Variability of Ignition Furnace Correction Factors (2017)

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.

I-1 A p p e n d i x i Proposed Standard Practice for Installation, Operation, and Maintenance of Ignition Furnaces with Commentary AASHTO Designation: R X-16 1. SCOPE 1.1. This standard practice is for the initial installation, operation, and maintenance of an ignition furnace for measuring the asphalt content of an asphalt mixture according to T 308. The aggregate recovered after ignition can be used for gradation analysis according to T 30. 1.2. Failure to properly install, operate, or maintain the ignition furnace may result in erroneous measurements and/or additional hazards. 1.3. The values stated in SI units are to be regarded as the standard. 1.4. This standard practice does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish safety and health practices along with determining the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: T 30, Mechanical Analysis of Extracted Aggregates T 168, Standard Method of Test for Sampling Bituminous Paving Mixtures T 308, Determining the Asphalt Binder Content of Hot Mix Asphalt (HMA) by the Ignition Method T 329, Standard Method of Test for Moisture Content of Hot-Mix Asphalt (HMA) by Oven Method R 18, Establishing and Implementing a Quality Management System for Construction Materials Testing Laboratories R 47, Standard Practice for Reducing Samples of Hot Mix Asphalt (HMA) to Testing Size

I-2 ThermoFisher, Thermolyne NCAT Asphalt Content Tester Installation and Operation Manual Troxler Electronic Laboratories, Inc., Manual of Operation and Instruction – Troxler NTO Asphalt Content Ignition Oven 2.3. Other Documents: HMA Lab Supply, Inc., NCAT Maintenance Tips 3. FURNACE INSTALLATION Prior to installing the furnace, read the manufacturer’s manual. 3.1. Locating the Furnace: There are a number of considerations when choosing a location to install an ignition furnace: Follow manufacturer’s recommendation for clear space between furnace and wall. Recommended clear space ranges from 6 to 12 inches and can be dependent on wall type. If possible, situate furnace such that there is adequate space to place hot baskets beside furnace for cooling. This minimizes the distance the hot baskets need to be moved. The Carbolite, ThermoFisher (Thermolyne), and Troxler doors are hinged on the left, so it is ideal to have clear space on the right side of the furnace. The Gilson furnace door swings down, so the cooling zone may be placed on either side of the furnace. If possible, situate the furnace so that the sample baskets are approximately at waist height when loaded. Carbolite recommends a counter height of 24 inches; ThermoFisher recommends 26 to 28 inches. Gilson sells a 28-inch tall stand for their furnace. Scale Access – The lower front panel of the ThermoFisher furnace is hinged for access to the scale. If possible, situate the ThermoFisher furnace so that the front panel can be opened without moving the furnace. The scale for the Carbolite furnace is accessed and installed through a panel on the lower left side of the furnace. The furnace should be situated with adequate clear space on the left side to allow this panel to be accessed. Read the manufacturer’s maintenance instructions. The Carbolite, ThermoFisher, and Troxler units require routine cleaning. For the ThermoFisher furnace, access the top of the furnace to clean and lubricate the blower motor. This requires detaching the exhaust duct. ThermoFisher recommends a minimum of 40 inches clear space above the furnace for this purpose. The exhaust plenum box on the right side of the Troxler furnace requires routine cleaning as well. Having clear space to place sample baskets on the right side of the Troxler furnace will also provide adequate space to access the 2.2. Manufacturer’s Manuals: Carbolite Gero, Operating and Maintenance Instructions – Asphalt Binder Analyser Gilson Company, Inc., Operating Manual – Gilson Binder Ignition System HM-378

