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69 Following are the conclusions and recommendations from NCHRP Project 9-56. ⢠Although not recommended in the AASHTO T 308 stan- dard, sharing correction factors between different furnaces should not be a significant problem when low correction factor aggregates (of 0.1% or less) are used. For higher mass loss aggregates (1.0% and larger), sharing correction factors should not be allowed. As the CF increases from 0.1% to 1.0%, the errors caused by sharing CFs will certainly increase. ⢠For the mixtures that did not contain lime, the ignition test conducted at 800°F significantly reduced the asphalt cor- rection factor, particularly for high-loss aggregates. As the correction factors decreased, the standard deviations also decreased. Lowering the test temperature should improve the accuracy of test results. ⢠Although the results of the sensitivity study showed that some of the variables under evaluation affect the aggregate gradation, in general, the differences in percentages passing were typically not practically different. ⢠The precision statement developed in this study showed that for Mixes 1 and 2, the within-laboratory and between- laboratory standard deviations were similar: 0.089 and 0.074 for the within-laboratory standard deviation and 0.131 and 0.111 for the between-laboratory standard deviation. These numbers are close to the standard deviations recommended in AASHTO T 308, 0.069 and 0.117 for within-laboratory and between-laboratory, respectively. As the correction factors increased for Mixes 3 and 4, their corresponding standard deviations also increased. The within-laboratory standard deviations for Mixes 3 and 4 were found to be 0.112 and 0.178, respectively, and the between-laboratory standard deviations were 0.264 and 0.403. This study sug- gests that different precision statements may be necessary for aggregates with higher correction factors. It also sug- gests that the precision statement included in AASHTO T 308 was developed with low-mass-loss aggregates and is not applicable to aggregates with higher mass loss. ⢠The troubleshooting study showed that the causes of the differences in correction factor test results were generally related to incorrect equipment settings before the tests were conducted. These findings emphasize the importance of a guideline (Appendix I) that provides information about proper installation, operation, and maintenance of different ignition furnaces. ⢠Although this study did not include any mixtures with RAP, conducting the ignition test for RAP materials at 800°F (427°C) may allow the ignition test to more accurately determine the RAP asphalt content, which can be difficult since the correction factor is not known. This would be particularly significant as the amount of these recycled materials allowed in the mixtures increases. C h a p t e r 7 Conclusions and Recommendations
