Engineering Brief # 46

January 17, 1991

Gentlemen:

Enclosed for your information and use is a copy of Engineering
Brief No. 46 and an advance copy of Change 3 to advisory
circular 150/5370-10A which withdraws Item P-625, Coal-Tar
Emulsion Seal Coat.

I sincerely hope that the revised specification will give us a
better product than the current specification. If you encounter
any problems in the laboratory or field while using the revised
specification please give me a call.

Sincerely,
ORIGINAL SIGNED BY:
RICHARD J. WORCH

Rlchard J. Worch
Acting Manager, Engineering and
Specifications Division

Enclosures

WORCH/rw/1/17/91/AAS-250
cc:
AAS-200/250
ARP-11B

ENGINEERING BRIEF NO. 46

ITEM P-625 COAL-TAR PITCH EMULSION SEAL COAT

Includes revisions contained in AAS-200
letter of June 24, 1991

DESCRIPTION

625-1.1 This item shall consist of an application of a
[rubberized] coal-tar emulsion seal coat, with or without mineral
aggregate, [and with the use of a latex rubber] applied on an
existing, previously prepared bituminous surface, in accordance
with these specifications for the area shown on the plans or as
designated by the Engineer. The material is intended for use as
a fuel resistant sealer.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Use or a rubberized seal coat may be specified by the
Engineer by incorporating the words enclosed in brackets.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

MATERIALS

625-2.1 AGGREGATE. The aggregate shall either be a natural or
manufactured angular aggregate and shall be composed of clean,
hard, durable, uncoated particles, free from lumps of clay and
all organic matter. The aggregate shall meet the gradation in
Table 1, when tested in accordance with ASTM C 136.

TABLE 1. GRADATION OF AGGREGATES

Sieve size Percentage By Weight Passing Sieves

No. 8 (2.36 mm) 100
No. 16 (1.18 mm) 97-100
No. 20 (0.85 mm) 85-100
No. 30 (0.60 mm) 15-85
No. 40 (0.40 mm) 2-15
No. 50 (0.30 mm) -
No. 100 (0.15 nM) 0-2

The gradation shown in Table 1 may be varied to conform with the
recommendations of the latex supplier.

625-2.2 BITUMINOUS MATERIALS. The bituminous material shall be a
coal-tar pitch emulsion prepared from a high temperature,
coal-tar pitch conforming to the requirements of ASTM D 490,
grade 11/12. Oil and water gas tar shall not be used even though
they comply with ASTM D 490. The coal-tar pitch emulsion shall
conform to all requirements of Federal Specification R-P-355
except that the water content shall not exceed 50 percent.

625-2.3 WATER. The water used in mixing shall be potable and
free from harmful soluble salts. The temperature of the water
added during mixing shall be at least 50 degrees F (10 degrees
C). The pH of the water added during mixing shall conform to the
requirements of the coal tar emulsion manufacturer.

625-2.4 LATEX RUBBER. The rubber shall be a copolymer latex
containing 51-70 parts butadiene and 30-49 parts acrylonitrile or
styrene with a minimum solids content of 40 percent. The rubber
shall be compatible with the coal-tar pitch emulsion used by the
Contractor and must mix homogeneously with the coal-tar emulsion,
water, and sand in the proportions specified to produce a mixture
that will adequately suspend the sand.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
The Engineer shall delete paragraph 2.4 if a rubberized
coal-tar pitch emulsion is not specified.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

COMPOSITION AND APPLICATION

625-3.1 COMPOSITION. The [rubberized] coal-tar pitch emulsion
seal coat shall consist of a mixture of coal-tar pitch emulsion,
water, [latex rubber] and aggregate in proportions that fall
within the ranges shown in Table 2.

625-3.2 JOB MIX FORMULA. For a rubberized seal coat, the
Contractor shall submit the supplier's recommended formulation
and application rate to a testing laboratory together with
sufficient materials to verify the formulation. The laboratory
shall verify the proportions of emulsion, water, aggregate and
rubber using the mix design procedures contained in Appendix A.
The mix design shall be within the range shown in Table 2 and
meet the requirements of Table 3. A copy of the mix design and
test data shall be submitted to the Engineer for approval at
least [ ] days prior to the start of operations. No seal coat
shall be produced for payment until a job mix formula has been
approved by the Engineer.