I-3 upper side access panel. A vacuum cleaner (with appropriate filter) can be used to remove accumulated soot. The motor/impeller assembly may need to be removed for better cleaning depending on the accumulation of soot. Consider how the furnace’s exhaust will be routed. Further details on exhaust requirements are provided below. 3.2. Electrical Requirements: The furnace should be wired by a licensed electrician. Prior to ordering the furnace, the available laboratory voltage should be confirmed. Only Troxler makes a furnace that can function on a 110 V circuit. Carbolite, Gilson, and Troxler make furnaces that will function on 208 to 240 V. ThermoFisher makes a model for 208 V and a model for 220/240 V. The ThermoFisher 220/240 model can function on 208 V with the addition of a transformer. Furnaces should generally be wired with a plug instead of hard wired unless required by local codes. If hard wired, a disconnect should be included for maintenance. Plugged connections allow the furnace to be rotated, if necessary, and provide a convenient method for disconnecting power when servicing. 3.3. Venting: Combustion products from burned asphalt and coke must be exhausted outside. Typically, furnaces are exhausted in one of three manners: Furnace is ducted directly outside using a short length (10–15 feet) of 3- to 4-inch- diameter duct (depending on manufacturer’s recommendations). Furnace is ducted into a fume hood system with an external fan system using a short length of 3- to 4-inch-diameter duct. This should be an “open air” connection to allow free flow of air around the end of the duct and into the hood. The small 3- to 4-inch-diameter pipe from the furnace is connected to a larger diameter pipe using a sealed connection. Larger diameter pipe uses a booster blower and damper control system activated when a test is started. Consideration needs to be given to the overall room air pressure when using furnaces in laboratories with strong exhaust systems. Negative air pressure could cause exhaust to be pulled out of the furnace through the combustion air intakes. Each of these options is discussed in greater detail below. 3.3.1. Follow manufacturer’s recommendations when selecting duct material. All furnaces use a secondary, higher temperature chamber to further oxidize volatiles. Temperatures in this secondary chamber range from 750°C to 900°C. Exhaust is then mixed with ambient plenum box. For the Carbolite furnace, soot must be removed from the plenum chamber, impeller, chimney, and ducts. The plenum chamber is accessed through the

I-4 temperature air before exiting the furnace. This can still result in hot exhaust gas temperatures. Manufacturer’s recommendations should be followed when venting exhaust pipes through walls or roofs that include the use of a larger diameter galvanized thimble when penetrating walls/roofs made of combustible materials. 3.3.2. Where possible, exhaust ducts should be less than 10 feet in length (Troxler maximum length is 15 feet; ThermoFisher may be up to 15 feet, depending on results from lift test.) and have a minimal number of 90-degree elbows. Depending on the manufacturer, 3- to 4-inch pipe is typically used. Use of flexible pipe prevents sharp bends, which inhibit exhaust flow. Dampers should not be used as these tend to collect soot. Exterior exhaust outlets should be positioned away from fresh-air intakes such that smoke is not pulled back into the laboratory. 3.3.3. In larger labs or buildings where exhaust cannot be ventilated outside in a 10-foot pipe run, the ignition furnace exhaust may be vented into a larger exhaust system. One example is to place the furnace inside a fume hood or under an exhaust hood and run the smaller diameter exhaust pipe from the furnace into the upper portion of the fume hood (Figure 1). Troxler recommends that the small diameter exhaust pipe should be at least 18 inches away from the intake to the external fan or blower. This is meant to keep the exhaust system from experiencing negative airflow. Figure 1—Ignition furnace vented into fume hood 3.3.4. Where several furnaces are used, they can be connected to a larger diameter exhaust pipe with the addition of a booster blower/fan (Figure 2). Carbolite does not recommend this configuration. The larger pipe should be equipped with a damper to allow air flow to be

I-5 adjusted to prevent too much air from being drawn through the furnaces. There must be negative pressure at the damper to prevent exhaust from entering the laboratory. The booster blower should only run when a test is being performed. Figure 2—Multiple unit installation with booster blower 3.3.5. For direct vent or multiple unit installations in laboratories with overall room exhaust systems, care must be taken that there is not excessive negative air pressure in the room that would result in fumes being pulled from the furnace through the air intakes or door seals. Excessive negative air pressure can be addressed by providing make-up air. In its most simple form, make-up air may be provided by opening a window. More elaborate systems with make-up air provided through heat exchangers can be designed. For furnaces that use internal balances, lift should be checked after the exhaust pipe is connected as described in Section 5. Insufficient lift with a new, clean ThermoFisher furnace is an indication of excess negative air pressure in the laboratory. 3.3.6. Laboratories maintaining AASHTO R 18 accreditation or equivalent agency programs will be required to calibrate furnaces containing internal scales upon installation. 3.3.7. For ThermoFisher furnaces, perform lift test after installation is complete to ensure compliance with recommended values for model.

