Oklahoma D.O.T.
Revised 12/01/10
OHD L-26
Page 1 of 29
OHD L-26
METHODS OF TEST FOR
DETERMINATION OF BITUMEN CONTENT IN
BITUMINOUS PAVING MIXTURES
SUMMARY OF METHODS
- Method A - Ignition Oven
- Method B - Nuclear Asphalt Content Gauge
- Method C - Centrifuge Extraction
- Method D - Reflux Extraction
- Method E - Tank Strap Method or Digital Printout
METHOD A - IGNITION OVEN
1SCOPE.
1.1This test covers the determination of asphalt content of bituminous paving mixtures by ignition of the asphalt cement at 1,000°F [538°C] in a furnace. The asphalt in a sample of bituminous paving material is burned by ignition at 1,000°F [538°C]. The asphalt content is calculated from the mass of ignited aggregate, moisture content, and temperature compensation for the change in mass of the sample container. The asphalt content is expressed as mass percentage of the moisture-free mixtures. This method may not be applicable to mixes containing fibers or ground tire rubber (dry process).
1.2This method may involve hazardous materials, operations, and equipment. This method does not purport to address all of the safety problems associated with its use. It is the responsibility of whoever uses this method to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2APPARATUS.
2.1A forced air ignition furnace, capable of maintaining the temperature at 1,202°F [650°C], with an internal balance thermally isolated from the furnace chamber accurate to 0.1 g. The balance will be capable of weighing a 3,500 g sample in addition to the sample baskets. The furnace will calculate a temperature compensation factor for the change in weight of the sample baskets and provide for the input of a correction factor for aggregate loss. The furnace will provide a printed ticket with the initial specimen weight, specimen weight loss, temperature compensation, correction factor, corrected asphalt content (%), test time, and test temperature. The sample chamber dimensions will be at least 14 x 10 x 14 in [35 x 26 x 35 cm] (WxHxD) A method for reducing furnace emissions will be provided. The furnace will provide an audible alarm and indicator light when the sample weight loss remains constant for two consecutive minutes. The furnace door will be locked until the completion of the test procedure.
NOTE: The National Center for Asphalt Technology (NCAT) Asphalt Content Tester manufactured by Barnstead/Thermolyne and distributed by QC Resource (800)296-7171 has been found to be suitable.
2.2Tempered stainless steel 3/32 in [2.36 mm] mesh or otherwise perforated baskets.
2.3One stainless steel catch pan.
2.4Oven capable of maintaining 257 ± 9°F [125 ± 5°C].
2.5Balance, 8-kg minimum capacity, sensitive to 1.0 g for weighing sample in baskets.
2.6Safety Equipment: safety glasses or face shield, high temperature gloves, and long sleeve jacket. Additionally, a heat resistant surface capable of withstanding 1202°F [650°C] and a protective cage capable of surrounding the sample baskets will be provided.
2.7Miscellaneous Equipment: pan dimensions (LxWxD) 15 x 15 x 2 in [38 x 38 x 5 cm] minimum for transferring samples after ignition, spatulas, bowls, and wire brushes.
3PREPARATION OF TEST SPECIMENS.
3.1The bituminous mixture used for preparing the test sample will be obtained in accordance with AASHTO T 168. The test sample will be prepared by splitting or quartering this material, in accordance with AASHTO R 47, to the appropriate size as shown in section 3.3.
3.2If the mixture is not sufficiently soft to separate with a spatula or trowel, place it in a large flat pan and warm to 257 ± 9°F [125 ± 5°C] for 25 minutes. The sample will not be heated for more than 1 hour.
3.3SAMPLE SIZES.
The minimum mass of the test sample is governed by the maximum aggregate size in the mixture. The maximum aggregate size for the purposes of these test methods is defined as the smallest sieve through which 100 percent of the material is required to pass. The maximum mass of the sample shall not be more than 500 g greater than the minimum mass. No sample shall be less than 1,000 g.