Rubberized coal-tar emulsion seal coat formulations are sensitive
to the characteristics of individual latex additives. Not all
products will provide satisfactory seal coat formulations for all
combinations of coal tar emulsion, water, and rubber additive.

The job mix formula for each mixture shall be in effect until
modified in writing by the Engineer.

For a non-rubberized seal coat the contractor shall submit the
proportions of water, emulsion, and sand proposed for use to the
Engineer at least 5 days prior to the start of operations. A
copy of test data showing the results of the fuel resistance test
in Appendix A shall also be submitted to the Engineer.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Improper formulations of coal-tar pitch emulsion seal produce
coatings that crack prematurely or do not adhere properly to the
pavement surface.

A minimum of 5 days is recommended for job mix approval.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

TABLE 2. COMPOSITION OF MIXTURE

Type of Seal Coat Composition and Quantities

Water Aggregate Rubber Application Rate
gal./gal. lbs/gal. gal./gal. gal./sq.yd.
of emul. of emul. of emul. (per application)

Rubberized
Sand slurry 0.80(max) 4-20 0.04-0.18 0.20-0.55

Rubberized
Emulsion 0.80(max) - 0.03-0.05 0.10-0.20

Sand Slurry 0.15(max) 2-5 - 0.15-0.20

Plain Emulsion 0.10(max) - - 0.08-0.10

TABLE 3 DESIGN CRITERIA

Test Property Purpose Criterion

Brookfield Viscosity Incompatibility 10-90
poises @ 77F between latex
and coal tar

Brookfield Viscosity Workability of 10-90
poises @ 77F composite mix

Freeze-Thaw Cracking
@ 5 cycles < 1
@ 10 cycles < 3

Adhesion Loss of adhesion Rating = 5A
Fuel Resistance Fuel penetration No penetration
Loss of adhesion or loss of
adhesion

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Delete Table 3 if a non-rubberized seal coat is specified.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
625-3.3 APPLICATION RATE. [The rubberized coal-tar emulsion seal
coat shall be applied in three coats. The first and second coats
shall consist of a rubberized sand slurry; the third coat shall
consist of a rubberized emulsion, if recommended by the
manufacturer.] [The sand slurry coal-tar emulsion seal coat shall
be applied in two coats.] The application rate submitted with the
job mix formula shall be verified during placement of the test
section and shall fall within the limits shown in Table 2.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
The Engineer shall incorporate the appropriate sentence in
the Project specifications, depending on whether the seal
coat is rubberized or non-rubberized. When, in the opinion
of the Engineer, an area will be subjected to heavy fuel
spillage, a final application of plain emulsion, on a sand
slurry seal coat, may be made at the rate of 0.075 to 0.10
gallons per square yard (0.36 to O.5 liters per square
meter).
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

625-3.4 TEST SECTION. Prior to full production, the Contractor
shall prepare a quantity of mixture in the proportions shown in
the approved mix design. The amount of mixture shall be
sufficient to place a test section a minimum of 250 square yards
at the rate specified in the job mix formula. The area to be
tested will be designated by the Engineer and will be located on
a representative section of the pavement to be sealcoated. The
actual application rate will be determined by the Engineer during
placement of the test section and will depend on the condition of
the pavement surface.

The test section shall be used to verify the adequacy of the mix
design and to determine the application rate. The same equipment
and method of operations shall be used on the test section as
will be used on the remainder of the work.

[Viscosity tests shall be made to determine conformance with the
requirements of Table 3. Test results shall be available within
2 days.]

If the test section should prove to be unsatisfactory, the
necessary adjustments to the mix composition, application rate,
placement operations, and equipment shall be made. Additional
test sections shall be placed and evaluated, if required. Full
production shall not begin without the Engineer's approval.
Acceptable test sections shall be paid for in accordance with
paragraph 625-7.1.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
The test section affords the Contractor and the Engineer an
opportunity to determine the quality of the mixture in place
as well as the performance of the equipment.

The application rate depends on the surface texture.

If operational conditions preclude placement of a test
section on the pavement to be sealed, it may be applied on a
pavement with similar surface texture.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
CONSTRUCTION METHODS

625-4.1 WEATHER LIMITATIONS. The seal coat shall not be applied
when the surface is wet or when the humidity or impending weather
conditions will not allow proper curing nor when the atmospheric
or pavement temperature is below 50 degrees F (10 degrees C),
unless otherwise directed by the Engineer.

