Testing Tack Coat Applications

Sampling Asphalt Emulsion

The purpose of sampling an emulsion is to choose a selection for testing that accurately represents the material in the storage tank. To accurately represent the material in question, only sample from the storage tank at the emulsion manufacturing facility.  Do not allow the sample to be taken from the onsite storage tank or distributor as contamination will be possible. 

Sample Containers

• Containers for anionic emulsified asphalt samples shall be one-gallon wide-mouth jars or bottles made of glass or plastic.
• Containers for cationic emulsified asphalt samples shall be one-gallon wide-mouth jars or bottles made of glass or plastic. (Bare metal cans are corroded by emulsified asphalts, particularly the cationic type.  They also may cause the emulsion to break.)

 Sampling Precautions

• The container should be new and free from contaminants
• Fill container completely to minimize skin formation
• Protect the sample from freezing
• The container should be sealed with a tight fitting top as soon as the sample is taken.
• Sample should not be transferred into another container
• The container shall not be submerged in solvent, nor shall it be wiped wiht a solvent saturated cloth.
• The samples should be shipped to the laboratory the same day the sample was taken
• The sample should be labeled for shipping

 Additional resources for sampling procedures:

AASHTO T - 40, ASTM D140, A Basic Asphalt Emulsion Manual

Testing Asphalt Emulsions

Viscosity, Saybolt Furol at 25°C (77°F), sec:

This test measures the “fluidity” or consistency of the emulsion. Viscosity is a key engineering property for asphalt materials and is a measure of the resistance to flow. A sample is poured into a viscosity container with a plugged hole in the bottom. At the test temperature, the plug is removed and the number of seconds for the sample to flow out of the container is measured and reported. This test ensures that the bond coat can be adequately applied to the pavement.  If the viscosity is too high, the emulsion will not spray or flow and level properly. If the viscosity is too low, the emulsion may run off the edge of the road.

Sieve Test, %:

This test is used to determine the percent of oversized particles of asphalt binder. These particles might clog the nozzles of the application equipment. The sample is washed over a No. 20 sieve to determine the retained percentage of asphalt particles. This test may be waived if successful field application can be demonstrated.

Storage Stability, 24 hrs, %:

The purpose of this test is to detect the tendency of asphalt particles to “settle out” during storage of asphalt emulsions. Unit Weight @ 25°C (77°F), lbs/gal: This test is to determine the mass of a known volume of emulsion. Asphalt emulsions are usually sold on a ton basis and therefore a pounds per gallon unit weight allows project personnel to convert that weight to volume to determine the average emulsion application or spread rate.

Cement Mixing, %:

This test is used for slow-setting emulsions to ensure that the products won’t rapidly coalesce in contact with fine-grained soils or dusty aggregates. Cement is mixed with emulsion and washed over a No. 14 sieve to determine the percent retained. While required by some specifications, this property is not generally considered critical to bond coat quality.

Residue by distillation to 260°C (500°F),%:

Asphalt and water are separated by distilling the water from the emulsion. The proportions of asphalt and water are determined. The type of emulsion will determine the minimum required residue percentage. (Distillations at lower temperatures of 400°F (204°C) or 350°F(177°C) are typically used for polymer-modified emulsions to ensure that the polymer does not deteriorate or change due to the high temperatures.)

Tests on Distillation Residue

Penetration at 25°C (77°F), 100 g, 5 sec, 0.1 mm:

This test is used to measure the hardness of the asphalt recovered from the distillation test. A 100-gram weight is applied to a needle placed on the surface of asphalt in a container at 77°F (25°C). The distance the needle penetrates in 5 seconds is recorded in tenths of a millimeter. Lower penetration rates indicate harder asphalt.

Ductility @ 25°C (77°F), 5 cm/min, cm:

A dog bone shaped sample of residue by distillation is formed in a mold, allowed to cool, and then brought to 77°F (25°C) in a water bath. The sample is then pulled at a rate of 5 cm per minute until it fractures. The ductility value is how far the material elongates, in centimeters, until it fractures.

Solubility in Trichloroethylene (TCE), %:

This test measures the purity of the asphalt residue. A sample of asphalt or residue by distillation is dissolved in solvent and then filtered to determine percentage purity. Many agencies and suppliers no longer measure and report solubility because the test involves the use of a dangerous solvent which many polymers and other additives may not be soluble in this solvent, and because the results of this test are not critical to tack coat quality.