Precision Estimates Of Aashto T 304 Aashto T 96 And Aashto T 11 And Investigation Of The Effect Of Manual And Mechanical Methods Of Washing On Sieve Analysis Of Aggregates

"This digest summarizes key findings obtained in 2009 and 2010 from continuing NCHRP Project 9-26A, "Data Mining and Interlaboratory Studies to Prepare Precision Statements for AASHTO Standard Test Methods." Project 9-26A was conducted by the AASHTO Materials Reference Laboratory under the direction of the principal investigator, Haleh Azari. This digest is based on the contractor's task reports, which are available online as NCHRP Web-Only Documents 163 through 166."

TRB's National Cooperative Highway Research Program (NCHRP) Research Results Digest 350: Continuing Project to Synthesize Information on Highway Problems is a digest of the progress and status of NCHRP Project 20-5, "Synthesis of Information Related to Highway Problems."

"Determining the Asphalt Binder Content of Hot Mix Asphalt (HMA) by the Ignition Method," requires determination of asphalt and aggregate correction factors for asphalt mix designs for each ignition furnace used to test a design. In some cases, where there are numerous asphalt mix designs or numerous ignition furnaces testing a particular mix design, correction factors may be shared between ignition furnaces, though this practice is not strictly permitted by AASHTO T 308 without supporting evidence. The objectives of this research were to (1) determine the significant influences that affect the variability of asphalt and aggregate correction factors for ignition furnaces; (2) develop guidelines for the installation, operation, and maintenance of ignition furnaces to minimize the variability in correction factors between furnaces; and (3) develop and document a statistically valid correction factor verification procedure to identify and troubleshoot causes for non-comparing, statistically different, or biased results of AASHTO T 308. The research was conducted in three parts: (1) a study of the sensitivity of asphalt and aggregate correction factors to variation in experimental factors such as furnace type, test temperature, asphalt content, and sample mass; (2) a round-robin study to identify correction factor outliers and determine the contributory cause(s); and (3) troubleshooting of outliers from the round-robin study. The research found that the primary factors affecting asphalt and aggregate correction factors determined by AASHTO T 308 are furnace type and test temperature. Conducting the test at 800°F appears to substantially reduce the magnitude and standard deviation of the correction factors for asphalt mixtures that do not contain lime. Sharing correction factors among different ignition furnaces appears acceptable for low correction factor aggregates (0.1% or less) but is problematic for aggregates with correction factors of 1.0% or greater. The current precision estimates in AASHTO T 308 appear applicable only to mixtures with low correction factor aggregates. The key product of this research is a Proposed Standard Practice for Installation, Operation, and Maintenance of Ignition Furnaces (Appendix I). Development of a verification procedure to identify causes for non-comparing, statistically different, or biased test results from ignition furnaces was found to be premature and further research is planned.