34) Extraction Of Bitumen From Paving Mixtures 72d2q

Extraction of Bitumen from Bituminous Paving Mixtures Introduction: These test methods cover the quantitative determination of bitumen in hot mixed paving mixtures and pavement samples. Aggregate obtained by these test methods may be used for sieve analysis using Test Method C 117 and Test Method C 136. The paving mixture is extracted with trichloroethylene, 1, 1, 1-trichloroethylene or methylene chloride using the extraction equipment applicable to the particular method. The bitumen content is calculated by difference from the mass of the extracted aggregate, moisture content, and mineral matter in the extract. The bitumen content is expressed as mass percent of moisture free mixtures. All of these test methods can be used for quantitative determinations of bitumen in hot mixed paving mixtures and pavement samples for specification acceptance, service evaluation, control, and research. Each method prescribes the solvent or solvents and any other reagents that can be used in the test method. Test method D 1856 requires that Method A be used when asphalt is recovered from solution. Objectives: Objective of these tests is to determine the quantity of bitumen in hot mixed paving mixtures and pavement samples. Aggregate obtained by these test methods may be used for sieve analysis using Test Method C 117 and Test Method C 136. Apparatus: The following apparatus are required. 1) Oven – capable of maintaining the temperature at 230 ± 90 F (110 ± 50 C). 2) Pan – flat, 12 in. (305 mm) long, 8 in. (203 mm) wide and 1 in. (25 mm) deep. 3) Balance or balances – having an accuracy of at least 0.01 % of the sample mass. 4) Hot Plate – electric, 700-W continuous or low, medium, and high settings. 5) Small-Mouth Graduate – 1000 or 2000 ml capacity. Optional small-mouth graduate, 100 ml capacity. 6) Ignition Dish – 125 ml capacity. 7) Desiccator. 8) Analytical Balance. 9) Reagents.

Figure 1 – Centrifugal Extractor.

In addition to the apparatus listed in above, following apparatus are required for Test Method A: 10) Extraction Apparatus – consisting of a bowl approximating that shown in Figure 2 and an apparatus in which the bowl may be revolved at controlled variable speeds up to 3600

r/min. The speed may be controlled manually or with a preset speed control. The apparatus should be provided with a container for catching the solvent thrown from the bowl and a drain for removing the solvent. The apparatus preferably shall be provided with explosion proof features and installed in a hood or an effective surface exhaust system to provide ventilation. Note 1: Similar apparatus of larger size may be used.

Figure 2 – Extraction Apparatus. 11) Filter Rings – felt or paper, to fit the rim of the bowl. Note 2: Low-ash paper filter rings may be used in place of the felt filter ring. Such filter rings shall consist of low ash filter paper stock 0.05 ± 0.005 in. thick. The nominal base weight of the paper shall be 330 ± 30 lb for a ream (500 sheets – 25 by 38 in.). The ash content paper should not exceed 0.2 % (approximately 0.034 g per ring). Procedure: Sampling Procedure: 

Samples were obtained in accordance with Practice D 979.

Preparation of Test Specimens: 1) If the mixture was not sufficiently soft to separate with a spatula or trowel, it was placed in a large, flat pan and warmed to 230 ± 9 0 F (110 ± 50 C) only until it could be handled or mixed. The material was split or quartered until the mass of material required for test was obtained. 2) The size of the test sample shall be governed by the nominal maximum aggregate size of the mixture and shall conform to the mass requirement shown in Table 1 (Note 3).

Note 3: When the mass of the test specimen exceeds the capacity of the equipment used (for a particular method), the test specimen may be divided into suitable increments, tested and the results appropriately combined for calculation of bitumen content. Nominal Maximum Aggregate Size standard, mm 4.75 9.5 12.5 19.0 25.0 37.5

Table 1 – Size of Sample Sieve Size Minimum Mass of Sample (kg) (No. 4) 3/8 in. ½ in. ¾ in. 1 in. 1½ in.

0.5 1 1.5 2 3 4

3) In addition, a test specimen was required for the determination of moisture in the mixtures. This test specimen was taken from the remaining sample of the mixture immediately after obtaining the extraction test specimen. Note 4: If recovery of bitumen from the solution obtained from the extraction test is not required, the entire test specimen may be dried to constant mass in an oven at a temperature of 230 ± 90 F (110 ± 50 C) prior to extraction instead of determining the moisture content. Determination of Moisture Content: 

The moisture content of the mixture in accordance was determined using the procedure described in Test Method D 1461.



The mass water, W2, in the extraction test portion was calculated by multiplying mass percent water by the mass of the extraction test portion, W1.

