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Effect of lime on ignition furnace calibration Prowell, Brian D ; Youtcheff, Jack

By: Prowell, Brian DContributor(s): Youtcheff, JackPublication details: Transportation Research Record, 2000Description: nr 1712, s. 74-8Subject(s): USA | Binder | Bitumen | Ignition | Calibration | Lime | Sulphur | | Variability | Mix design | 51Bibl.nr: VTI P8167:1712Location: Abstract: This study investigated mix components, other than aggregate source, that were perceived to affect the ignition furnace mixture calibration. Four sets of experiments with one aggregate were designed and run to evaluate the effects of the amounts of lime, sulfur, calcium carboxylates, and fines. Five asphalt binders with different chemistries were evaluated. Two binders had high and low sulfur contents, respectively; two other binders contained relatively high concentrations of carboxylates. Various concentrations of hydrated lime (0 to 3% by weight) were added to mixtures and were found to have a significant effect on the ignition furnace correction factor for all five binders. The magnitude of the effect was large enough to cause the quality control tests to fail the tolerances established by the Virginia Department of Transportation. The lime appears to react with the sulfur dioxide formed from the combustion of organic sulfur to generate calcium sulfate. The amount of sulfur present in the asphalt can significantly affect the ignition furnace correction factor. Initial thoughts that calcium carboxylates are reacting with carbon dioxide to produce some form of calcium carbonate were not substantiated. The influence of carboxylic acid groups, however, does come into effect in the presence of lime. This suggests that lime reacts with the combustion gases to produce some form of carbonate. Basalt fines and portland cement did not have a significant effect on the ignition furnace correction factor. Additional testing should be conducted to assess the effects of fines representing other aggregates, particularly carbonates.
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This study investigated mix components, other than aggregate source, that were perceived to affect the ignition furnace mixture calibration. Four sets of experiments with one aggregate were designed and run to evaluate the effects of the amounts of lime, sulfur, calcium carboxylates, and fines. Five asphalt binders with different chemistries were evaluated. Two binders had high and low sulfur contents, respectively; two other binders contained relatively high concentrations of carboxylates. Various concentrations of hydrated lime (0 to 3% by weight) were added to mixtures and were found to have a significant effect on the ignition furnace correction factor for all five binders. The magnitude of the effect was large enough to cause the quality control tests to fail the tolerances established by the Virginia Department of Transportation. The lime appears to react with the sulfur dioxide formed from the combustion of organic sulfur to generate calcium sulfate. The amount of sulfur present in the asphalt can significantly affect the ignition furnace correction factor. Initial thoughts that calcium carboxylates are reacting with carbon dioxide to produce some form of calcium carbonate were not substantiated. The influence of carboxylic acid groups, however, does come into effect in the presence of lime. This suggests that lime reacts with the combustion gases to produce some form of carbonate. Basalt fines and portland cement did not have a significant effect on the ignition furnace correction factor. Additional testing should be conducted to assess the effects of fines representing other aggregates, particularly carbonates.

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