Variability of Ignition Furnace Correction Factors (2017) / Chapter Skim
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18 3.1 Introduction A survey was developed to help focus the NCHRP Project 9-56 research (see Appendix A)
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19 68.5% 20.2% 5.6% 18.0% 6.7% 2.2% 0% 10% 20% 30% 40% 50% 60% 70% 80% Thermolyne Series 859/945 Fisher Thermo/Thermolyne Series 1087/1275 Troxler 4155 Asphalt Analyzer Troxler 4730/4731 NTO Gilson HM-378 Binder Ignition System Carbolite Asphalt Binder Analyzer Figure 13. Brands/models of ignition furnaces used by survey respondents.
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20 Additional factors were identified in the question's comment section. Two respondents indicated RAP or RAS as factors affecting the correction factor.
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21 A concern identified prior to the survey was the validity or quality of the calibration samples. The furnace calibration can only be as accurate as the calibration sample.
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22 • Minnesota DOT reevaluates calibration factors if there are consecutive tolerance issues between agency and producer, when aggregate percentages change by more than 10%, or when there are changes in limestone or dolostone content. • Connecticut DOT requires a new correction factor when the RAP proportion changes by more than 5% from the job mix formula, when the binder content in the processed RAP changes by more than 2%, or when the theoretical maximum specific gravity changes by 0.06.
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23 • One respondent noted that the sample size for RAS must be small, approximately 200 g. • One respondent indicated problems with consultant laboratories that were unfamiliar with procedures or not careful in weighing correction samples.
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24 content. While 93.3% of respondents reported using furnaces with internal balances, only 62.8% of 86 respondents answering the question indicated that they use the internal balance to calculate asphalt content.
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25 The length of the exhaust duct likely affects air flow through the furnace and may affect the sample burn. Reported duct lengths ranged from 1.5 to 40 ft.
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26 both hand washed and washed with aggregate drum washers. Only a third of respondents use correction factors for the recovered gradation.
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