Table 1
Maximum Aggregate Size (in) / Maximum Aggregate Size (mm) / Minimum Mass of Sample (g) / Mixture Types1.5 / 37.5 / 2500 / S2, OGBB
1 / 25.0 / 2000 / S3
3/4 / 19.0 / 1500 / S4, SMA, PFC, RBL, UTBWC (Type C)
1/2 / 12.5 / 1200 / S5, OGFSC, Micro Surfacing (Types II and III), UTBWC (Type B)
3/8 / 9.5 / 1000 / S6, Micro Surfacing (Type I), UTBWC (Type A)
NOTE: When the mass of the test sample exceeds the capacity of the equipment used, the test sample may be divided into suitable increments for testing. The results are appropriately combined for calculation of bitumen content
4MOISTURE AND VOLATILES DETERMINATION.
Split or quarter the remaining mixture to obtain a test sample for moisture and volatile determination. The size of the test sample should be the same as recommended in Table 1 or 1,000 ± 250 g. Place the test sample in a tared pan and determine the mass to the nearest 0.1 gand record as W1m. Dry to a constant mass in an oven at a temperature of 257 ± 9°F [125 ± 5°C]. Determine the mass of the sample to the nearest 0.1 g and record as W5m. The moisture and volatiles weights are used in the determination of bitumen content in section 7.
NOTE:The same test specimen may be used for the moisture and volatiles determination and bitumen determination.
5CALIBRATION.
Two calibration procedures are provided. Either method may be required by the engineer. For mix designs containing Recycled Asphalt Pavement (RAP) the mixture calibration procedure will be used. To compensate for the binder in the RAP the binder content of the RAP must first be determined. Certain aggregate types may result in an unusually high correction factor and erroneous gradation results. Such mixes should be calibrated and tested at a lower temperature, typically 900°F [482°C] or as approved by the Engineer.
5.1MIXTURE CALIBRATION.
5.1.1This method may be affected by the type of aggregate in the mixture. Accordingly, to optimize accuracy, a calibration factor will be established with the testing of a set of calibration samples for each mix type. This procedure must be performed before any acceptance testing is completed.
5.1.2Two calibration specimens conforming to the mass requirements of Table 1 shall be prepared at the design asphalt content ±0.5%. If RAP is used, adjust the asphalt quantity used in mixing the specimens to allow for the asphalt binder contained in the RAP.
5.1.3The freshly mixed specimens may be placed directly in the sample baskets. If allowed to cool, the samples must be preheated in a 257 ± 9°F [125 ± 5°C] oven for 25 minutes.
5.1.4Preheat the ignition furnace to 1,000 F [538°C]. Record the furnace temperature (set point) prior to the initiation of the test.
5.1.5Enter a correction factor of 0.00 in the ignition furnace.
5.1.6Weigh and record the weight of the two sample baskets and catch pan.
5.1.7Place the bottom sample basket in the catch pan. Evenly distribute approximately one half of the calibration specimen in the lower basket taking care to keep the material away from the edges of the basket. Place the upper sample basket on the bottom basket assembly. Evenly distribute the remaining specimen in the top basket. Use a spatula or trowel to level the specimen.
5.1.8Weigh and record the specimen, baskets, and catch pan. Calculate and record the initial weight of the sample specimen (total weight minus the weight of the sample basket assembly).
5.1.9Input the initial weight of the sample specimen in whole gram into the ignition furnace controller. Verify that the correct weight has been entered.
5.1.10Open the chamber door and place the sample baskets in the furnace. Close the chamber door and verify that the sample weight (including the baskets) displayed on the furnaces scale equals the total weight recorded in Section 5.1.8 within 5 g. Differences greater than 5 g or failure of the furnace scale to stabilize may indicate that the sample baskets are contacting the furnace wall. Initiate the test by pressing the start/stop button. This will lock the sample chamber and start the combustion blower.
5.1.11Allow the test to continue until the stable light and audible stable indicator indicates the test is complete. Press the start/stop button. This will unlock the sample chamber and cause the printer to print out the test results.
5.1.12Repeat steps 5.1.3 through 5.1.11 for the second calibration specimen.
5.1.13Once the calibration specimens have been burned, determine the difference between the actual and measured asphalt contents for each specimen. The ignition oven correction (IOC) factor is the average of the measured differences. If the difference is greater than 0.15 percent, run two more calibration specimens. Discard the largest and smallest IOC’s. Report the IOC as the average of the remaining two to the nearest 0.01 percent.