I-6 AASHTO T 308 describes the test procedure for asphalt content determination using an ignition furnace. The manufacturer’s manual describes operation of specific furnace models. The following describes additional practices that may help reduce variability. 4.1. Obtaining and Reducing Samples for Testing—Several round-robin ignition furnace tests performed on individual, laboratory-prepared samples indicated extremely low within- and between-laboratory standard deviations. This was particularly true for samples with low correction factors for aggregate loss. These low standard deviations do not include variability from sampling and splitting. Asphalt plant operators should follow best practices for loading trucks to minimize segregation. This includes such practices as ensuring adequate material is in the silo prior to loading (if silos are used) and the use of multiple drops. Based on AASHTO T 168, referenced in AASHTO T 308, truck samples should consist of material from three separate locations in the truck and the very top material should be removed. When sampling behind a paver, care should be used to ensure that all of the material inside the template is removed for the full depth of the layer. Obviously, placement segregation can affect the asphalt content and gradation of a sample taken behind the paver and may not represent the mix produced by the asphalt plant. Such a sample taken behind the paver should represent the expected performance of the mixture at that location. AASHTO R 47 describes several methods for reducing the bulk sample obtained according to AASHTO T 168 to the test size specified in AASHTO T 308 for the nominal maximum aggregate size of the mix. It is important to be consistent in the manner in which splitting devices, scoops, and spatulas are scraped, particularly when dealing with stone matrix asphalt, open-graded friction courses, or similar mixes with high binder film thickness. 4.2. Loading Sample Baskets—When loading the sample into the sample basket(s), it is important to evenly distribute the sample and to ensure that the sample is kept approximately ¾ to 1 inch away from the sides of the basket(s). Once the asphalt is burned off the aggregate, some of the aggregate particles are smaller than the basket opening. Keeping the sample away from the sides of the basket(s) helps to prevent the loss of aggregate outside of the baskets. Lost aggregate shows up as increased asphalt content and could alter the gradation (slightly). 4.3. Initial Sample Weight, Temperature, and Moisture Content—Most contractors will split out a hot sample from the truck, load the sample baskets, weigh the sample, and begin the asphalt content determination test immediately. Agencies and consultants may reheat the sample. Depending on the number of samples being tested, samples may be allowed to cool in the sample baskets prior to being loaded into the ignition furnace. The effects of 4. FURNACE OPERATION/ASPHALT CONTENT DETERMINATION

I-7 these different handling practices have not been studied. The following are recommended for consistency: AASHTO T 308 specifies that the sample be dried to constant mass at 110 ± 5°C or that the moisture content of a companion sample be determined according to AASHTO T 329. If the moisture content is determined according to AASHTO T 329, this sample should be conditioned in the same manner as the test sample for asphalt content. For example, it should be stored at room temperature or in an oven for the same time as the asphalt content sample and both initial weights determined immediately before loading the asphalt content sample into the furnace. When using a furnace with an internal balance, AASHTO T 308 specifies that the initial mass of the sample and basket(s) be compared with the mass measured by the furnace’s internal balance. This is to ensure that the baskets are not rubbing against the furnace wall or that the hearth plate was not shifted during placement of the basket(s), causing the hearth tray tubes to bind as they pass through the floor of the furnace. Differences greater than 5 grams may indicate the basket is in contact with the furnace wall. The Carbolite’s balance pan extension has a rim to prevent the basket assembly from contacting the walls of the furnace. When following AASHTO T 308 Method B, it is important that after the initial burn period the sample be allowed to cool for approximately 30 minutes before an initial weight is determined, the sample should be returned to the furnace for an additional 15 minutes, and then the cooling and weighing procedure repeated until a constant mass (less than 0.01 percent change from the initial mass) is determined, as described in AASHTO T 308, Sections 8.8 through 8.14. 4.4. Test Temperature(s) or Burn Profile—Test temperature has a significant influence on a mixture’s correction factor, particularly for high-loss aggregates. Gilson furnaces allow multiple set point temperatures throughout the test. Troxler uses “burn profiles” and Carbolite “recipes” in a similar manner. The Troxler burn profile controls the temperature of the infrared element and the blower speed. The following describes a typical ignition furnace burn cycle: The furnace is at an initial set point temperature. Gilson refers to this as the “preheat” temperature. The standard temperature is 538°C. The furnace exhaust blower is not running or is running at a low speed during the preheat, depending upon the furnace model. When the furnace door is opened to load the sample, the temperature in the furnace chamber decreases. The time the furnace door is open should be minimized. Once the furnace door is closed and the test is started, the heating elements begin to heat the basket(s) and sample back to the set point temperature. The exhaust fan is activated. (The Troxler NTO’s exhaust fan runs at a slow speed when the furnace is at idle and when the sample is coming up to ignition temperature.)