625-4.2 EQUIPMENT AND TOOLS. The Contractor shall furnish all
equipment, tools, and machinery necessary for the performance of
the work.

a. Distributors. Distributors or spray units used for the
spray application of the seal coat shall be self-propelled and
capable of uniformly applying 0.15 to 0.55 gallons per square
yard (0.69 to 2.5 liters per square meter) of material over the
required width of application. Distributors shall be equipped
with removable manhole covers,tachometers, pressure gauges, and
volume-measuring devices.

The mix tank shall have a mechanically powered, full-sweep, mixer
with sufficient power to move and homogeneously mix the entire
contents of the tank.

The distributor shall be equipped with a positive placement pump
so that a constant pressure can be maintained on the mixture to
the spray nozzles.

b. Mixing Equipment. The mixing machine shall have a
continuous flow mixing unit capable of accurately delivering a
predetermined proportion of aggregate, water, emulsion [and
rubber] and of discharging the thoroughly mixed product on a
continuous basis. The mixing unit shall be capable of thoroughly
blending all ingredients together and discharging the material to
the spreader box without segregation.

c. Spreading Equipment. Attached to the mixing machine
shall be a mechanical-type squeegee distributor, equipped with
flexible material in contact with the surface to prevent loss of
slurry from the spreader box. It shall be maintained to prevent
loss of slurry on varying grades and adjusted to assure uniform
spread. There shall be a lateral control device and a flexible
strike-off capable of being adjusted to lay the slurry at the
specified rate of application. The spreader box shall have an
adjustable width. The box shall be kept clean; coal-tar emulsion
and aggregate build-up on the box shall not be permitted.

d. Calibration. The Contractor shall furnish all equipment
and materials and labor necessary to calibrate the equipment. It
shall be calibrated to assure that it will produce and apply a
mix that conforms to the job mix design. Commercial equipment
should be provided with a method of calibration by the
manufacturer. All calibrations shall be made with the approved
job materials prior to applying the seal coat to the pavement. A
copy of the calibration test results shall be furnished to the
Engineer.

625-4.3 PREPARATION OF PAVEMENT SURFACE. Bituminous pavement
surfaces which have been softened by petroleum derivatives or
have failed due to any shall be removed to the full depth of the
damage and replaced with new bituminous concrete similar to that
of the existing pavement. Areas of the pavement surface to be
treated shall be in a firm consolidated condition. They shall be
sufficiently cured so that there is no concentration of oils on
the surface.

A period of [ ] days shall elapse between the placement of a
bituminous surface course and the application of the seal coat.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
The engineer shall specify the time period. In order to
ensure adequate adhesion and minimize cracking and curling,
the pavement surface must be sufficiently cured prior to
applying the seal coat. Experience has shown that
approximately 90 days of hot weather (daytime temperatures
or 70 degrees F) is needed for adequate curing.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

625-4.4 CLEANING EXISTING SURFACE. Prior to placing the seal
coat, the surface of the pavement shall be clean and free from
dust, dirt, or other loose foreign matter, grease, oil, or any
type of objectionable surface film. When directed by the
Engineer, the existing surface shall be cleaned with wire brushes
and a power blower.

Where vegetation exists in cracks, the vegetation shall be
removed and the cracks cleaned to depth of two inches where
practical. Those cracks shall be treated with a concentrated
solution of a herbicide approved by the Engineer. Cracks shall
then be [ ]. Areas that have been subjected to fuel or oil
spillage shall be wire brushed to remove any dirt accumulations.
The area shall then be primed with shellac or a synthetic resin
to prevent the seal coat from debonding.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
The Engineer shall specify the appropriate method of
treating cracks depending on the frequency and severity.
This may include filling or routing and filling with a
compatible crack filler, filling with a rubberized seal
slurry at the time it is applied to the pavement surface,
milling, etc.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

625-4.5 TACK COAT. After the surface has been prepared, a tack
coat of 3 parts water to 1 part emulsified binder, as specified
in paragraph 625-2.2, shall be applied at the rate of 0.05 to
0.10 gal/sy of surface. A tack coat or adhesion promoter shall be
applied only if recommended by the emulsion supplier.

When a tack coat is not specified the pavement shall be dampened
with a fog spray of water if recommended by the supplier. No
standing water shall remain on the surface.

