AASHTO TP 72-08(2015)

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Standard Method of Test for

Quantitative Determination of the

Percentage of Lime in Hot Mix

Asphalt (HMA)

AASHTO Designation: TP 72-08 (2015)1

American Association of State Highway and Transportation Officials

444 North Capitol Street N.W., Suite 249

Washington, D.C. 20001

TS-2c TP 72-1 AASHTO

Standard Method of Test for

Quantitative Determination of the Percentage

of Lime in Hot Mix Asphalt (HMA)

AASHTO Designation: TP 72-08 (2015)1

1. SCOPE

1.1. This method covers the quantitative determination of the percentage of lime in hot mix asphalt

(HMA) by calculation of the calcium hydroxide, Ca(OH)2, recovered from a sample of the

mixture. A specimen is obtained through drilling into the HMA and collecting the drilling dust.

The specimen is subjected to an acid filter boil and wash and is analyzed using either Atomic

Absorption (AA) Spectrometry or Ion Exchange Chromatography (IEC).

1.2. This standard may involve hazardous materials, operations, and equipment. This standard 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 appropriate safety and health practices and

determine the applicability of regulatory limitations prior to use.

2. REFERENCED DOCUMENTS

2.1. AASHTO Standards:

 M 231, Weighing Devices Used in the Testing of Materials

 T 308, Determining the Asphalt Binder Content of Hot Mix Asphalt (HMA) by the

Ignition Method

2.2. ASTM Standard:

 C25, Standard Test Methods for Chemical Analysis of Limestone, Quicklime, and

Hydrated Lime

3. SIGNIFICANCE AND USE

3.1. This test method is useful for determining the amount of lime added to an HMA mixture.

3.2. If the coarse aggregate contains limestone, the limestone aggregate will be dissolved by the acid

used in this method and can yield an unrealistically high result. If limestone is present in a

relatively minor amount, it is possible to run a background analysis on the raw aggregate. An

adjustment can then be made based on the background analysis in order to better approximate the

actual results. If the aggregate in the HMA contains an appreciable amount of limestone, this test

method is not suitable. Depending upon the concentration, the calcium content of any added lime

could be masked by the aggregate concentration. This effect would lead to a significant error in

overestimation of the amount of lime added.

TS-2c TP 72-2 AASHTO

4. APPARATUS

4.1. Atomic Absorption (AA) Spectrometry or Ion Exchange Chromatography (IEC)—These methods

are able to measure the concentration of chemical elements, in this case calcium, in aqueous

solutions. AA Spectrometry measures the intensity of a characteristic color imparted to a flame by

the presence of calcium ions in the test solution. IEC measures the change in electrical

conductivity of the solution. IEC can identify components of mixtures; AA Spectrometry can only

measure one element at a time.

4.2. Balance—An analytical balance conforming to M 231, Class B.

4.3. Heating Device—A small hot plate or other suitable device shall be available for supplying

sufficient heat under the flask to bring the solution to a boil. Suitable shields, baffle plates, or sand

baths shall be used on the surfaces of the hot plates to minimize localized overheating.

4.4. Rotary Hammer—An industrial size hammer drill with a 3/8-in. carbide drill bit.

4.5. Miscellaneous Equipment:

4.5.1. Automatic Pipette—Eppendorf or equivalent of adequate capacity to obtain a 1.0-mL sample.

4.5.2. Filter Funnel—Buchner or equivalent and filter paper, filter flask, and a vacuum source.

4.5.3. Glassware—100- and 250-mL flasks.

5. TEST SPECIMENS

5.1. Test specimens may be either laboratory-mixed HMA or sampled from HMA pavements.

5.2. Pavement specimens shall be taken from pavements with a core drill, diamond or carborundum

saw, or by other suitable means. Specimens will be further prepared as noted in Section 6.1.

5.3. Specimens shall be free from foreign materials such as foundation material, soil, paper, foil, etc.

5.4. If the core contains more than one pavement layer, it is recommended that the layers be separated

by sawing or other suitable means.

6. PROCEDURE

6.1. Preparation of Specimen:

6.1.1. A specimen is obtained from the drilling dust of a pavement core or laboratory-mixed HMA

sample. Stand the core on a thick piece of wood and use a heavy-duty rotary hammer with a 3/8-in.

carbide bit to drill into the sample.

Note 1—A rotary hammer that utilizes SDS, SDS Max, or spline shank bits is recommended.

Devices utilizing straight shank bits have been found to be insufficient. Depending upon the

number of samples, it may be worthwhile to make a frame to hold the core.

Note 2—It is recommended to wear safety glasses and protective gloves.

6.1.2. Drill to the depth of the drill flutes. This depth will yield about 15 g of dust. Discard any lumps of

the core that may break off.

TS-2c TP 72-3 AASHTO

6.1.3. Take the 15 ± 0.5 g of dust and determine its mass to the nearest 0.01 g. Place the dust in a

250-mL conical flask. Add 100 mL of 4 percent acetic acid and boil the mixture for 30 to 45 min.

Filter the mixture through a filter funnel (Buchner or equivalent) and wash the insoluble dust with

distilled water.

6.1.4. Transfer the filtrate to a 250-mL volumetric flask. Rinse the filter flask with distilled water and

add the washings to the contents of the volumetric flask. Add distilled water to the flask until the

total volume of its contents reaches 250 mL. Place a stopper in the flask, and shake it well to mix

the contents.

6.1.5. Use a pipette (an Eppendorf automatic pipette or equivalent) accurate to 0.1 mL to take a 1.0-mL

aliquot from the volumetric flask, and transfer this specimen to a 100-mL volumetric flask. Fill the

flask with distilled water until the total volume of its contents reaches 100 mL. Place a stopper in

the flask, and shake it well to mix the contents.

6.2. Analyze the drilling dust to determine the level of calcium ions present:

6.2.1. Run AA Spectrometry or IEC (according to the manufacturer’s recommendations) on the

specimen prepared in Section 6.1.5. Run calcium standards before and after the specimen analysis.

If using AA Spectrometry, do not add lanthanum salts.

Note 3—Theories exist that calcium is subject to interference with AA Spectrometry and this

condition can be overcome by adding lanthanum salts. However, in this procedure, it has been

found to provide an artificially high lime result.

6.2.2. The calcium ion concentration in the specimen should be in the range of 1 to 5 mg/L. If the

concentration is outside this range, it indicates the possible presence of limestone aggregate (see

Section 3.2).

7. CALCULATION OF RESULTS

7.1. Calculate the percentage of lime in the HMA as follows:

L = [[C × 46.25]/[10 × Wd × ((100 – AC)/100)]]/Lc (1)

where:

L = percentage of lime;

C = concentration of calcium from AA or IEC, mg/L;

Wd = mass of the dust, g;

AC = percentage of the binder in the mix, determined by T 308; and

Lc = percentage of calcium in the lime from ASTM C25 to the nearest 0.001 (e.g., 0.955).

7.1.1. Derivation of Equation 1:

The calcium content of the original solution is:

C × 100/4 mg/L or C × 25.

Hydrated lime is calcium hydroxide Ca(OH)2 with a molecular weight of 40 + 2(16 + 1) = 74.

To convert from mg/L of calcium to mg/L of lime, multiply by 74/40 or 1.85.

Therefore, the hydrated lime content is:

C × 25 × 1.85 mg/L or C × 46.25 mg/L

Hydrated lime is added to the mix as a percentage of the aggregate; therefore, the mass of the

aggregate in the dust specimen is included as [1000 × Wd × (100 – AC)/100] in grams or

[10 × Wd × (100 – AC)/100] in milligrams.

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