Transcript         Ditching Crack Seal Dig-outs Blade Patching Shoulders Chipseal Fog seal Striping   3/8” Rock vs. ½”-1/4” Shot rates  ½-1/4”+ ?

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Ditching
Crack Seal
Dig-outs
Blade Patching
Shoulders
Chipseal
Fog seal
Striping
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3/8” Rock vs. ½”-1/4”
Shot rates
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½-1/4”+ ?
Emulsion Classification
Emulsions are divided into three grades for
classification: cationic,anionic and non-ionic. In
practice, only the first two are used in roadway
construction and maintenance. The cationic and
anionic designation refers to the electrical charge of
the emulsifier surrounding the asphalt particles.
Cationic emulsions have a positive (+) electrical
charge surrounding the asphalt particles while
anionic emulsions have a negative (-) electrical
charge.
Since opposite electrical charges attract, anionic
emulsions should be used with aggregates having a
positive (+) charge. Similarly, cationic emulsions
should be used with aggregates having a negative (-)
charge. Failure to use materials with opposite
electrical charges may result in the materials
repelling each other, causing failure.
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Asphalt Emulsions
Asphalt emulsions use surface-active agents or surfactants to suspend the asphalt particles in water.
These surfactants or emulsifying agents are similar to soap, allowing the minute asphalt particles and
the water to form a uniform mixture. When the asphalt emulsion is applied to the roadway, the asphalt
cement and the water separate. This process is called breaking. The water then evaporates, leaving the
asphalt cement and the emulsifying agents behind.
Asphalt emulsions commonly used in road- maintenance operations are either anionic or cationic. The
asphalt in the anionic type has a negative electrical charge while the cationic type has a positive
electrical charge. Cationic emulsions are denoted by a letter “C” at the beginning of the emulsion type,
and the absence of “C” denotes an anionic emulsion. The emulsions are classified by the letters,
indicating the relative rate of curing. Rapid-setting (RS), medium-setting (MS), slow-setting (SS), and
quick-setting (QS) are the designations. Emulsions are further classified by a number indicating
viscosity “1” is more fluid than “2” and a letter for the hardness of the base asphalt (“h” for a harder
grade and “s” for a softer grade). High float emulsions are designated with the letters “HF” preceding
the emulsion grades.
MODIFICATIONS OF ASPHALT EMULSIONS
High-Float Asphalt Emulsions
High-float asphalt emulsions (HFEs) are being used more often. Usually, when an emulsion breaks, the remaining
emulsifying agent has little effect on the asphalt. This is not so with an HFE. The high-float emulsifying agent creates a gel
structure in the asphalt residue. The gel structure permits a thicker asphalt coating on the aggregate particles. The thicker film
prevents raveling and is more resistant to oxidation from exposure to the atmosphere. The high-float residue is resistant to
flow at high temperatures while not being affected as much by low temperatures. This allows a softer grade of the base
asphalt to be used that will resist bleeding at high temperatures. The softer asphalt does not become as brittle at low
temperatures and resists thermal cracking. HFEs are commonly used in hot arid environments with cold evenings.
Polymer-Modified Emulsions
Probably the most common modifier to asphalt emulsions is polymer additives. Polymers and polymer combinations are
being modified constantly to enhance the various properties of the asphalt cement binder. Polymers can be used for any
asphalt seal coat applications.
Polymers generally used in the asphalt industry are either elastomeric (rubber like) or plastomeric (plastic like). The
elastomeric polymers increase the elasticity and flexibility of the asphalt cement, while the plastomeric polymers improve the
strength and the durability of the asphalt cement. Polymerized asphalt emulsions are effective in improving stone retention
when construction conditions are less than ideal, such as in low air temperatures, shady areas, or sinuous alignment.
Polymers can improve the performance of the asphalt binder in both cold and hot temperatures. Some polymers allow the
emulsion to chemically break and do not depend on temperature to separate the asphalt cement from the water within the
emulsion. This allows the emulsion to break at lower temperatures and provides a longer construction season in some areas
or allows surface treatments to be done at night. Polymer modified binders usually cost more, but they increase the
performance of the asphalt cement, often reducing life cycle costs.
Rejuvenating Emulsions
As pavement ages, asphalt cement becomes brittle and loses some of its binding qualities. Rejuvenating emulsions penetrate
the asphalt pavement, soften the brittle asphalt, and improve the asphalt cement’s ability to bind with the aggregate. The
rejuvenating agent is also known to heal small cracks in the pavement.