625-4.6 APPLICATION OF PLAIN EMULSION. Plain emulsion shall be
applied at a uniform rate with a distributor at the rate as
determined in paragraph 625-3.4. When it is necessary to dilute
the emulsion in order to aid application, the emulsion may be
diluted with clean water but not by more than 10 percent.

625-4.7 APPLICATION OF [RUBBERIZED] SAND SLURRY. The
[rubberized] sand slurry shall be applied at a uniform rate with
a distributor or squeegee at the rate determined in paragraph
625-3,4. When the emulsion, water, aggregate, [and rubber] are
blended, the material shall be premixed to produce a homogeneous
mixture of uniform consistency. The quantities of materials to
be combined in each batch shall be in accordance with the
approved mix design.

The mixing sequence of the various components shall be the same
as indicated in the job mix formula. After all constituents are
in the mixer, the mixing shall continue for approximately five
minutes or longer, if necessary. The mixing shall produce a
smooth, free flowing homogeneous mixture of uniform consistency.
Slow mixing shall be continuous from the time the emulsion is
placed into the mixer until the slurry is applied by distributor
truck or poured into the spreading equipment. During the entire
mixing process, no breaking, segregating, or hardening of the
emulsion nor baIling, lumping, or swelling of the aggregate shall
be permitted. The slurry shall be applied at a uniform rate to
provide the quantity determined during placement of the test
strip.

When a spreader box is used, a sufficient amount of slurry shall
be fed in the spreader box to keep a full supply against the full
width of the squeegee, so that complete coverage of all surface
voids and cracks is obtained.

Manufacturer's recommendations regarding application by spraying
or squeegeeing should be followed. In areas inaccessible to
equipment, the slurry may be applied by means of a hand squeegee.

Upon completion of the work, the seal coat shall have no pin
holes, bare spots, or cracks through which liquids or foreign
matter could penetrate to the underlying pavement. The finished
surface shall present a uniform texture.

Each application shall be allowed to dry thoroughly before the
next coat is applied.

625-4.8 CURING. The mixture shall be permitted to dry for a
minimum of [ ] hours after the final application before opening
to traffic and shall be sufficiently cured to drive over without
damage to the seal coat. Any damage to the uncured mixture will
be the responsibility of the Contractor to repair.

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
A minimum of 24 hours is recommended.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

625-4.9 HANDLING. The mixture shall be continuously agitated
from the initial mixing until its application on the pavement
surface. The distributor or applicator, pumps, and all tools
shall be maintained in satisfactory working condition.

QUALITY CONTROL

625-5.1 CONTRACTOR'S CERTIFICATION. The Contractor shall furnish
the manufacturer's certification that each consignment of
emulsion shipped to the project meets the requirements of Federal
specification R-P-355, except that the water content shall not
exceed 50 percent. The certification shall also indicate the
solids and ash content of the emulsion and the date the tests
were conducted. [The contractor shall furnish the manufacturer's
certification to the Engineer that the latex rubber shipped to
the project meets the requirements or the material specified in
paragraph 2.4. It shall also indicate that the latex and
coal-tar emulsion proposed for use are compatible and that the
latex is recommended for combining with the coal-tar emulsion,
water, and aggregate.] The [certification] [certifications] shall
be delivered to the Engineer prior to the beginning of work. The
manufacturer's certification for the emulsion [and rubber] shall
not be interpreted as a basis for final acceptance. Any
certification received shall be subject to verification by
testing samples received for project use.

[The Contractor shall furnish manufacturer's certification that
the combination of latex and coal tar emulsion proposed for use
has been successfully used in coal tar emulsion seal coat
mixtures for a minimum of three years. The Contractor shall also
furnish a certification demonstrating their experience in the
application of a rubberized coal-tar emulsion seal coat for a
minimum of three years.]

625-5.2 INSPECTION. The Contractor shall have an independent
technical consultant on the job site at the beginning of
operations for application of rubberized seal coats. The
consultant shall have knowledge of the materials, procedures, and
equipment described in this specification and shall assist the
Contractor regarding proper mixing of the component materials and
application of the seal coat. The consultant shall have a minimum
of 3 years experience in the use of rubberized coal tar seal
coats. Documentation of this experience shall be furnished to the
Engineer prior to the start of operations.