Test Procedure: 1) The moisture content of the material was determined. 2) A 650 to 2500 g test portion was placed in to a bowl. 3) The test portion in the bowl with trichloroethylene, 1, 1, 1-trichloroethylene or methylene chloride was covered and allowed sufficient time for the solvent to disintegrate the test portion (not over 1 h). 4) The bowl containing the test portion and the solvent was placed in the extraction apparatus. 5) The mass of the filter ring was dried and determined and fitted it around the edge of the bowl. The cover on the bowl was clamped tightly and a beaker was placed under the drain to collect the extract. 6) The centrifuge was started revolving slowly and gradually increase the speed to a maximum of 3600 r/min or until solvent ceased to flow from the drain. 7) The machine was allowed to stop, 200 ml of trichloroethylene, 1, 1, 1-trichloroethylene or methylene chloride was added and repeated the procedure. A sufficient 200 ml solvent addition (not less than three) was used so that the extract was not darker than a light straw

color. The extract washings were collected in a suitable graduate. 8) The filter ring was removed from the bowl and dried in air. If felt filter rings were used, mineral matter adhering to the surface of the ring was brushed off and added to the extracted aggregate. The ring was dried to constant mass in an oven at 230 ± 9 0 F (110 ± 50 C). 9) All the contents of the bowl were carefully removed into a metal pan and dried on a steam bath and then, dried to constant mass in an oven or on a hot plate at 230 ± 9 0 F (110 ± 50C). If trichloroethylene or trichloroethane was used as the extraction solvent, the preliminary drying on a steam bath may be omitted. 10) The mass of the extracted aggregate, W3, was equal to the mass of the aggregate in the pan plus the increased in mass of the filter rings. 11) The following alternative procedure was used when low ash filter rings were used: The aggregate and filter rings were placed in a clean metal pan. Dried as specified above. The dried filter ring was carefully folded and stand it on the aggregate. The filter ring was burned by igniting with a Bunsen burner or match. The mass of the extracted aggregate in the pan, W3, was determined. Note 5: Since dry aggregate absorbs moisture when exposed to air containing moisture, determine the mass of the extracted aggregate immediately after cooling to a suitable temperature. 12) The amount of mineral matter in the extract was determined by any of the test methods such as Ashing Method, Centrifuge Method or Volumetric Method. 13) In here we used the Centrifuge Method. Centrifuge Method: 1) For this test method, any suitable high-speed (3000 g or higher) centrifuge of the continuous flow type was used. 2) The mass of a clean empty centrifuge cup (or bowl) to 0.01 ± 0.005 g was determined and placed in the centrifuge. 3) A container was positioned at the appropriate spout to catch the effluent from the centrifuging operation. 4) All of the extract from Test Method A was transferred to an appropriate (feed) container suitably equipped with a feed control (value or clamp, etc.). 5) To ensure quantitative transfer of the extract to the feed container, the receptacle containing the extract was washed several times with small amounts of clean solvent and the washings were added to the feed container. 6) The centrifuge was started and allowed to reach a constant operational speed. 7) The feed line was opened and feed the extract into the centrifuge at a rate of 100 to 150 ml/min. 8) After all the extract had ed through the centrifuge, the feed mechanism (with centrifuge still running) was washed with several increments of clean solvent, allowing each increment to run through the centrifuge until the effluent was essentially colorless. 9) The centrifuge was allowed to stop and removed the cup (or bowl). The outside was

cleaned with fresh solvent. The residual solvent was allowed to evaporate in a funnel or steam hood and then the container was dried in an oven controlled at 230 ± 90 F (110 ± 50 C). 10) The container was cooled and the mass was redetermined immediately. The increase in mass was the mass of mineral matter, W4, in the extract. Observation: Initial weight of bowl

= 1228.8 g

Weight of bowl with asphalt

= 2297.4 g

Initial weight of filter paper

= 13.87 g

Dry weight of filter paper

= 15 g

Weight of bowl with dry aggregate = 2252.8 g Calculations and result: Calculation of Bitumen Content 

The percent bitumen in the test portion was calculated as follows:

Bitumen content, % = (W1 – W2) – (W3 + W4) x 100 (W1 – W2) Where; W1 = mass of test portion. W2 = mass of water in the test portion. W3 = mass of the extracted mineral aggregate. W4 = mass of the mineral matter in the extract. Specimen Calculation: W1 = 2297.4 – 1228.8 = 1068.6 g W2 = 0 (Test portion was heated, therefore no moisture in the test portion.) W3 = 2252.8 – 1228.8 = 1024 g W4 = 15 – 13.87 = 1.13 g Bitumen content, % = (1068.6 – 0) – (1024 + 1.13) x 100 (1068.6 – 0) = 4.07 %

General Discussion: Determination of bitumen content of paving mixers is important for quality control, acceptance testing or forensic analysis. There are several methods which can be used to extract bitumen in paving mixers , namely solvent extraction, nuclear asphault content gauge, ignition furnance method. Solvent extraction This is an older method, uses a solvent(trichloroethylene or methylene chloride) to remove the asphalt binder from aggregates. Asphalt binder/solvent and aggregates are separated using a centrifuge. This test method takes longer time than others are it may be hazarded due to the nature of the specific solvent used. Nuclear asphalt content gauge In this method, asphault content is measured, by estimating the actual numbers of the hydrogen atoms contains within a sample. Hydrogen atom content is indirectly correlated to find the asphalt content of the mix. This test is relatively rapid test but it may give erroneous results when anything affecting the number of hydrogen nuclei in the sample. Ignition method This method determines asphault binder content by burning off the asphault binder of a loose HMA sample. This test replaces the solvent extraction method discussed earlier. A correction factor has to be used to any aggregate fines burned off during the ignition process. This method is also a relatively rapid method there are equipments have developed to produce automated statistic based results in soft format.