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CRS-2P ~
“C”- Cationic emulsions
“RS” - Rapid-setting
2 - viscosity “1” is more fluid than “2”
“P” - Polymer-Modified Emulsions
elastomeric (rubber like) or plastomeric (plastic
like)
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Apply the bituminous material above
the minimum limits specified below:
Bituminous Material Minimum
Temperature Ideal Temperature
CRS-2P [140° F]* [170-180º F]
CSS-1h [100° F]
* Intended for uniform lay down of
emulsion.
Rolling shall be performed with a pneumatic-tired roller that remains immediately behind the spreader.
The function of the roller is to embed the aggregate into the binder and orient it into
an interlocking mosaic. This is initially accomplished with pneumatic rollers, with
final compaction applied by traffic, finishing the process. Rolling should be
expedited in hotter weather to ensure proper embedment of the aggregate. Steel
rollers are not normally recommended because they can crush the aggregate.
Complete the initial rolling within 2 minutes after applying the aggregate.
Proceed at a recommended speed less than or equal to 5 miles per hour, to
prevent turning over aggregate and so that the rollers do not pick up
aggregates from the emulsified asphalt surface. Make a minimum of three
complete passes over the aggregate. Roll the aggregate so the entire width
of the treatment area is covered in one pass of all the rollers. The total
compacting width of each pneumatic-tired roller shall exceed 5 ft.
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Contact pressure depends on the vehicle weight, the
number of tires, tire size and rating, and the tire
inflation pressure. Rollers that can be ballasted are very
useful in assuring sufficient contact pressure. The
ballasted weight should be 4 to 6 tons, with a
corresponding tire pressure of 87 psi. Tires must have a
smooth tread, should not vary more than 7 psi in
pressure, and should not wobble during operation.
Rollers should follow aggregate spreading by no more
than
500 ft and should not be operated at more than 5 mph.
The rolling pattern will depend on the number of rollers
used. A minimum of two rollers should be used to cover
the full width of the chip spreader. When two rollers are
used, three passes are sufficient; one forward, one in
reverse, and the final pass extending into the next
section.
Following the application of the chip seal,
the entire surface shall be carefully
broomed to remove loose aggregate that
could damage vehicles. This brooming
shall be done as soon as possible without
damaging the chip seal but no more than
18 hours following the application of the
chip seal.
Chipseal : 100% Clean – up before
Fogging
Paved Driveways: 100% Clean-up
Do not use paved driveways for turning
around.
A fog seal consisting of a mixture of 50% CSS1H and 50% water shall be applied to the chip
seal surface after all extraneous aggregates
have been removed. The application rate of the
CSS-1H/Water mixture is estimated to be 0.12
gallons per square yard. Apply the fog seal to
minimize the amount of overspray. Do not allow
traffic on the fog seal until it has cured.
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CSS-1H ~
“C” - Cationic emulsions
“SS” - Slow-Setting
1 - viscosity “1” is more fluid than “2”
“H” - letter for the hardness of the base
asphalt (“h” for a harder grade and “s”
for a softer grade).
THE BENEFITS OF FOG SEALING
There are numerous benefits resulting from a fog seal application.
1. The traveling public thinks it is driving on a new HMA surface rather than a chip seal.
2. The emulsion is diluted, which yields a very low viscosity that allows most, if not all
of the additional asphalt binder to fill the chip voids increasing embedment by up to
15-percent with no bleeding.
3. The fog seal re-seals any chips that may have partially broken loose during
sweeping operations.
4. Darkening the pavement surface with a light application of asphalt emulsion allows
the pavement surface temperature to rise. The subsequent softening of the binder
allows the chips to orient to their least dimension more quickly. This factor is very
important where late season chip seal projects are more susceptible
to failure due to colder weather conditions.
5. Fog sealing can provide a designer with a chance for a “re-do” of a chip seal
application. If, after traffic has driven on the surface, it appears that embedment is
low, an engineer can add additional binder to the chip seal by increasing the fog seal
amount. In some cases, the amount of fog seal emulsion applied increased to over
0.20 gallon per square yard.
6. When a fog seal is applied, a reduced amount of paint is necessary to make
pavement markings visible on the surface.
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Before and after