5.1.14The calibration procedure for a given mix should be repeated for every 50,000 tons (45,350 metric tons) of material produced or as requested by the engineer.
5.2AGGREGATE CALIBRATION.
5.2.1This method may be affected by the type of aggregate in the mixture. Accordingly, to optimize accuracy, a calibration factor will be established with the testing of a set of calibration samples for each mix type. This procedure must be performed before any acceptance testing is completed. This procedure should not be used if RAP is contained in the mix design.
5.2.2Two blank (aggregate only) calibration specimens conforming to the mass requirements of Table 1 shall be prepared to meet the JMF.
5.2.3Preheat a specimen in a 257 ± 9°F [125 ± 5°C] oven for 20 minutes. Thoroughly mix the specimen with a spatula prior to introducing it into the sample baskets.
5.2.4Preheat the ignition furnace to 1,067°F [575°C]. Record the furnace temperature set point prior to the initiation of the test. Enter a correction factor of 0.0 in the ignition furnace.
5.2.5Weigh and record the weight of the two sample baskets and catch pan.
5.2.6Place the bottom sample basket in the catch pan. Evenly distribute approximately one half of the calibration specimen in the lower basket taking care to keep the material away from the edges of the basket. Place the upper sample basket on the bottom basket assembly. Evenly distribute the remaining specimen in the top basket. Use a spatula or trowel to level the specimen.
5.2.7Weigh and record the specimen, baskets, and catch pan. Calculate and record the initial weight of the sample specimen (total weight minus the weight of the sample basket assembly).
5.2.8Input the initial weight of the sample specimen in whole gram into the ignition furnace controller. Verify that the correct weight has been entered
5.2.9Open the chamber door and place the sample baskets in the furnace. Close the chamber door and verify that the sample weight (including the baskets) displayed on the furnaces scale equals the total weight recorded in Section 5.2.8 within 5 g. Differences greater than 5 g or failure of the furnace scale to stabilize may indicate that the sample baskets are contacting the furnace wall. Initiate the test by pressing the start/stop button. This will lock the sample chamber and start the combustion blower.
5.2.10Allow the specimen to remain in the furnace until the stable light comes on. If the light does not come on within one hour, note percent loss and recheck every 15 minutes until no change in percent loss occurs. At this time press the start/stop button to end. This will unlock the sample chamber and cause the printer to print out the test results.
5.2.11Repeat steps 5.2.3 through 5.2.11 for the second calibration specimen.
5.2.12Once the calibration specimens have been burned, determine the ignition oven correction (IOC) factor for each. If the difference in the two IOC’s is greater than 0.15 percent, run two more calibration specimens. Discard the largest and smallest IOC’s. Report the IOC as the average of the remaining two to the nearest 0.01 percent.
5.2.13The calibration procedure for a given mix should be repeated for every 50,000 tons (45,350 metric tons) of material produced or as requested by the engineer.
6TEST PROCEDURE.
6.1Preheat the ignition furnace to 1,000°F [538°C]. Record the furnace temperature (set point) prior to the initiation of the test.
6.2Enter the correction factor for the specific mix to be tested as determined in Section 5 in the ignition furnace.
6.3Weigh and record the weight of the two sample baskets and catch pan (with guards in place).
6.4Prepare the sample as described in Section 3. Place the bottom sample basket in the catch pan. Evenly distribute approximately one half of the specimen in the lower basket taking care to keep the material away from the edges of the basket. Place the upper sample basket on the bottom basket assembly. Evenly distribute the remaining specimen in the top basket. Use a spatula or trowel to level the specimen.
6.5Weigh and record the sample, baskets, and catch pan. Calculate and record the initial weight of the sample specimen (total weight minus the weight of the sample basket assembly).
6.6Input the initial weight of the sample specimen in whole gram into the ignition furnace controller. Verify that the correct weight has been entered.
6.7Open the chamber door and place the sample baskets in the furnace. Close the chamber door and verify that the sample weight (Including the baskets) displayed on the furnaces scale equals the total weight recorded in Section 6.5 within 5 g. Differences greater than 5 g of failure of the furnace scale to stabilize may indicate that the sample baskets are contacting the furnace wall. Initiate the test by pressing the start/stop button. This will lock the sample chamber and start the combustion blower.