625-5.3 SAMPLING. Two random samples of the composite rubberized
mix, from each days production, shall be tested for viscosity to
determine conformance with the requirements contained in Table 3.
One sample per day may be tested for the other properties of
Table 3. In addition, a one-quart sample will be obtained daily
and stored in a glass container. The container shall be sealed
against contamination and retained in storage by the owner for a
period of six months. Samples shall be stored at room temperature
and not be subjected to freezing temperatures.

A sample of undiluted coal tar emulsion and latex shall be
sampled from each consignment shipped to the job.

625-5.4 ENGINEER'S RECORDS. The Engineer will keep an accurate
record of each batch of materials used in the formulation of the
seal coat.

METHOD OF MEASUREMENT

625-6.1 The coal-tar pitch emulsion shall be measured by the
gallon (liter) of undiluted emulsion.

625-6.2 The mineral aggregate shall be measured by the ton
(kilogram).

625-6.3 The latex rubber shall be measured by the gallon (liter).

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Paragraph 6.3 shall be deleted if a rubberized seal coat is
not specified.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

BASIS OF PAYMENT

625-7.1 Payment shall be made at the contract unit price per
gallon (liter) for the coal-tar pitch emulsion, per ton
(kilogram) for the mineral aggregate[, ] [. ] [and per gallon
(liter) for the latex rubber.] These prices shall fully
compensate the Contractor for furnishing all materials; and for
all labor, equipment, tools, and incidentals necessary to
complete the items.

Payment will be made under:

Item P-625-7.1 Coal-Tar pitch Emulsion -per gallon (liter)
Item P-625-7.2 Aggregate - per ton (kilogram)
Item P-625-7.3 Latex Rubber - per gallon (liter)

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Item P-625-7.3 shall be deleted if a rubberized seal coat is
not specified.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

TESTING REQUIREMENTS

ASTM 136 Sieve or Screen Analysis of Fine and Coarse Aggregates

MATERIAL REQUIREMENTS

Fed. Spec. P-355 Pitch, Coal-Tar Emulsion (Coating for Bituminous Pavements)

ASTM D 490 Tars, (For Use In Road Construction)

APPENDIX A

MIX DESIGN PROCEDURE

ITEM P-625
MIX DESIGN PROCEDURE ITEM P-625
TEST METHODS
CRITERION

This procedure shall be used to determine the capability of the
materials furnished by the contractor to produce a seal coat mix
within the range of TABLE 2 and meeting the requirements of TABLE
3.

The formulation is a combination of coal tar pitch emulsion,
water, sand, and latex rubber. The samples furnished by the
contractor shall be combined in the proportions recommended by
the supplier and subjected to a sequence of six tests designed to
eliminate any materials or combination of materials which do not
meet the test criteria. Unacceptable materials in the formulation
shall be eliminated from further consideration.

BROOKFIELD VISCOSITY
Step 1 & Step 2

1. Scope
This method covers the determination of the Brookfield
viscosity, using materials and recommended formulations
provided by the Contractor. It is designed to detect
formulations that have incompatible quantities of latex and
coal tar emulsion, that might flocculate, that have
viscosities too low to suspend sand, and to identify any
incompatibilities created by introducing sand.

2. Definitions
2.1 Brookfield viscosity - the viscosity determined by this
method. The viscosity is expressed in centipoises (100
centipoises = 1 poise). Its value may vary with the spindle
speed (shear rate) due to the non-Newtonian behavior of the
coal tar emulsion, additive, and the water added.
2.2 Total liquids - coal tar emulsion, additive, and water.
2.3 Composite system - total liquids and sand.

3. Apparatus
3.1 Brookfield digital viscometer (model DV-II) and stand.
3.2 Number 1 and 3 HB spindles for DV-II viscometer.
3.3 Paint cans
3.3.1 quart capacity.
3.3.2 gallon capacity.

4. Sample preparation for Step 1 (4.1-4.3) and Step 2(4.1-4.4)

4.1 Allow components (coal tar emulsion, water, sand, and
additive) to reach 77 degrees F. This should take
approximately 24 hours.
4.2 Mix coal tar emulsion and water in container specified
in 3.3.2 with 50 strokes of a large laboratory mixing spoon.

4.3 Introduce additive to the mixture with an additional 50
strokes of the laboratory mixing spoon.
4.4 Add sand to total liquids with 50 strokes of a large
laboratory mixing spoon, for composite mixture. Sand must be
added slowly to avoid trapping air in the mixture. Stir
composite mixture for 5 minutes and immediately proceed to
Step 2.