I-8 Some volatiles in the asphalt will be driven off before the sample reaches ignition temperatures. Once the asphalt ignites, the furnace temperature may spike higher than the set point as the chamber is heated by the burning asphalt (assuming sufficient available oxygen). If the set point temperature is lower, it tends to take longer for the sample to ignite, allowing more volatiles to be driven off before ignition and minimizing the spike in temperature. Once the majority of the volatiles are burned off, there are still coke-type residual products that must be burned off. An initial decoking time (and temperature) is programmed as part of the Gilson furnace set up. Samples tested in furnaces without an internal balance need to be iteratively removed from the furnace, allowed to cool to room temperature (approximately 30 minutes), and weighed until the difference in loss does not exceed 0.01 percent of the initial mass per AASHTO T 308. Weighing the sample at a consistent temperature is important to obtain repeatable results. The standard end point is defined as a change in sample mass of less than 0.01 percent of the initial sample mass. For high-loss aggregates, continued aggregate degradation can occur even after all of the asphalt has been removed. AASHTO T 308 allows that the end point may be changed to a mass loss less than 0.02 percent of the initial sample weight for such aggregates. 4.5. Cooling Sample/Basket(s) After Removing from Furnace—A concrete paver block or manufacturer-supplied heat stand can be used as a heat sink to help cool sample/basket(s) more quickly. The sample should be covered with the manufacturer-supplied protective cage to protect against accidental contact with the hot basket(s). Fans are not recommended to aid in cooling as fines may be blown out of the basket(s). 4.6 Developing Correction Factors for Aggregate Loss—The Annex to AASHTO T 308 includes mandatory information on developing mix correction factors for aggregate loss. Correction factors are mix specific. All of the components that will be used in the mix need to be included when determining the correction factor (such as fiber, lime, etc.). To obtain accurate correction factors, a “butter” mix should first be prepared in the mixing bowl. Mixing paddle, whisk, and any spatulas should be scraped in the same manner that will be used for the actual calibration samples. If the correction factor exceeds 1.0% at 538°C, reducing the test temperature or changing the burn profile (Troxler) can lower the correction factor. It is typically impossible to determine the correction factor for recycled materials. Therefore, the asphalt content of recycled materials needs to be determined by solvent extraction and that asphalt content accounted for in the total asphalt content of the calibration sample.

I-9 4.7. Troubleshooting—The following can help troubleshoot asphalt contents that appear erroneous: Even when using a furnace with an internal balance, it can be beneficial to measure an overall mass of the cooled sample/basket(s) prior to removing the recovered aggregate. This mass can be used along with an initial mass to manually calculate the asphalt content. If the basket was touching the furnace wall and this was not initially noticed as described above, this method can be used as an alternate. However, some agencies may not accept asphalt contents calculated in this manner. Data should be viewed in context. Segregated samples may have a major effect on the measured asphalt content. This can be confirmed when the gradation analysis is performed according to AASHTO T 30. Trends can also be checked against theoretical maximum specific gravities measured on splits of the same sample. In some cases, coarse aggregate particles may fracture during testing. Research indicates that this small amount of fracturing does not typically have a significant effect on the measured gradation. Significant amounts of coke-type residue remaining on the sample can result from a number of factors: – The sample size may have been larger than specified. – The sample may not have been spread out uniformly. – The exhaust system may be dirty, inhibiting the blower from pulling additional air to support ignition into the furnace. Clean the exhaust system (see Section 5.). – This can occur with mixes with high asphalt contents or polymer-modified binders. The Troxler NTO’s burn profile Option 2 is designed for such mixes. The decoking period should be increased with Gilson furnaces. – Mixes containing hydrated lime tend to have a gray-colored residue remaining on the aggregate. For mixes containing cellulose or other fibers that burn at temperatures less than 538°C, fluctuations in fiber content may be observed as fluctuations in asphalt content. Glass fibers in reclaimed asphalt shingles do not typically burn. 5. FURNACE MAINTENANCE Recommended furnace maintenance varies from model to model. Please see the manufacturer’s instructions. 5.1. Scale Calibration—Furnaces with internal scales need to be calibrated every 12 months to meet AASHTO R 18 requirements. 5.2. Exhaust System—All furnaces require the exhaust system to be periodically cleaned. The filter on the Gilson furnace must be cleaned before each test.

