material needed
9 for testing three replicate samples. The samples were subjected to blending in their bottles using a turbo machine for duration of 2 minutes and at a speed of 60 revolutions per minute in order to obtain homogeneous mixtures of organic content and soils. 2.5 Interlaboratory Study Instructions The laboratory participants were provided with the testing instructions and data sheets to record the data. The laboratories were asked to shake the bottles thoroughly before taking representative samples. Then take three 100-g representative samples according to T267 test method and from each take 20-g test specimens to place in ignition oven. The laboratories were requested to follow AASHTO T267 to measure the mass of samples to the nearest 0.01 g before and after the test. The instruction and the data sheet are provided in Appendix A.