5. Procedure
Step 1
5.1Fill quart paint can specified in 3.3.1 to within one
inch of the top with the material prepared in
accordance with 4.1 through 4.3.
5.2 Insert spindle No. 3 HB in the material until the
mixture level coincides with the immersion groove on
the spindle shaft.
5.3 Avoid trapping air bubbles underneath the spindle.
5.4Adjust rotational speed on the Brookfield viscometer to
50 revolutions per minute (rpm).
5.5 Start motor and record viscosity value in centipoises
after five seconds of rotation. If the viscosity
reading is too low for spindle 3, repeat procedure 5.1
through 5. 5, using spindle No. 1.
Step 2
5.6 Repeat 5.1 - 5.5 with the composite mixture prepared in
accordance with 4.1 through 4.4.
5.7If the composite mixture does not fall within the
acceptance criterion of 10 to 90 poises the following
procedure for combining materials shall be used.
5.7.1 Discard materials from Step 1.
5.7.2 Mix coal tar emulsion and water in container
specified in 3.3.2 with 50 strokes of a large
laboratory mixing spoon.
5.7.3 Add sand to the mixture with 50 strokes of the
laboratory mixing spoon.
5.7.4 Introduce additive to the mixture with 50 strokes
of the laboratory mixing spoon, for composite mixture.
Stir composite mixture for 5 minutes and immediately
proceed to Step 1.

6. Report
6.1 The report should include:
6.1.1Date of test and complete identification of
the coal tar formulation tested.
6.1.2 Spindle number and rpm setting.
6.1.3 Temperature of the sample tested.
6.1.4 Viscosity of total liquids in poises. (Step 1)
6.1.5 Viscosity of composite system in poises. (Step 2)

Step 1 Criterion: Viscosities between 10 and 90 poises areacceptable
Step 2 Criterion: Viscosities between 10 and 90 poises are
acceptable

For materials to move into Step 2 testing the viscosity range
must be met in Step 1. Likewise Step 3 will not be continued
until viscosity range is met in Step 2 testing. If a material
fails to met testing criteria in any step it will be eliminated
from further testing.

CYCLIC FREEZE THAW CONDITIONING
Step 3

1. Scope
This method covers the analysis of crack development in a
composite rubberized coal tar emulsion seal coat when
exposed to multiple cycles of freezing and thawing.

2. Apparatus
2.1 12" x 12" square 16 gauge sheet metal mask with an
11" x 11" square center removed.
2.212" x 12" square section of aluminum panel 3/16" thick.
2.3Oven capable of maintaining 140 degrees F.
2.4Freezer capable of maintaining 10 degrees F.

3. Procedure
3.1 Using mask described in 2.1, apply uniform thickness of
the composite rubberized coal tar emulsion mixture to a
panel as described in 2.2.
3.2 Allow material to cure at 77 + 2 degrees F and 50 + 10
percent relative humidity for 24 hours.
3.3 Place sample in the 140 degree F oven for 24 hours.
3.4 Remove sample and record crack development.
3.5 Place sample in 10 degree F freezer for 24 hours.
3.6 Remove from freezer; this constitutes one freeze-thaw
cycle.
3.7 Repeat procedures 3. 3 through 3. 6 for a total of 10
cycles.
3.8 Inspect the samples after 5 and 10 cycles and rate the
cracking in accordance with the following scale and

Figure 1.
0 - No cracking
1 - Hairline cracking
2 - Slight cracking
3 - Moderate cracking
4 - Severe cracking

4. Report
4.1 Report the crack rating at 5 and 10 cycles.

Step 4 Criterion: Rating of 1 or less at 5 cycles is required.
Rating of 3 or less at 10 cycles is required.

Any materials not meeting this requirement shall be eliminated
from Step 4.

ADHESION
Step 4

1. Scope
This method covers the determination of adhesion of a
composite rubberized coal tar emulsion seal coat and
retention of sand by applying pressure sensitive tape.

2. Apparatus
2.112" X 12" square 16 gauge sheet metal with 3" X 6"
rectangular center removed.
2.212" X 12" aluminum panel 3/16" thick.
2.3 Razor sharp blade, scalpel, or other cutting device
with cutting edge in good condition.
2.4 Steel straight edge.
2.5 One inch wide semi-transparent pressure sensitive tape
with an adhesion strength of 38 + 5 oz./in. when
tested in accordance with ASTM D 3330. The backing of
the tape may consist of fiber-reinforced cellulose
acetate, unplasticized polyvinyl chloride, or polyester
film.
2.6 Hard, small head rubber eraser.
2.7 Table lamp.