6.8Allow the test to continue until the stable light and audible stable indicator indicate the test is complete. Press the start/stop button. This will unlock the sample chamber and cause the printer to print out the test result.
6.9Open the chamber door, remove the sample baskets and allow to cool to room temperature (approximately 30 minutes). Allow the specimen to cool to room temperature in the sample baskets.
6.10Empty the contents of the baskets into a flat pan. Use a small wire sieve brush to ensure that any residual fines are removed from the baskets.
6.11Perform the gradation analysis according to AASHTO T 30.
7CALCULATIONS.
Where:
% AC=Percent asphalt cement (percent bitumen);
P5m=Apparent asphalt content from ignition oven;
W1m=Mass of moisture sample before drying; and
W5m=Mass of moisture sample after drying.
8REPORT.
The report shall include the following:
The method used and the input data used to compute the percent bitumen.
Percent bitumen reported to the nearest tenth.
Oklahoma D.O.T.
Revised 12/01/10
OHD L-26
Page 1 of 29
METHOD B - NUCLEAR ASPHALT CONTENT GAUGE
1SCOPE.
1.1This method covers the determination of bitumen content in bituminous paving mixturesby the use of the Nuclear Asphalt Content Gauge.
1.2The paving mixture is examined with a device that utilizes neutron thermalization techniques.
1.3This method may involve hazardous materials, operations, and equipment. This method does not purport to address all of the safety problems associated with its use. It is the responsibility of whoever uses this method to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2APPARATUS.
2.1Asphalt Content Gauge. Consists of an encapsulated and sealed neutron source such as americium/beryllium, thermalized neutron detectors such as helium-3 or boron tri-fluoride, read-out instrument such as a scaler or a direct-reading digital device calibrated in percent asphalt cement. Variability of the apparatus as 6 percent asphalt cement content shall be no greater than 0.05% for a 4 minute count. The variability of the apparatus is determined from the slope of the calibration curve and the standard deviation of the count rate. Variability is calculated as follows:
Where:
V=Apparatus variability, in % asphalt cement
S.D.=Standard deviation, in counts per automatically timed period
S=Slope, in counts per % asphalt cement
The standard deviation is calculated from 20 individual automatically timed readings taken on a sample with asphalt cement content with ± 0.5% of the mix design. The range of control mix should be between 2% and 14% asphalt cement by weight.
NOTE:The equipment shall be so constructed as to be licensable in accordance with applicable health and safety regulations. Equipment operators shall wear an approved form of radiation dosimetry film badge capable of monitoring the occupational radiation exposure.
NOTE:This procedure is sensitive to changes in moisture content. Do not place the equipment where large amounts of hydrogenous material may be moved during calibration or testing procedures (for example, water or plastic materials).
NOTE:Keep any other source of neutron radiation at least 30 ft [10 m] from the equipment.
NOTE:The asphalt content gauge is calibrated to its surrounding environment through the background count. Take new background counts at the frequencies specified in section 3 and section 6 of this procedure.
NOTE:Nuclear devices are subject to long term aging of the radioactive source, detectors, and other electronic systems, which may change the relationship
between count rate and asphalt cement content. Because of this aging, new calibration curves should be run each year.
2.2Oven. Capable of maintaining the temperature at 221°F to 347°F [105°C to 175°C].
2.3Balance. Minimum capacity of 10,000 g with sensitivity of 0.1 g and accuracy of 0.2 g.
2.4Straightedge. Steel, approximately 18 in [460 mm] in length.
2.5Plywood. 3/4 in [19 mm] or heavier, or metal plate, 3/8 in [9.5 mm] or heavier having an area slightly larger than the top of the sample pans.
2.6Sample Pans. Designed for use with asphalt content gauge.
3CALIBRATION.
3.1This method is sensitive to the type of aggregate, the percentage and source of asphalt cement, and the aggregate gradation. Accordingly, a calibration curve must be developed for each mix design. The curve can be established with four or more points.
3.2Sample the aggregates in accordance with AASHTO T 2. Enough aggregate should be obtained for a minimum of six (6) samples. Dry aggregates to a constant mass in an oven at a temperature of 221°F to 347°F [105°C to 175°C].