I-10 The blower on the ThermoFisher (or older Thermolyne) models should be cleaned and oiled every 6 months or when the furnace fails the lift test. The lift test is performed by taring the scale in idle mode and starting a test with an empty chamber. Recommended lift will vary depending on serial number, but ranges from −2 to −6 grams. The lift test should be performed once per week when the furnace is used regularly (20 to 25 samples per week). More frequent monitoring may be required if running high asphalt/heavily modified mixtures. Cleaning involves removing the exhaust pipe from the blower motor, vacuuming, and lubricating the blower motor. For newer ThermoFisher models, hitting the #7 key when the furnace is idle will display both the chamber and filter temperatures. The filter temperature should be 750 +/- 10 °C. Low filter temperatures indicate the filter element is burned out and should be replaced to prevent clogging of the filter assembly. The Troxler NTO has a side exhaust plenum box that needs to be cleaned when total burn time, since the last cleaning, exceeds 1,050 minutes or there are other indications of blockage such as smoke leaking into the lab or incomplete burns. The exhaust fan blades should also be cleaned with a soft-bristled brush and the excess soot removed with a vacuum with appropriate filter. The Carbolite also has a side plenum box that needs to be cleaned with a vacuum along with the fan (impeller). Excessive soot build up may require the motor/impeller assembly to be removed from the back of the plenum chamber to allow access for complete cleaning. 5.3. Furnace Chamber—The furnace chamber can be cleaned of soot or other coke products by allowing the furnace to idle at a higher temperature for a period of two to four hours. ThermoFisher recommends setting the chamber temperature to 650°C for cleaning. Troxler has a built-in cleaning cycle. Carbolite recommends heating the chamber to 750°C for one hour. After the furnace has been allowed to cool, the chamber can be vacuumed. Some chambers contain refractory ceramic material, which can be hazardous. The manufacturer’s recommendations should be followed when cleaning or maintaining the inside of the furnace chamber. 5.4. Replacement of Heating Elements—The Carbolite, Gilson, and Troxler furnaces have exposed elements. The furnace power must be disconnected before touching the furnace elements—read the manufacturer’s warnings! The Gilson and ThermoFisher (or older Thermolyne) furnaces have replaceable heating elements. Failed elements in the Carbolite furnace require replacement of the complete insulation assembly. The Carbolite furnace includes indicator lights to confirm the elements are working. For the other furnace model/brands, a furnace that is slow to heat up or recover is a good indication of a failing element. Research conducted by the National Center for Asphalt Technology indicated that a failed heating element should not affect the measured asphalt content. However, if the furnace temperature is slow to preheat or recover temperature, the

I-11 manufacturers’ manuals contain instructions for replacing elements. Dense smoke from the furnace exhaust could indicate a problem with the after-burner heating element(s). HMA Lab Supply’s NCAT Maintenance Tips includes additional tips for identifying failed elements. 5.5. Door Seals/Alignment—With time, door seals may fail or furnace doors may come out of alignment. If there are indications of soot or volatiles around the door, contact the manufacturer. ThermoFisher includes instructions for realigning the door, which may solve the problem.

Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S.DOT United States Department of Transportation

TRA N SPO RTATIO N RESEA RCH BO A RD 500 Fifth Street, N W W ashington, D C 20001 A D D RESS SERV ICE REQ U ESTED ISBN 978-0-309-44637-2 9 7 8 0 3 0 9 4 4 6 3 7 2 9 0 0 0 0 N O N -PR O FIT O R G . U .S. PO STA G E PA ID C O LU M B IA , M D PER M IT N O . 88 V ariability of Ignition Furnace Correction Factors N CH RP Research Report 847 TRB