3. Procedure
3.1 Using the mask described in 2.1, apply a uniform
thickness of the composite mixture to the aluminum
panel as described in 2.2.
3.2 Allow mix to cure at 77 + 2 degrees at 50 + 10 percent
relative humidity for 24 hours.
3.3 Select a representative area.
3.4 Make a horizontal cut of about 1.5 inches. Then make
another cut of 1.5 inches about 40 degrees to the
horizontal cut. The cuts should intersect each other at
their centers. When making the cuts, use the straight
edge and cut through the coating to the substrate in on
steady motion. Brush off dislodged materials.
3.5 Inspect the cuts for reflection of light from the metal
substrate to establish that the coating has been cut
through completely. If the substrate has not been
reached, do not attempt to deepen the cut. Instead,
make another "X" in a different location. Remove the
dislodged materials by brushing lightly.
3.6 Remove two laps of the pressure sensitive tape from the
roll and discard. Remove an additional length at a
steady rate and cut a piece about three inches long.
3.7 Place the center of the tape at the intersection of the
cuts with the tape running in the same direction as the
smaller angles. Smooth out the tape in the area of thecuts and then rub firmly with the eraser.
3.8 Wait for 60 seconds, then rapidly pull one end of the
tape back on itself with the non-stick surfaces
touching and running parallel to each other.
3.9 Inspect the "X" cut area for removal of the coating
from the substrate and rate the adhesion in accordance
with the following scale:
5A No Peeling or removal
4A Trace peeling or removal along incisions
3A Jagged removal along incisions up to 1/16 inch either side to 1/8
2A Jagged removal along most incisions Up to l/8 inch on either side
1A Removal from most of the area of the "X" under the tape
OA Removal beyond the area of the "X"

3.10 Inspect the tape for adhesion of sand.
3.11 Repeat the test in two other locations on the test panel

4 Report

4.1Report the number of tests, their mean value and range.
4.2 Report whether sand adhered to the tape as yes or no.

Step 5 criterion: No sand can adhere to the tape. No debonding
of the seal coat or the test medium is allowed (adhesion rating
of 5A is required).

Any materials not meeting this requirement shall be eliminated
from being tested in Step 5.

FUEL RESISTANCE
Step 5

1. Scope
This method determines the resistance of the composite
rubberized coal tar emulsion seal coat to kerosene.

2. Apparatus
2.12 6" X 6" square 16 gauge sheet metal masks with a 4" by 4" square
center removed.
2.26" X 6" unglazed white ceramic tile with an absorption
rate of 10-18 percent (determined in accordance with

ASTM C 67.

2.3 Brass ring, 2" diameter and 2" high.
2.4 Kerosene meeting requirements of ASTM D 3699.
2.5 Silicone rubber sealant.

3. Procedure
3.1 Immerse the ceramic tile in distilled water for a
minimum of ten minutes.
3.2 Remove excess water from the tile to produce a damp
surface before applying the seal coat.
3.3 Using the mask described in 2.1 apply one layer of the
composite coal tar emulsion mixture to the tile. Spread
even with the top of the mask using a spatula or other
straight edge.
3.4 Allow the sample to cure for 96 hours at 77 + 2 degrees
F. and 50 + 10 percent relative humidity.
3.5 Position a second mask on top of the first mask.
3.6 Apply a second coat of coal tar emulsion mixture.
Spread even with the top of the second mask.
3.7 Cure as in step 3.4.
3.8 After curing, affix the brass ring to the seal coat on
the tile with silicone rubber.
3.9 Fill the brass ring with kerosene.
3.10 After 24 hours, remove the kerosene from the brass
ring, blot dry and immediately examine the film for
softness and loss of adhesion. Immediately after the
film is examined, break the tile in half, exposing that
part of the tile whose film was subjected to the
kerosene.
3.11 Evaluate for penetration of kerosene through the sealer
and loss of adhesion.

4. Report
4.1 Report the results as pass or fail. Visible evidence
of leakage or discoloration shall constitute failure of
the test.

Step 6 Criterion:A "pass" rating in the fuel resistance test
is required.

Engineering Brief # 46

Last modified: November 13, 2000

National Pavement Contractors Association.